Absorption Of Light Hydrocarbons In Ionic Liquids And Deep Eutectic Solvents

Methane?CH₄?,ethane?C₂H₆?and propane?C3H8?are significant fundamental chemical materials,it is important to develop the separation technology of these hydrocarbons.Ionic liquids?ILs?and deep eutectic solvents?DES?are unique "tunable" solvents with nearly non-volatility.Hence,we designed a series of ILs and DES according to the simulation results of COSMO-RS and the properties of ILs and DES.In the hope of finding new absorbents with high selectivity,excellent capacity and low viscosity in separating light hydrocarbons and providing the necessary experimental datas,the interaction mechanism and absorption performance between these solvents and light hydrocarbons was studied through experiments.We calculated the Henry's law constant of propane,ethane,methane and nitrogen in 364 kinds of ILs or more than 70 kinds of DES by COSMO-RS method.The prediction results showed that the selectivities of and solubilities of light hydrocarbons raised with the increase of carbon number in the molecular structure of solvents.Here we synthesized three new long-chain carboxylate ILs with asymmetric phosphonium cations that had relatively low viscosity and good thermal stability.The solubilities of propane,ethane,methane,and nitrogen in these tributylethyl-phosphonium long-chain carboxylate ILs were determined at temperature of 298.1 to 313.1 K and pressure of 20 to 150 kPa.The effects of molecular structure on the properties of ILs and their absorption performance were investigated.It was found that the introduction of asymmetric cation with short alkyl chains significantly reduced the viscosity of carboxylate ILs,while an extension on the alkyl chain of carboxylate anions enhanced the solubility.At 298.1 K and 150 kPa,the solubilities of propane,ethane,and methane in tributylethylphosphonium stearate reach 0.408,0.133 and 0.009 mmol/g with selectivities of propane/methane and methane/nitrogen up to 16.9 and 2.7,respectively.We have also synthesized 12 kinds of DES,and investigated the effects of mixing ratio of compounds,molecular structure and temparature on their absorption performance of propane,ethane,methane,ethylene and nitrogen at 308.1 K,20?150 kPa.It is indicated that these DES exhibit high solubilities and selectivities for light hydrocarbons and nitrogen.At 308.1 K and 150 kPa,the solubilities of propane and methane in these DES are 0.308?0.516 mmol/g and 0.024?0.035 mmol/g,respectively,higher than the benchmark ILs.Furthermore,the selectivities of ethane/ethylene in Bor/iso-Ste?1:2??Men/Lau?2:1?and Men/iso-Ste are relatively high,reaching 2.0?1.6 and 1.6,respectively.Therefore,tributylethyl-phosphonium long-chain carboxylate ILs as well as DES containing iso-stearic acid and alicyclic alcohol are promising in the application of light hydrocarbon separations.The selectivities of propane/methane and propane/nitrogen are 14.4?21.0 and 30.9?90.8,respectively,being generally higher than ILs.In addition,the selectivity of ethane/ethylene can be up to 2.0.