Simultaneous Removal Of H₂S And CO₂ By Alkaline Functionalized Deep Eutectic Solvents

There are a lot of acid gases（such as H₂S and CO₂）in natural gas,which affect human health and global climate.In the traditional processes of removal of H₂S and CO₂,there are some problems such as volatilization of absorbent and high energy consumption.Therefore,it is very important to develop green and efficient absorbent.Because of their good properties,deep eutectic solvents（DESs）are widely used in the study of acid gases removal.However,the reported results of acid gases absorption are still low,and there is no corresponding research on the simultaneous capture of H₂S and CO₂.Based on this,this paper designed some functional deep eutectic solvents with polyamine sites for H₂S absorption,and synthesized some alkaline functional deep eutectic solvents to explore the competitive effect of simultaneous absorption of H₂S and CO₂.The main research contents and conclusions are as follows:（1）Based on the excellent absorption characteristics of amino groups to H₂S,a functional deep eutectic solvent with polyamine sites was designed and synthesized with tetraethylene pentamine（TEPA）as hydrogen bond acceptor and hydroxyethyl ethylenediamine（AEEA）as hydrogen bond donor.The influencing factors of absorption were investigated and the absorption mechanism was explored.The results showed that:At 100 k Pa and 30°C,the saturated absorption of 5vol%H₂S by TEPA-AEEA(n _TEPA:n_AEEA=1:4)DES was up to 4.68 mol H₂S/mol DES.The absorption improves notably with the decrease of temperature and the increase of H₂S concentration.TEPA-AEEA(n _TEPA:n_AEEA=1:4)DES has good regeneration performance and can still reach 94%of the initial capacity after 5 times of recycling.Kinetic simulation showed that the hydroxyl group of AEEA can activate and improve the alkalinity of amino group in TEPA,so as to improve the absorption of H₂S.Quantum chemical calculations showed that the binding energy between amine sites on DES and H₂S was small,and the primary amine group acted preferentially with H₂S.（2）Using 1-ethyl-3-methylimidazole chloride（Emim Cl）as hydrogen bond acceptor and AEEA as hydrogen bond donor,a functional deep eutectic solvent was synthesized for simultaneous absorption of H₂S and CO₂.The influencing factors of absorption and the mechanism of competition were explored.The results showed that the absorption amount of DES was almost the same when absorbing low concentration H₂S and CO₂ alone,but it had high CO₂/H₂S selectivity when absorbing H₂S and CO₂ at the same time.Even if the two gases have the same concentration,the selectivity can still reach 3.33,and H₂S is easier to desorb.The increase of temperature and CO₂ concentration improved the selectivity.The amine group on AEEA was the main action site of acid gas absorption.Compared with H₂S,the interaction between CO₂ and amine group was stronger.In the process of absorption,the two gases had absorption equilibrium at the alkaline site.