Modified HZSM-5 zeolites for intensifying propylene production in the transformation of 1-butene

Abstract

The transformation of 1-butene was studied in order to intensify propylene production on catalysts prepared based on HZSM-5 zeolites of different SiO2/Al2O3 ratio modified as follows: (i) by incorporating K or P (1–5 wt.%) and (ii) subject to mild in situ steaming. The effect of zeolite modifications on the catalyst physical and acid properties and on their kinetic performance was analyzed, given that they are two key factors for selectively re-routing oligomerization–cracking reactions to propylene production and for minimizing coke formation. Experiments were carried out under the following operating conditions: 500 °C; space time, up to 1.6 (g of catalyst) h (mol of CH2)−1; time on stream, 5 h. The following criteria were used for assessing catalyst performance: (i) conversion; (ii) product yield and selectivity of each lump of reaction products (CH4, C2H4, C3H6, C2C3 paraffins, C4H10, C5+ aliphatics and BTX), with the aim of maximizing propylene, and (iii) deactivation by coke deposition. Although catalytic performance was improved by selecting a high SiO2/Al2O3 ratio, as well as by incorporating 1 wt.% P and mild in situ steaming, the incorporation of 1 wt.% K was the most effective treatment for maximizing propylene yield and minimizing coke formation, which is explained by the considerable attenuation of the acid strength of the zeolite sites. A steady propylene yield of 30% and a selectivity of 40%, for a conversion of 1-butene higher than 70%, have been obtained with a catalyst prepared by agglomerating (with bentonite and alumina) 1 wt.% K modified HZSM-5 zeolite with SiO2/Al2O3 = 280.