University of Groningen

Optimization of Jatropha curcas pure plant oil productionSubroto, Erna

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1

Chapter 1 Introduction

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1.1 Need for bio-based energy source

Fossil fuels such as petro-diesel, LPG and kerosene are the main energy sources within the

developing countries. However, fossil fuel is becoming more depleted and the price steadily

increased over the last decade to values between 100 and 110 USD per barrel at this

moment (Figure 1). Moreover, most developing countries are depending on fossil fuel

imports and government’s subsidization of those fuels becomes a burden for government’s

budgets. In addition, many negative environmental impacts are caused by the combustion

of fossil fuel, i.e. the greenhouse effect associated with CO2 emissions. Therefore, utilization

of alternative fuels is strongly recommended.

Figure 1 Price of NYMEX Light Sweet Crude Oil in the period 2003- 2013 [1]

An alternative fuel must be technically feasible, economically competitive, environmentally

acceptable, and easily available [2]. Biofuels such as pure plant oil (PPO), biodiesel and

ethanol have become promising alternative renewable and independent sources in

developing countries. In general, biofuels can be used in the transportation sector, for

electricity generation, and for domestic use such as cooking, lighting or heating.

Some countries have issued policies for the transition from fossil fuel to biofuel and

introduced specific legislation. For example, the European Commission has issued a binding

target of 20% for the share of renewables within the total energy consumption by 2020, and

a minimum of 10% of the transport fuel must be based on biofuels in 2020 [3]. For the same

year, China's Renewable Energy Law (RE Law) has set a binding target of 15% of all energy to

come from renewable sources [4]. Likewise, Indonesia has issued a policy, The President

3

Regulation No. 5 Year 2006 on National Energy Policy, aiming for at least 5% of total energy

consumption to be biofuel by 2025 [5]. For biodiesel in particular, Europe, Brazil, China, and

India each have targets to replace between 5 and 20% of the total diesel consumption by

biodiesel [6].

The term biofuel is defined as fuel produced from renewable biomass (organic materials

that are plant or animal based, including dedicated energy crops, agricultural crops and

trees, food, feed and fiber crop residues, aquatic plants, forestry and wood residues,

agricultural wastes and other waste materials [7]. Pyrolysis oil, pure plant oil (PPO), bio-

diesel and bio-ethanol are well-known examples of experimental and proven biofuels.

Pyrolysis oil is a product of thermochemical decomposition of organic material at elevated

temperatures in the absence of oxygen. Bio-ethanol is an alcohol made by fermentation,

mostly from carbohydrates produced in sugar or starch crops such as corn, sugarcane, or

sweet sorghum. Ethanol can be used as a fuel for vehicles in its pure form, but it is usually

used as a gasoline additive to increase the octane level and reduce vehicle emissions.

In this chapter, the use of vegetable oil as fuel will be described in more detail. Vegetable oil

has become the main feedstock for biodiesel production, especially as a petro-diesel

substitute. Pure Plant Oil (PPO) is vegetable oil used directly as a fuel in suitable diesel

engines without undergoing chemical change from its original characteristics [8]. Bio-diesel

is defined as a fuel comprised of mono-alkyl esters of long-chain fatty acids (chain length

C14-C22) derived from renewable lipid - vegetable oil - sources [2]. It can be used in

compression ignition engines with little or no modifications [9]. Biodiesel is produced by a

trans-esterification reaction of lipid sources with short-chain alcohols, preferably methanol

or ethanol.

1.1.1 Vegetable oils

Vegetable oil consists of mostly triacylglycerols (90-98%), but it also contains minor

components such as free fatty acids (FFA) (generally 1–5%), mono- and diacylglycerols,

phospholipids, chlorophylls, carotenes, sterols, tocopherols, phenolic compounds, metals,

sulfur compounds and traces of water [10]. Triglyceride is a lipid consisting of three

molecules of fatty acids covalently bonded to one molecule of glycerol (see Scheme 1).

Commonly found fatty acids in vegetable oils are palmitic, stearic, oleic, linoleic and linolenic

acid.

4

Scheme 1 Chemical structure of triglyceride

The main advantages of vegetable oils over petro-diesel are their ready availability,

renewability, non-toxicity, and biodegradability. Meanwhile, the main disadvantages are the

higher viscosity, lower volatility, and the reactivity of unsaturated hydrocarbon chains

[2,11]. All vegetable oils are extremely viscous with viscosities ranging from 9 to 17 times

greater than petro-diesel fuel [11,12]. Trans-esterification is the common method used to

reduce the viscosity of vegetable oils such that this product, termed biodiesel, can be used

directly in conventional diesel engines [12]. The use of vegetable oil-derived fuels led to

substantial reductions in emissions of carbon monoxide (CO), poly-aromatic hydrocarbons

(PAH), smoke, and particulate matter (PM) [13,14]. Furthermore, vegetable oil-derived fuels

contribute to the reduction of greenhouse gas emissions in comparison to petro-diesel,

since carbon dioxide (CO2) emitted during combustion is recycled in the photosynthesis

process in the plants [2]. Reductions in net carbon dioxide emissions are estimated at 77–

104 g/MJ of diesel displaced by biodiesel [15]. In addition, vegetable derived fuels have an

output-to-input energy ratio higher than petro-diesel. Typical results show that the life-cycle

output-to-input (fossil) energy ratio of soybean oil, soy-biodiesel and petro-diesel is around

6.2, 3.2, and 0.83, respectively [16].

Vegetable oils have chemical structures different from petro-diesel. Classic diesel fuel

consists of hydrocarbon molecules with chain lengths of C10-C15, while vegetable oils consist

of triglycerides whose chain lengths range mostly from C16 to C22; either saturated or

unsaturated. The average chemical formula for classic diesel fuel is C12H23, ranging from

approximately C10H20 to C15H28. Triglyceride molecules have molecular weights between 800

and 900 and are thus nearly four times larger than typical diesel fuel molecules. The large

size of vegetable oil molecules and the presence of oxygen in the molecules suggest that

some fuel properties of vegetable oil should differ markedly from those of hydrocarbon

fuels [11]. The chemical and physical properties of the fuel liquids are shown in Table 1.

5

Table 1 Fuel properties of common vegetable oil used as biodiesel feedstock

Type of oil CN LHV

(MJ/kg)

Density

(kg/L)

Kin.Visc.

mm2/s

FP

°C

CP

°C

PP

°C

Ref.

Diesel fuel #2 45.8 45.2 0.847 2.39 78 -19 -23 [17]

Edible oil

Palm oil 49 40.14 0.9139 40.33 275 23 12 [18, 19]

Rapeseed 37.6 39.709 0.9115 37.3 246 -3.9 31.7 [11, 20]

[11, 20]

[11, 20]

Sunflower 37.1 39.575 0.9161 34.4 274 7.2 -15

Soybean 37.9 39.623 0.9138 33.1 254 -3.9 -12.2

Non-edible oil

Jatropha 38 39.071 0.917 35.98 229 9 4 [21, 22]

Kinematic viscosity were measured at 38 oC, CN - cetane number, LHV - lower heating value, FP-flash point, CP-

cloud point, PP-pour point

Vegetable oil-derived fuels are usually produced from edible vegetable oils, such as

soybean, rapeseed, sunflower and palm oils. They are not economically attractive since their

prices are higher than diesel fuel, as can be seen in Figure 2. In addition, production of

biofuels from edible vegetable oils is the main cause of increased global food market prices

[23]. One of the most promising potential raw materials for biofuel production is from non-

edible sources such as jatropha oil [23-27].

Figure 2 Price of diesel # 2 and edible vegetable oils (2003-2013) [1, 28]

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Compared to other food-based crops such as palm, soybean and sunflower, jatropha is

considered as a more sustainable feedstock for fuel production [23,26]. It is a non-edible oil,

thus it will not impair any food security issue [29]. Jatropha oil provides a relatively high oil

yield per area compared to other vegetable oils. It has a yield per hectare of more than

twice that of sunflower and four times that of soybean (See Table 2). General description

and the application of jatropha oil is described in more detail in part 1.1.2.

Table 2 Oil production per area of different oil plants [30]

Vegetable Latin name Liters oil/ha/yr

Palm Elaeis guineensis 5,698

Coconut Cocos nucifera 2,578

Jatropha Jatropha curcas 1,812

Karanja Pongamia pinnata 1,250

Rapeseed Brassica napus 1,140

Peanut Ariachis hypogaea 1,018

Sunflower Helianthus annuus 915

Linseed Linum usitatissimum 458

Soybean Glycine max 430

1.1.2 Jatropha curcas L.: general description and application

Jatropha curcas, commonly known as physic nut (English) or purgeernoot (Dutch) or jarak

pagar (Bahasa Indonesia) is a perennial oil-bearing shrub (normally up to 5 m height)

belonging to the Euphorbiaceae family. The vegetable is a native to Central and South

America, whereas it has been distributed to tropical and subtropical countries and mainly

grown in Asia and Africa [31]. The tree has flexibility adaptation in the various

environmental growing conditions. In general, jatropha is toxic to humans and animals.

Phorbol esters, trypsin inhibitors, phytates, saponins and lectins (curcin) are known as the

toxic compounds found in the seed of toxic varieties of jatropha [32]. In addition to the

more common toxic varieties, non-toxic varieties of Jatropha curcas that contain negligible

amounts of phorbol esters are reported to exist in Mexico and Central America [24]. The

jatropha tree starts producing seeds from the first year and continues producing seeds up to

50 years with up to three harvesting times per year [33]. Typical seed production levels up

to 5 tons seeds per ha per year has been reported [8]. The seed yields and oil content are

highly dependent on environmental conditions (temperature, altitude, rainfall, sunlight, soil

conditions), genetics, plant age and plant management (use of pesticide and fertilizer,

irrigation, plant density, etc.) [8,34].

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Dry Jatropha curcas fruit contains about 30-40% hull and 60-70% seed. The fruits are 2.5 cm

long, ovoid, and have 2–3 seeds [35]. The seed contains about 30-40% shell and 60-70%

kernel with the weight of the seeds is about 0.45-0.86 g [36]. The oil content in jatropha

seed is reported to be in the range of 29 to 37% by weight of the seed or from 44 to 62%

weight of the kernel. The kernels are also rich in crude protein (22-35%) [36]. The oil

contains 63.9-91.6% unsaturated fatty acids (Table 3) with an iodine value of 92-112 which

classifies it as a semi-drying oil (partially hardens when the oil is exposed to air) [24,37]. A

representative figure of Jatropha curcas tree can be seen in Figure 3.

Table 3 Fatty acid composition of jatropha oil [24]

Fatty acid composition Jatropha oil

Myristic acid C14:0 0-0.1

Palmitat acid C16:0 14.1-15.3

Palmitoleic acid C16:1 0-1.3

Stearic acid C18:0 3.7-9.8

Oleic acid C18:1 34.3-45.8

Linoleic acid C18:2 29.0-44.2

Linolenic acid C18:3 0-0.3

Arachidic acid C20:0 0-0.3

Bahenic acid C22:0 0-0.2

Total Saturated 17.8-25.6

Total Unsaturated 63.3-91.6

Figure 3 Rpresentative figure of Jatropha curcas vegetable

All parts of the jatropha plant can be used for a wide range of purposes. The potencies of

several parts of jatropha plant can be seen in Figure 4. The jatropha plant itself has

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traditionally been used as a medicinal plant and as a live fence to reclaim land or to protect

gardens and crops from grazing animals [31,33]. The non-edible jatropha oil can be used

directly as fuel in lamps [38], stoves [39], and stationary or mobile diesel engines (pumps,

mills, tractor and electricity generators) [33] and as raw material for the production of

lubricants [40], alkyd resins (paints and varnishes) [41], candles, medicines, cosmetics and

soaps [42]. It is reported that the use of a blend of 10% (v/v) jatropha oil with diesel fuel

does not cause engine problems [35]. The oil also can be converted to a high-quality

biodiesel fuel, usable in a compression ignition (CI) diesel engine [43,44]. Furthermore, the

fuel properties of jatropha biodiesel fulfill the major specifications outlined in European (EN

14214) and American (US ASTM D 6751-02) standards [45].

Figure 4 Potential utilization of the jatropha plant (Modified from [24])

The economic evaluation has shown that the biodiesel production from jatropha is very

profitable provided the rest of the plants can be converted and sold as valuable products

[46]. The fruit hulls can be use as activated carbon [47] and bio-compost production [48].

The cake obtained after removing the oil from the seed or kernel can be used as as an

organic fertilizer [35], a fermentation substrate in enzyme production [49], or as feedstock

for biogas production [50]. Non-toxic varieties or detoxified press cake, can be used as

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animal feed as it is rich in protein (48 - 64%) [32,36]. In addition, there are several potential

applications of jatropha seed shell, for example as particle board [51], activated carbon [52],

pyrolysis oil [53] fuel for combustion units [54] and gasifier feedstock [55] which will add

some economic value.

1.2 Vegetable oil processing

Jatropha oil processing involves the extraction and processing of oils from oilseed as shown

in the general flow-scheme in Figure 5.

Figure 5 Schematic representations of “jatropha PPO production”; superscripts:

the corresponding chapter numbers in this thesis

To successfully produce jatropha PPO or the bio-diesel derived from it, many factors play a

role. The scheme illustrates the flow from harvested plant material to the final PPO product

and the possible processes that can or have to be applied. In this section, the available

literature regarding these processing steps will be summarized and analyzed, while the

characteristics that determine the initial and longer term quality, i.e. stability, and

performance of the oil will be summarized in the subsequent section. Each topic

summarizes the current state of art and also highlights the unknowns and the research

questions that will be dealt with in this thesis.

1.2.1 Growing conditions and harvesting

The seed yields are highly dependent on environmental conditions (temperature, altitude,

rainfall, sunlight, soil conditions), genetics, plant age and plant management (use of

pesticide and fertilizer, irrigation, plant density, etc) [8,34,57,58]. At low input condition, the

dry jatropha seed yield is in the range of 2-3 tons/ha/yr. In more favorable conditions dry

jatropha seeds yield up to 5 tons/ha/yr have been achieved [8]. Srivastava et al. (2011) [58]

10

studied the effect of growth performance on morphological characterization of seeds and

seed oil content.

The harvesting time is one of the critical steps in seeds production. Oil content has been

related to fruit maturity. The jatropha seed can be classified into four maturity stages: early

maturity (green fruit), physiological maturity (yellow fruit), over maturity (brown fruit), and

senescence (black-dry fruit). The best fruit maturity stage for seed oil content was found in

yellow and brown fruit [59]. It is recommended that seed should be harvested at low

moisture content [60]. But if the seeds are harvested at high moisture content, seeds should

be dried immediately.

1.2.2 Drying and storage

Fresh jatropha seeds are usually has a moisture content of approximately 75% d.b. [61].

Therefore drying the seeds is necessary to reduce the moisture content of fresh harvested

seed to a level that inhibits the biochemical, chemical and microbiological deterioration.

This allows safe storage over an extended period and provides optimum conditions for next

processing. Other objectives of drying are to substantially reduce weight and volume,

minimize packaging, storage and transportation costs and enable storability of the product

under ambient temperatures [62]. Drying must not impair the quality of the extracted oil.

During the drying process, the constituents in the seeds can undergo undesirable reactions

which cause loss of quality. The major deterioration of the seeds is due to lipid peroxidation

and lipid hydrolysis [63]. Some other negative effects of hot air drying methods on the

structure of some biological materials: changes such as shell cracking, color changes, cellular

shrinkage, endosperm damage, or protein denaturalization [64].

Proper handling and storage of oil-containing materials are very important to minimize

deterioration and maintain good quality of both contained oil and cake residue. There are

several factors that influence rate of deterioration during seed storage: initial moisture

content, temperature and humidity. The safe moisture content of seed for storage varies

between 3-9% d.b., with lower moisture content for seeds with higher oil content [65].

Moisture contents in the range of 7.9 – 8.4% w.b. are reported as safe for storage of

jatropha seeds up to five months inside plastic bags under ambient room conditions (24.4-

29.1 °C; 46-85.4% RH) [66].

1.2.3 Pretreatment before extraction

In industry, oilseeds undergo extensive preparation prior to extraction. Preparation may

consist of a number of steps, such as cleaning, deshelling, moisture conditioning, cracking or

11

flaking and heat treatment [67]. Oilseeds need to be cleaned to remove foreign material

such as plant stalk, debris or low quality seeds. Most oilseeds need to be separated from

their outer husk or shell prior to oil extraction since husk and shells of oilseeds do not

contain a significant amount of oil (less than 1 percent). Preparing and reducing the seed is

to break down or weaken the oil-cell walls and also to expose a greater area of oil-bearing

cells to the moisture and heat during heat treatment. Flaking facilitates oil release by

decreasing the distance that the oil will have to travel to reach the particle surface. Heat

treatment is essential because it completes the rupture of remaining cells to release oil,

lowers the viscosity of the oil, coagulates the protein for better diffusion during extraction.

Moisture conditioning of seed conducted to increases plasticity and adjusts the moisture

content of the seed to the optimum level for extraction. These steps are usually necessary

to enhance oil yield. Each type of oilseed requires a specific method of pretreatment [68].

1.2.4 Oil extraction

Oilseed processing and oil extraction processes are designed to obtain high quality oil with

minimal undesirable components, achieve high extraction yields and produce high value

cake. The choice of extraction method depends on the nature of the raw material, the oil

content of the material, the level of allowable residual oil in the cake, the extent of protein

denaturation allowed, product application and scale of production [69]. The maximum level

of oil that can be extracted from a given sample of seed depends on the method of

extraction. Industrial extraction of oil from seeds in general is carried out by two processes –

solvent and mechanical extraction. Both approaches have their advantages and

disadvantages with respect to scale of operation, centralization, extraction efficiency, and

environmental and health risks. For seed with high oil content (above 35%) such as,

flaxseed, safflower, sunflower seeds, groundnuts, palm kernels, rapeseed, and cottonseed,

both steps are involved. Whereas, materials with lower oil content, such as soybeans and

rice bran, can be directly solvent extracted [70]. Solvent extraction provides a high oil

recovery, but co-extraction of non-triglyceride components requires an additional refining

process [71]. It also requires a rigorous and energy intensive solvent recovery to reduce the

volatiles level in both oil and cake [72,73]. Mechanical extraction is simpler and generally

preferred because of its lower investment and operational cost. It can also be operated by

semi-skilled personnel and produces relatively good quality oil, and it enables the use of the

cake residue [74]. However, a disadvantage of mechanical extraction is the lower oil

recovery compared to solvent extraction. It has been reported that solvent extraction with

n-hexane could achieve about 90-99% oil recovery, against a maximum of 60-90% for

mechanical extraction. The most efficient mechanical extraction may lead to some 5-7% of

residual oil remaining in the cake [68,75]. Other extraction methods such as supercritical

CO2 extraction [76], aqueous extraction [77] with or without enzyme pretreatment [78] can

be carried out for oil extraction.

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Table 4 Comparison of extraction methods

Process Mechanical

Extraction

Aqueous

Extraction

Solvent

Extraction

SC-CO2

Extraction

Oil Yield 60- 90% 40-80% 90-99% 90-99%

Oil quality Low to Medium Pa

Medium FFA

Medium OS

Medium P

Medium FFA

Medium OS

Low to High Pb

Medium FFA

Low to medium OS

Low P

Low FFA

Low OS

Cake quality

Protein (NSI)

Oil residue

High

7-17%

Medium

10-20%

Low

<1%

Medium

<1%

Scale production Small to medium Medium to Large Large Medium to Large

Energy requirement Low Medium Large Medium

Total Cost Low Medium - High High High a Cold press gave lower phosphorus content than hot pressed

b Depends on the solvent used. Hexane extraction gives higher phosphorus content than alcohol extraction

c FFA – free fatty acid, P – phosphorus content, OS – oxidative stability

1.2.5 Oil purification

The crude oil that is extracted from the oilseeds is a mixture of FFA, mono-, di-, and

triglycerides, phosphatides, carbohydrate, protein, pigments, sterols and tocopherols. Trace

amounts of metals, oxidation products, flavor and odor compounds may also be present.

There are two basic methods in oil refining: chemical refining, and physical refining. These

methods are basically different and based on free fatty acid removal. In chemical refining,

FFA is removed by neutralization using alkali solution. Meanwhile in physical refining, FFA is

removed by steam stripping. Chemical refining is suitable for oil with low FFA content and

high phosphorus while physical refining is suitable for oils with high FFA content and low

phosphorus level [70,79].

Degumming

Degumming is the first stage in oil refining process, and it is used to precipitate metal salts

(phosphatides, carbohydrates, protein and mucilaginous materials likely to cause the oil to

develop flavors and odors [70]. Phospholipids should be removed because of their strong

emulsifying action and can join with pro-oxidant metal as they cause the problems during

next refining step and storage [80], biodiesel production [81] and when it burn in diesel

engine [82]. Table 5 show degumming methods of vegetable oil.

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Table 5 Degumming processes in vegetable oils

Methods Principle Ref

Water degumming Treatment of crude oil with hot water/steam; the gums for lecithin

production

[83]

Acid degumming Treatment of crude/water degummed oil with acid solution, the gums for

animal feed

[84]

Acid refining / Special

degumming

Treatment of crude oil/water degummed oil with acid solution, then

partially neutralized with alkali

[85]

S.O.F.T. degumming Degumming using chelating agent (EDTA) [86]

Ethanolamine

degumming

Treatment with di-ethanolamine, simultaneous degumming and

deacidification

[87]

Electrolyte degumming Treatment with electrolyte solution [88]

Enzymatic degumming Modification of phospholipids with enzymes to facilitate the hydration [89]

Membrane

degumming

Passage of crude oil through a semipermeable membrane retaining

phospholipids

[90]

Supercritical CO2

degumming

Extraction of phospholipid by supercritical CO2 [91]

Deacidification

The deacidification purpose is to remove non-triglyceride impurities, consisting principally of

FFA, along with substantial quantities of mucilaginous substances, phospholipids and

coloring pigments [70]. Chemical, physical and miscella deacidification are general method

for deacidification and have been used industrially. Table 6 shows features and limitations

of deacidification methods [92].

Table 6 Methods of Deacidification [92]

Features Limitations

Chemical deacidification (neutralization)

Versatile––produces acceptable quality oil from all

types of crude oil

Multiple effects––purifying, degumming, neutralizing

and partially decolorizing the oils

Excessive loss of neutral oil with high-FFA crude oil

Neutral oil loss due to hydrolysis, saponification,

emulsification, water washing

14

Physical deacidification (steam stripping)

Suitable for high-FFA oil

Low capital and operating costs

Greater oil yield

Pretreatments are very stringent

Not suitable for heat sensitive oil––e.g.,

cottonseed oil

Chances of thermal polymerization

Miscella deacidification

Lower strength of caustic solution

Increased efficiency of separation

Minimum oil occlusion in soapstock

Superior color of final product

Water washing eliminated

Higher investment––totally enclosed and

explosion-proof equipment

Solvent loss––requires careful operation and

greater maintenance

More suitable for integrated extraction and

refining plant

Cost intensive––homogenization necessary for

effective neutralization and decolorization

For efficient operation oil conc. in miscella should

be 50% (two-stage solvent removal)

Biological deacidification

A. Employing whole-cell microorganism that

selectively assimilate FFA e.g., Pseudomonas strain

BG1

B. Enzyme re-esterification––Lipase re-esterification

Increased oil yield

Low-energy consumption

Mild operating conditions

Linoleic acid and short-chain FA (C no. <12) not

utilized; they inhibit microbe growth

FA utilization depends on its water solubility

High cost of enzyme

Re-esterification (chemical modification)

With or without the aid of catalyst

Suitable for high-FFA oil

Increased oil yield

Random re-esterification

Thermal polymerization

Costly process

Solvent deacidification

Extraction at ambient temperature and atmospheric

pressure

Easy separation––large difference between boiling

points of solvent and fatty compounds

Higher capital cost

Energy intensive operation

Incomplete deacidification (TG solubility increases

with FFA in feed)

Supercritical fluid extraction (SCFE)

High selectivity, Low temp. and pollution free

Suitable for a wide range of FFA oils

Minimum oil losses

Costly process

Membrane deacidification

Low-energy consumption

Ambient temperature operation

No addition of chemicals

Retention of nutrients and other desirable

components

Molecular weight difference between TG and FFA

is small for separation

Non-availability of suitable membrane with high

selectivity

Low permeate flux

15

1.2.6 Oil stabilisation

Plant oils have a relatively short storage life as they are slowly oxidized by atmospheric

oxygen. Plant oils are more reactive to oxidation compared to petroleum oil which is due to

the presence of unsaturation in the fatty acid chain. Oxidative stability of plant oils is mainly

influenced by chemical structure of fatty acids, especially the unsaturation fatty acid degree

[93]. Other factors such as temperature, oxygen content, light exposure, heavy metal

compounds, water and pro-oxidant also have great influence on the formation of peroxides,

acids, volatile compounds, and insoluble polymers during aging [94].

Antioxidants are used to improve the stability of plant oils by delaying oxidation and thermal

degradation of plant oils. There are many types of antioxidants commonly used in oil and

fat-based products. Chain Breaking Antioxidants are commonly called primary antioxidants.

These types of antioxidants inhibit lipid oxidation by interfering with either chain

propagation or initiation [95]. Chain breaking antioxidants are capable of donating hydrogen

to lipid, alkoxy and peroxy radicals and convert them to more stable non-radical products.

These antioxidants have higher affinities for peroxy radicals than other lipid radicals and

react predominantly with peroxy radicals [96]. These antioxidant radicals can stabilize

themselves through hybridization and do not promote or propagate further oxidation [97].

In addition, these antioxidant radicals are capable of participating in termination reaction

with peroxy, oxy and other antioxidant radicals.

Other types of antioxidants are preferred to be named as secondary antioxidants. They do

not convert free radicals into stable molecules. They act as chelators for pro-oxidants or

catalyst metal ions (EDTA, citric acid, and phosphoric acid derivatives), decompose

hydroperoxides to non-radical compounds (phosphorus and sulphur based antioxidants),

provide hydrogen atoms to primary antioxidants, deactivate singlet oxygen (carotenoids),

absorb ultraviolet radiation (carbon black, phenylsalicylate), or act as oxygen scavengers

(ascorbic acid and erythorbic acid). They often enhance the antioxidant activity of chain

breaking antioxidants [96].

1.3 Product quality

1.3.1 Problems in using vegetable oil as fuel

There are several problems associated with using pure plant oil (PPO) as fuel in normal

diesel engines. These problems can be divided into two classes. The first class, operation

problems, includes ignition quality characteristics, e.g. poor cold engine start-up, misfire,

and ignition delay. The second class is durability problems such as deposit formation,

carbonization of injector tips, ring sticking and lubricating oil dilution. These are mainly due

16

to the high viscosity of vegetable oils which leads to poor fuel atomization and inefficient

mixing with air, which contributes to incomplete combustion. One severe problem

associated with the use of vegetable oils as fuels is carbon deposits. Low oxidative stability

and contaminants such as phosphorus, free fatty acid, water and sediment also contribute

to durability problems of the engine. Problems in using vegetable oils with probable cause

and potential solutions are presented at Table 7.

Table 7 Problems associated as using vegetable oil as fuel [modified from 82]

Properties Problems Solutions

Viscosity Poor cold engine starting Preheat the oil, add cold flow

improver, chemical modification

Phosphorus,

ash

Plugging and gumming of filters,

lines and injectors

Refine the oil (degumming)

Cetane

number

Engine knocking, ignition delay Preheat the oil, chemical

modification

Viscosity carbon deposits, nozzle coking,

excessive engine wear,

contamination of lubricating oil

Heat the oil, blend with diesel,

chemical modification

Oxidative

stability

Polymerisation causes deposition

on the injector, filter plugging,

ring sticking, engine wear,

thickening of lubricating oil

Add antioxidant, processing

control, maintain storage

condition, proper packaging

material.

Acid value Corrosiveness and oil instability Refine the oil (deacidification)

Phosphorus Form deposits, filter plugging,

abrasive

Refine the oil (degumming)

Water Form deposits, corrosiveness,

filter plugging, oil instability

Refining and filtering, drying

Note: One Example of chemical modification is trans-esterification

1.3.2 Oil quality parameters

Vegetable oil is obtained by pressing the seeds of the plants and may contain some

impurities. For a number of applications (e.g. fuel), the oil needs further refining to meet the

quality criteria. DIN V 51605-10 is used in Germany as a trading standard for rape-seed oil as

fuel. It is the only existing quality standard for fuel-grade straight vegetable oil which lists 15

fuel parameters with corresponding testing methods and limiting values (Table 8). A high oil

quality is essential to ensure the trouble-free engine use. A standardized fuel quality is an

17

important precondition for assessment of operational and emission characteristics, as well

as engine performance.

Table 8 Quality standard for rapesed oil fuel Standard DIN 51605:2010-10

Properties Unit Limiting value

Testing methods min max

Visual Inspection - Limpid, no free water visible,

no contaminations visible

-

Density at 15 oC kg/m3 910 925 DIN EN ISO 3675 or

DIN EN ISO 12185

Kinematic viscosity at 40 oC mm2/s - 36 DIN EN ISO 3104

Calorific value MJ/kg 36 - DIN 51900-1, -2,

DIN 51900-1, -3

Iodine number g I/ 100g 125 DIN EN 14111

Flash Point °C 101 - DIN EN 2719

Ignition Quality - 40 DIN EN 15195

Oxidative stability at 110 oC h 6 - DIN EN 14112

Acid value mg KOH/g - 2 DIN EN 14104

Total Contamination mg/kg - 24 DIN EN 12662:1998-10

Sulphur content mg/kg - 10 DIN EN ISO 20884 or

DIN EN ISO 20886

Phosphorus content mg/kg - 3 DIN EN 51627-6

Calsium content mg/kg - 1 DIN EN 51627-6

Magnesium content mg/kg - 1 DIN EN 51627-6

Water content % (m/m) - 0.075 DIN EN ISO 12937

There are a number of important parameters which determine the capability of plant oil as a

diesel fuel substitute. These parameters can be divided into two categories. The first one

concerns characteristic parameters that depend on the feedstock used, while the second

category concerns the properties that depend on the processing technology used.

Characteristic properties include density, viscosity, flash point, calorific value, iodine number

and ignition quality. Meanwhile, variable properties include total contamination, oxidative

stability, phosphorus content, acid value, ash content and water content. These variable

properties are needed to be controlled to meet the specification of the standard.

18

1.3.3 Critical product performance requirements

High quality oil requires a minimum content of acid value (free fatty acid), phosphorus and

moisture in the oil and has a high oxidative stability. The purity and composition of the oil

affect the engine performance. Generally, the lower the oxidative stability and the higher

the content of free fatty acids (FFA), water, phosphorus, and other contaminants, the more

engine problems occur.

The acid value is an indicator of the content of free fatty acids in plant oil. FFA are virtually

absent in fats/ oils of living tissue and mainly formed due to enzyme (lipase) action after the

oilseed has been harvested. It is known to be affected by the oil processing, duration and

conditions of storage of the oil. Free fatty acids are formed due to hydrolysis of triglycerides

especially when enough water is present in the oil. Hydrolysis of ester bonds in oil resulting

in the liberation of FFA, may be caused by enzyme action or by heat and moisture [98]. The

release of short-chain fatty acids by hydrolysis is responsible for the development of an

undesirable rancid flavor (hydrolytic rancidity). Furthermore, FFAs are more susceptible to

oxidation than the corresponding triglycerides; and this lipid oxidation, leads to further

oxidative rancidity in vegetable oils. Therefore, any increase in the acidity of the oil must be

absolutely avoided [92]. A high acid value in the fuel leads to corrosion, abrasion and

deposits in the engine. Furthermore the free fatty acids may react with the alkaline

components of the lubricating oil and affect its lubricity [99].

The phosphorus content is an indicator of phospholipids which are the major component of

cell membrane. Phospholipids commonly found in vegetable oil include phosphatidyl

choline, phosphatidyl inositol, phosphatidyl serine, phosphatidyl ethanolalamine.

Meanwhile, phosphatidic acids are mainly produced by enzymatic hydrolysis of

phospholipids. The molecule is acidic and bears a negative charge and thus requires a

counter ion. The presence of calcium and magnesium in crude oil can form salts with

phosphatidic acid. Phosphatidic acids and salts are not present in native oils but are

generated during the post-harvest stage. The levels depend upon the quality of oilseed

(unripe, damaged, or moist seeds), storage and extraction process [100].

Phospholipids should be removed because of their strong emulsifying action and because

they can join with pro-oxidant metal. Presence of phospholipid in plant oil or biodiesel also

causes problems in diesel engines such as plugging and gumming of fillters, lines and

injectors [82]. Phosphorus reduces the combustion temperature, leads to deposits in the

combustion chamber and eventually changes the emission behavior. The life and efficiency

of catalytic converters are affected by the presence of phosphorus compounds.

Furthermore phospholipids tend to form particles with water and can cause filter blockage

[99].

19

High water content leads to crystal growth at low temperatures and hence causes filter

blockage. Because of the high pressures in modern injection systems, free water is released

that could damage the injection system. At the boundary layer between water and fuel, the

growth of micro-organisms is promoted which can block the fuel filter and promote the

ageing process [99]. In addition, water can cause corrosion in fuel lines [82]. In plant oils the

water content is influenced by seed moisture, refining process parameters, condensation

effects and water uptake during storage [99].

Oxidative stability is an indicator of oil stability during storage and harsh processing.

Oxidative stability affects biodiesel primarily during extended storage. It is mainly influenced

by the degree of unsaturation. The higher the degree of unsaturation, the more susceptible

the fatty oils are to oxidation. Processing conditions such as temperature, oxygen content,

light exposure, heavy metal compounds, pro-oxidant and antioxidant content as well as

nature of the storage container also exert a great influence on oxidative rate of the

vegetable oils [101,102]. Vegetable oils with low oxidative stability demonstrate increased

acidity, viscosity, and more insoluble impurities during aging [103]. The resulting oxidation

products can in particular damage the fuel injection system of machines or vehicle motors,

by forming deposits. Harmful interactions between the fuel and the engine lubricating oil

also become more likely [99].

1.4 Thesis Outline

This research is aimed to deliver effective, economically feasible oil processing to produce

jatropha oil with a high and consistent quality to meet product specification requirements,

but still enable the proper usage of the protein-rich cake from which the oil has been

extracted.

Therefore, it is required to study different technical approaches to extract the oil, and to

develop processing /product property relationships that enable the design of extraction and

purification units that deliver excellent and consistent fuel performance.

The primary objective of this thesis is the achievement of optimum oil extraction levels

without deteriorating the product performance characteristics as delivered by nature. The

second objective is to develop extraction and purification technology that produces pure oil

of consistent and undisputable quality. The third objective is to develop extraction

technology that still enables the subsequent use of the protein-rich matrix from which the

oils have been extracted.

In this study, drying condition will be investigated, seed pressing technology will be

optimized, alternative oil recovery procedures will be explored (e.g. solvent-assisted

mechanical extraction), purification of oils will be established and the stabilization of oils will

20

be optimized. Jatropha oil has to meet a number of critical quality criteria (i.e. phosphor and

acid value, oxidative stability) to be applied as a diesel substitute.

In Chapter 2, the drying characteristics of jatropha in both seed and kernel are compared

and discussed. The effect of drying parameters, including air-drying temperature, on several

quality parameters of crude jatropha oil were evaluated in terms of acid value, phosphorus

content and oxidative stability.

In Chapter 3, the influence of process parameters on oil recovery from jatropha kernel are

investigated in more detail. The rate of pressure build-up, applied pressure, moisture

content of sample, pressing temperature, duration of pressing, feedstock size reduction,

shell removal and preheating time were studied as variables, and the quality of the obtained

oils was evaluated.

In Chapter 4, the most important pressing parameters obtained from chapter 3 were further

optimized to maximize the oil yield. This approach used the face centered central composite

design response surface method. The non-linear model was generated and predicted the

best condition to maximize oil yield. The experimental validation was conducted and the

quality of the obtained oils was evaluated.

In Chapter 5, the effect of solvent assisted pressing was evaluated in order to maximize oil

yield. Renewable solvents were used: bio-ethanol and bio-butanol. The purity of solvent,

solvent to feed ratio, pressure, temperature and time were studied as variables, and the

quality of the obtained oils was evaluated.

In Chapter 6, purification of jatropha oil was studied. The effect of purification parameters

including purification agent, concentration and temperature on several quality parameters

of crude jatropha oil were evaluated in terms of acid value, phosphorus content and

oxidative stability on batch scale. The best condition was applied in a novel continuous

process in a CCS unit, and the quality of the obtained oils was evaluated.

In Chapter 7, the stabilization of jatropha oil was evaluated. Various antioxidants were

studied to postpone the oxidation of the oil. The Oxidative Stability Index was analyzed and

maximized as a quality parameter for the stabilization of jatropha oil.

21

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