Study On Liquid-liquid Equilibrium Of Synergistic Extraction For Diphenols And The Treatment Of Coal-gasification Wastewater

One of the reasons that restrict the development of coal-to-natural gas project is that coal gasification wastewater is difficult to treat.The high concentration of diphenols in the effluent of phenol-ammonia recovery section in the existing wastewater treatment process will easily lead to the collapse of the biochemical system.In this paper,the qualitative of coal gasification wastewater in a Xinjiang project was analyzed.The total COD was 80000 mg/L,which contained various types phenols,total phenols was as high as 16000 mg/L and polyphenols was 10000 mg/L.It is difficult to treat using the existing extractant MIBK.Aiming at this kind wastewater,through the screening of extractants and mixed extraction experiments,it is found that alcohols + ketones have synergistic extraction effect.An efficient diphenol removal mixed extractant 2-pentanone + n-pentanol has been developed.The best results were obtained when the volume fraction of 2-pentanone is 80%.The distribution coefficient for hydroquinone increases to 22,which is twice as much the MIBK usually used in industry.The effects of pH,phase ratio and extraction stages on the extraction efficiency of actual wastewater were studied.The suitable extraction conditions were determined as follows: pH=7,phase ratio 1:4,extraction stage 3.The total phenols in wastewater were reduced to 320 mg/L after three-stage cross-flow extraction,and the removal rate was as high as 97%.On this basis,the liquid-liquid equilibrium data of 2-pentanone + diphenol + water and n-pentanol + 2-pentanone + hydroquinone + water were determined.The experimental data were correlated by NRTL and UNIQUAC activity coefficient model.The relative root mean square error(RMSD)of the experimental and calculated values were within 2%.The binary interaction parameters were obtained by regression.The data of liquid-liquid equilibrium were reliable and effective according to the checking results.The process simulation software was used to study the recovery process of mixed extraction,and the effect of replacing MIBK with mixed extractant on the operation parameters of stripper and phenol tower in the existing process.Under the condition of guaranteeing the operation requirements,the parameters such as distillate rate and reflux ratio were optimized.Comparing with MIBK,although the total energy consumption of mixed extractant recovery is somewhat higher,it is still of great significance for the treatment of wastewater with high diphenol concentration.