The Ohio State University
Biomass Energy and Biofuels: An Overview
Thanks to the industrial revolution that made it possible for exponential economic growth, human beings are currently living in an era characterized by the staggering amount of annual energy consumption. As we become extremely dependent on finite and diminishing energy sources such as coal, oil and gas, the Earth suffers from overexploitation and is at stake. The top priority of human beings thus becomes to transition to the use of renewable energy. Among the possible sources of renewable energy, biomass accounts for the largest proportion. Biomass is the biodegradable part of waste and remains resulting from agricultural, forestrial and related productions (de Vos, 2006). It is a major source of carbon that can renew itself over a short time span in order to maintain and supplement energy supplies (Klass, 1998). Biomass is recognized by many governments and policy makers as a feasible domestic energy resource that has the potential of reducing oil consumption and mitigating the dependency on imported oil (Klass, 1998). Historically, biomass has been one of the oldest forms of energy. Along with other renewables sources such as hydro, wind and solar energy, it was the dominant energy source globally, until it was replaced by coal in the beginning of the 18th century due to the increasing scarcity of wood fuel (Radetzki, 1997). Solar energy plays an indispensable role in the growth of biomass, as it is captured as fixed carbon in biomass through photosynthesis, during which carbon dioxide is converted to organic compounds (Klass, 1998). Normally, biomass is gathered to provide forage, food, fiber, and materials of construction or is left in the growth areas where the naturally decomposing biomass theoretically can be partially recovered as fossil fuels after a long period of time; alternatively, biomass and its processing waste could also be converted directly into synthetic organic fuels if suitable conversion processes were available (Klass, 1998). With efforts being put into producing and efficiently using biomass, it can be a universally available and flexible fuel source with most of the world's population residing in developing countries that usually lack fossil fuels and means to import them. There are several ways to convert biomass into energy. The most conventional and common way is through direct combustion, which is used to generate electricity. However, the efficiency of such way of electricity generation is low (Küçük & Demirbaş, 1997). Besides being used as a solid fuel, biomass can also be converted into liquid or gas to produce electricity, heat, chemicals, or fuels in gaseous and liquid forms (Demirbas, 2009). This process is known as thermochemical conversion, and it can be divided into three categories: pyrolysis, gasiﬁcation, and liquefaction (Demirbas, 2009). Pyrolysis occurs when organic matter thermally decomposes without oxygen being present or when considerably less oxygen is present than required for complete combustion (Demirbas, 2009). The fuel produced through pyrolysis is liquid pyrolysis oil, sometimes called bio-oil, which can be burned like fuel oil or reﬁned into chemicals and fuels. Gasiﬁcation is a process that involves mixing biomass with air, oxygen, or steam to convert it into gaseous products such as hydrogen, methane, and carbon dioxide (Swain, Das, & Naik, 2011). It can add value to low value materials by converting them to profitable fuels and products. Liquefaction consists of the thermal decomposition of feedstock large molecules into fragments of light molecules with a suitable catalyst being present, and then the unstable fragments can polymerize again into oily compounds (Alonso, Bond, & Dumesic, 2010). Another way to convert biomass is through biochemical conversion, the process by which biomass is broken down into gas, waste, and water by...