Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts
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Catalysis Letters Vol. 103, Nos. 3–4, October 2005 (Ó 2005) DOI: 10.1007/s10562-005-7155-5
Butene catalytic cracking to propene and ethene over potassium modified ZSM-5 catalysts Xiangxue Zhua,b, Shenglin Liua,b, Yueqin Songa,b, and Longya Xua,b,* a
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 110, 116023, P. R. China b Graduate School of Chinese Academy of Sciences, P. R. China
Received 24 November 2004; accepted 4 May 2005
Catalytic cracking of butene over potassium modified ZSM-5 catalysts was carried out in a fixed-bed microreactor. By increasing the K loading on the ZSM-5, butene conversion and ethene selectivity decreased almost linearly, while propene selectivity increased first, then passed through a maximum (about 50% selectivity) with the addition of ca. 0.7–1.0% K, and then decreased slowly with further increasing of the K loading. The reaction conditions were 620 °C, WHSV 3.5 h)1, 0.1 MPa 1-butene partial pressure and 1 h of time on stream. Both by potassium modification of the ZSM-5 zeolite and by N2 addition in the butene feed could enhance the selectivity towards propene effectively, but the catalyst stability did not show any improvement. On the other hand, addition of water to the butene feed could not only increase the butene conversion, but also improve the stability of the 0.7%K/ZSM-5 catalyst due to the effective removal of the coke formed, as demonstrated by the TPO spectra. XRD results indicated that the ZSM-5 structure of the 0.07% K/ZSM-5 catalyst was not destroyed even under this serious condition of adding water at 620 °C. KEY WORDS: butene; catalytic cracking; K modification; propene; ethene; ZSM-5 catalyst.
1. Introduction Propene is one of the fastest growing petrochemicals, driven primarily by the high growth rate of polypropene [1,2]. Traditional methods for propene production cannot meet the growing demand of propene [3]. For example, the production of the co-producing propene from steam cracking is determined largely by the feed state, and most of the new steam cracking capacity is based on ethane feed, which produces little propene [3]. In FCC units, propene is obtained with a relatively low yield, and increasing of the yield has been proven to be expensive and limited [4,5]. Another two on-purpose propene technologies are available, such as propane dehydrogenation and metathesis of ethene and butene, but both of them have seen only limited applications, which depend especially on feedstock economics [1,2,6]. An alternative process is the catalytic cracking of C4+ alkenes to propene and ethene, of which the feed can be any hydrocarbons containing sufficient amounts of C4+ alkenes, such as steam cracker by-products, low-value FCC refinery streams, catalytically cracked naphthas and light gasolines, etc. [7–11]. Several patents have been applied on the technology of catalytic cracking of C4+ alkenes, most of which were carried out on high-silica ZSM-5 zeolites (for example, Si/Al2>300) [1,2,4–6]. As the acidities of the high-
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