Japan Gas-Chemical Xylene Separation Process

Abstract

Japan Gas-Chemical Company, Inc. (JGCC) has successfully developed a new xylene separation process in which four isomers are separated consecutively in high purity. Efforts in the development were chiefly concentrated on the perfect separation of m-xylene to which little attention had been paid in conventional processes.
Continuous extraction of m-xylene from raw xylene mixture is carried out quite satisfactorily by using HF-BF₃ as solvent in the first section where HF-BF₃ is most economically used. HF-BF₃ is also used as isomerization catalyst at a higher temperature in the second section and available for the conversion of any desired amount of m- and/or o-xylene to p-xylene. This isomerization section is simply a small loop attached to the extraction section to obtain a higher p-xylene recovery yield or to increase plant, flexibility. HF-BF₃ is easily recovered in the third section which includess a fractionator where the extract is separated into HF-BF₃ and m-xylene. From m-xylene-free raffinate of the extractor, pure ethylbenzene and o-xylene are separated by fractionation with concentrated p-xylene left remaining at the bottom of the fractionator. 99.5% p-xylene is then obtained by single-stage crystallization which corresponds to the second stage of a conventional process.
This paper describes the basic chemical processes involved in the extraction and isomerization utilizing HF-BF₃. The flow sheet of the JGCC process is also given and is briefly explained.