Green Chemical Technology for the Synthesis of Basic Organic Chemicals

Xiaoxin Zhang

doi:10.7536/PC241116

Progress in Chemistry >

2024 , Vol. 36 >Issue 12: 1859 - 1873

DOI: https://doi.org/10.7536/PC241116

Chemistry: A Century of Life-Special Edition

Green Chemical Technology for the Synthesis of Basic Organic Chemicals

Xiaoxin Zhang

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State Key Laboratory of Petroleum Molecular & Process Engineering，SINOPEC Research Institute of Petroleum Processing Co. Ltd., Beijing 100083, China

* e-mail：zhangxx.ripp@sinopec.com

Received date: 2024-11-13

Revised date: 2024-11-20

Online published: 2024-12-20

Supported by

National Natural Science Foundation of China(22072182)

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Abstract

The rapid development of the chemical industry has contributed to global economic growth and improved people's quality of life. However, the massive consumption of fossil fuels in the chemical production process has also caused environmental pollution and climate change that cannot be ignored. Academician Min Enze has been committed to directional fundamental research in green chemistry since 1990. He has introduced and integrated new materials, processes, and reaction pathways into the traditional petrochemical industry, led and guided the implementation of multiple major national basic research projects, accumulated new technological knowledge in green chemistry, laid the foundation for green refining and petrochemical new processes, and developed multiple influential green chemical technologies, effectively promoting the development of green technologies in the petrochemical industry. This article summarizes the green chemical technology practice cases formed on the basis of the catalytic new materials and green chemistry new knowledge laid by Academician Min Enze in the past 20 years, including the green production technology of caprolactam, fluidized bed hydrogen peroxide technology, complete technology of epoxy propane production by hydrogen peroxide method, and green synthesis technology of cyclohexene esterification and hydrogenation. These condensed innovative practices and experiences in catalytic materials and chemical engineering will provide a foundation and reference for us to carry out new technological innovations.

Key words： directional fundamental research; green chemistry; new catalytic materials; reaction engineering; new reaction pathway

Cite this article

Xiaoxin Zhang . Green Chemical Technology for the Synthesis of Basic Organic Chemicals[J]. Progress in Chemistry, 2024 , 36(12) : 1859 -1873 . DOI: 10.7536/PC241116

1 Introduction

"In the eyes of chemists, there is no waste in the world." As early as the 1960s, American ecologist Rachel Carson published the groundbreaking work "Silent Spring". It was this book that deeply moved Academician Min Enze, for he saw that energy waste and environmental pollution in China were more severe than abroad. At the beginning of the 1990s, when the concepts of "green chemistry" and "environmentally friendly" had just begun to appear in the media internationally, Academician Min Enze took the lead in raising this new banner domestically. He responded to the demands of the times, integrating the research and development of green chemical technologies into the process of catalytic science innovation, regarding it as a new and important growth point for the expansion and application of catalytic science innovation, promoting the healthy development of China's chemical industry^[1].

The concept of green chemistry, on one hand, aims to achieve "atomic economy" in reactions, which requires that all atoms in the raw materials enter the product, without generating waste or by-products, and uses non-toxic and harmless raw materials, catalysts, and solvents; on the other hand, it is about producing environmentally friendly green products that do not cause environmental pollution throughout their entire lifecycle from use to existence. The production technologies for basic organic chemicals in our country were mostly established in the 1980s to 1990s, and due to the limitations of scientific knowledge at the time, these technologies had poor "atomic economy," with some using toxic and harmful raw materials, solvents, and catalysts. If these technologies were to be used to increase production, it would not only increase the cost of waste treatment but also damage the ecological environment, jeopardize community safety and personal health, going against our country's fundamental policies of resource conservation and environmental protection. Moreover, the green production technologies for basic organic chemicals developed abroad were not transferred to our country, leaving us to develop proprietary green production technologies domestically. In 1997, a major basic research project of the Ninth Five-Year Plan, "Environmentally Friendly Petrochemical Catalysis and Chemical Reaction Engineering," funded jointly by the National Natural Science Foundation of China and Sinopec Group, was launched, with Academician Min Enze appointed as the project leader. Thereafter, he extended his catalysis research field from petroleum refining catalysts and processes to organic chemical feedstocks and fiber monomers in petrochemicals, expanding the study of individual green petrochemical processes into technological integration, elevating the development and application of green petrochemical technologies to a higher and more comprehensive level. This project is considered to have pioneered green chemistry research in our country^[2-3]. This article summarizes the typical green chemical technologies for organic chemicals, from directed basic research, applied basic research to industrial application, laid out and guided by Academician Min Enze.

2 Green Production Technology for Caprolactam

Caprolactam (CPL), as a monomer for producing nylon-6 synthetic fibers, engineering plastics, and films, is widely used in new material fields such as textiles, packaging, electronics, automobiles, and aerospace, and is a major demand item related to national economic development and the improvement of people's living standards. More than 30 years ago, almost all CPL in China relied on imports. To meet the needs of the national economy, Sinopec invested 9 billion RMB to introduce foreign technology and build three 50 kt/a CPL production facilities. Among all the basic organic chemical productions, CPL has the longest production process, the most complex technology, and the highest product purity requirements. The first generation of CPL production technology introduced from abroad, due to its small scale, high investment, high production costs, and large waste emissions, was often in a state of severe loss once put into operation; at the same time, the equipment had a high failure rate and unstable operation, unable to meet the country's urgent needs for chemical fibers and engineering plastics. Based on the practice of green chemistry, in 1998, Academician Min Enze, at the age of 74, began to explore the unfamiliar field of fiber monomers, initiating innovation in the green synthesis process of CPL. By 2016, after more than 20 years of continuous innovation, a complete set of green CPL production technologies was successfully developed, including the integration of titanium-silicon molecular sieves with slurry beds for the synthesis of cyclohexanone oxime via cyclohexanone ammoximation, the new technology of cyclohexene esterification and hydrogenation to produce cyclohexanone, the integration of amorphous alloy catalysts with magnetically stabilized beds for CPL refining, and the integration of pure silicon molecular sieves with moving beds for the gas-phase rearrangement of cyclohexanone oxime. Among these, the technology that achieved the earliest breakthrough and brought revolutionary changes to China's CPL industry is the "integration of titanium-silicon molecular sieves with slurry beds for the synthesis of cyclohexanone oxime via cyclohexanone ammoximation"^[4].

2.1 Integration of Titanium Silicalite Molecular Sieve with Slurry Reactor for the Ammonia Oxidation of Cyclohexanone to Cyclohexanone Oxime

2.1.1 "Recrystallization" Preparation of Hollow Titanium Silicalite Molecular Sieves

In 1983, the Italian Enichem company pioneered the development of titanium silicalite (TS-1) catalytic material. They incorporated tetrahedral titanium species into the framework of all-silica zeolites with MFI structure, preparing a TS-1 molecular sieve with isomorphous substitution of titanium, which can efficiently activate and selectively oxidize hydrogen peroxide under mild conditions, with water as the only byproduct, thus avoiding the generation of toxic and harmful substances at the source^[5]. The emergence of titanium silicalite expanded the application of zeolites from traditional Brönsted acid catalysis to Lewis acid catalysis, being hailed as the third milestone in zeolite catalysis. Its excellent oxidative catalytic ability originates from the empty 3d orbitals of Ti in its framework, which can accept lone pair electrons from H₂O₂ molecules, enhancing the nucleophilic attack capability and oxidative activity of H₂O₂ molecules in heterogeneous catalytic processes. It has been widely used in reactions such as phenol hydroxylation, cyclohexanone ammoximation, propylene epoxidation, and aromatic oxidation.

When titanium-silicalite molecular sieves first appeared, although their performance was superior, they suffered from issues such as poor synthesis reproducibility, short lifespan, poor stability, and low activity, leading to slow progress in industrial scaling and application. The main reason for this is the significant difference in ionic radii and electron configuration between Ti and Si. Thermodynamically, Ti atoms prefer to exist in a hexa-coordinated form, making it theoretically difficult for them to isomorphously replace the framework Si atoms; although the MFI structure of the molecular sieve can undergo partial distortion and relieve the strain caused by the insertion of Ti atoms through framework hydroxyl defects, the embedding of Ti into the molecular sieve framework during hydrothermal crystallization remains a major challenge.

In response to the aforementioned challenges, Sinopec conducted in-depth research on Ti incorporation into the framework and enhancement of diffusion properties at the end of the 20th century. Based on the classic synthesis method reported by Taramasso, they optimized the TS-1 zeolite synthesis process parameters, established a fuzzy formulation model, and adjusted the number and distribution of intracrystalline hydroxyl defects; they proposed a new post-treatment concept of "dissolution-recrystallization," which involved rearrangement and modification treatment of calcined TS-1 zeolite in a high-temperature hydrothermal environment containing organic structure-directing agents, producing hollow titanium silicalite (HTS) with unique intracrystalline closed mesopores. HTS not only has a higher amount of framework Ti but also possesses a closed mesoporous structure that can significantly promote intracrystalline diffusion, successfully addressing many issues associated with traditional TS-1 zeolites^[6]. Sinopec was the first to achieve industrial production of HTS zeolites at the beginning of the 21st century.

Compared with TS-1 zeolite, the main characteristics of HTS zeolite are: (1) a unique intracrystalline closed hollow mesoporous/macroporous structure. Due to the dynamic equilibrium between dissolution and crystallization during the rearrangement of the zeolite intermediate, under the action of composite additives, the difference in crystallization rate and dissolution rate inside and outside the crystal leads to the formation of a hollow structure within the crystal, avoiding the ineffective loss of silicon. (2) The condensation of silanol and titanohydroxyl groups on the surface of the zeolite produces more framework tetrahedral titanium active centers, making the crystal form of the zeolite more perfect and enhancing the stability of the zeolite framework. (3) It breaks through the limitations of foreign patent intellectual property. On the basis of synthesizing traditional microporous TS-1 zeolite, it creatively introduces secondary mesoporous features, bringing the synthesis of titanosilicate zeolites into a new stage^[7-8].

2.1.2 A New Process for the Preparation of Cyclohexanone Oxime via Ammoximation of Cyclohexanone

Caprolactam is the monomer with the longest production process and the most complex technology among all polymer monomers, and improving existing technologies is a global challenge. In the 1990s, over 90% of industrial caprolactam was produced via the cyclohexanone-hydroxylamine method, through the cyclohexanone oxime technology route. The core process involves the preparation of cyclohexanone oxime from cyclohexanone, and this step in the process is used to name the entire caprolactam production method. Traditional processes include three methods: Raschig (HSO), NO method, and HPO method, all of which involve the reaction of cyclohexanone with a salt of hydroxylamine to produce cyclohexanone oxime. The preparation of the hydroxylamine salt always begins with the high-temperature combustion of ammonia to form nitrogen oxides or nitrogen-containing salts, followed by reduction. This process not only has a long production flow, complex technology, harsh conditions, and high equipment investment, but also poses serious corrosion and pollution problems due to the generation or use of NO_x and/or SO_x. At that time, the mainstream production process was the HPO process developed by Dutch DSM, which mainly includes four catalytic reactions^[9]:

ammonia oxidation reaction

2NH₃ + 4O₂ $\to $ N₂O₅+ 3H₂O

hydroxylamine reaction

NO₃^-+ 2H⁺+ 3H₂ $\to $ NH₃OH⁺+ 2H₂O

oximation reaction

ammonium decomposition reaction

2NH₄⁺+ NO + NO₂ $\to $ 2N₂+ 2H⁺ + 3H₂O

in the 1980s, Italy's Enichem company discovered that under the catalytic action of TS-1 molecular sieve, cyclohexanone can undergo an ammoximation reaction with ammonia and hydrogen peroxide (H₂O₂), directly producing cyclohexanone oxime in a highly selective one-step process. This is an atom-economical new reaction, characterized by its simplicity, mild conditions, and minimal generation of waste, showing good prospects for industrial application. The process of the ammoximation of cyclohexanone is as follows:

=O+ NH₃ + H₂O₂ $\xrightarrow{\mathrm{TS}-1分子筛}$

= NOH + 2H₂O + Q

in 1998, Enichem had not yet industrialized the process and kept the technical details highly confidential, with only brief introductions of the process available in a few patents and documents. The key issues that needed to be addressed for the new reaction process to achieve industrial application included: optimization and determination of catalysts and reaction process forms, inhibition of zeolite framework silicon loss in alkaline reaction media, efficient regeneration technology for expensive zeolites, and the engineering scale-up of the new process. Against this backdrop, Sinopec independently developed the core technology for caprolactam production, specifically the new process of cyclohexanone oxime preparation through cyclohexanone ammoximation, and achieved industrial application simultaneously with overseas counterparts^[9].

One of the innovations in the new process is the direct use of sub-micron high-activity molecular sieve raw powder as a catalyst. According to literature, in foreign countries, due to the use of conventional filtration technology for separating the catalyst, it is required to spray-form the molecular sieve into microspherical catalysts with an average particle size of about 20 μm. The microporous membrane filtration technology developed by Sinopec directly uses the molecular sieve raw powder as a catalyst, eliminating the complex process of spray-forming the catalyst and the loss of the molecular sieve during preparation, thus reducing the investment and cost of catalyst production; more importantly, because the content of active components in the catalyst is maximized, and the internal diffusion effect of larger particle catalysts after forming is eliminated, it avoids the possibility of catalyst particle pulverization under slurry bed reaction conditions, allowing the catalytic performance of the molecular sieve to be fully utilized. In the cyclohexanone ammoximation reaction, using a single reactor can achieve better reaction results than the two-reactor series reaction process used abroad, further reducing investment and operating costs^[2,10].

The second innovation in the new process is the pioneering development of a combined new process featuring slurry bed catalytic reaction, microporous membrane filtration separation, and catalyst recycling. The cyclohexanone ammoximation process is a strongly exothermic multi-phase (gas-liquid-solid) reaction that occurs under liquid phase conditions, with significant mass transfer resistance. Based on the establishment of a reaction kinetics model and comparisons of different reaction process forms, it was found that using a slurry bed reaction process is beneficial for enhancing mass transfer and timely removal of reaction heat, achieving the best reaction results. Given that the particle size of highly active zeolite is only about 0.2 μm, it was proposed to use microporous membrane filtration technology for the separation and recycling of the catalyst and reaction products; at the same time, this solved the technical problem of membrane clogging in alkaline reaction systems, achieving for the first time the application and long-term stable operation of this combined process in large-scale continuous production in petrochemicals. This is entirely different from the conventional filtration separation techniques proposed abroad, providing a new direct application pathway for sub-micron solid catalytic materials with high activity^[11].

The third innovation in the new process is the invention of a method to suppress the loss of molecular sieves. In the cyclohexanone ammoximation reaction, the dissolution and loss of the molecular sieve framework silicon caused by the alkaline action of ammonia, one of the reaction raw materials, is the primary factor leading to catalyst deactivation. During long-term operation, this results in a continuous decrease in the amount of catalyst in the reaction system, making it impossible to maintain a stable catalyst concentration. At the same time, this dissolution effect also damages the structure of the molecular sieve, causing the migration of titanium. In response to the problem brought about by the first application of molecular sieve-type catalysts in an alkaline liquid-phase reaction system, a systematic study was conducted on the mechanism and patterns of the dissolution of molecular sieves by ammonia. It was found that the alkalinity of ammonia has a universal effect on the dissolution of silicon-containing molecular sieves, but this dissolution process occurs relatively quickly and there exists a dissolution equilibrium, with the equilibrium value varying according to the polarity of the reaction system. Based on these insights, a new process method was invented using a principle similar to the "common ion effect" to effectively address the loss of molecular sieve framework silicon. Industrial implementation of this method has achieved good results: the single-pass operation cycle of the catalyst can be extended by approximately 50%, and after operation, both the relative crystallinity and Si/Ti ratio of the molecular sieve can remain almost unchanged. This invention not only significantly extends the life of the catalyst but also improves its regenerability^[12].

The fourth innovation in the new process is the development of a unique deactivated catalyst acid treatment-calcination regeneration technology. The regenerability and regeneration methods of zeolite catalysts are an important aspect in catalyst research and development. Research results show that another significant factor for catalyst deactivation in the cyclohexanone ammoximation reaction process is pore blockage; thus, the regeneration methods reported in literature and patents mainly involve solvent washing and calcination, with the best regeneration results achieving 84% of the activity of fresh catalyst. Through the study of the regeneration chemistry of deactivated catalysts, it was recognized that after deactivation, zeolites adsorb certain basic peroxide by-products which are difficult to remove by organic solvents. This led to the proposal of a new acid treatment-calcination regeneration method, which was industrialized for the first time. After regeneration, the catalyst activity can be restored to 95% of that of a fresh catalyst, and it can be regenerated more than three times, further significantly reducing catalyst consumption^[10,13].

The oximation of cyclohexanone to produce cyclohexanone oxime is the core of caprolactam production and has a decisive impact on the technical and economic aspects of caprolactam production. In 2003, Sinopec developed a single-reactor slurry bed technology for the ammoximation of cyclohexanone to produce cyclohexanone oxime, and constructed a 70 kt/a ammoximation plant, achieving the first industrial application. In 2022, based on years of development and application of ammoximation technology, an upgraded ammoximation technology with high efficiency and reduced emissions was first applied to the relocation and transformation project of the caprolactam industry chain at Hunan Petrochemicals. The capacity of a single unit was increased from 100 kt/a to 300 kt/a, reaching a world-leading level, and the technical and economic performance of the plant was significantly improved (Figure 1). The integrated set of technologies includes new catalytic materials, new reaction engineering, and new reaction pathways, which raised the overall process carbon atom utilization rate from 80% to 95%, and the nitrogen atom utilization rate from 60% to 90%. The emission of the three wastes was significantly reduced, the investment in the plant was greatly decreased, and the production cost was notably lowered. The development of green caprolactam production technology has driven the rapid development of China's caprolactam industry, transforming China from being completely dependent on imported technology and products to becoming the world's largest caprolactam producer, with self-sufficiency rising from less than 15% to 98%. In 2023, China's caprolactam production capacity reached 6780 kt/a, accounting for more than 65% of the global caprolactam production capacity.

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图1 300 kt/a环己酮氨肟化工业生产装置

Fig. 1 A 300 kt/a cyclohexanone oxime industrial production unit

2.2 Integration of Amorphous Ni with Magnetically Stabilized Bed for Hydrogenation Purification of Caprolactam^[14]

Caprolactam has the most complex process and the highest product purity requirements among all basic organic chemical productions. To ensure its spinning and coloring performance, the impurity content must be less than 5 ppm. These impurities, which have similar physical and chemical properties to caprolactam, cannot be removed by extraction or distillation. The first-generation caprolactam production technology used Raney Ni catalyst and a batch reactor for hydrogenation to refine caprolactam, increasing the boiling point difference between impurities and caprolactam, thus allowing the removal of impurities through distillation. This hydrogenation refining technology had a complex process flow, high catalyst consumption, low hydrogenation efficiency, and required filtration and separation of the catalyst. By converting the crystalline structure of the Raney Ni hydrogenation catalyst to an amorphous one, its hydrogenation activity was significantly increased. Combined with the excellent reaction process enhancement performance of the magnetically stabilized bed reactor, a product refining technology in caprolactam production was successfully developed, leading to improved caprolactam quality, increased yield, and reduced operating costs.

2.2.1 Amorphous Alloy Catalysts

In the 1990s, by overcoming the disadvantages of poor structural stability and small specific surface area of amorphous alloys, an amorphous Ni alloy catalyst was successfully developed. This catalyst exhibits superior hydrogenation activity compared to Raney Ni catalysts, allowing for the hydrogenation saturation of alkenes, alkynes, and nitro compounds at lower temperatures, making it a promising new type of hydrogenation catalyst with great application potential. Additionally, the amorphous Ni alloy catalyst possesses excellent magnetic properties, which perfectly meet the requirements for solid catalysts in magnetically stabilized beds. In magnetically stabilized beds, an external magnetic field can effectively prevent the carryover of fine particle catalysts, enabling high space velocity operations. The hydrogenation refining of CPL is carried out at low temperatures with a small amount of reactants and high space velocity. Therefore, using an amorphous Ni alloy catalyst in a magnetically stabilized bed for the hydrogenation refining of CPL not only takes advantage of the high hydrogenation activity of the amorphous Ni alloy catalyst at low temperatures but also fully leverages the advantages of magnetically stabilized beds.

2.2.2 Development and Application of Magnetic Stabilized Bed Technology for Caprolactam Hydrogenation Refining Process

In 1999, a laboratory-scale study on the hydrogenation refining of CPL using a magnetically stabilized bed with an amorphous Ni alloy as the catalyst was carried out. One of the quality indicators for CPL is the potassium permanganate value (PM value), and the higher the PM value, the lower the content of unsaturated impurities. The results of the small-scale test showed that in the magnetically stabilized bed reactor, the PM value of the CPL aqueous solution could be increased from 60 s to more than 3000 s, with the catalyst life reaching over 1350 h. In contrast, the PM value in the batch hydrogenation process only increased from 60 s to 300 s, indicating a significant improvement in the hydrogenation effect and demonstrating good prospects for industrial application.

Due to the fact that the magnetically stabilized bed is different from both fixed beds and ordinary fluidized beds, and has its own complexity, it is very important to conduct research on the hydrodynamic characteristics of the magnetically stabilized bed. In 2000, a cold model experimental setup for the magnetically stabilized bed was established, and subsequently, studies on the hydrodynamic characteristics, mass transfer characteristics, and reaction kinetics of the liquid-solid two-phase magnetically stabilized bed were completed. The relationship between the bed structure of the magnetically stabilized bed reactor and operating parameters such as magnetic field intensity, catalyst properties, and fluid velocity was found, achieving effective control of the catalyst by the magnetic field. A mathematical model of the magnetically stabilized bed reactor and operation phase diagrams for the magnetically stabilized bed with different particle sizes of catalysts were also established, providing a scientific basis for the industrialization of the magnetically stabilized bed.

Generating a uniform magnetic field is one of the keys to the industrial scaling of magnetically stabilized beds. The research results on the distribution pattern of the magnetic field show that after the electromagnetic coil is scaled up, the magnetic field intensity at the center of the coil is weaker and gradually increases along the radial direction; when the coil diameter is 770 mm, the magnetic field intensity at the inner wall of the coil is 15% higher than that at the center of the coil. To further improve the uniformity of the magnetic field, different density magnetic baffles were developed and designed to achieve a radially uniform distribution of the magnetic field. In addition, during use, the temperature of the coil rises due to heat generation, and the issue of coil heating was resolved using forced water cooling, achieving long-term, safe, and stable operation of the coil.

Based on the aforementioned research, in 2001, Sinopec Baling Branch established a magnetic stabilized bed CPL hydrogenation refining industrial side-line facility capable of processing 6000 t/a of pure caprolactam. The experimental results showed that for a 30% caprolactam aqueous solution with a PM value of 40~60 s, after hydrogenation refining through the magnetic stabilized bed, the PM value could reach 2000~4000 s, significantly outperforming the stirred tank process (200~400 s). The conditions for the magnetic stabilized bed hydrogenation process were: reaction temperature 80~100 ℃, reaction pressure 0.4~0.9 MPa, space velocity 30~50 h^-1, magnetic field strength 15~35 kA/m, and the lifespan of the amorphous alloy catalyst could reach 3500 h.

In 2003, an industrial facility with a capacity of 35 kt/a was built at the original Shijiazhuang Chemical Fiber Co., Ltd., realizing the industrial application of the magnetically stabilized bed reactor, with production capacity reaching 65 kt/a. In 2009, the company constructed a new 100 kt/a magnetically stabilized bed hydrogenation refining unit (Figure 2), which operated stably. The Baling branch completed the construction of a 70 kt/a magnetically stabilized bed CPL hydrogenation refining industrial unit in March 2005, achieving success on the first start-up. Long-term operation results showed that the unit operated stably, was easy to start and stop, and had high hydrogenation efficiency. A 30% CPL aqueous solution with a PM value of 50 s, after being hydrogenated through the magnetically stabilized bed, could achieve a PM value above 4000 s, an increase of more than ten times, significantly improving hydrogenation efficiency and catalyst utilization while reducing catalyst consumption by 50%. The successful industrial application of the magnetically stabilized bed reactor in CPL hydrogenation refining has laid the foundation for its application in other fields, promoting the development of magnetic field fluidization technology, with significant economic and social benefits.

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图2 100 kt/a磁稳定床己内酰胺加氢精制工业生产装置

Fig. 2 A 100 kt/a industrial magnetically stabilized bed reactor unit

3 Fluidized Bed Hydrogen Peroxide Process

Hydrogen peroxide is internationally recognized as an environmentally friendly and green product, with wide-ranging applications. Due to its reduction product being only water, it has "mutually promoted" the development of green chemistry, and the natural green attributes of hydrogen peroxide have spurred the emergence and development of a large number of green processes that use hydrogen peroxide as an oxidant. In recent years, the production of hydrogen peroxide both at home and abroad has been on a rising trend. In 2023, the domestic capacity for hydrogen peroxide was approximately 5.3 Mt (on a 100% basis), ranking first in the world, and growing at an annual rate of about 10%. Although China is a major producer of hydrogen peroxide, due to the huge domestic consumer market, overall, hydrogen peroxide in China still shows a situation where supply cannot meet demand, and imports continue to grow in recent years.

Currently, 95% of the global total production and 99% of the domestic total production of hydrogen peroxide are produced using the anthraquinone method. The anthraquinone method involves dissolving alkyl anthraquinones in a mixed solvent to form a working solution, which is then subjected to catalytic hydrogenation, air oxidation, pure water extraction, and post-treatment of the working solution to prepare an aqueous solution of hydrogen peroxide. Before 2018, all the hydrogen peroxide production technology using the anthraquinone method in China adopted the fixed-bed process. Although this process is simple to operate and does not require the separation of catalysts, it has obvious defects such as "the hydrogenation reaction of alkyl anthraquinones being an exothermic process, with poor heat transfer and heat removal performance of the fixed bed, resulting in a temperature rise of 8~10 ℃ in the bed layer, and the formation of local hot spots due to uneven flow." To avoid over-hydrogenation of the working solution, industrial production can only control the hydrogenation conversion rate of alkyl anthraquinones at 30%~40%, and the hydrogenation efficiency at 6~8 g/L. Due to the low efficiency of domestic hydrogen peroxide production technology, the maximum production capacity of the equipment is only about 50 kt/a, failing to meet the demand for large-scale green processes such as caprolactam and propylene oxide. The backward level of domestic hydrogen peroxide production has seriously restricted the development of downstream green chemical industries. Compared with the fixed bed, the fluidized bed process has excellent mass and heat transfer properties, uniform mixing of gas, liquid, and solid phases, and a uniform bed temperature, overcoming the shortcomings of the fixed bed. The conversion rate of alkyl anthraquinones can reach 60%, and the hydrogenation efficiency can achieve 10~15 g/L, significantly reducing the amount of circulating working solution, and having a clear advantage in large-scale production. Major international hydrogen peroxide producers, such as DuPont, Solvay, Akzo Nobel, MGC, FMC, Total, Degussa, and BASF, have all adopted the fluidized bed process for their recently constructed large-scale hydrogen peroxide production facilities. Due to the considerable difficulty in the research and development of the fluidized bed anthraquinone method for producing hydrogen peroxide, foreign companies implement strict technological blockades and restrictions on technology transfer^[15].

To develop green chemical technology with independent intellectual property rights, Academician Min Enze has been guiding research on magnetically stabilized bed hydrogen peroxide since 2000 and has applied for multiple Chinese invention patents^[16-17]. In 2012, in order to break the foreign technological blockade, improve the overall level of the domestic hydrogen peroxide industry, and eliminate the raw material bottleneck for downstream large-scale green chemical projects, Sinopec organized multiple units to form a development team led by the Sinopec Research Institute of Petroleum Processing (RIPP) to tackle the complete set of fluidized bed anthraquinone method for producing hydrogen peroxide. After going through laboratory, pilot, and model tests, in 2019, they successfully developed several innovative achievements, including high-efficiency anthraquinone hydrogenation microsphere catalysts, high-capacity working fluids, and fluidized bed reaction engineering technologies, forming a complete set of fluidized bed anthraquinone method for producing hydrogen peroxide with independent intellectual property rights. In August 2019, a 20 kt/a industrial demonstration unit designed and constructed using this complete set of technology was successfully started up and operated smoothly, achieving a hydrogenation efficiency of 10~12 g/L, with product concentration reaching 35%, and all indicators meeting the design targets.

3.1 Efficient Anthraquinone Hydrogenation Microspherical Catalyst

The hydrogenation self-oxidation of alkyl anthraquinones is a critical reaction process in the production technology of hydrogen peroxide, where the hydrogenation catalyst is at the core of the entire cyclic reaction, relating to the production capacity and economic benefits of the hydrogen peroxide production process. Through technological breakthroughs, the project team addressed the following scientific issues in the industrialization process of microsphere noble metal Pd catalyst: the relationship between carrier properties and the "firmness" of Pd loading, the fundamentals of carrier wear resistance and thermal stability, the relationship between Pd grain size and catalyst activity and selectivity, and the mechanism of the β-PdH phase during the hydrogenation of alkyl anthraquinones, achieving the industrial production and application of high-activity, high-selectivity, and high-stability fluidized bed anthraquine hydrogenation catalyst^[18].

For the research on noble metal catalysts that do not emphasize "practicality" and are purely theoretical, people rarely consider the loss of noble metals during use. However, in reality, due to the high cost of noble metals, for industrial catalysts, the primary consideration should be the loss of noble metals during use. Historically, there have been numerous examples where the operating costs of catalysts were too high, affecting the operation of industrial facilities. For instance, the SNIA toluene process for caprolactam production was eventually phased out because the expensive Pd/C catalyst used in its benzoic acid hydrogenation unit made it unviable^[19]. In the case of hydrogen peroxide plants, in addition to impacting process costs, the loss of palladium is more importantly a safety issue as the lost palladium entering "downstream" units can cause the decomposition of hydrogen peroxide. Therefore, for anthraquinone hydrogenation processes, it is crucial to have a catalyst that combines high activity, high selectivity, and secure metal fixation. The project team, focusing on the development of high-Pd-loaded anthraquinone hydrogenation catalysts for fluidized beds, systematically compared the performance of different Pd/Al₂O₃ catalysts prepared by impregnation, colloidal precipitation, and polyol reduction methods, finding that: while the impregnation method could achieve a Pd loading of over 99%, although the colloidal precipitation and polyol reduction methods could produce Pd/Al₂O₃ catalysts with nanoscale distribution and high dispersion, these methods had low Pd loading during preparation and the Pd was prone to detachment during use. Ultimately, the robustness issue was resolved through the selection of an optimal loading method.

The wear resistance and thermal stability of the carrier are involved in the long-term operation of the hydrogenated Pd catalyst. When the catalyst is used in a fluidized bed, wear occurs due to friction between catalyst particles, between particles and the working liquid, and between particles and the equipment walls, leading to an increase in the content of catalyst powder in the slurry, resulting in increased catalyst consumption and poorer solid-liquid separation. In the hydrogen peroxide fluidized bed process, if the catalyst powder carrying metallic Pd enters the oxidation tower with the hydrogenated liquid, it can lead to the decomposition of hydrogen peroxide in the oxidation tower, increasing the risk of accidents; therefore, the anthraquinone hydrogenation process in a fluidized bed has extremely high requirements for the wear resistance of the catalyst. Studies have shown that the wear resistance and mechanical strength of the alumina carrier and supported catalysts are closely related to their hydrothermal stability. When using γ-Al₂O₃-based carriers in catalytic processes involving water or water generation, Al₂O₃ undergoes rehydration, leading to a decrease in the specific surface area and strength of the catalyst. Hydrothermal test results show that γ-Al₂O₃ undergoes hydration reactions at 60 ℃ in the presence of water, forming a small amount of prismatic boehmite on the surface of γ-Al₂O₃ particles. The higher the boehmite content in the carrier, the worse its stability. To obtain a highly wear-resistant fluidized bed catalyst, improvements must be made in both mechanical wear strength and hydrothermal stability. Although no water is generated in the anthraquinone hydrogenation reaction, some water is inevitably introduced into the working liquid after the extraction process, and although it is dried in a drying tower, the working liquid still contains trace amounts of moisture. During the long-term use of the catalyst, this trace amount of moisture will affect the strength of the catalyst. To meet the requirements of the fluidized bed process for catalyst strength and thermal stability, and considering the mechanism of the anthraquinone hydrogenation reaction, doping SiO₂ into γ-Al₂O₃ was adopted, grafting Si-OH onto the surface of γ-Al₂O₃, which reduces the tetrahedral and octahedral vacancies on the surface of γ-Al₂O₃. According to the NH₃-TPD characterization results, the number of strong acidic sites on the catalyst surface is greatly reduced; the reduction of electron-deficient centers on the surface of γ-Al₂O₃ inhibits the adsorption of trace H₂O in the reaction system by the catalyst during the reaction, avoiding the rehydration of γ-Al₂O₃, thereby improving the hydrothermal stability and wear resistance of the catalyst. Moreover, Pd has a smaller particle size and higher dispersion, adjusting the adsorption strength of anthraquinone molecules on the catalyst surface, preventing over-hydrogenation and the formation of degradation products. The hydrothermal stability of the Si-modified catalyst is increased by 6.19 times, and the wear resistance is increased by 30.90 times.

3.2 Development of High-Productivity Working Fluids

The anthraquinone method for producing hydrogen peroxide involves dissolving alkyl anthraquinones as carriers in a mixed solvent of heavy aromatics and esters or higher alcohols to form a working solution, which undergoes processes such as hydrogenation, oxidation, and extraction. The properties of the working solution have a significant impact on production process operations, product yield and quality, and energy conservation. In the early stages of anthraquinone-based hydrogen peroxide production, the primary alkyl anthraquinone used was 2-ethylanthraquinone (EAQ), while in recent years, most newly constructed facilities have adopted 2-amylanthraquinone (AAQ) with higher solubility as the working carrier. For the organic mixed solvents used to dissolve alkyl anthraquinones, China initially utilized a mixture of benzene and hydrogenated terpene alcohol (HT). In the 1970s, heavy aromatics began to replace benzene as the solvent for anthraquinones, and in the 1980s, trioctyl phosphate (TOP) successfully replaced HT as the solvent for hydrogenated anthraquinones. By the end of the 20th century, some European and American patents introduced solvent systems that were mostly mixtures of new nitrogen-containing polar solvents and general non-polar solvents, with representative substances being diisobutyl carbinol (DIBC), tetrabutyl urea (TBU), and methylcyclohexyl acetate (MCA). Currently, the new polar solvents applied in domestic production facilities are TBU and MCA.

The solubility data of four anthraquinone systems and three types of solvent systems were determined by the equilibrium method under multiple temperature conditions. The anthraquinone systems involved are three single anthraquinones (2-ethylanthraquinone EAQ, 2-tert-butylanthraquinone BAQ, and 2-amylanthraquinone AAQ) and one mixed anthraquinone (a mixture of EAQ and AAQ). The solvent systems involved are three mixed solvents including mesitylene-trioctyl phosphate (TMB-TOP), mesitylene-diisobutyl carbinol (TMB-DIBC), and mesitylene-methylcyclohexyl acetate (TMB-MCA). In addition, the distribution of hydrogenation by-products of different anthraquinones is also different. The main over-hydrogenation by-products of EAQ are tetrahydroethylanthraquinone (H4EAQ), 2-ethylanthrone (EAN), 2-ethyl-1,2,3,4-tetrahydroanthraquinone, and 2-ethyl-1,2,3,4,5,6,7,8-octahydroanthraquinone. The over-hydrogenation by-products of AAQ are only tetrahydroamylanthraquinone (H4AAQ) and 2-tert-amylanthrone (TAAN). Moreover, at the same conversion rate, the yield of TAAN is significantly lower than that of EAN, indicating that using amylanthraquinone is beneficial for inhibiting degradation products.

3.3 Inherent Safety Integrated Process Based on High-Throughput Fluidized Bed Reactor

Using a large-scale cold-state fluidized bed test device as a model, a model suitable for the hydrogenation reactor in the anthraquinone process for hydrogen peroxide production was established. The characteristics of fluid flow inside the fluidized bed reactor were studied through CFD simulation to summarize the flow patterns. Subsequently, CFD simulation was utilized to optimize the reactor structure, ensuring uniform fluid flow and mixing within the reactor while retaining most of the catalyst inside, thus preventing the loss of precious metal catalysts. This ultimately provided valuable foundational data and computational models for reactor selection. Based on the process characteristics of the fluidized bed hydrogenation reactor, systematic continuous filtration and fluid mechanics experiments were conducted, mastering the fluid mechanics rules of the fluidized bed hydrogenation reactor and obtaining filter flux data. Through further structural optimization of the reactor using CFD simulation, a form of fluidized bed hydrogenation reactor suitable for the anthraquinone process for hydrogen peroxide production was finally determined.

Based on the development of a hydrogenation reactor, a complete set of fluidized bed reaction engineering technology has been developed, with its main features being: ① Uniform mixing of gas-liquid-solid three phases, almost no temperature rise in the bed layer, no local reaction hot spots, which can effectively control the occurrence of anthraquinone hydrogenation side reactions. By increasing the degree of anthraquinone hydrogenation, higher hydrogenation efficiency can be achieved; it solves the problems of gas-liquid separation and heat removal from the reaction; the friction effect of the gas-liquid-solid three-phase mixture is relatively mild, greatly reducing the amount of fine powder generated by the wear of the anthraquinone hydrogenation catalyst; the tail gas is recycled, resulting in less emissions, making it safe and environmentally friendly; the catalyst does not need to be frequently regenerated; the operation is simple and convenient. ② Automatic backflushing high-throughput filtration technology. The first-stage filtration uses self-developed filter elements that have high throughput and are not prone to clogging, with low manufacturing costs; a stable and reliable automatic backflushing program has been established to ensure the simplicity and convenience of the equipment's operation; it has high separation accuracy, capable of controlling the turbidity of the clear liquid within 1 NTU; through a real-time backflushing system, long-term stable operation of the filter is guaranteed. ③ A new type of anthraquinone oxidation form has been developed using enhanced mass transfer methods, significantly improving the oxidation efficiency and yield; it addresses the issues of scale-up and gas-liquid separation, featuring a simple structure that is easy to disassemble and inspect.

Combining the characteristics of hazards and safety control measures of each unit in the fluidized bed integrated technology, a detailed hazard and operability analysis is conducted, and in-depth research is carried out on the identified hazardous factors. This includes: ① Study on the gas phase explosion risk of the hydrogenation reactor. The fluidized bed anthraquinone process for hydrogen peroxide production greatly improves the hydrogenation efficiency, potentially leading to an increase in hydrogen peroxide content in the circulating working solution, which decomposes to produce oxygen in the hydrogenation reactor, forming an explosive mixture in the gas phase space. An isothermal test system was used to investigate the effect of residual hydrogen peroxide on the oxygen content in the hydrogenation reactor. It was found that trace amounts of hydrogen peroxide do not decompose rapidly but rather decompose slowly, with a noticeable release of oxygen after about 30 minutes. ② Study on the gas phase explosion risk at the top of the oxidation reactor. In the hydrogen peroxide production process, due to the potential decomposition of hydrogen peroxide in equipment such as the oxidation liquid receiving tank and extraction tower, these devices may be in a rich oxygen environment, posing an explosion risk. Nitrogen protection measures need to be designed for such equipment. ③ Study on the explosion risk of a multi-component system in the extraction tower. The new fluidized bed anthraquinone process for hydrogen peroxide production has increased the unit capacity, significantly raising the hydrogen peroxide content in the oxidation liquid, thereby providing the conditions for extracting high-concentration hydrogen peroxide. However, during the direct extraction of high-concentration hydrogen peroxide, it is possible to form an explosive mixture. To effectively simulate actual operating conditions, a suitable emulsifier should be selected to form a homogeneous system while ensuring that the added reagents do not react with the original system. Through experiments, the minimum amount of surfactant that can achieve emulsification was determined, and a hydrogen peroxide-surfactant system was prepared using this type and quantity.

3.4 120 kt/a Fluidized Bed Anthraquinone Process for Industrial Hydrogen Peroxide Production

Hydrogen peroxide, as an important raw material for the industrial chains of caprolactam, propylene oxide, and epichlorohydrin, has seen a gradual expansion in production capacity by related chemical enterprises both domestically and internationally in recent years. Since 2020, Sinopec, based on abundant experimental data obtained from a 20 kt/a industrial demonstration plant, has carried out comprehensive process optimization adjustments, product quality improvements, and energy-saving renovations through industrial trials. It developed a 120 kt/a fluidized bed anthraquinone method for hydrogen peroxide production, which was first applied to the relocation and upgrade transformation project of the caprolactam industry chain at Hunan Petrochemical. The construction of the facility was completed in May 2023 (Figure 3), and it successfully started up on October 18 with a single hydrogen feed. So far, the overall operation of the facility has been stable. The 120 kt/a hydrogen peroxide production facility adopts a full-process technology for fluidized bed hydrogen peroxide production, featuring slurry-bed anthraquinone hydrogenation, efficient filtration and automatic backflush procedures, multi-stage precision filtration, high-efficiency anthrahydroquinone oxidation, and post-treatment of working solution. This series of technologies ensures simple operation, high automation, and high production efficiency of the facility, while the fully acidic environment enhances the intrinsic safety of the entire facility.

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图3 120 kt/a流化床蒽醌法生产过氧化氢工业生产装置

Fig. 3 A 120 kt/a H₂O₂ industrial production unit with fluidized bed reactor

4 Hydrogen Peroxide Method for Propylene Oxide Production Technology

Propylene oxide (PO) is the second largest propylene derivative in terms of production capacity, after polypropylene, and is widely used in the production of many high-value chemicals such as propylene glycol, propylene carbonate, polyurethane, and unsaturated resins. Since the early 1990s, the domestic consumption of PO has shown a rapid growth trend, with an average annual growth rate of 18.5% from 1990 to 2008; since 2009, with the upgrade of consumption in China's transportation, home appliances, building energy conservation, and textile industries, the demand for downstream products has been strong, further driving the rapid growth of the PO industry, and the consumption of PO reached 2.6 Mt in 2014. The average annual growth rate of PO consumption from 2009 to 2014 was 29.8%. In 2023, China's PO consumption reached 4.20 Mt, accounting for about 32% of the global total^[20].

In contrast to the significant growth in demand, about 50% of PO in China is still produced using the traditional chlorohydrin method with chlorine as the raw material, which generates 40-80 t of chlorine-containing wastewater, 2.5 t of calcium chloride waste residue, and 0.14 t of organic waste liquid per ton of product. Since 2013, the chlorohydrin method has been listed by the state as a restricted project, and no new installations have been approved. The co-oxidation route using organic peroxides as oxidants, including the POSM method, PO-TBA method, and CHPPO method, can reduce the generation of toxic and hazardous waste, but it faces issues such as complex processes, high investment costs, foreign monopoly on technology, and the significant impact of co-product prices by the market. Therefore, the hydrogen peroxide propylene oxide (HPPO) process, reported by Italian EniChem company in 1986, which uses TS-1 zeolite as a catalyst, has advantages such as high atomic utilization, cleanliness, efficiency, and simplicity, and has been highly valued by countries around the world. The atomic utilization rate for the epoxidation reaction of propylene and hydrogen peroxide catalyzed by titanium silicalite reaches 76.3%, making it an atom-economical reaction. Compared to the HPPO method, the atomic utilization rates of existing PO production technologies are generally lower, for example, 31.2% for the chlorohydrin method, 37.7% for the ethylbenzene co-oxidation method, and 38.7% for the isobutane co-oxidation method. Compared to the chlorohydrin method, the HPPO method reduces wastewater by about 70%-80% and saves 35% of energy consumption; compared to the isobutane co-oxidation method, the HPPO method requires only 73.9% of the investment, has a production cost of approximately 71.3%, and emits CO₂ at just 71.4%. Unlike ethylene, propylene contains active hydrogen atoms that are easily oxidized, so how to avoid deep oxidation of hydrogen becomes a core problem to be solved. Research shows that using titanium silicalite to catalyze the epoxidation reaction between propylene and hydrogen peroxide is one of the key approaches to overcoming this challenge.

4.1 Surface-Rich Silicon Multi-Hollow Ti-Si Molecular Sieve Catalyst

As propylene oxide (PO) generated from the oxidation of propylene can further react to form propylene glycol and propylene glycol methyl ether, the acidity in the system easily promotes the secondary solvolysis reaction of PO. The sources of the system's acidity include: hydrogen peroxide itself being weakly acidic, the dissociation of a five-membered ring structure formed by hydrogen peroxide and titanium-silicon zeolite generating B acid, the surface and lattice defects of the zeolite, Ti active centers, and trace amounts of Al producing acidity. The acidity of hydrogen peroxide is inherent and unavoidable as long as it acts as an oxidant, and experiments have shown that hydrogen peroxide alone is insufficient to cause the ring-opening of propylene oxide. The five-membered ring formed by hydrogen peroxide and titanium-silicon zeolite is the active center for activating hydrogen peroxide and producing oxidative effects; thus, it is necessary to reduce the acidity on the zeolite. Based on the understanding of acidity control, the project team successfully developed technologies for regulating the radial elemental distribution of titanium-silicon zeolites, condensation of silicon-titanium hydroxyl groups, and intracrystalline framework reconstruction, pioneering a surface-rich silicon multi-hollow titanium-silicon zeolite active component. This introduced a hierarchical pore structure into high-crystallinity zeolites, forming abundant hollow structures, which promoted intracrystalline mass transfer and diffusion. By enhancing the condensation of silicon-titanium hydroxyl groups, more framework titanium active centers were obtained, reducing side reactions; the enrichment of silicon on the external surface of the zeolite reduced direct contact between hydrogen peroxide and titanium species, inhibiting the ineffective decomposition of hydrogen peroxide, thereby improving the utilization rate of raw materials and system safety. Compared with conventional TS-1, the mesopore volume of HTS increased by 3.57 times, the self-diffusion coefficient of cyclohexane increased by 4 times, PO selectivity increased by 26%, hydrogen peroxide utilization rate increased by 17%, and the single-pass evaluation life was extended by more than 1.5 times^[21].

Using surface-rich silicon multi-hollow titanium-silicon molecular sieves as the active component, further development of mesoporous "filling protection" and "stress elimination" technologies for molecular sieve active components is carried out to improve the utilization efficiency of intracrystalline pores. Combined with the understanding of the controllable removal mechanism of organic matter on the surface of templated molecular sieves, a combined treatment technology of solvent extraction and low-temperature thermal decomposition has been developed, forming a new efficient catalyst shaping technology. This new shaping technology selectively removes template molecules from the outer surface, increasing the contact area between surface silicon-titanium hydroxyl groups and binders, allowing hydroxyl groups in the composite binder to chemically couple with silanol groups in the molecular sieve under specific conditions, forming Si-O-Si chemical bonds. This not only increases the content of active components in the catalyst but also achieves high specific surface area and high mechanical strength, enabling the shaped catalyst to maintain high activity, high selectivity, and high stability. The specialized epoxidation catalyst HPO-1, prepared using HTS as the active component with the new technology, has been in industrial operation for over 9 years, and its catalytic performance has shown no decline^[22].

4.3 Green and Efficient Process for Low-Temperature Propylene Epoxidation and Dedicated Reactor

To master the complete set of HPPO technology, Sinopec began laboratory research on HPPO catalysts and processes since 2000, successively completing small-scale trials and pilot side-line tests of the HPPO process, and in 2014, built an industrial plant with a scale of 100 kt/a. Within four years, multiple technical challenges were resolved, and by 2018, full-load calibration of the plant was completed. All technical indicators surpassed those of similar foreign technologies, making China the third country after the United States and Germany to master this technology.

One of the key innovations in the engineering field of Sinopec's HPPO technology is the development of a low-temperature propylene epoxidation green and efficient process and a dedicated reactor, the research and development of composite additives that enhance the formation of transition states, the development of technologies for uniform material distribution and efficient rapid heat removal, the improvement of propylene and hydrogen peroxide utilization efficiency and system safety, the increase in PO selectivity, and the enhancement of the stability of highly active catalysts; the in-situ mild regeneration technology of epoxidation catalysts within the reactor ensures long-term full-load stable operation of industrial facilities. Based on the HPPO reaction mechanism, composite additives with specific functional group structures have been developed, which, by reducing the surface Gibbs free energy, enhance the contact between propylene and hydrogen peroxide at the molecular scale, thus increasing the reaction rate. The electron-donating functional groups in the composite additives can adjust the electronic cloud density distribution of the framework titanium, promoting the generation of active oxygen species and "five-membered ring" intermediates, controlling the preferential directed insertion of active oxygen into the propylene C=C double bond, and improving PO selectivity; the electron-rich functional groups can also form strong chemical interactions with the defect sites of the framework, significantly weakening the adsorption of PO molecules and side reactions such as ring-opening hydrolysis, etherification, and polymerization at these defect sites. Compared to systems without added composite additives, the conversion rate of hydrogen peroxide and PO selectivity increased by 3.5% and 27.5%, respectively, and the single-pass evaluation life of the catalyst was improved by 2.5 times.

The second key innovation in the field of engineering is the development of integrated epoxidation reaction technologies, such as multi-stage series and reaction mode switching control, to address the challenges of high heat release during the epoxidation reaction and the instability of PO product due to easy ring-opening. These technologies achieve high conversion rates and selectivity under low alcohol-to-olefin ratios. The development includes a multi-stage series, staged hydrogen peroxide addition, and reactor switching for regeneration processes, which make the reaction rate more controllable than with a single reactor, improving the efficiency and safety of the reactor while significantly reducing energy and material consumption. Fluid distribution technology, temperature control technology, and pressure drop control technology for the epoxidation reactor have been developed; these not only ensure the effectiveness of the epoxidation reaction but also enhance the utilization efficiency of the catalyst and the stable operation of the reactor. A large baffle and shell seamless gap sealing technology has been developed, where an elastic sealing strip is used between the baffle and the cylinder to reduce the leakage of heat transfer medium and improve thermal efficiency. Furthermore, the setting of mode switching and interlock schemes for multiple reactors in the epoxidation reaction system during operation, regeneration, and shutdown conditions has been established, enabling long-term stable operation of the facility.

The third key innovation in the engineering field is the development of product separation and purification technology that integrates low-temperature PO separation, chemical decontamination, and thermal integration, to improve product quality and reduce system energy consumption. PO has active chemical properties, and lower temperatures and higher space velocities are conducive to reducing side reactions such as etherification and hydration of PO. A low-temperature and low-pressure stripping technology has been developed where the reactor effluent first enters a propylene separation column, from which propylene oxide and propylene, among others, are separated at the top. The gaseous material from the top of the column enters the PO absorption tower, while the liquid phase goes into the propylene stripping tower, where propylene is stripped out. The purity of PO at the bottom of the stripping tower exceeds 96%. To enhance product purity, the PO product is refined using alkali and organic reductants to remove impurities such as methyl formate and acetaldehyde, achieving a 100% removal rate for these impurities. Further, through extractive distillation, methanol is removed, resulting in a PO product purity of 99.99%, meeting the production requirements for high-end polyethers. Methanol distillation consumes a large amount of steam, accounting for a significant proportion of the overall energy consumption. To reduce the energy consumption of the equipment, a dual-effect methanol distillation heat integration technology has been developed, utilizing the methanol vapor from the top of the first high-pressure distillation column as the heat source for the reboilers at the bottom of other distillation columns, thus realizing cascading use of energy. The high-purity methanol, after removing water and heavy organic compounds, continues to be recycled as a solvent.

The fourth key innovation in the engineering field is the development of technologies for preventing high-concentration hydrogen peroxide decomposition and explosion, controlling epoxidation reaction risks, and preventing flash vaporization system combustion and explosion accidents, ensuring the intrinsic safety of the entire process. A coupling treatment technology for alcohol-containing wastewater and catalytic cracking units has been developed to achieve the resource utilization of organic matter in wastewater. In response to the challenge of high-risk levels associated with high-concentration hydrogen peroxide, a study on the kinetics of out-of-control hydrogen peroxide decomposition was conducted, leading to the determination of an intrinsically safe reactor feed scheme. The risk assessment of the epoxidation reactor was completed, and research on the sensitivity of process reaction parameters and the danger of uncontrolled reactions in dead zones within the reactor was carried out. Safety technologies such as enhanced mixing of reactor feeds and rapid discharge were also developed. By studying the combustion and explosion hazards of oxidized tail gas under the operating conditions of the propylene flash vaporization system, a safe flash vaporization process route for oxidized tail gas was determined, and a control plan and interlock technology for tail gas combustion and explosion hazards were developed, minimizing propylene emissions while ensuring safety. A Hazard and Operability Study (HAZOP) for the entire process flow of the equipment was completed, and a comprehensive safety solution for the equipment was proposed. Wastewater from the HPPO unit is used as a terminator in the refinery's catalytic cracker, where organic compounds such as propylene glycol and propylene glycol monomethyl ether are cracked into high-value low-carbon hydrocarbons like ethylene and propylene. The remaining wastewater can then be efficiently treated through conventional wastewater treatment systems, achieving the resource utilization of wastewater.

Since 2000, Sinopec has been continuously tackling key issues from active components and catalysts to process engineering, developing HPPO technology with independent intellectual property rights, and constructing the first industrial plant in China using HPPO technology with its own intellectual property. This plant has achieved safe, full, long, stable, and excellent operation (Figure 4). Currently, Sinopec has granted HPPO technology licenses to four companies including North Huajin, and over the next three years, 300 kt/a industrial plants will be built using this technology, bringing the total production capacity of HPPO technology to 1.3 Mt. Following a similar approach and using HTS catalysts, Sinopec began researching the epoxidation of allyl chloride to produce hydrogen peroxide epoxy chloropropane (HPECH) in 2002. In 2019, a 50 kt/a HPECH process package was reviewed, and currently, an industrial demonstration plant is under construction at Sinopec.

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图4 100 kt/a过氧化氢法制备环氧丙烷工业生产装置

Fig. 4 A 100 kt/a hydrogen peroxide propylene oxide (HPPO) industrial production unit

5 Novel Technology for the Hydrogenation of Cyclohexene Esters to Produce Cyclohexanone

Cyclohexanone is the main intermediate for the preparation of caprolactam. There are mainly two industrial production processes for cyclohexanone: the air oxidation of cyclohexane and the hydration of cyclohexene. The oxidation of cyclohexane is the traditional mainstream production process, which mainly includes: hydrogenation of benzene to produce cyclohexane, oxidation of cyclohexane to form cyclohexyl hydroperoxide, decomposition of cyclohexyl hydroperoxide to yield cyclohexanol and cyclohexanone, and dehydrogenation of cyclohexanol to produce cyclohexanone. The hydration of cyclohexene mainly involves: selective hydrogenation of benzene to produce cyclohexene, separation of benzene-cyclohexane-cyclohexene, hydration of cyclohexene to produce cyclohexanol, and dehydrogenation of cyclohexanol to produce cyclohexanone. Among the two industrial production technologies, the carbon atom utilization rate of the cyclohexane oxidation process is about 80%, with large emissions of the "three wastes" and low production safety; the carbon atom utilization rate of the cyclohexene hydration process is about 95%, but it has high energy consumption for separating cyclohexane, cyclohexene, and benzene, and the single-pass conversion rate of the hydration reaction is only around 10%. In 2013, cyclohexanone was listed by the Ministry of Ecology and Environment as one of the key chemicals for national environmental risk control, making the development of new green production technologies with high atomic economy and low energy consumption an urgent necessity.

The hydration of cyclohexene to produce cyclohexanol was developed by Asahi Kasei in the 1980s. This method first involves the selective hydrogenation of benzene to cyclohexene, with cyclohexane as the main by-product; then, through multi-tower extractive distillation, benzene, cyclohexene, and cyclohexane are separated, with benzene recycled back to the selective hydrogenation section, cyclohexane sold as a by-product, and cyclohexene converted to cyclohexanol via hydration reaction, which is further dehydrogenated to produce cyclohexanone. The selective hydrogenation of benzene is a four-phase system of oil, water, gas, and solid, using an unsupported ruthenium catalyst, with a benzene conversion rate of 40%~50%, and a selectivity for cyclohexene of 75%~80%. For the hydration of cyclohexene to produce cyclohexanol, ZSM-5 zeolite is used as the catalyst, with a single-pass conversion rate of about 10% and a selectivity of 99.3%. The process of producing cyclohexanone from cyclohexene hydration has high carbon atom utilization and relatively high safety, but due to the very close boiling points of benzene, cyclohexene, and cyclohexane, the energy consumption for separating these three components is high. The low single-pass conversion rate of cyclohexene hydration leads to increased energy consumption due to large amounts of recycling, and the catalyst is prone to loss.

In response to the growing industrial demand and stringent national environmental control requirements, Sinopec has originally proposed a new green synthesis pathway for the production of cyclohexanone via esterification and hydrogenation of cyclohexene, as shown in Figure 5 ^[23]. Firstly, benzene is selectively hydrogenated to produce cyclohexene; then, the product from selective hydrogenation of benzene enters the esterification unit, where cyclohexene reacts with acetic acid under the action of a solid acid catalyst to form cyclohexyl acetate, cleverly achieving the separation of cyclohexene from benzene and cyclohexane, significantly reducing energy consumption; subsequently, cyclohexyl acetate undergoes hydrogenation to simultaneously produce cyclohexanol and anhydrous ethanol, converting low-value acetic acid into high-value anhydrous ethanol, thus enhancing economic benefits; finally, cyclohexanol is dehydrogenated to yield cyclohexanone. The carbon atom utilization rate of this process is approximately 95%, waste emissions are reduced by 90%, and due to the elimination of the need for cyclohexane-cyclohexene separation, energy consumption is greatly reduced. Compared to existing production technologies, the new technology of producing cyclohexanone through the esterification and hydrogenation of cyclohexene is clean, efficient, energy-saving, economically viable, safe, and environmentally friendly, representing an original technological innovation in cyclohexanone production.

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图5 环己烯酯化加氢法工艺流程图

Fig. 5 The novel cyclohexene esterification-hydrogenation process for the production of cyclohexanone starting from benzene

5.1 Development History of New Technology for the Production of Cyclohexanone via Esterification and Hydrogenation of Cyclohexene

In 2010, Sinopec originally proposed a new reaction pathway for the production of cyclohexanone via esterification and hydrogenation of cyclohexene, and conducted research on new catalytic materials and processes, proving the feasibility of the new technical route. In 2011, based on preliminary studies, Sinopec organized the study and development of selective hydrogenation of benzene to produce cyclohexene model, and the model test study of esterification and hydrogenation of cyclohexene to produce cyclohexanol, conducting systematic research on reaction processes, separation and purification processes, catalyst performance evaluation, and continuous operation of models, further verifying the feasibility and technological advancement of the new cyclohexanone technology. On June 1, 2015, through a technical review organized by the Science and Technology Development Department of Sinopec, it was concluded that: "The developed selective hydrogenation catalyst for benzene is innovative, with its performance superior to that of similar technologies; the proposed technical route for co-production of cyclohexanol and ethanol through esterification and hydrogenation of cyclohexene is a world-first. The model tests have validated the technical feasibility of the entire process from reaction to product separation and purification in the production of cyclohexanone via esterification and hydrogenation of cyclohexene, confirming that this process has high conversion rate and selectivity, stable long-term operation performance of the catalyst, good product quality, safety and environmental friendliness in the process, and can improve economic efficiency through co-production of ethanol; the data from the model tests provided a basis for the design of a 200 kt/a industrial cyclohexanone plant." In September 2020, within the project of relocation and upgrading transformation of a 600 kt/a caprolactam industry chain at Hunan Petrochemical, the green production technology for producing 200 kt/a cyclohexanone via esterification and hydrogenation of cyclohexene became an important technical support. Two sets of 200 kt/a industrial plants for producing cyclohexanone via esterification and hydrogenation of cyclohexene started construction in March 2021, and were handed over on July 5, 2023.

5.2 Construction of an Efficient Catalytic System for the Hydrogenation of Cyclohexene Esters to Cyclohexanone

The new process for the hydrogenation of cyclohexene ester to produce cyclohexanone includes the selective hydrogenation of benzene to cyclohexene, the separation of benzene/cyclohexene, the esterification of cyclohexene to form cyclohexyl acetate, the hydrogenation of cyclohexyl acetate to produce cyclohexanol and co-produce ethanol, and the dehydrogenation of cyclohexanol to cyclohexanone. It involves the development of 3 types and 4 kinds of new catalysts. After more than ten years of small-scale characteristic evaluation, pilot continuous evaluation, and industrial trials in a "assembly line" style R&D, Sinopec has finally completed the industrial production trials of supported selective hydrogenation catalysts for benzene, special resin catalysts for cyclohexene esterification, regular catalysts for cyclohexene esterification, and hydrogenation catalysts for cyclohexyl acetate. On the basis of solving multiple engineering scale-up issues, it achieved the continuous, stable, and green production of catalysts, meeting the application requirements of the new technology's industrial equipment for cyclohexanone.

The selective hydrogenation of benzene to cyclohexene is the primary step in a new green synthesis route for cyclohexanone, and its product composition determines the operational load of subsequent steps, significantly impacting the overall economic efficiency of the process. Meanwhile, the selective hydrogenation of benzene to cyclohexene is also recognized as a challenging problem. The standard Gibbs free energy of formation for cyclohexane and cyclohexene from benzene are −98 and −23 kJ/mol, respectively, indicating that the selective hydrogenation of benzene to cyclohexene is thermodynamically very unfavorable. Therefore, achieving the selective hydrogenation of benzene to cyclohexene requires the development of an efficient catalytic system and reaction process, which alters the reaction kinetics by accelerating the desorption of cyclohexene from the catalyst surface, inhibiting its readhesion and further hydrogenation, thereby improving the selectivity towards cyclohexene. Although foreign companies have already industrialized the technology for the selective hydrogenation of benzene to cyclohexene, this technology uses non-supported ruthenium catalysts, leading to low utilization of the precious metal ruthenium. In response to this issue, Sinopec has developed a novel supported catalyst and reaction process for the selective hydrogenation of benzene, through regulating the interaction between the support and active metal, and matching the additive species within the microenvironment of the water film on the surface of the supported catalyst, breaking the bottleneck where high activity and high selectivity are difficult to achieve simultaneously. On the basis of maintaining a cyclohexene selectivity of 75%~80%, the average activity of the catalyst has been increased threefold^[24].

The catalytic distillation esterification tower is one of the cores of the esterification and hydrogenation cyclohexanone process. Through catalytic distillation technology, the chemical equilibrium can be broken, achieving a cyclohexene conversion rate close to 100%. The key to catalytic distillation technology lies in the development of catalyst components, namely, structured catalysts. In the catalytic distillation process, the catalyst needs to be made into special "catalyst components" and placed at specific locations within the distillation column, allowing it to serve the dual function of accelerating chemical reactions and providing a mass transfer surface. The main type of catalyst component used in industry is the "bundled package" of the catalyst. Its production process involves first packing the catalyst particles into glass cloth bags, then rolling them together with corrugated wire mesh to form individual "bundles," which are then fixed at specific locations within the distillation column. Thus, the manufacture of "catalyst components" is complex, and their installation, removal, and regeneration are very inconvenient. Moreover, larger catalyst particles are required for making catalyst components, leading to significant internal mass transfer resistance within the catalyst particles, making it difficult for the catalyst's effect to be fully realized. Based on the research initiated by Academician Min Enze years ago, which focused on using "new types of catalyst components as an entry point into the field of catalytic distillation," and through pilot testing and long-term operation trials of the esterification process, combined with process design, especially the special requirements for manufacturing structured packing esterification catalysts, further optimization was conducted on the physicochemical properties and catalytic performance indicators of the esterification catalytic resin. This ultimately determined the final technical specifications for the specialized resin catalyst for cyclohexene esterification, which was then industrially produced by Sinopec Catalyst Co., Ltd. As this was the first time in the industry that a strongly acidic system-based structured catalyst was being produced, numerous challenges were encountered during processing, including the supply of qualified acid-resistant wire mesh raw materials, the preparation of "bundle" components, and the loading of the catalyst. With the concerted efforts of all parties involved, after one year of intensive work, the production of a structured esterification catalyst with hydraulic properties fully meeting the process requirements was successfully completed.

The selectivity of the process for the hydrogenation of cyclohexyl acetate to produce cyclohexanol and ethanol as a byproduct is crucial to the overall economy of the new process. There are few studies on catalysts specifically for the hydrogenation of cyclohexyl acetate, both domestically and internationally; however, there are more studies on catalysts for the hydrogenation of carboxylic acid esters. According to the active components, the catalysts for the hydrogenation of carboxylic acid esters can be divided into two major categories: copper-based and noble metal-based. Ru-based noble metal catalysts can selectively hydrogenate carboxylic acid esters into the corresponding alcohols with high selectivity. However, due to the large steric hindrance and structural stability of the esters, it is difficult to achieve high conversion rates. For copper-based catalysts, they can be further categorized into those containing Cr and those without Cr. Due to the high toxicity of Cr, catalysts without Cr have become the trend for future development. Overseas, fundamental research and related industrial applications mainly focus on supported Cu-based catalysts and bulk-type CuZn multi-metal catalysts. Based on the results of directed fundamental research, this study focuses on Cr-free Cu-based catalysts. To address the issue of easy aggregation of copper-based ester hydrogenation catalysts, a layered precursor topological method based on the 2D layered structure of hydrotalcite-like compounds was adopted, adjusting the conditions for the topological transformation of LDHs (composition, calcination temperature, and component content) to obtain high-performance Cu-based catalysts. By using a combination of various in-situ characterization techniques, the qualitative and quantitative relationship between Cu⁰ and Cu⁺ and its relation to catalyst performance were studied, revealing the synergistic catalytic effect between the catalytically active Cu⁰ species and the acidic or basic sites of the support, thereby optimizing the structure, performance, and preparation process of the Cu-based catalyst. Using the self-developed Cu-based catalyst, under reaction conditions of 180 ℃ and 5.0 MPa, the conversion rate of cyclohexyl acetate exceeded 99.5%, and the selectivity for cyclohexanol was greater than 99.5%. The self-developed catalyst underwent scale-up tests at Sinopec Catalyst Co., Ltd. Based on the results of small-scale and pilot-scale catalyst preparation and evaluation, through further optimization of the preparation formula, the technical specifications for the ester hydrogenation catalyst were finally determined, and the industrial production of the cyclohexyl acetate hydrogenation catalyst was completed by Sinopec Catalyst Co., Ltd.

5.3 Engineering of a New Technology for the Hydrogenation of Cyclohexene Carboxylate to Produce Cyclohexanone

The esterification reaction between cyclohexene, a product of selective hydrogenation of benzene, and acetic acid had not been reported in the literature before the proposal of a new route for cyclohexanone synthesis. The innovations in the industrial implementation of the new process, in terms of engineering, mainly include: a complete set of technologies for the selective hydrogenation of benzene to synthesize cyclohexene, separation technology for benzene/cyclohexene/cyclohexane, technology for the esterification of cyclohexene with acetic acid to produce cyclohexyl acetate, and technology for the preparation of cyclohexanol and co-production of ethanol through the hydrogenation of cyclohexyl acetate.

Benzene selective hydrogenation to cyclohexene is the primary step in the new process for cyclohexanone production. The development and research of catalytic technology for benzene selective hydrogenation to cyclohexene, abroad, mainly focuses on Asahi Kasei Chemicals Corporation in Japan. This company achieved the industrialization of benzene selective hydrogenation to cyclohexene in 1989, using a non-supported Ru-Zn catalyst and a two-reactor series reactor, under conditions of 150 ℃ and 5 MPa, with a benzene conversion rate of 40%~50%, cyclohexene selectivity of 75%~80%, and cyclohexene yield of 32%~38%. To ensure the activity and selectivity of the catalyst, it is necessary to periodically remove part of the catalyst for regeneration treatment, after which the regenerated catalyst is recycled. Since 2011, Sinopec has conducted in-depth studies based on its independently developed supported benzene selective hydrogenation catalyst, focusing on factors affecting the reaction process, catalyst deactivation mechanisms, and regeneration, etc. It has developed a continuous reaction and regeneration process control and operation optimization scheme suitable for the new catalyst, carried out model continuous experiments, invented supporting processes and key equipment for benzene selective hydrogenation, and formed a complete set of efficient benzene selective hydrogenation to cyclohexene technology. This has enabled China to achieve the localization of key equipment and the industrialization of overall technology.

The products of the selective hydrogenation of benzene contain cyclohexene, cyclohexane, and unreacted benzene. Benzene, cyclohexene, and cyclohexane form an azeotropic system under atmospheric pressure. Currently, in industrial applications, the extraction distillation method using N,N-dimethylacetamide (DMAC) as a solvent is commonly employed for separation. In actual production processes, issues such as high reflux ratio, large solvent-to-feed ratio, and high energy consumption are encountered. Based on systematic research into the phase equilibrium of the benzene-cyclohexene-cyclohexane-solvent system, Sinopec has for the first time developed a new sulfolane extraction distillation process. The purity, yield, and energy consumption of the extracted product are all superior to those of similar international technologies.

The application of catalytic distillation technology to the esterification reaction between cyclohexene and acetic acid requires overcoming two technical challenges: one is the processing of titanium structured packing, which must solve the processing difficulties of titanium corrugated plates and titanium wire mesh catalyst bags; the other is addressing the scale-up effect in the catalytic distillation process. Multiple literatures have disclosed the process of generating cyclohexyl acetate through the addition esterification of acetic acid and cyclohexene, including various solid acid catalysts and kettle reactors used. Even if the reaction raw material is pure cyclohexene and a very high acid-to-olefin ratio is adopted, it is difficult to achieve complete conversion of cyclohexene. The Sinopec system has studied the kinetics and thermodynamics of the esterification reaction between cyclohexene and acetic acid, created a dedicated resin catalyst for cyclohexene esterification and its components, developed a new process for cyclohexene esterification, and enhanced the cyclohexene esterification reaction process through catalysis-distillation coupling, breaking through the limitations of thermodynamic equilibrium, and increasing the single-pass conversion rate of cyclohexene from 80% to over 99%. The single-tower output of the catalytic distillation esterification tower in the industrialized esterification-hydrogenation cyclohexanone process by Hunan Petrochemical reaches 300 kt/a, making it the largest single-tower output catalytic distillation tower in the world. This breakthrough originates from the layout made by Academician Min Enze more than 20 years ago. In the 1990s, when chemical reaction process intensification was on the rise, after organizing a survey on domestic and international catalytic distillation technologies, Min Enze found that compared with traditional methods of separating reactions and distillation, catalytic distillation technology has advantages such as high conversion rates, good selectivity, low energy consumption, and less investment. Recognizing the advantages of catalytic distillation technology and its broad application prospects in petroleum refining and chemical processes, Academician Min Enze decided to make catalytic distillation a new research area for the newly established National Engineering Research Center for Refining Processes and Catalysts, and made detailed plans and layouts for how to catch up quickly with this kind of "people-first" technology.

On December 15, 2023, and May 25, 2024, two 200 kt/a production units of the world's first industrial facility for cyclohexene esterification and hydrogenation to produce cyclohexanone, independently developed by Sinopec, were successfully started up in one go (Figure 6). The units produced qualified cyclohexanone, and after adjustments and optimizations, achieved stable, long-term, full-load, and high-quality operation. This marks the substantive achievement of the first industrial application of the new technology for cyclohexene esterification and hydrogenation to prepare cyclohexanone, providing important technological support for the transformation and upgrading of China's caprolactam industry chain. Full-load technical performance benchmarking results show: a benzene selective hydrogenation reaction conversion rate of 40%~50%, with a cyclohexene yield ≥32%; the conversion rates/selectivities of the esterification reaction and the ester hydrogenation reaction both reach over 99%, with a cyclohexanone product quality fraction ≥99.90% and an ethanol product quality fraction ≥99.50%. The new green synthesis route for cyclohexene esterification and hydrogenation to produce cyclohexanone has a carbon atom utilization rate of about 95%, reduces waste emissions by 90%, significantly lowers energy consumption, and is economically viable, safe, and environmentally friendly. The successful development of this new green synthesis route for cyclohexanone enables China to achieve original innovation in basic organic chemical production technology, breaking through the technical bottleneck from benzene to cyclohexanone, and possessing a complete set of green production technologies from benzene to caprolactam, leading the global development of caprolactam technology.

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图6 200 kt/a环己烯酯化加氢制环己酮工业生产装置

Fig. 6 A 200 kt/a cyclohexene esterification-hydrogenation industrial production unit for the production of cyclohexanone

6 Conclusions and Prospects

Academician Min Enze is one of the pioneers of green chemistry in China. After the 1990s, he proposed suggestions for the development of green chemistry in our country and guided the successful development of multiple new green processes aimed at eradicating environmental pollution from the source; after entering the 21st century, he focused on "dual carbon" technologies, venturing into the new field of biomass resource utilization within green chemistry, guiding research on production processes for biodiesel using oilseed crops and CO₂-consuming microalgae. In the past decade, China's petroleum and chemical industry has transitioned from an era of high growth to one of high-quality development. Behind this significant change lies a profound transformation in the development model of China's petroleum and chemical industry, as the entire sector began to steadily implement structural adjustments and upgrades, vigorously promote scientific and technological innovation and industrial restructuring, with "green chemical engineering" gradually becoming mainstream. The practice of green chemical engineering technologies, represented by caprolactam production technology, embodies the concept of green chemistry and highlights the close relationship between green chemistry and sustainable economic development.

At the same time, Academician Min Enze, after studying the historical patterns of major chemical technology advancements abroad, conducting extensive research on foreign experiences in catalyst and process innovation, and summarizing his scientific research practices, proposed many ideas about scientific and technological innovation. For instance: "The selection of areas for scientific and technological innovation should revolve around the forefront of technology related to the survival, competition, or long-term strategic development of enterprises; the path to innovation is through conducting directed fundamental research, accumulating new scientific knowledge, aiding in the formation of new technical concepts, and then carrying out pioneering research to examine feasibility and economic rationality; the foundation of innovation lies in taking the enterprise as the base for independent innovation, forming an innovation team combining industry, academia, and research, with the goal of building the first set of industrial demonstration facilities with independent intellectual property rights, to mobilize the enthusiasm for independent innovation from all sides." In the context of the petrochemical research field, he pointed out that the frontier areas for independent innovation in petrochemical catalytic technology are new catalytic materials, new reaction engineering, and new reaction pathways. These are the "new weapons" for developing independently innovative petrochemical catalyst technologies. New catalytic materials are the source of original innovation for new catalysts and processes; new reaction engineering is an important approach to developing new processes; new reactions form the basis of new processes; the combination of new catalytic materials and new reaction engineering often leads to integrated innovation. Therefore, it is necessary to conduct directed fundamental research and pioneering exploration at the forefront of science and technology in new catalytic materials, new reaction engineering, and new reactions, to seek and accumulate these "new weapons." Regarding the transformation of achievements, he suggested: "For the first set of industrial demonstration facilities, based on the accumulated experience over many years from the Sinopec Ten-Dragon Offensive, led by enterprises, organizing a tripartite combination of industry, academia, and research, and a quadruple combination of research, design, construction, and production, can greatly accelerate the conversion of innovative results into productive forces." Over the past 30 years, a series of breakthroughs in new technologies have been achieved through new catalytic materials, green reaction processes, process coupling and intensification, and their integrated innovation, which re-enact the scientific and technological innovation thoughts of Academician Min Enze. This not only demonstrates that these methods and approaches to innovation are effective but also that the outcomes and experiences gained from these innovative practices provide a foundation and reference for future technological innovations. The scientific and technological innovation thoughts of Academician Min Enze are valuable spiritual wealth, offering excellent guidance and reference for a wide range of petrochemical science and technology workers.

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Abstract

Cite this article

1 Introduction

2 Green Production Technology for Caprolactam

2.1 Integration of Titanium Silicalite Molecular Sieve with Slurry Reactor for the Ammonia Oxidation of Cyclohexanone to Cyclohexanone Oxime

2.1.1 "Recrystallization" Preparation of Hollow Titanium Silicalite Molecular Sieves

2.1.2 A New Process for the Preparation of Cyclohexanone Oxime via Ammoximation of Cyclohexanone

图1 300 kt/a环己酮氨肟化工业生产装置

2.2 Integration of Amorphous Ni with Magnetically Stabilized Bed for Hydrogenation Purification of Caprolactam[14]

2.2.1 Amorphous Alloy Catalysts

2.2.2 Development and Application of Magnetic Stabilized Bed Technology for Caprolactam Hydrogenation Refining Process

图2 100 kt/a磁稳定床己内酰胺加氢精制工业生产装置

3 Fluidized Bed Hydrogen Peroxide Process

3.1 Efficient Anthraquinone Hydrogenation Microspherical Catalyst

3.2 Development of High-Productivity Working Fluids

3.3 Inherent Safety Integrated Process Based on High-Throughput Fluidized Bed Reactor

3.4 120 kt/a Fluidized Bed Anthraquinone Process for Industrial Hydrogen Peroxide Production

图3 120 kt/a流化床蒽醌法生产过氧化氢工业生产装置

4 Hydrogen Peroxide Method for Propylene Oxide Production Technology

4.1 Surface-Rich Silicon Multi-Hollow Ti-Si Molecular Sieve Catalyst

4.3 Green and Efficient Process for Low-Temperature Propylene Epoxidation and Dedicated Reactor

图4 100 kt/a过氧化氢法制备环氧丙烷工业生产装置

5 Novel Technology for the Hydrogenation of Cyclohexene Esters to Produce Cyclohexanone

图5 环己烯酯化加氢法工艺流程图

5.1 Development History of New Technology for the Production of Cyclohexanone via Esterification and Hydrogenation of Cyclohexene

5.2 Construction of an Efficient Catalytic System for the Hydrogenation of Cyclohexene Esters to Cyclohexanone

5.3 Engineering of a New Technology for the Hydrogenation of Cyclohexene Carboxylate to Produce Cyclohexanone

图6 200 kt/a环己烯酯化加氢制环己酮工业生产装置

6 Conclusions and Prospects

References

2.2 Integration of Amorphous Ni with Magnetically Stabilized Bed for Hydrogenation Purification of Caprolactam^[14]