From the axles of ancient Egyptian war chariots to the great iron machinery that powered the Industrial Revolution 3,300 years later, natural fats and oils extracted from plants and animals were used as lubric ants. It wasnt until the internal combustion engine was invented in the 19th Century that mineral oils began to dominate. But natural fats still kept a role in the growing lubricants market, in applications such as metalworking fluids.
Interest is once again on the rise in products based on natural fats or oils derived from fatty acids, using some very simple chemistry, rather than by physical extraction. The fact that these were (partly) renewable base fluids became part of the commercial proposition at the beginning of the 2000s. In the last 10 years there has been an explosionof synthetic bio-derived molecules in the lab and on the market.These substances are esters, usually based on a synthetic petrochemical core of trimellitic acid, neopentyl glycol or trimethylol propane, meaning that at least one building block of common esters is a petrochemical.
While esters are a small segment of the synthetic lubricants group, the global esters lubricants market is expected to grow to an estimated U.S. $1.83 billion by 2022 from $1.17 billion in 2012, according to a report by Crystal Market Research.
Renewable but not Sustainable
The popularity of renewable base oils has paralleled and been affected by the growing use of renewable fuels, which gained traction with the push for alternative energy sources and the reduction of greenhouse gas emissions. Many countries legislated for a portion of their gasoline or diesel supplies to be renewable, and the preferred solution for many was fatty acid methyl ester (FAME). The unfortunate side effect was that large swathes of virgin tropical rainforest have been cut down to create oil palm or soybean plantations to satisfy demand from Europe and North America.
The European Parliament has since rolled back the requirement for FAME and this episode of industrial development will go down as well-intentioned legislation with some bad consequences. Renewable was in this case not sustainable.
Meanwhile, some of the most exciting hydrocarbons developments have enabled suppliers to produce renewable diesel without resorting to esters such as FAME. In Europe, Finlands Neste and Italys Eni are producing renewable diesel. In common with the lubes components outlined below, these fuels offer advantages beyond renewability.
Both companies processes produce the equivalent of a very fine cut of diesel. This means that the two detriments of FAME use in fuels (engine deposits and contamination of the lubricant) are reduced because there is no need for FAME. From a lubricant perspective this is a much easier regime to work in, requiring less dispersant and antioxidant. But there are also performance advantages.
Nestes head of technical services Markku Honkanen explained to LubesnGreases that the narrower molecular size distribution means that a correctly tuned engine burns fuel more efficiently, thus lowering greenhouse gases, and produces fewer particulates than conventional diesel, improving local air quality. Honkanen also pointed out that Nestes MY Renewable Diesel is better for hybrid vehicles, as FAME must be stabilized for storage. In a hybrid vehicle the fuel could be in the fuel tank for weeks if not months.
Sustainable Synthetic Base Fluids
Innovation in biofuels has lead to a corresponding new phase of synthetic base fluid development. A host of molecules have recently become available to lubricants formulators and the chemicals industry that are based on novel chemistry and biochemistry. While some are completely new chemicals, the others are existing molecules historically manufactured as petrochemicals, which will change the chemical fingerprint of renewable molecules if commercially successful. These are all synthetic chemicals, but all can be generated from plant sources and some can even be generated from waste.
If one or more of these molecules is successful, consultancy Kline & Co.s projection of 5 percent per year growth in the bio-based lubricants market will be conservative. All these molecules come from renewable sources, most are biodegradable, and many have low toxicity, which is especially useful for food and pharmaceutical-grade applications.
Renewable Group III
While the Neste and Eni processes outlined above create molecules that would normally be refined from crude oil, those molecules are not large enough to be used in lubricants. However, there are companies – some with big financial backers – that are developing processes and product lines that have direct application in lubricants. These processes involve novel chemistry, or biochemistry based on bacteria, algae and other, often genetically modified, organisms.
U.S. base oil refiner Novvi has a high profile among these companies, with an impressive list of backers supporting its aim to produce renewable Group III+ base oils. Originally a joint venture between American biotech company Amyris Inc. and the Brazilian conglomerate Cosan SA, Novvi, which has Group III capacity of 12,000 tons per year, has received equity investments from American Refining Group, Chevron and H&R USA.
The venture exploits Amyris processes, which can use waste materials from sugar cane or wood cellulose and Cosans capacity to produce over 4 million tons of sugar cane via its subsidiaries and joint ventures. This means that any simple chemistry will produce large volumes of material at low cost.
The molecule of interest is farnesene, a hydrocarbon with 15 carbon atoms and four points of chemical unsaturation. The 15 carbons make the molecule (after hydrogenation) a near-ideal drop-in bio-component for diesel. However, unlike the molecules produced by Neste and Eni, the chemical unsaturation means that multiple farnesene molecules can be joined together to produce dimers, trimers, tetramers and pentamers, which are the right sized molecules for lubricant base fluids.
Estolides
Estolides are another naturally sourced option to create synthetic base stock that has strong performance characteristics for oxidative and hydrolytic stability, volatility, biodegradability and renewable carbon content. The conversion process involves the acid group of a fatty acid attacking one of the carbon-carbon double bonds of another fatty acid to produce a T-shaped ester. Further coupling can take place to produce a branched molecule with an ester linkage at each branch.
Biosynthetic Technologies, based in California, licenses its conversion technology from the U.S. Department of Agriculture, which developed and patented the production of estolide molecules while looking for new uses for crop oils. The company received an undisclosed investment from big players in 2017, namely Monsanto, BP and Evonik, to develop estolides, indicating confidence in their commercial viability.
A convincing demonstration of estolides potential was a 241,400 kilometer field trial in a Las Vegas taxi. Under severe stop and go conditions, the engine showed much less varnish in the engine run on one fluid made of estolide and additives and another with additives and equal amounts of estolide and Group III than when it was run on a fully synthetic GF-5 motor oil.
Polyalphaolefins
Specialty and intermediate chemicals producer Elevance Renewable Sciences exploits Nobel prize-winning chemistry to split the fatty acid chain at the carbon-carbon double bond using renewable resources such as vegetable oils. The initial products are linear alpha olefins (LAOs), also known as normal alpha olefins, and an unsaturated linear acid.
Once the building blocks are separated, they can be reacted together or with other molecules in a second stage. The LAOs could be reacted together to make renewable polyalphaolefins (PAOs), but Elevance has placed emphasis on the advantages of Elevance Aria WTP 40 relative to PAO or PAO/ester blends, so it would seem unlikely that they would then focus on renewable PAOs.
Conceptually, Elevance reacts some LAOs with an ester derived from the linear acid in a reaction like that used to produce PAO. Thus, its Elevance Aria WTP 40 synthetic base stock has been described as a functionalized PAO. Another second-stage reaction of two linear acids with each other produces long-chain diacids, which can be used as corrosion inhibitors.
Bio Building Blocks
The above processes can produce molecules that could be used as base fluids or additives, but there are other developments that could see certain existing additives become similarly more sustainable.
Companies have been established to exploit new opportunities in bio-derived butadiene (used in the production of synthetic rubber), isobutylene (an intermediate gas in the manufacture of numerous products) and succinic acid (a polymer, resin and solvent precursor).
Bio-butadiene could be reacted in the same reactors as now to produce styrene-butadiene viscosity modifiers with up to 50 percent renewable content by mass. Similarly, bio-isobutylene could be polymerized with no modification to the manufacturing process to produce polyisobutylene that is used as viscosity modifiers, tackifiers, smoke suppressants and the hydrocarbon tail of dispersants.Isobutylene can be sulfurized to produce an extreme pressure additive.
So, for many chemicals already in the market, an additive company would simply be making a procurement decision to source renewable, i.e., bio-derived, feedstocks for the existing reactor if the price was right or the market demanded it. Similarly, most alcohols used to produce zinc dialkyldithiophosphates (ZDDPs) could be obtained from bio sources.
A high specification motor oil could be formulated from bio-derived base fluid, with the carbon content of the dispersant and ZDDP also bio-derived, along with the alkyl chains of a sulfonate or salicylate detergent (derived from LAOs). This would probably leave the antioxidants and corrosion inhibitors as petrochemicals, plus the calcium carbonate, zinc, phosphorus and sulfur components.
Frontrunner
All is not completely positive, however. Brazilian petrochemicals company Braskem, which has been a leader in the conversion of sugar into petrochemicals, has abandoned plans to manufacture bio-polypropylene, leaving no bio-derived propylene on the market. While there are bio-based routes to ethylene, and Braskem does manufacture its Im green polyethylene, the changed economics of petrochemicals due to the shale gas boom means that ethylene will predominantly be a petrochemical for many years.
Picking a winner will depend on companies bringing forward products of consistent and appropriate quality at a competitive price.