Simulation and dynamic control of removal phenols from coal gasification wastewater by synergistic extraction

Coal chemical wastewater has a high organic content and poor biochemical performance. The phenolic substances in wastewater cannot meet the discharge standard, which damages the environment and endangers human health. In this study, to remove phenolic substances from coal chemical wastewater, a process of dephenol treatment was studied, which integrated the selection of extractant, process simulation, and dynamic control. In view of the low removal rate of polyphenols, a new extraction solvent was designed to reduce the polyphenol content. The four synergistic extraction solvents of Mesityl oxide + n-pentanol, MPK + n-pentanol, MIPK + n-pentanol, and MIBK + n-pentanol were optimized and calculated by molecular simulation, and electrostatic potential analysis, NBO analysis, interaction energy analysis, and non-covalent interaction analysis were used to elucidate the nature of the synergy between molecules. The results show that the interaction energy of mesityl oxide + n-pentanol + phenol and mesityl oxide + n-pentanol + catechol is higher than other solvents, which are -46.13 kJ mol(-1) and -40.36 kJ mol(-1), respectively. The difference of the interaction energy of mesityl oxide + n-pentanol + phenol and mesityl oxide + n-pentanol + water is -14.30 kJ mol(-1) and that of mesityl oxide + n-pentanol + catechol and mesityl oxide + n-pentanol + water is-8.53 kJ mol(-1), which shows the superiority of mesityl oxide + n-pentanol for the extraction and recovery of phenols. The results showed that the extraction performance of the synergistic extractants is stronger than that of the single extractants. Aspen Plus software was used to simulate the extraction and recovery of phenols with mesityl oxide + n-pentanol as the extractant, and the operation parameters were optimized with the smallest total annual cost as the target. The amount of fresh extractant added is only 0.95 kg/h, and the removal rate of phenol and catechol reached 99.95% and 97.97%, respectively, and the total phenol concentration dropped from 6499 mg/L to 56 mg/L. In addition, the little difference between experimental data and simulation results also indicates that mesityl oxide + npentanol is an effective extraction solvent. Finally, Aspen dynamic simulation investigated the dynamic response results under disturbances in the feed flow rate and feed component, and the results showed that the process operation under disturbances can quickly restore a stable value. The control scheme is effective.