A multidimensional gas chromatography method for the analysis of hydrogen sulfide in crude oil and crude oil headspace.

Two-dimensional heart-cutting gas chromatography is used to analyze dissolved hydrogen sulfide in crude samples. Liquid samples are separated first on an HP-PONA column, and the light sulfur gases are heart-cut to a GasPro column, where hydrogen sulfide is separated from other light sulfur gases and detected with a sulfur chemiluminescence detector. Heart-cutting is accomplished with the use of a Deans switch. Backflushing the columns after hydrogen sulfide detection eliminates any problems caused by high-boiling hydrocarbons in the samples. Dissolved hydrogen sulfide is quantified in 14 crude oil samples, and the results are shown in this work. The method is also applicable to the analysis of headspace hydrogen sulfide over crude oil samples. Gas hydrogen sulfide measurements are compared to liquid hydrogen sulfide measurements for the same sample set. The chromatographic system design is discussed, and chromatograms of representative gas and liquid measurements are shown.

Application of a quantitative structure retention relationship approach for the prediction of the two-dimensional gas chromatography retention times of polycyclic aromatic sulfur heterocycle compounds.

Information on the sulfur classes present in petroleum is a key factor in determining the value of refined products and processing behavior in the refinery. A large part of the sulfur present is included in polycyclic aromatic sulfur heterocycles (PASHs), which in turn are difficult to desulfurize. Furthermore, some PASHs are potentially more mutagenic and carcinogenic than polycyclic aromatic hydrocarbons, PAHs. All of this calls for improved methods for the identification and quantification of individual sulfur species. Recent advances in analytical techniques such as comprehensive two-dimensional gas chromatography (GC×GC) have enabled the identification of many individual sulfur species. However, full identification of individual components, particularly in virgin oil fractions, is still out of reach as standards for numerous compounds are unavailable. In this work, a method for accurately predicting retention times in GC×GC using a QSRR (quantitative structure retention relationship) method was very helpful for the identification of individual sulfur compounds. Retention times for 89 saturated, aromatic, and polyaromatic sulfur-containing heterocyclic compounds were determined using two-dimensional gas chromatography. These retention data were correlated with molecular descriptors generated with CODESSA software. Two independent QSRR relationships were derived for the primary as well as the secondary retention characteristics. The predictive ability of the relationships was tested by using both independent sets of compounds and a cross-validation technique. When the corresponding chemical standards are unavailable, the equations developed for predicting retention times can be used to identify unknown chromatographic peaks by matching their retention times with those of sulfur compounds of known molecular structure.

Measurement of H2S in Crude Oil and Crude Oil Headspace Using Multidimensional Gas Chromatography, Deans Switching and Sulfur-selective Detection.

A method for the analysis of dissolved hydrogen sulfide in crude oil samples is demonstrated using gas chromatography. In order to effectively eliminate interferences, a two dimensional column configuration is used, with a Deans switch employed to transfer hydrogen sulfide from the first to the second column (heart-cutting). Liquid crude samples are first separated on a dimethylpolysiloxane column, and light gases are heart-cut and further separated on a bonded porous layer open tubular (PLOT) column that is able to separate hydrogen sulfide from other light sulfur species. Hydrogen sulfide is then detected with a sulfur chemiluminescence detector, adding an additional layer of selectivity. Following separation and detection of hydrogen sulfide, the system is backflushed to remove the high-boiling hydrocarbons present in the crude samples and to preserve chromatographic integrity. Dissolved hydrogen sulfide has been quantified in liquid samples from 1.1 to 500 ppm, demonstrating wide applicability to a range of samples. The method has also been successfully applied for the analysis of gas samples from crude oil headspace and process gas bags, with measurement from 0.7 to 9,700 ppm hydrogen sulfide.

Diaromatic sulphur-containing 'naphthenic' acids in process waters.

Polar organic compounds found in industrial process waters, particularly those originating from biodegraded petroleum residues, include 'naphthenic acids' (NA). Some NA have been shown to have acute toxicity to fish and also to produce sub-lethal effects. Whilst some of these toxic effects are produced by identifiable carboxylic acids, acids such as sulphur-containing acids, which have been detected, but not yet identified, may produce others. Therefore, in the present study, the sulphur-containing acids in oil sands process water were studied. A fraction (ca 12% by weight of the total NA containing ca 1.5% weight sulphur) was obtained by elution of methylated NA through an argentation solid phase extraction column with diethyl ether. This was examined by multidimensional comprehensive gas chromatography-mass spectrometry (GCxGC-MS) in both nominal and high resolution mass accuracy modes and by GCxGC-sulphur chemiluminescence detection (GCxGC-SCD). Interpretation of the mass spectra and retention behaviour of methyl esters of several synthesised sulphur acids and the unknowns allowed delimitation of the structures, but not complete identification. Diaromatic sulphur-containing alkanoic acids were suggested. Computer modelling of the toxicities of some of the possible acids suggested they would have similar toxicities to one another and to dehydroabietic acid. However, the sulphur-rich fraction was not toxic or estrogenic to trout hepatocytes, suggesting the concentrations of sulphur acids in this sample were too low to produce any such effects in vitro. Further samples should probably be examined for these compounds.