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Selexol solvent is a mixture of dimethyl ethers of polyethylene glycols, nontoxic, with a high boiling point, and is an excellent solvent for acid gases. The selectivity for hydrogen sulfide (H2S) is much higher than that for carbon dioxide (CO2), so it can be used to selectively remove these different acid gases, minimizing CO2 content in the H2S stream sent to the sulfur recovery unit (SRU) with associated benefits on SRU sizing and economics, and enabling regeneration of solvent for CO2 recovery by economical flashing. These points are reflected in Figure 1, which depicts a dual-stage Selexol process. The first column (sulfur absorber) removes most of the H2S (and a limited amount of CO2) from the feed syngas, which then flows to the second column (CO2 absorber) which removes most of the CO2. The rich solvent leaving the CO2 absorption column is flashed in drums, from which relatively pure CO2 is recovered. The solvent in the sulfur absorber column must be stripped in a column with reboiler to remove the high H2S content gases.

Figure 1: Dual-stage Selexol Flow Diagram
Figure 1: Dual-stage Selexol Flow Diagram 
References/Further Reading

Syngas Clean Up


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