Synthesis and Characterisation of a Biolubricant from Cameroon Palm Kernel Seed Oil Using a Locally Produced Base Catalyst from Plantain Peelings

Biolubricant was synthesized from Cameroon palm kernel oil (PKO) by double transesterification, producing methyl esters in the first stage which were then transesterified with trimethylolpropane (TMP) to give the PKO biolubricant in the presence of a base catalyst obtained from plantain peelings (municipal waste). The yields from both catalysts were significantly similar (48% for the locally produced and 51% for the conventional) showing that the locally produced catalyst could be valorized. The synthesized biolubricant was characterized by measuring its physical and chemical properties. The specific gravity of 1.2, ASTM color of 1.5, cloud point of 0 ̊C, pour point of −9 ̊C, viscosities at 40 ̊C of 509.80 cSt and at 100 ̊C of 30.80 cSt, viscosity index of 120, flash point greater than 210 ̊C and a fire point greater than 220 ̊C were obtained. This synthesized biolubricant was found to be comparable to commercial T-46 petroleum lubricant sample produced industrially from mineral sources. We have therefore used local materials to produce a biolubricant using a cheap base catalyst produced from municipal waste.


Introduction
The world's crude oil reserves are rapidly depleting as a result of high consumption which exceeds the rate of natural formation of mineral deposits [1] and the world runs the risk of a severe energy crisis if rapid alternative energy solutions are not sought [2] [3]. These impending energy crises have provoked scientific and technological research on bio-based materials as alternative energy sources.
The long term solutions to our energy needs depend on the development of renewable, biodegradable, and environmentally friendly industrial products such as biodiesel, biolubricants and other fuels that potentially substitute or subsidize conventional fuels and reduce the dependence on fossil fuels [4] [5] [6] [7] [8].
Lubricants minimize frictional resistance between surfaces in relative motion.
They reduce mechanical wear and tear of machine components thereby increasing their life span and efficiency and also facilitate heat transfer, liquid sealing, contaminant suspension, and corrosion protection [1] [9]. There are two main types of lubricants namely, lubricants obtainable from fossil sources and those produced from vegetable oil sources. The demand for biodegradable and environmentally friendly bio-lubricants is on the increase, hence the need for scientific and technological research into the synthesis and production of such bio-lubricants from available vegetable oil sources. Similar work in this area includes the production of biolubricants from Nigerian Jatropha curcas seed oil [1]. Jatropha oil is not edible but highly unsaturated with attendant thermal instability. Consequently, biolubricant synthesis from Jatropha is a labor and capital intensive process.
We report here the synthesis and characterization of a bio-lubricant from Cameroonian palm kernel seed oil obtained from agricultural and industrial waste, emanating from palm oil processing industry in Cameroon. The oil is not edible and some is used as a raw material for the production of soaps and detergents.

Materials
Palm kernel seeds (Elaeis guineensis) were collected from the dumping site at an artisanal oil mill in Widikum (Cameroon) and mechanically cracked to separate the seeds from the hard shells. The seeds were sun-dried for 3 days to reduce the moisture content. The dried palm kernel seeds were used to extract palm kernel oil by mechanical press and solvent extraction. The palm kernel oil was and then characterized by physical and chemical methods. Reagent grade methanol, potassium hydroxide (KOH), ethanol, ether, chloroform were used as purchased without further purification.

Palm Kernel Oil Extraction
Two kilograms (2 kg) of palm kernel seeds were crushed to a particle size of about 3 mm to allow solvent penetration and oil percolation and heated to about 80˚C with open steam thereby humidifying the materials and raising the moisture content. The material was then flaked, and conveyed to the mechanical extracting system. For solvent extraction, 100 g of crushed palm kernel seeds was

Biolubricant Synthesis by Double Transesterification of Palm Kernel Oil
The PKO biolubricant was synthesized using the double transesterification method [1]. The first step produced intermediate products of methyl esters of fatty acids which were used in the second step to produce the biolubricant in the presence of trimethylolpropane (TMP). The two processes were carried out as described below.

Production of KOH Using Plantain Peelings
An alternative source of the base catalyst was explored primarily for the sake of economics of production. The catalyst precursor was derived from plantain fruit (Musa paradisiaca) peelings, an urban waste product. Three kilograms of plantains peelings were collected from an urban waste dump in the Bamenda (Cameroon) municipality, washed with water to remove soil, debris and other impurities and sun-dried for one week to reduce the moisture content and to render the peelings easily combustible [12] [13]. The plantain peelings were then burnt in an air-rich metallic container; the ash was collected and stored in a labeled polythene bag. The residual ash is predominantly potassium oxide (K 2 O) which dissolves in water to give KOH solution. The base catalyst (KOH) was extracted from the ash following a modified procedure by Enontiemonria et al. [13]. In this extraction, 30 g of dry ash was dissolved in 300 mL of mineral free water using 500-mL beakers. The beaker and its content were placed on a hot plate magnetic stirrer and kept at 50˚C for 4 hours. The resultant solution was then filtered using filter paper and stored. The filtrate was collected in a stainless steel container, verified with litmus paper for pH value and evaporated to dry- methyl esters layer and the lower impure glycerol layer (see Figure 1). The products were separated by allowing each fraction to flow into separate labeled measuring cylinders. The methyl esters were purified using the modified procedure by Aladetuyi et al. [14] and the yield of methyl ester calculated using Equa- yield of methyl esters 100 where V p is the volume of product and V s the volume of sample oil used for the synthesis.

Synthesis of Biolubricant
The synthesis of biolubricant from palm kernel oil methyl esters (PKOME) by transesterification with trimethylolpropane (TMP) is depicted by the following stoichiometric equation (Scheme 1). The previously prepared palm kernel oil methyl esters (PKOME) (100 mL) in a 500-mL reaction vessel was heated in a water bath to 70˚C and 0.9 g of KOH base catalyst solution was added. After 10 minutes, 20 g of TMP crystals were added to the reaction vessel and the reaction allowed to proceed for 4 hours at 100˚C under reflux. The reaction mixture allowed to cool to room temperature.
The mixture was transferred into a separatory funnel and the TMP triester (biolubricant) was collected as the bottom viscous layer. The biolubricant yield was calculated using Equation (3) [17].
% yield 100 where V p is the volume of product and V s the volume of sample taken.

Biolubricant Synthesis Using KOH from Plantain Peelings
Biolubricant was synthesized using locally made base-catalyst. 100-mL of palm kernel oil methyl esters (PKOME) was measured into a 500-mL reaction vessel.
4.62 g of locally made KOH corresponding to 5% weight of PKOME was dissolved in 10 mL of methanol with the aid of a magnetic stirrer. The catalyst solution was added to the 500-mL reaction vessel and the mixture swirled for five minutes followed by the addition of 20 g of TMP to the reaction mixture which was then maintained in a water bath at 100˚C for 4 hours. The reaction mixture was allowed to cool to room temperature. The mixture was transferred into a separatory funnel for the biolubricant to decant as the bottom viscous layer which was collected directly into a measuring cylinder. The supernatant layer was recycled by transferring it back to the reaction vessel and adding more catalyst and TMP and repeating the heating process for four hours. The lubricant formed in the recycled batch was separated and the total yield computed.

Characterization of PKO Biolubricant
The biolubricant was analyzed for its physical and chemical properties [18] [19].
The specific gravity was determined using the density bottle method while the rest of the properties were determined using standard analytical methods as shown in

Results and Discussions
The physico-chemical properties of the products are shown in Table 2  while that from locally produced base catalyst was 48.6%. This implies that the locally produced catalyst is almost as effective as the conventional, imported catalyst. This minimizes production cost, thus reducing the cost of the biolubricant and enhancing affordability and valorizing municipal waste through transformation into a useful product for the conversion of industrial wastes (palm kernel seeds) into biolubricant. This is in conformity with the observation that energy conversion is sustainable and cheaper when it is derived from waste and renewable biomass [26].
In order to evaluate the propinquity of the synthesized biolubricant to the conventional lubricant, a petroleum lubricant sample was also analyzed using similar parameters as those determined for the biolubricant. The results in Table 2 show that biolubricant is heavier and more viscous than the petroleum lubricant.

Variation of Specific Gravities (SG) of Products
From the results obtained, the specific gravity of PKO biolubricant catalyzed by locally produced base catalyst, 1.22 g/mL is similar that of the PKO biolubricant catalyzed by conventional base catalyst, 1.20 g/mL. Both SGs are higher than that of precursor PKO, 0.923 g/mL; with the petroleum lubricant having the lowest specific gravity value at 0.848 g/mL. The specific gravity value is lower for palm kernel seed oil than for biolubricant due to an increase in molecular complexity brought in by the trimethylolpropane (TMP) backbone. The specific gravity value for the biolubricant is higher than that of the petrolubricant due to a change in chemical structure of constituent molecules which are predominantly saturated aliphatic and few aromatic hydrocarbons. The specific gravity of the biolubricant catalyzed by locally produced base catalyst is higher probably due to slightly higher impurity level as suggested by the ASTM color values. The change in specific gravity leads to a corresponding change in the mass of the products.
The greater the specific gravity, the heavier and more viscous the oil is, and such DOI: 10.4236/gsc.2018.83018 a lubricant does not easily thin out at higher temperature and can withstand greater loads. The specific gravity is also an indicator of product adulteration.
The SG of the biolubricant for PKO, biolubricant and petrolubricant determines the compatibility of the products with either the heavy or light duty engines which is the ability of a sample to mix with other liquids [27]. Substances with smaller SG (<1) can float in water while those with SG greater than one sink in water. The persistence of biolubricant on applied surfaces and joints would be longer due to higher specific gravity and consequently, higher viscosity.

Kinematic Viscosities of Products at 40˚C and at 100˚C
The flow through an orifice of a specified size [28]. The viscosities of products at 40˚C are generally much greater than the viscosities at 100˚C due to the fact that intermolecular forces resisting flow in liquids such as hydrogen bonds and van der Waals forces are largely broken down at higher temperatures.

Viscosity Index Variation
The

Cold Flow Properties
The cloud point of oil refers to the temperature at which wax first become visible as the temperature is lowered while the pour point is the temperature at which the oil solidifies enough to resist flow [29]. The cloud point was reduced from

Flash Points of Products
The flash point of a fuel refers to the temperature at which the fuel can ignite

Conclusions
A biolubricant with good lubricant properties for higher temperature applications has been produced from Cameroon palm kernel oil. A new base catalyst was produced from municipal wastes (plantain peelings), whose performance was very close to that of conventional base catalyst (KOH) used in this work. We have therefore used local materials to produce a biolubricant using cheap base catalyst.
However, further research is required to improve on the yield of the biolubricant, optimize the production of the base catalyst from plantain peelings and improve the purity level. Also the performance of the synthesized biolubricant needs to be studied in a sample engine to evaluate its suitability in various engines.

Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this paper.