Drastic Impact of Pressure on Energy Consumption in a Xylene-Splitter Distillation Column

Abstract

The use of distillation to separate close-boiling components requires columns that feature many stages, high reflux ratios, and large reboiler duties. Many of these types of columns that are widely used in the petroleum and chemical industries include “C2-Splitters” separating ethylene and ethane and “C3-Splitters” separating propylene and propane. Other important examples include separating several types of hydrocarbon isomers. The normal boiling points of the ortho, meta, and para isomers of xylene differ by only a few degrees (144, 139, and 138 °C), so a column that produces a bottoms rich in ortho-xylene has high energy consumption and large capital cost (many trays and large heat exchangers). A recent paper [Dai and co-workers, “Methanol Aromatization for the Co-Production of Para-Xylene and Light Olefins: Process Simulation and Evaluation”, Ind. Eng. Chem. Res. 2025, 64, 11428–11440] included this xylene separation using both conventional columns and advanced configurations. However, the authors appear to have arbitrarily set the operating pressure of the xylene-splitter column at 1.2 bar. The purpose of this work is to demonstrate that drastic reductions in energy and capital costs can be achieved by operating under vacuum conditions (0.1 bar).