5-15: Biological conversion of Algefiber® to carboxylic acids for chemical upgrading to mixed alcohols liquid biofuel

Biomass is a renewable resource which can be used for energy production as a substitute for fossil fuels. Conversion of terrestrial lignocellulosic biomass in to ethanol is the widely known conventional process to produce liquid biofuel. However, the conversion of marine macro algae to biofuel draws attention at present. In this study, using the MixAlco™ process, carboxylic acids were produced from Algefiber^® which is an alkaline-pretreated waste biomass from carrageenan extraction process. Carboxylic acids make up a platform of chemical intermediates, which can be converted in to mixed alcohol fuels and chemicals.

The acidogenic fermentation of Algefiber^® carried out under conditions of inhibited methanogenesis at two temperatures, 35°C and 55°C. Produced carboxylic acids ranged from one to seven carbons (Formic acid to Heptanoic acid). Acetic acid was the prominent acid produced at both temperatures, though mesophilic temperature (35°C) gave a higher carboxylic acid yield and a higher percentage of longer chain acids. A combination of Algefiber^® and chicken manure gave the highest acid concentration of 18 g/L at 15 % solid concentration. Then, carboxylate salts of the fermentation-derived acids were thermally decomposed in to mixture of ketones which had acetone, 3-pentanone, 2-hexanone, 3-heptanone, 2-heptanone, and 4-octanone as major products. These ketones can be hydrogenated to form the longer chain mixed alcohols which can be used as a liquid biofuel. These mixed alcohols contain higher energy density than ethanol due to presence of longer chain alcohols such as propanol, butanol etc.