Thermodynamic analysis of steam assisted conversions of bio-oil components to synthesis gas

Abstract

The aim of this study is to investigate the thermodynamics of steam assisted, high-pressure conversions of model components of bio-oil – isopropyl alcohol, lactic acid and phenol – to synthesis gas (H 2 + CO) and to understand the effects of process variables such as temperature and inlet steam-to-fuel ratio on the product distribution. For this purpose, thermodynamic analyses are performed at a pressure of 30 bar and at ranges of temperature and steam-to-fuel ratio of 600–1200 K and 4–9, respectively. The number of moles of each component in the product stream and the product composition at equilibrium are calculated via Gibbs free energy minimization technique. The resulting optimization problems are solved by using the Sequential quadratic programming method. The results showed that all of the model fuels reached near-complete conversions to H 2, CO, CO 2 and CH 4 within the range of operating conditions. Temperature and steam-to-fuel ratio had positive effects in increasing hydrogen content of the product mixture at different magnitudes. Production of CO increased with temperature, but decreased at high steam-to-fuel ratios. Conversion of model fuels in excess of 1000 K favored molar H 2/CO ratios around 2, the synthesis gas composition required for Fischer–Tropsch and methanol syntheses. It was also possible to adjust the H 2/CO ratios and the amounts of CH 4 and CO 2 in synthesis gas by steam-to-fuel ratio, the value depending on temperature and the fuel type. Product distribution trends indicated the presence of water–gas shift and methanation equilibria as major side reactions running in parallel with the steam reforming of the model hydrocarbons.