| Coal is the principal energy in China based on the fossil energy structure of China.A large amount of wastewater is produced during the processing and utilization processes of the coal,and with high concentration of poisonous phenols,such wastewater causes a great threat to the environment and human health.Solvent extraction is a common method for the removal and recovery of the phenols from highly concentrated phenol-containing coal-chemical industry wastewater.The methyl iso-or n-propyl ketone were adopted as the extraction solvents to extract and recover phenols from the wastewater,by which the concentration of phenols in the wastewater could be reduced to a very low level to meet the concentration requirement of phenols in further biochemical treatment process of the wastewater.Phenol,cresol isomers,benzenediol isomers are common phenolic pollutants in highly concentrated phenol-containing coal-chemical industry wastewater.The liquid-liquid phase equilibrium data for ternary systems methyl iso-or n-propyl ketone + one of seven kinds of phenols(phenol,o-,m-or p-cresol,1,2-benzenediol,1,3-benzenediol or 1,4-benzenediol)+ water were determinted and then correlated by the UNIQUAC and NRTL models.The deviations between the predicted liquid-liquid equilibrium data and the experimental liquid-liquid equilibrium data were very small(almost lower than 0.5 percent).The distribution coefficients(D)of the seven kinds of phenols and selectivities(S)were calculated to make a comparison of the difficulty levels to be extracted with methyl iso-or n-propyl ketone of the seven phenols.The distribution coefficients(D)and selectivities(S)indicated that it was more difficult to extract phenol than other volatile phenols including o-,m-and p-cresol,while it was more difficult to extract 1,4-benzenediol than other non-volatile phenols including 1,2-benzenediol and 1,3-benzenediol.Phenol and 1,4-benzenediol were chosen as the representatives of volatile phenols and non-volatile phenols,respectively,in highly concentrated phenol-containing coal-chemical industry wastewater.And the liquid-liquid equilibrium data for the quaternary systems methyl iso-or n-propyl ketone + phenol + 1,4-benzenediol + water were determinted and then correlated by the UNIQUAC and NRTL models.The deviations between the correlated liquid-liquid equilibrium data and the experimental liquid-liquid equilibrium data were very small(even lower than 0.5 percent).The binary interaction parameters obtained in the data correlation by the UNIQUAC and NRTL models were essential for the process simulation of the phenols extraction from highly concentrated phenol-containing coal-chemical industry wastewater.The process simulation of extraction of highly concentrated phenols from coal chemical industry wastewater with methyl iso-or n-propyl ketone was carried out based on the determination and correlation of the liquid-liquid equilibrium data of the related quaternary systems.The process simulation results showed that,with stages of 5 and phase ratio of 1:7.52(methyl iso-propyl ketone)or 1:7.00(methyl n-propyl ketone),the concentration of total phenols in the highly concentrated phenol-containing coal-chemical industry wastewater could be reduced from 12700 mg·L-1 to 300 mg·L-1 by solvent extraction at the temperature of 40 ?.After the extraction process,the wastewater was suitable for further biochemical treatment.In addition,by the subsequent distillation and stripping processes,the majority of extraction solvent could be recovered and reused for the extraction process,with a fresh solvent addition of only 0.049 percent(methyl iso-propyl ketone)or 0.046 percent(methyl n-propyl ketone)out of the total solvent usage.According to the utilities cost estimation results,the utility cost was 15.65 yuan or 16.48 yuan for treating per ton highly concentrated phenol-containing coal-chemical industry wastewater with methyl iso-propyl ketone or methyl n-propyl ketone,respectively. |
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