Process for the preparation of synthetic hydrocarbons

Abstract

Synthetic hydrocarbons, especially high octane gasoline, are prepared by catalytic conversion in two steps of a synthetic gas containing hydrogen and carbon oxides. In the first step the synthesis gas is converted at 10-80 bar and 200.degree.-300.degree. C. into an intermediate containing methanol and/or dimethyl ether. Useful catalysts for methanol synthesis are oxides of chromium, aluminium and/or copper, and zinc; and for dimethyl ether synthesis certain zeolites. In the second step the entire intermediate from the first step is converted at the same pressure as in the first step and an inlet temperature of 300.degree.-340.degree. C. while supplying heat to obtain an outlet temperature of 410.degree.-440.degree. C.; the difference between inlet and outlet temperature being at least 30.degree. C. higher than the temperature increase caused by the conversion reaction. As catalyst in the second step one can use any conventional catalyst for converting methanol and/or dimethyl ether into hydrocarbons, especially synthetic zeolites. The raw product stream from the second step is cooled and thereby separated into a condensed hydrocarbon product stream and a gaseous recycle stream, the latter being recycled without further separation to the inlet of the first stream and here combined with fresh synthesis gas feed. There is obtained a low rate of deactivation of the catalyst used in the second step and a high quality hydrocarbon product.