Extractive Batch Fermentation with CO₂ Stripping for Ethanol Production in a Bubble Column Bioreactor: Experimental and Modeling

Abstract

In alcoholic fermentation processes, ethanol is the main component that is toxic to yeast because it acts as a noncompetitive inhibitor of metabolism. One way of overcoming the inhibition effect on yeast is to extract the ethanol from the broth during the fermentation. The present work evaluates ethanol production by extractive batch fermentation using CO 2 as a stripping gas. Investigation was first made of the influence of specific CO 2 flow rate (ϕ) and solution temperature on ethanol stripping. The best results, in terms of ethanol removal, were obtained at 2.0 vvm and 34.0 °C. Modeling of conventional and extractive ethanol fermentation was then performed considering cell growth, substrate consumption, ethanol production, and the entrainment of ethanol and water using first-order equations. The hybrid Andrews−Levenspiel model was able to describe the kinetics of the conventional fermentation process, and a model proposed here could accurately predict the behavior of the extractive fermentation. In all the extractive fermentations, there was faster substrate uptake and earlier substrate exhaustion, compared to the conventional fermentation. Extractive fermentation, with stripping initiated after 3 h at an ethanol concentration of 43.3 g•L −1 , resulted in an ethanol productivity (in g•L −1 •h −1 ) that was around 25% higher, and finished about 2 h earlier, compared to the control fermentation.

Microbubble Distillation for Ethanol-Water Separation

“…Gas stripping is an established technique for continuous ethanol removal during fermentation processes. Different gases such as nitrogen and CO 2 have been widely used in a wide variety of processes as they do not adversely affect culture media [5,22].…”

“…An ethanol concentration of approximately 63 g/L can cause damage to the membrane of an organism's cell wall. At higher concentrations of around 95 g/L, the cell growth of yeast is inhibited by ethanol [5]. One of the ways to overcome this problem is to remove the products from the fermentation bioreactor by a continuous separation unit, where the ethanol is extracted from the broth during the fermentation process [6].…”

Avaliação Da Remoção De Etanol De Soluções Hidroalcoólicas Por Stripping Utilizando Nitrogênio Como Gás De Arraste

“…Para os ensaios com vazões mais baixas, aumentos da temperatura e da concentração inicial de etanol também ocasionaram incrementos no valor de F A , conforme pode ser observado nos ensaios 8 (F A =18,8%) e 5 (F A =23,4%). Sonego et al (2014) ao estudar o arraste de etanol por CO 2 também observaram um aumento no valor do fator de arraste quando a vazão específica de gás aumentou de 0,5 vvm para 2,0 vvm e temperatura passou de 30 °C para 34 °C. Ademais, verificou-se que aumentos na vazão específica para uma mesma condição de temperatura e concentração inicial de etanol levaram a uma redução no fator de concentração, conforme pode-se observar nos ensaios 6 e 2 onde o valor do F C passou de 8,79 para 5,02, respectivamente.…”

“…As respostas analisadas foram o fator de arraste (F A ) e o fator de concentração (F C ) (SONEGO et al, 2014, ESPERANÇA, 2011, descritas nas equações 1 e 2, respectivamente. …”

“…Para contornar esse problema, atualmente a fermentação é realizada em grandes dornas para que a produção temporal seja satisfatória, o que gera altos custos de investimentos. Em adição a isso, o gasto energético durante a destilação e o grande volume de vinhaça são dois grandes problemas relacionados com a produção de etanol (SONEGO et al, 2014).…”