To reduce effectively sulfur gas content from shale processing to environmentally acceptable levels, hydrogen sulfide (H2S), carbonyl sulfide (COS), sulfur dioxide (SO2), and methanethiol (CH3SH) plus trace sulfur compounds must be removed. Of these, the trace sulfur compounds have not been well characterized but should be known to ppm levels in order to optimize gas cleanup procedures. Most techniques for analysis of trace sulfur components in oil shale gases have limitations. The applications we describe using triple quadrupole mass spectrometric techniques (TQMS) appear to have overcome many problems of trace sulfur analysis.
Basically, a TQMS produces a mass spectrum of a mass spectrum and is, therefore, highly sensitive, selective, and specific. Tests on a Finnigan TQMS at the University of Florida and on a totally computerized TQMS designed at Lawrence Livermore National Laboratory (LLNL) using pure standards, mixed gas standards, and Fisher assay gas grab samples show that we can quantitatively as well as qualitatively detect the following components:
1. methanethiol = < 1 ppm
2. ethanethiol = 3 ppm
3. n-propanethiol = < 1 ppm
4. isopropanethiol = 4 ppm
5. carbonyl sulfide = 1 ppm
6. carbon disulfide = 4 ppm
7. dimethyl sulfide = 10 ppm
8. dimethyl disulfide = < 1 ppm
9. thiophene = < 1 ppm
10. 2 or 3 methyl thiophene = < 1 ppm
For a rapidly changing gas stream, timing studies on the LLNL TQMS show that analytical results for 10 sulfur compounds (1000 readings on each parent and key daughter ions) can be acquired and quantitatively calculated in ∼ 30 s. For kinetics studies, data on selected daughters for ten compounds can be acquired in a total of 540 ms.