CHAPTER ONE

INTRODUCTION

There is a need for alternative energy sources to petroleum-based fuels due to the depletion of the worlds’ petroleum reserves,global warming and environmental concerns. American standard testing and materials defined biodiesel as a fuel composed of monoalkyl esters of long-chain fatty acids derived from renewable vegetable oils or animal fats and meets the requirements of ASTM 6751(ASTM, 2008). Ozone depletion,global warming,greenhouse gases concerns have promoted biodiesel as an alternative renewable and eco-friendly fuel.The concept of biofuel is notnew. Rudolph Diesel was the first to use a vegetable oil(peanut oil) in a diesel engine in 1911(Akoh et al ., 2007 ; Antczak et al., 2009). The use of biofuels in place of conventional fuels would slow the progression of global warming by reducing sulphur,carbon oxides and hydrocarbon emissions (Fjerbaek et al., 2009). Because of its high viscosity and low volatility, the direct use of vegetable oil in diesel engines can cause problems including;high carbon deposits,scuffing of engine liner,injection nozzle failure,gum formation,lubricating oil thickening,high cloud and pour point (Fukuda et al., 2001; Murugesan et al.,2009). In order to avoid these problems, the feedstock is chemically modified to its derivatives which have properties more similar to conventional diesel (Fukuda et al., 2001).Transesterification is the process by which biodiesel is produced,in this process vegetable oil reacts with an alcohol(methanol) to form methyl ester (biodiesel) and another alcohol (glycerol) with NaOH as catalyst (Pinto et al., 2005). Biodiesel can be used as a fuel for vehicles in its pure form, but it is usually used as a diesel additive to reduce levels of particulates, carbon monoxide, and hydrocarbons from diesel-powered vehicles. Biodiesel is produced from oils or fats using transesterification and is the most common biofuel in Europe.

In 2010, worldwide biofuel production reached 105 billion liters (28 billion gallons US), up 17% from 2009, and biofuels provided 2.7% of the world's fuels for road transport, a contribution largely made up of ethanol and biodiesel. Global ethanol fuel production reached 86 billion liters (23 billion gallons US) in 2010, with the United States and Brazil as the world's top producers, accounting together for 90% of global production. The world's largest biodiesel producer is the European Union, accounting for 53% of all biodiesel production in 2010. As of 2011, mandates for blending biofuels exist in 31 countries at the national level and in 29 states or provinces. The International Energy Agency has a goal for biofuels to meet more than a quarter of world demand for transportation fuels by 2050 to reduce dependence on petroleum and coal.There are various social, economic, environmental and technical issues relating to biofuels production and use, which have been debated in the popular media and scientific journals. These include: the effect of moderating oil prices the “food vs fuel debate, poverty reduction potential, carbon emissions levels, sustainable biofuel production, deforestation and soil erosion loss of biodiversity and impact on water resources (Mc Carthy et al., 2011).

Biodiesel refers to a vegetable oil- or animal fat-based diesel fuelconsisting of long-chain alkyl (methyl, ethyl, or propyl) esters. Biodiesel is typically made by chemically reacting lipids(e.g., vegetable oil, animal fat (tallow) with an alcohol producing fatty acid esters (Fletcher et al., 2011). Biodiesel is meant to be used in standard diesel engines and is thus distinct from the vegetable and waste oils used to fuel converted diesel engines. Biodiesel can be used alone, or blended with petrodiesel in any proportions. Biodiesel can also be used as a low carbon alternative to heating oil (Monyem and Van Gerpen, 2001).

1.1.Blends

Blends of biodiesel and conventional hydrocarbon-based diesel are products most commonly distributed for use in the retail diesel fuel marketplace (Demirbas, 2007). Much of the world uses a system known as the “B” factor to state the amount of biodiesel in any fuel mix:

100% biodiesel is referred to as B100
20% biodiesel, 80% petrodiesel is labeled B20
5% biodiesel, 95% petrodiesel is labeled B5
2% biodiesel, 98% petrodiesel is labeled B2

Blends of 20% biodiesel and lower can be used in diesel equipment with no, or only minor modifications, although certain manufacturers do not extend warranty coverage if equipment is damaged by these blends (Friedrick, 2004). The B6 to B20 blends are covered by the ASTM D7467 specification.Biodiesel can also be used in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems. Blending B100 with petroleum diesel may be accomplished by:

Mixing in tanks at manufacturing point prior to delivery to tanker truck
Splash mixing in the tanker truck (adding specific percentages of biodiesel and petroleum diesel)
In-line mixing, two components arrive at tanker truck simultaneously.
Metered pump mixing, petroleum diesel and biodiesel meters are set to X total volume, transfer pump pulls from two points and mix is complete on leaving pump.

1.1.1 Applications of Biodiesel

Biodiesel can be used in pure form (B100) or may be blended with petroleum diesel at any concentration in most injection pump diesel engines. New extreme high-pressure (29,000 psi) common rail engines have strict factory limits of B5 or B20, depending on manufacturer. Biodiesel has different solvent properties than petrodiesel, and will degrade natural rubber gasketsand hoses in vehicles (mostly vehicles manufactured before 1992), although these tend to wear out naturally and most likely will have already been replaced with FKM, which is nonreactive to biodiesel. Biodiesel has been known to break down deposits of residue in the fuel lines where petrodiesel has been used. As a result, fuel filters may become clogged with particulates if a quick transition to pure biodiesel is made. Therefore, it is recommended to change the fuel filters on engines and heaters shortly after first switching to a biodiesel blend (Fargione et al., 2008).

Distribution of Biodiesel

Since the passage of the Energy Policy Act of 2005, biodiesel use has been increasing in the United States. In the UK, the Renewable Transport Fuel Obligation obliges suppliers to include 5% renewable fuel in all transport fuel sold in the UK by 2010. For road diesel, this effectively means 5% biodiesel (B5). (Sheehan, 1998).

Vehicular use and manufacturer acceptance of Biodiesel

In 2005, Chrysler (then part of DaimlerChrysler) released the Jeep Liberty CRD diesels from the factory into the American market with 5% biodiesel blends, indicating at least partial acceptance of biodiesel as an acceptable diesel fuel additive. In 2007, DaimlerChrysler indicated its intention to increase warranty coverage to 20% biodiesel blends if biofuel quality in the United States can be standardized (Muralidharan and Vasudevan, 2011). The Volkswagen Group has released a statement indicating that several of its vehicles are compatible with B5 and B100 made from rape seed oil and compatible with the EN 14214 standard. The use of the specified biodiesel type in its cars will not void any warranty.Mercedes Benz does not allow diesel fuels containing greater than 5% biodiesel (B5) due to concerns about “production shortcomings”. Any damages caused by the use of such non-approved fuels will not be covered by the Mercedes-Benz Limited Warranty.Starting in 2004, the city of Halifax, Nova Scotia decided to update its bus system to allow the fleet of city buses to run entirely on a fish-oil based biodiesel. This caused the city some initial mechanical issues, but after several years of refining, the entire fleet had successfully been converted.In 2007, McDonalds of UK announced it would start producing biodiesel from the waste oil byproduct of its restaurants. This fuel would be used to run its fleet.The 2014 Chevy Cruze Clean Turbo Diesel, direct from the factory, will be rated for up to B20 (blend of 20% biodiesel / 80% regular diesel) biodiesel compatibility (Thevenot, 2006).

Railway Usage of Biodiesel

Biodiesel locomotive and its external fuel tank at Mount Washington Cog RailwayBritish train operating company Virgin Trains claimed to have run the UK's first “biodiesel train”, which was converted to run on 80% petrodiesel and 20% biodiesel.The Royal Train on 15 September 2007 completed its first ever journey run on 100% biodiesel fuel supplied by Green Fuels Ltd. His Royal Highness, The Prince of Wales, and Green Fuels managing director, James Hygate, were the first passengers on a train fueled entirely by biodiesel fuel. Since 2007, the Royal Train has operated successfully on B100 (100% biodiesel).Similarly, a state-owned short-line railroad in eastern Washington ran a test of a 25% biodiesel / 75% petrodiesel blend during the summer of 2008, purchasing fuel from a biodiesel producer sited along the railroad tracks. The train will be powered by biodiesel made in part from canola grown in agricultural regions through which the short line runs.Also in 2007, Disneyland began running the park trains on B98 (98% biodiesel). The program was discontinued in 2008 due to storage issues, but in January 2009, it was announced that the park would then be running all trains on biodiesel manufactured from its own used cooking oils. This is a change from running the trains on soy-based biodiesel.In 2007, the historic Cog Railways added the first biodiesel locomotive to its all-steam locomotive fleet. The fleet has climbed up the Mount Washington in NewHampshire since 1868 with a peak vertical climb of 37.4 degrees.On 8th July 2014, Indian Railway Minister announced in Railway Budget that 5% bio-diesel will be used in Indian Railways' Diesel Engines (Chen et al., 2013).

1.1.5 Aircraft usage of Biodiesel

A test flight has been performed by a Czech jet aircraft completely powered on biodiesel. Other recent jet flights using biofuel, however, have been using other types of renewable fuels.On November 7, 2011 United Airlines flew the world's first commercial aviation flight on a microbially derived biofuel using Solajet™, Solazyme's algae-derived renewable jet fuel. The Eco-skies Boeing 737-800 plane was fueled with 40 percent Solajet and 60 percent petroleum-derived jet fuel. The commercial Eco-skies flight 1403 departed from Houston's IAH airport at 10:30 and landed at Chicago's ORD airport. December 2008, Air New Zealand, Boeing 747 Jatropha completed a two hour test flight using a 50-50 mixture, the engine was then removed to be scrutinized and studied to identify any differences between jatropha blend and regular Jatropha, no effect to performance were found (Bailis and Baka, 2010).

1.1.6 Cleaning of Oil Spills

With 80-90% of oil spill costs invested in shoreline clean-up, there is a search for more efficient and cost-effective methods to extract oil spills from the shorelines.Biodiesel has displayed its capacity to significantly dissolve crude oil, depending on the source of the fatty acids (Zhang et al., 1998). In a laboratory setting, oiled sediments that simulated polluted shorelines were sprayed with a single coat of biodiesel and exposed to simulated tides. Biodiesel is an effective solvent to oil due to its methyl ester component, which considerably lowers the viscosity of the crude oil. Additionally, it has a higher buoyancy than crude oil, which later aids in its removal. As a result, 80% of oil was removed from cobble and fine sand, 50% in coarse sand, and 30% in gravel. Once the oil is liberated from the shoreline, the oil-biodiesel mixture is manually removed from the water surface with skimmers. Any remaining mixture is easily broken down due to the high biodegradability of biodiesel, and the increased surface area exposure of the mixture (DeMello et al., 2007).

1.2 Biodiesel in Generators

Biodiesel is also used in rental generators, In 2001 University of California Riverside installed a 6-megawatt backup power system that is entirely fueled by biodiesel. Backup diesel-fueled generators allow companies to avoid damaging blackouts of critical operations at the expense of high pollution and emission rates. By using B100, these generators were able to essentially eliminate the byproducts that result in smog, ozone, and sulfur emissions. The use of these generators in residential areas around schools, hospitals, and the general public result in substantial reductions in poisonous carbon monoxide and particulate matter (Tippayawong et al., 2002).

1.2.1 Fuel efficiency of Biodiesel

Biodiesel will have a varying amount of power output depending on its blend, quality, and load conditions under which the fuel is burnt. The thermal efficiencyfor example of B100 as compared to B20 will vary due to the BTUcontent of the various blends. Thermal efficiency of a fuel is based in part on fuel characteristics such as: viscosity, specific density, and flash point; these characteristics will change as the blends as well as the quality of biodiesel varies. The American Society for Testing and Materials has set standards in order to judge the quality of a given fuel sample (Wang et al., 2007).A study on the brake thermal efficiency of varied biodiesel blends were tested under a series of load conditions as well as compression ratios. A part of the trial was comparing the thermal efficiency of B40 to traditional petrodiesel, as well as varying blends of biodiesel; as a result it was found that B40 performed at greater levels of efficiency over its traditional counterpart at higher compression ratios (this higher brake thermal efficiency was recorded at compression ratios of 21:1). It was noted that as the compression ratios increased the efficiency of all fuel types as well as blends being tested increased; though it was found that a blend of B40 was the most economical at a compression ratio of 21:1 over all other blends. The study implied that this increase in efficiency was due to fuel density, viscosity, and heating values of the fuels (Jessica, 2012).

1.2.2 Combustion of Biodiesel

Fuel systems in modern diesel engine were not designed to accommodate biodiesel. Traditional direct injection fuel systems operate at roughly 3,000 psi at the injector tip while the modern common railfuel system operates upwards of 30,000 psi at the injector tip (Monyem and Van Gerpen, 2001). Components are designed to operate at a great temperature range, from below freezing to over 378 ⁰C. Diesel fuel is expected to burn efficiently and produce as few emissions as possible. As emission standards are being introduced to diesel engines the need to control harmful emissions is being designed into the parameters of diesel engine fuel systems. The traditional inline injection system is more forgiving to poorer quality fuels as opposed to the common rail fuel system. The higher pressures and tighter tolerances of the common rail system allows for greater control over atomization and injection timing. This control of atomization as well as combustion allows for greater efficiency of modern diesel engines as well as greater control over emissions. Components within a diesel fuel system interact with the fuel in a way to ensure efficient operation of the fuel system and so the engine. If a fuel is introduced to a system that has specific parameters of operation and you vary those parameters by an out of specification fuel you may compromise the integrity of the overall fuel system. Some of these parameters such as spray pattern and atomization are directly related to injection timing (Ryan et al., 1984). One study looked at these characteristics of biodiesel in a fuel system. It was found that during atomization biodiesel and its blends produced droplets that were greater in diameter than the droplets produced by traditional petrodiesel. The smaller droplets were attributed to the lower viscosity and surface tension of traditional petrol. It was found that droplets at the periphery of the spray pattern were larger in diameter than the droplets at the center which was attributed to the faster pressure drop at the edge of the spray pattern; there was a proportional relationship between the droplet size and the distance from the injector tip. It was found that B100 had the greatest spray penetration, this was attributed to the greater density of B100. Having a greater droplet size can lead to; inefficiencies in the combustion, increased emissions, and decreased horse power. In another study it was found that there is a short injection delay when injecting biodiesel. This injection delay was attributed to the greater viscosity of biodiesel. It was noted that the higher viscosity and the greater cetane rating of biodiesel over traditional petrodiesel lead to poor atomization, as well as mixture penetration with air during the ignition delay period. Another study noted that this ignition delay may aid in a decrease of Noxemission (Wang et al., 2006).

1.2.3 Emissions

There are a number of emissions that are inherent to the combustion of diesel fuels that are regulated by the Environmental Protection Agency, E.P.A. As these emissions are a byproduct of the combustion process in order to ensure E.P.A. compliance a fuel system must be capable of controlling the combustion of fuels as well as the mitigation of emissions. There are a number of new technologies that are becoming phased in order to control the production of diesel emissions. The exhaust gas recirculation system, E.G.R., and the diesel particulate filter, D.P.F., are both designed to mitigate the production of harmful emissions. While studying the effect of biodiesel on a D.P.F. it was found that though the presence of sodium and potassium carbonates aided in the catalytic conversion of ash, as the diesel particulates are catalyzed, they may congregate inside the D.P.F. and so interfere with the clearances of the filter. This may cause the filter to clog and interfere with the regeneration process. In a study on the impact of E.G.R. rates with blends of jathropa biodiesel it was shown that there was a decrease in fuel efficiency and torque output due to the use of biodiesel on a diesel engine designed with an E.G.R. system. It was found that CO and CO₂emissions increased with an increase in exhaust gas recirculation but NOx levels decreased. The opacity level of the jathropa blends was in an acceptable range, where traditional diesel was out of acceptable standards. It was shown that a decrease in NOx emissions could be obtained with an E.G.R. system. This study showed an advantage over traditional diesel within a certain operating range of the E.G.R. system (EPA, 2002).

1.2.4 Material Compatibility of Biodiesel

Plastics: High density polyethylene (HDPE) is compatible but polyvinyl chloride (PVC) is slowly degraded. Polystyrene is dissolved on contact with biodiesel.
Metals: Biodiesel (like methanol) has an effect on copper-based materials (e.g. brass), and it also affects zinc, tin, lead, and cast iron. Stainless steels (316 and 304) and aluminum are unaffected.
Rubber: Biodiesel also affects types of natural rubbers found in some older engine components. Studies have also found that fluorinated elastomers (FKM) cured with peroxide and base-metal oxides can be degraded when biodiesel loses its stability caused by oxidation. Commonly used synthetic rubbers FKM- GBL-S and FKM- GFS found in modern vehicles were found to handle biodiesel in all conditions (Singh et al., 2012).

a. Technical standards

Biodiesel has a number of standards for its quality including European standard EN 14214, ASTM International D6751, and others (Jakeria et al., 2014).

b. Low temperature gelling

When biodiesel is cooled below a certain point, some of the molecules aggregate and form crystals. The fuel starts to appear cloudy once the crystals become larger than one quarter of the wavelengths of visible light – this is the cloud point (CP). The lowest temperature at which fuel can pass through a 45 micrometre filter is the cold filter plugging point(CFPP). As biodiesel is cooled further it will gel and then solidify. Within Europe, there are differences in the CFPP requirements between countries. This is reflected in the different national standards of those countries. The temperature at which pure (B100) biodiesel starts to gel varies significantly and depends upon the mix of esters and therefore the feedstock oil used to produce the biodiesel. For example, biodiesel produced from low erucic acidvarieties of canola seed (RME) starts to gel at approximately −10 °C (14 °F). Biodiesel produced from tallow and palm oil tends to gel at around 16 °C (61 °F). There are a number of commercially available additives that will significantly lower the pour point and cold filter plugging point of pure biodiesel. Winter operation is also possible by blending biodiesel with other fuel oils including no 2 low sulfur diesel fuel and no1 diesel / kerosene.Another approach to facilitate the use of biodiesel in cold conditions is by employing a second fuel tank for biodiesel in addition to the standard diesel fuel tank. The second fuel tank can be insulated and a heating coil using engine coolant is run through the tank. The fuel tanks can be switched over when the fuel is sufficiently warm. A similar method can be used to operate diesel vehicles using straight vegetable oil (Fazal et al., 2011).

c. Contamination by water

Biodiesel may contain small but problematic quantities of water. Although it is only slightly miscible with water it is hygroscopic. One of the reasons biodiesel can absorb water is the persistence of mono and diglycerides left over from an incomplete reaction. These molecules can act as an emulsifier, allowing water to mix with the biodiesel. In addition, there may be water that is residual to processing or resulting from storage tank condensation. The presence of water is a problem because:

Water reduces the heat of fuel combustion, causing smoke, harder starting, and reduced power.

Water causes corrosion of fuel system components (pumps, fuel lines, etc.)

Microbes in water cause the paper-element filters in the system to rot and fail, causing failure of the fuel pump due to ingestion of large particles.
Water freezes to form ice crystals that provide sites for nucleation, accelerating gelling of the fuel.
Water causes pitting in pistons.

Previously, the amount of water contaminating biodiesel has been difficult to measure by taking samples, since water and oil separate. However, it is now possible to measure the water content using water-in-oil sensors.Water contamination is also a potential problem when using certain chemical catalystsinvolved in the production process, substantially reducing catalytic efficiency of base (high pH) catalysts such as potassium hydroxide. However, the super-critical methanol production methodology, whereby the transesterification process of oil feedstock and methanol is effectuated under high temperature and pressure, has been shown to be largely unaffected by the presence of water contamination during the production phase (ORNL, 2012).

1.2.5Biodiesel production Levels

In 2007, biodiesel production capacity was growing rapidly, with an average or which actual production figures could be obtained, total world biodiesel production was about 5-6 million tonnes, with 4.9 million tonnes processed in Europe (of which 2.7 million tonnes was from Germany) and most of the rest from the USA. In 2008 production in Europe alone had risen to 7.8 million tonnes. In July 2009, a duty was added to American imported biodiesel in the European Union in order to balance the competition from European, especially German producers. The capacity for 2008 in Europe totalled 16 million tonnes. This compares with a total demand for diesel in the US and Europe of approximately 490 million tonnes (147 billion gallons). Total world production of vegetable oil for all purposes in 2005/06 was about 110 million tonnes, with about 34 million tonnes each of palm oil and soybean oil.US biodiesel production in 2011 brought the industry to a new milestone. Under the EPA Renewable Fuel Standard, targets have been implemented for the biodiesel production plants in order to monitor and document production levels in comparison to total demand. According to the year-end data released by the EPA, biodiesel production in 2011 reached more than 1 billion gallons. This production number far exceeded the 800 million gallon target set by the EPA. The projected production for 2020 is nearly 12 billion gallons (Gerpen, 2005).

1.2.6Biodiesel Feedstock

A variety of oils can be used to produce biodiesel. These include:

Virgin oil feedstock – rapeseed and soybean oils are most commonly used, soybean oil accounting for about half of U.S. production. It also can be obtained from Pongamia, field pennycress and jatropha and other crops such as mustard, jojoba, flax, sunflower, palm oil, coconut, hemp.
Waste vegetable oil (WVO);
Animal fats including tallow, lard, yellow grease, chicken fat, and the by-products of the production of Omega-3 fatty acids from fish oil.
Algae, which can be grown using waste materials such as sewage and without displacing land currently used for food production.
Oil from halophytes such as Salicornia bigelovii, which can be grown using saltwater in coastal areas where conventional crops cannot be grown, with yields equal to the yields of soybeans and other oilseeds grown using freshwater irrigation

Sewage Sludge – The sewage-to-biofuel field is attracting interest from major companies like Waste Management and startups like InfoSpi, which are betting that renewable sewage biodiesel can become competitive with petroleum diesel on price.Many advocates suggest that waste vegetable oil is the best source of oil to produce biodiesel, but since the available supply is drastically less than the amount of petroleum-based fuel that is burned for transportation and home heating in the world, this local solution could not scale to the current rate of consumption.Animal fats are a by-product of meat production and cooking. Although it would not be efficient to raise animals (or catch fish) simply for their fat, use of the by-product adds value to the livestock industry (hogs, cattle, poultry). Today, multi-feedstock biodiesel facilities are producing high quality animal-fat based biodiesel. Currently, a 5-million dollar plant is being built in the USA, with the intent of producing 11.4 million litres (3 million gallons) biodiesel from some of the estimated 1 billion kg (2.2 billion pounds) of chicken fat produced annually at the local Tyson poultry plant. Similarly, some small-scale biodiesel factories use waste fish oil as feedstock. An EU-funded project (ENERFISH) suggests that at a Vietnamese plant to produce biodiesel from catfish (basa, also known as pangasius), an output of 13 tons/day of biodiesel can be produced from 81 tons of fish waste (in turn resulting from 130 tons of fish). This project utilises the biodiesel to fuel a CHP unit in the fish processing plant, mainly to power the fish freezing plant (Kinast, 2003).

1.2.7Quantity of feedstocks required

Current worldwide production of vegetable oil and animal fat is not sufficient to replace liquid fossil fuel use. Furthermore, some object to the vast amount of farming and the resulting fertilization, pesticide use, and land use conversion that would be needed to produce the additional vegetable oil. The estimated transportation diesel fuel and home heating oil used in the United States is about 160 million tons (350 billion pounds) according to the Energy Information Administration, US Department of Energy. In the United States, estimated production of vegetable oil for all uses is about 11 million tons (24 billion pounds) and estimated production of animal fat is 5.3 million tonnes (12 billion pounds).If the entire arable land area of the USA (470 million acres, or 1.9 million square kilometers) were devoted to biodiesel production from soy, this would just about provide the 160 million tonnes required (assuming an optimistic 98 US gal/acre of biodiesel). This land area could in principle be reduced significantly using algae, if the obstacles can be overcome. The US Department of Energy estimates that if algae fuel replaced all the petroleum fuel in the United States, it would require 15,000 square miles (38,849 square kilometers), which is a few thousand square miles larger than Maryland, or 30% greater than the area of Belgium, assuming a yield of 140 tonnes/hectare (15,000 US gal/acre). Given a more realistic yield of 36 tonnes/hectare (3834 US gal/acre) the area required is about 152,000 square kilometers, or roughly equal to that of the state of Georgia or of England and Wales. The advantages of algae are that it can be grown on non-arable land such as deserts or in marine environments, and the potential oil yields are much higher than from plants (Moser, 2009).

1.2.8Efficiency and economic Arguments

According to a study by Drs. Van Dyne and Raymer for the Tennessee Valley Authority, the average US farm consumes fuel at the rate of 82 litres per hectare (8.75 US gal/acre) of land to produce one crop. However, average crops of rapeseed produce oil at an average rate of 1,029 L/ha (110 US gal/acre), and high-yield rapeseed fields produce about 1,356 L/ha (145 US gal/acre). The ratio of input to output in these cases is roughly 1:12.5 and 1:16.5. Photosynthesis is known to have an efficiency rate of about 3-6% of total solar radiation and if the entire mass of a crop is utilized for energy production, the overall efficiency of this chain is currently about 1% While this may compare unfavorably to solar cells combined with an electric drive train, biodiesel is less costly to deploy (solar cells cost approximately US$250 per square meter) and transport (electric vehicles require batteries which currently have a much lower energy density than liquid fuels). A 2005 study found that biodiesel production using soybeans required 27% more fossil energy than the biodiesel produced and 118% more energy using sunflowers.However, these statistics by themselves are not enough to show whether such a change makes economic sense. Additional factors must be taken into account, such as the fuel equivalent of the energy required for processing, the yield of fuel from raw oil, the return on cultivating food, the effect biodiesel will have on food prices and the relative cost of biodiesel versus petrodiesel, water pollution from farm run-off, soil depletion, and the externalized costs of political and military interference in oil-producing countries intended to control the price of petrodiesel.The debate over the energy balance of biodiesel is ongoing. Transitioning fully to biofuels could require immense tracts of land if traditional food crops are used (although non food crops can be utilized). The problem would be especially severe for nations with large economies, since energy consumption scales with economic output.If using only traditional food plants, most such nations do not have sufficient arable land to produce biofuel for the nation's vehicles. Nations with smaller economies (hence less energy consumption) and more arable land may be in better situations, although many regions cannot afford to divert land away from food production.For third world countries, biodiesel sources that use marginal land could make more sense; e.g., pongam oiltree nuts grown along roads or jatropha grown along rail lines.In tropical regions, such as Malaysia and Indonesia, plants that produce palm oil are being planted at a rapid pace to supply growing biodiesel demand in Europe and other markets. Scientists have shown that the removal of rainforest for palm plantations is not ecologically sound since the expansion of oil palm plantations poses a threat to natural rainforest and biodiversity.It has been estimated in Germany that palm oil biodiesel has less than one third of the production costs of rapeseed biodiesel. The direct source of the energy content of biodiesel is solar energy captured by plants during photosynthesis. Regarding the positive energy balance of biodiesel:When straw was left in the field, biodiesel production was strongly energy positive, yielding 1 GJ biodiesel for every 0.561 GJ of energy input (a yield/cost ratio of 1.78).

When straw was burned as fuel and oilseed rapemeal was used as a fertilizer, the yield/cost ratio for biodiesel production was even better (3.71). In other words, for every unit of energy input to produce biodiesel, the output was 3.71 units (the difference of 2.71 units would be from solar energy) (Zeller Jr., 2008).

1.2.8.1Economic impact of Biodiesel

Multiple economic studies have been performed regarding the economic impact of biodiesel production. One study, commissioned by the National Biodiesel Board, reported the 2011 production of biodiesel supported 39,027 jobs and more than $2.1 billion in household income. The growth in biodiesel also helps significantly increase GDP. In 2011, biodiesel created more than $3 billion in GDP. Judging by the continued growth in the Renewable Fuel Standard and the extension of the biodiesel tax incentive, the number of jobs can increase to 50,725, $2.7 billion in income, and reaching $5 billion in GDP by 2012 , 2013 and 2014 (Stephen, 2008).

1.2.8.2Energy security of Biodiesel.

One of the main drivers for adoption of biodiesel is energy security. This means that a nation's dependence on oil is reduced, and substituted with use of locally available sources, such as coal, gas, or renewable sources. Thus a country can benefit from adoption of biofuels, without a reduction in greenhouse gas emissions. While the total energy balance is debated, it is clear that the dependence on oil is reduced. One example is the energy used to manufacture fertilizers, which could come from a variety of sources other than petroleum. The US National Renewable Energy Laboratory (NREL) states that energy security is the number one driving force behind the US biofuels programme, and a White House “Energy Security for the 21st Century” paper makes it clear that energy security is a major reason for promoting biodiesel. The EU commission president, Jose Manuel Barroso, speaking at a recent EU biofuels conference, stressed that properly managed biofuels have the potential to reinforce the EU's security of supply through diversification of energy sources (Juan et al., 2014).

1.2.8.3Global biofuel policies

Many countries around the world are involved in the growing use and production of biofuels, such as biodiesel, as an alternative energy source to fossil fuels and oil. To foster the biofuel industry, governments have implemented legislations and laws as incentives to reduce oil dependency and to increase the use of renewable energies.Many countries have their own independent policies regarding the taxation and rebate of biodiesel use, import, and production (Silitonga et al., 2013).

1.2.8.4 CANADA

It was required by the Canadian Environmental Protection Act Bill C-33 that by the year 2010, gasoline contained 5% renewable content and that by 2013, diesel and heating oil contained 2% renewable content. The EcoENERGY for Biofuels Program subsidized the production of biodiesel, among other biofuels, via an incentive rate of CAN$0.20 per liter from 2008 to 2010. A decrease of $0.04 will be applied every year following, until the incentive rate reaches $0.06 in 2016. Individual provinces also have specific legislative measures in regards to biofuel use and production (Sokhansanj et al., 2006).

1.2.8.5UNITED STATES

The Volumetric Ethanol Excise Tax Credit (VEETC) was the main source of financial support for biofuels, but was scheduled to expire in 2010. Through this act, biodiesel production guaranteed a tax credit of US$1 per gallon produced from virgin oils, and $0.50 per gallon made from recycled oils (EPA, 2002).

1.2.8.6 EUROPEAN UNION

The European Union is the greatest producer of biodiesel, with France and Germany being the top producers. To increase the use of biodiesel, there exist policies requiring the blending of biodiesel into fuels, including penalties if those rates are not reached. In France, the goal was to reach 10% integration but plans for that stopped in 2010. As an incentive for the European Union countries to continue the production of the biofuel, there are tax rebates for specific quotas of biofuel produced. In Germany, the minimum percentage of biodiesel in transport diesel is set at 4.4%, and will remain at that level until 2014 (Banse et al., 2008).

1.2.8.7Environmental effects

The surge of interest in biodiesels has highlighted a number of environmental effectsassociated with its use. These potentially include reductions in greenhouse gas emissions, deforestation, pollution and the rate of biodegradation. According to the EPA’s renewable fuel standards program regulatory impact analysis released in February 2010, biodiesel from soy oil results, on average in a 57% reduction in greenhouse gases compared to petroleum diesel, and biodiesel produced from waste grease results in an 86% reduction. However, environmental organizations for example, rainforest rescue and Greenpeace, criticize the cultivation of plants used for biodiesel production, e.g oil palms, soybeans and sugarcane. They say that the deforestation of rainforests exacerbates climate change and that sensitive ecosystems are destroyed to clear land for oil palm, soybean and sugarcane plantations. Moreover, that biofuels contribute to world hunger, seeing as arable lands is no longer used for growing foods. The Environmental Protection Agency (EPA) published data in January 2012, showing that biofuels made from palm oil won’t count towards the nation’s renewable fuel mandate as they are not climate-friendly.

1.2.8.8Food,land and water vs. fuel

In some poor countries the rising price of vegetable oil is causing problems. Some propose that fuel only be made from non-edible vegetable oils such as camelina, jatropha or seashore mallow which can thrive on marginal agricultural land where many trees and crops will not grow, or would produce only low yields(Searchinger et al., 2011).

Others argue that the problem is more fundamental. Farmers may switch from producing food crops to producing biofuel crops to make more money, even if the new crops are not edible. The law of supply and demand predicts that if fewer farmers are producing food the price of food will rise. It may take some time, as farmers can take some time to change which things they are growing, but increasing demand for first generation biofuels is likely to result in price increases for many kinds of food. Some have pointed out that there are poor farmers and poor countries who are making more money because of the higher price of vegetable oil.Biodiesel from sea algae would not necessarily displace terrestrial land currently used for food production and new algaculture jobs could be created (Atabani et al., 2012)

1.2.8.8.1Current research

There is ongoing research into finding more suitable crops and improving oil yield. Other sources are possible including human fecal matter, with Ghana building its first “fecal sludge-fed biodiesel plant.” Using the current yields, vast amounts of land and fresh water would be needed to produce enough oil to completely replace fossil fuel usage. It would require twice the land area of the US to be devoted to soybean production, or two-thirds to be devoted to rapeseed production, to meet current US heating and transportation needs (Evans, 2008)

Specially bred mustard varieties can produce reasonably high oil yields and are very useful in crop rotation with cereals, and have the added benefit that the meal leftover after the oil has been pressed out can act as an effective and biodegradable pesticide (Divakara et al., 2010).

The NFESC, with Santa Barbara-based Biodiesel Industries is working to develop biodiesel technologies for the US navy and military, one of the largest diesel fuel users in the world.A group of Spanish developers working for a company called Ecofasa announced a new biofuel made from trash. The fuel is created from general urban waste which is treated by bacteria to produce fatty acids, which can be used to make biodiesel.Another approach that does not require the use of chemical for the production involves the use of genetically modified microbes (Choi and Lee, 2013).

1.2.8.8.2 Algal Biodiesel

From 1978 to 1996, the U.S. NREL experimented with using algae as a biodiesel source in the “Aquatic Species Program”. A self-published article by Michael Briggs, at the UNH Biodiesel Group, offers estimates for the realistic replacement of all vehicular fuel with biodiesel by utilizing algae that have a natural oil content greater than 50%, which Briggs suggests can be grown on algae ponds at wastewater treatment plants. This oil-rich algae can then be extracted from the system and processed into biodiesel, with the dried remainder further reprocessed to create ethanol.The production of algae to harvest oil for biodiesel has not yet been undertaken on a commercial scale, but feasibility studieshave been conducted to arrive at the above yield estimate. In addition to its projected high yield, algaculture — unlike crop-basedbiofuels — does not entail a decrease in food production, since it requires neither farmland nor fresh water. Many companies are pursuing algae bio-reactors for various purposes, including scaling up biodiesel production to commercial levels.Prof. Rodrigo E. Teixeira from the University of Alabama in Huntsville demonstrated the extraction of biodiesel lipids from wet algae using a simple and economical reaction in ionic liquids (Teixeira, 2012).

1.2.8.8.3Jatropha

Several groups in various sectors are conducting research on Jatropha curcas, a poisonous shrub-like tree that produces seeds considered by many to be a viable source of biodiesel feedstock oil. Much of this research focuses on improving the overall per acre oil yield of Jatropha through advancements in genetics, soil science, and horticultural practices.SG Biofuels, a San Diego-based Jatropha developer, has used molecular breeding and biotechnology to produce elite hybrid seeds of Jatropha that show significant yield improvements over first generation varieties. SG Biofuelsalso claims that additional benefits have arisen from such strains, including improved flowering synchronicity, higher resistance to pests and disease, and increased cold weather tolerance.Plant Research International, a department of the Wageningen University and Research Centre in the Netherlands, maintains an ongoing Jatropha Evaluation Project (JEP) that examines the feasibility of large scale Jatropha cultivation through field and laboratory experiments (Divakara et al., 2010).The Center for Sustainable Energy Farming (CfSEF) is a Los Angeles-based non-profit research organization dedicated to Jatropha research in the areas of plant science, agronomy, and horticulture. Successful exploration of these disciplines is projected to increase Jatropha farm production yields by 200-300% in the next ten years (Openshaw, 2000).

1.2.8.8.4 Fungi

A group at the Russian Academy of Sciences in Moscow published a paper in September 2008, stating that they had isolated large amounts of lipids from single-celled fungi and turned it into biodiesel in an economically efficient manner (Andrianova et al., 2008). More research on this fungal species; Cunninghamellajaponica, and others, is likely to appear in the near future.The recent discovery of a variant of the fungus Gliocladium roseum points toward the production of so-called myco-dieselfrom cellulose. This organism was recently discovered in the rainforests of northern Patagonia and has the unique capability of converting cellulose into medium length hydrocarbons typically found in diesel fuel (Sergeeva et al., 2008).

1.2.8.8.5Biodiesel from used coffee Grounds

Researchers at the University of Nevada, Reno, have successfully produced biodiesel from oil derived from used coffee grounds. Their analysis of the used grounds showed a 10% to 15% oil content (by weight). Once the oil was extracted, it underwent conventional processing into biodiesel. It is estimated that finished biodiesel could be produced for about one US dollar per gallon. Further, it was reported that “the technique is not difficult” and that “there is so much coffee around that several hundred million gallons of biodiesel could potentially be made annually (Henry, 2008).

1.2.8.8.6 Biodiesel to hydrogen cell Power

A microreactor has been developed to convert biodiesel into hydrogen steam to power fuel cells.

Steam reforming, also known as fossil fuel reforming is a process which produces hydrogen gas from hydrocarbon fuels, most notably biodiesel due to its efficiency. A **microreactor**, or reformer, is the processing device in which water vapour reacts with the liquid fuel under high temperature and pressure. Under temperatures ranging from 700 – 1100 °C, a nickel-based catalyst enables the production of carbon monoxide and hydrogen:

Hydrocarbon + H₂O ⇌ CO + 3 H₂ (Highly endothermic)

Furthermore, a higher yield of hydrogen gas can be harnessed by further oxidizing carbon monoxide to produce more hydrogen and carbon dioxide:

CO + H₂O → CO₂ + H₂ (Mildly exothermic)

1.2.8.8.7Hydrogen fuel cells background information

Fuel cells operate similar to a battery in that electricity is harnessed from chemical reactions. The difference in fuel cells when compared to batteries is their ability to be powered by the constant flow of hydrogen found in the atmosphere. Furthermore, they produce only water as a by-product, and are virtually silent. The downside of hydrogen powered fuel cells is the high cost and dangers of storing highly combustible hydrogen under pressure.

One way new processors can overcome the dangers of transporting hydrogen is to produce it as necessary. The microreactors can be joined to create a system that heats the hydrocarbon under high pressure to generate hydrogen gas and carbon dioxide, a process called steam reforming. This produces up to 160 gallons of hydrogen/minute and gives the potential of powering hydrogen refueling stations, or even an on-board hydrogen fuel source for hydrogen cell vehicles. Implementation into cars would allow energy-rich fuels, such as biodiesel, to be transferred to kinetic energy while avoiding combustion and pollutant byproducts.

1.2.8.8.8 Engine Wear

Lubricity of fuel plays an important role in wear that occurs in an engine. An engine relies on its fuel to provide lubricity for the metal components that are constantly in contact with each other.Biodiesel is a much better lubricant compared with petroleum diesel due to the presence of esters. Tests have shown that the addition of a small amount of biodiesel to diesel can significantly increase the lubricity of the fuel in short term. However, over a longer period of time (2–4 years), studies show that biodiesel loses its lubricity. This could be because of enhanced corrosion over time due to oxidation of the unsaturated molecules or increased water content in biodiesel from moisture absorption (Graboski and McCormick, 1998).

1.3 Fuel Viscosity

One of the main concerns regarding biodiesel is its viscosity. The viscosity of diesel is 2.5–3.2 cSt at 40(°C) and the viscosity of biodiesel made from soybean oil is between 4.2 and 4.6 (cSt). The viscosity of diesel must be high enough to provide sufficient lubrication for the engine parts but low enough to flow at operational temperature. High viscosity can plug the fuel filter and injection system in engines. Vegetable oil is composed of lipids with long chains of hydrocarbons, to reduce its viscosity the lipids are broken down into smaller molecules of esters. This is done by converting vegetable oil and animal fats into alkyl esters using transesterification to reduce their viscosity Nevertheless, biodiesel viscosity remains higher than that of diesel, and the engine may not be able to use the fuel at low temperatures due to the slow flow through the fuel filter (Freedman et al., 1986).

1.3.1Engine Performance

Biodiesel has higher brake-specific fuel consumption compared to diesel, which means more biodiesel fuel consumption is required for the same torque. However, B20 biodiesel blend has been found to provide maximum increase in thermal efficiency and lowest brake-specific energy consumption. The engine performance depends on the properties of the fuel, as well as on combustion, injector pressure and many other factors, since there are various blends of biodiesel, that may account for the contradicting reports in regards to engine performance (Huzayyin et al., 2004).

1.1 AVOCADO FRUIT

Avocado (Persia Americana) is a native plant of Southern Mexico and Central America (Human, 1987).The fruit’s pulp which contains a large quantity of oil is utilized in the cosmetic industries especially in New Zealand and US to manufacture skin care products like body moisturizers and facial creams (Bizimana et al., 1993).

Avocado (a member of Lauraceae family) is well known in Nigeria, and in all the tropical parts of the world.The fruit tree can attain a height up to 20 metres, with large spreading and flat topped crown. The leaves are ovate-lanceolate, 5-20cm long and about 15cm broad, cuneate to truncate at the base and gradually acuminate with 6-10 pairs of lateral nerves. The leaves are crowded towards the end of the twigs. Flowers are pale yellow in compact inflorescences at the end of the twigs. Calyx are densely covered with grey hairs, deeply divided into 6 parts. Stamens are 12 of which only 9 are developed. The Fruits are large, 5-15cm long, ovate to spherical, shining green and fleshy (Fig.1) (Keay, 1989).In addition the fruit is a large fleshy berry with a single seed. Avocado is a nutritious and valuable fruit tree found in the tropics.The pulp of mature avocado fruit has a sweet pleasant that is consumed as human food.The pollination of avocado when it flowers is a classic example of protogyny. This means that the females matures before the males, so the flower cannot self pollinate but requires pollen from another flower or another plant. Avocado flowers bloom from January to March and these flowers open twice on two consecutive days. The flowers are of two types: Type A and Type B. Type A flowers are receptive to pollen in the morning of day 1 but reopen in the afternoon of day 2 with stamens shedding pollens. Type B on the other hand bear flowers that are receptive to pollen in the afternoon of day 1 and shed pollen in the morning of day 2. Growing plants bearing the two different types of flowers together will allow cross pollination to occur and increase the chances of production.

Fig 1 : Pictorial view of avocado fruit. (a) Complete fruit.

Source: (Arpaia et al., 2006)

(b)

Lateral section

1.1.1CULTIVARS AND VARIETIES

Avocado has many cultivars and they include:

FUERTE– This tall tree is a hybrid and produces a shiny green, round pear shaped, large to very large fruits. Oil content is around 18-26%, good flesh but also tends to bear fruits in alternate years. Season is December.

HAAS-This is of Guatemalan race and regarded as the industrial standard fruit. Tree and fruit are medium sized, thick skin, roundish and purple at full maturity.It has a good shelf life, wide consumer acceptance and oil contentis around 19-30%.It produces from April to September and is the most popular cultivar used around the world (Bergh, 1992).

GWEEN-The most popular and productive dwarf tree. Fruits are small, elongated and remain green when ripe. Season is February to October. It is an “A”cultivar.

PINKERTON-A dense productive tree and it is an “A”cultivar.Fruits look like long pears with pebbly green skin. The fruits darken when ripe, has small seeds and is in season in November (Bergh, 1992).

REED-Known as the summertime variety avocado. It is an “A” cultivar and produces a large fruit with thick green skin which stays green when ripe. Its season is August and its flesh becomes buttery yellow when ripe.

ZUTANO-It is a hybrid and is a columnar tree bearing mediumto large fruits. Fruits has a shiny yellow skin and is pear-shaped.It is similar to Fuertebut is inferior and has fibres. It is a “B”cultivar and its colour remains the same when ripe.

1.1.2 Taxonomy of Avocado Fruit

Avocado (Ube oyibo) is classified as follows:

Scientific name Persea Americana

Symbol PEAM3

Domain Eukarya

Kingdom Plantae

Subkingdom Tracheobionta

Phylum Anthrophyta

Class Magnoliopsida

Subclass Magnoliidae

Order Laurales

Division Magnoliophyta

Subdivision Spermatophyta

Family Lauraceae

Genus Persea

Species Persea americana

1.1.3 Description of the avocado pulp oil

Avocado fruit pulps are rich in protein but more in oil (about 50%). Monounsaturated fatty acids is 70%,it has low levels of polyunsaturated and saturated fats (Arpaia, 2006). Oleic acid is 38.7%, palmitoleic (0.7%), Stearic (9.8%), Linoleic (18.2%), Linolenic (1.2%), palmitic (31.2%). It contains high amount of anti-cholesterol agent beta-sitosterol,a wide variety of vitamins and antioxidants and other plant chemicals which impart beneficial functional properties on humans.These notwithstanding, avocado pulp oil can also be exploited for the production of biodiesel (Lozano et al., 1993).

1.1.4Biodiesel and other Fuels

Any material which are burned or altered to obtain energy, heat or to move an object is referred to as fuel (World Encyclopedia, 2005). Biologically derived fuels which were produced from bioenergy sources are known as biofuels (Nass et al., 2007). Biodiesel is a biofuel, among other biofuels are; charcoal,livestock manure, biogas,wood, bio-hydrogen, microbial biomass, bio-alcohols, agricultural wastes and byproducts, energy crops (FAO, 2000). These materials are obtained from recently dead or lifeless organisms, plants and animals alike. Biodiesel and bioethanol represents the first generation biofuels whose bio-refineries utilize readily processable bioresources such as starches,sucrose and plant oils (Marchetti et al., 2007). There is a direct or indirect dependence of biofuels on the photosynthetic process.Plant oils (and animal fats) are the primary source of biodiesel, starch and sucrose serve as the major feedstock for bioethanol production via fermentation. Biodiesel, bioethanol and liquid biofuels are used predominantly in the transport sector due to their high volumetric density and convenience of use just as with liquid hydrocarbons (Agrawal et al., 2007). Biogas as well as other gaseous biofuels can be used in cooking, lighting and electricity generation. Bio-hydrogen and especially bio-methanol, are of particular interest as fuel for fuel cells, which are used to produce energy (Bullen et al., 2006). Alternative fuels such as biofuels tend to reduce dependency on fossil fuels globally.Biofuels are equally considered as offering many priorities, including sustainability, reduction of green-house gas emissions, regional development, social structure, agriculture and security of supply (Reijnders, 2006).

1.2 Biodiesel Production

The production requires eithervegetable oil or animal fats, alcohol (especially, of short chain length), catalyst and certain necessary conditions such as temperature and optimum reaction time. These are put together in a reaction process known as transesterification (equally known as alcoholysis).Biodiesel production is technically a simple process (Gerpen, 2005).

Fig.2. Biodiesel processing flow diagram

Source: (Demirbas, 2007).

1.2.1 Transesterification process

Transesterification or alcoholysis is the displacement of alcohol from an ester by a process similar to hydrolysis, except that alcohol is used instead of water (Meher et al., 2006).

Transesterification has been demonstrated as the simplest and most efficient route for biodiesel production in large quantities.It is the exchange of the alcohol moiety of an ester (contained in the feedstock) with another alcohol moiety, often from another alcohol (Ma and Hanna, 1999; Ranganathan et al., 2008)

It is the stepwise reversible reactions of a triglycerides (fat/oil) with an alcohol to form esters and glycerol. Little excess of alcohol is used to shift the equilibrium towards the formation of esters. Transesterification using an alcohol is a sequence of 3 reversible consecutive steps. In the first step, triglycerides are converted to diglycerides. In the second step, diglycerides are converted to monoglycerides. In the third step, monoglycerides are converted to glycerin molecules (Freedman et al., 1984; Noureddini and Zhu, 1997; Marchetti et al., 2008). Each conversion step yields one Fatty acid alkyl ester molecule,giving a total of 3 FAAEs per triglyceride molecule as described by the following equations (Murugesan et al., 2009).

Biodiesel is a clean and renewable fuel which is considered to be the best substitution for diesel fuel (Singh and Singh, 2010).

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Fig 3.Conversion of triglycerides to diglycerides (DAG).

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Fig 4 .Conversion of diglycerides to monoglycerides (MAG) molecules.

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Fig 5.Conversion of monoglycerides to glycerin molecules.

1mole 3moles 3moles 1mole

Source:(Mittleback and Trathnigg, 2006).

Fig. 6.Transesterification reaction of TAG to yield fatty acid alkyl esters (biodiesel).

Transesterification is simply based on the use of the main constituent of oil and fats known as triglycerides or triacylglycerol (TAG), which compose about 90-98% of the total mass of the lipids (Srivastava and Prasad, 2000). TAG consists of 3 long-chain fatty acids, which are chemically bound to a glycerol (propan-1,2,3-triol) backbone, making TAG an ester of glycerol. TAG undergoes transesterification by reacting with a short chain monohydric alcohol, normally in the presence of a catalyst at elevated temperature to form fatty acid alkyl esters (FAAE) and glycerol.This conversion is a step-wise process whereby the alcohol initially reacts with TAG as the alkoxide anion to produce the first FAAE molecule and diacylglycerol (DAG) (Reaction (1), (Fig.3). The DAG produced reacts with another mole of alcohol (alkoxide) to liberate another FAAE and MAG (Reaction 2 (Fig.4) , which in the same manner liberates the third FAAE molecule and then, glycerol (Reaction 3 (Fig.4). One mole of glycerol is co-produced with one molecule of FAAE on each of the three steps, and the combined FAAE molecules are collectively known as biodiesel (Moser, 2009).

1.2.2 Catalysts for biodiesel production

The transesterification reaction is anequilibrium and the transformation occurs essentially by mixing the reactants. However, the presence of a catalyst considerably accelerates the adjustment of the equilibrium (Ma and Hanna, 1999). Catalysts conventionally used in biodiesel production are strong bases (usually NaOH, KOH and NaOCH₃) and strong acids (usually H₂SO₄ and HCl) (Narasimharao et al., 2007). Homogeneous basic catalysts are more employed in commercial biodiesel production because transeserification reactions are generally faster, less expensive and more complete with them (Boocock et al., 1996). These basic catalysts however, cannot be used in feedstocks (vegetable oils or animal fats) with high free fatty acid (FFA) content since it will result in saponification side reaction (Fig. 4). In this case, acid catalysts are more appropriate as they do not engage in such side reaction. Soap formation reduces catalyst efficiency, causes an increase in viscosity, leads to gel formation and makes the separation of glycerol difficult (Guo and Leung, 2003).

R OH + NaOH (or NaOCH₃) R O^–Na⁺+H₂O (or CH₃OH)

FFA Soap

Fig. 7: Saponification takes place as a side reaction when a basic catalyst is used for feedstocks high in FFA.

Source: (Moser, 2009).

A further complicating factor of high FFA content is the production of water upon reaction with homogeneous base catalyst (Fig.4). Water is particularly problematic because its presence gives rise to hydrolysis of some of the produced ester to produce free fatty acids (FFAs) (Fig.8). The formed FFAs here can therefore retard transesterification as well as biodiesel yield (Rashid et al., 2009).

R OCH₃ R OH

Fig. 8.Hydrolysis of biodiesel to yield FFA and methanol.

Source: (Moser, 2009).

Transesterification process can also be catalyzed by lipase enzymes, for instance methanolysis of triacylglycerols. The most promising results in this case were obtained using immobilized candida antartica lipase (Novozyme 435) (Fukuda et al., 2001)

1.2.3Types of Biofuels

Vegetable oil is used in several old diesel engines that have indirect injection systems. This oil is also used to create biodiesel, which when mixed with conventional diesel fuel is compatible for most diesel engines. Used vegetable oil is converted into biodiesel. Sometimes, water and particulates are separated from the used vegetable oil and then this is used as a fuel (El-Diwani et al., 2009).Biodiesel is a famous biofuel in Europe. Its composition is just like mineral diesel. When biodiesel is mixed with mineral diesel, the mixture can be used in any diesel engine. It is observed that in several nations, the diesel engines under warranty are converted to 100% biodiesel use. It has also been proved that most people can run their vehicles on biodiesel without any problem. A large number of vehicle manufacturers recommend the use of 15% biodiesel mixed with mineral diesel. In Europe, a 5% biodiesel blend is generally used at gas stations. Bioalcohols are biologically produced alcohols. Common among these are ethanol and rare among these are propanol and butanol. Biobutanol can be used directly in a gasoline engine and hence is considered a direct replacement for gasoline. The butanol can be burned straight in the existing gasoline engines without any alteration to the engine or car. It is also claimed that this butanol produces more energy. Also, butanol has a less corrosive effect and is less soluble in water than ethanol. Ethanol fuel is the most commonly used biofuel in the world and particularly in Brazil. Ethanol can be put to use in petrol engines as a substitute for gasoline. Also, it can be mixed with gasoline in any ratio. The contemporary automobile petrol engines can work on mixtures of gasoline and ethanol that have 15% bioethanol. This mixture of gasoline and ethanol has more quantity of octane. This indicates that the engine would burn hotter and more efficiently. In high altitude spots, the mixture of gasoline and ethanol is used as a winter oxidizer and thereby atmospheric pollution is decreased. The ethanol fuel has less British Thermal Unit energy content. Thus, to drive the same distance, more fuel is required. Also ethanol has a corrosive effect on combustion chambers, aluminum, rubber hoses and gaskets and fuel systems. Biogas is created when organic material is anaerobically digested by anaerobes. During production, there is a solid byproduct called digestate. This can be used as a biofuel or fertilizer. Biogas consists of methane. Landfill gas is created in landfills due to natural anaerobic digestion and is a less clean form of biogas. Dried manure, charcoal and wood are examples of solid biofuels. The combined processes of gasification, combustion and pyrolyis gives rise to syngas which is a biofuel. This syngas can be directly burned in internal combustion engines. Syngas can be used to create hydrogen and methanol. By using the Fischer-Tropsch process, it can be transformed to a synthetic petroleum substitute (BajPai and Tyagi, 2006).

Some second generation biofuels that are being developed are Fischer-Tropsch diesel, bio-dimethyl ether, Dimethyl formamide, biomethanol, biohydrogen, wood diesel, mixed alcohol and biohydrogen diesel. Algae fuel is a third generation biofuel derived from algae. This is also called oilgae (Kulik, 1995).

1.2.4Alcohols used in biodiesel production

The most commonly used alcohol in the production of biodiesel is ethanol and methanol (Moser, 2009). Others are propanol, butanol and iso-propanol (Lang et al., 2001; Alamu et al., 2008). In the regions of the world where ethanol is less expensive than methanol, like in Brazil, ethanol is of particular interest. When methanol is used in transesterification, the reaction proceeds in two immiscible phases as a result of the solubility of TAG in the methanol (Stavarache et al., 2003). As a result of the biphasic nature of the reaction mixture, there is a lag time at the beginning of the methanolysis reaction before FAME begins to form, after which the reaction speeds up, but quickly decelerates (Darnoko and Cheryan, 2000). Ethanol and other higher alcohols are less polar than methanol. Because the methoxide anion of the methanol has highest reactivity, methanolysis in its entirety, tends to proceed faster than others. Moreover, there is a simultaneous separation of glycerol when methanol is used. The same reaction (transesterification) using ethanol is more complicated as it requires a water-free alcohol as well as an oil with a lower water content, in order to obtain glycerol separation (Schuchardt et al., 1998).

1.2.5Biodiesel Standard Fuel Properties

The properties that affects the suitability of any material for diesel fuel are cetane number, viscosity, cold flow, oxidative stabilityand lubricity (Knothe, 2009). Flash point and heat of combustion can also apply.

Cetane number (CN): is one of the fuel properties of biodiesel. As an indicator of ignition quality, the CN is a prime indicator of fuel quality in the realm of diesel engines (Knothe, 2005). An arbitrary cetane scale assigns at one end a CN of 100 to cetane (C₁₆H₃₄ ; IUPAC-Hexadecane), which has a very short ignition delay and at the other end, a CN of 15 to 2,2,4,4,6,8,8-heptamethylnonane (HMN; also C₁₆H₃₄) with very poor ignition qualities. CN measures the readiness of the fuel to autoignite when injected into the engine. It is dependent on the composition of the fuel and can impact the engine’s startability, noise level and exhaust emissions. Cetane number is a measurement of the combustion quality of diesel fuel during compression ignition. It can as well be defined as a measure of a fuel’s ignition delay, the time/period between the start of injection and the first identifiable pressure increase during combustion of the fuel. The higher the cetane number, the shorter the ignition delay or the more easily the fuel will combust in a compression setting ( such as a diesel engine), low CN causes ignition delay, starting difficulties and knock. The characteristic diesel “knock” occurs when the first portion of fuel that has been injected into the cylinder suddenly ignites after an initial delay, minimizing this delay results in less unburned fuel in the cylinder at the beginning and less intense knock. Therefore higher cetane fuels usually causes an engine to run more smoothly and quietly. Fuels with higher CN have shorter ignition delays, providing more time for the fuel combustion process to be completed. Hence higher speed diesel engines operate more effectively with higher cetane number fuels (Knothe, 2005b).

Viscosity: viscosity in the form of kinematic viscosity, is another biodiesel standard fuel property, it is the most important property of biodiesel since it affects the operation of the fuel injection equipment, particularly at low temperatures when the increase in viscosity affects the fluidity (the ability to flow easily) of the fuel. It is a measure of fuel’s resistance to flow, high viscosity means the fuel is thick and does not flow easily. Viscosity affects the atomization of a fuel upon injection into the combustion chamber and when high, it can result in formation of engine deposits and other related engine problems (Knothe and Steidley, 2005). In terms of automotive liquid fuels, atomization occurs by forcing fuel through a small jet (opening) under high pressure to break it into a fine misted spray (Darnoko et al., 2000).

Cold flow properties: Biodiesel is a mixture of compounds (fatty acid alkyl esters), hence does not possess a melting point, but rather melting ranges. In other words, biodiesel does not deal with melting point but low temperature properties known as cold flow properties, which includes cloud and pour points.

The cloud point: is the temperature at which the first solids appear in a fuel and it can still flow, although these solids can lead to fuel filter plugging.

The pour point, usually a few degrees below the cloud point is the temperature at which the fuel can no longer be freely poured.

Oxidative stability and lubricity: As a lipid material, biodiesel has a tendency to be autoxidized. However, the autoxidation affects the long term stability or aging of the fuel commonly referred to as oxidative stability (Frankel, 2005). Biodiesel possesses inherent good lubricity, especially when compared to petrodiesel (Goodrum and Geller, 2005). Though not prescribed in standard fuel properties (ASTM D6751 and EN 14214), lubricity is essential for proper functioning of vital engine components such as fuel pumps and injectors (Knothe, 2005).

1.2.6Uses of biodiesel co-products:Glycerol

Glycerol or glycerin (propan-1,2,3-triol) is produced in addition to biodiesel during transesterification of vegetable oils and animal fats. Its application has risen since the emergence of the biodiesel industry, which generated a surplus of it (Moser, 2009). Glycerol now has many important applications, in cosmetics, toothpastes, pharmaceuticals, food, alkyl resins, plastics, lacquers, cellulose processing, tobacco, explosives etc. (Moser, 2009). Another recent significant advancement in the use of glycerol is in the production of propylene glycol, an antifreeze component that replaces the toxic ethylene glycol (Feng et al., 2008).

1.6Aim and Specific Objectives of the Study

1.6.1 Aim of the Study

The aim of this work is to compare the physico-chemical properties of the methyl ester and ethyl ester (biodiesels) produced from the Avocado pulp oil.

1.6.2 Specific Research Objectives

The specific research objectives are:

To extract oil from the avocado fruits’ pulp.
To determine the percentage oil yield.
To characterize the avocado oil extracted using GC analysis.
To determine the physicochemical parameters of the oil which are; colour, relative density, refractive index, conductivity, kinematic viscosity, ash content,volatile matter, heat of combustion, flash point, cloud point, pour point, acid value, peroxide value, iodine value, saponification value, free fatty acids .
Production of the methyl and ethyl esters (Biodiesels) from avocado oil.
To characterize both the methyl and ethyl esters (Biodiesels) using GC analysis.

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COMPARATIVE PROPERTIES OF THE METHYL AND ETHYL ESTERS PRODUCED FROM AVOCADO (Persea americana) PULP OIL