| Description |
A renewed emphasis on the development of liquid synthetic fuels from coal has prompted an increase in the variety of analytical methods employed for the chemical characterization of these products. These characterizations have been necessitated as product composition directly affects the choice of process variables, and inherently, the overall success of the process. Complete characterization, however, is often inhibited due to the complex nature of these liquids. The successful operation of any coal liquefaction process is ultimately dependent upon the efficiency of hydrogen consumption. Ideal levels of hydrogen consumption involve not only increased hydrogen to carbon (H/C) ratios of initially formed hydrocarbon fragments, but also removal of heteroatoms in reduced form, principally as NHg, h^S and 1^0. Of the major heteroatomic species found in coal, less attention has been devoted to the analysis of oxygen-containing compounds, although recent evidence indicates that oxygen functionalities may play important roles in the effectiveness of hydrogen utilization as well as in the yield of quality end-products. Several distillates from the Exxon Donor Solvent (EDS) and H-Coal processes were investigated for oxygen-containing compounds by a combination of analytical techniques including open-column liquid chromatography (LC), capillary gas chromatography (GC), gas chromatography coupled with mass spectrometry (GC/MS) and pyrolysis mass spectrometry (Py/MS). These analyses resulted in the tentative identification of several series of hydroxyaromatic and hydroxyhydroaromatic compounds. The two major classes of oxygen-containing compounds found in the distillates examined were a series of alkylphenols and a second series thought to consist of 4-indanol, 5-indanol and their respective homologs. This latter series was deemed noteworthy because of unexpectedly high abundances and the apparent reactivity of 5-indanol (and corresponding homologs) during hydrotreatment. Whether this reactivity occurred with a correspondingly beneficial or detrimental effect on the overall process has not been determined. Exact identities of the indanols could not be confirmed directly due to a lack of reference spectra. Since unambiguous identification of mass spectra usually requires matching unknown spectra with spectra obtained from standard compounds and/or reference libraries, and only a limited number of suitable standards were available, computerassisted pattern recognition was used in an attempt to assign mass spectra of these "unknown" species to correct compound classes. Selected spectra from GC/MS analyses were extracted to form two sets of data. The first data set contained spectra of a variety of hydrocarbons as well as spectra of suspected alkylphenols and alkylindanols and was used to examine the degree of separation possible between hydroxy- and nonhydroxy-containing compounds. The second data set consisted of spectra of suspected alkylphenols, alkylindanols and several reference compounds and was used to examine the degree of separation possible between these classes and the indanol relationships to isomers of differing molecular structure. Examinations were achieved through the formation of data files of two types. From each original data file (containing fragment ion spectra) a corresponding "reverse" file (containing neutral-loss spectra) was formed. Original files were used to obtain molecular core information while the "reverse" files were employed to investigate fragmentation tendencies of the various classes. Each data file was subjected to specific data processing routines, as available in the ARTHUR computer program package, including factor analysis, discriminant analysis and non-linear mapping. The combined results obtained from these analyses indicated separation not only between the various classes, but in certain instances, between class homologs and isomers of the same molecular weight. In spite of the absence of sufficient reference spectra, the classification of spectra into correct categories was successful and further validated previously assigned class identities. |
