Energy-economic purification of n-hexane from low benzene concentrations via extractive distillation with propylene carbonate as solvent: A comparative study with liquid–liquid extraction processes
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abstract
n-Hexane is one of the most widely used products in the petrochemical industry, where regulatory toxicology policies require benzene content to be < 100 ppm in polymer-grade n-hexane. The n-hexane/benzene mixture forms a homogeneous azeotrope, making its separation challenging. This study focuses on the purification of an n-hexane/benzene mixture with a benzene concentration of 10 mol%25, as no established methodology exists for the purification of mixtures with aromatic concentrations below 20 mol%25. Extractive distillation (ED) and liquid–liquid extraction-extractive distillation (LLEx-ED) processes using propylene carbonate (PC) and ethylene carbonate (EC) as solvents are proposed as alternatives to sulfolane (SF) and liquid–liquid extraction (LLEx) processes. According to simulations in Aspen Plus V9®, using PC in ED processes allows for obtaining n-hexane with a concentration of 99.99 mol%25 with benzene impurities of 66.81 ppm, while benzene is obtained at a purity of 99.91 mol%25. This approach results in energy savings of 42.90 %25, a 22.62 %25 reduction in the Total Annual Cost (TAC), and a 54.77 %25 decrease in CO2 emissions compared to the use of SF in conventional LLEx processes. Compared to LLEx-ED processes using EC, the use of PC in ED processes results in energy and CO2 emission savings of 50.06 %25 and 60.50 %25, respectively. The results demonstrate the high efficiency of using PC in ED processes for separating systems with low aromatic content.
