Production of Light Hydrocarbons from Syngas Using a Hybrid Catalyst

A hybrid catalyst consisting of a Cu-ZnO/Al2O3 methanol synthesis catalyst and a SAPO-34 molecular sieve was shown to convert syngas into a narrow mixture of short chain paraffins centered at C2-C3 with little methane and C5+ made. This product mix is expected to be an excellent cracker feedstock for the production of olefins. The hybrid catalyst system closely couples sequential reactions on each of the two independent catalysts. The function of each of the components was unraveled by performing experiments in which the reactor was loaded with discrete layers of the individual catalysts. Methanol (MeOH) synthesis over Cu-ZnO/Al2O3 is followed by methanol conversion to dimethyl ether (DME) + steam over the acidic SAPO-34 or Cu-ZnO/Al2O3 component. Simultaneously, the so generated water feeds into the water gas shift (WGS) reaction over Cu-ZnO/Al2O3, producing H-2 + CO2, and the DME/MeOH undergoes methanol to olefins (MTO) conversion over SAPO-34. The olefins are subsequently hydrogenated to paraffins over the Cu-ZnO/Al2O3 and SAPO-34 catalysts using hydrogen from the feed or hydrogen produced in the WGS reaction. Comparison of fully mixed vs layered catalyst bed systems indicated that a mixed catalyst bed is preferred to give a high CO conversion and selectivity to desired paraffin products. This scheme enables high single stage conversion by consuming methanol, thereby removing the thermodynamic constraint on that reaction step. The interactions between all the reactants and catalysts in this system create a complex relationship that is probed in this paper.