Methanol conversion to light olefins over commercial zeolites

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" Methanol conversion to light olefins over commercial zeolites "
U. A. El-Nafaty

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112529
Doc. No	:	TLpq303925344
Main Entry	:	U. A. El-Nafaty
Title & Author	:	Methanol conversion to light olefins over commercial zeolites\ U. A. El-Nafaty
College	:	King Fahd University of Petroleum and Minerals (Saudi Arabia)
Date	:	1990
student score	:	1990
Degree	:	M.Sc.
Page No	:	183
Abstract	:	The conversion of methanol to light olefins (MTO) over commercial narrow pore Silicoaluminophophate SAPO-34, and pentasil type ZSM-5 and Silicalite S-115, was studied in a fixed bed tubular reation system. Nitrogen was used as carrier gas. Experiments were caried out at various temperatures, space velocities (WHSV) and methanol-to-nitrogen (wt) ratio to study their effects on catalyst activity, selectivity, product distribution and coke deposition. ZSM-5 and S-115 were modified by impregnation with various metal elements to investigate their effects on catalyst active life time and selectivity to lower olefins. At 400C and 4 hr WHSV SAPO-34 exhibited higher initial selectivity to lower olefins than both ZSM-5 and S-115 but also deactivated more rapidly (< 2hrs). This was attributed to the catalyst's narrow pore size which enhanced coke formtion leading to poisoning of active sites an blockade of pore channel entrances. The optimum operting conditions for S-115 and ZSM-5 were found to be 375C and 450C respectively at 4hr WHSV and 2.67 methanol-to-nitrogen (wt) ratio. S-115 showed higher overall selectivity to olefins than ZSM-5 at optimum conditions. Active life-on-stream was also longer for S-115 than ZSM-5 with 58.1 and 25.5 hr respectively. Since both zeolites have identical pore-sizes and strucutres, the better performance of S-115 was attributed to its higher silica/alumina ratio of 300 as compared to ZSM-5 which had a silica/alumina ratio of 40. Modification of the two zeolites with various elements showed the degree of selectivity to light olefins to vary according to the modifying element. With S-115, the selectivity was found to vary according to the order usd\rm Ba>La>Ag>Cu>Ca>Sr>Ga>Cd>In,usd while for ZSM-5, the selectivity decreased in the order usd\rm In>Ag>Cu>Cd.usd Optimum Ba-loading on S-115 for high olefin yield was found to be 5.2% by impregnation and 0.03% by ion-exchange.
Subject	:	Applied sciences
	:	Chemical engineering