Phase Equilibrium Study Of Aromatic Carboxylic Acid Compounds In Common Organic Solvents

Aromatic carboxylic acids are essential basic chemical products in industry,and also important components of organic acids.They are widely used in food,medicine,clothing and other aspects of life.The common aromatic carboxylic acids are benzoic acid,aromatic dicarboxylic acid isomers,methyl benzoic acid isomers,nitromethyl benzoic acid isomer,trimesic acid,etc.In the industrial production of aromatic carboxylic acid,in order to get high purity aromatic carboxylic acid compounds,it is necessary to purify and separate the reaction products.The solvent crystallization method has the characteristics of simple and efficient,mild operating conditions and environment-friendly,so it has become a common separation method in industry.In this paper,some common solvents are selected as possible crystallization solvents,and the solubility data of aromatic carboxylic acids in these common organic solvents become the key basis for the selection of crystallization solvents.In this paper,the solid-liquid equilibrium data of several representative aromatic carboxylic acids in common organic solvents are determined to provide theoretical data for the design of separation process and solvent recovery,and the data are correlated by thermodyn amic model.The main contents of this paper are as follows:1.The solubility of some aromatic carboxylic acids in common organic solvents was measured by synthetic method:(1)Solubility of benzoic acid in ethylene glycol,diethylene glycol butyl ether,n-octane,diethylene glycol,N,N-Dimethylacetamide,p-xylene,m-xylene,o-xylene,propionic acid,cyclohexanone,decalin and sulfolane;(2)Solubility of terephthalic acid in N-Methylformamide,N-Methylformanilide and isooctanol;(3)Solubility of isophthalic acid in methanol,n-propanol,isopropanol,n-butanol,n-octanol,isooctanol,diethylene glycol,propionic acid,N-Methylformamide,N-Methylformanilide,N,N-Dimethylacetamide,dimethyl sulfoxide and sulfolane;(4)Solubility of phthalic acid in n-propanol,isooctanol,N-Methylformamide,N-Methylformanilide,N,N-dimethylformamide,N,N-Dimethylacetamide,dimethyl sulfoxide,N-Methylpyrrolidone and acetonitrile was studied;(5)Solubility of p-toluic acid in n-propanol,isooctanol,N-methylformamide,N-Methylformanilide,tetrahydrofuran,dimethyl sulfoxide and cyclohexanone;(6)Solubility of m-toluic acid in methanol,ethanol,n-propanol,isopropanol,n-butanol,isooctanol,diethylene glycol,propionic acid,N-Methylformamide,N-Methylformamide,N,N-Dimethylacetamide,dimethyl sulfoxide,acetone,cyclohexanone,N-Methylpyrrolidone,sulfolane,acetonitrile and tetrahydrofuran;(7)Solubility of o-toluic acid in ethanol,n-propanol,n-butanol,isooctanol,propionic acid,N-Methylformamide,N-Methylformanilide,N,N-Dimethylformamide,N,N-Dimethylacetamide,dimethyl sulfoxide,cyclohexanone,N-Methylpyrrolidone and tetrahydrofuran;(8)Solubility of 3-methyl-2-nitrobenzoic acid,3-Methyl-4-nitrobenzoic acid and 3-methyl-6-nitrobenzoic acid in n-butanol,isobutanol,tert butanol and sec butanol;(9)Solubility of trimesic acid in N,N-dimethylformamide,N,N-Dimethylacetamide,N-Methylformamide,N-ethylformanili-de,n-propanol,n-butanol,sec butanol,t-butanol,n-pentanol,t-pentanol,iso octanol and n-octanol;2.The thrmodynamic functions of aromatic carboxylic acids in different solvents were calculated by van der Hoff equation,and the dis solution behavior of each system was expressed by enthalpy,entropy and Gibbs free energy.The positive values of₇)and₇)indicate that the dissolution process is endothermic and not spontaneous;In different solvents,?%is greater than?%,which indicate that the enthalpy mainly contributes to the Gibbs free energy of benzoic acid;In most systems,the standard molar entropy of the dissolution process is positive,which indicates that entropy is the driving force for the dissolution of each system.In addition,the solubility of aromatic carboxylic acids in solvents is inversely proportional to the Gibbs free energy;3.Use?h,Apelblat and NRTL thermodynamic models were used to correlate the solubility data of aromatic carboxylic acids in different solvents,and the corresponding average relative deviation(ARD)was calculated as,The Akaike information criterion(AIC)was applied to select the most suitable correlation model for the solubility of aromatic carboxylic acids in each solvent;4.UNIFAC(Dortmund)model groups p-ACCOOH,m-ACCOOH and o-ACCOOH were used to correlate the solubility of methyl benzoic acid in various solvents,and the binary interaction parameters between these three groups and the solvent groups were obtained.The results of UNIFAC(Dortmund)model were compared with the experimental data,and the average relative deviation was 2.84%.The results show that this model is suitable for the dissolution of methyl benzoic acid isomers in different solvents,and that these three groups can effectively predict the thermodynamic properties of aromatic carboxylic acid isomers.