The compatibility of seventeen elastomer materials with two heavy biofuels (fast pyrolysis bio-oil and hydrothermal liquefaction (HTL) bio-crude) and diesel was assessed through volume change measurements. The elastomers included two fluorocarbons, six acrylonitrile rubbers (NBRs), and one each of fluorosilicone, neoprene, polyurethane, silicone, epichlorohydrin rubber (ECO), a blend of polyvinyl chloride and NBR (OZO), styrene butadiene rubber (SBR), hydrogenated NBR (HNBR) and ethylene propylene diene monomer (EPDM). The specimens were immersed in each test fuel for four weeks at 50°C and then measured for volume change. Afterwards, the specimens were dried, and the volume was remeasured. Ingeneral, the bio-oil produced unacceptable swelling in the fluoroelastomers, ECO, OZO, neoprene, polyurethane, SBR, HNBR, EPDM, silicone and five of the NBRs. In most cases, the HTL bio-crude produced lower (though still unacceptable) swelling than the bio-oil. Materials that showed good compatibility with the HTL biocrude were the fluoroelastomers, OZO, and silicone.
Fast pyrolysis-derived bio-oils and hydrothermal liquefaction bio-crudes are being explored as renewable fuels for use in home heating, transportation (especially as marine fuels) and electrical power generation.1-3 These fuels are attractive in that the processes used to develop these fuels can utilize a wide range of feedstocks. The fast pyrolysis process is defined by rapidly heating (around 1000°C/sec) of biomass feedstock in the absence of oxygen. Liquid yields may reach 75% depending on feedstock type, reactor design and other processing variables.4-9 The resulting oils have high viscosity and water content relative to petroleum distillates and are considered corrosive. The bio-oil derived from fast-pyrolysis contains high levels of water, acids, ketones and other oxygenates.
Hydrothermal liquefaction (HTL) uses a combination of high pressures and high temperatures to break apart (depolymerize) long chains of feedstock molecules to form a crude-like oil. Oxygen is removed through dehydration (of water) and by forming CO2. In contrast to pyrolysis oils, the feedstock does not need to be dried beforehand to remove moisture to improve process efficiency. The resulting bio-crude contains much lower quantities of acid or water content. Because of this feature and the reduced oxygen content, the energy density of HTL bio-crudes is generally higher than bio-oils. Like pyrolysis oils, bio-crudes may contain appreciable levels of ketones, which may impact polymer compatibility. Bio-crudes also typically contain high concentrations of phenolics and alkanes.2