Imidazolium-based Ionic Liquids In The Liquid-liquid Extraction Of DMAC From Aqueous Solution

In the pharmaceutical industry,N,N-dimethylacetamide(DMAC)is often used as a solvent in the synthesis of cephalosporins,such as cephalexin,cefoperazone,cefuroxime and cefaclor,etc.There will be a high content of DMAC in pharmaceutical wastewater.If discharged directly,it will not only cause a certain degree of harm to the human body and the environment,but also cause a great waste of resources.Therefore,it is critical to find a suitable process to treat the wastewater properly.Experience shows that solvent extraction can perfectly achieve the purpose of processing wastewater and recycling resources.Moreover,the extraction process can also extract and reuse DMAC from wastewater with low consumption and high efficiency,which can greatly reduce costs of production.The aim of this paper is to find green and efficient ionic liquids as extractants to extract DMAC from its aqueous solution.According to the selection principle of extractant and purpose of extraction,the ionic liquids selected in this experiment must have the properties of hydrophobicity,moderate viscosity and complete miscibility with DMAC.What's more,from the literatures we know that the hydrophobicity of ionic liquids depends on the properties of their anions.Further studies have shown that the three imidazolium-based ionic liquids,1-butyl-3-methylimidazolium hexafluorophosphate,[BMIM][PF₆],1-hexyl-3-methylimidazolium hexafluorophosphate,[HMIM][PF₆],and1-octyl-3-methylimidazolium hexafluorophosphate,[OMIM][PF₆],were selected as extractants in the experiment,which because they are hydrophobic,moderately viscous and completely miscible with DMAC.First of all,the COnductor-like Screen MOdel for Segment Activity Coefficient(COSMO-SAC)model was used to predict the extraction efficiency of three imidazolium-based ionic liquids,and the results showed that the experimental scheme was feasible.Secondly,the liquid-liquid equilibria data of three ternary systems,namely,DMAC+water+[Bmim][PF6],DMAC+water+[Hmim][PF6],and DMAC+water+[Omim][PF6],were studied at 25 ^oC and 35 ^oC,respectively.The results show that the change of temperature has little effect on the phase behavior of each ternary system,while the alkyl chain length of cations in ionic liquids plays a positive role in extraction performance.The longer the chain length,the higher the extraction efficiency.And then,the non-random two liquid(NRTL)model was used to correlate the liquid-liquid equilibria data of each system.Finally,the consistency of the tie-lines and the binary subsystems were checked by the Gibbs tangent plane stability test in order to verify the reliability of experimental data and binary interaction parameters.Moreover,the results show that the phase equilibrium achieved in the experiment is indeed steady-state equilibrium,and the phase behavior of the systems reproduced by the binary interaction parameters is completely consistent with the actual one,so the reliability of the experimental data and the model parameters are very high.