Experimental Study And Process Simulation Of Solvent Extraction And Phenols Removal From Coal Chemical Industry Wastewater With Methyl Butyl Ketone

The inferior coal gasification process is usually carried out in the temperature range of 400-1000℃. This process produces a large mount of wastewater which contains high concentration of phenols. At present, solvent extraction is usually used as a pre-treatment to recover phenols in industry wastewater. After most phenols are removed,the wastewater is subjected to a biological treatment process and then discharged. Thus, solvent extraction is a key process to recover phenols.In this work, the solvent extraction process was studied. Based on the properties of coal chemical industry wastewater, Methyl butyl ketone(MBK) was chosen as an extraction solvent and its performance on recovering phenols was evaluated. The experimental results show that, MBK is an excellent extractant with high extraction efficiency for both volatile phenols and non-volatile phenols. Futhermore, the effect of extraction process conditions such as temperature and p H value was investigated. Taking the properties of actual industrial coal gasification wastewater into consideration, the optimal temperature and p H value were found to be: T=40-50 ℃, p H=7-8. Under these extraction process conditions, a three-stage countercurrent extraction was studied and the suitable phase ratio was R=1:4-1:5.Liquid-liquid equilibria(LLE) data are the basis for simulating and designing extraction process. In this work, LLE data for ternary systems MBK–phenol/(o-, m-, p-)cresol/hydroquinone–water and a quaternary system MBK-phenol-hydroquinone-water were determined. The experimental data were correlated with the UNIQUAC and NRTL activity coefficient models, and the corresponding binary interaction parameters were calculated. Both models yield results in good agreement with experiment for the studied systems.Based on binary interaction parameters calculated from UNIQUAC model in the above LLE study, the chemical process simulation technology was used to simulate the corresponding extraction process. The operation parameters for phenol extraction, solvent recovery, and solvent stripping process were optimized. The simulation results showed that, at 313.2K and atmospheric pressure, when R=1:7.77(mass ratio), the four-stage countercurrent extraction process reduced total phenols in the coal-gasification wastewater from 12700 mg·L-1 to 300 mg·L-1. The utility calculation results showed that, when MBK instesd of MIBK was used as the extractant to treat 100 t·hr-1 wastewater, 93 t·hr-1 of cooling water, 682 kg·hr-1 of medium-pressure steam and 309 kg·hr-1 of low-pressure steam would be saved. These simulation results can provide reference for the industrialization of removing phenols from wastewater by MBK.