Kinetic modelling of synthesis gas into hydrocarbons

A bi-functional catalyst for the conversion of synthesis gas (carbon monoxide and hydrogen) into C₁ to C₅ hydrocarbons was synthesized. The catalyst comprised methanol synthesis and methanol conversion components. The methanol synthesis component (MSC) was a mixed oxide of zinc and chromium with a Zn/Cr atomic ratio of 1:10. The methanol conversion component (MCC) was ZSM-5, with a Si/Al ratio of 20:1. Phosphorus was loaded onto the ZSM-5 at variable levels between 0 and 2.4 percent by weight. Catalyst pellets 3 mm in diameter and 6 mm in length were formed by the compression of 67 wt % of the MSC and 33 wt % of the MCC.; Catalyst characterization methods employed were XRD, TPD, SEM-EDX, ICP and BET surface area.; Four catalyst compositions with different phosphorus loadings were tested under reaction conditions in a Berty well-mixed fixed-bed reactor. The reaction temperature was varied between 385 and 480°C. The feedstock H₂:CO ratios tested were 3, 2, and 1. The feedstock space velocity varied from 30 to 300 mmol/g_cat/hr. Feedstock pressure was constant at 35 bar (absolute).; Reaction results were analyzed in terms of CO conversion as well as selectivity to and yields of reaction products. CO conversion was found to increase with temperature and space-time. The highest selectivity for olefins was observed at low temperature and low space-time conditions. The paraffin/olefin ratio in the product stream varied from 6 to 52 over the phosphorus-modified catalysts and from 3.4 to 23 over the unmodified catalyst.; An expression for the reaction rate of carbon monoxide consumption was developed and the parameters estimated by non-linear regression. The CO consumption rate was found to be approximately first order in terms of carbon monoxide partial pressure and was inhibited by increased carbon dioxide partial pressure. The activation energy was in the range of 90 to 120 kJ/mol.; A detailed model, comprising nine independent chemical reactions and 12 differential equations, that described the change of various chemical species with respect to space-time was proposed. This model's parameters were estimated using non-linear regression. The model described the changes in reaction species' molar fractions with respect to space-time.