The Process Study On Separating M-Cresol Fromphenol Systems By Complex Crystallization

M-cresol is an important chemical intermediates, widely used in pesticides, plastics, fragrances, pharmaceuticals, adhesives and other fields. China is a country rich in coal and the coke yield in china accounted one third in the world. But the phenols contained in the tar pollute the environment as a waste of resources every year.In this paper, we study the separation on the tricresols for getting m-cresol. The model mixed Phenol, investigation and analysis of impurities, solvent selection and tricresol experiment were made successively to achieve the craft of separating tricresol.we mix the pure p-cresol and m-cresol (np-cresol:nm-cresol=1:1) as the raw materials to study the factors. the complex time and temperature, crystalliztion time and temperature, the amount of solution, the amount of urea can impact on the complex crystallizaion greatly. The optimum conditions were chosen:the Molar ratio of urea and m-cresol was 1.5 and the reaction temperature was 95℃,the reaction time was 60min,the crystallization temperature was -18℃,the crystallization time was 120min and the reaction temperature was 95℃.In this way, the yield of m-cresol was 64.7%, the purity of product was 99.22%. we analyze complex via IR and find that there are hydrogen bond between C=O and O-H.the tricresol getting from crude phenol include o-cresol and phenol. We study the influence of o-cresol and phenol on the complex crystallization besides p-cresol. o-cresol and phenol were more diffcult to separate from m-cresol than p-cresol. we study the amount of p-cresol, o-cresol and phenol impact on the purity of m-cresol. It was found that the reason of difference is that p-cresol-urea, m-cresol-urea, o-cresol-urea and phenol-urea have different solubility in toluene and hexane. Mole fraction of m-cresol, p-cresol, o-cresol and phenol complex with urea was 0.088～0.212,0.192～0.465,0.138～0.300 and 0.0004～0.008 respectively between 244.15k and 273.15k by calculating.Toluene as solution exist some problem such as low yield, toxic and so on. According the solubility parameter theory, we chose toluene, 1.2-dichloroethane and hexane as the solution. When the hexane was the solution, we found the yield was better than the others. The reason is that polarity of hexane is very low so that it will not damage the hydrogen bond.Then, tricresol was used as the raw materials. Toluene and hexane respectively was chosen as the solvent. In the same condition, the yield of m-cresol was 61.4% and the purity of product was 98.9% in toluene while the yield of m-cresol was 74.81%, and the purity of product was 99.0% in hexane. Besides, the process of producing m-cresol from tricresol was made by integrating the craft of produing tricresol from tar.