It is almost impossible to escape the word sustainability these days, between all the corporate self-congratulating, emerging electric equipment, and hyped hydrogen-powered prototypes.
Less discussed, and less sexy from a marketing standpoint, is what can be done sustainability-wise with the most readily available power source on job sites as of right now: diesel fuel.
Enter "renewable" diesel.
Renewable diesel, as defined by the U.S. Department of Energy (DOE), is a fuel made from fats and oils, such as soybean oil or canola oil, and is processed to be chemically the same as petroleum diesel. It meets the ASTM D975 specification for petroleum in the United States and EN 590 in Europe.
Renewable diesel can be used as a replacement fuel or blended with any amount of petroleum diesel.
It’s important to make the distinction between renewable diesel and biodiesel—they are not the same.
See also: Biodiesel profitability suffering
Renewable diesel, previously known as “green” diesel, is a hydrocarbon produced most often by hydrotreating and other biochemical and thermochemical technologies.
Biodiesel is a mono-alkyl ester produced via transesterification. Biodiesel meets ASTM D6751, a different standard, and is also approved for blending with petroleum diesel.
How is renewable diesel made?
Renewable diesel can be produced by several different technology pathways, according to DOE. Currently, commercial production facilities are using the hydrotreating pathway and fats, oils, and greases are the most common feedstocks. Beyond hydrotreating, there are several technology pathways to produce renewable diesel, including:
- Biological sugar upgrading: This pathway uses a biochemical deconstruction process, similar to that used with cellulosic ethanol with the addition of organisms that convert sugars to hydrocarbons.
- Catalytic conversion of sugars: This pathway involves a series of catalytic reactions to convert a carbohydrate stream into hydrocarbon fuels.
- Gasification: During this process, biomass is thermally converted to syngas and catalytically converted to hydrocarbon fuels.
- Pyrolysis: This pathway involves the chemical decomposition of organic materials at elevated temperatures in the absence of oxygen. The process produces a liquid pyrolysis oil that can be upgraded to hydrocarbon fuels, either in a standalone process or as a feedstock for co-feeding with crude oil into a standard petroleum refinery.
- Hydrothermal processing: This process uses high pressure and moderate temperature to initiate chemical decomposition of biomass or wet waste materials to produce an oil that may be catalytically upgraded to hydrocarbon fuels.
With the chemistry lesson out of the way, the key questions are is it readily available, and does it actually help the environment?
What are the benefits of renewable diesel?
The DOE says renewable diesel offers many benefits, including:
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Engine and infrastructure compatibility: Renewable diesel meets the conventional petroleum ASTM D975 specification allowing it to be used in existing infrastructure and diesel engines.
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Fewer emissions: An NREL study found renewable diesel reduced both carbon dioxide and nitrogen oxide emissions when compared with petroleum diesel. California's Low Carbon Fuel Standard Certified Carbon Intensities shows renewable diesel reduces carbon intensity on average by 65 percent when compared with petroleum diesel.
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More flexibility: Renewable diesel is a replacement for diesel and can be used to fully replace diesel or blended with any amount. Renewable diesel can be made from multiple feedstocks and at plants that also produce sustainable aviation fuel.
The federal government paints a rosy picture of renewable diesel availability, as one would expect.
As of Jan. 1, 2022, the Energy Information Agency (EIA) reported 11 domestic plants in 6 states with capacity of 1.75 billion gallons per year. Domestic production data shows that production has increased, and overall consumption is met with imports from plants operated by a company called Neste in Singapore, the Netherlands, and Finland.
EIA's Today in Energy Brief on renewable diesel suggests that production will increase rapidly in the next few years, with added capacity of 2.4 billion gallons per year currently under construction and an additional 1.8 billion gallons per year of planned capacity. Another EIA Today in Energy Brief projected that renewable diesel supply would surpass biodiesel as early as the end of 2022.
For a start on nongovernmental answers, we turn to the state where environmental trends seem to quickly become laws that influence national policy: California.
Nearly all domestically produced and imported renewable diesel is currently used in California due to economic benefits under the Low Carbon Fuel Standard. That's because in November last year, the state (through the California Air Resources Board, or CARB) mandated amendments to the Off-Road Regulation requiring the use of R99 or R100 renewable diesel in off-road diesel vehicles.
CARB expects the program is to yield more than $5 billion in health benefits from 2024 to 2038.
"CARB renewable diesel requirements for fleets start January 1, 2024," says David Bolderoff, CEM, fleet manager, Los Angeles County Sanitation Districts, and a member of the Under 40 in Construction Equipment Class of 2015.
How heavy equipment uses renewable diesel
Bolderoff started his first pilot program with renewable diesel in September 2018. Today, his entire diesel-powered fleet--including dozers, wheel loaders, material handlers, graders, scrapers, and waste compactors--is running on renewable diesel.
"This has helped us meet our sustainability goals and be carbon negative over the past few years," he says. "No infrastructure upgrades are required; it's truly 'drop-in' fuel."
According to Bolderoff, the fleet has seen a greenhouse gas reduction of 65 to 90 percent, a 33-percent drop on particulate matter, a NOx reduction of 15 to 18 percent, and CO2 reduction of 4 to 9 percent. There is also a possible maintenance benefit. "A 30-percent reduction in particulate matter and soot can potentially increase the service intervals on DPFs from 5,000 to 6,500 hours," he says.
His testing on a dozer equipped for waste handling operated under high engine loads revealed similar numbers, but had a higher reduction (32 percent) in particulate matter. Tests under low engine loads conducted on standby generators resulted in larger PM reductions of 47 to 85 percent.
Bolderoff explains that most OEMs have detailed guidelines for use of biodiesel blends but limited published guidelines for renewable diesel. Renewable diesel meets the same ASTM standards for diesel, he stresses. "It's chemically similar to petroleum diesel, and OEMs cannot void the engine warranty."
Elsewhere, large mining contractor Rio Tinto is working to replace conventional diesel in haul trucks at U.S. mining sites.
The company told the Elko (Nevada) Daily Free Press it successfully completed a renewable diesel trial at its U.S. Borax mine in Boron, California, and is on to a second trial in Utah.
“The renewable diesel trials at our U.S. Borax and Kennecott [Salt Lake City] operations could pave the way for Rio Tinto to be the first mining company in the U.S. to operate a fully renewable fleet,” Simon Richmond, Rio Tinto VP of global procurement, told the paper. “It’s a very exciting step towards reducing the carbon footprint of our U.S. operations.”
Rio Tinto’s first trial was conducted through 2022 in partnership with global renewable international diesel maker Neste and Rolls-Royce. The U.S. Borax mine used Neste MY Renewable Diesel, a hydrotreated vegetable oil made from sustainably sourced renewable raw materials such as used cooking oil and animal fat from food waste. Rio Tinto said the results showed that a truck running on renewable diesel delivered similar performance and reliability as trucks running on conventional diesel.
Based on these results, Rio Tinto says U.S. Borax will continue to work with the Environmental Protection Agency, the State of California, and engine manufacturers with a goal of having a full transition of the heavy machinery fleet onsite to renewable diesel by 2024. This would represent an anticipated carbon dioxide equivalent reduction of up to 45,000 metric tons per year, according to the article.
The second trial, underway at the company's Kennecott Bingham Canyon copper operation in Salt Lake City, involves a collaboration with Cummins on a different equipment category.
Rio Tinto’s global decarbonization objectives include a 50-percent reduction in scope 1 & 2 emissions by 2030, and a commitment to reach net zero by 2050. The company estimates carbon emissions from the use of diesel in its mobile fleet and rail account for 13 percent of its scope 1 & 2 emissions.
Much like the electrical charging infrastructure for EVs and access to hydrogen, the supply of renewable diesel is what potential users question.
Production in the U.S. as of January 2022 was 1.75 billion gallons per year, up from 791 million gallons per year the prior year for a 120 percent increase, but is it enough?
Bolderoff says Neste is the biggest player in the industry, and that they have just increased capacity with expansion of their refinery in Singapore. And he told an audience at Conexpo in March that Phillips66, Global Clean Energy, and Marathon Oil all plan to convert their California petroleum refineries to producing renewable diesel from plant oils and animal fats.
Demand in California is expected to be 6.3 million gallons per day, he says, and "big oil" is backing it with billions of dollars in investments.
But some are skeptical.
“Even with the current supply chain issues involved with petroleum diesel, renewable diesel is not yet a serious consideration here in North Carolina, at least not for Sunrock right now,” says Leigh Dennis, CEM, manager of fleet services, Carolina Sunrock LLC, in Butner, North Carolina.
“Its production requires the incentives, facilities, and supply chain that have yet to present themselves to us in the form of a readily available, plentiful product,” Dennis says. “Although more expensive, its Cetane number is significantly higher, 75 to 85, than other diesel products, which provides much greater combustion efficiency. And its cloud point is so low, it would eliminate any cold weather fuel flow issues around here.” [See the nearby chart comparing diesel, biodiesel, and renewable diesel properties.]
Dennis also wonders if renewable diesel might replace the need for some traditional diesel additives.
“I’d love for us to have access to a blend of petroleum and renewable diesel. It could possibly eliminate the need for Cetane additives and flow improvers,” he says. “Petroleum and biodiesel fuels have issues with water, microbiological organisms, temperature, and storage time/conditions. Additives reduce some negative characteristics but can also create all sorts of other problems.
“There have been efforts to update relevant ASTM/EPA petroleum diesel standards—I think the ASTM minimum cetane number is still at 40, has been for the same number of years, I think, which is far below what most engine manufacturers recommend to ensure basic combustion efficiency and aftertreatment system reliability in modern diesel engines,” Dennis says. “In my experience, diesel suppliers regularly reference that standard, which absolves them from providing anything more than that. And with every new application of engine technology, they have less understanding of how their product is used."
There are also concerns about cost. The Wall Street Journal reports that renewable diesel is expensive to manufacture. A producer of renewable diesel who sold it in California for the same price as regular diesel would have lost an estimated $3.88 a gallon last year if not for government incentives averaging $4.59 a gallon, according to an S&P Global Commodity Insights model.
Fleets not in states that have mandates backed up by tradable credits may find renewable diesel is cost-prohibitive at present.
With mass availability still up in the air, the widespread adoption of renewable diesel is as much as question mark as the future of any of the alternative power sources--for now.
