In the wake of rising prices and unstable supply besides environmental issues, renewed attention has been paid to shifting away from the use of petroleum based fuels. The world’s energy demand is commencing its dependency on alternative fuels. Such alternative fuels in use today consist of bio-alcohols (such as ethanol), biomass, and natural oil/fat-derived fuels. In search for new energy sources, much attention is focused on biodiesel as a reliable and renewable resource that is to satisfy a significant part of the energy demands (Fan et al., 2009).
Currently, biodiesel is considered a promising alternative due to its renewability, better gas emissions, non toxicity and its biodegradability (Akbar et al., 2009). Biodiesel is defined as mono alkyl esters of long chain fatty acids derived from vegetable oils or animal fats (Knothe et al., 2002). The term ‘mono alkyl esters’ indicates that biodiesel contains only one ester linkage in each molecule. Plant oils and animal fats (triglycerides) contain three ester linkages between fatty acids and glycerol which makes them more viscous.
Generally, it has been observed that transesterification of triglycerides to alkyl esters (biodiesel) generates a mixture that approximates the properties and performance of petroleum diesel fuel, which allows it to be used directly as substitute fuel without modifications or as blending agents for diesel fuel (Bello and Makanju, 2011).
Various vegetable oils are potential feedstock for the production of fatty methyl esters or biodiesel but the quality of the fuel is affected by the oil composition (Akbar et al., 2009). Research results abound in literature on the production of biodiesel through transesterification of edible and non edible oil from different parts of the world (Abayeh et al., 2007; Berchmans and Hirata, 2008) The production of biodiesel from edible vegetable oils has progressively stressed food uses, price, production and availability of oils (Rashid et al., 2008). New oil-seed crops that do not compete with traditional food crops are needed to meet existing energy demands (Xu and Hanna, 2008). In Nigeria, there is an abundance of oil seeds that are relatively unexplored (Abayeh et al., 2007; Eze, 2012), with no competing food uses.
1.1 BACKGROUND OF STUDY
The recent research developments in the exploitation of biodiesel provide a reliable platform for adoption of biodiesel as an alternative energy source. The following could be key reasons to adopt and promote biodiesel production and research;
1.1.1 Availability of feed-stocks
The availability of vast biodiesel resources which include crude oil from avocado pear fruit, Beni seed, soybean, castor seed, cotton seed etc has a reliable potential for production of biodiesel that will immensely help in its utilization an alternative energy source.
1.1.2 Global warming
Another key justifiable reason for embracing and promoting the use of biodiesel is Global warming. This is the increase in the average temperature of the atmosphere, oceans and land mass of the earth (Iduyisi et al, 2012)
Environment Researchers have found out that global warming is humanly induced. Its chief cause includes burning of fossil fuels such as coal, oil and natural gas by automobiles which continually release carbon dioxide, oxides of nitrogen etc into the atmosphere. According to UNDP 2007/2008 Human Development Report, the world temperature has increased around 0.70C since the advent of industrialization and the rate is skyrocketing yearly. It is argued that bio-fuel is environment friendly because carbon dioxide released from burning bio-fuels is balanced by carbon dioxide intake by growing plants from where bio-fuels are made.
1.1.3 Greenhouse effect
Biodiesel has the ability to reduce green house gas emissions when compared to those of fossil fuels. Greenhouse effect is the process that occurs when atmospheric greenhouse gases absorb thermal radiation and re-radiates in all direction, leading to the average increase in the surface temperature. Carbon dioxide emitted by engines is the primary source of greenhouse gas emissions. Burning of biodiesel produces carbon dioxide just as fossil fuels but the former is more advantageous as the carbon dioxide released from burning biodiesel is balanced by carbon dioxide intake by growing plants from where biodiesel are made through the process of photosynthesis.
Biodiesel has a higher cetane rating than fossil fuels do. As a result, biodiesel has a higher performance and clean up emissions. When compared to petro diesel, biodiesel contains fewer aromatic hydrocarbons. It has it capacity of reducing direct tailpipe emission of particulates to the environment.
1.1.5 Safety and stability
Biodiesel is safer to handle than petroleum diesel fuel because of its low volatility. Due to thehigh energy content of all liquid fuels, there is a danger of accidental ignition when the fuel isbeing stored, transported or transferred. The possibility of having an accidental ignition is relatedin part to the temperature at which the fuel will create enough vapours to ignite, known as theflash point temperature. The lower the flash point of a fuel, the lower the temperature at which itwill form a combustible mixture (Adebayo et al., 2011). For example, petroleum diesel has aflash point of 640C, which means that it can form a combustible mixture at temperature as lowas 640C. Biodiesel on the other hand has a flash point of over 1500C, meaning it cannot form acombustible mixture until it is heated well above the boiling point of water (Rodriques-Acosta etal., 2010). It is rare that biodiesel fuel is subjected to these types of condition, making biodieselquite safe to store, handle and transport. Biodiesel is therefore classified as a non-flammableliquid.
1.2 Disadvantages of biodiesel
Although the advantages make biodiesel seem very appealing, there are also some disadvantageswhen using biodiesel. Due to the high oxygen content, it releases relatively high NOx levelsduring combustion. But this can be reduced to below petroleum diesel levels by adjusting enginetiming and using a catalytic converter (Rao, 2011). Storage conditions of biodiesel must bemonitored strictly as biodiesel has a lower oxidative stability (Afolabi, 2008). Biodiesel haslower temperature flow properties than petroleum diesel which means it will crystallize into a gelat low temperatures when used in its pure form (Abayeh et al., 2007). Biodiesel is also moresusceptible to degradation, which is promoted by the presence of oxygen, high temperatures, andthe presence of certain metals (Leiner, 1980).
1.3 BIODIESEL LITERATURE
Bio-diesel is the mono alkyl esters of long chain fatty acids obtained when vegetable oil is converted by the process of transesterification which meets the registration for fuels and fuel additives established by the Environmental Protection Agency (EPA) and American Standard of Testing and Materials (ASTM). (Radich, 2003).
This involves the reaction between triglyceride and methanol to give the fatty acid methyl ester (biodiesel) and glycerol.
Biodiesel and petroleum diesel are not chemically similar. Biodiesel is composed of long-chainmethyl esters, whereas petroleum diesel is a mixtureof aliphatic and aromatic hydrocarbons thatcontain approximately 10 – 15 carbons. Because biodiesel and petroleum diesel have differingchemical compositions, they have differing fuel properties.
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