Production of High-Value Medium-Chain Fatty Acids from Cellulosic Biomass Via Mixed-Culture Fermentation

To create sustainable system and reduce the dependency on fossil fuels, it is important to produce chemicals and fuels from renewable sources. Carboxylate platform can produce short and medium-chain fatty acids in inexpensive way, which can be further converted into fuels and chemicals. Medium-chain fatty acids (MCFA, e.g., valeric, caproic, heptanoic, caprylic acid) are more valuable than short-chain fatty acids (SCFA, e.g., acetic, propionic, butyric acid). SCFAs are major products in methane-inhibited mixed-culture anaerobic fermentation. By feeding ethanol to the fermentor, MCFA formation is enhanced through chain elongation. Microorganisms such as Clostridium kluyveri elongate short-chain acids by combining them with ethanol. To maximize MCFA production, effect of ethanol concentration and temperature were investigated in the mixed-culture fermentation. At 10 g/L ethanol concentration, 13.3 g/L MCFA was formed and caproic acid was the major product (approximately 10 g/L). At low temperatures (≤40 °C), chain elongation is favored and does not occur at 55 °C. Based on these results, a process strategy is proposed to maximize the MCFA production.