Methane conversion to light olefins—How does the methyl halide route differ from the methanol to olefins (MTO) route?

The methyl halide to hydrocarbons (MeXTH) reaction represents the second step in a potential two-step route from methane to light olefins or gasoline-range hydrocarbon mixtures. In this contribution, the methyl chloride to olefins reaction (MeXTO) was studied over a H-SAPO-34 catalyst with (Al + P)/Si = 19 by means of catalytic testing at 350–400 °C and WHSV = 11.7 h−1, infrared spectroscopy and isotopic labelling experiments. Only minor degradation of the H-SAPO-34 material was observed by X-Ray diffraction or infrared spectroscopy after 5 sequential test-regeneration cycles at 400 °C and 550 °C, respectively. Co-feed experiments using 13C-methyl chloride and 12C-ethene or 12C-propene at 400 °C indicated that the conversion level of each compound is directly related to its proton affinity. Furthermore, under the conditions used, no inhibitive effect of the alkenes on methyl chloride conversion was observed. Transient isotopic labelling experiments suggested that hexamethyl benzene is an important reaction intermediate in alkene formation from methyl chloride. However, the isotopic labelling of effluent products during 13C-methyl chloride–12C-alkene co-feed experiments suggested that alkene methylation and interconversion reactions may contribute significantly to C3+ formation. The findings are in general agreement with similar studies of the methanol to olefins reaction over the same catalyst topology.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (82 K)Download as PowerPoint slideHighlights► In this study we compare methyl chloride and methanol as hydrocarbon precursors. ► The reactions are carried out over H-SAPO-34 catalysts. ► Both reactions proceed via a hydrocarbon pool mechanism with hexamethyl benzene as intermediate. ► The lower proton affinity of methyl chloride leads to lower reaction rates. ► The catalyst is regenerable although HCl formed by MeCl conversion leads to breaking of Al–O bonds.