OPTIMIZATION OF PROCESS VARIABLES IN BIOLUBRICANT PRODUCTION FROM PAWPAW SEED (Carica papaya) OIL USING RESPONSE SURFACE METHODOLOGY

Abstract

Biolubricant was produced via double transesterification process of pawpaw seed oil with Ethylene Glycol (EG) as a polyol in the presence of potassium hydroxide catalyst. Pawpaw Methyl Ester (PME) was synthesized at the mole ratio of methanol-to-oil 6:1, the amount of catalyst used was 5% w/w of the oil and the reaction was conducted at a temperature of 60°C for two hours. Central composite design (CCD) in response surface methodology (RSM) was applied to this experimental layout and effects temperature, reaction time, and catalyst concentration on the synthesis of pawpaw seed oil biolubricant (PBL) were evaluated. The EG ester of pawpaw seed oil was characterized for its flash point, pour point, viscosity at 40 o C and at 100 0 C and viscosity index. Fourier Transform Infra-Red (FT-IR) and Gas Chromatography-Mass Spectrophotometer (GC-MS) analysis were carried out on the biodiesel and biolubricant to confirm the presence of ester group and the composition of the synthesized lubricant, the characterization showed favorable lubricating properties. The pawpaw seed oil methyl ester yielded 86.50 % based on the weight of the oil, while transesterification the in pawpaw seed methyl ester with EG yielded 97.00 % with desirability of 1.000 at optimum conditions of temperature at 130 oC, reaction time at 180 minutes, catalyst concentration of 0.5 % w/w KOH and a molar ratio of 3.5:1(pawpaw seed methyl to ethylene glycol) of the EG ester (Bio-lubricant). The validated bio-lubricant yield was 80.750 % obtained at a molar ratio of 3.5:1(pawpaw seed methyl to ethylene glycol), time of 128.102minutes and temperature of 97.616 oC. The presence of ester group in the resulting biolubricant was confirmed by FT-IR analysis and the percentage of the composition of biolubricant determined by GC-MS analysis revealed a saturated fatty acid composition is much higher than unsaturated fatty acid composition, this is promising as high saturation content in the biolubricant will leads to higher resistance towards thermal- oxidative treatment. The bio-lubricant produced is comparable to the standards commercial lubricants ISO VG- 32 and 46 for light and industrial gears applications.