The CO2 content in the process gas downstream of the low temperature shift converter is approximately 18 %. Carbon dioxide is a strong catalyst poison. It also reacts with the ammonia present in the synthesis recycle gas to form ammonium carbamate and ammonium carbonate. These salt-like products form deposits in the machinery and equipment, and this might cause serious damage.
Various processes are available for removing the CO2 from the synthesis gas. If the quantity of CO2 to be absorbed is large, the only efficient method of removing the CO2 is by a regenerative process using liquid absorbents. One normally differentiates between physical and chemical scrubbing methods.