Traditionally, bio-butanol is produced with the ABE (Acetone Butanol Ethanol) process using Clostridium species to ferment sugars from biomass. However, the route is associated with some disadvantages such as low butanol yield and by-product formation (acetone and ethanol). On the other hand, butanol can be directly produced from ethanol through aldol condensation over metal oxides/ hydroxyapatite catalysts. This paper suggests that the chemical conversion route is more preferable than the ABE process, because the reaction proceeds more quickly compared to the fermentation route and fewer steps are required to get to the product.

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Sweet sorghum is a hardy crop that can be grown on marginal land and can provide both food and energy in an integrated food and energy system. Lignocellulose rich sweet sorghum bagasse (solid left over after starch and juice extraction) can be converted to bioethanol using a variety of technologies. The largest barrier to commercial production of fuel ethanol from lignocellulosic material remains the high processing costs associated with enzymatic hydrolysis and the use of acids and bases in the pretreatment step. In this paper, sweet sorghum bagasse was pretreated and hydrolysed in a single step using microwave irradiation. A conversion efficiency of 96% (0.82 g sugar/g bagasse) was obtained in a 5wt% sulphuric acid solution under 20 minutes of 180W microwave irradiation. An ethanol conversion efficiency of 98% (0.5 g ethanol/g sugar) was obtained after 24 hours of fermentation using a mixed culture of organisms to convert both hexose and pentose sugar in the broth. These results show the potential of producing 13 000 L/ha which is high enough to make the process economically attractive.

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