Compatibility Assessment of Elastomeric Infrastructure Materials with Neat Diesel and a Diesel Blend Containing 20 Percent Fast Pyrolysis Bio-oil

The compatibility of elastomer materials used in fuel storage and dispensing applications was determined for an off-highway diesel fuel and a blend containing 20% bio-oil (Bio20) derived from a fast pyrolysis process. (This fuel blend is not to be confused with B20, which is a blend of diesel fuel with 20% biodiesel.) The elastomer types evaluated in this study included fluorocarbon, fluorosilicone, acrylonitrile rubber (NBR), styrene butadiene rubber (SBR), polyurethane, neoprene, and silicone. All of these elastomer types are used in sealing applications, but some, like the nitrile rubbers are also common hose materials. The elastomer specimens were exposed to the two fuel types for 4 weeks at 60°C. After measuring the wetted volume and hardness, the specimens were dried for 65 hours at 60°C and then remeasured. A solubility analysis was performed to better understand the performance of plastic materials in fuel blends composed of bio-oil and diesel. All of the elastomers exhibited higher solubility (volume swell) with the Bio20 fuel blend consistent with a solubility assessment. However, many of the elastomers (except neoprene, SBR, and silicone) exhibited very little swelling with exposure to the baseline diesel which was not predicted in the solubility study. When dried, those elastomer specimens that swelled when immersed in the test fuel, remained swollen (albeit to a lesser degree) when dried. All of the elastomers showed the highest extent of swelling with Bio20 (even when compared to specimens exposed to ethanol-blended gasoline test fuels). The lone exception was silicone which exhibited lowered volume expansion in diesel and Bio20 than in ethanol-blended gasoline. Even fluorocarbon, which is rated as highly compatible in most fuel types, swelled over 60% when exposed to Bio20. The bio-oil used in this study, like most bio-oils contained appreciable levels of ketones and phenols. The compounds are notorious solvents for many elastomers and likely contributed to the observed volume expansions.