Single-Cell Oils from Oleaginous Microorganisms as Green Bio-Lubricants: Studies on Their Tribological Performance

Alok Patel,Yijun Shi,Liwen Mu,Ulrika Rova,Leonidas Matsakas,Paul Christakopoulos

doi:10.3390/en14206685

Abstract

Biolubricants refer to eco-friendly, biodegradable, and non-toxic lubricants. Their applications are still limited compared to mineral oils; however, their sustainable credentials are making them increasingly attractive. Vegetable oils are frequently used for this purpose. However, vegetable oils have issues of low lipid productivity, dependence on climatic conditions, and need for agricultural land. Microbial oils represent a more sustainable alternative. To ensure their widespread applicability, the suitability of microbial oils from a physicochemical point of view needs to be determined first. In this study, oils obtained from various oleagenic microbes—such as microalgae, thraustochytrids, and yeasts—were characterized in terms of their fatty acid profile, viscosity, friction coefficient, wear, and thermal stability. Oleaginous microalgal strains (Auxenochlorella protothecoides and Chlorella sorokiniana), thraustochytrids strains (Aurantiochytrium limacinum SR21 and Aurantiochytrium sp. T66), and yeast strains (Rhodosporidium toruloides and Cryptococcus curvatus) synthesized 64.5%, 35.15%, 47.89%, 47.93%, 56.42%, and 52.66% of lipid content, respectively. Oils from oleaginous microalgae (A. protothecoides and C. sorokiniana) and yeasts (R. toruloides and C. curvatus) possess excellent physicochemical and tribological qualities due to high amount of monounsaturated fatty acids (oleic acid C18:1 content, 56.38%, 58.82%, 46.67%, 38.81%) than those from oleaginous thraustochytrids (A. limacinum SR21 and Aurantiochytrium sp. T66; 0.96%, 0.08%, respectively) supporting their use as renewable and biodegradable alternatives to traditional mineral oil-based lubricants. Oil obtained from microalgae showed a lower friction coefficient than oils obtained from yeasts and thraustochytrids.

Highlights

Along with industrialization and automation, a growing global population is contributing to a rise in energy usage
The results of cell dry weight (CDW) g/L, total lipids (g/L) and lipid content (%, w/w) of all oleaginous microorganisms used in this study is compiled in Figure 1A, where the data for A. protothecoides, S. limacinum, Aurantiochytrium sp
As it was mentioned in our previous manuscript, A. protothecoides synthesized maximum CDW of 8.40 g/L and 5.43 g/L lipids which corresponded to 64.52% of lipids content when cultivation was performed with

Summary

Introduction

Along with industrialization and automation, a growing global population is contributing to a rise in energy usage. The heavy dependence on fossil fuels over the past century has led to a steady decline in non-renewable fuel stocks, whose depletion is estimated for the medium term. As a result of this situation, researchers are looking for renewable sources to replace conventional fossil fuels and chemicals [1]. Biomass is the only one that can replace petroleum both as an energy source and for the synthesis of organic products [2]. A lubricant is added to reduce friction, minimize wear, transfer heat, remove contaminants, and generally improve processes across two contacting surfaces. The worldwide demand for lubricants amounted to 39 million tons in 2017, of which more than

Methods

Results

Conclusion