The strains of bacteria utilized for industrial production of butanol were acetone-butanol producing bacteria and butanol-isopropanol producting bacteria which produce butanol and isopropanol, a reduced product of acetone. The reaction pathway is shown in Fig. 5.3.1. Glucose is decomposed to pyruvate, acetyl-CoA, and acetoacetyl-CoA via EMP pathway, and finally acetone, butanol, isopropanol and ethanol are produced. The stoichiometrical equation of acetone-butanol fermentation is shown in Eq. 5.3.1.

95C6H12O6 -► 6OC4H9OH + 3OCH3COCH3 + 1OC2H5OH + 220CO2 + 120H2 + 30 H2O (5.3.1) In acetone-butanol fermentation, butanol is gradually accumulated and cause production

inhibition at more than 3 kg/m3 (g/L) of the butanol concentration. When the production inhibition occurs, the growth of bacteria cells, consumption of substrates, and accumulation of products are suppressed. Final concentration of butanol reaches about 30 kg/m3 (g/L). After fermentation, the culture solution is distilled and products are separated by the difference in their boiling points, e. g. acetone (BP 56.3°C), ethanol (BP 78.3°C) and butanol (BP117°C).

4.1.6 Energy efficiency of acetone-butanol fermentation.

From Eq. 5.3.1, 60 mol butanol (170 MJ), 30 mol acetone (54 MJ), 10 mol ethanol (14 MJ) and 120 mol hydrogen (34 MJ) are produced from 95 mol glucose (273 MJ) in acetone-butanol fermentation. Almost all energy in glucose can be moved to butanol, acetone, ethanol and hydrogen.