Economics of Butanol Production

In recent years a number of economic studies have been performed on the production of butanol from corn (Marlatt and Datta, 1986; Qureshi and Blaschek, 2000a; 2001a), whey permeate (Qureshi and Maddox, 1991b; 1992), and molasses (Qureshi and Maddox, 1991b; 1992). In these studies, it has been determined that distillative recovery of butanol from fermentation broth is not economical as compared to butanol derived from petrochemicals (current route). It has also been identified that new developments in process technology for butanol production from renewable substrates allows for a significant reduction in the price of butanol. The price of butanol derived from corn also depends upon the coproducts credit, which is significant. Currently, it is anticipated that the petrochemical industries would reduce the price of butanol in an attempt to prevent the fermen­tative production of butanol from being successful. At present, the petrochemical industries have a monopoly with respect to the butanol market.

To bring fermentatively derived butanol closer to commercialization and compete with petrochemically derived butanol, it is suggested that research be focused on the development of superior cultures (as compared to the existing strains: C. beijerinckii BA101 and C. acetobutylicum PJC4BK). These cultures produce total ABE on the order of 25-33 gL-1 (Formanek et al., 1997; Chen and Blaschek, 1999; Harris et al., 2000). Further improvements in ABE yield, which is 0.40-0.42 when using C. beijerinckii BA101, should also be examined. Other cultures have been reported to result in a product yield of approximately 0.30. Material balance suggests that approximately 53% of carbon is lost as CO2, indicating that only 47% of the substrate is directed for the product conversion.

Another problem with butanol fermentation is the inability of these cultures to use sugars derived from economically available substrates such as corn fiber hydrolysate (Ebener et al., 2003). As with corn fiber hydrolysate, it is anticipated that sugars derived from hydrolysed corn stalks, wheat straw, and rice husk would not be utilized without pretreatment of these substrates, which would further add to the processing cost. In order to meet these challenges, new strains capable of utilizing agricultural biomass derived sugars should be developed. Alternately, economic methods capable of removing inhibitors from the hydrolysates should be developed. Simultaneous saccharification and fermentation is another approach that should be investigated for this process.

CONCLUSION

The production of butanol via the fermentation route is a relatively complicated process because the solventogenic clostridia are obligate anaerobes and the fer­mentation product (butanol) is toxic to the producing cultures. The possibility of incorporating in-line product recovery processes such as liquid-liquid extraction, perstraction, pervaporation, and gas stripping has generated a lot of interest.

Simultaneous butanol fermentation and recovery has dramatically improved the productivity of butanol production from corn. By employing in-line recovery systems during butanol fermentation, substrate inhibition and butanol toxicity to the culture are drastically reduced. Given that butanol is an excellent potential fuel and the United States is rich in biomass, butanol production from corn has a bright future. As it is seen at this stage, the technology of butanol production from corn (and other substrates) is ready for commercialization; however, this also depends upon the fluctuations in crude oil prices.