Characterization of Recycled Base Oils for Lubricants Using Statistical Approaches on Orbitrap Mass Spectrometry Data

Nowadays, the production of recycled oils (ROs) is a strong environmental and economic issue. The incorporation of recycled base oils (BOs) into lubricants has become an increasingly popular topic in the industry due to its potential to reduce environmental impact and promote sustainability. Incorporating regenerated raw materials into the manufacture of new lubricants can reduce the amount of virgin feedstock that is derived from fossil sources and extend the useful life of used oils. However, many unwanted products are found in used oils, such as metal oxides, traces of water, soot, varnish, and gums, that can result from the degradation of certain additives. It is therefore of essential importance to evaluate the recycling processes as toxic chemicals can cause environmental pollution if not properly handled. In this work, molecular-level characterization using Orbitrap mass spectrometry (MS) was used to evaluate and classify 3 different RO samples compared to 11 BO samples from 4 different American Petroleum Institute (API) groups. The atmospheric pressure chemical ionization source was used to enable ionization of nonpolar and semipolar compounds including HC and S1 class molecules. Comparison of mass distributions and molecular maps between BO and RO samples was carried out to discriminate the samples according to their aromaticity and the presence of heteroelements. In addition, multivariate statistical approaches are used to classify RO compared to the BO database. Electrospray ionization was also used to selectively ionize acidic impurities in ROs. An apparent Kendrick mass defect plot allows evidence of the presence of additives such as hindered phenols, polydimethylsiloxanes, or sulfonates. This study demonstrates the interest of Orbitrap MS in characterizing impurities remaining from recycling processes and classifying ROs according to the API BO groups.