Biofuel production biofuels

Xu P, Koffas MA (2010) Metabolic engineering of Escherichia coii for biofuel production. Biofuels 1 493-504... 

U.S. capacity for producing biofuels manufactured by biological or thermal conversion of biomass must be dramatically increased to approach the potential contributions based on biomass availabiUty. For example, an incremental EJ per year of methane requires about 210 times the biological methane production capacity that now exists, and an incremental EJ per year of fuel ethanol requires about 14 times existing ethanol fermentation plant capacity. 

The need to meet environmental regulations can affect processing costs. Undesirable air emissions may have to be eliminated and Hquid effluents and soHd residues treated and disposed of by incineration or/and landfilling. It is possible for biomass conversion processes that utilize waste feedstocks to combine waste disposal and treatment with energy and/or biofuel production so that credits can be taken for negative feedstock costs and tipping or receiving fees. 

Alternatively, short-rotation hybrid poplar and selected grasses can be multicropped on an energy plantation in the U.S. Northwest and harvested for conversion to Hquid transportation fuels and cogenerated power for on-site use in a centrally located conversion plant. The salable products are Hquid biofuels and surplus steam and electric power. This type of design may be especially useful for larger land-based systems. 

Table 32. Biofuels Utilization and Production and Biomass-Fueled Electric Power Plant Capacities in the United States ...

Capacity Limitations and Biofuels Markets. Large biofuels markets exist (130—133), eg, production of fermentation ethanol for use as a gasoline extender (see Alcohol fuels). Even with existing (1987) and planned additions to ethanol plant capacities, less than 10% of gasoline sales could be satisfied with ethanol—gasoline blends of 10 vol % ethanol the maximum volumetric displacement of gasoline possible is about 1%. The same condition apphes to methanol and alcohol derivatives, ie, methyl-/-butyl ether [1634-04-4] and ethyl-/-butyl ether. 

Physical Properties. Physical properties of waste as fuels are defined in accordance with the specific materials under consideration. The greatest degree of definition exists for wood and related biofuels. The least degree of definition exists for MSW, related RDF products, and the broad array of ha2ardous wastes. Table 3 compares the physical property data of some representative combustible wastes with the traditional fossil fuel bituminous coal. The soHd organic wastes typically have specific gravities or bulk densities much lower than those associated with coal and lignite. 

Fig. 7. Biofuels and biomass electricity production. Courtesy of the National Renewable Energy Laboratory.

The sources of biofuels and the methods for bioenergy production are too numerous for an exliaustive list to be described in detail here. Instead, electricity production using direct combustion, gasification, pyrolysis, and digester gas, and two transportation biofuels, ethanol and biodiesel, are discussed below. 

Most electricity from biofuels is generated by direct combustion. Wood fuels are burned in stoker boilers, and mill waste lignin is combusted in special burners. Plants are generally small, being less than 50 MW in capacity. There is considerable interest in combustion of biomass in a process called cofiring, when biomass is added to traditional fuels for electricity production. Cofiring is usually done by adding biomass to coal, but biomass also can be cofired with... 

Biofuel generation from sweet sorghum Fermentative hydrogen production and anaerobic digestion of the remaining biomass. Biores. Technol. 99 (1), 110-119. 

Biofuels rely on organic feedstocks such as plant oil, food wastes and trees but their larger scale and rapid exploitation to meet government targets is stressing large areas of land and associated systems such as water, food production and recreation. A truly sustainable future for biofuels and other eco-system exploitation for industrial value requires a better understanding and more quantitative assessment of a number of critical issues ... 

Several practices have been suggested to reduce enteric CH4 emissions and emissions from wasfe. These include improving feeding practices, use of diefary supplemenfs, vaccines, improving livestock management, improving manure management, and production of biofuels. 

Chappie, C. Ladisch, M. Meilan, R. Loosening lignin s grip on biofuel production. Nat. Biotechnol. 2007, 25, 746-748. 

---