Research progress in ethylene catalytic cracking and olefin cracking technologies

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(1) Catalytic cracking technology. Catalytic cracking helps to improve the degree of cracking and selectivity, and it enables higher yields of olefins under milder conditions than those in thermal cracking, while reducing energy consumption. Additionally, the ratio of ethylene to propylene yields can be adjusted according to market demands; hence, this technology has attracted widespread attention. The new naphtha catalytic cracking process for producing large amounts of propylene, developed jointly by the Institute of Materials and Chemistry at the Japanese Academy of Industrial Sciences and the Japanese Chemical Society, achieves significant energy savings and a reduction in environmental impact. It also allows for flexible adjustment of the ratio of olefins produced in response to changes in the market demand for ethylene and propylene, with the mass ratio of propylene to ethylene able to be increased from the traditional 0.6:1 to 0.7:1. In the laboratory, using La/ZSM-5 with a mass fraction of 10% as a catalyst in a fixed-bed reactor at 650°C, the total yield of ethylene and propylene was 61%, which is more than 10% higher than that of the conventional steam cracking method. A naphtha catalytic cracking process developed by LG Petrochemical in Seoul, South Korea, increases the ethylene yield by 20% and the propylene yield by 10% compared to conventional steam cracking processes. This process uses a proprietary metal oxide catalyst, and the reaction temperature is about 50–100°C lower than that of standard pyrolysis reactions; as a result, it requires less energy compared to conventional steam pyrolysis. The company estimates that the coking rate on the inner wall of the pyrolysis furnace tubes will decrease, thereby allowing for longer operation periods, an extended lifespan of the furnace tubes, and reduced carbon dioxide emissions. (2) Olefin cracking technology. Olefin cracking technology is a technique for converting higher-grade olefins into lower-grade olefins such as ethylene and propylene. Its process is based on the thermodynamic equilibrium of olefins, and it uses a suitable catalyst (such as modified ZSM-5 or other types of zeolites) to convert higher-carbon olefins such as C4 and C5 into lower-carbon olefins (mainly ethylene, propylene, and butylene). The specific composition of low-carbon olefins is independent of the carbon number of the feed olefins, and is determined by the reaction conditions and catalyst. The commonly used raw materials are the C4 and C5 fractions from steam cracking units, the C4 fraction from FCC units, and the C5 fraction in gasoline. Since the dienes in the raw material tend to coking, they should be selectively hydrogenated into olefins in advance. Due to the short lifespan of the catalysts used, FCC-type reactors that facilitate catalyst regeneration are generally chosen. Recently, new processes for fixed-bed reactors have been reported that can extend catalyst life by coexisting with steam. Currently, Exxon Mobil/Washington, Lyondell/HalliburtonKBR, Lurgi, and Atofina/UOP can provide the transfer of olefin cracking technology, while ABBLummus is carrying out industrial trials of its Auto-Metathesis process.