Isomerization catalysts and processes

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The key to improving the isomerization process lies in the catalyst. There are many types of light alkane isomerization processes. Classified by catalyst, they can be divided into two main categories: low-temperature types (reaction temperature of 100–180°C) and medium-temperature types (reaction temperature of 210–300°C) ； Based on whether hydrogen is involved in the reaction, it mainly includes two types: normal isomerization and hydroisomerization ； Thanks to the development of catalytic reforming, refineries now have a low-cost source of hydrogen. In recent years, many hydroisomerization processes that utilize bifunctional catalysts under hydrogen pressure have been adopted. Based on the requirements for product octane number or different processes, they can be classified into processes such as one-pass, C5 cycle, C6 cycle, full isomerization, C5 cycle + full isomerization, and C6 cycle + full isomerization. Since the isomerization reaction is subject to thermodynamic limitations, a lower reaction temperature helps to increase the equilibrium value of the reaction; as a result, the octane number of catalyst products designed for low temperatures is 2–3 units higher than that of catalysts designed for medium temperatures. If the operating temperature of the medium-temperature HS-10 zeolite catalyst is higher than that of the aluminum chloride catalyst, the octane number and yield of the product are also lower. However, low-temperature catalysts are of the halogen type; their operation requires that the halogen content in the circulating gas be maintained at a very high level. They cause significant corrosion to the equipment, impose high requirements on the materials used, result in high investment costs, and present difficulties in operation. Moreover, since low-temperature isomerization catalysts contain large amounts of chlorine, their performance is highly sensitive to the levels of impurities in the feedstock, such as sulfur, water, fluorine, and oxygen. This leads to extremely strict requirements regarding the quality of the crude oil and hydrogen used, thereby affecting the widespread adoption of low-temperature catalysts. For this reason, the development of current heterogenization catalysts focuses more on improving their adaptability to raw materials, thereby eliminating the need for accompanying raw material treatment systems and reducing plant investment and operating costs. At present, in terms of the number of operational units, medium-temperature units account for the majority.