take advantage of lower unit train rates a larger gasifier would be necessary. There would be a corresponding increase in the pipeline capacity required as well as a need to find more customers. On the sur face at least, the optimum size for a chemical energy pipeline as represented by the IGT near-term option would ap pear to lie somewhere between that of a huge regional energy complex and an inplant boiler. The IGT study was the first step in as sessing possibilities of opening the EVA-
ADAM closed loop. The result had some unexpected economic attractions. Whether or not the chemical energy pipeline evolves into a practical energy delivery system remains to be seen. The criticism that the chemical energy pipe line is little more than an SNG plant strung out over the landscape contains an element of truth. It is also true that stringing the SNG plant out over the landscape has presented some interesting technical and economic options for energy planners. Π
NMR used to analyze structure of coal Advances in nuclear magnetic resonance (NMR) spectroscopy techniques have been sparking a surge of activity in NMR of solids (C&EN, Oct. 16,1978, page 22). Some of those techniques have now been applied to analysis of the structure of coal in a project that could lead to more eco nomical ways of converting coal to gas or liquids. That project is the work of an inter disciplinary group of scientists at the University of Utah. This group includes a coal conversion research team, headed by Dr. Wendell H. Wiser, professor of fuels engineering, and members of the regional NMR facility at Utah, directed by Dr. David M. Grant, professor of chemistry. Also involved are Dr. Ronald J. Pugmire, research professor of fuels engineering and a member of the NMR lab, and Kurt Zilm, a graduate student sponsored by both departments. In the project, the researchers hydrogenated coal to liquids using a hydrogénation process developed at Utah. They used standard carbon-13 Fourier transform NMR to study the liquids produced, and a combination of rapid magic-angle spinning and cross polarization to study the solid coals. The result was an insight into mechanisms of the conversion process that they say could be of considerable help in further developing conversion processes and their operations with different types of coal. Magic-angle spinning and cross polarization are two of the techniques that have recently made NMR of solids a useful analytical tool. Before development of these techniques, use of NMR on solids gave featureless spectra that provided little information relative to that obtainable from NMR spectra of liquids. Magic-angle spinning is a technique that overcomes the orientation effects of molecules in a solid. Molecular orientation can affect the NMR signal, because the molecular environment of a particular group appears different, for example, when viewed down the long axis of a molecule than when viewed perpendicular to the axis. In a liquid, such orientation effects cancel out, because with rapid tumbling of the molecules, no particular orientation is favored. In a solid, such effects simply smear out. However, it happens that when a solid sample is rotated along an axis that is
54.7° from the magnetic field of the NMR, an averaging occurs that is similar to tumbling in liquids. The angle is a property of the local fields that electrons exert on nuclei. Spinning the sample at the magic angle as fast as possible causes the smear to disappear and the spectrum to become liquidlike. Cross polarization is a technique developed by Dr. John S. Waugh and his coworkers at Massachusetts Institute of Technology. It dramatically enhances detection sensitivity of NMR to carbon atoms. Normally, NMR is insensitive to the less abundant elements, such as carbon, in a sample. But, if the hydrogen atoms in a sample are pulsed with a magnetic field of a particular strength and frequency, they can be made to spin effectively in unison with the carbon atoms. When this happens, the polarization of the abundant hydrogen atoms is transmitted to the rarer carbon atoms, enhancing the signal. In their studies, the Utah researchers converted coal to liquids with a process in which zinc chloride catalyst was applied to the coal before it was fed into a coiledtube reactor. The coal—dry and finely ground—was fed to the reactor with a stream of hydrogen in turbulent flow so as to avoid reactor plugging by the caking coal. Using hydrogen gas instead of a liquid solvent also made it possible to shorten the time required for reaching temperatures needed for conversion. Using the appropriate techniques, the
researchers took solid and liquid spectra. For the solid spectra, they used an exceptionally high-speed spinner constructed by graduate student Zilm, which can be set accurately and repeatedly at the magic angle. Broadening the liquid spectra artificially until the line widths were comparable to those in the solid sample spectra revealed important features of the liquefaction process. Comparing liquid and solid samples, the researchers note that the skeletal structure of the coal remained very similar in both states. The process didn't affect the skeletal backbone of the coal in any appreciable way. "We haven't greatly perturbed the chemistry of the coal in the liquefaction process," Grant explains. "About 90 to 95% of the spectral features of the solid and liquified samples agree, indicating that much of the chemistry of the two samples stays the same." However, the researchers point out, there are subtle changes in specific structural moieties and selective bond cleavages that can be related directly to the details of the conversion process. The results, they say, support a Friedel-Crafts mechanism of dealkylation followed by elimination of highly branched centers. "A couple of NMR 'peaks vanish upon liquefaction," Grant says. "They correspond to carbons at highly branched centers or those next to aromatic rings." He calls this "the simplest explanation"—one that's consistent with textbook descriptions of how a Friedel-Crafts reaction ought to work. Importantly, the catalyzed hydrogénation involves limited "snipping" of crucial groups in coal instead of major hacking. The Utah scientists expect that the technique will help in analyzing the effects of different catalysts, reactor temperatures, pressures, and other factors on process efficiency. It might also help to explain differential conversion rates of various types of coal. Three types of coal were used in the studies. One was a high-volatile, bituminous coal from a Utah underground mine, another a subbituminous coal from a Wyoming strip mine, and the third a lignite from a Montana strip mine. D
Utah researchers Zilm (sitting), Pugmire, Wiser, and Grant in NMR lab Jan. 8, 1979 C&EN
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