Even though biomass includes all plants and plant-derived materials, all plant matter is not equal as biomass feedstock for bioenergy and biofuels production. The success of the biofuels and bioenergy industry depends on the quality and quantity of biomass available as well as the ability to utilize it cost-efficiently to produce biofuels and bioenergy [12]. Various factors are taken into consideration for suitability determination and choice of biomass for the biofuels program and they include:

• Sustainable feedstock production

• Arable land requirement

• Feedstock logistics

• Regional strength

• Food crops or not

• Grains or nongrains

• Feedstock properties and compositions

• Pretreatment cost

• Availability of efficient conversion/transformation technology

• Feedstock cost

• Capital investment and operating cost involved

• Environmental benefits

• Desirable biofuel products and their values

A variety of biomass feedstock can be converted into alternative trans­portation fuels. Currently, a dominant majority of biofuels produced in the United States are corn ethanol. Although corn is an excellent source of starch which can be easily converted into fuel ethanol and is also the most abun­dantly produced U. S. crop, the corn feedstock also has concerns of being a food crop and demanding high feedstock cost. More R&D is being focused on the development of cellulosic feedstock such as corn stover, switchgrass, and woody cellulose. Figure 1.2 shows resource-based biorefinery pathways, as presented in the Biomass Program’s website, U. S. DOE, Office of Energy Efficiency and Renewable Energy [12]. The Biomass Feedstock Platform has three phases of program foci in its R&D Platform and they are

• In the immediate and near term, it will focus on the sustainable pro­duction, collection, and use of readily available low-cost agricultural residues and industrial wastes.

• In the near to mid-term, it will address additional agricultural and for­estry residues and a potentially few dedicated energy crops.

• In the longer term, it will involve the development and use of both herbaceous and woody dedicated energy crops.

FIGURE 1.2

Resource-based biorefinery pathways by U. S. DOE, EERE. (From U. S. Department of Energy, 2011. Energy Efficiency & Renewable Energy, Biomass Program. Biofuels, Biopower, and Bioproducts: Integrated Biorefineries. http://www1.eere. energ y. gov/biomass/in dex. html.)

Biofuels are classified into two broad categories, namely first-generation and second-generation biofuels, based on the kinds of feedstock as well as the types of process technologies applied or applicable. First-generation (1G) biofuels refer to fuels that have been derived from biological sources such as starch, sugar, animal fats, and vegetable oil. These conventional biofuels are produced from oil crops, sugar crops, and cereal crops, using estab­lished technology. Some of the most typical types of first-generation biofu­els include vegetable oils, conventional biodiesel, bioalcohols, biogas, and biosyngas. On the other hand, second-generation (2G) biofuels are derived from cellulosic materials (lignocellulosic feedstock). These raw materials for 2G biofuels may result in more biofuel per unit area of agricultural land and also require less chemical and energy input for production and har­vesting, which in turn results in a higher net energy yield [9]. As such, raw materials for 2G biofuels may be considered more sustainable than those for 1G biofuels and do not create the issues of "food versus fuel," either. Many second-generation biofuels are under active research and develop­ment and include cellulosic ethanol, algae fuel, biohydrogen, biomethanol, bio-dimethylether (bio-DME), Fischer-Tropsch diesel, 2,5-dimethyl furan (DMF), mixed alcohols, and wood diesel. The second-generation biofuels are also referred to as advanced sustainable biofuels.