Gas 2025 Issue

essentially free of benzene to be recovered in the former toluene column. Performing the prefractionation distillation steps with these composition targets ensures that the final aromatics product specifications are easily met after the intermediate product pairs are separated in the new main column. Product pair distillation has been shown to be effective at increasing the capacity of a series of heavy olefin distil - lation columns by greater than 27% of the original capacity through the addition of a single new side draw column.⁴ Many BTX distillation systems may be able to achieve capacity increases significantly greater than 27% through a PPD revamp because BTX applications are better suited to PPD than heavy olefins applications. PPD revamps of BTX distillation systems can make use of proven column heat integration schemes as well as energy-efficient features that are unique to PPD config - urations to produce energy-efficient designs. One such example is the use of a column heat integration scheme described earlier in this article in which xylene column vapours are used as a heat source for upstream columns. This heat integration scheme can be implemented in the PPD configuration shown in Figure 3 in exactly the same manner that it would be implemented in a conventional series of BTX columns. Summary Much progress has been made in the development of pro- cesses for recovery and separation of aromatics products. In the earliest days of production of aromatics from COLOs, fractional distillation was used to separate nonaromatic contaminants from the aromatic products. As demand for aromatics grew, it became apparent that new sources of aromatics and new separation processes were needed. The development of LLE processes and the subsequent devel - opment of ED technology were the most important inno - vations that emerged to meet the increasing demand for high-purity aromatics products. These new technologies shaped the development of today’s aromatics production industry. References 1 Martel, E.H., Extraction and Multistage Fractional Distillation with Indirect Heat Exchange of Liquid and Vapor Process and System for Recovering Aromatic Products, US 3,639,497, February 1, 1972. 2 Kumar, S., Ghosh, P., Nanoti, S., Boosting energy efficiency in aro - matics processing, PTQ Q2 2018 . 3 Emmrich, G., Gehrke, H., Ranke, U., Working with an extractive distil - lation process, PTQ Q3 2001 . 4 Kockler, D., Debottlenecking product recovery using product pair dis - tillation: Part II, PTQ Q3 2023 , pp.81-89. David Kockler is a Principal at Dividing Wall Distillation and Separations Consulting, LLC, where he specialises in the development and implementation of advanced distillation processes for the chemi- cal and refining industries. He has more than 30 years’ process design experience, and holds a bachelor’s degree in chemical engineering from Northwestern University and a Master’s in chemical engineering from the University of Virginia. Email: dwc-separations-consulting@outlook.com