Vegetable oil (m)ethyl esters, commonly referred to as biodiesel, are prominent can­didates as alternative diesel fuels. The name biodiesel has been given to transesteri — fied vegetable oil to describe its use as a diesel fuel (Demirbas 2002). There has been renewed interest in the use of vegetable oils for making biodiesel due to its less pol­luting and renewable nature as against the conventional diesel, which is a fossil fuel that will eventually be exhausted. Biodiesel is technically competitive with or offers technical advantages over conventional petroleum diesel fuel. The vegetable oils can be converted into their (m)ethyl esters via a transesterification process in the presence of a catalyst. Methyl, ethyl, 2-propyl, and butyl esters were prepared from vegetable oils through transesterification using potassium or sodium alkoxides as catalysts. The purpose of the transesterification process is to lower the viscosity of the oil. Ideally, transesterification is potentially a less expensive way of transform­ing the large, branched molecular structure of bio-oils into smaller, straight-chain molecules of the type required in regular diesel combustion engines.

Biodiesel is a domestic fuel for diesel engines derived from natural oils like soy­bean oil. It is the name given to a variety of ester-based oxygenated fuel from renew­able biological sources that can be made from processed organic oils and fats. The inedible oils such as jatropha curcas, madhuca indica, ficus elastica, azardirachta indica, calophyllum inophyllum jatropha, neem, pongamia pinnata, rubber seed, mahua, silk cotton tree, tall oil, microalgae etc. are easily available in developing countries and are very economical comparable to edible oils. Biodiesel obtained from waste cooking vegetable oils, tallow fat, and poultry fat have been consid­ered promising options. Waste cooking oil is available at relatively cheap prices for biodiesel production in comparison with fresh vegetable oils.

The biodiesel esters were characterized for their physical and fuel properties in­cluding density, viscosity, iodine value, acid value, cloud point, pure point, gross heat of combustion, and volatility. The biodiesel fuels produced slightly lower power and torque and higher fuel consumption than No. 2 diesel fuel. Biodiesel is bet­ter than diesel fuel in terms of sulfur content, flash point, aromatic content, and biodegradability (Bala 2005).

Most of the biodiesel that is currently made uses soybean oil, methanol, and an alkaline catalyst. The high value of soybean oil as a food product makes production of a cost-effective fuel very challenging. However, there are large amounts of low- cost oils and fats such as restaurant waste and animal fats that could be converted into biodiesel. The problem with processing these low-cost oils and fats is that they often contain large amounts of free fatty acids (FFA) that cannot be converted into biodiesel using an alkaline catalyst (Demirbas 2003).

Biodiesel is an environmentally friendly alternative liquid fuel that can be used in any diesel engine without modification. There has been renewed interest in the use of vegetable oils for making biodiesel due to its less polluting and renewable nature as against the conventional petroleum diesel fuel. If biodiesel is used for engine fuel, this would in turn benefit the environment and local populations.

Microalgae contain oils, or lipids, that can be converted into biodiesel. The idea of using microalgae to produce fuel is not new, but has received renewed attention recently in the search for sustainable energy. Biodiesel is typically produced from plant oils, but there are widely voiced concerns about the sustainability of this prac­tice. Biodiesel produced from microalgae is being investigated as an alternative to conventional crops, such as rapeseed: microalgae typically produce more oil, con­sume less space, and can be grown on land unsuitable for agriculture. However, many technical and environmental issues, such as land use and fertilizer input, still need to be researched and large-scale commercial production has still not been at­tained.

Using microalgae as a source of biofuels could mean that enormous cultures of algae will be grown for commercial production, which would require large quan­tities of fertilizers. While microalgae are estimated to be capable of producing 10 to 20 times more biodiesel than rapeseed, they need 55 to 111 times more nitrogen fertilizer: 8 to 16 tons/ha/year. Such quantities of nitrogen and phosphorus could damage the environment. Additionally, it could limit the economic viability of mi­croalgae. Nitrogen and phosphorus found in algal waste, after the oils have been extracted, must therefore be recycled.

Microalgae contain lipids and fatty acids as membrane components, storage products, metabolites, and sources of energy. Algae present an exciting possibil­ity as a feedstock for biodiesel, especially when you realize that oil was originally formed from algae.

Algal oil is converted into biodiesel through a transesterification process. Oil extracted from algae is mixed with alcohol and an acid or a base to produce the fatty acid methylesters that makes up biodiesel (Chisti 2007).

Many algae are exceedingly rich in oil, which can be converted to biodiesel. The oil content of some microalgae exceeds 80% of dry weight of algae biomass. The use of algae as energy crops has the potential, due to their easy adaptability to growth conditions, of growing either in fresh or marine waters and avoiding the use of land. Furthermore, two thirds of earth’s surface is covered with water, thus algae would truly be renewable option of great potential for global energy needs. Figure 5.1 shows world production of biodiesel from 1980 to 2008.

Possessing approximately identical energy potential with mineral diesel fuel, the bio-diesel engine has a number of essential advantages:

— It is not toxic, contains practically no sulfur or carcinogenic benzene;

— Decays in natural conditions;

— Provides significant reduction in harmful emissions in the atmosphere upon burn­ing, both in internal combustion engines and in technological units;

— Increases cetane number of fuel and its greasing ability, which essentially in­creases the engine performance;

— Has high ignition temperature (more than 373 K), which makes its use rather safe;

— It is derived from renewable resources.