Phase behavior and solid–liquid equilibria of aliphatic and aromatic carboxylic acid mixtures

• Apparatus for the solid–liquid equilibrium (SLE) was developed.
• SLEs for binary systems of aliphatic and aromatic carboxylic acids were measured.
• Peritectic and eutectic points were observed in phase diagram.
• Experimental results were correlated successfully within thermodynamic framework.
• Thermodynamic approach of Slaughter and Doherty was applied to represent SLE.

We newly developed an apparatus for the solid–liquid equilibrium measurements to examine the phase equilibria of carboxylic acid mixtures. The equilibrium freezing temperatures obtained from the cooling curve of the liquid state to solid were measured for the stearic acid + benzoic acid, adipic acid + benzoic acid, and p-toluic acid + benzoic acid systems. The experimental results were correlated successfully by Wilson, NRTL, and UNIQUAC models Moreover thermodynamic approach of Slaughter and Doherty was applied to represent the solid–liquid equilibria of peritectic and eutectic compound exists in the solid phase due to the reaction of complex formation. Good agreement between the experimental and calculated values for the binary carboxylic acid mixtures was obtained.