CO2 Reduction to Substitute Natural Gas: Toward a Global Low Carbon Energy System

Methane has proven to be an outstanding energy carrier and is the main component of natural gas and substitute natural gas (SNG). SNG may be synthesized from the CO2 and hydrogen available from various sources and may be introduced into the existing infrastructure used by the natural gas sector for transport and distribution to power plants, industry, and households. Renewable SNG may be generated when H-2 is produced from renewable energy sources, such as solar, wind, and hydro. In parallel, the use of CO2-containing feed streams from fossil origin or preferably, from biomass, permits the avoidance of CO2 emissions. In particular, the biomass-to-SNG conversion, combined with the use of renewable H-2 obtained by electrolysis, appears a promising way to reduce CO2 emissions considerably, while avoiding energy intensive CO2 separation from the bio feed streams. The existing technologies for the production of SNG are described in this short review, along with the need for renewed research and development efforts to improve the energy efficiency of the renewables-to-SNG conversion chain. Innovative technologies aiming at a more efficient management of the heat delivered in the exothermic methanation process are therefore highly desirable. The production of renewable SNG through the Sabatier process is a key process to the transition towards a global sustainable energy system, and is complementary to other renewable energy carriers such as methanol, dimethyl ether, formic acid, and Fischer-Tropsch fuels.