Thermodynamic modelling and energy balance of direct methanation of glycerol for Bio-SNG production

Glycerol can be considered a waste product when the cost of processing is higher than the processed glycerol value. In these situations, conversion of glycerol to an energy vector may be more beneficial. The aim of this work was to design and assess the feasibility of a process for low temperature steam reforming of glycerol (GLT-SR). GLT-SR is a novel form of direct methanation that produces a CH rich, renewable fuel gas (Bio-SNG) that could substitute the current natural gas consumption associated with biodiesel production.

In this work, thermodynamic modelling to determine the conditions that suited CH₄ production and minimised carbon below 600 K as well as the impact of molar steam to carbon ratio (S/C) and pressure on the biomass to fuel efficiency of a GLT-SR plant were carried out using Aspen Plus® (V8.8) chemical processing software. Operating at 8 atm provided the benefits of high conversion to CH₄ whilst minimising the outlet reformer temperature and achieving the required inlet temperature for catalyst operation.

The Bio-SNG produced had an LHV of 16.7 MJ kg¯¹ and had properties like landfill gas and biogas. An energy balance of the process determined that the electricity demand was negligible due to the low energy use of pumps and fans without the need for compressors. Operating at 8 atm, the production of Bio-SNG in the GLT-SR plant has the potential to offset 30% of the natural gas embodied energy requirement or 8.9% of the total embodied energy requirement for soybean biodiesel production from farm to use.