Construction and Application of a Ternary Solid–Liquid Phase Diagram of 3‑Methyl-4-nitrobenzoic Acid and 3‑Methyl-2-nitrobenzoic Acid in Methanol and Acetone

A ternary system solid–liquid equilibrium phase diagram is very useful to design industrial separation and purification operation. The ternary phase equilibrium for 3-methyl-4-nitrobenzoic acid (4,3-NMBA) and 3-methyl-2-nitrobenzoic acid (2,3-NMBA) in methanol and acetone at 298.15, 308.15, and 318.15 K was studied under atmospheric pressure in this work. In each ternary phase diagram, the saturated liquids divided the phase diagram into four regions, including three crystallization regions (pure 4,3-NMBA, 2,3-NMBA, and a mixture of 4,3-NMBA and 2,3-NMBA) and an unsaturated region. The crystallization region of 4,3-NMBA was larger than that of 2,3-NMBA in methanol and acetone at all evaluated temperatures. Moreover, the NRTL model was used to correlate the phase equilibrium data, and the interaction parameters of solute–solute were obtained. These parameters are of great importance to control the separation and purification process of 4,3-NMBA and 2,3-NMBA. To demonstrate the implementation of diagram application in industrial separation and purification, ternary equilibrium phase was analyzed and discussed.