Sustainability is more than just a buzzword in todays lubricants market. The proof was in the pudding at the European Lubricating Grease Institutes annual meeting, where sustainability was the conference theme and presenters delved into the practical and philosophical meaning of the concept.
Sustainability refers to the social, economic and environmental consequences of human activity, Siegfried Lucazeau of Nyco told the group gathered in Venice, Italy, in April. The potential for harm to people or the environment, depletion of natural resources, long-term effects and political consequences are all part of the sustainability equation, he elaborated.
Particular concerns for the lubricants industry include depletion of fossil resources, competition with food resources (e.g., production of fatty acids from palm oil), energy savings through reduced friction, reduced CO2 emissions, and increased durability that can reduce waste and downtime. Going beyond environmentally friendly lubricants to sustainable products requires a big-picture view that takes into account the impact of production, transport, disposal and raw materials in addition to the impact of a lubricant itself, pointed out Lucazeau, who is based in Paris.
National and international standards, legislation and product labeling schemes show that the world is paying attention to the need for sustainability. Among 463 ecolabels across the world, Lucazeau highlighted several standards specifically dealing with lubricants: the European Union Ecolabel, Nordic Swan, Swedish Standards, Blue Angel and others in Europe; the federal EPA Vessel General Permit and USDA BioPreferred programs in the U.S.; and the international OSPAR Convention.
The voluntary EU Ecolabel scheme, Lucazeau continued, seems to come closest to full sustainability considerations, including guidelines on toxicity, renewability, performance and durability. Ecolabel standards demand that greases contain over 75 percent biodegradable components and over 45 percent carbon from renewable sources, along with having aquatic toxicity below 1,000 mg per liter, among other criteria.
George Dodos of Eldons S.A. in Athens, Greece, estimates the European market potential for biobased lubricants is 1.5 million metric tons per year – a number that Dodos believes will gradually rise. Global biobased grease production is nearly 0.6 percent of total grease production, according to a 2014 National Lubricating Grease Institute (U.S.) survey. In Europe, this number is four times higher at 2.18 percent.
Generally, the biolubricants market is considered to be one of the most growing sectors universally, Dodos told ELGI attendees. Especially in the last years, there is an increased market acceptance. The EU consumes 100,000 tons of biolubes per year, mostly in total loss lubrication and high risk applications. This number could increase four-fold in the 2020s thanks to regulations mandating use of biolubricants in environmentally sensitive areas, he predicted.
The projected increase in biolubes demand is driving volumes of research to improve performance and manufacturing techniques and to explore alternative feedstocks, Dodos said.
Cooking Up Feedstocks
Dodos turned his own research toward finding a more sustainable feedstock for biolubes, which are typically based on fatty oils. Why not exploit some residual fat material like used cooking oil, which is an everyday material, and try to see if we can convert it to a high added value lubricating grease? he asked.
The EU has infrastructure in place for collecting used cooking oil, and Dodos estimates the region could collect up to seven times more than what it gathers now. While this is not a new idea for lubricants, the majority of the oil collected today is recycled in the biofuel industry, and has become one of the major feedstocks for biodiesel.
Dodos and his team gathered two types of used cooking oil: one from household cooking, which was mainly a monounsaturated oleic acid, and one from a local restaurant, which had a high concentration of polyunsaturated linoleic acid. Anhydrous calcium greases were produced from both straight and modified forms of these oils.
The researchers discovered that up to half of the base oil used to formulate lubricating grease could be substituted with straight used cooking oil without significant effects on the physicochemical or structural properties of the product. However, additives were needed to control oxidative stability and hardening was typical at low temperatures.
To address this problem, a mixture of the two straight cooking oils was converted to the corresponding trimethylolpropane (TMP) tri-ester. This processing step substantially improved the greases thermal-oxidative stability and minimized acidity, allowing these renewable base stocks to be considered for applications with higher thermal requirements.
Some challenges are inherent in this feedstock. The type of cooking oil used as base oil in Dodos experiments had a direct effect on finished lube properties, such as low-temperature performance and oxidation stability, with the latter also affected by the severity of the cooking process. Supply of used cooking oil varies in quality and composition, limiting its use on an industrial scale.
Dodos pointed out that this was the first study of its kind, and that more research is needed. It seems from this work that used cooking oil has the potential for being exploited for sustainable biobased lubricating greases. It is also a way to achieve the target of sustainable development.
A Material Difference
When the focus is on performance properties rather than biobased content, Nycos Lucazeau believes that synthetic esters rise to the top for formulating European Ecolabel-certified, VGP-compliant, OSPAR-listed lubricants, including greases.
These Group V base fluids are mainly used to formulate high performance lubricants because of their thermo-oxidative stability that extends lifetime, natural lubricity that reduces wear and improves energy efficiency, and low volatility that extends durability and adds safety through fire resistance. The majority of synthetic esters are harmless to human, animal and aquatic life, are readily biodegradable – even at high viscosity – and unlikely to bioaccumulate, explained Lucazeau, who is product manager for industry and automotive.
Raw materials for production can include up to 100 percent renewable carbon resources, though the chosen materials may impact performance of the final product, according to Lucazeau. Extensive use of controversial palm oil as feedstock for renewable fatty acids has been a concern, so he encourages sourcing feedstock from Roundtable for Sustainable Palm Oil (RSPO) certified producers.
Production of sustainable esters may require some adjustments to the manufacturing process, he admitted, but resulting greases are expected to show most of the benefits listed for ester base fluids.
As a result, synthetic esters do contribute to improved sustainability, as they deliver added human safety, they exhibit excellent environmental profiles, they may decrease dependency on fossil resources, and they contribute to fuel economy improvement and reduction of CO2 emissions, Lucazeau enthused. This is a unique set of properties combining performance and good environmental profile.
Looking at the big picture, Lucazeau explained that Nyco cannot yet compare the carbon footprint of synthetic esters to other base fluids, but he hopes to conduct a Life Cycle Analysis to obtain an estimate.
Loss-lubrication systems – in which grease cannot be easily prevented from coming into contact with the surrounding environment – are an increasingly important target market for biobased greases. Forestry is a significant industry for such systems, and saw chain lubrication is one of that industrys top concerns, explained Johanna Persson of Axel Christiernsson in Nol, Sweden.
In harvesters lubricated with saw chain oil, top-bearing failure frequently can necessitate changing the entire saw sword – with costs stacking up in new components and downtime. Changing the lubricant from saw chain oil to a high performance anhydrous calcium thickened grease has enabled sword failures to be significantly reduced, Persson explained in her presentation in Venice. Field trials have supported this, showing sword consumption dropped by up to 50 percent. Overall uptime increased, and the lower risk of chains breaking made a safer work environment. Also impressive: Lubricant consumption was cut to a tenth of earlier levels.
The biobased anhydrous calcium grease has shown very good performance in forestry applications, where it is often very wet both in the form of rain and snow, and where operating temperatures can be low, she continued.
To come to this conclusion, Axel Christiernsson tested several combinations of base oils, thickeners and additives.
Calcium grease thickener is characterized by resistance to water, good low-temperature rheology, shear stability and adherence to surfaces. The company found that calcium-thickened greases performed similarly both when fresh and after water contamination – which was not the case with lithium greases or a mix of the two.
Water can be trapped in grease in different ways. Bound water effects the thickener more than emulsified water. It seems to be the type of thickener that is the cause of how water is taken up rather than the type of oil, Persson said. By carefully selecting the components of a grease, it is therefore possible to control how much water a product can emulsify. The researchers found that anhydrous calcium greases showed the highest amount of emulsified water, contributing to their performance in wet conditions.
As for base oils, high pour point rapeseed oils performed poorly in low-temperature tests, while low pour point ester products fared better. Ester based calcium grease, however, showed outstanding low-temperature performance. This can most probably be explained by the combination of the type of thickener and base oil, surmised Persson.
By formulating an anhydrous calcium grease with biobased fluids and additives compliant with the EU Ecolabel, a high performance, sustainable grease can be produced. For multipurpose greases such as those used in harvesters, a biodegradable ester with improved high temperature properties would be best. However, she pointed out, in total-loss-lubrication applications, a rapeseed oil based product would probably would have the least environmental impact.