Chapter 2: Literature Review
2.3 Jatropha curcas
Jatropha curcas is a hardy tree that produces non-edible seeds with a high oil content of about 37% on average (Katembo & Grey 2007) and under optimal conditions it can produce up to 40%
oil yields (Wood 2005). Jatropha curcas is an agro-forestry crop which offers advantages over other feedstock in that it grows rapidly from cuttings and seeds taking about two to three years to reach maturity and generate economic yields with minimum water and nutrients (Wood 2005).
Jatropha curcas is well adapted to arid and semi- arid conditions and generally occurs in seasonally dry areas. It is said to grow in savannah, scrub vegetation and other open vegetation (Edje and Mngometulu 2005). It is said to grow well on well-drained soils and even on poor gravelly land not suitable for most arable crop production. Brinks (2005) in Edje and Mngometulu (2005) says it can grow even on saline soil, drought tolerant growing in areas with rainfall from 300 to 1000 mm/annum and can survive seven or eight months of drought.
Jatropha curcas grows wild across Sub-Saharan Africa, India, South East Asia and China and is often cultivated as a living fence.
The hardy tree is able to tolerate a wide range of climatic conditions with a productive span of over 30 years going up to 50 years (Nabi, Akhter & Islam 2007). Jatropha curcas is said to be sensitive to wind but can withstand mild frost (Wiesenhutter 2003). It is a deciduous plant shedding it leaves in the dry season. It grows in climatic conditions commonly found in a band around the globe 30degrees north and south of the equator which places most of the viable Jatropha curcas growing regions in the developing world (D1 Oils (undated)). This is because like most oil crops it does well in areas with warm tropical climate (Edje and Mngometulu 2005). Under rain fed conditions, the growth of Jatropha curcas is regulated by rainfall, temperature and light. The flowers of Jatropha curcas produce nectar, may be scented and are insect pollinated. Their sweet perfume at night and greenish yellow colour suggest that the species is pollinated by moths (Edje and Mngometulu 2005).One of its unusual features is that before falling to the ground, the dry fruits and seeds remain on the tree for some time especially under dry conditions (Nabi, Akhter and Islam 2007). The seed and oil yields vary greatly according to origin and production conditions (climate, soil, plant spacing, water supply, fertilizer). Dry conditions, in particular, increase the oil content of the seeds (Wiesenhutter 2003).
Nabi, Akhter and Islam (2007) highlighted some of the benefits of Jatropha curcas oil as follows:
Jatropha curcas oil has a very high saponification value hence it has been traditionally used for making soaps and candles. The oil is also used as an illuminant and burns without emitting smoke.
Jatropha curcas is also used in folk medicine; the latex of jatropha contains an alkaloid known as
“j trophi ” hich i b i v to h v ti-cancerous properties. The bark of jatropha yields a dark blue dye which is used for colouring clothes, fishing nets and lines (Nabi, Akhter and Islam 2007).
Notwithstanding the above mentioned benefits, Jatropha curcas until recently had no commercial application (Wood 2005).
2.3.1 Biodiesel
Vegetable oils, such as soybean oil, rapeseed oil, coconut oil and palm oil are major sources of biodiesel (Nabi, Akhter and Islam 2007). However these oils are edible and thus make biodiesel
The extracted crude Jatropha curcas oil has been found to have the most exciting properties in the field of biodiesel fuel (Nabi, Akhter and Islam 2007). The oil can be refined into high qualit y biodiesel through a process called transesterification whereby the chains of fatty acids in the oil are broken down to alcohol esters (biodiesel) and glycerine (Nabi, Akhter and Islam 2007) shown as : Oil + ethanol + catalyst Biodiesel + glycerol (Nabi, Akhter and Islam 2007). The catalyst may be an alkali such as Potassium Hydroxide (KOH) or Sodium Hydroxide (NaOH) or it may be an acid such as Hydrochloric acid (HCl) or Sulphuric acid (H2SO4). Below is the bio-energy cycle of Jatropha curcas:
COMBUSTIBLE
BIODIESEL
TRANSESTERIFICATION SEED SHELLS
SEED OIL
FRUIT HULLS
FERMENTATION
COMBUSTIBLES BIOGAS (~CH4)
FERTILIZER
Figure 2.2 Bio-energy cycle of Jatropha curcas (Wood 2005; Dubois 2008) SEEDS
FRUIT
OIL EXTRACTION
SEED CAKE
COMPOST
Jatropha curcas biodiesel fully complies with the current European EN14214 standard for automotive diesel with even a higher cetane value that that of mineral diesel which allows it to burn cleaner at higher temperatures (Wood 2005).
In addition to that, as the Jatropha curcas trees grow they capture carbon dioxide (CO2) thus reducing the impact of greenhouse gas emissions significantly. A study from the United States National Renewable Energy laboratory has concluded that Biodiesel reduces net CO2 emissions by 78 %( Wood 2005).
D1 Oils is a company that was founded to design and build scalable biodiesel refineries for the UK road haulage industry. They first investigated rapeseed as their primary feedstock but found it commercially unattractive because of the relatively high cost when using mid-sized refineries.
This prompted the company to search for alternative edible and non-edible vegetable oils suitable for producing biodiesel in volume at low cost. This is how the company identified Jatropha curcas as one of the best feedstock in making biodiesel (D1 Oils (undated)). Until recently, the European Union biofuel policy had relied on the assumption that the heavily subsidized production of rapeseed would meet its biofuel targets. Accordingly some three million hectares of agricultural land across Europe produces ten million tonnes of rapeseed but since only about 20% is used to produce biodiesel an equal area would be required to meet the EU targets (Edje and Mngometulu 2005; UNCTAD 2006). However rapeseed is expensive to produce, has heavy demand on soil nutrients and requires expensive crop rotation which is what made Jatropha curcas an important optional feedstock for the production of biodiesel (Edje and Mngometulu 2005; UNCTAD 2006).
D1 estimates that a plantation set on waste or marginalized land can support a minimum of 2000 productive trees per hectare and each tree yielding about 3.5 kg of seed, a hectare would have a harvest of 7 tonnes of seed which when crushed would produce about 2.8 tonnes of crude vegetable oil. D1 estimates that each tone of crude Jatropha curcas oil produces about 1100 litres of biodiesel (Wood 2005). However according to Jumbe, Msiska and Mhango (2007) all countries in Africa that grew Jatropha curcas realised a yield of 1892 litres of oil per hectare. D1 Oils in Swaziland encouraged households to at least have 1 hectare plantations of Jatropha curcas in order for the activity to be viable.