Gasoline conversion

Table VII. Yields of Olefin Isomers During Gasoline Conversion...

The process, referred to as methyl alcohol-to-gasoline conversion, involves initial dehydration of methyl alcohol to dimethyl ether, with a subsequent carbenoid-type reaction. It goes probably through an oxonium ylide-type intermediate that is readily methylated by excess methanol (dimethyl ether) producing the crucial Ci —> C2 conversion and then cleaves to ethylene. Once a C precursor is converted into a C2 derivative (i.e., ethylene), the further conversion to higher hydrocarbons of the gasoline range (or to aromatics) follows well-known chemistry. 

A review of this field has been given by Haw (1999). Reactions can be followed either in sealed glass ampoules or flow-through cells constructed within the spectrometer. The formation of intermediates can be studied in real time. An elegant example of this was shown in an early study of methanol to gasoline conversion over HZSM-5 zeolites. As a result of the shape selectivity of the catalyst, spectroscopic evidence of reaction intermediates, which were not seen as reaction products, was observed (Anderson and Klinowski, 1990). 

Methanol to gasoline conversion ZSM-5 High gasoline yield with high-octane rating... 

Conversion of methanol to gasoline occurs in two stages. In the first stage, the crude methanol is partly dehydrated to an equilibrium mixture of dimethyl ether (DME), methanol and water. The reaction occurs at temperatures of 300°C to 420°C over an alumina catalyst in a fixed-bed reactor. The DME equilibrium mixture is then combined with recycle gas and passed to the gasoline conversion reactors where the second stage reactions to form gasoline take place. 

The results of this study using addition of hydrogen or model studies of the methoxymethal radical give clear evidence against the involvement of a gas phase carbene or methoxymethyl radical intermediates in the mechanisms of initial C-C bond formation in the methanol to gasoline conversion reaction. 

There are now several industrial processes that use the shape selectivity afforded by zeolite catalysts. These include aromatic substitution, aromatic alkylation and alkylbenzene isomerization, and methanol to gasoline conversion reactions. 

It should be noted that using five lump model (Dave and Saraf, 2002), maximisation of conversion is equivalent to maximisation of gasoline conversion. 

The activity results in pyrolysis gasoline conversion of styrene, measured at 120 °C for the three selected samples, are shown in Fig. 15.1. 

A.G. Gayubo, P.L. Benito, A.T. Aguayo, M. Olazar, J. Bilbao et al.. Effect of Si/Al ratio and of acidity of H-ZSM5 zeolites on the primaiy products of methemol to gasoline conversion. J. Chem. Tech. Biotechnol. 65, 183-191 (1996)... 

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