Recently, tert-butyl alcohol (TBA) has emerged as a commercially competent reagent for biofuel production, but forms a minimum boiling azeotrope with water which restricts its applicability. This paper presents a comprehensive methodology for the dehydration of TBA by extractive distillation (ED). In entrainer selection, glycolic and ionic liquids were investigated followed by VLE measurements and thermodynamic modeling. On the basis of evaluated results, pseudobinary, isovolatility and equivolatility curves have been explored to rank accurately the selected entrainers. Triethylene glycol (TEG) and 1-ethyl-3-methylimidazolium chloride [emim][Cl] emerged as the most appropriate entrainer. Finally, the process design and optimization was carried out with the minimization of total annualized cost (TAC) as the objective function. The process economics demonstrated a notable reduction of 13.9% in the TAC for [emim][Cl] as compared to TEG as an entrainer for obtaining anhydrous TBA, thereby justifying the use of ionic liquids as the new generation entrainers.

The solid−liquid phase equilibrium of para-tertbutylbenzoic acid in methanol, ethanol acetic acid, propan-2-ol, hexane, toluene, 1-octanol, para-tert-butyltoluene, methyl 4-tert-butylbenzoate, and binary (methanol + methyl 4-tertbutylbenzoate) mixed solvent have been determined experimentally within the temperature range of 293.15−333.15 K at atmospheric pressure using a static equilibrium method. The solubility of para-tert-butylbenzoic acid increased with the increase in temperature for the pure solvents, while in the case of methanol + methyl 4-tert-butylbenzoate a maximum solubility effect is achieved at 0.6115 solute-free mole fraction of methanol. The experimental solubility data in pure and binary solvent system were correlated by the modified Apelbat equation, the λh (Buchowski) equation, and the NRTL model, among which the modified Apelbat equation provided better agreement than those with the other models. Furthermore, to understand the nature of interactions involved in a solute−solvent system, the dissolution thermodynamic properties, including enthalpy, entropy, and Gibbs free energy, were determined. This experimental data will be an aid for the design and optimization of the separation and purification processes involving para-tert-butylbenzoic acid.

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Isobaric vapor−liquid equilibrium for the binary system of tert-butyl alcohol (TBA) + glycerol were obtained at local atmospheric pressure of 95.9 kPa and subatmospheric pressures of 66.6 and 79.9 kPa over the entire composition range using a modified Othmer-type ebulliometer. Wilson and NRTL models were used for correlating the experimental data. The results suggest that the NRTL model represented the experimental data better with lower RMSD and AAD values. Furthermore, at local atmospheric pressure of 95.9 kPa, the densities and refractive indices for the three binary systems TBA + glycerol, TBA + water, and water + glycerol involved in the dehydration of TBA by extractive distillation were measured over the entire composition range from 303.15 to 333.15 K. The volumetric properties in terms of excess molar volume, partial molar volume, and isobaric thermal expansivities as well as molar refractivity were evaluated and analyzed for the three different binary systems. A Redlich−Kister polynomial was used to the fit the excess molar volume and deviations in molar refractivity. Different empirical mixing relations were also investigated for predicting the refractive indices of the three binary mixtures and are reported in terms of their average percentage deviation.

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