Studies On H₂S And CO₂ Captured With Tetraalkylammonium Amino Acid Ionic Liquids

Mixed gases containing natural gas and syngas usually dope with H2S,C02 and other acidic gases. H2S has stench and corrosivity, which not only endanger human health seriously, but also lead to catalyst poisoning and not conducive to the occurrence of the reaction. CO2 not only reduce the calorific value of natural gas and syngas, but also lead to global warming so that the human confront more severe environmental problems. At the same time, H2S and C02 are important chemical raw materials, which can be converted into a variety of chemicals. Tetraalkylammonium amino acid ionic liquids are a new type of functional ionic liquids. In addition to the basic properties of conventional ionic liquids, they have many features, such as low viscosity,biodegradability and so on. Due to high viscosity of ionic liquids, a variety of tetraalkylammonium amino acid ionic liquids with low viscous were synthesized in this paper. Then, they were applied to the absorption of H2S and C02. The absorption mechanisms of H2S and C02 by ionic liquids were discussed. Finally, the absorption of various acidic gases by tetraalkylammonium amino acid ionic liquids was discussed. The main conclusions are as follows:1. The effect of absorbents mixed with different tetraalkylammoniunm amino acid ionic liquids on the absorption of H2S was studied. It was found that the solubility of H2S in the ionic liquids was related to the pKb of -NH2 (or-NH-) in amino acids formed the anion of ILs. The smaller of the pKb, the higher of the solubility. In addition, ethylene glycol not only accelerated the absorption rate of H2S by mixed absorbents, but also changed the absorption mechanism. Finally, the absorption mechanism of H2S by an absorbent mixed ionic liquid with ethylene glycol was proposed.2. The absorption mechanism of CO2 in tetraalkylammonium amino acid ionic liquids is not clear. A variety of tetraethyl ammonium amino acid ionic liquids were designed and synthesized. In this paper, absorption experimental data, CO2 physical and chemical absorption calculation, in situ FTIR and 13C NMR characterization were used to research the absorption mechanism of CO2 by ionic liquids systematically. It was found that the solubility of C02 in[N2222][L-Pro] was highest at 50 0C and 0.1 MPa, which was 1.038 mol C02/mol IL. The chemical absorption was 0.989 mol CO2/mol IL by solubility calculation, which was close to equimolar chemical absorption. In situ FTIR and 13C NMR also showed that the -NHCOOH group appeared in[N2222] [L-Pro] after the absorption of CO2.3. Due to the lack of awareness of the absorption common of acidic gases by ionic liquids, the absorption of three kinds of acidic gases by tetraalkylammonium amino acid ionic liquids was studied, such as H2S, CO2 and SO2. It was found that four kinds of ionic liquids have strong absorption ability to the three kinds of acid gases. The order of solubility was SO2> CO2>H2S. The absorption ability of different ionic liquids to the same acid gas is related to the type of amino acid anions.