Methodological Study On The Computer Aided Extractant Design And Optimization For The Treatment Of Coal Chemical Wastewater

The phenols,polycyclic aromatic compounds and heterocyclic compounds,have strong toxicity as well as poor biodegradability,which should be removed in pretreatment process to meet the quality requirements of biochemical treatment.The main problems of pretreatment are poor extraction performance on other pollutants and large solvent loss,resulting that biochemical treatment process is difficult to run stably for a long time.It is important to improve the pretreatment effect by designing and selecting extractants with high-efficiency co-extraction effects on phenolics as well as heteropolycyclics.The strategies of screening pure extractants and blended extractants from existing commercial chemicals were proposed in this paper.The detailed studies are following:(1)The Existing Commercial Compounds database(Existing Commercial Compounds Database,ECCD)was established.In order to avoid candidate extractants with unknown risk,an existing commercial compound database was developed based on the chemical substances lists of China,the United States and the European Union,which totally containing 34177 compounds.The compound property estimation program was developed to estimate the main properties,based on the molecular structure of the compounds,using group contribution method and group matching tool.The properties expands the physical information of the database and meets the needs of molecular screening.(2)A database-based candidate pure extractant generation strategy was proposed.Phenol was set as a representative component of phenols in coal chemical wastewater,and the single-component extractant with good extraction effect for it was screened from ECCD.Multiple standards for extractant screening were set to generate a list of potential candidate molecules,according to the characteristics of the de-phenol extractant commonly used in the industry.The candidate solvents list contains 491 chemical compounds,including ketones,ethers,esters,alcohols,and benzene compounds,not only consistent with the de-phenol extractants commonly used,but also include 15 commonly used extractants.There are 11 compounds having higher partition coefficient m,selectivity ? and extraction rate p than Methyl isobutyl ketone(MIBK),which was selected as the reference extractant.(3)A design and screening method of blended extractants was proposed.Two pure compound candidates containing 382 and 219 compounds,were screened from the ECCD,with high extraction performance for phenolic and heterocyclic contaminants.60857 binary extractants were obtained by one-to-each traversing the compounds in two candidate lists.Pseudo-components were constructed to simplify various contaminants in wastewater and avoid complex multiphase LLE calculations.The screening problem of blended extractant was transformed into NLP mathematical optimization model.The model was solved by parallel computing method to reduce the solution time of GAMS model,according to the characteristics of GAMS software optimization solution.(4)Binary extractants for coking and coal gasification wastewate were design.The deviations of content in two phases as well as extraction rate between the pseudopollutant and total pollutants are within the acceptable error range,indicating that pseudo-components can represent pollutants in coal chemical wastewater with chemical rationality.The constraints of extraction rate and solvent loss were set based on methyl isobutyl ketone(MIBK)and diisopropyl ether(DIPE).390 and 333 binary extractants with good extraction effect on coal gasification wastewater and coking wastewater were obtained respectively.Binary extractants mainly include "Aliphatic(di)ketone+" and "Aromatic ether ketone+" two series.The main solvents and assistant solvents of binary extractants are those top-ranked compounds in de-phenolics and de-heteropolycyclics lists,respectively.The binary extractants have better comprehensive extraction effect on coal chemical wastewater than single extractant,with better extraction effect and lower solubility in water.Furthermore,the binary extractants have better extraction effects on pollutants than MIBK and DIPE in a wide range of pollutant concentration and temperature(5)The experiment results of the binary extractants S1?S5 on simulated coal chemical wastewater show that the binary extractants screened have good co-extraction ability to replace the single extractants.The extraction rates of monophenols and dihydric phenols are same as MIBK,while the extraction rate of heterocyclic pollutants is significantly higher than MIBK.The extraction rates of monophenols,dihydric phenols and heterocyclic pollutants calculated by the screening optimization model show good consistency with ASPEN Plus.It shows that the screening strategy and screening optimization model of mixed extractant established in this paper have good feasibility and reliability.