Alternatives to distillation: multi-membrane permeation and petrol pre-blending for bio-ethanol recovery

Stacey, Neil Thomas
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Separation of materials is crucial to the operation of the majority of chemical processes, not only for the purification of final products but also for the processing of feed-stocks prior to chemical reaction. The most commonplace method of materials separation is distillation which, unfortunately, is often an energy-intensive process and contributes significantly to mankind’s energy consumption and carbon dioxide emissions. Alternative approaches to separation are therefore a crucial element of the ongoing pursuit for sustainability in chemical industries. There are two principal ways of going about this. The first is to replace distillation units with alternative unit operations that can achieve the same separation with less energy expenditure. The second approach is overall flowsheet revision, fundamentally changing a separation cycle to minimize its energy requirements. The greatest improvements to energy efficiency will be achieved by applying both approaches in tandem. However, each must be developed separately to make that possible. This thesis lays the groundwork for radical revision of major separation operations by showcasing a new overall flowsheet for bioethanol separation that promises tremendous improvements in separation efficiency, reducing the energy usage involved in ethanol purification by as much as 40% in some scenarios. It also develops a novel method for the design of multi-membrane permeation units, showing how area ratio can be manipulated to fundamentally alter separation performance from such units, resulting in superior separation performance to conventional units, achieving higher recoveries than conventional setups. With membranes being an increasingly popular separation method, the potential for superior performance from multi-membrane units promises improvements in separation efficiency.
A thesis submitted for the degree of Doctor of Philosophy to The Department of Chemical and Metallurgical Engineering, Faculty of Engineering, University of the Witwatersrand, Johannesburg, 2016
Stacey, Neil Thomas (2016) Alternatives to distillation: multi-membrane permeation and petrol pre-blending for bio-ethanol recovery, University of Witwatersrand, Johannesburg, <>