390
Anal. Chem. 1984,56,390-395
Determination of Sulfur-Containing Gases from Oil Shale Pyrolysis by Triple Quadrupole Mass Spectrometry Carla M. Wong,* Richard W. Crawford, and Alan K. Burnham Lawrence Livermore National Laboratory, P.O. Box 808, L-310, Livermore, California 94550
A fully computer automated trlple quadrupole mass spectrometer was used to determine 10 sulfur contalnlng gases from oil shale pyrolysls, ranging In concentratlon from several percent to less than 1 ppm. The raw shales used were from three geographlcal areas and were analyzed both untreated and acld leached to remove carbonates, sulfates, and pyrlte. A bulb type pyrolysls apparatus was used to give quantltatlve results for the composite pyrolysis gas. A Pyroprobe was used to pyrolyze samples In the TQMS source and monitor gas evolutlon vs. temperature. The two techniques were found to give very complementary data. The probable source of several of these gases Is discussed. The TQMS was found to have excellent speed, speclflclty, sensitivity, and reproduclblllty for this task.
The reactions of sulfur in oil shale processing are important for health and environmental considerations because toxic atmospheric pollutants such as H2S,CS2,and SO2are common reaction products (1). In addition, H2S and other reduced sulfur compounds such as thiols, thiophenes, COS, and sulfides can poison catalysts and cause corrosion, erosion, and embrittlement of equipment leading to costly repairs and replacement. The effective removal or utilization of these trace sulfur-containing compounds is dependent upon identification, quantification, and an understanding of the reactions producing them. Previous work in identification and quantification has involved gas chromatography with FID and FPD detectors, GC/MS, on-line pulsed fluorescence analyzers, microwave rotational spectrometry and FTIR spectrometry (2, 3). Attempts to study the chemical reactions that are dependent upon processing conditions or shale type with respect to sulfur-containing compounds have been largely unsuccessful due to lack of speed, selectivity, or sensitivity of the analytical methods for complex oil shale pyrolysate mixtures. Green River Formation shale from Utah and Colorado was used in this study. The average Mahogany Zone shale from this formation typically contains sulfur in pyritic form (73%),as sulfates (3%), and as organics (24%), with a total sulfur '. During retorting, sulfur is released content of 0.7 wt 7 primarily as H2S (concentrations up to 15%) and COS and methanethiol (concentrations as high as 0.1%), and unknown amounts and types of other trace sulfur compounds (4). The chemistry of the reactions and the kinetics of formation of H2, CO, C 0 2 ,CHI, and various hydrocarbons and how they relate to changes in processing conditions and the variability of the oil shale composition have been studied a t LLNL for several years (5, 6). However, for sulfur-containing compounds, this understanding has been illusive because both organic sulfur from kerogen and inorganic sulfur from pyrite occur in oil shale, and each can produce sulfur gases. Kinetic measurements are useful in characterizing the chemical reactions leading to H2S and various trace sulfur species. Real-time measurements are desirable in terms of both convenience and minimizing reactions of sulfur products with
other species and with container walls (7). In order to satisfy these requirements, we have used the totally computerized triple quadrupole mass spectrometer (TQMS) that was developed at LLNL (8, 9). Triple quadrupole mass spectrometers have been described previously (10-15). The most common use of these multistage instruments is for mixture analysis using the normal mass spectra and daughter spectra operating modes. This system provides enhanced specificity, selectivity, and sensitivity over conventional mass spectrometers. Our TQMS was designed to allow for real-time, self-adaptive modification of experiments based upon display and interpretation of analytical results. Studies done on this system show that it has the speed for real-time analysis (milliseconds to seconds) and the selectivity to differentiate sulfur-containing compounds from hydrocarbons in a complex pyrolysis gas mix. Also, the sensitivity (low ppm range), and the wide dynamic range (tenths of part per million to tens of percent) enable us to measure trace sulfur species in oil shale as it is being pyrolyzed (16). These measurement characteristics permit kinetics studies so we can start to define the reactions leading to trace sulfur gas species formation in oil shale processing without the tedious calibration procedures and inherent slowness associated with chromatographic techniques.
EXPERIMENTAL SECTION Instrumentation. The TQMS system uses two separate LSI-11/23 minicomputers: one for total computer control of source and ion axial potentials as well as all other instrumental data acquisition parameters; the second for simultaneous data manipulation and processing concerns. The hardware includes a standard Hewlett-Packard 5985B GC/MS source, two quadrupole analyzers and a quadrupole CAD region using Balzers QMG 511 rods and controllers, and a PPINICI detector made by Finnigan Corp. The mechanical, electronics, and computer design for linking these diverse elements into a functional TQMS have been described previously (8, 9). The mass spectrometer was operated under 70-eV electron impact conditions, in positive ion mode, at a sample pressure in the source of up to 6 X lo4 torr. The source temperature was 200 "C. Argon of 99.9% purity was used as the collision gas in quadrupole region two for the daughter ion scans. The CAD argon gas pressure was 0.8 mtorr. Normal mass scans and daughter ions scans were used for all experiments. For normal mass scans, quadrupoles one and two were operated in rf only mode, passing all ions, which were scanned (analyzed) in quadrupole three to give a normal mass spectrum. Daughter ions from collisionally activated dissociation (CAD) mass spectra of the trace sulfur compounds were obtained by setting quadrupole one to transmit the parent ions of interest. The ions were then passed through the collision cell (quadrupole two) which was filled with argon and operated in rf only mode transmitting all ions. Then all daughter ions produced in the collisionally activated dissociation process were analyzed by scanning quadrupole three. Since on-line analysis gives greater analytical accuracy, the speed of the data acquisition and interpretation then becomes very important because we are dealing with a dynamic process in oil shale retorting procedures. On the TQMS system all functions of instrument operation are under total computer control and data are acquired by peak
0003-2700/84/0356-0390$01.50/00 1984 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 3, MARCH 1984 T R I P L E QUADRUPOLE F‘8,S.
Table I. Computerized Autoranging of TQMS Giving Wide Dynamic Range Tract C-a (560 f t ) hydrogen sulfide methane thiol ethanethiol propanethiol dimethyl sulfide dimethyl disulfide carbonyl sulfide carbon disulfide thiophene methylthiophene
64076 5 13 198 48 9 0.5
199 34 34 83
PPm Geokinetics (78-79 f t )
391
NEEDLE VALVE
7
GLASS L I N E D PRCBE EXPANSION V C L ,
r
CLAM SHELL YEATEQ
22 6
1 0.1
