Thermodynamic evaluation of dry reforming of vegetable oils for production of synthesis gas

Abstract

The dry reforming (DR) is a promising technology for utilization of greenhouse gas, carbon dioxide, to produce synthesis gas for downstream synthesis of valuable chemicals and fuels. In this study, equilibrium of DR and autothermal dry reforming (ATDR) of vegetable oils was investigated by Gibbs free energy minimization method. The effects of various process variables of DR and ATDR of vegetable oils such as temperature (673–1273 K), carbon dioxide-to-carbon mole ratio (CCMR) (0.5–3.0), and oxygen-to-carbon mole ratio (OCMR) (0–1.0) were studied to obtain equilibrium products composition, thermodynamically promising operating conditions, and thermoneutral conditions of the process. The study revealed that insignificant amount of coke and compounds containing two or more carbon atoms were formed for both DR and ATDR of vegetable oils. The hydrogen yield was found to increase with increase in temperatures for DR of vegetable oil. At temperature 983 K and above, the hydrogen yield was found to increase with CCMR, reach maxima, and then decrease with further increase in CCMR. The carbon dioxide conversion and yield of CO and water were increased and yield of methane was decreased with increase in temperature. The yield of CO and water were increased and the conversion of carbon dioxide and yield of methane were decreased with increase of CCMR. For ATDR of vegetable oils, the reduced yield of CO and methane and enhanced yield of water and hydrogen (up to temperature of maximum hydrogen yield) were observed compared to that of DR. From critical analysis of the results of DR and ATDR of vegetable oil, the optimum conditions for maximum yield of hydrogen with very low yield of methane were determined as 1000–1050 K, CCMR of about 1, and oxygen-to-carbon mole ratio of 0.6–0.7. It was observed that about 80% hydrogen yield with 78–83 moles of CO and 0.2–0.6 moles of methane per mole of vegetable oil could be obtained under the optimum conditions.