Daniel A. Netzel

13C NMR measurements of the genetic potentials of oil shales

Cross polarization, magic-angle spinning 13C NMR measurements have been made on raw oil shales that represent a variety of geologic ages, origins, depositional environments and source locations. A high degree of correlation was established between the fraction of aliphatic carbon measured by 13C NMR, and the genetic potential, calculated from Fischer assay data. The correlation is independent of the type of kerogen in the raw shale, and its degree of evolution. A short discussion on the validity of various correlations between physical/chemical properties of oil shales and Fischer assay oil yields is given.

N.m.r. characterization of coal pyrolysis products

Abstract Isothermal pyrolysis studies were conducted on an Illinois No. 6 and a Wyodak coal at 375 °C, 400 °C and 425 °C, using a fluidized sandbath reactor system. The amount of coal converted to tar, gas and residue was determined for different reaction durations at each temperature. Solid- and liquid-state 13 C n.m.r. techniques were used to characterize the residue coal and tars produced during varying stages of pyrolysis. Solid-state 13 C n.m.r. measurements showed that the residue coal reached its limiting aromaticity value fairly early during decomposition, and on a mass basis, the aromatic carbon in the residue remained relatively constant during pyrolysis. The aliphatic carbon mass loss was similar to the total carbon mass loss. The mass of aromatic carbon in the products was found to increase by 13% and 16% over that in the starting material for the Wyodak and Illinois No. 6 coal, respectively. The amount of aliphatic carbon that aromatized to produce the increase in aromatic carbon was 37% and 35% for the Wyodak and Illinois No. 6 coal.

NMR imaging studies of asphaltene precipitation in asphalts

Abstract Nuclear magnetic resonance (NMR) images were obtained on asphalts which were dissolved in toluene and titrated with iso-octane to the point of onset of flocculation. When iso-octane was added to the asphalt and the mixture stirred, asphaltene precipitation proceeded in a normal fashion. However, when the titrant was added slowly to minimize mixing at the iso-octane-asphalt-toluene interface, the images showed that a layer of material formed at the solvent interface which was different from the asphaltenes or the maltenes. The formation of this layer appeared to depend on asphaltene concentration and degree of aging, i.e. the greater the asphaltene content and the degree of aging, the more prominent the layer. The H C ratio of the layer was similar to the resin fraction of the asphalt. These observations suggest that NMR imaging might be used to assess asphalt compatibility in aged asphalts.

Carbon-13 solid-state n.m.r. investigation of coke deposits on spent catalysts used in coal liquefaction

Catalysts of the CoMo type were prepared on four different surface-modified alumina supports: (1) TiO2-coated by impregnation, (2) ZrO2-coated by impregnation, (3) TiO2-coated by deposition, and (4) carbon-coated by pyrolysis. These catalysts were used in a catalytic coal liquefaction microreactor. The coke deposits on the spent catalysts were investigated using 13C solid-state nuclear magnetic resonance techniques of cross polarization with magic angle spinning (CP-MAS) and dipolar dephasing (DD). CP-MAS 13C spectral data of the coke deposits were used to quantify the aromatic and aliphatic carbon types, and 13C DD spectral data of the same samples to quantify the aromatic quaternary carbon types, from which the aromatic cluster size of the coke deposits was determined. Catalysts which promote the most coke deposition were found to perform poorly in terms of coal liquefaction conversion. The aromatic cluster size of the coke deposited on the spent catalysts appears to depend on the initial pore volume of the fresh catalyst and on the percentage of surface coating of the alumina support.

Nuclear Spin Relaxation Spectroscopy

From the time dependence of the nuclear spin relaxation phenomena, molecular structure, conformation, motions, interactions, diffusion, and adsorption can readily be studied. Aside from the studies at the molecular level, nuclear spin relaxation phenomena have been applied to qualitative and quantitative analysis in the areas of polymer research, agriculture and food research, petroleum research, and medical research. This article presents an introduction to the theory, techniques, and applications of nuclear spin spectroscopy.

A 1H CRAMPS n.m.r. investigation of chemically and thermally treated asphalt ridge tar sand

Abstract An exploratory investigation was conducted using the n.m.r. technique CRAMPS (combined rotation and multiple-pulse spectroscopy) to provide information on the types of organic hydrogen functionality present on the surface of tar sand residues. These residues were obtained from solvent extraction using solvents of different polarity and isothermal pyrolysis at four different temperatures. The solvents hexane, toluene, and methylene chloride were used to extract the bitumen from a native tar sand. From carbon and hydrogen analyses, all three solvents removed essentially all of the bitumen from the mineral matrix. However, solid-state 1 H n.m.r. and diffuse reflectance infrared spectra show the presence of a small amount of organic material still in contact with the mineral matrix. After extraction with methylene chloride, the most polar solvent, tar sand residues contain less organic material than the tar sand residues obtained after solvent extraction with hexane, the least polar of the solvents. The hydrogen spectra of the tar sand residues show a greater amount of aromatic hydrogens than aliphatic hydrogens presumably because heteroaromatics associate more strongly with the mineral matrix. The 1 H CRAMPS spectra of the tar sand residues obtained from the isothermal pyrolysis of the native tar sand show that a relatively large amount of unpyrolysed bitumen still remains with the mineral matrix even at a temperature of 380 °C. For the native tar sand pyrolysed above 400 °C, the 1 H spectrum changed dramatically, but the spectrum of the pyrolysate tar sand residues still did not have the chemical shift resolution that was apparent in the spectra of the tar sand residues from solvent extraction. The major change in the 1 H spectrum of the tar sand residue after pyrolysis above 400 °C was the loss of paraffinic hydrogens, as expected.

Carbon-13 molecular structure parameters of RTFOT aged asphalts : Three proposed mechanisms for aromatization

The determination of average molecular structural parameters of asphalts represents an important step in describing their skeleton. Using a new method based only on the analysis of carbon-13 nuclear magnetic resonance measurements, the average molecular parameters were determined for three asphalts before and after Rolling Thin Film Oven Test aging. From the analysis of the changes in the parameters, three mechanisms are proposed to explain the aromatization process in asphalts during oxidation.

N.m.r. determination of aromatic carbon balances and hydrogen utilization in direct coal liquefaction

Abstract Solid- and liquid-state 13 C n.m.r. measurements were made on a suite of samples obtained from different stages of a coal liquefaction run at the Wilsonville Two-Stage Advanced Coal Liquefaction Research and Development Facility. The n.m.r. measurements were combined with elemental analysis and mass balance data to measure aromatic carbon balances and hydrogen utilization for Wilsonville coal liquefaction run 259G. This was a catalytic/catalytic integrated two-stage liquefaction run on a deeply cleaned, Pittsburgh seam, high volatile bituminous (hvAb) coal from the Ireland mine in West Virginia, USA. The n.m.r. measurements showed that on the basis of the feed coal, about 58% of the aromatic carbons in Pittsburgh coal were hydrogenated during two-stage liquefaction, and 55% of the hydrogenation occurred during the second stage. A net of 68.1 mol of hydrogen per 100 mol of coal carbon was consumed during the first stage of Wilsonville run 259G. This amounted to 69% of the total overall two-stage hydrogen consumption. Matrix cleavage and hydrogenation reactions accounted for 31% and 27%, respectively, of the total first-stage hydrogen consumption. Hydrogenation reactions accounted for most (69%) of the hydrogen consumed during the second stage, and accounted for 40% of the overall two-stage total hydrogen consumption. Most of the total hydrogen consumed for hydrocarbon gas generation (70%), and for heteroatom removal and heterogas production (71%) occurred in the first stage. Overall hydrogen consumption was 14% for hydrocarbon gas production and 27% for heteroatom removal and heterogas production.