Synthesis Of Hydrophobic Ionic Liquids And Their Applications In Extraction Of Glycine

Glycine,also known as aminoacetic acid,is the amino acid with the simplest structure,and is widely used in food,medicine,pesticides and other fields.It is an important chemical raw material.Chloroacetic acid ammoniation is one of the main approaches to produce glycine.However,equal molar amount of ammonium chloride is formed as the byproduct during the chloroacetic acid ammoniation process,and it needs a lot of methanol to separate glycine from ammonium chloride,with a large amount of waste liquor and low separation efficiency.Ionic liquids,as a kind of "green" medium,are widely used in the fields of biomass separation and gas absorption because of their low volatility,good thermal stability,adjustable structure and properties.In this study,different kinds of functional ionic liquids were prepared and their structures and purities were characterized.These ionic liquids were used as the extractants to replace traditional solvents for glycine separation.A novel process for glycine separation was proposed,and the main work of this study includes:(1)In this work,imidazolium and ammonium ionic liquids were synthesized and characterized.Their abilities to extract glycine were compared,and it was found that choline bis(trifluoromethylsulfonyl)imide([N1112(OH)][NTf2]),with a hydroxyl group,gave the best extraction efficiency.The addition of dicyclohexyl-18-crown-6(DCH18C6)to the system could enhance the extraction efficiency,and that of the[Ni112(OH)][NTf2]-DCH18C6 system could reach 85.4%.The effects of pH,extraction temperature,time,and the initial concentrations of glycine and DCH18C6 on the partition coefficient and extraction efficiency were investigated.Under the optimal conditions,the partition coefficient and extraction efficiency could reach 10.9 and 94.4%,respectively.The IL system was recycled and reused for glycine separation,and the results showed that the extraction efficiency remained 90%after the IL was recycled for 5 times.(2)The effects of the interactions between pH of glycine solution,initial concentration of glycine and concentration of DCH18C6 on the extraction efficiency were investigated by response surface methodology(RSM).The influences of these parameters on the extraction efficiency decreased in the following order:pH of glycine solution>initial concentration of glycine>concentration of DCH18C6.The optimum conditions were 2 for pH value of the glycine solution,0.04 mol/L for the initial concentration of glycine,and 0.186 mol/L for concentration of DCH18C6,and the theoretical extraction efficiency was 97.88%.The glycine separation experiments were performed under the above predicted optimal conditions for four times.It was found that the average extraction efficiency was 98.04%,with the relative standard error of 0.56%,indicating that the model obtained in RSM can predict the extraction efficiency accurately.(3)The extraction mechanism was revealed by FTIR and quantum chemical calculation,and it was demonstrated that the strong hydrogen bonds between[N1112(OH)][NTf2],DCH18C6 and glycine play an important role in the extraction of glycine.(4)Since hydrogen bonding plays an important role in glycine extraction,the protic ionic liquid[Bmi][NTf2]was also synthesized.Its structure and purity were characterized by FTIR and NMR.The ability of this ionic liquid for glycine separation was evaluated.The partition coefficient of glycine in the[Bmi][NTf2]separation system was 10 times higher than the corresponding value of the aprotic ionic liquid[Bmim][NTf2],with the extraction efficiency of the protic system 4 times higher.