Absorption solvents for upgrading biogas to biomethane

A 100-fold increase is expected in Biomethane's role as a primary energy carrier for Germany till 2020. Yet know-how of the process for upgrading biogas to biomethane is still limited. The absorption process is well performing the task of removing CO2 and/or H2S from natural gas, syngas and flue gas, and the process can be used for biogas, too. However, not all solvents from those units are suitable for biogas treatment because of differences in gas composition and conditions under which these gases are available. The implications of these differences on the choice of the appropriate absorption solvent for biogas treatment have been discussed. Then, from a catalogue of 32 popular commercial solvents, suitable solvents are shortlisted based upon their ability to operate either at atmospheric pressure or at low pressure (< 8 bar). They are further classified based upon their capability to deal with H2S and O2. For these solvents, data such as typical solvent composition, recommended operating conditions in the absorber and the regeneration column, and solvent's qualitative volatility, corrosiveness, and chemical and thermal stability have been presented. Furthermore, reasons why certain solvents are unsuitable have also been mentioned. Once the technical feasibility of popular solvents is discussed, a quantitative comparison of solvent properties and an economic analysis may follow.