RESEARCH PAPER CHINESE JOURNAL OF CATALYSIS Volume 30, Issue 10, October 2009 Online English edition of the Chinese language journal Cite this article as: Chin J Catal, 2009, 30(10): 1049–1057. Received date: 30 March 2009. *Corresponding author. Tel: +86-10-62785464; Fax: +86-10-62772051; E-mail: wf-dce@tsinghua.edu.cn Foundation item: Supported by Higher Education Commission, Islamabad, Pakistan (2007PK0013) and the National Natural Science Foundation of China (20606020, 20736004, 20736007). Copyright © 2009, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved. DOI: 10.1016/S1872-2067(08)60137-0 Catalytic Cracking of 1-Hexene to Propylene Using SAPO-34 Catalysts with Different Bulk Topologies Zeeshan NAWAZ 1 , TANG Xiaoping 1 , ZHU Jie 1 , WEI Fei 1, *, Shahid NAVEED 2 1 Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China 2 Department of Chemical Engineering, University of Engineering and Technology Lahore, Lahore 54890, Pakistan Abstract: Three SAPO-34 catalysts, 100% SAPO-34, 30% SAPO-34, and meso-SAPO-34, with different bulk topologies were prepared. The catalysts were characterized by N 2 adsorption, scanning electron microscopy, X-ray diffraction, and infrared spectroscopy techniques. The pore size, total acidity, and internal cage structure of the catalysts were almost identical, but they had different bulk appearances. The role of the bulk topology/structure of the catalysts was studied using 1-hexene cracking. On 30% SAPO-34, the surface acidity and diffusion rate decreased due to blocking by binder, which adversely affected catalytic activity. 100% SAPO-34 gave better cracking ability and higher propylene selectivity because of suitable acid sites and effective shape selectivity, respectively. In order to study the effect of diffusion, meso-SAPO-34 was used. The different bulk structure gave different feed conversion and selectivity profiles. A superior control of the stereochemistry was observed in the cracking by the meso-SAPO-34 and 100% SAPO-34 catalysts, in which enhanced diffusion mass transport played an appreciable role. Most of the propylene was produced by the direct cracking pathway by the ȕ-scission carbenium ion mechanism. Hydrogen transfer reactions became significant at higher conversions. Decreasing the residence time to a certain extend is an appropriate way to obtain high propylene yield and selectivity. Activity and selectivity patterns for 1-hexene cracking to propylene were compared to justify superior SAPO-34 topology for 1-hexene cracking to propylene. Key words: 1-hexene; catalytic cracking; propylene; diffusion; SAPO-34 Propylene is a traditional petrochemical building block. There is a need at this time to enhance propylene production to meet the increasing market demand. Propylene is the word’s second largest petrochemical commodity and the principal raw material for the production of many important petrochemicals, especially polypropylene. According to market statistics, it is forecasted that propylene demand for 2010 will be about 85–92 million tons with an annual growth rate of 5.8% [1–6]. About 64% of propylene is produced as a by-product from the steam cracking of naphtha. Fluid catalytic cracking (FCC) units typically produce around 3%–7% propylene, depending on the feed composition, operating conditions, and catalysts [7]. Therefore, at this time, purposely developed propylene pro- duction technologies are considered the better option to meet the production-demand gap [8,9]. Among these propylene technologies, the transformation of higher olefins to lower olefins is the most economical and viable route to produce propylene because of the cheap and easy availability of the raw material [10]. A solid acid zeolite is used in the petrochemical industry for cracking applications [4,10,11]. The cracking reactions of olefins over zeolites have been studied extensively and ex- plained in terms of carbenium ion mechanism [12], while the superiority of these catalysts were explained in terms of shape selectivity [13]. The concept of shape-selective catalytic cracking was mainly shown in two ways: improved conversion of raw materials and increased desired product selectivity [13]. Therefore, catalysts having selective pores for desired products and that do not allow higher hydrocarbons to form are highly desirable for olefin cracking. In earlier studies, this concept of shape selectivity was studied for SAPO-34 catalysts [14]. It was widely accepted that 1-hexene cracked over Brønsted acid