Process Intensification in Bio-Ethanol Production–Recent Developments in Membrane Separation

Abstract

Ethanol is considered as a renewable transport fuels and demand is expected to grow. In this work, trends related to bio-ethanol production are described using Thailand as an example. Developments on high-temperature fermentation and membrane technologies are also explained. This study focuses on the application of membranes in ethanol recovery after fermentation. A preliminary simulation was performed to compare different process configurations to concentrate 10 wt% ethanol to 99.5 wt% using membranes. In addition to the significant energy reduction achieved by replacing azeotropic distillation with membrane dehydration, employing ethanol-selective membranes can further reduce energy demand. Silicalite membrane is a type of membrane showing one of the highest ethanol-selective permeation performances reported today. A silicalite membrane was applied to separate a bio-ethanol solution produced via high-temperature fermentation followed by a single distillation. The influence of contaminants in the bio-ethanol on the membrane properties and required further developments are also discussed.

Application of Zeolite Membranes to Dehydrate a Bio-Ethanol Solution Produced by High-Temperature Fermentation

“…Employing ethanol-selective membranes instead of distillation is an option to concentrate bioethanol after fermentation that can reduce the energy required for the concentration [10]. For example, the permeate through hydrophobic inorganic membranes, such as silicalite membranes, can be over 85% when 10% ethanol solution is applied [11].…”

“…For example, the permeate through hydrophobic inorganic membranes, such as silicalite membranes, can be over 85% when 10% ethanol solution is applied [11]. After an ethanol-selective membrane, a dehydration membrane can be applied to concentrate the ethanol further [10]. The separation properties of membranes are often evaluated by a pervaporation (PV) process, where a mixture liquid is supplied to the membrane and some fraction permeates through the membrane as a vapor.…”

“…A chiller may be used in larger-scale applications. The possibility of concentrating a few percent of ethanol to over 80% in a single step using an ethanol-selective membrane is attractive; however, the energy demand at the chiller can be similar to the energy demand of distillation [10]. In addition, the capital cost of the chiller and related facilities may be a challenge to realize in a small-scale process.…”

Ethanol purification using membrane technology

“…and concluded that the proposed system requires one-fourth of the energy required by distillation. Nevertheless, more research is required to develop RO membranes with such robustness (Kumakiri et al 2021).…”

“…Among many membrane processes, pervaporation has been one of the most extensively studied for ethanol recovery from aqueous solutions and fermentation broth (Kumakiri et al 2021;Peng et al 2021;Vane 2008;Zentou et al 2019). It separates volatile compounds from the liquid feed by creating a difference in effective concentration between the feed and permeate.…”