Conversion of n-Pentane to light olefins over modified Zr/HZSM-5-based catalysts

Abstract

Ethylene and propylene are important raw materials for producing several types of chemicals and polymers. According to the increase of propylene demand in recent year, the P/E ratio was increased to 0.85. In order to meet the propylene demand, the development of hybrid HZSM-5 catalyst for catalytic cracking becomes more interesting owing to the cracking activity from HZSM-5 zeolite acid site and loaded metal on HZSM-5 that expected to promote the dehydrogenation activity to the catalyst which could possibly enhanced the P/E ratio. The alternative feedstock for this process is n-pentane which is the low-value product from distillation process. The most studied catalyst in n-pentane catalytic cracking is based on Zr/HZSM-5 which provides a good activity and stability. This work was divided into two major parts. In the first part, the effect of second metal Pd, Ni and Ag on Zr/HZSM-5 catalysts were studied. It was found that AgZr/HZSM-5 catalysts exhibited the best dehydrogenation and cracking activity that can be observed from highest P/E ratio (0.89) when compared to the effect from other second metals, related to the acidity of catalysts that AgZr/HZSM-5 showed the lowest acidity. In the second part, the effect of SiO₂/Al₂O₃ ratios (23, 50 and 80) in AgZr/HZSM-5 catalysts were studied. It was found that AgZr/HZSM-5 (80) shows the lowest acidity, resulting in the highest P/E ratio (1.25) but poor stability. In conclusion, the appropriated low acidity catalyst convenient for n-pentane catalytic cracking in order to enhance propylene selectivity.