Thermodynamic analysis of steam assisted conversion of bio oil components to synthesis gas

Abstract

Steam reforming is a well-established route for hydrogen production, but the processing of fossil-based hydrocarbons leads to the generation of carbon dioxide, a well-known greenhouse gas. Recently, the use of biomass-driven resources such as bio-oil has been recognized as a viable solution in terms of its sustainability and its CO2 neutral behavior. The aim of this study is to investigate the thermodynamics of steam assisted conversions of model components of bio-oil – formic acid, isopropyl alcohol, lactic acid and phenol – and to understand the effect of process variables such as temperature, pressure and inlet steam-to-fuel ratio on the product distribution. For this purpose, a thermodynamic analysis is performed at ranges of temperature, pressure and steam-to-fuel ratio of 600–1000 K, 1–30 bar and 4–9, respectively. The number of moles of each component in the product stream at equilibrium is calculated via the method of Gibbs Free Energy (GFE) minimization technique. The resulting optimization problems are solved using Sequential Quadratic Programming (SQP) algorithm under General Algebraic Modeling System (GAMS) environment. The results indicate that, for all model hydrocarbons and operating conditions, almost complete conversion to H2, CO, CO2 and CH4 are achieved. Temperature and steam-to-fuel ratio have positive effects in increasing hydrogen content of the product mixture at different magnitudes, whereas the increase in pressure suppressed hydrogen production. These trends provide insight about the reaction mechanism and indicate the existence of water-gas shift, methanation and methane steam reforming as major side reactions running parallel to steam reforming of the model hydrocarbon.