Optimization of solvent cooling crystallization process for separating phenanthrene from 9-fluorenone by COSMO-RS and solubility calculation approach

Phenanthrene (Phe) and fluorene (Flu) are crucial chemical intermediates with applications in materials, medicine, and pesticides. However, conventional separation methods struggle to effectively isolate phenanthrene from fluorene due to their similar physical properties. To address this challenge, a reaction–separation coupling technique was employed to convert fluorene into 9-fluorenone (9-Fluo), followed by the separation of phenanthrene from 9-fluorenone using solvent-cooling crystallization. Initially, the relative solubilities of phenanthrene and 9-fluorenone in 2072 solvents were calculated using COSMO-RS for preliminary screening. Among various conventional short-chain aliphatic alcohols and low-carbon saturated hydrocarbons, methanol, and cyclohexane were identified as the most effective solvents based on their solubility selectivity (SS). The molecular interactions between phenanthrene or 9-fluorenone and these solvents were analyzed using theoretical methods such as σ-potential/profile, infinite dilution activity coefficients in COSMO-RS, and Hansen solubility parameters, with further confirmation from FTIR tests. The optimal liquid–solid ratios were determined using both phase diagram measurements and solubility calculations. The reaction conversion of fluorene to 9-fluorenone was complete regardless of the raw material used. Phenanthrene and 9-fluorenone were effectively separated using methanol and cyclohexane with optimum liquid–solid mass ratios of 1.6:1 and 2.8:1, respectively. In the model mixture, the contents of phenanthrene and 9-fluorenone exceeded 98 wt%, with yields above 91 wt%. For anthracene residue, the content of 9-fluorenone reached 93.98 wt% with a yield of 84.52 wt%, while its content was only 76.58 wt% due to the accumulation of other components in phenanthrene. © 2024 Elsevier B.V.