The general formula of the organic material produced during photosynthesis process is (CH2O)n which is mainly carbohydrate material. Some of the simple carbohydrates involved in this process are the simple carbohydrates glucose (C6H12O6) and sucrose (C12H22O11) and constitute biomass, which is a renewable energy source due to its natural and repeated occurrence in the environment in the presence of sunlight. The amount of biomass that can be grown certainly depends on the availability of sunlight to drive the conversion of carbon dioxide and water into carbohydrates. In addition to limitations of sunlight, there is a limit placed by the availability of appropriate land, temperature, climate and nutrients, namely nitrogen, phosphorus and trace minerals in the soil.
Biomass is clean for it has negligible content of sulfur, nitrogen and ash, which give lower emissions of sulfur dioxide, nitrogen oxides and soot than conventional fossil fuels. Biomass resources are many and varied, including (i) forest and mill residues, (ii) agricultural crops and waste, (iii) wood and wood waste, (iv) animal waste/s, (v) livestock operation residues, (vi) aquatic plants, (vii) fast-growing trees and plants, (viii) municipal waste, and (ix) and industrial waste. The role of wood and forestry residues in terms of energy production is as old as fire itself and in many societies wood is still the major source of energy. In general, biomass can include anything that is not a fossil fuel that is based on bio-organic materials other than natural gas, crude oil, heavy crude oil, extra heavy crude oil and tar sand bitumen (Lucia et al., 2006; Speight, 2008, 2011c; Lee and Shah, 2013).
There are many types of biomass resources that can be used and replaced without irreversibly depleting reserves and the use of biomass will continue to grow in importance as replacements for fossil fuel sources and as feedstocks for a range of products (Narayan, 2007; Speight, 2008, 2011c; Lee and Shah, 2013). Some biomass materials also have particular unique and beneficial properties which can be exploited in a range of products including pharmaceuticals and certain lubricants. In this context, the increased use of biofuels should be viewed as one of a range of possible measures for achieving self-sufficiency in energy, rather than a panacea to completely replace the fossil fuels (Crocker and Crofcheck, 2006; Worldwatch Institute, 2006; Freeman, 2007; Nersesian, 2007).
Worldwide biofuels production is still small at approximately 70 billion (70 x 109 tons) oil equivalent. With the volatility of crude oil prices of crude oil, the relative competitiveness of renewable and alternative fuels is drastically improving. Further, technological advances in the alternative renewable energy areas as well as public awareness backed by strong governmental supports and incentives, make the outlook of the alternative and renewable energy very promising (Energy Security Leadership Council, 2013). There are seven countries that can be considered the leaders in biofuels (particularly bioethanol) production. The leaders are (as a percentage of the total production): United States (43.5%), Brazil (24%), France (3%), Germany (4%), Argentina (3%), China (3%), and Indonesia (2.5%). But this still represents minor amounts of the total energy consumption in these countries.
Ethanol (bio-ethanol) from corn has been used in an accelerated pace as gasoline blending fuel as well as a new brand of fuel E85, which contains 85% ethanol and 15% gasoline. The majority of the gas stations in the United States supply E85 fuels regularly and many automakers are offering multiple lines of automobiles that can be operated on either conventional gasoline or E85. This not only contributes to cleaner burning fuels but also supplements the amount of gasoline sold.
One extremely important aspect of biomass use as a process feedstock is the preparation of the biomass (also referred to as biomass cleaning or biomass pretreatment), the removal of any contaminants that could have an adverse effect of the process and on the yields and quality of the products. Thus, feedstock preparation is, essentially, the pretreatment of the biomass feedstock to assist in the efficiency of the conversion process. In fact, pretreatment of biomass is considered one of the most important steps in the overall processing in a biomass-to-biofuel program and can occur using acidic or alkaline reagents (Table 1.3) as well as using a variety of physical methods (Table 1.4) and the method of choice depends very much upon the process needs. With the strong advancement in developing lignocellu-lose biomass-based refinery and algal biomass-based biorefinery, the major focus has been on developing pretreatment methods and technologies that are technically and economically feasible (Pandey et al., 2015).
Table 1.3 Acidic and alkaline methods for biomass treatment.
| Method | Conditions | Outcome |
| Acid based methods | Low pH using an acid (H2SO4, H3PO4) | Hydrolysis of the hemicellulose to monomer sugars |
| Minimizes the need for hemicellulases | ||
| Neutral conditions | Steam pretreatment and hydrothermolysis | |
| Solubilizes most of the hydrocarbons by conversion to acetic acid | ||
| Does not usually result in total conversion to monomer sugars | ||
| Requires hemicellulases acting on soluble oligomers | ||
| Alkaline methods | Leaves a part of the hydrocarbon in the solid fraction | |
| Requires hemicellulases acting hydrocarbons |
Table 1.4 Summation of the methods for the pretreatment of biomass feedstocks.
| Physical methods | Miscellaneous methods |
| Milling: | Explosion:* |
| - Ball milling | - Steam, NH3, CO2, SO2, Acids, Alkali |
| - Two-roll milling | - NaOH, NH3, (NH4)2SO3 |
| - Hammer milling | Acid: |
| Irradiation: | - Sulfuric, hydrochloric, and phosphoric acids |
| - Gamma-ray irradiation | Gas: |
| - Electron-beam irradiation | - Chlorine dioxide, nitrous oxide, sulfur dioxide |
| - Microwave irradiation | Oxidation: |
| Other methods: | - Hydrogen peroxide |
| - Hydrothermal | - Wet oxidation |
| - High pressure steaming | - Ozone |
| - Extrusion | Solvent extraction of lignin: |
| - Pyrolysis | - Ethanol-water extraction |
| - Benzene-water extraction | |
|
- Butanol-water
|