Transformation of LPG to light olefins on composite HZSM-5/SAPO-5

Abstract

To selectively transform LPG (liquefied petroleum gas), composite HZSM-5/SAPO-5 zeolite catalysts were fabricated with an adjustable Brønsted acid/Lewis acid (BA/LA) ratio and a weak acid/strong acid (WA/SA) ratio. HZSM-5 powder (SiO₂/Al₂O₃ = 100) and SAPO-5 synthetic gel (SiO₂/Al₂O₃ = 0.2) were employed as the starting materials. Adopting a gel/solid weight ratio of 20 mL g⁻¹ and a crystallization temperature of 180 °C, the synthetic HZSM-5/SAPO-5-20–6 h catalyst showed a BA/LA ratio of 3.25 and a WA/SA ratio of 1.47, and during the conversion of LPG, the propylene and ethylene selectivity and the P/E ratio reached 72.22%, 62.56%, and 1.39, respectively, in a 600 °C fixed bed gas-phase reaction and a W/F value of 15 g h mol⁻¹ was obtained. As the crystallization time was extended to 24 h, the BA/LA ratio became 2.83, and the propylene and ethylene selectivity increased to 68.50% while the selectivity for C₅₊ HCs and CH₄ was reduced to 14.88% and 8.59%, respectively.