Submitted to: Bioprocess and Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2005
Publication Date: 5/1/2005
Citation: Ezeji, T.C., Karcher, P.M., Qureshi, N., Blaschek, H.P. 2005. Improving performance of a gas stripping-based recovery system to remove butanol from Clostridium beijerinckii fermentation. Bioprocess and Biosystems Engineering. 27:207-214. Interpretive Summary: Studies were performed on energy efficient recovery of butanol (a superior liquid fuel to ethanol; currently 2.6 billion pounds of butanol are produced in the United States from petrochemical sources) from model (synthetic) solutions and fermentation broth. A simple technique called gas stripping was used for this purpose. The gases that were used for the recovery were produced (carbon dioxide and hydrogen) in the butanol fermentation system. The parameters that were studied included rate of gas recycle through the solution/fermentation broth and bubble sizes that were developed in the reactor. A higher gas recycle rate removed butanol faster than a lower gas recycle rate. Bubbles of smaller sizes were advantageous in recovering butanol efficiently from the model solution. However, smaller size bubbles created excessive foam during fermentation, thus requiring a high amount of antifoam addition to the reactor which affected butanol fermentation adversely. It was concluded that gas be recycled at a higher rate and bubbles of 5 mm diameter be produced. Mathematical equations were developed to test the system. This research will benefit U.S. corn growers/farmers.
Technical Abstract: The effect of bubble size on the ability of gas stripping to remove ABE from a batch bioreactor was tested using two different bubble delivery systems. An impeller and a gas sparger were used to produce a bubble population of 0.5-5 mm and <0.5 mm diameters, respectively. Gas stripping of butanol present in a solution containing 8 g dm**-3 was performed at either a 43 or 80 cm**3 s**-1 gas recycle rate. The results demonstrated that bubble sizes <0.5 mm to 5 mm had no effect on the stripping rate of butanol under the conditions tested. However, the stripping rate was seen to be proportional to the gas recycle rate. An experiment was carried out using a model solution containing ABE in proportions which are typical when employing Clostridium beijerinckii BA101. The presence of acetone and ethanol had no effect on the stripping rate of butanol. When the two gas delivery systems were used in a C. beijerinckii BA101 batch fermentation and recovery system, the bubbles produced by the gas sparger led to large amounts of foam in the reactor which required addition of high levels of antifoam. The solvent productivity of the bioreactor using impeller or sparger-based gas delivery systems was 0.47 and 0.25 g dm**3 h**-1, respectively. The low productivity observed when a sparger gas delivery system was used is attributed to toxic effect of high levels of antifoam.