Insights into the effect of Si/Al ratio on Isobutane/1-butene ratio in the pore of H-BEA zeolite in C4 alkylation process

The isobutane/butene (I/O) ratio in the pore is a crucial factor for enhancing the catalytic stability of zeolitic catalysts in C4 alkylation process. In this work, the influence mechanism of the Si/Al ratio on the I/O ratio in the pore for H-BEA zeolite was investigated via CB-GCMC methods under realistic alkylation conditions. It is found that the I/O ratio in the pore decreases dramatically with decreasing the Si/Al ratio due to the higher adsorption heats of 1-butene over the acid sites than that of isobutane. Therefore, there will be an optimal Si/Al ratio for C4 alkylation, which is in good agreement with the experimental results. Furthermore, the relationship between the I/O ratio in the pore and feedstock over the H-BEA zeolite with different Si/Al ratios was built. We found that increasing the I/O ratio in the pore by improving the I/O ratio in the feedstock is limited, when the Si/Al ratio is much low. The external surface modification of catalyst will be an effective method to improve the I/O ratio in the pore. These results are of great significance to the rational design of high-efficiency C4 alkylation catalysts.