Methane production from CO₂
After the discovery of the reaction by Sabatier and Senderens in 1902, the reaction to convert CO and CO2 to methane has now been investigated and developed for more than 100 years [Rönsch etal. 2016]. Here we focus on the process starting from CO2. In an exothermal reaction CO2 is hydrogenated with H2 to produce methane, water, and heat.
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Both H2 and CO2 are provided in this case from external sources. CO2 methanation is a linear combination of CO methanation and reverse water–gas shift reaction and the equilibrium of both reactions is influenced by pressure (1-100 bar) and temperature (200-550 °C). Typically, a couple (2-7) of adiabatic fixed bed reactors are coupled in series to enhance temperature controle and conversion. Intermediate recycles are used to increase carbon conversion efficiency and product yield. To regulate temperature, recycles, and pressures, several compressors and heat-exchangers are integrated in the process.
The product, often called synthetic natural gas (SNG), is mainly methane but may also contain some other gasses, such as H2. Depending on the required purity of the methane, additional purification may be necessary, which can increase costs and energy use. We assume here that methane is produced at sufficient purity for use in other applications. Main developments are occuring in new technological approaches, such as isothermal, sorption enhanced, and fluidised bed methanation. The methanation process is also relevant in the context of bio-SNG production.