A Full-Service Package

Fuel storage practices are critical to ensuring a quality supply, and because biodiesel can degrade rapidly through oxidation, the shelf life of the fuel is viewed as a weakness. However, a new product from Eastman Chemical Company is now available that may be the most developed additive technology to date for increasing oxidative stability.
By Nicholas Zeman | April 06, 2007
Eastman Chemical Company has been making food-grade antioxidants for various consumer markets for many years. The company recently adapted this experience to develop BioExtend 30, a new oxidative stability system for biodiesel fuel. The new product was unveiled in February at this year's National Biodiesel Conference & Expo in San Antonio.

Founded in 1920, the Kingsport, Tenn.-based Eastman employs nearly 11,000 people worldwide and had a 2006 sales mark near $7.5 billion. The chemical conglomerate's leaders on this fuel-stability project were Bill Sade business development manager, and Sharon Cline, technical associate. Both work for the company's performance chemicals and intermediates business organization. They talked with Biodiesel Magazine in February, about their innovative work to improve the quality of biodiesel fuel. Both career chemists, Sade and Cline relied on their backgrounds for the development of BioExtend. They were also backed by Eastman's more than 50 years of antioxidant expertise. "We have been able to leverage our long history of supplying innovative antioxidants across an extensive range of markets-from cosmetics and personal care to food, oils and fats," Sade says

The processes responsible for oil and butter rancidity also occur with biodiesel. In other words, the fuel can spoil. Ultimately, fuel degradation and polymer formation can clog fuel filters, and create damaging engine deposits and residues. Therefore, oxidative stability is ultimately a fuel-quality issue, and specs are in place, which assure that biodiesel plants produce fuel with a reliable shelf life.

The BioExtend 30 platform is a full-service antioxidant solution in which each fuel sample is evaluated individually along with the logistical demands of each biodiesel producer. Eastman's laboratories are well-equipped with Oil Stability Index (OSI) testing equipment, which can be used to analyze fuel and determine exactly what dosage will be required by a particular fuel sample to maintain stability. The OSI test is commonly used by the biodiesel industry to measure the susceptibility of a particular fuel sample to oxidation. "Every case is different," Cline says. "We can select the stability [that] different producers require."

Figure 1

As BQ-9000 certification becomes increasingly necessary for existing or would-be producers to assure a trusted and respected place in the market, most biodiesel producers will need antioxidant solutions. "As BQ-9000 certification becomes expected, most producers will recognize the need for antioxidants to meet the fuel stability requirements," Cline says.

Dual Functionality
BioExtend is a combination of 30 percent mono-tert-butylhydroquinone (MTBHQ), a powerful antioxidant with an effective chelating agent. The synergistic effect achieved in the inhibition of oxidation is greater than the sum of the two effects alone, Eastman says. "This is the first antioxidant system with dual functionality, meaning that it attacks both the primary and secondary phases of degradation," Cline says. The metal chelator in the Eastman system hinders not only the propagation, but also the initiation phase of degradation.

The oxidation process consists of three phases: an initiation phase, in which the free radicals are formed; a propagation phase, where the free radicals react with oxygen to produce peroxides that attack other fat molecules; and a termination phase, in which stable decomposition products are formed.

A free radical is an atom or group of atoms with at least one unpaired electron. The process of oxidation occurs when an oxygen molecule loses an electron and stabilizes itself by stealing an electron from a nearby molecule. Antioxidants interrupt oxidative decomposition by reacting with fat radicals to form a stable molecular group, which is less susceptible to oxygen.

Biodiesel contains molecules that can easily lose an electron. The process of oxidation occurs when a hydrogen atom is lost to form a free radical. Because of their unique structure, antioxidants further stabilize the free radical and are less prone to react with oxygen to form a perioxiradical. This is all a part of the cycle. The perioxiradical then attacks another fat molecule, and the cycle continues. Oxidation, however, can't be prevented-only slowed-and no antioxidant treatment can "fix" fuel that has already decomposed.

Even with Eastman's past experience, there were some challenges involved in adapting its antioxidant platform for the biodiesel market. "Since some of the food-grade products weren't soluble in diesel fuel, some modifications were required," Cline says. But their efforts were successful, and the resulting product is different than other antioxidant treatment systems.

Most antioxidant solutions use biodiesel as a solvent, which means that the additive is dissolved in the fuel. However, Eastman designed a unique solvent matrix that brings the two active ingredients-the antioxidant and metal chelator-into solution. "Chelating agents bind metal ions, making them unavailable for catalyzing the initiation phase, thus slowing the oxidization process," according to Eastman.

BioExtend's solvent system is designed for use in extremely cold temperatures. It prevents separation from the antioxidant and remains liquid at temperatures below minus 25 degrees Fahrenheit. When asked what solvent was employed in the BioExtend system, Sade says that he wasn't at liberty to discuss the chemical specifics of the product because the material is proprietary. "We have a patent pending, and we need to have some intellectual property protection in place before we can talk about that," he says.

Biodiesel producers don't need any special equipment or capabilities on-site to introduce BioExtend into their fuel. "It comes [to the producer] readily miscible and mixable, so there is no need to dissolve it," Cline says, adding that all of the attributes that make the additive easy to use were considered in the research and development stages of commercialization. "We have delivered a solvent matrix with a low viscosity that facilitates ease in mixing," Sade says.

Figure 2

Every Case Is Different
The idiosyncrasies inherent in the multitudinous biodiesel-refining processes affect the level of BioExtend that the fuel would need to guarantee oxidative stability. Specifically, distillation, which is often used to "finish" the fuel in the refining process as well as recover glycerin, strips vegetable oil of many of its natural antioxidants. In that case, producers might need additional levels of BioExtend. "Those distilled products are, however, very amenable to BioExtend," Cline says. "Even all soy biodiesel is not the same. Soybeans grown in different parts of the country have different levels of trace metals contained in them that ultimately affect oxidative stability." Each case must be evaluated individually, Cline says. "We can't provide the same amount of product to every soy producer just because it's soy," she says, adding that BioExtend has been tested in a variety of samples made from different feedstocks including soybean, rapeseed, palm, cottonseed and sunflowers, which have all "yielded excellent stability results."

In Europe, biodiesel is required to have an OSI of at least six hours by the time it reaches consumers. That said, it is also important to mention that the OSI can change over the course of the fuel's lifecycle, which involves the travel time between the plant and the pump. So, an OSI of nine or higher might be needed by the biodiesel producer to ensure that the consumer-required six-hour standard is met. In January, the United States implemented an OSI standard of three hours. The ASTM standard for biodiesel was also updated and published in January.

A variety of factors can affect the dosage level of BioExtend in refined biodiesel shipments. "First of all, it could be related to use," Sade says. Whether the product is sold into transportation, marine or heating oil markets are variables that need to be kept in mind when calculating stability requirements. Distance also must be considered, he says. "For example, if North American companies plan on exporting biodiesel to European markets, those producers are going to need more transit time," Sade says. "That is one of the benefits of BioExtend."

Nicholas Zeman is a Biodiesel Magazine staff writer. Reach him at [email protected] or (701) 746-8385.
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