Thermodynamic analysis for methanol synthesis using biomass-derived syngas

This study presents multi-variable analysis for prediction and optimization of the methanol yield from biomass-based syngas using a thermodynamic model. The biomass-based syngas has a lower H2 content and higher CO2 than the typical syngas obtained from natural gas reforming which is used for the commercial methanol synthesis process. Consequently, a thorough examination was done to determine the working range for the input parameters for a biomass-derived syngas, so that the output of the process becomes comparable to the existing commercial technologies. Two cases were examined, case 1 where the H2 enriched bio-syngas was used for methanol synthesis and case 2 where the methanol was directly synthesized by the bio-syngas obtained by oxy-steam gasification process. A multi-variable analysis of the selected parameters is first performed; then, surrogate model for the methanol yield is constructed for both the cases. A selective set of response surfaces from the surrogate mathematical model for both the cases were used to illustrate the mutual effect of two parameters by keeping the other parameters at the base values. The analysis indicated that the methanol yield is most sensitive to temperature followed by pressure, CO2/CO, and H2/(CO + CO2) molar ratios in both the cases. The optimized values of methanol yield obtained for case 1 and case 2 were 92.72% and 45.35%, respectively, achieved at 473 K, 9 MPa. The CO2/CO and the H2/(CO+CO2) molar ratios were at 0.42 and 4.88 respectively for case 1 and for case 2; the values were 0.90 and 1.13 respectively. The high-pressure analysis involves the use of equations of states (EoS) to account for the deviations from ideality. Although many equations of state (EoS) are available, there is no one equation that would predict the properties of all the substances under all the conditions. An attempt has been made in this work to address the use of three such equations of state, namely Peng-Robinsons, Soave-Redlich-Kwong EoS and Newton’s universal curves, and to compare the results for the components involved in the methanol synthesis reaction. The results indicate that all three EoS provide similar correction factors in the studied temperature and pressure range for methanol synthesis.