Studies On Liquid-liquid And Solid-liquid Equilibrium For Xylene Oxidation Systems

Terephthalic acid,isophthalic aicd and o-toluic acid are very important basic chemical raw materials.Commercially,they are manufactured by liquid-phase catalytic oxidation of xylene isomers,in which acetic acid is used as the solvent and air as oxidant;water is one of the main byproducts.In order to set the operating conditions for solvent recovery and separation of products,it is essential to measure the liquid-liquid equilibrium(LLE)and solid-liquid equilibrium(SLE)data for the these reaction systems.Therefore,the main aim of this paper is to measure LLE and SLE data for the aforementioned systems and to correlate the measured experimental data with different thermodynamic models for obtaining the model parameters.The main contents are as follows:1.The LLE data for three ternary systems water + acetic acid + p-xylene,water +acetic acid + m-xylene and water + acetic acid + o-xylene were measured by using the static analytical method.The reliability of the experimental tie-line data was checked by applying two empirical equations as well as verified by comparison with the literature data.Both the nonrandom two-liquid(NRTL)and universal quasichemical activity coefficient(UNIQUAC)models were adopted to correlate the measured LLE data,and the binary interaction parameters were obtained by data-fitting.The root-mean square deviation(RMSD)values as low as 0.97%and 1.10%were obtained for the two models,respectively.The reliability of model parameters were checked by performing thermodynamic stability tests,and the results indicate that the obtained NRTL and UNIQUAC parameters can accurately describe the LLE.Moreover,the LLE data for the ternary system water + acetic acid + o-xylene at 293.15 K were predicted by using the NRTL model parameters,and compared with literature data.The results indicate that the obtained NRTL model parameters are predictable and can be extrapolated to a wider temperature range.2.The SLE data of p-toluic acid,m-toluic acid,isophthalic aicd,o-toluic acid and phthalic acid in binary acetic acid + water and acetic acid + xylene isomers solvent mixtures were measured by using the synthetic method,respectively.Both the NRTL model and Apelblat model were adopted to correlate the SLE data in this paper,and the corresponding model parameters were also obtained by data-fitting.The results show that two models can correlate the SLE data of the aforementioned systems well.3.In view of the molecular structure characteristics of terephthalic acid,isophthalic aicd,phthalic acid,p-toluic acid,m-toluic acid and o-toluic acid,three new groups of UNIFAC(Dortmund)model,p-ACCOOH,m-ACCOOH and o-ACCOOH,were defined and their surface area(Qk),van der Waals volume(Rk)and binary interaction parameters were determined by regressing the solubilities of six solutes in acetic acid + water solvent mixtures.In order to verify the reliability of the determined new group parameters,the solubilities of 1,3,5-benzenetricarboxylic in acetic acid + water solvent mixtures were predicted by applying these new group parameters,and compared with literature data.The averaged relative deviation(ARD)is 8.09%,which shows the determined new group parameters are reliable.In this paper,the method of defined new groups can solve the problem that the original UNIFAC model cannot be used to predict the related properties of aromatic carboxylic acid isomers.