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The effect of varying glucose, mannose and xylose concentrations on continuous solvent production at various dilution rates was studied by multiple linear regression (MLR) modeling using an immobilized column reactor. The factors affecting the solvent production were dilution rate and concentrations of glucose and mannose. MLR-models also showed a preference of glucose as well as its inhibitory effect on xylose consumption. The fermentation process was studied at bigger scale with a volume factor of 17 with an added recirculation loop in the system. The up-scaled reactor produced 12.5 g/l of acetone-butanol-ethanol (ABE) solvents at a dilution rate of 0.23 h(-1), as compared to 13.4 g/l with a smaller column reactor. The xylose utilization was significantly higher in the modified reactor (73%) as compared to the small scale (43%)., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The production of acetone, butanol, and ethanol (ABE) by fermentation is a process that had been used by industries for decades. Two stage immobilized column reactor system integrated with liquid-liquid extraction was used with immobilized Clostridium acetobutylicum DSM 792, to enhance the ABE productivity and yield. The sugar mixture (glucose, mannose, galactose, arabinose, and xylose) representative to the lignocellulose hydrolysates was used as a substrate for continuous ABE production. Maximum total ABE solvent concentration of 20.30 g L(-1) was achieved at a dilution rate (D) of 0.2h(-1), with the sugar mixture as a substrate. The maximum solvent productivity (10.85 g L(-1)h(-1)) and the solvent yield (0.38 g g(-1)) were obtained at a dilution rate of 1.0 h(-1). The maximum sugar mixture utilization rate was achieved with the present set up which is difficult to reach in a single stage chemostat. The system was operated for 48 days without any technical problems., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The objective of this study was to optimize continuous acetone-butanol-ethanol (ABE) fermentation using a two stage chemostat system integrated with liquid-liquid extraction of solvents produced in the first stage. This minimized end product inhibition by butanol and subsequently enhanced glucose utilization and solvent production in continuous cultures of Clostridium acetobutylicum B 5313. During continuous two-stage ABE fermentation, sugarcane bagasse was used as the cell holding material for the both stages and liquid-liquid extraction was performed using an oleyl alcohol and decanol mixture. An overall solvent production of 25.32g/L (acetone 5.93g/L, butanol 16.90g/L and ethanol 2.48g/L) was observed as compared to 15.98g/L in the single stage chemostat with highest solvent productivity and solvent yield of 2.5g/Lh and of 0.35g/g, respectively. Maximum glucose utilization (83.21%) at a dilution rate of 0.051/h was observed as compared to 54.38% in the single stage chemostat., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Highlights • Use of Southern Pine wood sugars is demonstrated for production of solvents. • Fermentation of C6 and C5-rich streams is shown with productivity above 10 g/L/h. • Membrane assisted continuous fermentation is demonstrated for solvent production. • Use of butyl butyrate as an extractant for solvent extraction demonstrated. • Raffinate after solvent extraction was recycled back without any toxicity issues. Abstract The aim of this work was to demonstrate an industrially relevant pilot scale integrated process to produce butanol and other solvents from lignocellulosic sugars produced with AVAP® biomass fractionation technology from southern pine wood. The concentrated sugars were concurrently fermented using genetically engineered Clostridium acetobutylicum to n-butanol, acetone, isopropanol and ethanol in continuous membrane assisted cell recycle fermentation with steady-state solvent productivity exceeding 10 g/L/h. The solvents from the cell free permeate were recovered with extractant of butyl butyrate in a continuous liquid-liquid extraction column and aqueous product (raffinate) along with unused sugars, nutrients, and metabolic intermediates were recycled back to the fermentors. The total solvent yield approached 0.30 g/g sugars. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel modeling approach for Clostridium acetobutylicum solvenotogenic phase is proposed. [•] Continuous fermentation with immobilized cells is studied. [•] The solvent fluxes are predicted quantitatively. [•] A novel optimization procedure is introduced for constraint-based modeling. [ABSTRACT FROM AUTHOR]