ORIGINAL PAPERS Thaddeus C. Ezeji Æ Patrick M. Karcher Nasib Qureshi Æ Hans P. Blaschek Improving performance of a gas stripping-based recovery system to remove butanol from Clostridium beijerinckii fermentation Received: 3 November 2004 / Accepted: 21 January 2005 / Published online: 2 April 2005 Ó Springer-Verlag 2005 Abstract The effect of factors such as gas recycle rate, bubble size, presence of acetone, and ethanol in the solution/broth were investigated in order to remove butanol from model solution or fermentation broth (also called acetone butanol ethanol or ABE or solvents). Butanol (8 g L 1 , model solution, Fig. 2) stripping rate was found to be proportional to the gas recycle rate. In the bubble size range attempted (<0.5 and 0.5–5.0 mm), the bubble size did not have any effect on butanol removal rate (Fig. 3, model solution). In Clostridium beijerinckii fermentation, ABE productivity was reduced from 0.47 g L 1 h 1 to 0.25 g L 1 h 1 when smaller (<0.5 mm) bubble size was used to remove ABE (Fig. 4, results reported as butanol/ABE concentration). The productivity was reduced as a result of addition of an excessive amount of antifoam used to inhibit the production of foam caused by the smaller bubbles. This suggested that the fermentation was negatively affected by antifoam. Keywords Butanol fermentation Æ Gas bubble size Æ Selectivity Æ Gas recycle rate Æ Stripping rate List of symbols A Area of the bubble (cm 2 ) a Interfacial area (cm 2 ) b Powers function constants (no units) c 10 Bulk liquid concentration of butanol (mol cm 3 ) C s Solvent concentration in the aqueous phase (mg cm 3 or g L 1 or kg m 3 ) C s0 Zero time solvent concentration in the aqueous phase (mg cm 3 or g L 1 or kg m 3 ) D Diffusion coefficient (cm 2 s 1 ) H Henry’s law constant (atm cm 3 mol 1 ) H c Dimensionless Henry’s law constant (no units) k g Gas film mass transfer coefficient for the solvent (cm s 1 ) k p Gas film mass transfer coefficient (based on partial pressure (mol cm 2 s 1 atm 1 ) k l Liquid film mass transfer coefficient for the solvent (cm s 1 ) K p Overall gas side mass transfer coefficient (mol cm 2 s 1 atm 1 ) K s a Gas stripping rate constant for solvent in the aqueous phase (s 1 or h 1 ) L Liquid film thickness (cm, usually 0.01 cm) m Power function constant (no units) N 1 Flux of butanol (mol cm 2 s 1 ) p 10 Partial pressure of butanol in the bulk gas bubble (atm) p 1 * Hypothetical partial pressure of butanol in equilibrium with the bulk liquid concentration (atm) Q Gas flowrate (cm 3 s 1 ) r Radius of the bubble (cm) R Universal gas constant (82 cm 3 atm mol 1 K 1 ) R p Rate of production of solvent (mg cm 3 s 1 or gL 1 h 1 or kg m 3 h 1 ) R s Rate of solvent stripping from the aqueous phase into the gas phase (mg cm 3 s 1 or gL 1 h 1 or kg m 3 h 1 ) t Time (s or h) Mention of trade names of commercial products in this article is solely for the purpose of providing scientific information and does not imply recommendation or endorsement by the United States Department of Agriculture. T. C. Ezeji Æ P. M. Karcher Æ H. P. Blaschek (&) Biotechnology and Bioengineering Group, Department of Food Science and Human Nutrition, University of Illinois, 1207 W Gregory Drive, Urbana, IL 61801, USA E-mail: blaschek@uiuc.edu Tel.: +1-217-3338224 Fax: +1-217-2442517 N. Qureshi United States Department of Agriculture, National Center for Agricultural Utilization Research, Fermentation Biotechnology, 1815 N University Street, Peoria, IL, 61604 Bioprocess Biosyst Eng (2005) 27: 207–214 DOI 10.1007/s00449-005-0403-7