CMHC:: coupled methanol hydrocarbon cracking -: Formation of lower olefins from methanol and hydrocarbons over modified zeolites

Coupled methanol hydrocarbon cracking (CMHC) combines exothermic methanol conversion with the highly endothermic hydrocarbon cracking reaction on zeolites with the MFI structure in fixed-bed reactors to obtain the lower olefins in a nearly thermoneutral reaction. The CMHC reaction is investigated with liquid hydrocarbons as well as lower gaseous hydrocarbons as the co-feed. The reaction is carried out in tubular reactors, and in addition, the conversion is also studied in a miniplant with two reactors working in a swing regime for reaction and regeneration. Space-time yields of lower olefins of about 1000 g kg(-1) h(-1) are realized. The catalysts are subject to different deactivation reactions, particularly the deposition of coke which can be removed by oxygen treatment, but also irreversible changes due to the dealumination of the zeolite framework. Different modifications of the parent zeolites can moderate the deactivations. Catalyst characterization is focused on the determination of the acid properties of fresh and used samples as well as regenerated samples by FTIR spectroscopy using pyridine as the probe molecule and the temperature-programmed desorption of ammonia. (C) 1999 Elsevier Science B.V. All rights reserved.