Keep Biodiesel Stable, Flowing & Growing

An overview of antioxidants and cold flow improvers for B100 and blends
By Ron Kotrba | November 02, 2012

For B100 and biodiesel blends, two main fuel additive categories dominate the sector: stabilizers and cold flow improvers. Biodiesel can be produced from many fats, oils and greases, each possessing unique chemical make-ups that affect stability and cold temperature performance differently. Saturated feedstocks like palm oil are more stable but have worse cold flow properties. Conversely, unsaturated feedstocks such as canola oil carry more desirable cold flow properties but will oxidize and go rancid quicker.

Oxidation is a three-step process consisting of initiation, propagation and termination, says Andy Singleton with Eastman Chemical Co., which offers BioExtend 30 (U.S.) and BioExtend 30 HP (EU) stabilizers. BioExtend 30 HP is certified by the biodiesel quality management board AGQM as a “no-harm” additive tested to ensure that chemical and physical properties aren’t affected by the use of oxidation stabilizers in biodiesel; that no inadmissible reciprocal effects occur with other stabilizers used in a B7 blend; and that security datasheets are available for the additive. The “no-harm” list includes 36 positively tested products from 22 manufacturers, including Eastman, Innospec, Infineum, Evonik, Kemin, Albemarle, International Fuel Technology, Lanxess, BASF and more. The U.S. has no such additives oversight, says Gary Pipenger, owner of Amalgamated Inc. He says while U.S. EPA polices chemical ingredients in additives, there’s no regulation on performance. “The biggest thing I’ve wanted for 40 years,” he says, “is some way of holding additive companies accountable for what they’re selling.” Eastman’s BioExtend 30 and 30 HP products both contain a metal chelator that works in the initiation phase to sequester metal ions from residual processing catalyst or adsorbents, and from mild steel or yellow metals in transport or storage vessels. “No antioxidant will stop oxidation,” Singleton says, “but they’re used to inhibit oxidation. The antioxidant we use interrupts the propagation cycle where free radicals that are formed in the initiation cycle react with oxygen and form peroxides. Stable, oxidized products such as aldehydes and alcohols are formed in the termination cycle.”

Time, temperature, moisture, air and contaminants all contribute to accelerated oxidation. A rule of thumb for hot, humid regions like the Gulf Coast is that biodiesel shelf life is six months; in colder, dryer regions, it can be longer. But if you leave biodiesel in a tank, the oxidative stability score will go down. Additives raise the starting value on the oxidation stability test, part of U.S. and European quality specifications (three-hour Rancimat minimum in U.S., six-hour minimum for Europe), and they change the oxidation curve’s slope.

Biodiesel is treated with antioxidant at the plant by the producer, unless perhaps the fuel stays local for immediate use. Treated biodiesel can be retreated after oxidation begins, but if 200 ppm is the recommended treat rate for fresh fuel, adding that same dose to oxidized fuel will not achieve the same results. Some fuels are just unable to meet spec no matter how much additive is used. “I’ve tested samples from waste grease where the original oxidative stability index is less than five minutes,” Singleton says. “So we work with customers and they go back and maybe make process improvements.”

Frank Moran with International Fuel Technology says IFT offers nine different biodiesel stabilizers in its DiesoLIFT BD-series, each with slightly different chemistries depending on feedstock. “We try to customize our formulations to the feedstock,” Moran says. “We send samples so they can test finished product,” but, he notes, some multifeedstock producers switch inputs at the drop of a dime—literally. A 10-cent swing in price, plus availability, is incentive to move from one to another.

Innospec also has a line of antioxidants. “We’ve got a few products in the BioStable line,” says Jim Vrzak, a sales director for Innospec Fuel Specialties. BioStable inhibits peroxide formation, protects against metal-catalyzed oxidation, minimizes effects of gum formation from peroxide decomposition, and defends against acid-induced degradation.

Kemin Industries’ biodiesel stabilizer is BF320. Kevin Custer, business director, says as biodiesel clients switch feedstocks, he encourages them to send samples so Kemin can test and inform the client of the best treat rate. BF320, like Eastman’s BioExtend 30, contains a metal chelator to sequester metals. Custer also says Kemin offers consultation on application equipment, dosage rates, application sites, antioxidant storage and execution of product into biodiesel. Kemin can also design and install application equipment. 

Magellan Midstream Partners LP requires a six-hour Rancimat performance at the point of fuel origin. “To a great extent, this specification is established by our customers who are the companies that own the biodiesel in our storage tanks,” says Bruce Heine with Magellan. “Generally, our customers have asked us to administer a Rancimat specification of six hours from origins. We target a delivery value of five hours, but have the latitude to release product down to three hours. This increased stability provides added protection for the ultimate consumer. This is especially important in markets where biodiesel is stored for extended periods of time.” Magellan approves a handful of stabilizers. “We receive requests for approval of all performance additives from our position holders,” Heine says. “If a customer would like to add a specific additive, we request data that supports the claims from the additive manufacturer. At our option, we may request a sample of the additive be sent to our laboratory in Kansas City for analysis.” Once a biodiesel producer is on Magellan’s approved list, companies that hold positions in its tanks can purchase biodiesel from the plant and the biodiesel can be stored at a Magellan terminal. Samples are taken from all B100 deliveries, and random testing is conducted.

For performance and cost comparisons of four commercial antioxidant additives, the University of Idaho’s Department of Biological and Agricultural Engineering, led by Jon Van Gerpen, department chair, conducted tests and published results in Biodiesel Tech Notes that can be found at

Using the appropriate stabilizer isn’t just about meeting a spec for purposes of selling product though. Today’s modern, high-pressure common rail fuel systems recycle fuel under high pressure and temperature, and an unstable fuel will form deposits that can foul fuel injector inlets and nozzles. Badly degraded fuel can even exhibit cold-flow-like problems. Moran says IFT is working with a bus fleet in Europe that uses B30 and the buses were breaking down due to filter clogging. After experimenting with a blend of its DiesoLIFT10 and antioxidant, the buses’ fuel mileage increased by 7 percent. “More encouragingly, they stopped breaking down in the middle of their route,” Moran says. IFT Global Business Development Manager Axel Farhi says, “What we did was improve the physical stability and oxidation stability of the B30 blend, thus avoiding formation of residues collected in the filters, and thus improving combustion and fuel economy.”

Infineum, a 50/50 joint venture between Shell and ExxonMobil, recently unveiled its R536 filterability additive, says Joanne LaBarge, a global advisor with Infineum USA LP. R536 was developed to improve biodiesel filterability in the three tests used to gauge whether precipitate formation above the cloud point will occur: D6751’s Cold Soak Filtration Test, the Canadian General Standards Board’s Cold Soak Filter Blocking Tendency Test, and Europe’s Cold Soak IP 387 Test. Infineum says R536 also significantly reduces vehicle filter pressure.

Cold Flow Improvers

No. 1 diesel fuel (kerosene) is used in colder region winter diesel fuel blends at various percentages depending on temperature extremities. It works well at driving down cloud and cold filter plugging point (CFPP), but it is costly and reduces fuel mileage due to lower Btu content. Because of its high cut rate, kerosene is not a cold flow improver but rather a winter blend agent to diesel fuel. The right cold flow improver—meaning effective in both performance and price—should reduce costs and improve mileage by reducing the percent of No. 1 needed.

Biodiesel producers generally don’t treat with cold flow improvers unless on rare occasion they need to bump the CFPP down a degree or two in order to meet a purchaser’s spec. There are very few, if any, cold flow improvers on the market that are effective on B100 at a reasonable treat rate. Instead, most biodiesel cold flow additization is performed downstream at the rack when blended, and in some cases only work on the petroleum side of the blend equation.

“There’s no chemistry out there that will materially affect B100,” Pipenger says. “My company (Amalgamated Inc.) and a few others out there can drop the cold flow properties about eight to 10 degrees, but that’s really not that great for a B100 since you’re starting at plus 25 for pour point, 30 for CFPP and 32 for cloud on a soy product. Animal fats and palm are higher than that, so if you drop those eight or 10 degrees, that’s not that big a deal. No one has anything that is going to materially affect the B100.” Amalgamated Inc.’s wax dispersing additives (trademarked WDA) work like other cold flow improvers, by changing the size and shape of the diesel paraffin wax crystals, allowing them to flow through fuel filters. While this concept works on diesel and some biodiesel blend concentrations, for B100, even modest dips in CFPP temperatures might be an “embellishment,” Vrzak says. “It’s very minimal at best.” The difficulty is so great that some who have tried quickly gave up.

Farhi tells Biodiesel Magazine that IFT began looking at B100 cold flow technologies on the market and “was not particularly impressed with their performance,” he says. “All were working better on the more unsaturated feedstocks, but the more saturated feedstocks could not be significantly improved. A major problem we found in unsaturated feedstocks was the poor repeatability. The other critical aspect was the very high dosages necessary, up to 3,000 ppm or more, to obtain significant cold flow improvement in B100. We were extremely concerned by these high dosages, the impact on the biodiesel price, and certain reluctance from fuel distributors and OEMs to accept such high additive levels due to the risks of potential instability and compatibility issues.” He says IFT concluded that these problems were related to the type of polymer chemistries used in these materials, which are very similar to the CFPP additive technology used in diesel. “We assumed that was the reason it wasn’t performing particularly well in biodiesel, as wax crystallization processes differ in diesel and biodiesel (paraffin vs. fatty acid) and would therefore require different types of polymer chemistries,” he says. “We finally decided to drop this biodiesel cold flow improver project.” He also adds that current standard methods—CFPP, pour point, LTFT, etc.—might not apply to biodiesel feedstocks. “Last winter was particularly harsh in Europe,” Farhi says. “Problems were observed even with B7 blends meeting the latest EN590 low-temp specs, and made from biodiesel meeting the latest EN14214 low-temp specs.” 

Instead of treating the biodiesel portion of the blend, some say what many blenders selling fuel in cold climates do is a little rough math by considering the blend ratio, the bio and diesel cloud points or operational parameters like CFPP or pour point, and drive the diesel portion well below the desired target and then add bio, which raises the final blend to the desired point. Vrzak says petroleum cold flow improvers can be effective in biodiesel blends up to B20 by either increasing the treat rate or adding in more and greater dispersant-type technology.

Most biodiesel is consumed in low-level blends. “If you are using a blend up to B7, chances are the [diesel] additive you were using before would work,” says LaBarge with Infineum, “but it’s a question of, is it optimized? Can someone say you can use the same system for biodiesel blends? Yes, but it definitely wouldn’t be an optimized solution, which means the fuel source and the biodiesel you’re using, unless you go through the full testing and really pick the right additive for it, you may meet spec, but not necessarily in the most cost-optimized fashion.” Vrzak says Innospec has cold flow additives that suppress CFPP tailored for B10 and B20, primarily, but he, like most additive suppliers, says the only way to optimize cold flow performance is to send samples of the diesel, biodiesel and the intended blend ratio to your current or prospective supplier so the best-performing, most cost-effective solution can be sought.

“If you are trying to effectively treat a biodiesel blend, then obviously you want to treat both phases and you need two different ingredients,” says Erik Bjornstad, technical director with Bell Performance. “The chemistry we use in our cold flow formulations, specifically with respect to the ingredient that actually targets the esters, is more of a viscosity modifier for those esters—they don’t flow the same way diesel does.” Bell Performance offers Bio Dee-Zol, an antioxidant and water eliminator, and Bio Dee-Zol Plus, a cold flow improver, primarily to downstream markets.

Vrzak says while the refining industry business is huge for additive suppliers, the end-user market, especially with EPA-required ultra-low sulfur fuel and low-level biodiesel blends incentivized or mandated in various states, is growing as refiners and obligated parties take economic advantage of blending B5. “The downstream opportunity for additization has definitely increased,” Vrzak says. Bjornstad says as low-level biodiesel blends become more widely implemented by fuel distributors and jobbers, it’s “a bit of a game changer,” mainly because biodiesel displaces the need for Bell Performance’s lubricity additives. Conversely, it opens new additive opportunities.

Heine says Magellan’s stance is that cold flow properties of the finished fuel should be determined by the blender. “The blender can select an array of cold flow improvers available at our terminals, and adjust treat rates based on anticipated climatic conditions with consideration of the level of biodiesel that will be in the finished fuel.” 

What’s Next?

Vrzak says cold flow improver work is always high on the list of Innospec’s R&D program, including biodiesel CFPP additives. “And we continue to keep in queue a cloud point depressant for B100,” he says. “We always have ongoing work related to that. We’re always hopeful to find that B100 silver bullet additive.” Jeff Thompson, a North American fuels group manager with Infineum, says Infineum will continue improving its cold flow additives “to treat traditional FAME better than we do today.”

LaBarge adds that Infineum is developing additives for renewable, hydrogenated diesels made from nonfood sources, citing Europe’s recent biofuel policy alterations to limit traditional oilseed biodiesel. Bjornstad says he doesn’t foresee any new problems with biodiesel that people aren’t aware of today, so Bell Performance’s focus is trying to combine most effective treatment for those major problems and create the best value for end-users and bulk purchasers. Moran of IFT says, like what it did with those buses, “there is technology out there that we’re trying to create or shape to adapt to new [biodiesel] requirements and regulations.” Eastman says it’s not ready to share ongoing developmental work. And Pipenger … well, he says trust no additive company’s claims, not even his own. Send samples to independent labs and verify their, and his, assertions.

Biodiesel producers should also test stabilizers themselves in their labs. And for blenders or end-users who want to test their cold flow improvers, do a simple, free test by placing an additized sample in the freezer for a day. If particles develop, make a new sample with more additive and repeat. If more than 1 ounce of additive per 3 gallons of fuel is required to stop particle formation, then maybe it’s time to shop around. 

Author: Ron Kotrba
Editor, Biodiesel Magazine
[email protected]

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