Synthesis and Characterization of Biodiesel from Non-Edible Seed Oils Extracted from Cameroon Bioresources

This work aimed at valorizing non-edible seed oils from some plants found in Cameroon videlicet Acacia hockii (AH), Garcinia livingstonei (GL) and Moringa oleifera (MO), through production of biodiesel. Two extraction methods used were; the Soxhlet extraction and surfactant assisted extraction with sodium dodecyl sulphate (SDS) as surfactant. The extracted oils were characterized using physicochemical parameters. The characterized oils were used to synthesize biodiesels via acid and base catalyzed transesterification reactions. The purification of the biodiesels was done using chromatographic columns. The biodiesels obtained were also characterized using physicochemical analysis in a manner similar to the oils with additional parameters like cold f low properties, f lammability, ignition qualities and cetane number determinations. Qualitative analysis was realized using the Fourier Transformed Infrared Spectrophotometer (FT-IR). The Soxhlet extraction method gave higher yields for all the plants with MO being the highest, compared to the surfactant assisted extractions. The results from the physicochemical properties of the oils were as follows: specific gravity, 0.876 g/mL, 0.843 g/mL and 0.865 g/mL for AH, GL, and MO. The free fatty acid contents of the oils were 0.436% FFA, 0.547% FFA and 1.60% FFA for AH, GL, and MO respectively. The saponification values gave 143.03 mgKOH/g, 72.93 mgKOH/g, 126.22 mgKOH/g for AH, GL and MO in that order. Iodine values for the oils were 46.54 mgI2/g, 22.41 mgI2/g, 68.10 mgI2/g for AH, GL, and MO, respectively. The peroxide values gave 10.05 meq/kg, 8.50 meq/kg, 8.0 meq/kg for AH, GL, and MO, respectively. The kinematic viscosities were 21.0 mm2/s, 22.0 mm2/s and 43.0 mm2/s for AH, GL, and MO, respectively. The acid catalyzed reaction gave greater crude yields of 90.00% for all three plants while the base catalyzed reaction gave, 87.00% (AH), 84.00% (GL) and 74.00% (MO). The purified biodiesel samples had the following acid numbers: 0.028% FFA for BAH, 0.022% FFA for BGL, and 0.028% FFA for BMO. The kinematic viscosities values for biodiesel were 4.00 mm2/s, 4.23 mm2/s, and 5.22 mm2/s for BAH, BGL, and BMO, respectively. The cetane numbers of the synthesized biodiesel samples were 142.73 (BAH), 167.29 (BGL), and 82.40 (BMO). The IR spectra of the biodiesels corroborated the chemical make-up of biodiesel. Hence non-edible seed oils from the Cameroon rich bioresources can be valorized in biodiesel synthesis and other forms of green energy production in Cameroon and beyond.

Introduction

The gradual depletion of traditional fossil fuels, the increase in environmental pollution, and global warming after their use make the science community think of alternative renewable energy sources for both industrial and transportation purposes. Biodiesel (methyl or ethyl esters of fatty acids) or vegetable oils are alternative fuels of organic origins which have garnered a lot of attention due to the possible depletion of fossil fuel reserves and environmental benefits [1]. The world’s biodiesel supply grew from 3.9 billion liters in 2005 to 18.1 billion liters in 2010 and is expected to exceed 33 billion liters in 2016 and reach 41.4 billion liters in 2025, a 25% increase over 2016 levels [2]. Biodiesel is less toxic, non-flammable with low exhaust gas emission [3], [4]. Renewable energy is an alternative option to reduce the energy crisis, increase energy security and sequester dangerous amounts of carbon in the atmosphere [5]. Biodiesel has lower sulfur content, zero aromatic content, higher cetane number, and higher flash point than petroleum diesel [6], [7]. Biodiesel is generally produced by the trans-esterification of triglycerides from vegetable oils or animal fats, as well as the esterification of free fatty acids [8]. The transesterification reaction has a deep-seated effect on the viscosity as it reduces the viscosity of oils from five to eight folds to give that of biodiesel. This reduction in viscosity modifies the cold flow properties of the fuel such that the fuel does not clog the engine tiny pipes even at very low temperatures [4]. The use of biodiesel is safe in all conventional ignition engines and has similar engine performance and better engine shelf life compared to diesel. The technique and condition for the extraction of the active ingredients from plants greatly influence their quality and quantity [9]. As part of the economic development, valuation and popularization of local raw materials are essential to the production of a variety of useful products, the creation of novel opportunities, and research in general. Cameroon is fraught with a potent bioresource which is exploited in various ways for different industrial applications such as medicinal, cosmetic applications, green energy applications amongst others. This research is based on the valorization of some plant seeds for oil extraction targeting biodiesel synthesis from some Sahelian plants: Acacia hockii (Fabaceae), Garcinia livingstonei (Clusiaceae), and Moringa oleifera (Moringaceae).

Materials and Methods

Materials

Plant Materials

The scientific names of the plants used in this study were identified by botanists at the Faculty of Science of the University of Ngaoundere. Acacia hockii (Fabaceae) seeds were collected from Poli, North Cameroon. Garcinia livingstonei (Clusiaceae) and Moringa oleifera (Moringaceace) seeds were harvested from Ngaoundere and dried under laboratory conditions.

Materials and Equipment

Other materials used to realize this work were solvents and reagents such as n-hexane, sodium dodecyl sulphate (SDS), ethanol, ether, methanol, ethyl acetate, chloroform, sulfuric acid (98%), hydrochloric acid (36%), potassium hydroxide, phenolphthalein, sodium thiosulphate, acetic acid, potassium iodide, Wijs reagent and starch. These chemicals were gotten from the chemical warehouse of the Faculty of Science at the University of Ngaoundere and used as such without further purification. Other materials used in this research were glassware and equipment like Soxhlet apparatus, electronic balance, magnetic stirrer, Clarus 500, purification, chromatography column, TLC silica gel 60 F₂₅₄ from Merck KGaA. The rotary evaporator was used to purify the extracted oils and also recover the extraction solvents for possible recycling.

Extraction of Vegetable Oils

The extraction process involved two main methods: Soxhlet extraction (SE) and surfactant-assisted extraction (SAE). The cleaned seeds were dried for 18 h at 105°C in an oven, and then ground with a coffee grinder and passed through a standard sieve of 0.5 mm, and the fine powder obtained was stored until use [9]. Conventional Soxhlet extraction was used to determine the oil yield for comparative studies, along with other methods like surfactant-assisted extractions.

Soxhlet Extraction Procedure

Soxhlet extraction was done following a modified procedure of Djilani and Dicko [9]. Here, 300 g of milled seeds were loaded in a cotton bag and inserted into the thimble of the Soxhlet apparatus. 500 mL of n-hexane was measured into the distillation flask of the Soxhlet apparatus, the flask was installed into a heating mantle, the condenser was mounted, and cooling water was connected from the tap. The heating mantle was put on and its temperature adjusted to 80°C. The solvent boiled from the flask below and the vapor condensed and extracted the oil molecules from the sample and siphon them back into the distillation flask below and the cycle begins again. This extraction went on for 4 hours until the sample was ripped of its organic oil content. The mantle was put off, the mixture cooled down and the rotary evaporator was used to recover the solvent and purify the oil. The oils obtained were dried in the oven at 70±1°C for two hours, after which they were cooled in desiccators before weighed and the yields were calculated using the formula earlier employed by [10]: (1)% Oil content=Mass of oil extracted Dry mass of milled seeds×1001

Surfactant Assisted Extraction (SAE)

A standard solution of the surfactant was prepared by dissolving 0.01 g of sodium dodecyl sulphate (SDS) in 2 mL of distilled water in a 50 mL beaker. The solution obtained was transferred into a 200 mL volumetric flask and topped to the mark with ethyl acetate. A 20 g sample of each seed powder was mixed with 200 mL of the standard solution of surfactant in a flat bottom flask at 40°C. The suspension was mixed for one hour at 1500 rpm (13.9 kW-h/sample) on a PMC Data Plate® digital hot plate/stirrer model 730, and the slurry was sieved and then allowed for 30 minutes for decantation to occur in a beaker. After decantation, two fractions were obtained: liquid fraction (oil, emulsion, and extraction medium) and extracted meal. The liquid fraction was transferred into a separating funnel, and then 200 mL of distilled water was added, which led to the formation of two layers. The upper layer containing oil, emulsion and ethyl solvent was sieved to remove emulsion. Then, the emulsion was rinsed with 25 mL of ethyl acetate solvent. A rotatory evaporator was used to separate the solvent leaving the oil behind. The oils obtained were dried for two hours, cooled weighed and the yields calculated following a modified method of Tuntiwiwattanapun [11]. The oils were stored at 4°C in a refrigerator for further analyses and applications in biodiesel synthesis.

Physicochemical Analysis of Oil Extracts

The physicochemical properties of the oils and biodiesels were determined following the procedures of the American oil chemical society AOCS (2003). To determine the specific gravity of samples, A clean and dried bottle was weighed (W₀), then 10 mL of oil was poured in it, a stopper was inserted, and reweighed to give (W₁). The oil was substituted with water and weighed again to give (W₂). The specific gravity was calculated using the formula below: (2)Specific Gravity=W1−W0W2−W0

To determine the viscosity of seed oils, a rotary viscometer was used. This operates on the principle of torque moment. A sensor was used to measure the torque moment when the rotor is rotated constantly by the variable speed motor. The torque moment is proportional to liquid viscosity because of the liquid viscose hysteresis. The oil sample (10 mL) was placed in a 25 mL beaker, and the rotor of the instrument was inserted by lifting the screw and the power switch turned on. The rotation speed of 30 rpm was selected, and the viscosity was measured.

Titrimetric analysis was employed to determine the acid value of the seed oils under study. One gram of filtered seed oil was poured into a conical flask, and 25 mL of fat solvent (95% ethanol: ether 1:1 v/v) was added. The content was shaken, and two drops of phenolphthalein were added and shaken again. The mixture was titrated against 0.1 M solution of KOH to a pink coloration titre value V. The acid value was calculated using a modified formula of Bong et al. [10]: (3)AV=56.1×N×VTWwhere AV is Acid value (mgKOH/g), V_T is Titre value, N is Normality of KOH solution, and W is Weight of sample (g).

The saponification value of seed oil was determined by dissolving one gram of seed oil in 3 mL of fat solvent (95% ethanol; ether 1:1 v/v), and 25 mL of 0.5 M ethanolic KOH was added. Then the mixture refluxed for an hour and allowed to cool at room temperature and then two drops of 1% phenolphthalein were added. The content was titrated with 0.5 M HCl till the pink color disappeared (titre value denoted a). A blank titration was carried out under the similar experimental conditions but void of the oil sample (titre value denoted b) and then the saponification value was calculated using the formula below [12]: (4)Saponification value =titre value(b−a)weight of seed oil(g)×28.05

The iodine value of seed oil was determined by titrimetric method. 0.2 g of oil was dissolved in 15 mL of chloroform in a stoppered flask, and 25 mL of 0.1 N Wijs reagent solution was added. Then the flask was kept in dark cupboard for one hour. The content was mixed with 150 mL of distilled water and 20 mL of 5% potassium iodide solution. Then liberated iodine was titrated with 0.1 M sodium thiosulphate containing then 0.5 mL of 1% starch solution till color disappears. Then, a blank was prepared by replacing seed oil with chloroform and titrated in a similar manner as the test sample. Then iodine value calculated using the formula below [11]: (5)Iodine number=(b−a)×12.71000×100wwhere b is volume of thiosulphate used for blank (mL), a is volume of thiosulphate used for the sample (mL), w is weight of the oil sample (g).

The peroxide value of the oil was determined by titrimetric method. One gram of seed oil was placed into a dried test tube, and 20 mL of solvent mixture (2:1) of glacial acetic acid and chloroform was added. Then the content was boiled for one minute and poured into a conical flask containing 1 mL of 5% potassium iodide, then allowed in the dark for 5 minutes, 75 mL of distilled water was added, and it was titrated with 0.01 M sodium thiosulphate using 0.5 mL of 1% starch indicator. Then the blank titration was carried out by replacing oil with chloroform and titrated in similar manner as done for the test sample. The peroxide value of the oil then calculated using the formula below: (6)PV=(b−a)×M×1000Wwhere PV is Peroxide value, b is Volume of Na₂S₂O₃ used for blank (mL), a is Volume of Na₂S₂O₃ used for sample (mL), M is Molarity of Na₂S₂O₃, and W is Weight of sample (g).

The cetane number of products was calculated from previous analysis data according to the American Society of Testing and Material (ASTM) D2015 using the formula below: (7)CN=46.3+5458SV−0.225×IVwhere CN is Cetane number, SV is Saponification value and IV is Iodine value.

Acid Catalyzed Synthesis of Biodiesel

The acid catalyzed synthesis of biodiesel was carried out as follows; 50 mL of oil sample was heated to 60°C. The oil was mixed with 50 mL of a 20% (v/v) solution of concentrated H₂SO₄ in methanol. The mixture was shaken all through the reaction time using a magnetic stirrer at 1000 rpm and heated at 110°C for 4 hours in a round bottom flask at reflux. After the reaction time, the heating under reflux was halted. The mixture was transferred into a separating funnel and allowed to settle for three hours or more, during which biodiesel was separated from the glycerol and other impurities. The upper, less dense layer (biodiesel) was afterwards separated by opening the tap of the separating funnel. The biodiesel was washed with 100 mL of distilled water, and the biodiesel was heated to 120°C for 15 minutes to expel all traces of moisture.

Base Catalyzed Transesterification of Seed Oils

The fatty acid methyl esters (FAMEs) or biodiesels were synthesized by a modified method Alang et al. [4], Bello et al. [8], Alamu et al. [13], [8] and [4]. In this procedure, 50 mL of purified oil was transferred into a heating pan and warmed to 60°C (below the boiling point of methanol). Then, 26.8 mL of methanol (excess) was transferred into a beaker, 0.440 g of KOH was added to the beaker containing methanol. The mixture was magnetically stirred until methanol completely dissolved the potassium hydroxide. The warm oil was transferred into a 500 mL reaction vessel, and the alcoholic KOH solution was added. The contents of the reaction vessel were swirled vigorously for four minutes. The reaction mixture was then refluxed in a water bath at 70°C for 40 minutes, during which trans-esterification took place. The contents of the reaction vessel were transferred into a separating funnel after cooling and separation of biodiesel as the uppermost layer was observed a few minutes later. The lower denser layer was glycerol. The reaction products were separated using the tap of the separator funnel and collecting each fraction in separate labelled recipients. The crude biodiesel was washed with warm distilled water [14] in order to remove impurities as follows: 25 mL of hot distilled water was sprinkled into 50 mL of crude biodiesel in a separating funnel, and the wastewater containing dissolved impurities settled into the bottom while the washed biodiesel floated. The separated biodiesel was heated at 120°C to get rid of the moisture content. The volume of the purified biodiesel was measured after cooling. The yield Y of biodiesel was then computed by employing the equation below [4]: (8)Y=VpVs×1001where Vp is the volume of biodiesel produced, and Vs is the volume of sample oil used for the synthesis.

Purification of Biodiesel by Column Chromatography and IR Analysis

The purification was done using a purification column containing silica gel. For 10 g of biodiesel, 100 g of silica gel was used. Then, the recovered solvent + pure biodiesel was placed in a rotatory evaporator to remove the pure solvent. The TLC plate was used to verify the purity. The biodiesel was analyzed by FT-IR, using Bio-Rad Excalibur Model FTS3000MX in the 4000−400 cm⁻¹ range.

Determination of Lipid Content

30 g of each seed powder was weighed then allowed in an oven for 24 hours to remove humidity. Then, the seed powder is transferred into a filter paper of known mass and allowed in an oven for 30 minutes. After 30 minutes, the filter paper containing the seed powder was weighed, and the masses were recorded (M₁). The weighed filter paper containing the seed powder was Soxhlet extracted for 8 hours hexane. After eight hours, the filter paper was removed, dried, weighed, and mass recorded (M₂). The lipid content is then the difference expressed as a percentage of the original powdered mass taken. The lipid content was calculated using the formula below: (9)Lipid content=M1−M230×1001

Results and Discussion

Results of Oil Extractions

The oil yields of the extraction methods and lipid content is given in Table I.

Table I. Extraction Yields

Methods	Plants	Yield (%)
Soxhlet extraction (SE)	AH	9.57
	GL	10.21
	MO	36.83
Surfactant assisted extraction (SAE)	AH	3.00
	GL	7.30
	MO	33.00
Lipid content	AH	9.22
	GL	10.11
	MO	35.00

From Table I, apart from MO, the oil yields are generally low, probably due to poor oil content of the plant seeds, as reflected and corroborated by the lipid contents. Comparing the oil extraction methods, it is observed that the SE gives higher yields of oil on all the plants compared to those of the SAE. Hence, the Soxhlet extraction method may, according to this research, be recommended for use when attempting to determine the percent oil content of novel breeds of plant seeds.

Results of Physicochemical Analyses

The various seed oils were subjected to physicochemical analysis aimed at characterizing the seed oils and sort out appropriate transformation methods and applications due to their inherent physical and chemical properties. Depending on the properties, the oils may be candidates for the cosmetic industries, pharmaceutical industries, or green energy production, as is the case in this study.

From Table II, the three oils are light oils and can all float in water, attested to by their specific gravity values. The specific gravity values indicate how weight may vary and help to select storage conditions and materials. The salient property that affects the biodiesel yield during transesterification reactions is the acid value. From these results, GL and AH oils have low acid values and are suitable for biodiesel synthesis through base catalysis while MO has a higher acid number and is more suitable for biodiesel synthesis through acid catalysis. From literature [13], [4], the lower the acid value, the smaller the free fatty acid content and, therefore, the lower the saponification rate of the oil, which leads to higher biodiesel yields for the faster base-catalyzed transesterification reaction. The acid value for MO (32 mgKOH/g) obtained in this work is higher than that reported by [15], which was 1.71 mg KOH/g but lower than that reported by [9], which gave 80.50 mg KOH/g. Therefore, most results here fall in the range of values previously reported in the literature. The oxidative state of oils and, hence, their shelf life can be estimated by the peroxide index of each sample. The values obtained in this work (Table II) show that all the oils have low peroxide values, conferring on them desirable stability for the targeted applications. The results obtained in this work are similar to those obtained for MO by [16]. Low peroxide values also indicate the absence of hydroperoxides, relatively unstable compounds, and indicators of early-stage oxidation, catalyzed mainly by the joint action of oxygen, temperature, and light [17]. The results of this work also expose these oils as plausible candidates for other applications like cosmetics, food industries, medical applications, paint and varnish applications in addition to biofuel generation [18], [19]. The saponification number is inversely proportional to the average chain length of constituent fatty acid molecules in each oily sample [20]. The saponification value of MO in this study (126.22) is lower than most values previously reported by some authors [21]–[24]. Meanwhile the peroxide values of some authors, like [21]–[24], were higher than those obtained in this work, while [22] had a lower value (0.14 meq O₂/kg) compared to that obtained with MO oil in this study (0.67±0.02 meq O₂/kg) showing that this research results fortify previous literature findings. Furthermore, the iodine value is an indication of the degree of unsaturation of the fatty acid moieties in the constituent glycerides of each oil sample. The higher the iodine number, the greater the degree of unsaturation. The iodine values obtained in this work are generally lower, showing that the constituent fatty acid moieties in the oils are moderately unsaturated and, therefore, relatively stable. This is confirmed by the higher oxidative stabilities suggested by the lower peroxide numbers. From the physicochemical characteristics brought out here, AH oil is identified as a better candidate for biodiesel production.

Table II. Physicochemical Analyses Seed Oil

Properties	AH	GL	MO
Specific gravity (g/mL)	0.876	0.843	0.865
Acid value (mgKOH/g)	8.730	10.95	32.00
Free fatty acids (mgKOH/g)	4.36	5.47	16.00
%FFA	0.436	0.547	1.600
Saponification value (mgKOH/g)	143.03	72.93	126.22
Iodine value (mgI2/g)	46.54	22.41	68.10
Peroxide value (meq O2/kg)	10.05	8.50	8.00
Kinematic viscosity mm2/s	21.00	22.00	43.00

Results of Biodiesel Synthesis

The characterized oil samples were then utilized to synthesize biodiesel by making use of two methods which included the acid catalyzed and base catalyzed transesterification reactions. The results are given in Table III.

Table III. Biodiesel Yields

	% Yield
Catalyst	BAH	BGL	BMO
Acid	90.0	90.0	90.0
Base	87.0	85.0	74.0

The results shown in Table III indicate that biodiesel synthesis through acid catalysis is not affected by the chemical properties of the oils, while biodiesel synthesis through base catalysis is influenced by chemical properties like the acid number, as earlier mentioned in this work. Oils with significant acid numbers need some pretreatment to decrease the acid value and minimize the saponification side reactions, which have negative effects on the biodiesel yield. The pretreatment is intended to sequester the FFA or convert them to esters so that they will not be available for the undesired saponification side reaction. Though the saponification side reaction does not occur during the acid catalyzed transesterification reaction, the acid catalyzed reaction is quite slow and time consuming as noticed in the reaction time of acid catalytic transesterification. Hence, in most biodiesel synthetic processes, the base catalysis is preferred because the kinetics are higher, and commercial quantities can be produced over relatively short periods of time.

Results of Biodiesels Analyses

The synthesized and purified biodiesels were made to undergo thorough physicochemical analysis to determine their suitability as a renewable fuel. The results are given in Table IV.

Table IV. Properties of Biodiesel

Properties	BAH	BGL	BMO
Specific gravity (g/mL)	0.865	0.836	0.85
Acid value (mgKOH/g)	0.561	0.448	0.561
Free fatty acids (mgKOH/g)	0.280	0.224	0.28
%FFA	0.028	0.022	0.028
Saponification value (mgKOH/g)	56.10	44.88	143.55
Iodine value (mgI2/g)	34.26	24.53	76.0
Peroxide value (meqO2/kg)	1.50	13.00	10.00
Kinematic viscosity at 40°C (mm2/s)	4.00	4.23	5.22
Cetane number	142.73	167.29	82.40

Table IV shows the physico-chemical properties of biodiesels synthesized from various non-edible seed oils. % FFA contents of the biodiesel samples are negligibly low for BAH, BGL, and BMO, and hence they can be used in diesel engines as neat or blended with petroleum diesel. The table above implies that GL has the smallest acidity; therefore, it will not corrode engine parts; for AH and MO, the acid value is within the range required by the ASTM for biodiesel [4]. The cetane number of diesel fuel is used as a quality indicator related to ignition delay time and combustion quality [8]. The cetane numbers for the present research reported in Table IV shows that GL has the highest ignition abilities, followed by AH and then MO. The properties of the biodiesels are in the same range as that of the standards [25].

Viscosity Variation from Oils Biodiesels

It is clear from Fig. 1 that viscosity reduces drastically from the oils to biodiesels. The viscosity of the oils dropped by five to eight folds after the transesterification. In this work, the viscosity of AH is 21.0 mm²/s while that of BAH is 4.0 mm²/s, representing a fivefold decrease. A similar observation holds for GL and BGL, while the viscosity of MO is 43 mm²/s and that of BMO is 5.22 mm²/s, representing an eightfold drop in viscosity. The primary objective of transesterification of vegetable oils is to reduce their viscosities and improve their cold flow properties. Literature sources hold that vegetable oils may be used as fuels in diesel engines and have a major limitation: their high viscosities, which clog engine tubes at lower temperatures [4], [8].

Fig. 1. Viscosity variation from oils to biodiesels.

Infrared Spectroscopic Analysis (IR) of Oils and Biodiesel

The position of a carbonyl group in FT-IR is sensitive to substituent effects and to the structure of the molecule [26]. The esters have two characteristically strong absorption bands arising from carbonyl (C = O) at 1750–1730 cm⁻¹ and that of C-O at 1300–1000 cm⁻¹ [27], [28]. Stretching vibrations of CH₃ occur at 2980 – 2950 cm⁻¹, those of the CH₂ groups appear at 2950–2850 cm^−1, while the stretching vibrations of the CH groups appear at 3050–3000 cm⁻¹. The bending vibrations of CH₃ groups appear at 1475–1350 cm⁻¹, CH₂ groups appear at 1350–1150 cm^−1, while CH bending vibrations occur at 722 cm⁻¹ [29], [30]. For saturated esters, the absorption bands of C − C, C = O, and C-O bond occur between 1230 and 1160 cm⁻¹. For unsaturated esters vibrations occur at lower frequencies. The main difference between the IR spectrum of an oil molecule and the IR spectrum of a biodiesel molecule is the presence of an oxygen atom attached to a secondary and saturated carbon in the oil molecule at frequencies close to 3000 cm^−1, and this should be absent in the IR spectrum of a biodiesel molecule. Secondly, the intensity or the area under the absorption peaks the C-O stretching bonds is greater for oils and less for biodiesel due to removal of the glycerol molecule, a carrier of many C-O bonds. In this work, natural numbers from 1 to 9 are used on the spectra to identify the wave numbers of some of the bands, especially those relevant to structure elucidation.

The Infrared Spectroscopy of Acacia hockii (AH) Seed Oil

The absorption peaks of Acacia hockii (AH) oil observed in Fig. 2 includes 1 (3734.73 cm⁻¹), 2 (3670.75 cm⁻¹), 3 (3009.35 cm⁻¹), 4 (2923.04 cm⁻¹), 5 (2853.68 cm⁻¹), 6 (1743.73 cm⁻¹), 7 (1160.25 cm⁻¹), 8 (722.22 cm⁻¹) inter alia. The ester group is confirmed by 6 (1743.73 cm⁻¹) and 7 (1160.25 cm⁻¹). Then other wave numbers identify the presence of CH₂ by a band around 5 (2853.68 cm⁻¹) and CH by 3 (3009.35 cm⁻¹). Moreover, the vibrations around 1 (3734.73 cm⁻¹), 2 (3670.75 cm⁻¹), identifies the C-H bond whereas 8 (722.22 cm⁻¹) confirms the bending vibration (CH₂). The broad absorption band between 1300 cm⁻¹ – 100 cm⁻¹ confirms the numerous C-O bonds in oil samples.

Fig. 2. The infrared spectrum Acacia hockii oil seed oil.

The Infrared Analysis of Acacia hockii Biodiesel

Biodiesel of Acacia hockii (BAH) absorption peaks are given in Fig. 3 and includes 1 (3972.73 cm⁻¹), 2 (3735.20 cm⁻¹), 3 (3623.67 cm⁻¹), 4 (3009.53 cm⁻¹), 5 (2923.55 cm⁻¹), 6 (2854.10 cm⁻¹), 7 (1742.42 cm⁻¹), 8 (1168.85 cm⁻¹), 9 (722.22 cm⁻¹) amongst others. For BAH the ester group is confirmed by 7 (1742.42 cm⁻¹) and 8 (1168.85 cm⁻¹) then the other wave numbers identify the presence of CH₂ by a band around 6 (2854.10 cm⁻¹) and CH by 4 (3009.53 cm⁻¹). Moreover, the vibrations around 1 (3972.73 cm⁻¹), 2 (3735.20 cm⁻¹), 3 (3623.67 cm⁻¹), identifies the C-H bond whereas 9 (722.22 cm⁻¹) confirms the bending vibration (CH₂). Distinctive features between the two spectra include the absorption at 2923.04 cm⁻¹ for the secondary C-O bond present in oil but absent in the biodiesel IR spectrum. Secondly, the intensity of the C-O absorptions between 1300 cm⁻¹ and 1000 cm⁻¹ or the area under the peaks is much greater for the oil IR spectrum compared to that of the biodiesel IR spectrum. This is probably due to the exclusion of the glycerol molecule from biodiesel which goes away with a high density of C-O bonds with attendant drop in concentration in the biodiesel samples.

Fig. 3. Fourier transform infrared (FT-IR) spectrum of BAH.

Similar trends are observed in the IR spectra of the other two oils and their respective biodiesels with negligible variations. These include Garcinia livingstonei (GL) seed oil and Moringa oleifera (MO) seed oil with their respective biodiesels. The spectral similarities are due to the fact that vegetable oils have virtually the same chemical compositions being the triglycerides of fatty acids. Slight differences in the IR spectra of both oils and biodiesels may be due to differences in the chemical properties of the oils, such as the degree of unsaturation of the respective fatty acid moieties, translated into differences in iodine and peroxide values, which are further related to oxidative and thermal stabilities. The IR spectra of GL and MO with their respective biodiesels are given in Figs. 4–7, respectively.

Fig. 4. Infrared analysis spectrum of GL seed oil.

Fig. 5. The infrared spectrum of BGL.

Fig. 6. The infrared spectrum of MO seed oil.

Fig. 7. The infrared spectrum of Moringa oleifera biodiesel.

Conclusion

This research aimed at valorizing non-edible seed oil from some plants found in Cameroon videlicet Acacia hockii (AH), Garcinia livingstonei (GL) and Moringa oleifera (MO) through biodiesel synthesis. It turned out from the extraction methods that the Soxhlet method was more efficient than the surfactant assisted extraction. The physico-chemical analyses of the oils showed that AH oil was more suited for biodiesel synthesis due to its low acid value inter alia. For clean oils in general, %FFA is usually less than unity, and the base catalyzed procedure is preferred due to its higher kinetics. The physico-chemical analysis of the biodiesels Acacia hockii (BAH), Garcinia livingstonei (BGL), and Moringa oleifera (BMO) was done, and there was a significant difference in the properties, of the biodiesels (FAMEs) compared to their oils. The cetane number of a biodiesel sample is an indication of its ignition qualities. IR analyses data of the synthesized biodiesels agreed with those of previous literature reports. The drastic drop in the viscosity of biodiesel (five to eight folds) compared to that of oil samples improved the cold flow properties of the biodiesels, permitting them still to be used even in very cold weather conditions.