Separation of dimethylnaphthalene isomers by extractive crystallization

Abstract

This study is aimed to develop and evaluate extractive crystallization processes for separating 2,6-dimethylnaphthalene, a starting material for high performance engineering plastics and liquid crystallization polymers, from 2,7-dimethylnaphthalene. At first, the solubility of 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene in three solvents, i.e. ethyl acetate, ethanol, and hexane, was studied. Secondly, two extractive crystallization processes, called process 1 and process 2, for separating 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene were developed and evaluated based on equipment and operating costs. The processes developed fractionate 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene into pure components with yields of 100% by involving dissolution, crystallization, evaporation, and filtration. It was found that the larger the difference of hot and cold temperatures, the lower the capital and operating costs. Process 1 was found to be the best when hexane is used as solvent, on the other hand, process 2 was found to be the best when ethyl acetate is used as solvent. Lower costs were observed when 2,6-dimethylnaphthalene is removed from the first filter. Under the studied condition, process 2, with ethyl acetate as solvent and operates at hot and cold temperatures of 50 and 35 °C, respectively, was found to be the best alternative. Further studies are necessary to find out if the processes developed are more economic than the other separation processes.