Study On Extraction Performance Of Extractant In Phenolic Wastewater From Coal Chemical

At present, China is facing the increasing shortage of water resources and itsindustrial wastewater pollution is still serious. Phenolic wastewater from coal chemicalindustry is hard to be biological degradated due to its biological toxicity, whichbecomes a tough problem for environmental protection. It is of great significance todevelop efficient phenolic wastewater treatment technique for water reuse andenvironmental protection. Since solvent extraction is efficient for treating wastewatercontaining high concentrations of phenols, measurement methods for contaminants,enhancement of extractant performance and stability of the extractant related to coalchemical industry wastewater treatment by solvent extraction is studied in this paper,which paves the way for industrial application.At first, for the analysis of phenolic wastewater quality, a method for directlydetermining phenols and several short-chain fatty acids in coal chemical industrialwastewater by gas chromatograph is developed. The linear regression is fine, with acorrelation coefficients of above0.999. The method is simple, without complicatedpretreatments, and to be showed effective and accurate with a case study.As we all known, butyl acetate is an excellent dephenol extractant, but it is hardlyapplied in industrial due to its high consumption caused by rapid hydrolysis. So, inorder to improve the stability of butyl acetate, extraction and hydrolysis conditions ofthe extraction system with butyl acetate is studied in the third chapter. According to thestudy results, optimum extraction conditions for industrial applications is proposed: pHis less than8, water-oil ratio is about1:4and the extraction stage number is above3.the residual concentration of total phenols can be reduced to less than540mg/L. Whenconcerning the problem of unstability and easy hydrolysis of butyl acetate.Experimental results also show that the hydrolysis rate of butyl acetate is stronglyinfluenced by pH of the solution. when the pH approximates6-7just equals to a slightly acidic and neutral environment, the hydrolysis of butyl acetate will be veryslight, but under alkaline conditions, hydrolysis rate will be more than50times higherthan the previous condition, after a mouth. Thus, the loss of the hydrolysis of butylacetate can be significantly reduced by keeping the pH of the extraction system inneutral and slightly acidic condition.Finally, in order to enhancing the extraction performance of middle oil extractionsystem, TBP、Pyridine、N-235and N-503are respectively added to different middle oilsample as complexing agents, the extraction performance of volatile phenols andpolyhydric phenols is investigated.The results show that distribution coefficient of total phenols using middle oil canbe increased by adding TBP. when the concentration of TBP in middle oil is15%, thedistribution coefficient will be increased to more than4.5. Therefore, when the factoryon the existing industrial condition that extraction temperature is60°C, Water-oil ratiois1:1and extraction stage number is2, the total phenolic residual concentration can bereduced to800mg/L by adding10%of TBP concentration and keeping the ph＜8. Theresults also shows that afer several times reuse, the extraction performance usingmiddle oil containing TBP is stable.