CO/HZSM-5 CATALYST FOR SYNGAS CONVERSION - INFLUENCE OF PROCESS VARIABLES

The effects of process variables on the activity of a Co/HZSM-5 zeolite bifunctional catalyst for the conversion of syngas to hydrocarbons were studied. The catalyst was prepared by incipient-wetness impregnation from aqueous solutions of cobalt and thorium nitrate, the latter used as promoter. The reactions were carried out in a fixed-bed integral reactor. A simple two-level factorial design was not sufficient to describe the dependence of C-6+ yield and C-6+ selectivity on the process variables. A composite factorial design led to two response surfaces, describing the dependence of yield and selectivity on temperature (240-320 degrees C), space velocity (0.5-1.3 h(-1)), CO/H-2 feed ratio (0.5-1.9 molar) and pressure (0.1-4.3 MPa), with a deviation error of similar to 20%. The catalyst showed a better selectivity towards higher hydrocarbons than a physical mixture of ZSM-5 zeolite and a conventional Fischer-Tropsch catalyst and only slow deactivation, affecting mainly the C-6+ selectivity. This deactivation is probably due to coke deposition on the active surface sites, that is, cobalt particles and acid sites of the zeolite.