Ethanol Recovery from Stripping Gas Mixtures by Gas Absorption: Experimental and Modeling

Ethanol removal by CO₂ stripping during alcoholic fermentation is one way of overcoming the problem of inhibition by the product. However, the lack of efficient methods to recover ethanol from the gas phase still makes the use of stripping unviable. In this work, gas absorption was evaluated as a method for the recovery of ethanol from the gas mixture generated by CO₂ stripping. First, the solvents water, monoethylene glycol (MEG), and diethylene glycol were evaluated in terms of their performance in ethanol absorption. MEG was selected as the most appropriate absorbent because it provided a satisfactory ethanol recovery percentage, in addition to the fact that it is already used in distilleries to obtain anhydrous ethanol. Subsequent assays using MEG were conducted to investigate the influence of the initial MEG volume in the absorber, the recirculation volumetric flow rate of solvent, and the use of two absorbers connected in series. A modeling procedure was developed based on mass balance equations for the species involved (ethanol, water, CO₂, and MEG), stripping and absorption kinetics, and vapor–liquid equilibrium concepts and was able to accurately describe the process behavior. The use of two absorbers, each with 0.80 L of MEG, enabled recovery of up to 93.1% of the ethanol from the stripping gas mixture. The results showed that gas absorption with MEG is a highly promising strategy for ethanol recovery, with potential for applications in industrial ethanol fermentation processes.