The ongoing trend to sustainability is prompting lubricant manufacturers to determine how their products are sourced, manufactured, used, and then, hopefully, recycled, so they can continue to provide benefits even in a different application. This “cradle-to-cradle” approach provides the best opportunity for lubricant manufacturers to minimize their carbon footprint and achieve carbon neutrality.
The hopeful result is for lubricant manufacturers to contribute to a “Circular Economy.” A significant aspect in determining if a specific lubricant will contribute to carbon neutrality is to understand the sourcing and manufacturing of the raw materials used in the manufacturing process. While a good deal of attention has been paid to evaluating the carbon footprint of base stocks because they comprise the largest percentage of any lubricant formulation, additives also need to be taken into consideration because of the strong contribution they make to the performance of lubricants.
Additives need to be evaluated for sustainability both on the merits of their manufacture and how they are used to improve the functioning and durability of a specific lubricant. The second characteristic may be just as important because, if an additive facilitates a significant improvement in the lifetime of a lubricant, this will improve its sustainability profile.
Definition of a sustainable additive
Dr. Gemma Stephenson, technical marketing manager — performance technologies for Cargill Bioindustrial in Snaith, U.K., indicates there is no single definition for a sustainable additive but rather a range of views and opinions.
“In Europe, European Union (EU) policymakers for the Chemicals Strategy for Sustainability (CSS) envision that sustainable chemicals are ‘used and produced in such a way that maximizes their benefits to society while avowing harm to planet and people [1],’ ” she said. “The ambition of the European Commission is to support the transition to an economy where chemicals, materials, and their use in products are safe and sustainable, taking consideration of the entire life cycle: production, use and end of life.”
“In taking this approach, industry must think beyond the intrinsic properties of additives (e.g., biodegradability, toxicity and bioaccumulation) and consider their use-phase and their ultimate-fate,” Stephenson said. “The EU’s voluntary framework, ‘Safe and Sustainable by Design (SSbD),’ [2] was published in December 2022 as a commission recommendation. This framework provides the most comprehensive definition of safe and sustainable for chemicals (including lubricant additives) and materials.”
Joerg Simon, sustainability implementation lead for Infineum in Milton Hill, U.K., agrees that there is no commonly agreed definition of a sustainable additive.
“Sustainable and non-sustainable is not as clear cut as some might think,” he said. “Sustainability is a holistic view, not a rigid classification that limits sustainability to just a single specific market segment criterion. Additives are added to improve the application, and, in the case of lubricants, most are added to improve lubrication, e.g., reduce friction losses and increase durability. The statement can be made that all additives contribute in varying degrees to sustainability — some more, some less.”
“In seeking a suitable definition, the three aspects of sustainability (social, environmental, and economic) must be taken into consideration,” Simon said. “The focus should be on determining the impact of an additive across its life cycle and evaluating the in-use benefits provided to a specific lubricant. In-use benefit analysis is particularly important because a specific additive may not have a better environmental footprint, but it may generate sustainability/environmental benefits through its use or enable more sustainable operation/application. An additive can be defined as sustainable where the in-use benefits outweigh the impact of the product itself, e.g., in terms of carbon footprint.”
Benn Heatley, sustainability leader of Afton Chemical in Bracknell, UK, believes the definition of a sustainable additive can be found through evaluation of three issues.
“The role of additives is to reduce emissions, improve fuel economy, and extend engine and equipment life,” he said. “Improving reliability and efficiency, while reducing the use of fossil fuels, can decrease the carbon footprint for the end-user and is critical in establishing sustainability credentials for a specific additive.”
“Minimizing the overall carbon footprint through evaluation of the additive’s manufacturing process and supply chain also must be taken into consideration,” Heatley said. “A final factor in defining a sustainable additive is considering its environmental profile by eliminating chemicals of concern, considering bio-derived substances and their sources and increasing circularity.”
“Our definition of a sustainable additive includes minimizing the additive’s footprint compared to available alternatives while maximizing the handprint or performance of the finished lubricant to allow fluid suppliers to meet and exceed customers’ and other end-users’ performance and sustainability goals,” said STLE member Thomas Wolak, industrial technology development manager for The Lubrizol Corp. in Wickliffe, Ohio.
STLE member Stephanie Cole, formerly senior formulation chemist for Clariant in Mount Holly, North Carolina, believes a sustainable additive must touch one or more of the three pillars of sustainability: people (social), planet (environmental), and performance (economic).
“The ideal additive would touch all pillars of sustainability, but working toward touching at least one is ideal,” she said. “An additive is felt to be favorable toward the social pillar if it does not contribute to human hazard warning labels in the finished lubricant. Increasing energy efficiency, by reducing energy usage, would address the environmental pillar, and the improving lubricant performance meets expectations for the economic pillar. Multifunctional additives that contribute to less formulation complexity and help leave room in the formulation for cost-effective components also would be considered sustainable.”
STLE member Dr. Min Chen, global business manager — metalworking fluids for Advancion Corporation in Buffalo Grove, Illinois, defines a sustainable additive as being benign by design and encompasses the manufacture and use of efficient, effective, safe, and environmentally responsible chemistry.
“In metalworking fluids, an example of a sustainable additive is one that extends the life of the lubricant and tools that use it,” he said. “Another example is an additive that improves the overall labeling and sustainability scorecard of the finished lubricant.”
STLE member Jim Cancila, formerly account manager for Ingevity in North Charleston, South Carolina, indicates that sustainable additives are derived from materials of biological origin.
“Essentially, these materials come from living organisms, capable of reproduction,” he said. “Every definition of ‘sustainable’ excludes materials from fossil sources and/or geological formations. Any manufacturing or refining procedures are restricted to natural processes (for example, fermentation).”
STLE member Dr. Jun Dong, global technology manager fuels and lubricant additives (FLA) at SONGWON Industrial Group provides the following definition:
“A performance enhancing additive for lubricants (is one) that can be sourced, manufactured, transported, utilized, and disposed/recycled in sustainable ways,” he said.
How to determine if an additive is sustainable
To answer this question, Cole said he feels it may be easier to determine if an additive is not sustainable.
“With all of the news of supply chain issues, global warming, and social issues readily available, it is easier to determine what is not working,” she said. “We can isolate why it is not working and determine what could work instead. Among the common buzzwords of green ingredients, bio-derived formulations, carbon-neutral, or net-zero carbon, it is easy to get lost in the actual requirements and needs.”
Dong furnished a list of five criteria for whether an additive is sustainable. He said an additive can be sustainable if it exhibits one or more characteristics:
- The raw materials used to make the additive are from renewable resources or recycled.
- The manufacturing process uses green energy.
- The additive can help with fuel economy, thus reducing dependency on natural resources and cutting carbon dioxide emissions.
- The additive prolongs the useful life of lubricants, thus reducing the environmental impact of lubricants.
- The additive is biodegradable and environmentally friendly.
Chen offered a similar set of criteria for whether an additive is sustainable in the form of questions. They include:
• Does the additive offer an improved environmental health and safety (EHS) profile compared to alternative chemistries that helps reduce hazardous exposure to workers/operators and reduce overall impact to the environment?
• Does the additive help enhance the sustainability performance of the fluid formulation such as extending fluid longevity, which reduces the total waste of finished lubricants?
• Can the additive better enable the formulation of biobased products by enhancing overall stability of formulation to create a fluid with an improved environmental/biobased profile while maintaining performance?
Cancila indicated programs are available that define whether an additive is sustainable.
“These programs are voluntary, and not every additive supplier is required to use these resources,” he said. “Examples include the USDA BioPreferred® Program and the EU Ecolabel.”
“When assessing the sustainability of an additive, a life cycle assessment (LCA) is performed, which includes a review of both its environmental footprint (for example, consumption of natural resources during the manufacturing process and any environmental impacts measured in carbon dioxide equivalents per kilogram [CO2 equivalent per kilogram]) as well as the handprint (or performance benefits the additive enables in the finished lubricant),” Wolak said.
Heatley said he believes taking a life cycle approach is important in assessing whether an additive is sustainable.
“The life cycle approach considers high priority topics such as carbon impact and broader topics including eutrophication, particulate matter, and water consumption,” he said. “This deep understanding of the additive allows proper consideration of its attributes and allows for continuous development. Studying broader topics such as circularity, responsible sourcing, and end-of-life considerations also are important.”
Simon and Stephenson both cite the World Business Council for Sustainable Development (WBCSD) as establishing a framework for how sustainable performance of chemicals can be evaluated. [3].
“The WBCSD framework can be tailored to fit the needs of the lubricant industry and translate relevant criteria into tangible parameters by taking into account the environmental footprint of the product, in-use benefits, market relevant criteria such as the regulatory environment and key stakeholder activities,” Simon said. “It can be tailored to compare the products of specific lubricant additives, in particular, applications against a reference in several sustainability aspects such as climate impact, renewable materials, and circularity. The same logic can be applied during product development by comparison to an existing product or similar baseline to ensure sustainability also is considered at this early stage of an additive’s life cycle.”
Simon said the sustainability can change during an additive’s useful lifetime, which means there is no guarantee that a highly sustainable additive introduced at a specific time will be rated in this manner over time. An example is additives that enable fuel economy.
“Consider an additive that delivered fuel economy improvements of 1 percent, which was seen as a more sustainable solution,” he said. “Nowadays, the market requires a fuel economy performance of 3 percent and more, which means that this additive delivering 1 percent fuel economy improvement is less sustainable.”
“In the absence of agreed definitions or prescribed sustainability frameworks for innovation, companies are adopting their own ‘in-house Portfolio Sustainability Assessments (PSAs)’ to accompany new product development, and scorecards are becoming commonplace to help assess the sustainability credentials of products during the product design phase,” Stephenson said. “Forward-thinking companies are acting now and integrating the fundamental principles of the SSbD initiative into their corporate and research and development strategies.”
“Determining if an additive is sustainable should be conducted through a series of evaluation processes starting with an initial sustainability impact assessment (SIA) methodology for scoring and comparing products against various sustainability metrics, followed by advancement to widely recognized LCAs,” she said. “This process helps to guide internal decision-making through a new product development process but is only one consideration. An ideal design also must take into consideration the creation of products that can be suitably reused or recycled at the end of their useful life. For lubricant additives, however, creating circularity can be challenging to impossible. Additives are typically included at low levels in finished lubricant formulations, and it can be generally assumed that their fate is part of a linear economy; they may be consumed during the use phase of the lubricant, destroyed during a re-refining phase, or they can be burned when the lubricant is collected and incinerated in order to generate heat or electricity.”
The aim in developing and commercializing a new additive is to hit the “sweet spot” among sustainability, safety, and performance, according to Stephenson (see Figure 1). This is the objective of SSbD.
“Intrinsic hazards of a specific additive should be minimized while simultaneously maximizing the additive’s in-use benefits,” Stephenson said. “Performance benefits to be evaluated include improved energy efficiency, reduced greenhouse gas (GHG) emissions and improved durability, while maximizing safety and sustainability credentials. The lubricant manufacturer and end-user also should be considered when a new additive is developed.”
One example given by Stephenson is corrosion inhibitors that can provide excellent performance benefits, but some types may be classified as dangerous for the environment and may pose a threat to human health.
“In many applications, the risk associated with using harmful additives is mitigated by the fact that they are used in a controlled manner, with little to no opportunity for human or environmental contact, if used correctly,” she said.
Strong need for sustainable additives
After providing a definition for sustainable additive and determining a process for whether a specific component used in a lubricant formulation is sustainable, when is the need strong enough for such an additive?
“All lubricant applications have a need for sustainable additives,” Cancila said. “However, there are situations where the lubricant is consumed, rather than being contaminated and reused. Lubricant applications that do not contain and reuse the lubricant, such as wire rope dressing or roller chain fluids, should be prioritized for sustainable formulations.”
Heatley highlighted electric vehicles and wind turbines as two high-profile examples where sustainable additives can facilitate the development of technological advances required to meet the world’s challenges.
“Beyond these new applications, the world still needs to keep moving, which means that existing machines and vehicles, such as existing vehicle fleets and heavy-duty applications, also will require continuing focus,” he said. “In all areas of lubricants, many stakeholders have an increasing desire to see continually improving products and services. The need for sustainable additives is across the industry and at all levels of the supply chain.”
Stephenson said she believes there are applications where sustainable additives are justifiably inescapable such as when used lubricants are used in environmentally sensitive areas where there is the risk of leakage to the environment. An example is vehicles operating in agricultural or forest environments. They will be better served by lubricant additives with minimal effect on the surrounding ecosystems.
“Today, there are schemes in place that provide more prescriptions and/or limitations as to what can and cannot be used, including but not limited to the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR), Vessel General Permit (VG), and the European Ecolabel for Lubricants,” Stephenson said. “The latter is a voluntary scheme that rewards products and services for having a reduced impact on the environment, and Ecolabel approval is achieved through a verification process, usually referred to as a ‘certification.’ Lubricant products satisfying the Ecolabel must be biodegradable, have low aquatic toxicity and bioaccumulation potential, and must be sustainable sourced. While these initiatives promote the use of less toxic substances in environmentally sensitive areas, they do not make any end-of-life commitments regarding the fate of a specific lubricant and the components contained in its formulation.”
“Initially, applications with lubricants formulated at high-additive treat rates, possible spillage or environmental contamination and higher fluid changeover will have a strong need for sustainable additives,” Cole said. “Examples include compressor fluids, gear oils, greases, hydraulic fluids, metalworking fluids, and transmission fluids. Eventually, all industrial lubricant applications will require only sustainable additives.”
Wolak said environmentally acceptable lubricants get much of the attention at this time, mainly because of existing regulations that are either voluntary or enforceable.
“The main lubricant applications in environmentally sensitive areas are industrial in nature and are usually bio-derived: hydraulic fluids, industrial gear oils, and chain saw oils,” he said.
Simon said all lubricant applications that increase efficiency need more sustainable additives.
“This is true for mature applications such as automotive engine oils and more recent ones such as electric vehicle fluids and for future applications,” he said. “Efficiency increases can be achieved in various ways, e.g., through using lower additive treat rates or using additives in lubricants that display greater durability. For example, increasing fuel economy is a sustainable contribution and so is the extension of the lifetime of a heavy-duty engine. While battery electric power may emerge as more of a major contributor to automobiles, additives that can contribute to reducing frictional losses and/or destructive processes in internal combustion engines by reducing the amount of fuel not burned now and optimizing energy consumption will be sustainable. They can facilitate the reduction in GHG emissions and limit global temperature rise. Existing lubricant applications will be around for some time, and improvements must be made to move toward sustainability while waiting for future technologies to be applied more broadly and others to be commercialized.”
“Specific lubricant applications exist where certain sustainable attributes are required,” Simon said. “For example, the lubricant used in chain saws will be released into the environment during use. In this case, aspects of no harm occur in the environment during use, and biodegradability requirements play a very specific role.”
“There is strong need to reduce waste, minimize hazard exposure, and develop environmentally responsible lubricants in total-loss and partial-loss applications, as well as accidental loss lubricants, such as metalworking fluids and hydraulic fluids,” Chen said.
Dong listed three applications that require sustainable lubricant additives: Automotive lubricants due to their sheer volume. Marine and forestry machinery lubricants due to their use in environmentally sensitive areas.
Sustainable vs. environmentally friendly
One aspect of a sustainable additive that can be confusing is whether it needs to be environmentally friendly. Drawing a distinction between the two terms can be challenging.
“This question pre-supposes that there are well-defined meanings for environmentally friendly and bio-based additives,” Stephenson said. “It is generally understood that ‘environmentally friendly’ refers to additives that impart minimal or no harm upon the environment. But to make such a claim, a point of reference is required, be that tests by which additives are assessed, or the quantity in which they are used. Several schemes apply substance exclusions and limitations based on human and environmental hazards, and some include a positive list such as the European Ecolabel Lubricant Substance Classification List (LuSC).”
“Bio-based additives are derived from living organisms or biomass, e.g., crops, wood or algae,” she said. “There is no guarantee that the raw materials used in producing these additives or these additives themselves are sustainable. As an example, bio-based materials that are grown on areas of deforestation or on land defined as critical for human food consumption should not be considered sustainable, as the overall environmental benefit can be considerably worse than leaving the land area unchanged.”
As shown in Figure 2, one approach for working with sustainable and environmentally friendly is to find a “sweet spot” among these two terms and bio-based.
“The three terms in Figure 2 can be closely linked but are independent concepts,” Stephenson said. “A sweet spot among the three terms can be reached, but these concepts are not necessarily mutually inclusive.”
With the lack of definitions or standards for these terms, Simon said he believes sustainable moves beyond environmentally friendly to include people, planet, and profit.
“This can range, e.g., from making sure the additive is produced in a safe way and limiting the use and exposure of highly hazardous substances, especially to non-professionals, to the avoidance of child labor in the whole supply chain,” he said.
Simon said “bio-based” on its own does not make for a sustainable additive.
“A biobased raw material might need a different, higher carbon intensive processing or might not be recyclable, and, at the bottom line, even when you take the GHG benefits into the account as the raw material is made, the LCA might be worse than a non-biobased alternative,” he said. “Other parameters such as water consumption also must be taken into consideration.”
Heatley said it is important to not focus on one feature or metric when considering terms such as sustainable and environmentally friendly that have unclear or varying definitions.
“Continuing the journey toward sustainable lubricant additives will require careful consideration of many factors from where the raw materials are sourced (biobased or otherwise), to where and how they are manufactured,” he said. “Other factors include how the end-user utilizes the finished lubricant and end-of-life treatment. All along the life cycle, potential impacts require consideration and careful balance. Only through dedicated R&D, extensive engagement with stakeholders and detailed life cycle analysis can all the aims of a sustainable additive be met.”
“A sustainable additive can be derived from raw materials that are not categorized as ‘environmentally friendly’ or bio-based but can improve the overall sustainability scorecard of a formulation by extending fluid longevity to reduce waste or improving the overall carbon footprint of the finished lubricant,” Chen said. “A sustainable additive also can take into account the impact reduction along the life cycle of the additive (e.g., manufacture, use, and disposal). Since an environmentally friendly raw material implies it is not harmful to the environment and a biobased component is derived from renewable, carbon-based biological sources, both can contribute to a specific lubricant additive’s overall sustainability profile.”
“Sustainable additives refer to a wider range of products that show sustainable characteristics for their entire life cycles,” Dong said. “Bio-based or environmentally friendly additives can be sustainable.”
Cancila drew a distinction between an environmentally friendly and a sustainable additive.
“It is possible for an additive to be ‘environmentally friendly’ but not sustainable,” he said. “An environmentally friendly additive may be non-toxic and biodegradable but not derived from a sustainable source.”
Cole gave an example of a biobased additive that is not sustainable and a non-biobased additive that is sustainable.
“The production of palm oil has involved the destruction of animal habitats in order to grow palm trees,” she said. “This is not a sustainable solution, and organizations such as the Roundtable on Sustainable Palm Oil (RSPO) have been established to ensure palm-oil production is more sustainable. An ethoxylated amine, prepared from non-biobased components, is a sustainable additive because it helps to improve metalworking fluid durability in a recirculating system. The result is that an end-user should realize lower operating and fluid disposal costs and should benefit from greater productivity due to lower downtime.”
Wolak indicated a sustainable additive can be environmentally friendly, but there are examples where an environmentally friendly additive can have a larger carbon footprint and not be that sustainable.
“Often, additive and base oil attributes required to meet environmentally friendly status (biodegradable, non-toxic, non-persistent in the environment, etc.) take precedence over the LCA value in terms of carbon dioxide equivalents per kilogram of the finished lubricant,” he said. “Therefore, an environmentally friendly lubricant could have a larger footprint and contribute more carbon dioxide equivalents per kilogram compared to conventional lubricants.”
Sustainable but not bio-based
Distinguishing between sustainable and bio-based is an important issue because there are additives used that are not derived from bio-based raw materials yet can be considered sustainable.
“Bio-based raw materials are not always the most sustainable from a LCA perspective,” Wolak said. “For example, synthetic esters may be bio-derived, but the energy intensity used to make an ester-base stock is usually much higher compared to a Group I or Group II derived base oil especially when scale of the operation is a major factor.”
Figure 3 shows a decision tree that can be used to not only determine if a sustainable lubricant is needed for a specific application but also distinguishes between bio-lubricants and non-bio-lubricants.
Cancila said an additive that does not meet the definition of sustainable may contribute to the overall sustainability of a lubricant or a process.
“This point is illustrated routinely in metalworking fluid applications,” he said. “The concept of sustainability is being translated into ‘sustainability plans’ with specific goals by many lubricant end-users. Additives that extend the useful life of a metalworking charge contribute toward achieving the sustainability goals of the end-user. Extending metalworking fluid ‘sump life’ achieves many sustainability goals.”
Heatley said he feels that, in determining whether an additive is sustainable, a balanced approach will often need to consider the nature of the raw materials, the product life cycle, and the product’s overall performance.
“Sourcing bio-based raw materials is one way a product’s carbon impact can be reduced across its life cycle,” he said. “However, there is rarely a single solution to every issue or a one-size-fits-all approach. Bio-based raw materials are not without their challenges. Careful consideration must be made to ensure that prioritizing bio-based feedstocks does not unintentionally compromise the wider environment. When using alternative products, it also is important to thoroughly explore their effectiveness and efficiency.”
Simon said he believes evaluating the ability of an additive to be circular and act to enable more sustainable applications are two other strategies that can be used in determining sustainability without relying on whether the additive is bio-based.
“Examples of additives that enable sustainability are those that maximize in-use benefits such as fuel economy and extending oil-drain intervals,” he said. “An essential element of sustainability is circularity or the circular economy, i.e., reusing and extending the lifetime of materials and products for as long as possible. Re-refined base oils, as an alternative for virgin base oils, represent one example since base oils make up a part of modern additive components and a substantial part of finished formulations. Converting components present in waste streams for use in additives or additives at the end-of-life in one application into another application are additional examples of sustainability.”
Chen said non-bio-based additives are widely used today to improve the sustainability profile of a lubricant by extending the fluid longevity or improving the compatibility of the fluid for recyclability to reduce the overall waste.
“The use of lubricants formulated with non-bio-based additives can facilitate highly efficient manufacturing processes that lead to less waste and strain on natural resources,” he said. “Bio-based additives used in lubricants are from renewable sources and are biodegradable, but frequently, they do not display the performance requirements needed particularly from the standpoint of oxidative stability. This issue has been investigated for more than 50 years, and higher total costs from the economic and environmental standpoints can be found in using biobased additives compared to non-biobased alternatives.”
“Figure 1 outlines the basic design profile for developing a specific additive based on safety, sustainability, and performance,” Stephenson said. “Performance is normally well-defined with regards to what is expected of the additive and the lubricant in which it is included, be that energy efficiency, lubricant lifetime, or equipment durability. If higher performance and, therefore, greater environmental benefit can be derived from using petrochemical raw materials, then the impact of petrochemically-derived additives can be considered a step forward in terms of sustainability compared to alternatives.”
Stephenson also said she believes “bio-based” does not translate to “100 percent bio-based.”
“There are many examples of additives that are derived from a combination of both bio-based and petrochemical raw materials, the raw materials being chosen to derive the maximum performance from the additive,” she said.
Examples of sustainable additives
Dong said a primary aromatic amine antioxidant is a good example of a sustainable additive.
“As shown in Figure 4, this additive exhibits a low global warming potential of 2 kilograms of carbon dioxide equivalent per 1 kilogram of product,” he said. “There are zero impacts to environmental areas including photochemical oxidation, abiotic depletion, acidification, eutrophication, and ozone depletion potentials.”
The major contribution to global warming potential for this additive is the raw materials used in its manufacture with the rest coming from the energy used.
“Utilization of primary amine antioxidants to prolong the useful life of lubricants and extend drain intervals demonstrates how this additive type can be sustainable by reducing crude oil consumption and minimizing the environmental impact incurred from disposal,” Dong said.
Another example showing how extending the life of a lubricant makes an additive sustainable comes from the use of alkanolamines in metalworking fluids. Figure 5 shows how seven amines (AMP, 4AA, AB/AEPD, DGA, MIPA, MEA and TEA) and sodium hydroxide (NaOH) affect the life of a metalworking fluid over time in weeks. Three of the amines display double the operating life compared to the other additives.
“Three of the amines listed in Figure 5 can be considered to have a higher sustainability profile due to their ability to improve the longevity of metalworking fluids and reduce waste,” Chen said.
Cancila said a carboxylic acid dimer shows sustainability by providing improved corrosion and rust inhibition, enhanced emulsion stability, and increased lubricity in metalworking fluids. Figure 6 illustrates the performance of the carboxylic acid dimer vs. other carboxylic acids in reducing the staining of 7050 aluminum.
“Wettability of metal surfaces enhances metalworking fluid lubricity,” he said. “As shown in Figure 7, the carboxylic acid dimer produces better wettability through lower contact angles than other carboxylic acids.”
Stephenson considers esters to be a good example of sustainable additives that offer a variety of functions.
“Esters can be designed so that they are inherently environmentally acceptable or ‘intrinsically sustainable,’” she said. “Many are highly biodegradable, non-toxic, and non-bio-accumulative, making them excellent technologies for use in environmentally sensitive areas, where lubricant leakage may be a concern.”
A second example offered by Stephenson is friction modifiers that have excellent built-in sustainability credentials (for example, a low-carbon footprint) and bring outstanding benefits in use.
“Friction modifiers have long been used in engine-oil formulations to deliver low levels of boundary and mixed lubrication friction and, thereby, better fuel economy, which translates into reduced or avoided carbon dioxide emissions from passenger cars,” she said.
Cole said polyalkylene glycols (PAGs) are a good example of a sustainable additive.
“PAGs exhibit superior lubricating properties, corrosion protection, and work with other lubricant additives to lower energy cost at end-user facilities,” she said.
Heatley gave two examples of lubricant applications that will be using sustainable additives.
“New technologies are rapidly being developed to enable the electric-vehicle market growth to help reduce carbon emissions,” he said. “The need for future lubricants to consider conductivity, the effect of electric fields, low friction/high speed, noise and battery cooling or copper wire drawing are performance attributes to consider.”
A second example is wind-turbine oil solutions that reliably support the growing renewable energy market.
“Wind-turbine manufacturers and gearbox suppliers can achieve more efficient output and productivity with the right additives,” he said. “With many countries turning to wind energy as an alternate electricity source, the demand for efficient and reliable lubrication will continue to grow.”
Simon pointed to efforts that are continuing to balance lubricant additive packages to maximize the performance of finished lubricants.
“In my view, an additive package and a final oil formulation need to be seen as one, as this is the final application,” he said. “As the majority of a lubricant is base oil, changing the sustainability credentials of this component might have a bigger impact on the sustainability of the finished lubricant than most changes done to additives. With a lubricant-additive package, the right balance of all components is vital. Many components in the additive package contribute to the sustainability performance of the finished lubricant. For example, anti-wear additives protect surfaces to extend the lifetime of the engine. While the focus of in-use improvements to the additive package is to increase performance, the potential impact on the social, environmental, and economic aspects must be kept in mind to find the right balance.”
Wolak said sulfurized vegetable oils are an example of a sustainable additive.
“These additives contain renewable carbon content and improve the lubricant’s handprint by providing excellent extreme pressure and anti-wear (EP/AW) performance to extend tool life and surface finish in metal-removal processes,” he said.
Effectiveness of sustainable vs. non-sustainable additives
Simon said he considers sustainability to be not as simple as determining whether additives are sustainable or non-sustainable.
“An additive is more or less sustainable depending among others upon its benefits in the application and environmental footprint,” he said. “If a discussion about sustainability is limited to just the carbon footprint, then there is little difference in the technical performance between less sustainable and more sustainable additives at this stage. Additive solutions are created to deliver a certain performance that can be reached with more or less sustainable solutions. Looking forward, a better understanding of any dilemma that might occur between rising technical and sustainable expectations must be realized to find the optimal balance of technical and sustainability performance meeting future requirements. These dilemmas might arise from higher technical performance requirements or more sustainable solutions that are less effective.”
Stephenson said the priority factor in designing an additive is performance, whether the specific component is sustainable or non-sustainable. Bio-based additives can provide good performance not because of their content but because their in-use benefits are maximized.
“An increasingly competitive advantage stems from designing more sustainable solutions, perhaps using bio-based raw materials or more efficient production processes, but which maintain or increase performance benefits,” she said. “The age-old perception can be that a bio-based additive will be less effective than its petrochemically-derived counterpart, but defining what this means needs to be clarified. It could be due to function or due to the same molecule being produced from both bio-based and petrochemically-derived raw materials.”
“Currently, the bio-based raw material portfolio is limited, and the choice of naturally derived building blocks available to lubricant formulators is small,” Stephenson said. “However, it is rapidly widening, and it is hoped there will soon be a broader offering of bio-based raw materials that can be used as drop-in replacements for petrochemical building blocks, as well as more unique building blocks found in nature. A good example is ethylene oxide, a key precursor to many additive components in lubricant formulations. Ethylene oxide has traditionally been produced from petrochemical resources but can now be produced using bioethanol to make 100 percent bio-based emulsifiers, wetting agents, and dispersants with no sacrifice in performance.”
Specific needs for sustainable additives
Wolak gave two examples of specific needs for sustainable additives: Additive chemistry is required to unlock the performance of sustainable base oils in order to first meet industry, OEM, and end-user performance requirements and, second, to meet sustainability goals as measured by improved LCAs versus conventional lubricants.
Cancila said sustainable additive needs are linked to the properties of base oils.
“The biggest formulation component need for sustainable material is base fluids,” he said. “An assessment of the capabilities of and chemistry of the base fluid must determine what other additives will be required in a specific formulation.”
Chen gave four examples of areas where sustainable additives are needed:
- Extending metalworking fluid life to reduce waste.
- Additives to improve worker health through reducing exposure to hazardous components.
- Improving the formulation and the stability of plant-based lubricants.
- Sustainable additives for use in food-grade lubricants, total-loss lubricants, and one-time-use lubricants.
Dong said antioxidants and friction modifiers are two additive types that contribute sustainability to lubricants.
“Antioxidants prolong the useful life of lubricants and extend drain intervals, thus effectively reducing crude-oil consumption and minimizing the environmental impact of disposal,” he said. “Friction modifiers improve fuel economy in automotive lubricants, reducing energy consumption and carbon-dioxide emissions.”
“Within an industrial setting, additives are needed to deliver crucial in-house benefits such as greater efficiency, maximizing output, reducing equipment downtime, conserving energy, and reducing waste (rejected components),” Stephenson said. “These concepts are central to a large number of market sectors including electric vehicles, wind-turbine gearbox lubricants, manufacturing and high temperature chain oils. Formulators are increasingly keeping these issues in mind because they are now starting to prioritize the sustainability credentials of their products.”
Simon said the development and selection of additive components needs to follow specific sustainable deliverables, including increasing energy efficiencies, and for use in lubricants with known release to the environment.
“Categories that involve boosting energy efficiency (such as increasing fuel economy improvement expectations) and where the needs and lifetime of products and materials can be optimized (use less, reuse, recycle, and bio-based), are the ones that can make the biggest contribution to a more sustainable world,” he said. “Additional examples are lubricants that enable more sustainable applications (such as e-fluids), and those that can be directly released to the environment (for example, chain saw fluids).”
Future use of sustainable additives
“Stakeholders throughout the lubricant value chain are likely to continue striving to improve the sustainable credentials of additives and lubricants,” Heatley said. “New additive technologies will be needed to meet the world’s future challenges to continue reducing emissions, improving fuel economy, and extending engine and equipment life. These challenges have the potential to offer great opportunities to meet and exceed the needs of end-users and OEMs.”
Simon highlighted the role end-users and OEMs are taking in raising their sustainability ambitions as leading to the growth in the use of sustainable additives.
“With the majority of industries and industry stakeholders setting GHG reduction targets, supplier expectations and net-zero ambitions as a means to move toward sustainability, additives will play a vital role,” he said. “Demand for more sustainable additives is anticipated to grow significantly in the future, especially the ones impacting carbon emissions positively. This driver will occur through circularity, energy efficiency improvements, extending product and material lifetime, or enabling more sustainable applications. Additional applications will accelerate growth in the use of sustainable additives through specific criteria such as biodegradability and ecotoxicity.”
Stephenson pointed out the past objective of developing additives, base oils, and finished lubricants based on performance will not be sufficient, and there will be a greater push toward additives that also do not compromise on safety and sustainability aspects.
“Companies in the EU are beginning to weave elements of the SSbD and other anticipated initiatives into their product development processes as implementation will be taking place in the near future,” she said. “Innovation to find the ‘sweet spot’ among safety, sustainability, and performance (see Figure 1) is now being accelerated.”
“The entire lubricants value chain is on a journey toward sustainable growth through better use of resources and the materials that make up lubricant formulations used today,” Stephenson said. “Demands from end-users intertwined with tightening legislation to meet climate ambitions are forcing OEMs and the rest of the value chain to rethink and redesign their products to fit the new sustainability agenda.”
“Demand for sustainable additives is expected to rise due to more stringent legislation, customer demands, industry trends, and growing public awareness for sustainability,” Dong said. “Applications where sustainable additives will be needed are automotive lubricants, environmentally friendly lubricants, and fuels, including biofuels.”
“With the growing concern around the sustainability profile of the individual components as well as the overall formulations themselves, formulators, manufacturers and end-users are increasingly focused on the use of sustainable additives and lubricants,” Chen said. “Their use will be accelerated in total-/partial-loss fluid applications, food-grade lubricants, and medical device manufacturing.”
“Corporate sustainability plans are gradually defining sustainability initiatives for larger lubricant and metalworking fluid end-users,” Cancila said. “Optimized management of lubricants and metalworking fluids are more valuable at this point than the use of sustainable additives. Lubricant formulators and end-users will ultimately judge the measurable benefits of sustainable additives to the application and ‘cost of use.’ ”
“The call to a more sustainable future is here,” Wolak said. “Whether that means using existing additive chemistry to enable increased usage of sustainable base stocks or simply lowering the footprint of additive chemistry in general, fluid marketers and governments are setting expectations and goals to reach sustainable targets now and in the future. As a result, sustainable lubricants are forecasted to grow significantly faster than conventional lubricants.”
The growing use of sustainable additives will be spurred by end-users and regulations. This will lead to a systematic move toward lubricant additives that cannot only demonstrate the required performance to meet specific application requirements but also meet criteria that are being established for sustainability.
References
- Chemicals Strategy for Sustainability Towards a Toxic-Free Environment, Annex to the European Green Deal, COM (2020), 667 Final, Oct., 14 2020.
- https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32022H2510
- Chemical Industry Methodology for Portfolio Sustainability Assessments (PSA), WBCSD, April 2018.
