Production of engine biolubricant oil from non-edible vegetable oil through chemical modification and formulation.

Abstract

Recently, the 26th Climate Change Conference (COP26) has pledged R130 billion to assist South Africa in transitioning to environmentally friendly energy sources. Some of the funds are being allocated to developing new sectors such as electric vehicles. This commitment highlights the urgency of developing environmentally friendly resources such as biolubricant to preserve the environment for the future generation. In this study chemical modification of castor oil and waste cooking oil was carried out to produce environmentally friendly engine biolubricants. The chemical modification methods carried out in this study comprises of a two-stage base-catalysed transesterification method and ring-opening of the epoxidized vegetable oil. The first stage transesterification was carried out using methanol in the presence of a sodium hydroxide catalyst producing Fatty Acid Methyl Esters (FAME). The FAME produced was then reacted with Trimethylolpropane (TMP) in the presence of a sodium methoxide catalyst producing TMP based esters (biolubricant). The transesterification of FAME was optimised in terms of TMP based triesters’s yield. The actual optimum TMP based triesters’s yield of 80.80 and 76.20% for waste cooking oil and castor oil, respectively were achieved. The optimised conditions to produce waste cooking oil TMP triesters were obtained at the temperature of 140°C, catalyst loading of 0.5wt%, the reaction time 3 hours of and WCOME to TMP ratio of 4.55:1 molar ratio. The optimised conditions to produce castor oil TMP triesters were obtained at the temperature of 140°C, catalyst loading of 0.52wt%, the reaction time of 3 hours, and the COME to TMP 5:1 molar ratio. The second modification method was the epoxide ring-opening using 2-hexyldecanol. The reaction took place in two parts. The first part was the epoxidation of the vegetable oil which was carried out under the optimum conditions reported in the literature. The oxirane content of 5.6 and 5.2% were measured for the epoxidized castor and waste cooking oil, respectively. The second part of the reaction was the ring-opening of the epoxidized vegetable oil using 2-hexyldecanol alcohol. The reaction was optimised based on the hydroxy value measured at the end of reaction. The optimised conditions for the production of ring-opened epoxidized waste cooking oil using 2-hexyldecanol were obtained at the 120°C, 1.06wt% catalyst loading, 20 hours of reaction time and 2-hexyl decanol: epoxidized WCO molar ratio of 1:1. Whereas the optimum conditions for the ring-opening reaction for epoxidized castor oil were obtained at the temperature of 140°C, catalyst loading of 2wt%, the reaction time of 20 hours and 2-hexyl decanol to eCO molar ratio of 1:1. All the products were successfully confirmed through a and Gas Chromatography-Mass Spectrophotometer (GC-MS) and Fourier Transform Infra-Red (FI-TR) analysis. Four biolubricants were produced from the above-mentioned chemical methods, which are Waste Cooking Oil-based TMP esters (WCO-TMP), Castor Oil-based TMP esters (CO-TMP), Ring Opened epoxidized waste cooking (RO-eWCO) and Ring Opened Castor Oil (RO-CO). The produced biolubricants were subjected to various property tests to determine their suitability for engine oil application. The tests conducted included the Total Acid Number (TAN), Density, Viscosity, Viscosity index, Pour point, cloud point and thermal stability. In addition, tribological characteristics viz Coefficient of friction, was determined via a regressed correlation as the equipment was not available for measurements. WCO-TMP showed very poor performance in terms of the pour point (+1°C), viscosity and thermal stability. Therefore, it was conclusive that its not suitable for use as an engine biolubricant. RO-eWCO, RO-eCO and CO-TMP biolubricants conformed to the requirements for engine oil application and were classified as SAE 20 viscosity grade lubricant. Thus, their properties were satisfactory for engine lubrication application. Silicon dioxide (SiO2) and Copper Oxide (CuO) were also added to the lubricants to improve the lubricity of the biolubricant. It was found that the nanoparticles increased both the density and viscosity of the biolubricant. Subsequently, affecting the COF based on the regressed correlation. The effect of nanoparticles on the thermal stability of the biolubricant could not be investigated due to the limited access to the hermogravimetric analysis.