Thermodynamic Analysis of Hydrogen Generation from Methanol–Formic Acid–Steam Autothermal System

Abstract

This work examines the H2 production from methanol (MeOH)–formic acid (FA)–steam (H2O) system (FSRM) by thermodynamic analysis using the Gibbs free energy minimization method. The compounds considered in FSRM are CH3OH, HCOOH, H2O, CO2, CO, H2, HCOOCH3, HCHO, and CH3OCH3 and together with or without CH4 and C (graphite). The addition of FA lowers the enthalpy of the system and favors the heat recycle. Thermal-neutral (TN) conditions are obtained, at which the heat released from exothermic reactions makes up exactly for the requirement of the endothermic reactions. For the case with consideration of CH4 and C formation, C and CH4 formation is thermodynamically dominated at a low temperature (<400 °C). High temperature is favorable for H2 production and can effectively inhibit CH4 and carbon formation, but it also leads to high CO yield. High H2O/MeOH ratio can effectively suppress CO, CH4, and C formation and improve H2 mole fraction at 200, 400, and 600 °C. Although the increase in FA/MeOH ratio leads to low equilibrium H2 mole fraction and high CO concentration, TN conditions can be realized for wide range of H2O/MeOH and FA/MeOH ratios. For the case without consideration of CH4 and C formation, which are only applicable to situations in which byproducts C and CH4 formation are limited, the thermodynamic data may be more agreeable with the reported experimental results. Under TN conditions, the H2 mole fraction can be around 0.51 with a CO mole fraction as low as ∼0.001 for H2O/MeOH = 2 and FA/MeOH = 5 or 6.