**3. Materials and methods**

soybean (22%) and palm (11%). The rest (19%) was distributed among other unspecified

Density (kg/m3), 300C 1885 2620, 3879 4860, 5882 6877, 7884 1[15]; 2[21]; 3[22]; 4[23]; 5,6[24];

Calorific Value (MJ/kg) 137.4 241.0, 338.5 439.7 540.4 1[15]; 2[21]; 3[22]; 4,5[24]. Viscosity (mm2/s), 400C 14.5 25.3, 34.8 44.719, 54.24 65.18, 76.1 1[15]; 2[21]; 3[22]; 4[23]; 5,6[24],

Flash Point (0C) 1155 2191 3183 4163 1[15]; 2[22]; 3[23]; 4[25]. Pour Point (0C) 1-6 23 3-5 4-15, 5-6 1[15]; 2[22]; 3[23]; 4[24]; 5[25].

This work evaluated chemical properties and engine performance of birrea biodiesel to as‐

Birrea tree, commonly called marula tree, is indigenous to most parts of Southern Africa. In Botswana, for example, it is widely distributed over the entire country but concentrated in the north eastern part of the country, approximately 250 km north east of Gaborone, Botswa‐ na's capital city. The patterns of abundance and distribution can be used to help infer key demographic stages or ecological variables that merit special focus when implementing a management scheme [26]. At maturity, the tree can grow up to approximately 10m to 18m tall with a sterm diameter of approximately 0.8 m on average. The tree grows in warm and dry climatic conditions and is single stemmed with a dense spreading crown and deciduous foliage. It has a thick, relatively short taproot reaching depths of approximately 2.4 m, with lateral roots branching at the upper 0.6m of soil. It bears fruits in clusters of up to three (3) at the end of the twigs (Figure 1(a)). The fruits are round or oval in shape with a diameter of approximately 2.5 to 5.0 cm, and turn pale yellow when ripe [27, 28]. The fruit consists of a hard woody seed covered by pulp and juice which makes the fleshy part of the fruit. It has a delicate nutty flavour and contains a high concentration of vitamin C. The hard seed con‐

There is now a worldwide trend to explore wild plants for oil to augment the already ex‐ plored sources of feedstock oil for biodiesel production. The fact that the birrea tree grows in drier areas where common oil seeds cannot thrive has stirred interest in it as a valuable source of biodiesel feedstock. Moreover, birrea seeds are normally discarded as by-products

**Sunflower Rapeseed Reference**

7[25].

7[25].

vegetable oils and animal fats.

**Property Soybean Jatropha**

188 Advances in Internal Combustion Engines and Fuel Technologies

**Curcas**

**Table 1.** Properties of biodiesel fuels from selected plant oil feed stocks

sess its suitability for use as fuel in diesel engines.

**2. Sclerocarya birrea tree**

tains mostly two oil rich nuts (kernel).

### **3.1. Extraction of birrea kernel oil**

Solvent extraction was done to establish true oil content of birrea nuts grown under natural conditions. The process involved seed grinding, soxhlet extraction, filtration, distillation and purging. 200 g of birrea nuts were ground into powder using a mini grinding machine. The powder was then used in the solvent extraction process. The solvent was prepared by mix‐ ing 300 ml of hexane and 100 ml of iso-propyl alcohol in a 500 ml flask. The mixture ensures total extraction of all lipids as hexane extracts all non-polar lipids and iso-propyl alcohol po‐ lar lipids. Then 3 g of anti-bumping stones (boiling stones) were added to the mixture to en‐ sure non-violent boiling of the solvent during oil extraction. In addition, 75 g of powdered sample was charged into a thimble and placed inside a soxhlet. A soxhlet cover, condenser and heating mantle were then mounted to complete the soxhlet solvent extraction set-up. The solvent was heated until boiling and maintained in that phase for the entire extraction process, which took about 6 hours. After 5 syphones, the extracted liquid became clear, sug‐ gesting that there was no more oil in the sample. The process was stopped and the oil rich solvent was allowed to cool to room temperature. Filtration process was then performed to eliminate any possibility of solid particles in the oil rich solvent. The separation of solvent from the oil was achieved through a distillation process performed using a rotary evapora‐ tor. The heating bath of the rotavapor used distilled water maintained at approximately 400 C. The condenser used water that is slightly above freezing temperature and was main‐ tained at that temperature using ice blocks. This process should ideally extract all the sol‐ vent, starting with hexane (boiling point of 40–600 C) and then iso-propyl alcohol (due to the double bond). However, to ensure that no trace of solvent remains in the oil sample, the oil was purged with nitrogen gas (nitrogen drying) for approximately 40 minutes. Nitrogen is used because it is inert and does not react with oil components.

avoiding over loading the system. The extracted oil was bottled and kept in a cooler box

Sclerocarya Birrea Biodiesel as an Alternative Fuel for Compression Ignition Engines

Birrea biodiesel was produced through an alkali catalyzed transesterfication process in the laboratory under strict observation and controlled conditions. Alkaline transesterification was preferred since the oil sample had free fatty acid content below 2% [29]. One litre of

reaction vessel. A solution of methanol of 99.5% purity and 7.5g of potassium hydroxide pel‐ lets of 98% purity as catalyst was prepared and charged to the reaction vessel. The molar ratio of methanol to oil was fixed at 1:6, which is optimal ratio for the transesterification of vegetable oils [23]. The reaction vessel was tightly closed and contents agitated using a me‐ chanical shaker for one hour. The reaction vessel was then set up-side down and allowed to cool for a further 3 hours. Two distinct layers were formed, the upper layer being the methyl ester and the lower layer was glycerol (due to its higher specific gravity). Glycerol was drained off from the bottom of the reaction vessel until only biodiesel (and possibly traces of unreacted methanol) remained. The biodiesel was then water washed twice with distilled water to ensure removal of all traces of glycerol. A rotary vacuum evaporator was used to

The petroleum diesel used for comparison was purchased from a Shell petrol Station and had properties including boiling point of 422 K, vapour pressure of 53 Pa, density of 871Kg

Chemical analysis was done to identify esters present in the birrea biodiesel sample. The method involved analysing standard (reference) samples, generating calibration curves for esters identified in the standard samples, and identifying and quantifying esters present in

To establish the chemical composition of the standard samples, Methyl Arachidate was in‐ jected into the standard mixtures as an internal standard (IS) and the samples were run ten (10) times through the Gas Chromatograph - Mass Spectrometry (GC-MS) system at ten (10) concentrations of equal interval from 10ppm (parts per million) to 1ppm. At each concentration, peak areas and retention times for all esters present were captured from the chromatogram. Peak area ratios (Analyte/IS) were calculated for all esters present at all concentrations, and these were used to generate calibration curves for each ester in the standard samples. The birrea biodiesel sample was also run through the GC-MS system under similar conditions. Peak area ratios (Analyte/IS) were calculated for each ester de‐ tected in the biodiesel sample and ester concentration was then determined by interpola‐ tion from a calibration curve of corresponding compounds. The instrument used for

C, acidity of 0.2 mgKOH/g, calorific value of 50.4 MJ/Kg and

C to eliminate water.

http://dx.doi.org/10.5772/54215

191

C and then charged to a 2 litre transparent

with ice gel pending conversion to biodiesel as described in Section 3.2.

crude birrea plant oil was filtered, pre-heated to approximately 105o

The oil was allowed to cool to approximately 58o

recover the unreacted alcohol from the biodiesel.

/s at 400

m-3, viscosity of 2.3 mm2

cetane number of 48.

**3.3. Chemical analysis**

the birrea biodiesel sample.

**3.2. Birrea biodiesel preparation**

To ensure that properties of the oil are not distorted, mechanical extraction was done to yield crude oil for subsequent analyses. The mechanism for the extractor consists mainly of a piston, a multi-perforated cylindrical stainless steel compression chamber of approximate‐ ly 0.15m diameter and 0.3m high, and a hydraulic jack system. The schematic diagram of the mechanism is shown in Figure 2.

**Figure 2.** Schematic of mechanical oil extraction mechanism

Eight kilograms (8kg) of birrea nuts were charged into a multi-perforated stainless steel compression chamber, with stainless steel discs placed at intervals of 2kg of birrea nuts. The piston was located to keep the top disc into position. The hydraulic system was then operat‐ ed manually to lift up the platform upon which the multi-perforated stainless steel compres‐ sion chamber sits, thereby compressing the seeds and forcing the oil out of the kernel and through the 1mm diameter perforations of the compression chamber. The hydraulic system was operated to a maximum pressure of 30 bars to ensure maximum oil extraction while avoiding over loading the system. The extracted oil was bottled and kept in a cooler box with ice gel pending conversion to biodiesel as described in Section 3.2.
