Investigations on the thermal stability and kinetics of biolubricants synthesized from different types of vegetable oils

Authors: Sarker, Majher; MAINALI, KALIDAS - Oak Ridge Institute For Science And Education (ORISE); Sharma, Brajendra

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2025
Publication Date: 2/27/2025
Citation: Sarker, M.I., Mainali, K., Sharma, B.K. 2025. Investigations on the thermal stability and kinetics of biolubricants synthesized from different types of vegetable oils. Chemosphere. https://doi.org/10.3390/lubricants13030105.
DOI: https://doi.org/10.3390/lubricants13030105

Interpretive Summary: Petroleum-based lubricants are environmentally unfriendly because they don't break down and therefore accumulate. Conversely, more environmentally benign biobased lubricants don't work as well because they don't hold up well at high temperatures. This research looked at three vegetable oils and their chemically modified versions, and their usefulnesses as high temperature tolerant biolubricants. Chemical changes were made to high oleic soybean oil, regular soybean oil, and waste cooking oil. Isopropyl groups were added to the fatty acid chains of the oils, which made branched oils. Thermogravimetric analysis was used to test the high temperature stability of the original modified oils and determined the kinetic parameters, which include activation energies, response rates, and pre-exponential factors. Using differential thermal gravimetric (DTG) less of the modified oils volatilized at the onset temperature compared to samples that had not been modified. Overall the chemical modification made the oils more resilient to high temperatures. This information will be useful to those finding new uses for agricultural oils or interested in replacing petroleum based lubricating oils with a renewable option.

Technical Abstract: Petroleum-based lubricants raise environmental concerns due to their non-biodegradability and toxicity, whereas biobased lubricants underperform owing to low thermal stability. This study examined and compared three vegetable oils along with their chemically modified versions to better understand their suitability as biolubricants. High oleic soybean oil-HOSOY, regular soybean oil-RSOY, and waste cooking oil-WCO were subjected to chemical modification where isopropyl groups were attached to the fatty acid chains of the oils producing branched oils, i.e. b-HOSOY, b-RSOY and b-WCO. The detailed kinetic study of each regular and modified sample was investigated using the thermogravimetric analysis. The kinetic parameters such as activation energies, reaction rates, and pre-exponential factors were generated via Friedman methods. The differential thermal gravimetric (DTG) analysis showed low volatilization at onset temperature in each modified oil as compared to unmodified samples under an oxidative environment. Furthermore, the comparative kinetic studies demonstrated enhanced thermo-oxidative stability of the modified products relative to their unaltered counterparts. Among the tested oils, b-RSOY showed an average activation energy of 325 kJ/mol followed by b-WCO:300 kJ/mol; and b-HOSOY:251 kJ/mol indicating the most stable modified product under an oxidative environment. For all samples, the pre-exponential factors are in good agreement with the activation energies, which validates that finding the pre-exponential components is crucial to the kinetic analysis.