Purification of Indole Contained in Wash Oil by Combination of Extraction and Crystallization (Part 2: Highly Efficient Purification of Indole in Indole-Concentrated Oil via Solute Crystallization)

To develop a novel process to purify indole in wash oil with high efficiency, a previous study investigated the indole concentration in wash oil using a process combining methanol extraction and n-hexane re-extraction, which allowed the recovery of a raffinate phase containing 73.3 wt% indole-concentrated oil (ICO). In this study, model ICO, prepared based on the components and compositions present in ICO, and n-hexane were used as the raw material and solvent for the solute crystallization (SC) process, respectively, to examine the effect of SC experimental factors and conditions on the purification of indole. A Pyrex batch crystallizer with a jacket was used as the experimental apparatus. The purity and yield of indole in the generated crystals under optimal SC conditions (crystal washing, a crystallization temperature of 283 K, a crystallization time of 10 min, an impeller speed of 0 s⁻¹, and an initial volume ratio of the solvent to model ICO of 15.5) were 99.5 wt% and 57.5%, respectively. Furthermore, this study proposed a novel process for the highly efficient purification of indole contained in wash oil by utilizing the experimental data accumulated from processes in previous research and this study.