Feasibility of Capacity Increase of Batch Distillation by Applying a Second Column

Németh, Bence and Hégely, László and Láng, Péter (2021) Feasibility of Capacity Increase of Batch Distillation by Applying a Second Column. In: PRES'21, 2021. okt. 31.-nov. 3., Brno, Csehország. (In Press)

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Abstract

Increasing the processing capacity of batch distillation is important, for example, in the pharmaceutical industry, where a given amount of waste solvent must be processed in a specific time period, else the remaining amount of waste solvent must be incinerated, which results in solvent loss and considerable environmental impact. It was shown in the previous works of the authors that, depending on the feed composition, the processing capacity of batch distillation can be increased by applying a second, even smaller distillation column as pre-fractionator. Previously, the separation of three specific, highly non-ideal mixtures were studied by the authors: dichloromethane-acetone-water and acetone-water, water-acetic acid. The goal of the present paper is to study whether general conclusions can be drawn regarding the processing capacity increase. In contrast to the previous works, where the columns were operated with constant reflux ratio policy, they are operated with constant distillate composition policy in the present study. A simplified model is developed both for the single- and two-column processes, describing the relationship between the processing capacity, the product specifications (including the recovery), the feed composition and the numbers of trays by assuming constant relative volatility. The equations derived are used to study the influence of each parameter (purity specifications, feed composition, numbers of trays, specified recovery and relative volatility) on the distillation times for both processes. The conclusions obtained by these equations are validated in a case study (separating n-heptane-n-octane) by using a professional flow-sheet simulator.

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