Production of Branched Chain Higher Alcohols from Cellulosic Sugars

The reliability of fossil fuels for the world’s energy needs is a big question due to environmental concerns along with the depletion of its sources. So, the increasing demand for energy is leading to the development of alternative sources of energy; among them, biofuels are getting increased emphasis as these are sustainable. Biofuels research and development through the first, second, third, and fourth generations have accumulated a lot of insights and new challenges. These insights include the possible utilization of branched-chain higher alcohols (BCHA) as a biofuel. BCHA, as fuel alcohols in ethanol fermentation, emerged as the main product during the years due to their better fuel properties than ethanol. Major advantages of BCHA include higher octane number, lower hygroscopicity, higher energy density, and lower vapor pressure. Its blending ability is also high due to lower oxygen content. In this chapter, four BCHA, that is, isobutanol, isopropanol, 3-methyl-1-butanol, and 2-methyl-butanol, are discussed. Chemical synthesis as well as microbial production of each one of them is described. Metabolic pathways for its production are depicted and production of these alcohols from renewable substrates (such as cellulose) has also been discussed briefly. Current developments in metabolic engineering and fermentative processes provide a lot of promising results. However, effective addressing of challenges for yield enhancement and cost reduction is required for commercial production of BCHA.