https://orcid.org/0000-0003-2932-479X
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ABSTRACT
In this study, palmitic acid/stearate acid was reacted with methanol, ethanol, propanol, butanol, and amyl alcohol, respectively, by esterification to obtained palmitate and stearate esters. According to fix-others-vary-one experimental method, the yield of palmitate and stearate esters was measured under different reaction time, temperature, catalyst dosage, and molar ratio of alcohol to acid. Under the optimal conditions, the yield of all palmitate and stearate esters could reach 97%. Furthermore, the lubricity of palmitic and stearate esters were also explored. High-frequency reciprocating friction wear test machines, optical microscope, and scanning electron microscopy (SEM) were used to determine the spot diameter of palmitate and stearate esters. At the same time, the adsorption behavior of esters on the iron surface was studied based on density functional theory. The results indicated that the spot diameters of palmitic and stearic esters decreased with the increasement of alkyl chain length in eaters, while the adsorption energy of esters on the iron surface was gradually increased. The minimum spot diameter and maximum adsorption energy appeared in amyl stearate with 200.73 μm and 2553.93 kcal/mol, respectively. In addition, with the increase of the carbon number in alcohol chain, the cohesive energy between molecules was also improved. It contributed to the formation of a stable boundary film on the metal surface and enhanced the lubricity of biodiesel. It was concluded that long-chain alcohol for esterification process could effectively reduce the spot diameters of biodiesel and enhance lubrication performance of biodiesel.
Disclosure statement
No potential conflict of interest was reported by the author(s).