| There are solid residues in process of manufacturing terephthalic acid, including phthalic acid, isophthalic acid, benzoic acid, p-toluic acid and terephthalic acid itself. Solvent dissolving, crystallizing and separating is an effective way to separate mixed solids, and exact and intact solubility data are needed in this method. In this paper, it was discussed whether ethanol is one proper crystallizing solvent for the first time, and solubilities of these substances in aqueous acetic acid and ethanol were determined systemically.In order to choose the suitable solvents to separate and recycle these useful chemicals by crystallization operation, with terephthalic acid, phthalic acid, isophthalic acid, benzoic acid and p-toluic acid as solutes, acetic acid, 75%wt aqueous acetic acid, ethanol, 95%wt ethanol and 75%wt aqueous ethanol as solvents, the solid-liquid equilibrium were determined by laser-scattering synthetic method over the temperature range from 17.77℃to 80.10℃at 1 atm; meanwhile the solubilities of the above-mentioned substances in acetic acid and ethanol were determined over the temperature range from 90.8℃to 160.8℃at high pressure.Solubilities of the substances in different solutes are descended in the order of benzoic acid, p-toluic acid, phthalic acid, isophthalic acid and terephthalic acid largely. With acetic acid and aqueous acetic acid as solutes, the solubilities(mole fraction) are in the magnitude of 10-1,10-2,10-3,10-4 and 10-5; with ethanol and aqueous ethanol as solutes, the solubilities are in the magnitude of 10-1,10-2,10-3 and 10-4; at high pressure there are not saltant augmentations of the solubilities data. According to the experimental data, first at low temperature, ethanol is chosen to apart the residues into benzoic acid, terephthalic acid, and the leavings of phthalic acid , isophthalic acid and p-toluic acid; then, isophthalic acid is detached from phthalic acid and p-toluic acid by 75%wt aqueous ethanol; at last, 75%wt aqueous acetic acid is chosen to separate phthalic acid and p-toluic acid.Meanwhile, solubility data of determined systems were correlated by the experiential equation, the abbreviated three parameters equation, Wilson equation andλh equation. The average relative error of the correlations of the determined systems by every equation mentioned is under 8%, and the correlation is satisfactory. As the average error of the prediction of SLE of ternary systems by Wilson equation is 7.62%, Wilson equation is fit for the aqueous ethanol and aqueous acetic acid systems and can be used to predict the SLE of mixed solvents.
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