Investigating the Benefits of Using Biolubricants Over Petroleum-Based Lubricants: An Interview with Julien Crepier

A recent study examined the use of comprehensive off-line liquid chromatography supercritical fluid chromatography (LCxSFC) hyphenated with an Orbitrap analyzer to analyze the complex molecular composition of synthetic biolubricants. These bio-lubricants are partially bio-based and biodegradable alternatives to petroleum oils, containing over 400 molecules with high chemical similarity (1). The study focused on structural elucidation of a polyol ester synthesized from fatty acids of varying lengths and ricinoleic acid polyesters (1). By combining LC and SFC, researchers achieved detailed separation of isomers, while high-resolution mass spectrometry (HRMS) confirmed molecular formulas and structural features, providing a robust method for bio-lubricant characterization (1).

Oil platform on the ocean. Offshore drilling for gas and petroleum | Image Credit: © Photocreo Bednarek - stock.adobe.com

Julien Crepier of TotalEnergies was one of the researchers that conducted this study, and he recently sat down with LCGC International to talk about his team’s findings.

Can you explain the main goal of your structural elucidation study on synthetic complex esters and polyol esters?

The main goal of our structural elucidation study on synthetic complex esters and polyol esters is to gain a deeper understanding of the relationship between structure, properties, and product performance. Such methods enable detailed characterization of the chemical composition and structural features of these derivatives, providing insights into how specific molecular arrangements impact their physical and chemical behavior, such as viscosity, thermal stability, and oxidation resistance. This knowledge enables us to optimize their formulation and performance in various lubricant applications, ensuring they meet or exceed the performance standards of traditional lubricants. By linking molecular structure to functional properties, researchers can tailor the synthesis and modification of these compounds to achieve desired outcomes, thereby advancing the development of high-performance, sustainable materials and products.

What motivated you to explore partially bio-based and biodegradable alternatives to petroleum base oils in lubricant formulations?

The use of partially bio-based and biodegradable alternatives to petroleum base oils is a response to growing environmental concerns and regulatory pressures to reduce the environmental footprint of industrial products. Vegetable oil derivatives have long been used as conventional alternatives in lubricants due to their inherent properties and the requirements of specific applications. Their natural origin and biodegradability make them particularly suitable for environmentally sensitive applications. By developing biobased and biodegradable lubricants, we aim to create sustainable solutions that minimize environmental damage, reduce dependence on fossil fuels and align with global efforts to promote greener, more sustainable industrial practices.

Can you describe the environmental impact and potential benefits of using biolubricants over traditional petroleum-based lubricants?

Biolubricants offer several environmental advantages over traditional petroleum-based lubricants. They are derived from renewable resources, helping to reduce dependence on finite fossil fuels.In addition, biolubricants are generally biodegradable, which means they break down more easily in the environment, reducing the risk of long-term pollution and damage to ecosystems. In some cases, the environmental footprint of the component can be significantly reduced. In addition, biolubricants often have lower toxicity levels, making them safer for human health and wildlife. By switching to biolubricants, we are contributing to a more sustainable and environmentally friendly industrial landscape.

How do these bio-lubricants perform as compared to traditional petroleum-based lubricants for lubricant applications?

Bio-lubricants have shown promising performance in various lubricant applications, often comparable to, and sometimes even surpassing, traditional petroleum-based lubricants. They typically exhibit excellent lubricity, thermal stability, and oxidative resistance. Advances in formulation technology have allowed us to tailor bio-lubricants to specific applications, ensuring they meet the rigorous demands of modern machinery and engines. However, the performance can vary depending on the specific bio-based materials used and the application context. Overall, although there may be some trade-offs in certain scenarios, the benefits of bio-lubricants, particularly in terms of sustainability and environmental impact, make them a highly attractive alternative to conventional lubricants.

Why did you choose to use comprehensive off-line LCxSFC hyphenated with an orbital trap analyzer for your analysis?

First, the use of SFC offers a wider range of stationary and mobile phases and therefore potential orthogonality with conventional RPLC. However, an on-line LCxSFC system does not exist commercially. Off-line processing is preferred as it facilitates method development and its implementation in industrial environments. Comprehensive mode is favored for a full characterization of the sample. Secondly, decorrelating the two separation dimensions enables to work more slowly in 2D SFC, compared to an automated system, by reducing the normalized gradient slope, thus increasing the method’s peak capacity and favoring the isomer separation. Finally, Orbitrap analyzer offers higher resolution than a TOF spectrometer or a simple quadrupole and thus greater precision in assigning raw formulas. As the off-line 2D method works slower than on-line method, chromatographic conditions in SFC (relatively low flow rate entering the source, average peak widths allowing enough points per peak) are compatible with the slower acquisition frequency of an Orbitrap. Thus, the off-line LCxSFC-Orbitrap coupling offers high chromatographic peak capacity and HRMS resulting in a powerful method for structural elucidation.

Can you explain the principle behind using LC and SFC in this study?

Various analytical approaches were considered upstream. Nuclear magnetic resonance (NMR) provides information on structural distribution of polyesters polyols, but because of a repeating motif, the signal may be confused. Mass spectrometry (MS) can be used to obtain molar masses, but because of competition for ionization and the large number of compounds, the spectra obtained are too dense for processing. Gas chromatography (GC) allow analytes separation upstream of MS but is limited because of low volatility. LC and SFC techniques have overcome the above problems and were therefore of interest in the study. On the other hand, co-elutions were numerous and the separation of isomers compromised. As the two methods provided different information because of their orthogonal and complementary retention mechanisms, they were ideal for two-dimensional analysis.

How does high-resolution mass spectrometry (HRMS) enhance the structural elucidation of the complex mixtures you have analyzed?

The level of dynamic range and the sensitivity of Orbitrap analyzer allowed the attribution of raw formulas with calculated mass errors that never exceeded 2 ppm. The fragile nature of the complexes resulted in in-source fragmentation (that is, without the use of MS/MS), and the analysis of the spectra enabled the structural elucidation. Combination of both information allowed fine characterization.

What were the main challenges you faced in resolving the complex mixture of over 400 molecules?

From a chromatography perspective, the main challenge was to obtain the highest peak capacity while compromising between saving analysis time and still separating isomers. From a mass spectrometry point of view, the distribution between homologs facilitated the assignment of raw formulas. However, the numerous isomers required in-depth study of in source fragmentation spectra and thus correlation with retention mechanisms for the attribution of developed formulas.

How did the degree of oligomerization of ricinoleic acid and the chain length of the fatty acid affect the retention time in the LC first dimension?

Reverse-phase LC (RPLC) using a C8-type stationary phase favors hydrophobic interactions. Increasing the chain length of a polyester, or its degree of oligomerization, increases its apolar property and thus its affinity for the stationary phase. So, the longer the complex, the more it will be retained.

In the SFC second dimension, how did you determine the esterification degree of the polyalcohol and the number and positions of fatty acids double bonds?

The SFC 1-aminoanthracene column allows interaction between the free OH group(s) of the analyzed complexes and the amino groups of the stationary phase. As a result, the greater the number of OH groups and the greater their accessibility on the molecule, the more it will be retained. In this way, groups of molecules with the same degree of esterification are grouped together on the 2D plot in a same family. On the other hand, the anthracene property of the stationary phase creates interactions with fatty acids doubles bounds. The more it has, the more its complex will be retained compared to its H2 homolog. The method also permits the separation of positional isomers of double bounds, but their position cannot be confirmed with the present conditions.

References

(1) Sanchez, M.; Lacroix-Andrivet, O.; Crozet, D.; Crepier, J.; Faure, K. Structural Elucidation of Complex Polyesters Polyols from Bio-Lubricant Using Off-Line Liquid Chromatography x Supercritical Fluid Chromatography Coupled with Orbitrap Mass Spectrometry. Talanta 2024, 276, 126295. DOI: 10.1016/j.talanta.2024.126295