Energy Requirements for Butanol Recovery Using the Flash Fermentation Technology

Abstract

Acetone–butanol–ethanol (ABE) facilities have traditionally presented unattractive economics because of the large energy consumption during recovery of the products from a dilute fermentation broth (∼13 g/L butanol). This problem results from the high toxicity of butanol to microorganisms that catalyze its production. Flash fermentation is a continuous fermentation system with integrated product recovery. The bioreactor is operated at atmospheric pressure and the broth is circulated in a closed loop to a vacuum chamber where ABE is continuously boiled off at 37 °C and condensed afterward. With this technology the beer achieved a concentration of butanol as high as 30–37 g/L. This paper studies the energy requirements for butanol recovery using the flash fermentation technology and its effect on the energy consumption by the downstream distillation system. Compressors are used to remove the vapors from the flash tank, thus maintaining the desired vacuum. The heat recovery technique of vapor recompression is used to reduce energy requirements. With this technique the heat generated by the compression and partial condensation of the vapors provides the energy for boil up (heat of vaporization) in the flash tank. Thus the energy requirement for the flash fermentation is essentially the electrical power demanded by compressors. Energy for recirculation pumps accounts for approximately 0.5% of the total energy consumption. Small increments in butanol concentration in the beer can have important positive impacts on the energy consumption of the distillation unit. Nonetheless, the energy use of the recovery technology must be included in the energy balance. For a fermentation with a wild-type strain, the total energy requirement for butanol recovery (flash fermentation + distillation) was 17.0 MJ/kg butanol, with 36% of this value demanded by the flash fermentation. This represents a reduction of 39% in the energy for butanol recovery in relation to the conventional batch process. In the case of a fermentation with a hyper-butanol producing mutant strain, the use of the flash fermentation could reduce the energy consumption for butanol recovery by 16.8% in relation to a batch fermentation with the same mutant strain.

Economic comparison of a continuous ABE fermentation with and without the integration of an in situ vacuum separation unit

“…As a result, the partial vaporization of the fermentation broth, in a separate vacuum unit, would generate a vapour phase richer in solvents (ABE) and an ABE-depleted liquid stream. [5][6][7] A schematic diagram of the continuous fermentation process with an integrated vacuum unit that was evaluated in this study is presented in Figure 1. In the vacuum-integrated process, a stream is continuously withdrawn from the fermentation broth and passed through a heat exchanger to provide the necessary energy input to sustain the desired evaporation rate before entering a vacuum flash unit, in which a fraction of the inlet stream is then vaporized.…”

“…All these techniques have advantages and disadvantages in terms of capacity, selectivity, energy requirements, and most importantly the cost. [4][5][6] Studies have shown that conventional ABE fermentation facilities have always had unattractive economics. [5,7] Incorporating an in situ separation technique to partly remove ABE solvents during the course of fermentation increases productivity, but at the expense of additional process complexity and cost.…”

“…[4][5][6] Studies have shown that conventional ABE fermentation facilities have always had unattractive economics. [5,7] Incorporating an in situ separation technique to partly remove ABE solvents during the course of fermentation increases productivity, but at the expense of additional process complexity and cost. Therefore, it is essential to perform an economic analysis of the integrated techniques in order to establish the most feasible and cost-effective process.…”

Biodigestão anaeróbia termofílica de vinhaça em sistemas combinados do tipo acidogênico-metanogênico para potencialização da recuperação de bioenergia em biorrefinarias de cana-de-açúcar de primeira geração

“…Por sua vez, a produção de solventes como o etanol e butanol a partir de resíduos tende a aumentar diretamente o balanço energético em biorrefinarias (Xie et al, 2014 (Mariano et al, 2011). A solventogênese constitui um processo subsequente à acidogênese, uma vez que os solventes são obtidos a partir da conversão dos ácidos orgânicos (biohidrogenação), especialmente o butirato e acetato (Harde et al, 2016), sob condições controladas de pH e tamponamento.…”

“…A solventogênese constitui um processo subsequente à acidogênese, uma vez que os solventes são obtidos a partir da conversão dos ácidos orgânicos (biohidrogenação), especialmente o butirato e acetato (Harde et al, 2016), sob condições controladas de pH e tamponamento. 23 O ácido butírico pode ser usado como matéria-prima para produção de butanol, caracterizado como um biocombustível promissor (Mariano et al, 2011), tanto pelo emprego de rotas catalíticas (Sjöblom et al, 2015) quanto por bioquímicas (Regestein et al, 2015). N-butil butirato ou butanoato de butila, um combustível alternativo para aviação, também pode ser obtido a partir do ácido butírico por meio de sua esterificação com o butanol (Sarma et al, 2015;Sjöblom et al, 2015).…”