Thermodynamic Analysis of Ethanol Synthesis from Glycerol by Two-Step Reactor Sequence

Conversion of biomass-derived syngas to ethanol has recently received significant attention because of strong demands for alternative and renewable energy sources; therefore glycerol has been suggested as promising raw material for obtaining ethanol in two consecutive steps. In this work, a thermodynamic study of glycerol dry reforming to produce syngas and subsequent ethanol production, as two-step process, was evaluated by means of the method of Gibbs free energy minimization. The effect of parameters such as reaction temperature, CO2/glycerol ratio (CGR), and pressure (P) on system performance was investigated. Reactions were simulated between 700-1,500 K and CGR range of 0-5, at 1 atm pressure. Calculations were performed with Aspen Plus 8.4, using Peng-Robinson thermodynamic method for properties estimation. Optimum conditions for syngas and ethanol production were determined, in order to prevent carbon deposition and methane formation. At temperatures above 900 K and CGR <1, between 3 and 7 mole of H-2/mole of glycerol can be generated. Results indicated that the addition of CO2 to the glycerol dry reforming reactor favored syngas and ethanol synthesis. The maximum yield obtained was 1 mole of ethanol per mole of glycerol at CGR >= 2. Simulations indicate that temperature and CGR are essential factors for determining the process efficiency of the production of ethanol from syngas. These results suggest that glycerol wasted from biodiesel manufacturing should be useful as efficient raw material for syngas and ethanol production.