Study On Liquid-liquid Equilibria And Process Simulation Of The Extraction System To Remove Phenols From Coal-gasification With MTBE

Coal-gasification wastewater is produced in the process of gas cooling, washing andpurification. The wastewater quality is very complex and it contains high concentration ofpolyhydric phenols which are extremely resistant to biological oxidation. Until now, inindustry, solvent extraction is usually used as a pre-treatment to recover phenols in wastewater.After the most of phenols is removed，the wastewater is subjected to the biological treatmentbefore the discharge.This work studys on coal-gasification wastewater which was produced by a coalgasification plant. Base on the characteristics of coal gasification wastewater, severalalternative solvents such as diisopropyl ether(DIPE), methyl isobutyl ketone(MIBK) andmethyl tert-butyl ether(MTBE) were selected. Considering the extraction performance, energyconsumption of solvent recovery and the cost, MTBE was selected as the solvent for theremoval of phenols from coal-gasification wastewater. Then, the extraction process conditionsuch as the temperature and the pH value were investigated, and the suitable temperature andpH value were determined: T=40-50℃, pH=8-9. Under these extraction process condition, thethree-stage countercurrent extraction was studied and the suitable phase ratio was R=1:3-1:4.In order to provide the fundamental data for the simulation and design of the Coalgasification wastewater extraction process, the liquid-liquid equilibria(LLE) data of theternary system MTBE-phenol-water, MTBE-hydroquinone-water and the quaternary systemMTBE-phenol-hydroquinone-water were determined. The NRTL and UNIQUAC modelswere applied to correlate the LLE data to obtain the binary interaction parameters of these twomodels. The root-mean-square-deviation(RMSD) was used to check the agreement ofcalculated data and the experimental data. The results shows that both models gave goodrepresentation of the tie-line data for the system.At last, the global simulation and calculation of the developed coal-gasificationwastewater extraction process was carried out. And the operation parameters of each unitwere designed and optimized. From the global simulation results, it could be seen that theprocess could successfully deal with the wastewater with a capacity of150t/hr. At40℃andunder atmosphere pressure and the operation conditions the work provided, the concentration of phenols in the coal-gasification could be reduced from12700mg/L to300mg/L. Theoperation parameters of the extraction process, the solvent recovery distillation process andthe solvent stripper process were obtained. The work is useful for the design andindustrialization of the phenols recovery from the coal-gasification by extraction.