Coproduction of Bioethanol with Other Biofuels

Abstract

Large scale transformation of biomass to more versatile energy carriers has most commonly been focused on one product such as ethanol or methane. Due to the nature of the biomass and thermodynamic and biological constraints, this approach is not optimal if the energy content of the biomass is supposed to be exploited maximally. In natural ecosystems, biomass is degraded to numerous intermediary compounds, and we suggest that this principle is utilized in biorefinery concepts, which could provide different fuels with different end use possibilities. In this chapter we describe one of the first pilot-scale biorefineries for multiple fuel production and also discuss perspectives for further enhancement of biofuel yields from biomass. The major fuels produced in this refinery are ethanol, hydrogen, and methane. We also discuss the applicability of our biorefinery concept as a bolt-on plant on conventional corn- or grain-based bioethanol plants, and suggest that petroleum-base refineries and biorefineries appropriately can be coupled during the transition period from a fossil fuel to a renewable fuel economy.

Energetics of methanogenic benzoate degradation by Syntrophus gentianae in syntrophic coculture

“…This assumption could be proved by showing that benzoate degradation resumed after removal of acetate from methanogenic cell suspensions that had ceased degrading benzoate. A comparable effect was seen in butyrate-degrading assocications (Ahring 8c Westermann, 1988). The same effect was observed with sulfate-reducing cocultures.…”

Plants as Sources of Energy

“…This not only uses fuel but increases the cost to the customer at the pump. In addition, the subsidies paid to fuel blenders and ethanol refineries have often been cited as the reason for driving up the price of corn, in farmers planting more corn, and the conversion of considerable land to corn production, which generally consumes more fertilizers and pesticides than many other land uses and also leads to serious environmental consequences such as dead zones in the Gulf of Mexico (Ahring and Westermann, 2007).…”

“…Critics and proponents both agree that there is a need for sustainable biofuels, using feedstocks that min-imize competition for prime croplands. These include farm, forest, and municipal waste streams; energy crops engineered to require less water, fertilizers, and pesticides; plants bred to grow on marginal lands; and aquatic systems such as algae used to produce alcohol, oil, and hydrogen gas (Ahring and Westermann, 2007). In short, biofuels, produced and utilized irresponsibly, could make our environmental/climate problems worse, while biofuels, done sustainably, could play a leading role in solving the energy supply/demand challenges ahead.…”

“…It should be noted here that, while most efforts have focused on acid pretreatment and enzymatic hydrolysis of lignocellulose, gasification of the lignocellulosic raw material into gaseous carbon monoxide and hydrogen is also useful for ethanol production (Ahring and Westermann, 2007). The gasification process does not rely on chemical decomposition of the cellulose chain (cellulolysis).…”

“…The gas is the result of two high-temperature reactions (above 700 • C or 1,292 • F): an exothermic reaction, where carbon burns to CO 2 ; and an endothermic reaction, where carbon reacts with steam to produce carbon monoxide (CO), hydrogen (H 2 ), and carbon dioxide (CO 2 ). Wood gas is flammable mainly because of the carbon monoxide and hydrogen content, but it also contains nitrogen and small amounts of methane, which is also flammable (Ahring and Westermann, 2007).…”