Selective Electrochemical Regeneration of Aqueous Amine Solutions to Capture CO2 and to Convert H2S into Hydrogen and Solid Sulfur

Abstract

Removing CO2 from natural gas or biogas in the presence of H2S is technically challenging and expensive as it often requires separation of both acid gases from the gas, typically using an aqueous amine solution, followed by separation of CO2 from H2S and conversion of H2S into solid S. In this work, the proof of concept of electrochemical, instead of thermal, regeneration of an aqueous amine solution is developed. This invention might be a very promising technology and has several advantages. It has H2S versus CO2 selectivity of 100%, can directly convert H2S into S and H2, and is economically competitive with CO2 desorption energy around 100 kJmol−1 and H2S conversion around 200 kJmol−1. If renewable energy is used for electrochemical regeneration, CO2 emissions due to the CO2 capture process can be significantly reduced.

Selective H2S Absorption in Aqueous Tertiary Alkanolamine Solvents: Experimental Measurements and Quantitative Kinetic Model

“…To simultaneously respect the asymmetrical H 2 S (<4 ppm) and CO 2 (<2.0–2.5 vol %) specification, a selective solvent can be used that preferentially absorbs H 2 S over CO 2. Techno-economic studies have shown that a further increase of the selectivity might lower the cost of CO 2 capture from natural gas containing H 2 S. , …”

“…Natural gas can contain significant amounts of acid gas (typically 0−30 vol % CO 2 , 0−30 vol % H 2 S), but the specifications of treated natural gas are very similar to biogas (around 4 ppm H 2 S and 50 ppm or 2.0−2.5 vol % CO 2 for LNG or pipeline, respectively) and can be reached with solely an amine scrubber, thanks to the high operating pressure of the absorption column. To simultaneously respect the asymmetrical H 2 S (<4 ppm) and CO 2 (<2.0−2.5 vol %) specification, a selective solvent can be used that preferentially absorbs H 2 S over CO 2. economic studies have shown that a further increase of the selectivity might lower the cost of CO 2 capture from natural gas containing H 2 S. 4,5 Low-pressure selective absorption is also applied in the natural gas industry, for example, in the acid gas enrichment (AGE) unit or the tail gas treatment unit (TGTU), in the upstream and downstream Claus sulfur recovery units, respectively. The main driving forces to improve the selectivity of the solvents in both TGTU and AGE are the reduction of CO 2 emissions, Claus unit optimization (only for AGE), and lower SO 2 emissions.…”