Hart discusses biofuel hoses

Feb. 1, 2007
WHILE ENVIRONMENTALISTS may be on the band wagon for alternative fuels, such as biodiesel and ethanol, participants in the tank truck industry are singing

WHILE ENVIRONMENTALISTS may be on the band wagon for alternative fuels, such as biodiesel and ethanol, participants in the tank truck industry are singing a different tune, particularly where hoses are concerned.

“There's a host of new fuels on the market,” said Kip Hart of Hart Industries Inc. “There's one family of the ethanol blends, which are in two parts, gasoline with ethanol as an additive and ethanol with gasoline as an additive. They're not hard to handle in transfer applications, but they do affect nitrile rubbers, which most of the petroleum transfer hoses are made from.”

Ethanol 85 (E85) is a blend of 85% ethanol with 15% gasoline. It is expected that this blend will be a fast growing alternative to standard gasoline grades as more flexible fuel cars hit the road and the delivery infrastructure is developed.

“Fortunately, E85 is not an aggressive fuel to rubber compounds,” Hart said. “Most grades of nitrile rubber hose are designed to handle gasoline and should handle E85.”

That's not the case, however, for the blend of 15% ethanol/85% gasoline. “At the 15% ethanol level, this blend is relatively aggressive towards rubber compounds,” Hart said. “However, those blends are not expected to catch on commercially. High ACN (acrylonitrile) or ECO (epichlorohydrin) compounds, along with FKM (fluoroelastomer) compounds, have been recommended for fuel line applications. “For transfer hose applications, a good medium-high ACN compound should be acceptable.”

Hoses exposed to ethanol-blended fuels can cause plasticizers or processing oils to leach out of the elastomers, causing a drying effect, which can lead to a cracking of the hoses inner lining and outer cover. “You're really going to have to educate your employees in what to look for when examining a hose,” Hart said.

The pure grade of ethanol is not expected to be used as a fuel due to its tendency to absorb moisture. But, it is expected to play a big role in fuel blending with the E85 and E10 (10% ethanol and 90% gasoline) grades that are gaining popularity. Ethanol can be safely transferred through most chemical hoses or nitrile hoses, Hart said.

He pointed out that Underwriters Laboratories Inc has suspended authorization to use UL markings on components for fuel dispensing devices that specifically reference compatibility with alcohol blended fuels of greater than 15% alcohol (such as ethanol, methanol, or other alcohols).

Turning to biodiesel, he said B100 permeates quickly through standard grade fuel hoses built with low-medium ACN polymers. “Biodiesel fluid (B100) is much less fugitive than other fuels,” Hart said. “It tends to remain on the outside surface of the hose rather than evaporate, allowing biodiesel fluid to attack reinforcement layers, as well as cover stocks that may have limited resistance to B100.”

Under the influence of temperature, air, and water, biodiesel fuels can decompose into various by-products, including organic acids, free radicals, and alcohols. Standard rubber test methods, such as room temperature immersions tests, do not show the effect of decomposition by-products or permeation. “This can lead to a false assumption that standard nitrile hoses are acceptable for biodiesel use,” he said.

Biodiesel is usually blended with standard petroleum diesel in a 20% blend. A permeation rate of B20 is expected to be much less than B100. However, it is unknown if there will be separation issues that could cause B20 blends to behave similarly to B100.

Another new fuel on the market, ultra low sulfur diesel (ULSD), has very little sulfur content, which results in a significant reduction of the fuel's lubricity. At some stage of distribution, additives may be blended to keep the fuel flowing smoothly. “It is not always known if and when these additives have been added, so be cautious,” Hart advised. “Close visual inspections and periodic conductivity tests should be routine. Nitrile hoses for ULSD at ambient temperatures in intermittent loading/unloading applications should be fine. FKM (fluoroelastomer compounds) such as Viton or Florel are the recommended seal applications for hauling ULSD in continious service.”

Hart said that more information will be coming in the next year or so from the manufacturers of rubber products and the products' reaction to the new fuels entering the market.