|
Physical and Chemical Properties Fundamental Properties of Trace Components of Fuel Gas Fundamental and Applied Properties of Adsorbents Thermophysical Properties of Supercritical Fluids and Alternative Solvents Thermophysical Properties of Lubricants for Alternative Refrigerants Properties and Metrology for Membrane Separations Pressure-Dependent Chemical Reactions Information For Modern Chemists NIST/EPA/NIH Mass Spectral Database Deconvolution of Complex Gas Chromatographic Data Properties of Alternative Refrigerants Thermophysical Properties of Natural Gas Systems Properties of Fluids and Fluid Mixtures Properties of Gels, Micelles, and Clays Dilute-Solution Thermodynamics |
Physical and Chemical Properties Division Contact: Gregory Rosasco Fundamental Properties of Trace Components of Fuel Gas Natural gas and liquefied petroleum gas are complex mixtures that can consist of between 300 and 400 organic and inorganic components, many of which are present at relatively low or trace concentrations. Most of these materials are naturally occurring, while some are intentionally added during processing, such as odorants and anti-corrosives. The properties of many of these trace constituents are important since they can strongly affect the overall behavior of the natural gas. We have developed several interactive databases that facilitate identification of fuel gas components by gas chromatography, using the highly accurate concept of the retention index. We have constructed dedicated chromatographic instrumentation specifically to provide the accuracy required for these measurements, which are needed for custody transfer, quality assurance, and calorific value calculations. Physical property measurements are also an important part of our work to support the fuel gas industry. We have measured the vapor pressures of chlorinated contaminants with the gas saturation method. These measurements are critical to the prediction of contaminant transport in pipelines. We recently have completed measurements of the diffusion of odorants in natural gas. We perform these measurements on a Taylor-Aris apparatus that was constructed for high-pressure fluids. This work will provide a fundamental understanding of odorant fading, a problem that often plagues fuel gas distribution companies. Currently, we are measuring the kinetics and chemical equilibrium of the hydrolysis chemistry of carbonyl sulfide in liquefied petroleum gas. Contact: Thomas J. Bruno Fundamental and Applied Properties of Adsorbents The industrial consumption of adsorbents for separation processes is in the range of a megaton per year. These adsorbents include silicas, aluminas, carbons, and zeolites, and their uses range from commodity chemical separations to small-scale environmental applications. An understanding of the properties of these materials is vital to efficient separation process design and operation. We are focusing on the measurement and modeling of the fundamental parameter: the enthalpy of adsorption. We have designed and constructed a new concept in measurement apparatus for these measurements and have applied it to clay and carbon adsorbents. The techniques we
have developed also allow the study of the effects of surface modifications
of adsorbents that are produced by compounds such as surfactants. These
measurements are especially applicable to nanostructured organo-clay adsorbents
and controlled fillers for polymers. These measurements are combined with
surface observations obtained from neutron scattering and dynamic light
scattering to elucidate the surface structure. This microscale understanding
will permit design of novel special-purpose adsorbents and nanostructured
solids, since the researchers will have a clear idea of what components
or areas of an adsorbent structure are important for a given process.
Contact: Thomas J. Bruno Thermophysical Properties of Supercritical Fluids and Alternative Solvents All facets of chemical process technology require an accurate knowledge, or reliable predictive capability, of various thermophysical and chemical properties of pure chemicals and their mixtures. This is especially true of separations because of the great diversity of chemicals involved, with widely varying molecular sizes, shapes, and polarity. In addition to this inherent complexity, industry now is exploring the application of alternative solvents for separation processes because many traditional solvents have environmental and health risks associated with their use. We are exploring the modeling of processes using alternative solvents through multivariate statistical analysis incorporating a number of empirical and semi-empirical chemical and thermophysical variables as input. We are working to
extend the Kamlet-Taft solvatochromic chemical parameters to the alternative
solvents in the subcritical and supercritical phases. Both chemical and
thermophysical variables are incorporated into a multivariate statistical
model to better predict solution processes of industrially relevant compounds
in the alternative solvents. This requires the experimental determination
of acidity, basicity, polarity, polarizability, and density of potential
solvents. These measurements are performed spectroscopically. In addition
to providing a predictive approach to solvent behavior, this work provides
insight into understanding the solution process itself. In addition to
spectroscopic techniques, we have developed a magnetic levitation solubility
instrument to measure phase equilibria of mixtures not amenable to spectroscopic
measurement. Currently, we are developing an apparatus to measure phase
equilibria non-invasively, with spectroscopic probes used for quantitation. Contact: Thomas J. Bruno Thermophysical Properties of Lubricants for Alternative Refrigerants Because of differences in chemical properties, lubricants previously used with Freon refrigerants are not compatible with the new alternative refrigerants. We are very active in providing industry with the properties needed to design and operate new lubrication systems. For a selected class of polyolester lubricant fluids, we have measured the fluid vapor pressures with the gas saturation method. These data are needed for modeling and for solubility parameter determinations. As part of this effort, we also measure the normal boiling temperature of the fluids and their chemical compositions. In order to quantify the interaction of refrigerant fluids with the lubricants, we measure the enthalpy of mixing using physicochemical gas chromatography, solvatochromic parameters (using spectroscopy), and the dipole moments. This has led to a correlation of refrigerant fluid miscibility with polarity. We have performed tribologic measurements on the lubricants, in the elastohydrodynamic and transition regimes. After each tribologic measurement, we analyze the lubricant for chemical decomposition and measure wear tracks on the tribometer with atomic force microscopy. This allows for correlation of chemical effects and lubricant performance in real-world situations. Contact: Thomas
J. Bruno
Properties and Metrology for Membrane Separations Membranes are used
increasingly in conventional and novel separation and synthesis processes;
as components of process sensors and microscale devices; and to ensure
high-quality water supplies for industry and the general populace. To
add to the science and engineering base of membrane technology, we are
working on improved methods of measuring and correlating membrane chemical
and structural properties with transport-properties for a variety of applications.
We are developing and refining methods for measuring surface energy and
pore size of membrane materials and the transport of simple and complex
mixtures of gases, vapors, and liquids through membranes and model films.
These data and methods will increase our ability to predict both micro-
and macroscopic performance and, therefore, increase the economic return
from this technology. Contact: Chris D. Muzny We use precision
oxygen-bomb calorimeters to determine data on enthalpies of combustion,
from which enthalpies of formation can be derived. The addition of a new
low-temperature heat capacity calorimetry facility now gives us the capacity
to carry out the full range of measurements necessary to determine chemical
equilibrium constants for systems of interest. Our focus is on the determination
of thermodynamic properties of materials important to modern technologies,
such as chemical process modeling and simulation, as well as on the certification
of calorimetric Standard Reference Materials®. Contact: Robert Huie Our chemical kinetics program provides reliable measurement methods, chemical kinetics data, and theoretical models. Applications of this research include combustion, new chemical and energy-related technologies, environmental chemistry, effects of ionizing radiation on materials, and pulse radiolysis of aqueous solutions. We are studying free-radical kinetics using heated single-pulse shock tubes and flash-photolysis kinetic-absorption and resonance-fluorescence techniques. Currently, our emphasis
is on developing and using cavity-ring-down laser absorption spectroscopy
to study chemical kinetics in the gas phase and at surfaces. We focus
on producing databases of evaluated chemical data, including kinetic data
and spectral data for analytical chemistry, as well as designing databases
and relevant software. Contact: Robert Huie Pressure-Dependent Chemical Reactions While many chemical reactions proceed at rates that are independent of pressure, there is a group of important reactions that have pressure-dependent rate constants. A number of theories have been used to explain and predict the rates of these reactions, but none has been successful for some of the most complex reactions. It is often these very complex reactions, with multiple pathways, that are important in understanding how complex mixtures such as gasoline react at high temperatures. Our work has provided a new way to calculate these rate constants so that the many pathways that are observed in these reactions can be predicted. This work is important in the analysis of the experimental data from these complex reactions as well as in providing the fundamental understanding of how to use modern quantum mechanical calculations to predict the pressure dependence of these reactions. These calculations have been used to reinterpret older experimental data to derive fundamental thermochemical information. More importantly, the work has led to a better understanding of the role of highly energetic species formed in recombinations. The theoretical results
are being applied in a number of practical reacting systems. We have studied
the destruction of chemical weapons, the decomposition of hydrocarbons
in complex mixtures, and the reactions involved in chemical vapor deposition
using these new techniques. In each case, better and more consistent models
have been created using these new tools. Contact: Wing Tsang The quality and efficiency of chemical product development and chemical process optimization can be greatly enhanced through computer simulation. However, reliable simulation of chemical processes often is inhibited by the lack of accurate chemical and physical property data for individual molecular species, mixtures, and reactions. This situation is exacerbated by the recent development of combinatorial approaches to R&D that generate massive chemical data requirements for chemical compounds and mixtures that have never been synthesized before. Industrial scientists and engineers are beginning to look to computational chemistry as a source of timely and cost-effective estimates of needed property data. This has generated a need for systematic testing, evaluation, and benchmarking of computational chemistry methods in order to establish the accuracy, reliability, applicability, and relative merits of different computational tools or approaches for different problems. We are developing databases and computational archives that will function as a resource for scientists and engineers who want to compare the economics and accuracy of various computational methods for estimating properties. Currently, we are focusing on thermochemical and kinetic properties. We develop, test, and evaluate computational algorithms. We make benchmark comparisons against accurate experimental data for classes of chemical compounds and reactions. We also develop databases of computational and experimental comparisons to provide reliable estimates of the accuracy and precision of well-defined computational methods. Then we apply advanced computational chemistry methods to prototypical problems in emerging areas such as nanotechnology and molecular electronics to anticipate infrastructural needs for future chemical industry research. Our long-range interests
include the development of computational methods for predicting reaction
mechanisms and reaction rates in solution; the development of more accurate
methods for determining the structures and thermodynamic properties of
large molecules; the development of new hybrid quantum chemistry methods
with empirical corrections for predicting thermochemical properties; the
development of robust density functional methods that are applicable to
transition states; and the development and testing of quantum chemistry
methods for molecules containing heavy atoms. Contact: Carlos Gonzalez Information For Modern Chemists The amount of chemical information and data is always growing, but the tools needed to access this information have not evolved as rapidly. We have developed a tool to provide access to chemical data over the Internet. Using the conventions of the World Wide Web, the NIST Chemistry WebBook is providing a growing audience with thermochemical, thermophysical, and spectral data for a large set of substances. The goal of the WebBook
is to provide a single point of access to all NIST chemical data. The
current edition contains data for more than 36,000 molecules. We provide
data from NIST archival collections used in developing evaluated data,
NIST evaluated data, archival data from non-NIST sources, and evaluated
data from non-NIST sources. Every data item is individually referenced,
and cross-references by author, research paper, and other molecules are
provided. The WebBook is designed to be easy to use, even for novices.
For example, users can search for molecules by name, molecular formula,
and partial molecular formula, as well as by property values. Data can
be graphed and the resulting graphs expanded for more detail. This is
especially useful for complex spectral data such as infrared spectra. Contact: Peter Linstrom or Gary Mallard NIST/EPA/NIH Mass Spectral Database One of the most widely used techniques for identifying organic compounds is gas chromatography/mass spectrometry. In this technique, complex mixtures of chemicals are separated using gas chromatography, and then each compound is "fingerprinted" using the mass spectrometer. The resulting spectra are analyzed and compared to a library of known spectra. To be successful, the library of known spectra must have only high-quality, complete spectra, and the algorithms used to compare the library and unknown spectra must be robust and well tested. We develop and test
algorithms for matching and predicting, evaluate spectra from other contributors,
and fill in missing data with an ongoing experimental effort. Our goal
is to develop a mass spectral database containing every compound in commerce.
The result of these efforts is an increasing acceptance of the NIST database
and algorithms as the standard. In addition to experiments, evaluation,
and algorithm development, we promote the use of high-quality tools within
the mass spectrometry instrument community. Contact: Stephen E. Stein or Gary Mallard Deconvolution of Complex Gas Chromatographic Data Difficulty in extracting pure mass spectra from complex chromatograms limits the use of gas chromatographic/mass spectrometric techniques. While there has been a great deal of work in the past to improve this, there has never been a robust set of algorithms for extracting the pure component spectra. We have developed an automatic mass spectral deconvolution and identification system (AMDIS) that is being provided to the analytical community. The underlying algorithms have been extensively tested and shown to provide a level of analysis equal and in some cases superior to the best possible analysis by an expert. The goal of AMDIS
is to provide all of the information available in a chromatographic data
file in a transparent manner. The tools are being provided in a number
of modes, and we are working to improve the utility of these tools to
improve the productivity of analytical chemists. Contact: Stephen E. Stein or Gary Mallard Properties of Alternative Refrigerants Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been used widely for the past 50 years as refrigerants, as foam-blowing agents, and in many other applications. Recent evidence has shown, however, that CFCs and, to a lesser extent, HCFCs, are breaking down the stratospheric ozone layer that protects the Earth from harmful levels of ultraviolet radiation. These fluids also contribute to greenhouse warming. Alternative chemicals must be found to replace the existing fluids as quickly as possible. To replace the CFCs and HCFCs, accurate knowledge of the thermophysical properties of the substitutes is required. We provide these
data to industry. Our research includes extensive experimental measurements
on pure fluids and mixtures, including saturation and single-phase densities,
vapor pressure, heat capacity, thermal conductivity, viscosity, sound
speed, and surface tension. The program includes a substantial effort
in modeling fluid properties and in developing equations of state. We
also lead efforts to arrive at international standards for refrigerant
properties. Contact: Mark O. McLinden Thermophysical Properties of Natural Gas Systems Our comprehensive experimental and modeling research program is focused on the thermophysical properties of natural gas systems needed by the gas industry for custody-transfer operations, for energy optimization in gas industry operations, and for the design and control of gas processes. Our goals are to develop the means to accurately model and predict the thermodynamic, phase equilibrium, and transport properties of complex hydrocarbon fluid mixtures; other constituents such as carbon dioxide, nitrogen, and hydrogen sulfide; and trace constituents such as water, helium, hydrogen, carbon monoxide, argon, oxygen, and others. We provide state-of-the-art measurements on selected systems needed to support the modeling efforts. These models and data cover the ranges of temperature (90 kelvin to 700 kelvin), pressure (70 megapascal), and composition (full range) necessary for efficient operation of the gas industry, with emphasis on the major region for custody transfer operations. The models cover all fluid states (gas, vapor, and liquid), including properties along phase boundaries, and can be used to calculate the properties of natural gas, liquefied natural gas, natural gas liquids, substitute/synthetic natural gas, compressed natural gas, and wet, dry, and sour gases. We make extensive
experimental measurements on both pure fluids and mixtures, including
saturation and single-phase densities, vapor pressures, heat capacities,
sound speeds, thermal conductivities, and viscosities. We also study vapor-liquid
and solid-fluid phase boundaries. Our modeling effort involves the development
of highly accurate mixture models and pure fluid equations of state. A
new generalized mixture model, based on the excess Helmholtz energy and
standard reference quality formulations for the constituents, shows promise
to be the most accurate model available for mixture properties. We incorporate
these models in computer databases that serve as the major mechanisms
for technology transfer of the data to industry. We also participate in
efforts to arrive at national and international standards for natural
gas properties. Contact: Joe W. Magee or Eric W. Lemmon Properties of Fluids and Fluid Mixtures Thermophysical properties of fluids and fluid mixtures are essential for process design and control in the chemical, natural gas, aerospace, environmental, and energy-related industries. Our research program in fluid properties involves experimental and theoretical research and computer simulation studies on the thermodynamic and transport properties of pure fluids and fluid mixtures. One of our primary goals is to develop highly accurate predictive models for thermophysical properties of fluids and fluid mixtures. We accomplish this through an integrated program of measurement, theory, and correlation. Apparatus are available for state-of-the-art measurements of the thermodynamic and transport properties of pure fluids and mixtures, including pressure-volume-temperature relations, speed of sound, heat capacity, dielectric constant, viscosity, phase equilibria, and thermal conductivity over wide ranges of temperature and pressure. We also make measurements in the critical and extended critical region. In concert with our experimental work, we conduct theoretical studies to develop wide-range predictive models and computer codes. We direct a wide
variety of research, both experimental and theoretical, toward the understanding
of complex fluid behavior, the microscopic structure of fluids, and the
liquid-solid phase boundary. Included are studies of non-Newtonian fluids,
colloidal suspensions, shear-induced chemical reactions, supercooled fluids
and melting phenomena, and macromolecules. Contact: Daniel G. Friend or Joe W. Magee Properties of Gels, Micelles, and Clays We use small-angle neutron diffraction, static visible laser-light scattering, dynamic time-correlation spectroscopy, and computer simulation to study the structure and properties of systems containing particles with sizes in the range of 10 nanometers to 1,000 nanometers. In addition to the fundamental information being obtained about complex fluids, these suspensions are interesting in their own right. For example, we are using sol/gel technology increasingly in the production of ultrahigh-purity optical glasses. Using neutron diffraction and computer simulation, we are improving understanding of the formation dynamics and structure of the precursor gel (a state of matter intermediate to liquid and solid). We also use dynamic light scattering studies, coupled with experiments using neutron scattering, to better understand the interaction between surfactant micelles and clay platelets. This will improve understanding of how organic pollutants interact with clay. Current activities include the study of colloidal silica solutions, gelation of silica at high volume fraction, cationic surfactant micelles, and adsorption of large organic molecules on suspended and dispersed clay platelets. Much of our research
is directed toward understanding complex fluids. The characteristic time
scales governing the dynamics of colloidal solutions are many orders of
magnitude slower than in molecular fluids. Colloidal solutions thus provide
us with experimentally accessible models for the study of complex fluid
behavior. We are studying non-Newtonian fluid behavior using the NIST
Couette-flow shearing cell at the small-angle neutron scattering beam
lines of the NIST Center for Neutron Research. Contact: Chris D. Muzny Dilute-Solution Thermodynamics Much chemical technology, particularly in the environmental area, involves solutions where the concentration of the substance of interest is near zero. The thermodynamics of these dilute solutions presents special challenges and opportunities. One area of interest is the solubility of substances in liquid solvents. Water is the most important solvent, but dilute-solution thermodynamics (usually in the form of Henry's law) has many different applications in non-aqueous systems as well. Recently, we have used new theoretical understanding of the high-temperature behavior of Henry's constant to produce an improved model for correlating Henry's constants over a wide temperature range and for extrapolation of existing data to higher temperatures. Dilute-solution thermodynamics
also can be used to analyze the solubility of solids in vapors and supercritical
fluids, which is important for a variety of processes, including extraction
using carbon dioxide and deposition of minerals in steam power plants.
Our modeling efforts focus on using the density of the solvent as the
key variable. We use molecular computer simulation to test the validity
of modeling approaches. Contact: Allan H. Harvey Advanced Low-Temperature Refrigeration Many new and developing technologies rely on the use of cryogenic temperatures. Some of these technologies include the cooling of infrared sensors for night vision, atmospheric studies, and process monitoring; semiconducting and superconducting electronics for increased speed and reduced noise; cryopumps for the production of clean vacuums in semiconductor processing; magnetic-resonance imaging superconducting magnets; some medical catheters; and the liquefaction of natural gas for clean-burning fuel. Specialized refrigerators known as cryocoolers are required to reach cryogenic temperatures. Significant research and development of cryocoolers has occurred in the last 15 years to meet the reliability, cost, and efficiency requirements of many different applications. We have been leaders in this advanced refrigeration field and have led the development of a new type of cryocooler, known as the orifice pulse tube refrigerator (OPTR), that is being considered for all of the above applications. In its normal configuration, it has only one moving part at room temperature and can reach temperatures below 40 kelvin in a single stage. Using thermoacoustic drivers in place of mechanical compressors, NIST and Los Alamos National Laboratory scientists developed an OPTR that became the first cryogenic refrigerator with no moving parts. We have received a patent, a Strategic Defense Initiative Office innovative technology award, and an R&D 100 award for this device, called a TADOPTR. We have collaborated with dozens of companies and other government laboratories to transfer this and other new cryocooler technologies into specific application areas. Our computer models on regenerator performance are used extensively in the field to aid in the optimization of regenerative cryocoolers. We conduct performance and loss measurements to compare with models and improve their accuracy for a wide range of operating conditions. We have carried out
substantial research on many types of cryocoolers to improve their technologies
so they may be useful for various applications. In the area of Joule-Thomson
refrigerators, we have developed a model to optimize gas mixtures for
use at any temperature down to 70 K to improve process efficiency. We
have also helped companies develop such refrigerators for use as cryogenic
catheters. Contact: Ray Radebaugh
Date
created:
September 28, 2001 |