Our focus will be on properties relevant to the refining, blending, and engine performance areas; thus, our data, models, and software tools will be useful to a broad range of scientists and engineers. Many of these properties will also be important for flow metering (i.e., legal metrology). Our work will be enabling. It will establish a thermodynamic foundation for the biofuels, and will thus impact the billions of dollars the U.S. spends each year on transportation fuels. More significantly, the widespread adoption of biofuels would reduce the emissions of global warming gases. Policy and economic decisions require accurate and consensus thermophysical property data.
Objective and Goals
Transportation fuels will undergo major changes in the coming years, and liquid fuels derived from biological materials have very bright prospects. The thermophysical properties of biofuels are required for the efficient design of every step in their production, distribution, and utilization. These properties include the thermodynamic properties (density, heat capacity, enthalpy, etc.) and the transport properties (viscosity, thermal conductivity, etc.). There is presently no comprehensive, consensus source of reliable property data for use by industry, and that is the void we propose to fill.
Research Activities and Technical Approach
The technical plan is based on three areas of activity, proceeding in parallel. The end products will be disseminated as SRD databases, including the collection and evaluation of existing literature data. Feeding into the databases will be the modeling of biofuel blends and their constituent pure components. An experimental effort will provide data needed to develop and refine the models.
The modeling will be based on the concept of a "surrogate blend," i.e., a blend of 10 to 20 components that captures the essential characteristics of a complex fuel. Surrogate blends will be formulated from a "suite" of well-characterized pure compounds, including alcohols and esters from biological sources as well as hydrocarbons representative of petroleum or synfuels. To define a suitable surrogate, a fuel must be characterized in terms of its distillation curve, combustion characteristics, and other behaviors. The simple distillation curve measurement has been extended recently at NIST to include much more quantitative information.
Models are based on experimental data. Extensive measurements on reference systems will provide the high-quality data needed for model development. Rapid measurements will characterize the many types of mixture interactions present in the fluid suite.
We have begun work in all three areas. In the "Data" area we have collected the literature data for the five most important fatty acid methyl esters (FAMEs) that comprise biodiesel derived from vegetable oils. These data have been incorporated into Thermo Data Engine (TDE-SRD 103), and are part of the TDE evaluations..
In the "Measurements" and "Modeling" areas we made initial measurements for the five fatty acid methyl esters (FAMEs) that are the primary constituents of soy-based biodiesel fuel, namely, methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, and methyl linolenate. The measurements of density, speed of sound and boiling point were combined with literature data to develop an equation-of-state approach to modeling the thermodynamic properties of a soy-derived biodiesel. Preliminary experimental measurements of two actual biodiesel fuel samples were compared with the results of the model.
To help prioritize our efforts, the Division organized and hosted a workshop July 10–11, 2008 in Boulder entitled "Properties Needs for Biofuels and Blends: Production, Distribution, and End Use." The 44 attendees included representatives from industry, academia, professional groups, and other federal labs. The workshop focused on what property data were needed to assist industry in deploying biofuels across the economy. A wide range of needs were identified, reflecting the broad diversity of the attendees. The fluids of interest ranged from the current ethanol and biodiesel products, to other alcohols, to synthetic gasoline and diesel, and to fuels derived from algae. Blends were very important, since ethanol and biodiesel are almost always mixed with petroleum fuels for retail sale. The most wide-ranging and demanding needs were for properties needed in chemical process design. A consistent theme was that better knowledge of fuel properties would lead to better designs and shorter development times of everything from production facilities to emissions control systems.