Development Of Synergistic Extraction Process From Solvent Design To Process Synthesis For Highly Efficient Removal Of Dihydric Phenols From Coal Gasification Wastewater

The shortage of water resource has become a bottleneck for the sustainable development of coal chemical industry.The realization of zero liquid discharge(ZLD)of coal chemical wastewater is mandatory.It is of great significance to achieve the sustainable management of the water resource.At present,a large number of ZLD technologies had been developed and implemented into the industry.However,there was no set of processes that can truly achieve ZLD of coal chemical wastewater.Industrial application showed that dihydric phenols especially hydroquinone is a key problem for coal chemical wastewater treatment.It is of great significance for achieving ZLD to control the concentration of total phenols to less than 300 mg/L.Due to the limitation of the existing solvents,the phenols recovery process cannot control phenols concentration to less than 300?mg/L,with about 350-800 mg/L.In order to solve the problems of low extraction distribution coefficient caused by low binding force between group of solvent functional and phenolic hydroxyl group,and steric hindrance effect of branched chain,the method of structural characteristics integrated computer-aided molecular design(CAMD)was established to develop a highly efficient extraction dihydric phenols process.It aims to reduce the concentration of total phenols to less than 300 mg/L.The solvents are first preselected from DECHEMA database based on hydrogen bond.This is followed by the analysis of regularity of structural characteristics,screening of preferred molecular structure and prediction of the properties of the solvents.It is suggested that solvents with low carbon number,straight chain or C=C bond are beneficial.This paper determined that methyl propyl ketone(MPK)is the optimum single solvent.The phenols removal efficiency with MPK is analyzed.The concentration of dihydric phenols can be reduced to 260 mg/L,and the concentration of total phenols can be reduced to 288?mg/L after two-stage extraction.The concentration of dihydric phenols can be reduced to 68 mg/L,and the concentration of total phenols can be reduced to 71?mg/L after three-stage extraction.To deal with the problems of limited extraction capacity of a single solvent and contradiction of the removal efficiency and solubility,the synergistic effect was used to improve the extractability of single solvent.This paper analyzed the synergistic effect of the solvent functional groups.Then,the method of structural characteristics integrated CAMD was used to select the best solvent mixture.It can be seen that the hydrogen bond is formed between functional groups of hydroxyl and(carbonyl,ester,or ether).The synergistic extraction distribution coefficient,mutual solubility and azeotropic point of solvent mixture methyl isobutyl ketone(MIBK)+ n-pentanol were compared with MPK + n-pentanol,propyl acetate + n-pentanol and diisopropylether(DIPE)+ n-pentanol.The solvent mixture was proposed with the volume ratio of MIBK to n-pentanol 6:4.After two-stage extraction,the concentration of total phenols can be reduced to less than 300mg/L if the volume fraction of n-pentanol between 10%-70%.At volume fraction of 40% n-pentanol,the concentration of dihydric phenols can be reduced to 171 mg/L,and the concentration of total phenols can be reduced to 190?mg/L after two-stage extraction.The concentration of dihydric phenols can be reduced to 36 mg/L,and the concentration of total phenols can be reduced to 38?mg/L after three-stage extraction.Liquid–liquid equilibria(LLE)data for quinary(MIBK + n-pentanol + phenol + hydroquinone + water)system were determined under atmospheric pressure at T = 298.15 K.The extraction effectiveness of MIBK + n-pentanol was compared with the MPK and MIBK.NRTL and UNIQUAC models were used to correlate LLE data by using Aspen Plus,and corresponding binary interaction parameters were obtained.The estimated data from the two models agree well with experimental LLE data,the room-mean-square-deviation(RMSD)of the NRTL and UNIQUAC models are 0.027% and 0.039%,respectively.The NRTL model gives a better agreement than the UNIQUAC model.The synergistic extraction process by using 60% MIBK + 40% n-pentanol had been developed with treatment 130?t/h coal gasification wastewater.Major units of synergistic extraction process were modelled and simulated,inclusive of phenols extraction unit,raffinate stripper unit and solvent distillation column.The operation parameters of three major units were analyzed.The concentration of total phenols can be reduced to 161 mg/L after two-stage countercurrent extraction.Moreover,the synergistic extraction process realized recovery solvent mixture without changing the size of the existing distillation equipment.The composition of solvent mixture MIBK + n-pentanol can't change after distillation.