Introduction to C2–C5 light hydrocarbon processing technologies in China

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I. Introduction to C2 Processing Technology At present, the catalytic cracking units in operation across China have a processing capacity of over 150 million tons, with a dry gas output of more than 6 million tons; these gases generally contain 10–18% ethylene, resulting in an overall ethylene production of 600,000–1 million tons. Although the catalytic dry gas to ethylbenzene process can utilize some of the ethylene, for companies that do not have sufficient benzene resources, refinery dry gas still has to be fed into the gas pipeline network as fuel gas. As oil resources become increasingly depleted and their prices keep rising, it becomes crucial to find ways to save resources. Utilizing ethylene from dry gas can generate significant economic benefits. Through the refinery dry gas aromatization technology, a portion of high-octane gasoline blending components rich in aromatics can be obtained, while the remaining product is essentially dry gas, offering good economic efficiency. Using refinery dry gas with an olefin content of 15% as raw material, a liquid product with a content of around 10% can be obtained; this product has an aromatic content of over 50% and an octane number RON greater than 95, making it an excellent component for blending high-octane gasoline. Currently, this technology has undergone industrial pilot tests in domestic enterprises, achieving good application results. II. Introduction to C3 Processing Technologies Besides propylene, which is the main chemical raw material, China’s C3 resources also include propane, which is primarily used as a component in liquefied petroleum gas for domestic use. Additionally, propane can be used as a feedstock for ethylene cracking or for propane dehydrogenation units. In recent years, several private enterprises in China have been planning to build such propane dehydrogenation units in order to produce propylene from propane. Currently, propane dehydrogenation technology is primarily in the hands of American companies Lumus and UOP. China is also developing its own fixed-bed propane dehydrogenation catalysts and processes. III. Introduction to Existing C4 Processing Technologies At present, China’s catalytic cracking capacity has reached 150 million tons per year, with an annual production of C4 liquefied gas of over 20 million tons. However, at present, among the catalytically converted C4 compounds, isobutylene is mainly utilized for the production of MTBE and thus is used to a considerable extent; the rest of butane and butenes are used very little, primarily as fuel for household liquefied gas. The existing C4 processing technologies mainly include C4 alkylation, MTBE production, C4 aromatization, C4 cracking, maleic anhydride production, methylethylene homologation, and disproportionation. The following is a brief analysis of the development of some of these key technologies and their application prospects in China: 1) C4 alkylation – The alkylation of butenes and isobutane is an important technique for producing high-octane gasoline components. It has been widely used abroad; however, this technology still relies on liquid sulfuric acid or hydrofluoric acid as catalysts, which poses issues related to corrosion and pollution, thus limiting its application in China. In previous years, over a dozen alkylation units were introduced in the country, but few of them are currently in operation. Due to potential risks such as hydrofluoric acid leaks in alkylation units using hydrofluoric acid, newly planned alkylation units in China in recent years generally use sulfuric acid as a catalyst; however, challenges such as equipment corrosion and the treatment of acid residues still exist. 2) MTBE and isobutylene production technologies: At present, producing MTBE from isobutylene in C4 fractions represents a relatively ideal way to utilize these C4 compounds. Firstly, the MTBE process is mature and reliable, with lower investment requirements ； Secondly, as an important component for blending high-octane gasoline, there is a constant demand for MTBE in the market. **The current national standards for gasoline grades 4 and 5 also do not impose any restrictions on the use of MTBE; therefore, MTBE technology still has great potential for development in China. Furthermore, the further decomposition of MTBE can also produce isobutylene of high purity, which can be used as a raw material for manufacturing butyl rubber, MMA (methyl methacrylate), tert-butyl phenol, and pesticides intermediates, offering very promising market prospects. Given the limited isobutylene content in existing catalytic cracking C4 and ethylene cracking C4, some technologies for increasing isobutylene production, such as n-butyl skeleton isomerization and isobutane dehydrogenation, also hold great potential for market application. The butene skeleton isomerization processes mainly include Lyondell/CDTECH’s ISOMPLUS process, Mobil/BP’s Isofin process, Texas Company’s SKIP process, and IFP’s Iso-4; these processes enable the isomerization of butene-1 and butene-2 in C4 hydrocarbons into isobutylene through skeleton isomerization. Among them, the ISOMPLUS process developed by the American company Lyondell has been put into operation in multiple facilities across China. Our country is also currently developing its own butylene skeleton isomerization process. Molecular sieve materials with good catalytic performance for the butylene skeleton isomerization reaction have been developed, and research and development on the accompanying catalysts and processes are also in progress; these will be launched on the market in the near future. The currently industrialized isobutane dehydrogenation processes include Phillips’ Star process, Lummus’ Catofin process, IFP’s FDB-4 process, and UOP’s Oleflex process. Among these, the Catofin process developed by Lummus and the Oleflex process developed by UOP are widely used internationally, with nearly ten industrial units of each in operation. Several alkane dehydrogenation units are currently under planning in China, but all of them involve the use of propane dehydrogenation to produce propylene; there are no reports yet in China on the use of isobutane dehydrogenation to produce isobutylene. Our country is currently developing its own propane/isobutane dehydrogenation catalysts and process technologies, which will be introduced to the market at an appropriate time. 3) C4 aromatization: The C4 aromatization technology can convert C4 compounds into aromatics or high-octane gasoline blending components rich in aromatics. Currently, there are two process routes for tetra-carbon aromatization. The main product of one of these routes is aromatics primarily consisting of triphenyl compounds; the reaction temperature is high (above 500°C). This approach enables the conversion of the olefins present in tetra-carbon compounds, as well as the conversion of tetra-carbon alkanes. However, a drawback is that it generates a significant amount of dry gas (over 15%). Another process route uses high-octane gasoline blending components as the target product; the reaction temperature is low (typically 300–450°C), and it can only convert tetraenes. The advantage is that the yield of dry gas is low (below 2%). Current international low-carbon hydrocarbon aromatization technologies include UOP’s CYCLAR technology, Sanyo’s alpha process, and Mobil’s M2-forming technology, among others. Domestic institutions such as the China Petroleum Research Institute, Dalian University of Technology, and the R&D Institute of Luoyang Design Institute have also developed their own aromatization technologies. Among them, the light naphtha and C4 non-hydrogenation reforming (aromatization) technology developed by the China Petroleum Research Institute has been applied in more than 20 industrial plants across the country. Currently, the aromatization units in use in China for industrial applications still employ fixed-bed reactors; the catalyst’s single-cycle operation period is generally 1 to 2 months, requiring regeneration. The Institute of Petrology, in collaboration with Luoyang Ruize Petrochemical Company, developed mobile-bed aromatization technology, which was successfully implemented in the first operation at Shandong Hualong. The application of this technology has taken China’s aromatization technology to a new level. 4) C4 cracking: The cracking of C4 olefins under the action of specific catalysts can yield propylene and ethylene. Well-established technologies include KBR’s Superflex technology (fluidized bed) and Lurgi’s Propylur technology (fixed bed). In China, the Shanghai Research Institute of Petrochemical Technology has also developed a technology for producing propylene from butenes, which has been put into industrial use at Zhongyuan Petrochemical. The current C4 cracking processes that use fixed-bed reactors are plagued by short catalyst operation cycles and frequent catalyst regeneration; C4 cracking processes utilizing fluidized or moving-bed reactors should represent the future direction of development. IV. Introduction to Existing Technologies for the Processing and Utilization of C5 Hydrocarbons The existing C5 resources consist of two main components: one is found in the fractions obtained from straight-run or hydrogenated light naphtha, and it mainly consists of saturated n-pentane and isopentane. Currently, some of this material is used as a feedstock for ethylene cracking, while another portion is used as an ingredient in gasoline formulations. Due to the low octane rating of n-pentane (RON 63), hydroisomerization technology using light naphtha is widely adopted abroad to appropriately increase the octane rating of the C5 fraction through isomerization. Sinopec’s Zhanjiang Dongxing Petrochemical and Hainan Refining & Chemical also have C5/C6 isomerization units, but due to the lack of a recycling process for unreacted products, the octane number of the isomerized products is low (RON 80), which reduces the enthusiasm for using them by these companies. As the processing volume of imported crude oil increases, the availability of straight-run light hydrocarbons such as C5 also grows. People are gradually realizing the importance of C5/C6 isomerization technology; for example, PetroChina has begun to plan and construct C5/C6 isomerization units in some of its new large-scale refining projects (in Kunming, Sichuan, etc.). Isomerization technologies from foreign companies such as AXENS and UOP are also starting to be introduced into China. The Research Institute of Petrochemicals of Sinopec has been working on the development of this technology. The first generation of isomerization technology using molecular sieve catalysts was successfully applied in China’s first C5/C6 isomerization industrial plant (Zhanjiang Dongxing Petrochemical). Subsequently, this technology was also used in industrial plants in Zepe, Yumen, and Iran. In addition, the second generation of solid superacid isomerization catalysts developed by the Research Institute of Petrochemicals has also been completed and is ready for industrial application. Another portion of C5 resources is primarily present in the catalytic cracking gasoline fraction, which has a high content of olefins; it is currently used mainly as a high-octane component for gasoline. However, too high a content of pentene also results in a high level of olefins in gasoline in our country, along with a higher vapor pressure. Many companies abroad use light gasoline etherification technology to convert C5 isomeric olefins into TAME, which not only improves the octane rating of light gasoline but also effectively reduces its vapor pressure; it represents an effective method for utilizing C5 olefins in catalytic cracking gasoline. The catalytic distillation-isomerization process developed by the American company CD-TECH is capable of effectively converting pentadiene compounds in catalytic cracking light gasoline into TAME; two companies in China, namely those in Golmud and Nanchong, have also adopted this technology. Furthermore, the pentene compounds in catalytic cracking light gasoline can also be converted into ethylene and propylene through catalytic pyrolysis; for example, KBR’s Superflex technology (fluidized bed) can convert pentene compounds into ethylene and propylene.