A biofuel is made from a biological process known as carbon fixation. These biofuels are gotten from the conversion of biomass, solid biomass, liquid fuels as well as biogases. The biofuels are continued to be known because of the high prices of fossil fuels and also for the purposes of ensuring fuel security in various countries. (Caye, D. & Terry W.2008). The biofuels are produced from two distinct ways; that is through metabolic by-products or from living organisms. Examples of biofuels include; bioethanol which is an alcohol made from fermentation process. Another example of biofuels is biodiesel which is made from vegetable oils as well as animal fats. Biofuels have got several ways in which they are made. Therefore in this essay I am going to analyze few methods.
Biofuels are made from materials known as feedstock. This comprises mostly of crops or products mainly waste vegetable oil. (Mitchell, D. 2010). These materials are converted to biofuels or bioenergy. These feedstocks have got merits and demerits depending on what percentage of biofuel can be gotten from them.
Feedstocks can further be classified as first and second generation. The former refers to those which are widely grown by people and at the same time used for some other purposes. They are mostly used for food and feed production. (Lane, J. 2010). Hence, they serve the purpose of being used as food as well as to produce biofuels. The examples of first generation feedstock include maize and vegetables.
Second generation feedstocks are those which produces high percentage of biofuel but they are not widely grown. They are at times referred to conventional crops and they produce a lot of biofuels. Examples of second generation feedstock are mustard and cellulosic feedstocks. ( Lane, J. 2010).
This is a process which relies entirely on organic or fossil based carbonaceous materials and converts them into carbon dioxide, hydrogen and carbon dioxide. This is achieved by the reaction of the materials at a very high temperature of up to 700 °C without combustion process. The process takes place under controlled oxygen and steam and produces gas mixture known as syngas or producer gas which in itself is a fuel. (Caye, D. & Terry W. 2008). The energy which is gotten from both combustion and gasification is a source of renewable energy when the compounds which are gasified are obtained from biomass.
Gasification has the advantage of being efficient compared to direct combustion. This is because there is a possibility of it being combusted at very high temperatures or even in fuel cells. The thermodynamic to the efficiency which is pointed out by Carnot’s rule is very high. (Caye, D. & Terry W. 2008). The resultant gas known as syngas can be burned directly in gas engines or it can be used to manufacture methanol and hydrogen. This process uses waste materials which would otherwise be disposed off. The use of high temperatures ensures that corrosive as elements such as chloride and potassium are gotten ride of. This results to the production of clean fuel which is not problematic to the environment.
Gasification takes place in a gasifier in which several reactions take place. Firstly, the drying of the feedstock takes place at a temperature of 100°C.This followed by the combustion process which depend on the properties of carbonaceous materials. The combustion equation is as follows. (Mitchell, D. 2010). .The gasification process takes place when carbon reacts with steam to produce hydrogen and carbon monoxide.The equation is as follows .The final reaction is the water gas shift reaction which balances the concentration of carbon monoxide,steam,carbon dioxide and hydrogen.(Pimentel, D. &Patzek, T. W. 2005).
The reason why a limited a mount of oxygen is added to the gasifier is to enable the burning of organic materials to convert them to hydrogen and carbon dioxide.more reaction takes place when the resultant carbon dioxide and water inform of steam reacts to form methane and carbon dioxide.The reaction rates can be increased by adding catalysts such as the reaction moves closer to equilibrium with a fixed a mount of time. (Li, H. & Cann, A. F. 2010).
This process involves the use of catalysts and transesterification to produce biodiesel. There are two processes involved here. Depolymerization which creates renewable diesel and the other one is hydrotreating which produces green diesel or hydrogenation derived renewable diesel. Hydrotreating involved the use of hydrogen and catalysts.
This is one of the methods used to make biofuels. It involves burning of biomass such as dead trees in the absence of oxygen.This is a very important chemical reaction which takes place before combustion and gasification processes. (Li, H. & Cann, A. F. 2010). It occurs very fast in approximately within two seconds. The products of this process are gases such as methane, hydrogen, carbon monoxide, and carbon dioxide. Others include biochar and biodiesel. This process depends on the thermal environment and temperature. At low temperatures, pyrolysis yields biochar, and when the temperatures are too low, the process yields bio-oil and at very high temperatures it gives mainly gases .Bio-oil can as well be produce at high heating rates and in intermediate temperatures. Pyrolysis process is endothermic and transfer of heat takes place at a high rate.(Pimentel, D. &Patzek, T. W. 2005). This process gives attractive way of converting solid biomass into a liquid which can be easily stored and transported and can as well be used to produce heat, power and chemicals.
Feedstock for Pyrolysis Pyrolysis process has got many types of feedstock to choose from. The process is dependent on the moisture found in feedstock. Therefore it needs feedstock with high content of moisture. Water is produced mainly at high moisture content while at low moisture contents, there is a possibility of dust being produced rather than oil. (Li, H. & Cann, A. F. 2010). The feedstocks are first being subjected to drying before pyrolysis takes place. Another factor which must be considered when choosing feedstock is particle sizes. Small size particles are required since they offer easy transfer of heat within the particles. This means that large particles will have to be reduced before they are used for pyrolysis process.
Pyrolysis processes can be classified into two distinct categories. These categories are fast pyrolysis and slow pyrolysis.(Pimentel, D. &Patzek, T. W. 2005). The method which is widely used is fast pyrolysis because slow pyrolysis takes a lot of time before it yields the final product. In addition, fast pyrolysis produces high content of bio-oil which is 60%.Pyrolysis involves very high temperatures and very fine feedstock. It also entails control reaction temperature and residence time of less than one second in the reactor. Finally, cooling of pyrolysis vapor must also be considered at the end.
Biofuels have got very many competitive advantages over fossil fuels. One of them is that they are renewable. As long as there is soil and rain, feedstock can be planted and harvested for use. This is in contrary with fossil fuels such as natural gas and oil which takes several years before they are formed. (Li, H. & Cann, A. F. 2010) Research has it that fossil fuels will eventually disappear and there is need to shift to fossil fuels. Biofuels do not interfere with the environment since they burn cleaner. Even though they contain some sulphure; the percentage is very small and can be neglected. With biofuels, energy security can be assured since they are renewable and cannot be finished. With fossil fuels, the reserves which have not been exploited are few and furthermore, drilling tampers with the environment and poses danger to the wild animals. Since feedstock used to make biofuels comes from crops such as maize, it encourages farming and at the same time, food security is ensured. (Pimentel, D. &Patzek, T. W. 2005).
Compared to fossil fuels, biofuels are easy to transport and also to store. They are not bulky and require less space .Consequently, they can be used in a very limited space.
Conclusions Biofuels are used widely due to the fact that they are efficient and environmentally friendly. Most importantly, they use waste products such as agricultural residues, wood wastes and municipal solid waste to produce clean energy. They continue to replace fossil fuels which not friendly to the environment. The technologies involved as discussed above are simple and easy to use. (Li, H. & Cann, A. F. 2010)
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