A two-step chemistry for highlighting heteroatom species in petroleum materials using carbon-13 NMR spectroscopy

Abstract

A variety of characterization techniques have been reported for probing the type and distribution of heteroatom species in fossil fuel materials, usually coal and coal extracts. Often, a chemical transformation of the fossil fuel material has been used in combination with a suitable analysis technique in order to enhance the detection and identification of classes of heteroatom groups and to relate this information to aspects of the material's physical and chemical properties. These chemical reactions range from mild treatments including phase-transfer alkylation to rather more severe treatments such as metal reductions and oxidative degradation. Although these latter chemistries can provide information on heteroatom species which are normally unreactive to mild chemical treatments, the severity of these techniques reduces the selectivity for specific molecular types and greatly increases the probability for side reactions. In order to avoid some of the shortcomings inherent in one-step chemistries, we wish to report a two-step approach which combines an alkali metal reduction reaction with a phase transfer (PT)) methylation reaction. A petroleum vacuum residuum (975 /sup 0/F/sup +/) has been chosen to demonstrate the application of this technique for highlighting heteroatom species, particularly sulfur species. Isotopically enriched methyl groups--93.1 mol% /sup 13/CH/sub 3/I in allmore » samples discussed here--are used as chemical tags in the second step of this process to facilitate the detection of reaction products in the residuum by high resolution /sup 13/C NMR spectroscopy. The corresponding one-step products from these two chemical reactions are compared to the sequential two-step product.« less