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Subtopics: Oil Seeds
Feedstock can be any oil-producing material, but are generally derived from one of the following:
- Vegetable oils such as Coconut oil, Soybean, canola, rapeseed, sunflower oil, etc.
- Restaurant and other commercial frying and cooking oil waste from the kitchens.
- Animal fats such as beef tallow, lard, and rendered materials.
The source of feedstock influences the final cost and the quality of the biodiesel produced. The cheapest feedstocks are waste oil, while the more expensive ones are the high-quality palm, coconut, and other premium oils.
The choice of botanical feedstock is highly dependent on the environmental and economic conditions prevalent in the host country. For example, tropical countries like Malaysia and Indonesia focus mainly on Oil Palm, while the Philippines targets Coconuts because of its importance in the export industry. Temperate regions with large agribusinesses concentrate on local crops such as soybeans, although these plants generally have lower oil content and final yields.
Jatropha is a fast-growing, drought-resistant perennial plant that can survive in semi-arid marginal soil with low nutrient content. Optimum conditions for the plant are temperatures above 20 degrees Celsius, although it can tolerate slight frost, and the plant can be found in drier regions in the tropics with annual rainfall totals of 300-1000 mm.
In addition to its use in biodiesel production, J. curcas can be used for erosion control, property boundaries, and animal fencing. It is also widely-used as a medicinal plant.
The oil content of Jatropha plants is approximately 40%. Given a crop yield of 6-8 MT/hectare, fuel production would be around 2,100–2,800 liters/hectare.
Elaeis guineensis (Palm Oil)
Palm oil is obtained from the fruit of the palm tree Elaeis guineensis, which is native to West Africa, but which has been widely-introduced into other tropical regions around the world. This tree is extensively grown in plantations in Indonesia and Malaysia. Palm oil constitutes about 45-55% of the fleshy part of the fruit, and yields approximately 6000 liters of oil per hectare of crop. Palm oil has a relatively high cloud point (the temperature at which the first wax crystals form), and it currently represents about 1% of the total global biodiesel market.
Cocos nucifera (Coconut Oil)
Coconut oil is obtained from the seed produced by the coconut tree (Cocos nucifera), which is a pantropical plant that thrives along coastlines around the world. The tree is relatively tall at 30-40 m in height, and each tree produces around 60 fruits per year. The Philippines is one of the top producers of Coconut products in the world. Coconut yields about 2700 liters per hectare of crop.
Because of the premium pricing of Coconut oil, which is due in part to the higher costs associated with its processing, biodiesel from this source is typically blended with petrodiesel to between 1-10% of the final product. However, studies in the Philippines by the DOE have shown that this still results in higher engine efficiencies and less pollution, while increasing mileage by as much as 18 percent in engines that ran on even 1% coconut methyl ester.
Ricinus communis (Castor Bean Plant )
Ricinus communis is native to East Africa, but has spread throughout the tropical and warm temperate regions of the world as a fast growing weed. These annual plants like well-drained, nutrient-rich soil, and are an extremely vigorous species, growing from 2-5 meters per season when conditions are optimum. In frost-free areas, the Castor Bean develops into a woody and tree-like plant, and lives for many years.
A plant produces dense clusters of male and female flowers throughout the year, and these in turn give rise to spiny seed pods which contain shiny, extremely poisonous seeds with beautiful and intricate designs and patterns on their surfaces. The oil content of Castor Bean seeds range from 24% in traditional varieties to nearly 50% in hybrid plants, and yields are typically 750 kilos of seeds per hectare. In order to help in the harvest of these seeds, new and shorter varieties of Castor Bean plants have been bred with heights of less than 2 meters.
There are several disadvantages to using Castor Bean as a source of biodiesel. First, the highly-toxic nature of the chemical ricin in the seeds create problems in terms of disposal of seed husks during processing. Second, Cator oil has a viscosity approximately 100x higher than that of #2 diesel due to ricinoleic acid in the oil, and 100% biodiesel produced from this oil still has viscosity (kinematic viscosity) that exceeds all standards. Thus, Castor oil biodiesel has to be blended with petrodiesel in order to lower the kinematic viscosity to acceptable ranges. Third, Castor oil prices are typically high in world markets because of high demand in certain industrial markets (e.g. lubricating grease, surfactants, surface coatings, telecom, engineering plastics, pharma, rubber chemicals, etc) which is a large negative factor by raising the final production costs.
Glycine max (Soybean Oil)
Soybean oil is derived from the seed of the legume plant Glycine max, which is native to China, but is now widely grown around the world in both tropical and temperate climates. Like other legumes, the seeds are borne in elongated pods, and each seed may contain from 14-24% oil. The United States of America is the leading producer of soybeans in the world, with approxiately 26% of the available acreage in the USA devoted to this crop. Soybean only produces about 450 liters of edible oil per hectare of crop.