LIANG Cui-cui1, XU Rui-fang1, CHANG Xu-sheng1, 2, LIU Guo-dong1, LIU Jia-xu1, GUO Hong-chen1*
(1. State Key Laboratory of Fine Chemicals, Dept. of Catalytic Chemistry and Engineering, Dalian University of Technology, Dalian 116012, China; 2. Shandong Qilong Chemical Co. Ltd, Zibo, 255400, China)
Abstract: The cracking of butenes in post-MTBE C4LPG over modified nano-sized HZSM-5 zeolite catalyst was investigated with small fixed-bed reactor, ammonia temperature-programmed desorption (NH3-TPD) and pyridine-adsorption infrared spectroscopy (Py-IR). Results show that, the propylene selectivity of the butenes catalytic cracking is mainly limited by hydrogen-transfer and dehydrogenation reactions. These C-H bond related side-reactions produce by-products such as alkanes and aromatics, and are responsible for the coking of the catalyst. The decrease of the reaction temperature favors hydrogen-transfer (especially the hydrogen-transfer of isobutene),while the increase of the reaction temperature favors dehydrogenation. On the other hand, dehydrogenation needs strong acid sites, whereas hydrogen-transfer can occur with weak acid sites. As a result, the weakening of catalyst acidity can suppress the C-H bond related side-reactions, and even completely stop dehydrogenation when all the strong acid sites disappear, but it is impossible to avoid hydrogen-transfer under the conditions of butene catalytic cracking. When the catalytic cracking was carried out at 450 ℃ and above, the decrease of butene conversion occurs because of the disproportionation of propylene to butene and ethylene, and the isomerization of normal butenes to isobutene.
Key words: Catalytic cracking, C-H bond related side-reactions, Post-MTBE C4LPG, Butenes, Nano- sized ZSM-5 zeolite
E-mail: hongchenguo@163.com
Journal of Molecular Catalysis, Vol. 25, Issue 1, 2011, 69~77.
