"Coking" of zeolites during methanol conversion: Basic reactions of the MTO-, MTP- and MTG processes

Deactivation of acidic zeolite catalysts during methanol conversion is investigated for elucidating how spatial constraints interfere mechanistically. Detailed product composition - including retained organic matter - is determined in a time resolved mode. At 270-300 degrees C with H-ZSM-5, first unsaturated hydrocarbons are formed-methane being the indicative co-product. Then the reaction rate increases auto-catalytically, but soon declines because of exhaustive pore filling. The retained organic matter consists mainly of ethyl-trimethyl-benzene-and isopropyl-dimethyl-benzene molecules. Alkylation of benzene rings with ethene and propene produces the deactivating molecules. At 475 degrees C, alkylation of benzene rings with olefins has shifted to the reverse, reactivating the H-ZSM-5 catalyst. Coke forms slowly on the surface of H-ZSM-5 crystallites. Spatial constraints suppress the formation of 2-ring aromatics. With the wide pore zeolite H-Y, fast deactivation is noticed-bigger aromatic molecules can be formed and are retained. Methanol reactions on the protonic catalyst sites are visualized as CH3+ attack for methylation and dehydrogenation, methane being the hydrogen-rich co-product. Methanol conversion on zeolites H-ZSM-58, H-EU-1 and H-Beta is comparatively investigated. Zone ageing is discussed for favorable reactor design. It is shown, how a multi-compound product composition is the source of information for elucidating complex reaction mechanisms. (C) 2010 Elsevier B. V. All rights reserved.