New Lubricity Additives for Ultra Low Sulphur Diesel: Synthesis, Characterization and Evaluation of Lubricity Properties

Abstract

In order to limit the emission of polluting elements such as sulphur and polar trace components from fossil fuels, standard norms and regulations have been formulated throughout the world. The maximum permitted sulphur concentration in diesel fuel is 10 ppm, according to the most recent European 6 standard (Euro 6, since 2014 to present). The fuel with less than 15 ppm of sulphur is called as ultra-low sulphur diesel (ULSD). Most of the refineries prefer hydrodesulphurization (HDS) process to produce ULSD, which removes sulphur from the fuel along with nitrogen and oxygen-based polar trace compounds. The loss of sulphur and other polar trace compounds makes the fuel harder. As a result, the direct use of ULSD produces a lot of friction between the moving parts of the fuel injection system. Therefore, diesel fuel needs external lubricating agents to balance its lubricity qualities. Blending of lubricity improvers with ULSD is one of the solutions to increase its lubricity property. Based on a detailed literature survey, more than 100 new lubricity enhancers were designed in the present study. New additives were synthesized using low-cost raw materials such as methyl oleate, light cracked naphtha, glycidyl methacrylate, methacrylic acid, fatty acid and maleic anhydride by following simple reaction protocols. The tribological study was carried out for all the molecule using high frequency reciprocating rig (HFRR). The wear scar diameter was measured through optical microscope. Interestingly, the lubricity additive derived from oleic acid and stearic acid -based esters showed the best lubrication enhancing property at low (below 200 ppm) dosage level. Further, studies on physiochemical properties of blend fuel revealed that blending of these additives do not alter the key parameters of the diesel fuel. The mechanism of lubricity action of newly synthesised molecules on metal surface were studied using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. Conspicuously, the formation of defensive thin layer of the additive between the metal surfaces reduces the direct contact between the metal surfaces and hence protects the metal surfaces from wear and tear.