An Alternative Process for Butanol Production: Continuous Flash Fermentation

Abstract

The objective of this work is to introduce and demonstrate the technical feasibility of the continuous flash fermentation for the production of butanol. The evaluation was carried out through mathematical modeling and computer simulation which is a good approach in such a process development stage. The process consists of three interconnected units, as follows: the fermentor, the cell retention system (tangential microfiltration) and the vacuum flash vessel (responsible for the continuous recovery of butanol from the broth). The efficiency of this process was experimentally validated for the ethanol fermentation, whose main results are also shown. With the proposed design the concentration of butanol in the fermentor was lowered from 11.3 to 7.8 g/l, which represented a significant reduction in the inhibitory effect. As a result, the final concentration of butanol was 28.2 g/l for a broth with 140 g/l of glucose. Solvents productivity and yield were, respectively, 11.7 g/l.h and 33.5 % for a sugar conversion of 95.6 %. Positive aspects about the flash fermentation process are the solvents productivity, the use of concentrated sugar solution and the final butanol concentration. The last two features can be responsible for a meaningful reduction in the distillation costs and result in environmental benefits due to lower quantities of wastewater generated by the process.

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

“…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.…”

Recent advances on biobutanol production

“…In this technology, a partial separation of the solvents and water occurs in the flash tank separator, where the liquid fraction returns to the fermentor and the vapor fraction (after condensation) plus the purge and permeate streams will compose the final stream that is sent to distillation. Thus, butanol concentration is always less than the critical concentration (for inhibition by product) [17]. Furthermore, they developed a mathematical model to predict the behavior of the process.…”

“…For the development of the model the differential equations for the batch reactor assume constant volume and factor in the removal of butanol during the process. The objective of this work was to demonstrate that the use of flash fermentation was able to decrease product inhibition [17]. The Figure 1 demonstrates the cyclic process that can be generated using this technology.…”

“…So it becomes necessary to control the removal of butanol, since natural oscillations can occur during the dynamic process. The mathematical modeling is similar to the one used in [17] with some minor changes in the differential equations due to the alteration of the reaction volume. The objective of the control was to keep sugar and butanol concentrations constant in the fermentor.…”

“…Alternative methods are reported with the objective to promote a cheaper and efficient separation. More recently, mathematical models have been developed to design the process as well as to simulate its behavior on an industrial scale without the need to carry out experiments to optimize the operational conditions of the reactor [17][18][19].…”