Study On Separation Of Benzene Carboxylic Acid Mixtures Via Forming Deep Eutectic Solvents And The Mechanism Of Separation

Benzene carboxylic acids(BCAs,including 12 different structures)serve as important chemical raw materials.However,BCA mixtures are always obtained in the processes of production.It is difficult to separate these products because they have similiar properties.At present,deep eutectic solvents(DESs)are very hot on account of their advantages of low vapour pressure,recyclability,good biodegradability and null toxicity.Deep eutectic solvents are now used in many fields such as chemical reaction,electrochemistry and extraction separation,and so on.Our research group’s previous study shows that quantanary ammonium salts(QASs)can be used to separate benzene carboxylic acids in butanone via forming DESs.However,the solubility of benezene carboxylic acids in butanone is much low,which limits the application of the DES method.In this work,we has found that the solubility of benezene carboxylic acids in acetone is much higher than that in butanone,and importantly,DES does not dissolve in acetone.As well as QASs,inner salts and other hydrgen bond acceptors could form DESs with benezene carboxylic acids.Therefore,we used those HBAs to separate mixtures of PMA and TMA and mixtures of isomers of benzene tricarboxylic acids.In order to reveal the separation mechanism,the method of DFT/B3LYP was used to calculate dipole moment,molecular electrostatic potential,frontier molecular orbitals of these BCAs and HBAs,as well as hydrogen bond energies of DESs.The main results were shown as follows.(1)The dipole moment of PMA is greater than TMA and the hydrogen bond energy between PMA and hydrogen bond acceptor(HBA),including Choline Chloride(ChCl),L-camitine(L-car)and Hexamethylenetetramine(HA)is greater than the hydrogen bond energy between TMA and hydrogen bond acceptor(HBA).Therefore,in the experiment the extraction order is PMA and TMA.(2)The calculation results show that the hydrogen bond energy between ChCl and TMA is smaller than the interaction energy between acetone and TMA.For the separation of mixtures of PMA and TMA,ChCl can not form DES with TMA in acetone and can form with PMA,which results in the high separartion efficiency.(3)TEAC can separate the mixtures of isomers of benzene tricarboxylic acids.The calculation results show that the dipole moment of isomers acid in the following order,hemimelitic acid>trimesic acid>trimellitic acid and the hydrogen bond energy ofHemimellitic acid with TEAC is the largest and that of TMA with TEAC is the smallest.Therefore,in the experiment the extraction order isHemimellitic acid,trimesic acid and TMA,which results in the separartion isomers of benzene tricarboxylic acids;...