Assessment of the
potential of Jatropha curcas for
energy production and other uses in developing countries
Introduction
There is growing interest in Jatropha curcas as a biodiesel
miracle tree to help alleviate the energy crisis and generate income in rural
areas of developing countries. Jatropha is becoming a poster child among some
proponents of renewable energy and appropriate energy, especially as an oil
bearing, drought resistant tree fro marginal lands for small farmers. Forgotten
perhaps is that a great share of the farmers in developing countries only have
access through some form of limited tenure to a very small plot of land needed
to grow food crops. To be economical as a biodiesel fuel, Jatropha must be
produced in volume, and those who stand to profit the most are the processors,
retailers and the middle-men, the latter have a history of exploiting
vulnerable small producers by paying only a fraction of the actual value of
their product.
Some common names
Common names include: Jatropha, physic nut,
Jatropha Oil
It is unclear how much genetics play in the amount of oil
contained in Jatropha seed and kernels; nevertheless, estimates of the oil
content in seeds range from 35-40% oil and the kernels 55-60% (www.jatropha.org). However, the amount of actual oil
produced from seeds and kernels is contingent upon the method of extraction,
with hand presses extruding only 20% and more sophisticated a much higher
quantity. The by-product of oil extraction from the seeds and kernels is called
seed cake, and when oil is extracted as a cottage industry the resulting cake
is said to still contain approximately 11% oil. The more sophisticated and
efficient method of extraction produces seed-cake with much lower oil content.
The clear oil
expressed from the seed has been used for illumination and lubricating, and
more recently has been suggested for energetic purposes as a substitute for
diesel. One source reports that one ton of nuts yield estimated 70kg refined
petroleum, 40kg “gasoil leger”, 40kg regular fuel oil, 34kg dry tar, 270kg
coke-like char, and 200kg ammoniacal water, natural gas, creosote, etc.
Biodiesel
Biodiesel is a variety of ester-based oxygenated fuels
derived from natural, renewable biological sources such as vegetable oils. Its
name indicates, use of this fuel in diesel engine alternate to diesel fuel.
Biodiesel operates in compression ignition engines like petroleum diesel
thereby requiring no essential engine modifications. Moreover it can maintain
the payload capacity and range of conventional diesel. Biodiesel fuel can be
made from new or used vegetable oils and animal fats. Unlike fossil diesel,
pure biodiesel is biodegradable, nontoxic and essentially free of sulphur and
aromatics.
The market
that excites the most interest is that for biodiesel. However there are several
points of view that differ considerably regarding Jatropha’s suitability for
petroleum products. Right now these views yield less in actual sales than in
prospects. How quickly these prospects will develop depends on the observer’s
point of view. Jatropha oil has long been seen as a possible substitute for
fuel oil for diesel engines. This is the product where interest is the highest
and most research is being conducted.
A fuel
comprised of mono alkyl esters of long chain fatty acids derived from
vegetables oils or animal fats, designated B100. Biodiesel must meet the
specifications of ASTM 6751-02.
|
Property |
Limits |
|
Flash point, closed cup ⁰C Water and sediment Kinematic viscosity, 40⁰C Sulfated ash Total sulphur Copper strip corrosion Cetane number Cloud point Carbon residue Acid number Free glycerin Total glycerin Phosphorus Vacuum distillation end point |
130 min. 0.05 max 1.9 – 6.0 0.02 max 0.05 max No.3 max 47 min Report to customer 0.05 max 0.08 max 0.02 0.240 0.001 360⁰C max at T-90 |
Advantages of biodiesel
1. Produced from sustainable / renewable
biological sources
2. Ecofriendly and oxygenated fuel
3.
4. Income to rural community
5. Fuel properties similar to the
conventional fuel
6. Used in existing unmodified diesel
engines
7. Reduce expenditure on oil imports
8. Non toxic, biodegradable and safety
to handle
Chemistry of biodiesel production
Biodiesel
is produced by transesterification of large, branched triglycerides into
smaller, straight chain molecules of methyl esters, using an alkali or acid or
enzyme as catalyst. There are three stepwise reactions with intermediate
formation of diglycerides and monoglycerides resulting in the production of
three moles of methyl esters and one mole of glycerol from triglycerides.
Alcohol such as methanol, ethanol,
propanol, butanol and amyl alcohol are used in the transesterification process.
Methanol and ethanol are used more frequently because of its low cost, and
physical and chemical advantages. They can quickly react with triglycerides and
sodium hydroxide is easily dissolved in these alcohols.
Process flowchart for
biodiesel production from Jatropha seeds
According to IPGRI publication, the transesterification
process is normally carried out in centralized plants since the small scale
economy of transesterification has not been determined.
During the
process, methanol, a highly flammable and toxic chemical has to be used, and
this requires explosion proof equipment that might not be available in
developing countries. The WSU study contradicts the IPGRI statement by claiming
that the process is simple to carry out by just mixing the oil with methanol
and caustic soda and leaving it to stand; nevertheless, the chemicals are toxic
and highly flammable, and the processing dangerous. Regardless, this could be
dangerous. Glycerin settles to the bottom of the tank, leaving methyl ester, or
biodiesel at the top. This warrants further investigation in order to determine
which statement is true. Perhaps both statements are true, and the former
process is for more commercial scale operations, and the latter is an
appropriate technology developed for small scale cottage industry producers.
Standard recipe
100lb oil + 21.71 lb methanol 100.45lb biodiesel + 10.40lb glycerol +
10.86lb XS methanol
Plus 1lb of NaOH catalyst.
Reaction time
Transesterification reaction will proceed at ambient temp.
70⁰F but needs 4-8 hours to reach completion. Reaction time can be
shortened to 2-4 hours at 105⁰F and 1-2 hours at 140⁰F.
Product quality
Product quality is important – modern diesel engines are very
sensitive to fuel. It is not biodiesel until it meets ASTM D6751. Critical
properties are total glycerol (completeness of reaction) and acid value (fuel
deterioration). Reaction must be >98% complete.
The Jatropha curcas
plant and oil
The oil
yielding plant Jatropha curcas L. is a multipurpose and drought resistant large
shrub, which is widely cultivated in the tropics as a live fence. The Jatropha
plant can reach a height up to 5m and its seed yield ranges from 7.5 to 12
tonnes per hectare per year, after five years of growth. The oil content of
whole Jatropha seed is 30-35% by weight basis.
Table 1. Problems in
use of Jatropha oil as fuel in diesel engine
|
Problems |
Causes |
|
Coking of
injectors on piston and head of engine |
High viscosity of
raw oil, incomplete combustion of fuel. Poor combustion at part load with raw
oil |
|
Carbon deposits on
piston and head of engine |
High viscosity of
oil, incomplete combustion of fuel |
|
Excessive engine
wear |
High viscosity of
raw oil, incomplete combustion of fuel. Dilution of engine lubricating oil
due to blow-by of raw oil |
The
above problems can be solved by converting raw Jatropha oil in to biodiesel
through trasesterification process.
Pilot biodiesel plant
operation
In the pilot biodiesel plant, Jatropha oil is blended with
alcohol and catalyst mixture in transesterification reactor. The reactor is
kept at reaction temperature for specific duration with vigorous agitation.
After reaction, the biodiesel is collected and washed to get pure biodiesel.
Depending upon the need, the size of the unit can be scaled up to get higher
production capacity. The fuel properties of Jatropha biodiesel produced in the
pilot are given in Table 2.
Jatropha oil + Alcohol + catalyst Jatropha
biodiesel + glycerol
Table 2. Fuel properties of Jatropha oil and its biodiesel
|
Properties |
Jatropha biodiesel |
Diesel |
|
Density, g/ml Viscosity @ 40⁰C Calorific value MJ/kg Flash point , ⁰C Cloud point, ⁰C |
0.865 5.2 39.2 175 13 |
0.841 4.5 42.0 50 9 |
Conclusion
1. Jatropha biodiesel is ideal solution
to meet our higher diesel demand and oil imports. By mixing of 20% biodiesel
with diesel (B20) will help
2. Biodiesel is an alternative fuel for
diesel engines that can be made from virtually any oil fat feedstock. The
technology choice is a function of desired capacity, feedstock type and
quality, alcohol recovery and catalyst recovery. Maintaining product quality is
essential for the growth of the biodiesel industry.
References:
1. Mike Benge, “Assessment of the potential
of Jatropha curcas for energy production and other uses in developing
countries”, July 2006.
2. D.Ramesh, A.Samapathrajan,
P.Venkatachalam, “Production of biodiesel from Jatropha curcas oil by using
pilot biodiesel plant”,
3. Jon Var Gerpen, “Biodiesel Production
Technologies”, Dept of Biological and Agricultural Engineering,
6.