Biobased Solvents as Entrainers for Extractive Distillation in Isobutyl Acetate–Isobutanol Separation: Experimental Investigation, Toxicity Evaluation, and Mechanism Analysis

In the industrial synthesis of isobutyl acetate (IbAC) from isobutyl alcohol (IbOH) and acetic acid, excess IbOH forms an azeotrope with IbAC. Extractive distillation is widely used for azeotrope separation, yet conventional solvents are often toxic and volatile. Biobased solvents, being biodegradable and ecofriendly, offer a promising alternative. Screening with the conductor-like screening model for segment activity coefficient identified cinene and α-pinene as effective entrainers to break the IbOH–IbAC azeotrope. Ternary vapor–liquid equilibrium experiments confirmed that both solvents, when added at 20 mol %, eliminated the azeotrope. The nonrandom two-liquid model accurately correlated the experimental data. However, α-pinene formed a new azeotrope with IbOH at an atmospheric pressure. Toxicity assessment showed cinene has lower mammalian toxicity but higher aquatic toxicity than those of conventional solvents. Quantum chemical calculations revealed that stronger van der Waals interactions between cinene and IbAC reduce the activity coefficient of IbAC, facilitating separation.