Syngas methanation from the supercritical water reforming of glycerol

An overall heat-integrated process of SCW (supercritical water) reforming of glycerol for methanation of the syngas obtained and power generation is proposed and analyzed. Methanation is the methane synthesis from the hydrogenation of CO and CO₂. The SCW reforming is performed at 240 bars. Reforming temperatures from 700 °C to 900 °C and glycerol feed concentrations between 25 wt.% and 50 wt.%, needed to reach an energy self-sufficient process, are studied. For methanation, three adiabatic, fixed-bed reactors are connected in series with intermediate gas cooling, operating at 30 bars. The exit temperatures of these reactors range from 600 °C to 300 °C, respectively. The feed for the methanation section is previously conditioned by a Pressure Swing Adsorption unit to achieve a stoichiometric number of 3. The recommended operating conditions are a reforming temperature of 800 °C and a glycerol concentration of 33 wt.% to obtain 0.166 kg CH₄/kg glycerol, 0.433 kWe/kg glycerol and an overall energy efficiency of 61.6%, which may increase up to 76.1% if the hot water leaving the process at 90 °C is considered (cogeneration water). The results of this process were compared to those of the methanol synthesis, previously published, resulting in a better performance, because the carbon proportion converted into methane is higher than into methanol from SCW reforming of glycerol, and the higher specific overall value for the methane production, which considers the price of the product and the electricity jointly. - Highlights: • Methane can be efficiently produced using syngas from supercritical water reforming of glycerol. • Electrical power by two expanders is also obtained and the energy scheme involves cogeneration. • Methanation is performed in three-fixed bed reactors in series with intermediate gas cooling. • Optimal conditions are a glycerol concentration of 30–33 wt.% reforming at 750–800 °C and 240 bars