Catalytic systems for dewaxing diesel fractions

The article discusses modern molecular sieves with different structures that can be used in the processes of dewaxing straight-run diesel fractions. The existing problem is the need to create a catalyst for the isomerization of n-paraffins, capable of ensuring the highest possible efficiency and selectivity of the process. The structural properties of molecular sieves, such as the size and shape of pores and channels, the geometry of channels in space, and the topology of their interrelationships are analyzed. The influence of these characteristics on the diffusion of reagent molecules, isomerization efficiency, and yield of target products is considered. Channel systems of molecular sieves based on zeolites (ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-48, Faujasite, Mordenite, Beta) and silicoaluminophosphates (SAPO-5, SAPO-11, SAPO-31, SAPO-41) are described in detail. A key factor determining the effectiveness of catalysts based on molecular sieves has been established, which is determined by the correspondence of the pore geometry to the sizes and conformation of n-paraffin molecules and their isomers. For diesel fractions containing C10–C20 hydrocarbons, the following parameters are critical: the size of the input window is 5.3–5.6 Å, straight channels, one–dimensional channel systems that do not intersect with each other. Diffusion restrictions in narrow channels act as a natural regulator of selectivity. Based on the information provided, the most promising media (ZSM-22, ZSM-23, ZSM-48, SAPO-11, SAPO-31, SAPO-41) were selected, which are best suited for the isodeparaffination of the diesel fraction. They will be used in the future for the synthesis of the catalyst. The results of the study provide a methodological basis for the rational selection and creation of more advanced catalysts, which, in turn, will ensure an increase in the productivity of isomerization processes.