Biodiesel

Biodiesel is a mixture of fatty acid methyl esters obtained by transesterification of vegetable oils or animal fats. These lipid feedstocks are composed by 90–98% per weight of triglycerides and small amounts of monoglycerides, diglycerides, free fatty acids, and residual amounts of phospholipids, tocopherols, sulphur compounds, and traces of water. Transesterification is a multiple step reaction, including three reversible steps in series, where triglycerides are converted to diglycerides, then diglycerides are converted to monoglycerides, and monoglycerides are then converted to esters (biodiesel) and glycerol (by-product). The overall transesterification reaction is described in Figure 1. For the transesterification reaction, oil or fat and a short chain alcohol (usually methanol) are used as reagents in the presence of a catalyst (like NaOH). Although the alcohol:oil theoretical molar ratio is 3:1, the molar ratio of 6:1 is generally used to complete the reaction accurately.

Figure 1. Transesterification of triacylglycerides extracted from algal oil for fatty acid methyl ester (biodiesel).

Food Versus Fuel

Using of edible plants (mainly sugarcane, maize and oilseeds) for biofuel production has a domino effect, since it resulted in all grain prices to double. This leads to trickle through food chain and the price of all food should double soon and little grain will be available for food emergency aid. Also, burning of grain for fuel to run luxury cars has bioethical issue when people are undernourished. More arable land than is available in the USA would be required for a 15% blend in fuels to use soybean or maize as a source of biofuel for US (Table 1). The use of food for fuel can replace a small proportion of the fossil fuel used, and thus cannot have any major effect on fuel prices, with a major effect on food and feed prices.

Table 1. Cropping area needed to replace 15% of transport fuels in the USA.

In a recent study, we cultivated Scenedesmus obliquus in large scale to compare biodiesel production from crop seeds with S. obliquus. In our study, the annual productivity of oil from S. obliquus was calculated as 22 t ha^-1 y^-1 which is more than 800% compared to Jatropha. This makes microalgae to be the main source of biodiesel that has the potential to displace fossil diesel.