Ethanol Recovery from Fermentation Broth via Carbon Dioxide Stripping and Adsorption

Abstract

With the depletion of fossil fuels, research in alternative energy sources that can provide the world's energy demand has increased significantly during the past decade. One alternative energy source in particular that has gained worldwide recognition as a potential replacement to oil is bioethanol. It is renewable and environmentally friendlier than fossil fuels. In this study, adsorption is used to increase the efficiency of ethanol production by decreasing the effect of product inhibition using carbon dioxide stripping technology. The reduction in product inhibition is particularly important when ethanol is produced from lignocellulosic biomass because microorganisms that are able to use all fermentable sugars are less tolerant to ethanol. Carbon dioxide removes ethanol from the fermentation broth and reduces the level of ethanol toxicity, while adsorption is used to recover the entrained ethanol from the vapor phase. The literature review showed that activated carbon and hydrophobic zeolites would be the most appropriate adsorbents for ethanol recovery in the vapor phase. A series of adsorption screening experiments were performed to compare four activated carbon adsorbents (Filtrasorb 200, Nuchar RGC 40, Sorbonorit B4, and WV-B 1500) and two hydrophobic ZSM-5-type zeolites (HiSiv 3000 and CBV 8014). The vapor composition used was controlled to resemble the fermenter outlet vapor concentration after stripping with carbon dioxide. Activated WV-B 1500 exhibited the highest ethanol capacity among activated carbons, having higher ethanol adsorption capacities than the two zeolites. Adsorption isotherms for ethanol and water in the presence of carbon dioxide at different temperatures were determined using WV-B 1500 as the adsorbent with the temperature-dependent Toth isotherm model providing satisfactory fits for these isotherms. Ethanol adsorption experiments with and without the presence of water were conducted and showed similar ethanol adsorption capacities, indicating that the presence of water has a negligible effect on ethanol adsorption.

Bioethanol Production from Renewable Raw Materials and its Separation and Purification: a Review

“…It is therefore necessary to conduct further research in order to check the influence of other components on adsorption, or to investigate other methods that can be coupled with adsorption to facilitate the separation and purification of ethanol. Some of the methods that can be used with adsorption are ozonation ( 178 , 179 ) or gas stripping ( 180 , 181 ). …”

Vapour permeation for ethanol recovery from fermentation off–gas

“…This process option avoids the circulation of fermentation broth through the membrane unit thereby avoiding membrane fouling and additionally utilizes the fermentation byproduct, CO2, which otherwise is mostly vented-off from the process. Ethanol stripping from fermentation broth by CO2 and recovery by different separation techniques, such as adsorption, rectification and condensation, has been successfully demonstrated [15][16][17]. To our knowledge, this is the first report proposing the above mentioned process option.…”

Overview of Alternative Ethanol Removal Techniques for Enhancing Bioethanol Recovery from Fermentation Broth

“…Activated carbon is the most commonly used ethanol adsorbent. Hashi et al [71] compared four activated carbon adsorbents (Sorbonorit B4, Filtrasorb 200, WV-B 1500 and Nuchar RGC 40) and two hydrophobic ZSM-5-type zeolites (HiSiv 3000 and CBV 8014), it was found that activated WV-B 1500 has the highest ability to adsorb ethanol, and activated carbons showed higher ethanol adsorption ability than the two zeolites. Despite different types of adsorbents has been reported as a potential adsorbent for ethanol recovery, the majority of the reported works used ethanol/water, ethanol/glucose or ABE mixture models during the investigation [72][73][74][75][76][77][78][79].…”