Comparison of energy efficiency and economics of process designs for biobutanol production from sugarcane molasses

Development of technologies for biobutanol production by fermentation has resulted in higher final butanol concentrations, less fermentation by-products and higher volumetric productivities during fermentation, together with less energy intensive separation and purification techniques. These new technology developments have the potential to provide a production process for butanol from sugarcane molasses that is economically viable in comparison to the petrochemical pathway for butanol production. This objective was investigated by developing process models to compare three different possible process designs for biobutanol production from sugarcane molasses. The first two process routes incorporate well established industrial technologies: Process Route 1 consisted of batch fermentation and steam stripping distillation, while in Process Route 2, some of the distillation columns were replaced with a liquid–liquid extraction column. Some of the best production strains in these process routes, which include Clostridium Acetobutylicum PCSIR-10 and Clostridium Beijerinckii BA101, can produce total solvent concentrations up to 24 g/L. Process Route 3 incorporated fed-batch fermentation and gas-stripping with CO2, an unproven technology on industrial scale. Process modeling in ASPEN PLUS® and economic analyses in ASPEN Icarus® were performed to determine the economic feasibility of these biobutanol production process designs. Process Route 3 proved to be the only profitable design in current economic conditions in South Africa. Improved fermentation strains currently available are not sufficient to attain a profitable process design without implementation of advanced processing techniques. Gas stripping is shown to be the single most effective process step of those evaluated in this study, which can be employed on an industrial scale to improve process economics of biobutanol production.