Research And Application On Liquid-Liquid Equilibrium For The N-Butyl Acetate-Phenol-Pyrocatechol-Water System

The coal-gasification wastewater contains high concentration pollutants,such as phenols,ammonia and hydrogen sulfide,etc.Among these compounds the phenols are considered to be the main poison.So the extraction of phenols wastewater is the key step for the treatment of coal-gasification wastewater.At present,the solvents which have already been applied to industrial plant have a few disadvantages,such as the high price and the high energy consumption.Thus,n-butyl acetate is chosen as the solvent in our work for its low price and good quality to extract phenols.The working condition of n-butyl acetate was confirmed and optimized.Further more,the LLE data of systems containing n-butyl acetate,water and phenols was measured,and the binary parameters was used in the process simulation of dephenolization.All these work can be a guide for industrial application.To obtain a suitable experimental condition for the extraction of phenols,the influence of temperature and pH on the extraction effective of n-butyl acetate was studied.The relationship of the extraction effective of three-stage cross-current extraction and the energy consumption of n-butyl acetate recovery with the phase ratio was analyzed.The results show that the suitable experimental condition was T=303.15-313.15 K,pH<8.0,and the phase ratio was 1:11-1:10.To obtain credible data for the scientific simulation of pyrocatechol separation from water,the LLE data for the system of n-butyl acetate + pyrocatechol + water and n-butyl acetate + phenol + pyrocatechol + water under atmospheric pressure were measured.The NRTL and UNIQUAC activity coefficient models were employed to correlate the experimental data and the values of the interaction parameters were obtained.The root-mean-square deviation(RMSD)provides a way to check the accordance between the calculated data from NRTL and UNIQUAC models and the experimental data.The values of RMSD indicate that both models correlated the experimental tie-line data successfully,while the correlation of the UNIQUAC model was inferior to that of the NRTL model.At last,the triple-stage cross flow extraction were simulated by Aspen Plus,and the simulation results were consistent with the experimental data.The simulation process of the extraction phenols from coal-gasification wastewater by n-butyl acetatewas set up.The operation parameters of phenols extraction,solvent recovery,and solvent stripping unit were designed and optimized by using the correlated activity coefficient model.The results of simulation show that at 308.15 K and atmospheric pressure,the phase ratio was 1:13.3(mass ratio),the concentration of total phenols in wastewater was reduced from 7866 mg/L to 300 mg/L after the extraction by n-butyl acetate.The results of simulation can provide reference for the industrialized application of n-butyl acetate in the process of removal phenols from coal-gasification wastewater.