Catalytic Cracking Process of 1-Pentene over H-ZSM-5 Molecular Sieves with Different Silica-Alumina Molar Ratios at Ultra-High Temperatures

To investigate the modulation effects of high temperature and molecular sieve acidity on olefin cracking pathways and product selectivity, the catalytic cracking performance of 1-pentene was systematically studied under catalytic cracking temperatures of 700, 750 and 800 °C over H-ZSM-5 molecular sieves with silica-alumina molar ratios (SAR) of 23, 42 and 95. The contributions of catalytic cracking and thermal cracking were quantified, and the synergistic effects of temperature and SAR on monomolecular cracking, bimolecular cracking, confined catalytic radical (CCR) reaction and side reactions were analyzed by composition of the cracking products. Results showed that catalytic cracking dominated the cracking of 1-pentene over H-ZSM-5 in 700–800 °C. Higher temperature promoted monomolecular cracking and CCR, thus significantly increasing ethylene selectivity. Lower SAR enhanced acidity and catalytic cracking activity but intensified aromatization and C5+ formation. HZ-95 with weak acidity favored bimolecular cracking and exhibited low ethylene selectivity. HZ-42 achieved the optimal performance at 800 °C, with 1-pentene conversion of 98.80% and ethylene molar selectivity of 82.41%; both hydrogen transfer reactions and methane formation were effectively suppressed. This work provides mechanistic insights and theoretical support for the targeted catalytic cracking to olefins (TCO) process.