This process uses propylene carbonate as a physical solvent to remove CO2 and H2S. Propylene carbonate also removes C2+ hydrocarbons, COS, SO2, CS2, and H2O from the natural gas stream. Thus, in one step the natural gas can be sweetened and dehydrated to pipeline quality. In general, this process is used for bulk removal of CO2 and is not used to treat to less than 3% CO2, as may be required for pipeline quality gas, The system requires special design features, larger absorbers, and higher circulation rates to obtain pipeline quality and usually is not economically applicable for these outlet requirements.
Propylene carbonate has the following characteristics, which make it suitable as a solvent for acid gas treating:
1. High degree of solubility for CO2 and other gases.
2. Low heat of solution for CO2.
3. Low vapor pressure at operating temperature.
4. Low solubility for light hydrocarbons (Cl5 C2).
5. Chemically nonreactive toward all natural gas components.
6. Low viscosity.
7. Noncorrosive toward common metals.
These characteristics combine to yield a system that has low heat and pumping requirements, is relatively noncorrosive, and suffers only minimal solvent losses (less than 1 Ib/MMscf). Solvent temperatures below ambient are usually used to increase the solubility of acid gas components and therefore decrease circulation rates.