Exhaustive determination of hydrocarbon compound type distributions by high resolution mass spectrometry

Abstract

The need to obtain detailed chemical information about heavy petroleum fractions, where the usefulness of chromatographic separation techniques is limited, has been addressed by using high resolution mass spectrometry (HRMS). A magnetic sector mass spectrometer was used for the experiments. The instrument meets the mass and dynamic range criteria for the analysis of compounds in complex hydrocarbon fractions, but not the resolving power needs for the separation of overlapping mass doublets. A simple and fast method has been developed that permits the calculation of the relative amounts of the ion species in overlapping mass doublets by consideration of the unresolved peak abundance and the difference between the theoretical and measured masses. The exhaustive determination of hydrocarbon compound type distributions is achieved by the sequential comparison of the theoretical masses of compounds with a given formula against those measured in the mass spectrum. All compound types described by the general hydrocarbon formula CnH2n+ZSaObNcYd are exhaustively considered in the calculations. Four levels of information are produced by the method: (1) percent amount for each element (C, H, S, O, N, Y), (2) relative% amounts for compound classes containing different combinations of heteroatoms, (3) Z-series (aromaticity) distributions for each compound class, and (4) molecular weight and carbon number distributions for each Z-series. The capabilities of the method are illustrated by the analysis of representative sets of samples from thermal treatment and hydrocracking processes. Copyright © 1999 John Wiley & Sons, Ltd.