from conventional approach (coal, petrol, diesel, natural gas, hydrates, oil, shale, natural bitumen, extra heavy oil, etc.) is reducing day by day due to finite availability on this globe [1]. The reasons behind this energy crisis are given in Figure 1.1. With great benefits, the sources of conventional energy are also creating huge adverse impacts such as global warming and ocean acidification. In global warming, the average temperature of the atmosphere increases which in turn results in many climatic problems such as high speed of melting glaciers, intense storm threat, disbalances in atmosphere’s chemical composition, scarcity of water, possibility of fire in forests, etc. Ocean acidification is the consequence of some anthropogenic excess that is responsible for global warming in which there is release of more amount of carbon dioxide at faster rates. Due to this impact, the pH level of ocean lowers down causing the absorption of carbon dioxide in the ocean water forcefully creating more and more acids in the oceans.
Figure 1.1 Reasons for energy crisis on earth.
The fuels obtained from conventional sources of energy are costly in nature and also influence the global economy. To overcome all these kinds of concerns and keeping an important point of view in mind for the future, there is a great need to focus on research related to renewable sources energy for producing clean and environmental friendly fuels. The possible pathways to obtain fuels from conventional and renewable sources of energy are presented in Figure 1.2.
Figure 1.2 Distribution of sources of energy.
1.2 Renewable Energy Sources: The Great Hope of the Future
To reduce the harmful effects created by the exploitation of conventional sources of energy, there are two prime ways [2]:
1 (i) Find an alternate way to catch the carbon dioxide and release after treatment (generated by fossil fuel consumption) or do not let release carbon dioxide directly into the atmosphere.
2 (ii) To search for other alternative fuels which do not release carbon dioxide gas.
Among the available sources of renewable energy, solar energy and biomass are attaining great attention by researchers worldwide because the combination of solar energy and biomass provides a great platform to pursue a significant research for producing clean and pure renewable fuel.
In solar energy, photons are used to provide heat (low temperature) instead of thermal energy to carry out a chemical reaction and this process is known as photocatalysis (a subcategory of catalysis). There are basically three big advantages of photocatalysis valorization such as purification of air or water, production of clean fuel from renewable sources, and generation of quality chemicals. It is a well-known fact that the less quantity of absolutely freely available solar radiation on the surface is utilizing.
Still, many industries are dependent on the use of conventional fuels due to lack of research in the field of green chemistry in terms of photocatalysis. Plants manufacture their food due to photochemical reactions which is initiated by sunlight and considered as only renewable source for production of food for human beings and animals, conversion of energy into useful ways, and production of various chemicals. This book chapter discusses in brief about types of biomass and their conversion technologies for obtaining valuable chemicals due to photocatalytic valorization.
1.2.1 Biomass Types and Their Composition
Biomass can be obtained from nature directly in the form of waste. According to many varieties, biomass can be divided into several categories which are given below [3]:
1 (a) Biomass from wood (Stems, branches, sawdust, etc.)
2 (b) Herbaceous biomass (Flowers, grasses, straws, corncob, rice husk, etc.)
3 (c) Aquatic biomass (Marine and freshwater algae, microalgae, etc.)
4 (d) Animal and human waste biomass (Bones, various other manures, etc.)
5 (e) Contaminated biomass and industrial biomass wastes (semi-biomass: Municipal solid wastes, fiberboard, plywood, etc.)
6 (f) Biomass mixture.
Feedstocks of biomass are divided into several analyses such as proximate, ultimate, and structural. The compositional values of various biomass types are given in Table 1.1 according to chemical/elemental analysis.
Table 1.1 Elemental and chemical composition of biomass types [4].
| Biomass groups/elemental composition | Wood biomass | Herbaceous biomass | Aquatic biomass | Animal and human waste biomass | Contaminated biomass and industrial biomass wastes | Biomass mixture |
|---|---|---|---|---|---|---|
| C (%) | 49–57 | 42–58 | 27–43 | 57–61 | 43–45 | 45–71 |
| O (%) | 32–45 | 34–49 | 34–46 | 21–25 | 36–41 | 16–46 |
| H (%) | 5–10 | 3–9 | 4–6 | 7–8 | 5–6 | 6–11 |
| S (%) | <1–1 | <1–1 | 1–3 | 1–2 | 0.25–0.4 | <1–2 |
| N (%) | <1–1 | <1–3 | 1–3 | 6–12 | 1.5–1.75 | 1–6 |
| VM (%) | 30–80 | 41–77 | 42–53 | 43–62 | 76–77.5 | 41–79 |
| FC (%) |