(445d) Novel Technology for Producing High Purity n-Hexane and Benzene

N-hexane is one of the most representative non-polar solvent. It is widely used in pharmaceutical, chemical, polymer materials etc., and owning a great market demand. Benzene is one of the most important petrochemical materials. The yield and production technology of benzene stand for the petrochemical development level of the country. However, the traditional separation and purification technologies, for example, molecular sieve adsorption, batch azeotropic distillation and extractive distillation etc., are difficult to get high yield production of n-hexane and benzene with high purity. Moreover, the energy consumption is high in these processes. Our team has developed a series of new technologies coupling the normal distillation and extractive distillation to produce high purity n-hexane and benzene, and iso-hexane as a by-product. N-methyl pyrrolidone was chosen as the extractant in the process. C3~C8 alkane mixtures from raffinate of aromatics extraction unit, pyrolysis gasoline or straight-run gasoline were used as feed. Gradual separation was used to get the final products. Firstly, the iso-hexane was obtained after removal of the impurities with boiling point lower than 2-methylpentane. Then, the remaining materials were separated by extractive distillation to acquire n-hexane product. Finally, the benzene product was got by further separation. The multi-effect thermal coupling technique was employed in the distillation unit. With the heat integration and optimization, the usage of steam and cooling water was saved. The usage of extractant was also reduced by the way of the cycling between the extractive distillation column and the recovery column. To prevent impurities accumulated in the extractant, removal of the heavy component impurities was implemented by taking a small part of material into the falling film evaporation system. High purity n-hexane and benzene product were finally produced by the above mentioned method. The purity of n-hexane product is higher than 99 wt% with the content of benzene is lower than 100 ppm. At the same time, the concentration of benzene product is higher than 99.9 wt%. Currently, a 30,000 MTA n-hexane and benzene plant has been built up using this technology.