Pilot-scale experimental studies on ethanol purification by cyclic stripping

Cyclic distillation is a proven process intensification method for enhanced separation of various mixtures. It uses an alternative operating mode based on separate phase movement which leads to important practical advantages (vs conventional mode) such as increased column throughput, lower equipment cost (using much less trays at the same reflux ratio) and reduced energy requirements by 20-35% (smaller reflux ratio at the same number of stages), and better separation performance (up to three times). However, if the impurities to be separated are in very low amounts in the feed then distillation is not favorable from an energy use viewpoint. This article is the first to report the practical performance of a continuous process for ethanol purification by air stripping using a cyclic mode of operation, a novel process that avoids the costs of distillation. The purification of ethanol food grade (96.4 vol%) from volatile impurities (0.5 vol%) such as esters, aldehydes, and alcohols, is carried out in a hydro-selective column with five stages. The lightweight impurities are removed from a stream that is the head fraction of a distillation column. This is usually a waste stream amounting to 3-6% of the plant production rate. By concentrating the stream with impurities, more ethanol is produced such that the losses are reduced to only 1-1.5% of the plant capacity. Based on the experimental results presented in this work, a process consisting of two air stripping columns using cyclic operation is proposed for industrial implementation.