Optimization of Fed-Batch Fermentation with in Situ Ethanol Removal by CO₂ Stripping

Abstract

One way of overcoming the substrate and ethanol inhibition effects in the industrial ethanol production process is to use fed-batch fermentation coupled with an ethanol removal technique. This work describes the optimization and experimental validation of sugar cane ethanol production by fed-batch fermentation with in situ ethanol removal by CO2 stripping. The optimization employing a genetic algorithm (GA) was used to find the optimum feed flow rate (F) and the ethanol concentration (C E0) in the medium at which to initiate stripping, in order to obtain maximum ethanol productivity. Conventional ethanol fermentation employing the optimum feed flow rate was performed with must containing 257.1 g L–1 of sucrose (180 g L–1 of total sucrose concentration), resulting in achievement of an ethanol concentration of 82.2 g L–1. The stripping fed-batch fermentation with high total sucrose concentration (260–300 g L–1) or 371.4–428.6 g L–1 in the must feeding was performed with optimal values of the feed flow rate and the ethanol concentration (C E0) in the medium at which to initiate stripping. At the highest sucrose feed (total concentration of 300 g L–1), the total ethanol concentration reached 136.9 g L–1 (17.2 °GL), which was about 65% higher than the value obtained in fed-batch fermentation without ethanol removal by CO2 stripping. This strategy proved to be a promising way to minimize inhibition by both the substrate and ethanol, leading to increased sugar cane ethanol production, reduced vinasse generation, and lower process costs.

In situ product recovery as a strategy for bioprocess integration and depletion of inhibitory products

“…This technique has been mainly studied for bio‐fuels extraction, particularly in the acetone–butanol–ethanol (ABE) extractive fermentation, showing high potential in reducing product inhibition and increasing yields 13,77‐81 . Chen et al .…”

“…This technique has been mainly studied for bio-fuels extraction, particularly in the acetone-butanol-ethanol (ABE) extractive fermentation, showing high potential in reducing product inhibition and increasing yields. 13,[77][78][79][80][81] Chen et al realized a technoeconomical evaluation of ABE distillation from a condensate obtained by gas stripping ISPR. They determined that the total annual cost was reduced by 17.4%, mainly by decreasing energy requirements.…”

Mid‐infrared spectroscopy as a tool for real‐time monitoring of ethanol absorption in glycols

“…It is important to mention that these experimental conditions (temperature, ethanol concentration, and volumetric CO 2 flow rate) represented the conditions of ethanol fermentations with in-situ ethanol removal by CO 2 stripping. [8,9,13,33]…”

“…Several literature reports have shown the benefits of using CO 2 stripping for ethanol removal during ethanol fermentation from corn starch, [6,7] sugarcane, [8,9] and sweet sorghum, [10] and for removal of butanol during acetone-butanol-ethanol fermentations. [11,12] However, efficient and cost-effective methods to recover ethanol from the gas phase are still needed, in order to make it feasible to use stripping in the ethanol fermentation process.…”

Fermentação Alcoólica Extrativa in Situ Em Batelada Alimentada Usando Biorreator Coluna De Gotas

“…O tempo de enchimento de 6 h e o início da extração em 3 h resultou em uma fermentação com consumo total do substrato em 14 h, com uma produção de etanol 34% superior à convencional. Sonego et al (2018) relatam que em condições similares, porém com retirada de etanol por arraste com CO2, obteve-se uma concentração máxima de etanol de 72,0 kg•m -3 , mostrando que a extração líquido-líquido pode ser tão eficiente quanto outros tipos de processos extrativos. Neste caso, no qual foram removidos 35,4% de etanol, a energia gasta para separar o etanol do ácido oleico por flash é menor à da destilação convencional (JASSAL et al, 1994), além do ácido oleico recuperado poder ser utilizado numa próxima extração, não causando danos ao meio ambiente com seu descarte após um único uso.…”