Gas Chromatographic Separation of Carbon Dioxide, Carbon Oxysulfide, Hydrogen Sulfide, Carbon Disulfide, and Sulfur Dioxide SIR: The classical wet techniques for the analysis of mixtures of C O z , HzS, SO2, COS, and CS2 in the p.p.m. range leave much t o be depired with respect to speed and precision. A need has existed for the rapid determination of these gases in areas such as the production and transportation of elemental sulfur, commercial processes ut,ilizing sulfur, and research projects involving sulfur and sulfur compounds. Adams and Koppe ( 1 ) described a gas chromatographic separation of H2S, SOz, and a number of mercaptans and organic sulfides using various Triton-X liquid phases. These same authors, in a later publication ( 2 ) , {developed a technique for adsorption sampling of certain volatile sulfur compounds on silica gel a t -78.5" C. and subsequent desorption into a chromatograph. Staszewski et al. (3) investigated three different liquid phases on Teflon 6 (DuPont) for t'he isothermal separation of COS, H2S, CS2, and SO,. The liquid phases reported were squalene, dinonylphthalate, and polyethylene glycol 400. Squalene was totally unsat,iafactory, since it did not resolve H2S and SO2 over a wide range of temperatures. X %foot column of 20% dinonylphthalate a t 22" C. provided only partial resolution of H2Sand COS, yet it retained CS2 for 78 minutes. Increased column length or lower flow rates would probably result in a separation of H2S and COS, but the CS2 would have a n w e n greater retention time. Therefore, tjhese techniques are not satisfactory for an isothermal separation. Nine feet of polyethylene glycol 400 at 46" C. provided only partial resolution of COS and H2S but retained the SO2 for 30 minutes. Attempts to improve t,he COS and H2S resolution would also lengthen SOz retention time unless programmed temperature or a t least the two-temperature technique were employed. Although polyethylene glycol 400 could conceivably be used for a quantitative isot,hermal analysis, not only would the analysis require an excess of 30 minutes per sample, but also the long retention time for SO1 would result in extreme peak spreading and considerable reduction in sensitivity for this gas. EXPERIMENTAL
An F&M Model 720 dual-column, programmed - temperature chromatograph equipped 111th a Gow Mac W-2 thermal conductivity detector and a 1-mv. Honeyme11 recorder was used in this study. Helium carrier gas was
I
n
MINUTES
Figure 1. Separation of HzS, CSz, and SOz on 3Oy0 Triton X-305 at 25" and 75" C. Temp. increased to 75' C. 2 min. after sample injection
used throughout all tests. Gas mixtures for calibration were obtained from Matheson Corp. and other test mixtures were prepared in the laboratory. Additional work was done with a Consolidated Electrodynamics Model 26212A process chromatograph equipped with a Gow Mac W-2 thermal conductivity detector and a Honeywell Model 153 5-mv. recorder. RESULTS AND DiSCUSSiON
A number of liquid phases, solid supports, and solid absorbents were examined t o determine the most satisfactory column and conditions for the resolution of CO,, H2S, SO,, COS, and
cs2.
The solid supports examined included C3 firebrick, Diatoport S, Teflon 6, and Chromsorb G . I t was determined very early in the study that, regardless of the liquid phase, an inert support, such as Diatoport S or Teflon, was a n absolute requirement to reduce tailing to a minimum. Several liquid phases were studied including Benzycellosolve, diisodecylphthalate, squalene, dinonylphthalate, tricresylphosphate, Dow Corning 200/ 500 silicone oil, Carbowax 400, Triton X-305, and Kel-F oil. Most of the liquid phases which did resolve the components of interest,
such as Benzylcellosolve, tricresylphosphate, Carbowax 400, and Dow Corning 200/500, gave results which were similar to the polyethylene glycol 400 used bystaszewski (3). Inall casesit was difficult to obtain satisfactory results under isothermal conditions. I t should be noted that 6 feet of 30% Triton X-305 on Diatoport S provides a fairly satisfactory separation for at least three of the compounds of interest by using the two-temperature t e c h n i q u e Le., 25' and 75" C.-as can be seen in Figure 1. A slightly longer column should provide better resolution of air and COS. This would necessitate a higher final temperature but should cause no difficulty. Six feet of 2Ooj, Benzocellosolve at 30" C. separates air, COS, H2S,SOz,and CS2,in that order, as seen in Figure 2. This separation could be improved by using a longer column and employing the two-temperature technique as with the Triton column. Solid absorbents which have been evaluated include: Molecular Sieve 5A, activated charcoal, silica gel, and activated alumina. Activated charcoal and activated alumina, over a wide range of column lengths and temperatures, retained H2S indefinitely and were therefore unsatisfactory. Excessive column lengths required for the separation of air and H2S on molecular sieve caused severe tailing of the HzS and for t h a t reason all further work with molecular sieve was discontinued. After a continued study, it was determined that a 1-foot by '/+-inch column of aluminum tubing packed with Davison grade 08,80- to 100-mesh silica gel a t 100' C. with a helium flow of 40 ml./minute is satisfactory for resolving air, C 0 2 , COS, H2S, CSn, and SO,. Less than 10 minutes are required for a complete analysis (Figure 3 ) . If the concentration of CO2, COS, and HzS are of the same order of magnitude, the separation ran be carried out in 5 minutes by increasing the column temperature to 120" C., which causes a decrease in the retention time and improves the peak shape of all components (Figure 4). This also results in an improvement in sensitivity. However, when the column temperature is maintained a t 120" C., the resolution will not be quite so good as a t 100" C., and if the sample contains appreciably more COS than HzS, the COS will interfere with the H2S peak. A sample containing only air and SO2 may be separated in less than 2 minute5 by using a column temperature of VOL. 37, NO. 8, JULY 1965
1065
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90
80
AIR,
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50
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z 0
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MINUTES MINUTES
Figure 2. Separation of sulfur gases a t 20% Benzocellosolve
30" C.
on
Figure 3. Isothermal separation of a 2-ml. sample of sulfur gases on 1 -foot 80- to 1 00-mesh silica gel a t 100" C., 40 ml. of helium per minute Concnr. and attentuotions of each component are: 5.9% C O Z X 64, 5.15% C O S X 32, 3.21% H2S X 16, 1.12% CS2 X 4,
8.96% SO2 X 8
0
1
2
3
4
5
8
MI N U T ES Figure 4. Isothermal separation of a 2-ml. mixture of air, COZ, COS, H2S, CS2, and SO2on a 1 -foot 80/100 silica gel column in 6 minutes at 120" C., 40 ml./min. of helium showing partial resolution of COS-H2S and
c s2-so2
1066
ANALYTICAL CHEMISTRY
160" C. or by using a 6-inch column at 100" C. with a limit of detection of approximately 25 p.p.m. of SO2 for a 5-ml. sample. Villalobos (4) reported problems related to interaction of acid gases such as H2S and SO2 with the support material in liquid coated columns. This was not experienced when using silica gel. If water vapor is present in excess of 100 p.p.m., i t will show u p as a broad band which begins to exit from the column about 20 minutes after sample injection. This does not interfere with the components of interest. However, heating the column between sample injection may be desired to decrease the elution time of the water. Experience with the process instrument equipped with a 5-inch silica gel precut column and a 7-inch silica gel analytical column has not indicated any adverse effects when samples saturated with water vapor were analyzed. This instrument was operated continuously for 24 hours a day; a sample was taken every 10 minutes for a 3-day period. A number of grades and meshes of silica gel supplied by manufacturers other than Davison, as well as various mesh ranges and grades of Davison
silica gel, were evaluated for the separation of these components. None of the other silica gels performed as well as the 80- to 100-mesh Davision grade 08 because of increased tailing, particularly for the SOz. Columns should, in all cases, be prepared with aluminum or stainless steel tubing instead of copper because of the corrosive nature of the sulfur gases. It may also be necessary to clean occasionally the detector block and filaments, depending on usage. I n most cases cleaning can be accomplished in the normal manner using carbon disulfide as the solvent, which may be followed with acetone or methylene chloride. LITERATURE CITED
(1) Adams, D. F., Koppe, R. K., Tappi
(7), (July 1959). D. F., Koppe, R. K., Junnroth, D. M., Zbid., 43, (6), (June 1966). ( 3 ) Stassewski, R., Janak, J., Pompowski, T.. Chem. Anal. (Warsaw) 8 (6). 897905, (1963). (4) Villalobos, R., presented at the 1960 ISA Meeting, Montreal, Canada. C. T. HODGES 42,
(2) Adams,
R. F. MATSON
Research and Development Freeport Sulphur Co. Belle Chasse, La.
