To attain extremely high purity in the product gas, chemical conversion method can be
used. It reduces the undesirable gas concentrations to trace levels. Usually the chemical
conversion process is used after bulk removal has been accomplished by other methods.
One such chemical conversion process is methanation, in which CO2 and H2 are
catalytically converted to methane and water. Chemical conversion process is extremely
expensive and is not warranted in most biogas applications [17].