Jatropha curcas : A Promising Plant For Biodiesel Production
The genus name “Jatropha” is derived from Greek words jatros (doctor) and trophe (nutrition) that enfolds its medicinal uses. J. curcas , commonly called Purging nut, Barbados nut, or Physic nut, is a perennial drought-resistant plant (bush or small tree) native to South and Central America and its genus contains 170 species. J. curcas grows in drier regions with a rainfall of 500–600 mm /year (250 mm in special conditions, such as on Cape Verde island). J. curcas is a 5-7 m tall shrub or small tree that can live up to 50 years .The branches of J. curcas contain latex. More than 1,000,000 ha of Jatropha has been propagated throughout the world. The majority (85%) of them are in Asian countries (India, China, and Myanmar), 12% in Africa, and 2% in Latin America (Brazil and Mexico). India is the largest cultivar of Jatropa. Several earlier reports predicted that the seed yield of Jatropha range from 2 to 5 Mg/ha and even 7.8 to 12 Mg/ha- without any scientific and technological backup. Jatropha pohliana, Jatropha gossypiifolia, Jatropha multifida, and J. curcas are some of the oil yielding types. Out of these, J. curcas has gained importance due to several reasons.
Why Jatropha curcas for biodiesel production?
A variety of feedstock is available throughout the world for biodiesel production. Biodiesel can be obtained from vegetable oils, animal fats, waste cooking oils, and so on. Some of the frequently used vegetable oils for biodiesel synthesis are sunflower oil, canola oil, soybean oil, palm oil, and Jatropha oil. The use of non-edible Jatropha oils for biodiesel production has put forward its importance because of the increasing demand for other edible oils as food.
The J. curcas oil is potentially relevant because of the properties such as low acidity, better oxidation stability compared with soybean oil, less viscosity compared with castor oil, good cold properties compared with palm oil, and less processing cost compared with corn ethanol. Moreover, Jatropha oil is odorless and colorless when fresh and turns yellow on standing. It is a slow-drying oil. The oil content of the seed varies from 30 to 50% by weight and from the kernel it ranges from 45 to 60% indicating that it is a good raw material for biodiesel production. The presence of phorbol esters and curcin in the seeds and oil are toxic but the oil is still acceptable for biodiesel production. The fatty acid composition of J. curcas oil consists of oleic acid (43.1%), linoleic acid (34.3%), stearic acid (6.9%), palmitic acid (4.2%), and other acids (1.4%).
Curcas has gained popularity as “green gold” for the biodiesel industry around the world because of its potential to replace petroleum-based diesel. The carbon dioxide emissions from Jatropha biodiesel are about 78% lesser than those from petroleum-based diesel which makes Jatropha biodiesel superior to regular diesel fuel. Biodiesel from Jatropha complies with European biodiesel standards. An increase in the volatility of oil and prices of first-generation plants (palm, soybean, rapeseed, e.t.c) represent an opportunity for implementing production of second-generation biodiesel such as J. curcas. It aids to wane GHGs both directly by substituting fossil fuel with oil extracted from seeds and indirectly by fixing carbon stocks in soil and plant biomass.
Chemical transesterification and energy balance:
Curcas oil can be extracted from seeds by a conventional mechanical press. New techniques such as enzyme-assisted three-phase partitioning (TPP), aqueous enzymatic method of oil extraction are now available. The amount of oil produced from seeds and kernels depends upon the method of extraction. The energy value of Jatropha seed oil (39MJ/kg) is higher than anthracite coal and is comparable to crude oil. Improper handling and inappropriate storage lead to an increase in water content which can deteriorate oil. Jatropha oil contains higher free fatty acid (FFA )i.e. 14% making a pretreatment step important before chemical transesterification to reduce the amount of FFA in the oil. Lipase converts the FFA to biodiesel during enzymatic transesterification of Jatropha oil.
The high viscosity of vegetable oils leads to the clogging of fuel lines, filters, and injectors which is its major obstacle. This is why vegetable oils cannot be used directly in diesel engines at room temperatures. Conversion of vegetable oil to biodiesel can be done by using a base-catalyzed transesterification process. This chemical reaction is catalyzed by a strong base and involves filtered fat or oil reacting with an alcohol (usually methanol) to form crude methyl ester biodiesel and crude glycerol. The obtained biodiesel from this process has a viscosity comparable to that of normal diesel. Nevertheless, unrefined J. curcas oil is used in certain types of diesel engines such as Lister-type engines which are used to run small-scale flour mills or electric generators (the so-called Multifunctional Platform For Village Power — PTFM) in developing countries.
Transesterified J. curcas oil or biodiesel is more efficient than pure J. curcas oil because transesterification is an energy-consuming process that not only produces a larger percentage of oil from the seeds but also permits the use of end-products and by-products. Several studies have revealed that the energy balance and the GHG balance of biodiesel produced from J. curcas are positive, strictly positive if seedcake is used for organic manure or as fodder manure. Therefore, the non-edible vegetable oil of J. curcas L. is a potential candidate for the commercial production of biodiesel since it has both the physicochemical and the performance characteristics compared with conventional diesel to facilitate continuous operation without many changes in the design of the diesel engines.
Toxicological studies on J. curcas revealed that it acts as a deterrent to pests and is used as a hedge plant because of its natural toxic nature. Phorbol esters (phorbol-12-myristate-13- acetate) and curcin (a protein) have been confirmed as the major toxic compounds in Jatropha. The oil also contains some anti-nutritional factors making it unsuitable for cooking purposes. The fact that this oil cannot be used for nutritional purposes without detoxification makes it attractive as a non-edible vegetable oil feedstock in the oleochemical industries (biodiesel, fatty acids, soap, surfactants, detergents, etc.).
Phorbol esters are present in relatively high concentrations in the seeds of toxic J. curcas varieties but in Mexican J. curcas it is present in very low concentration in the seeds. The phorbol esters can be reduced by different alkali treatments. The phorbol ester content was reported to be reduced up to 89% in whole and dehulled seed meal after alkali treatment. Thus, a pivotal hindrance in the establishment of J. curcas as a commercial crop can be overcome by detoxifying the oil. However; scanty research has been carried out in this area for complete removal of toxic compounds from J. curcas.
Besides biodiesel production, there are multiple uses of J. curcas. A recent study has revealed that the cultivation of J. curcas resulted in an 11% average increase in mean weight diameter of the soil and a 2% increase in soil macro aggregate turnover. Recovery of soil structure under cultivation of J. curcas implies a sustainable improvement in the surface integrity by ensuring more water infiltration. Jatropha has been used in various fields such as storm protection, soil erosion control, firewood, hedges, and traditional medicines since prehistoric times. Jatropha act as a nutrient pump because the roots can uptake the leached down minerals and return them in the form of leaf fall, fruit debris, and other organic remains. Jatropha seed cake can supplement animal feed and organic fertilizers as it bears a higher percentage of protein and other nutrients after detoxification. Preparation of soap and cosmetics, lamp fuel, firewood, fishing nets are some of its common applications besides biodiesel production. The therapeutic compounds from Jatropha can be used as anti-microbial, anti-inflammatory healing, homeostatic, anti-cholinesterase, anti-diarrheal, anti-hypertensive, and anti-cancer agents in the modern pharmaceutical industry. Toxicological studies must be conducted before using Jatropha or its derivatives as a therapeutic agent.
Good commercial variety with a higher yield and disease resistance is still lacking. It is a drought-resistant plant but it requires proper irrigation and nutrients for fruiting. It has a relatively long gestation period as it requires 3–5 years to become commercially productive. The presence of toxic components limits its use as feed and therapeutic agents. A recent study reveals that Jatropha is susceptible to pests and diseases as well as sensitive to frost and waterlogging. Jatropha may be hosts for some diseases (cassava diseases). The high viscosity of Jatropha seed oil limits its use in cool climatic conditions. Commercial biodiesel production from Jatropha is quite expensive.
The present scenario of biodiesel production from J. curcas as future fuel is acceptable both technically and environmentally but not economically. It would be wise to focus on this plant and to standardize the methods of biodiesel production especially in the field of enzymatic transesterification rather than continuing the search for more feedstocks. Such new processing technologies are anticipated to ameliorate the operating efficiencies of diesel engines. Also, much research is still essential in the field of Jatropha oil extraction, lipase immobilization, optimization of reaction time for enzymatic transesterification, qualitative analysis of the biodiesel produced, and performance of engines. With the earth being blanketed by harmful gases from pollution, it is high time that we focus more on environment-friendly enzymatic methods of biodiesel production. So, attention must be paid regarding the reusability of lipase to design an immobilized lipase for biodiesel production with less reaction time and a higher conversion rate. This environment-friendly technique can lead to the production of biodiesel from immobilized lipase on a commercial scale making it economically feasible. Also, more studies are anticipated for the development of nontoxic varieties for the complete removal of the toxic compounds from the seeds and oil to uplift this plant for both fuel and feed.
J curcas is not used extensively in developing countries like ours due to a lack of knowledge about its uses. So, we should start and encourage its use at least from the local level. Utilizing simple and cheap technological instruments such as plant oil stoves and Lister-type diesel engines or Elsbett engines, J. curcas cultivation could be used for the production of fuel for local use along with added income from other activities related to the commercialization of its by-products: soap, excellent organic fertilizer, lamp fuel, paint, Lubricant and exceeding seedcake for gas production through a biogas digester. Since J. curcas can be plants cultivated successfully in degraded, marginal, or abandoned lands, it appears to be a promising candidate for bioenergy production in such regions and an optimal decentralized renewable source of energy for rural and remote areas where it is impossible to ensure a stable supply of energy.