Isobaric Vapor-Liquid Equilibrium of Methyl Salicylate + Ethyl Salicylate and Methyl Salicylate + α-Pinene Binary Systems at 20.0 and 50.0 kPa

Gandapura oil, also called wintergreen oil in international trade, is evaluated based on the purity of its methyl salicylate content. Gandapura oil has several impurities including mainly ethyl salicylate and α-pinene, which can lower its quality and price. Indonesian local farmer's gandapura oil has a low methyl salicylate content of only 82.23%, and appears in a dark red colour instead of clear. The low grade product may have been caused by thermal degradation of compounds within gandapura oil by constant heating during atmospheric distillation at temperature above its thermal threshold. The determination of their vapor-liquid equilibrium data can provide basic data for the separation and purification of methyl salicylate towards its two main impurities in gandapura oil. The vacuum pressure condition was selected to lower the distillation temperature, aiming to reduce the chance of thermal decomposition. The vapor-liquid equilibrium under isobaric conditions in the binary systems of methyl salicylate + ethyl salicylate and methyl salicylate + α-Pinene at 20.0 and 50.0 kPa were measured experimentally using modified Glass Othmer-Still. Gas Chromatography (GC) was utilized to analyze the composition of both the liquid and vapor phases in the samples. The thermodynamic consistency of experimental data was confirmed through the L-W Wisniak method. The experimental results were successfully correlated with Wilson, NRTL, and UNIQUAC models. The average absolute deviations of temperature (AAD T) and vapor phase composition (AAD y) between experimental data and models are less than 0.8058 and 0.0196, respectively for all systems. In terms of quality, all samples collected post-experiment maintained a clear color, suggesting that vacuum pressure distillation effectively prevents the thermal decomposition of compounds in gandapura oil.