Operability of the Modified Petlyuk Process for Separation of Benzene, Toluene, and p -Xylene Ternary Mixture

Abstract

Distillation is one of the main separation methods used in the chemical industry, as well as petroleum refining and petroleum chemistry. However, distillation consumes large amounts of energy, so to reduce the environmental load of the process, energy savings are required in the distillation process. Several possible methods of realizing such energy savings have been proposed1),2). The Petlyuk process is one such energy-saving distillation process, which features two thermally coupled distillation columns3),4), a prefractionator and a main column. Products can be recovered from the distillate, side-cut, and bottom-out streams. Therefore, the Petlyuk process can separate a ternary mixture. The prefractionator has no condenser or reboiler, as the liquid and vapor in the prefractionator are fed into the main column. Since the prefractionator and the main column are thermally coupled, overall energy consumption is reduced. A practical application of the Petlyuk process uses a dividing-wall column5),6), which achieves the same level of performance as the Petlyuk process by dividing the distillation column into two with a partition plate. However, the flow rates of the vapor and liquid into the prefractionator are determined by the position of the partition plate, so a major disadvantage of this design is that the ratio of the vapor and liquid flow rates cannot be adjusted after construction of the column. This issue also affects the Petlyuk process. A modified Petlyuk process would allow for the adjustment of the vapor or liquid flow rates to the prefractionator. The separation characteristics of a modified Petlyuk process were studied with either a condenser at the top or a reboiler at the bottom of the prefractionator7). The condenser at the top of the prefractionator allows liquid reflux operation, so no liquid interconnection between the main column and the prefractionator is necessary. The reboiler at the bottom of the prefractionator supports vapor feed, so no vapor interconnection between the main column and the prefractionator is necessary. Examination of the steadystate condition found that the operability of the modified Petlyuk process was improved by incorporat45 Journal of the Japan Petroleum Institute, 62, (1), 45-51 (2019)