On Absorptive Separation Of HCL And Trifluoromethane By Deep Eutectic Solvents

During the production of the refrigerant chlorodifluoromethane,trifluoromethane is discharged as a tail gas together with hydrogen chloride.Although water can efficiently trap hydrogen chloride,it generates a large amount of dilute hydrochloric acid with low product value,which poses a serious environmental problem.Deep eutectic solvents(DESs)not only have the characteristics of ionic liquids such as designable structure,non-volatility,and wide liquid range but also the advantages of low cost,simple preparation,and no pollution,which provide a new way to develop green solvents capable of separating and recovering hydrogen chloride.The specific research of this thesis is as follows:A series of polyol DESs were synthesized by a one-step method using tetramethylammonium chloride(TMAC)and tetraethylammonium chloride(TEAC)as hydrogen bond acceptors and 1,3-propanediol(1,3-PDO),glycerol(Gly)and 1,4-butanediol(BDO)as hydrogen bond donors.The solubility of trifluoromethane in DESs at 30～70℃and 100～600 k Pa was determined by the constant volume method,and the factors affecting the absorption of trifluoromethane by DESs were investigated in terms of temperature,pressure,and the ratio of hydrogen bond donor and hydrogen bond acceptor.Then the standard Gibbs free energy,enthalpy,and entropy for the dissolution of trifluoromethane in DESs were calculated by correlating experimental data with thermodynamic models.The solubility of hydrogen chloride in DESs was determined by weighing method,and the selectivity of hydrogen chloride-trifluoromethane was calculated.TMAC-Gly has a selectivity of up to 341 for hydrogen chloride with good recycling performance,which provides a new idea for the separation and recovery of hydrogen chloride in industry.Then the interaction mechanism between different DESs and hydrogen chloride was analyzed by combining FT-IR and ~1H NMR.Finally,the density of DESs was correlated using a perturbed-chain statistical association fluid theory model(PC-SAFT)to obtain their characteristic parameters.In this paper,the PR-Wilson and PC-SAFT equations of state were used to predict the phase equilibria of the DESs-trifluoromethane system.The results show that the PR-Wilson model can predict the phase equilibrium of the experimental system more accurately with an average relative deviation of 4.07%,which is a guideline for process calculations.