Analysis of Chlorine
Cell Gas by Gas Chromatography
E. E. NEELY Columbia-Southern Chemical Corp., Corpus Christi, Tex.
t A chromatographic method for the analysis of chlorine cell gas, which requires a twa-column separation, has been developed. Two cammerciol laboratory chromatographs a r e used with a manifold in the carrier gas streom sa that the gases unresolved on the first column may be passed ta the second column whila the resolved gases, being detrimental to the second column, a r e diverted from the second column. This method i s adaptable to any sample which requires a twocolumn separation. An unusual sample collection system is used. Constant valume sample loops are filled a t the sample point and transported to the laboratory for analysis.
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has appeared in the literature on the chromatographic analysjs of chlorine cell gas. Two reports (f,)'3 have described a chromatographic chlorine cell gas analyzer which analyses for per cent rhlorine only, hut none which describes an analysis for all gases present. Chlorine cell gas normally contains 90 to 98% CL, 1to 3% 02, 1to 3% COa 0 to 1% H1,0 to 1% CO, and 0 to 3% Nz. No one chromatographic column has been found which will efficiently separate these six gases within a reasonable length of time; therefore, a twocolumn separation is necessary. A Molecular Sieve column effectively separates Os, N?, Hz, and CO, hut C1, and COS must he separated by other means and at the same time must be diverted from the Molecular Sieve column to avoid damaging the column. The use of a two-column separation has been reported many times; however, either the two columns are in a straight series where all components of the sample pass through both columns or an especially designed instrument is used for the analysis. The method presented here uses two commercial laboratory chromatograuhs connected with a manifold in the carrier gas line so that each chromatograph may be used separately for other types of analyses or can be used with one another for a chlorine cell gas analysis. Even though H1 is separated on the Molecular Sieve column, its normal concentration is so low and its detection in a He carrier is so poor that another analysis is made on a second sample for its determination. The sample is injected ERY LITTLE INFORMATION
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ANALYTICAL CHEMISTRY
Figure 1. Ten-milliliter sample loop connected to sample valve
into a N? cnrrier stream and passed through a thermal conductivity detector cell without column resolution. APPARATUS
The two commercial chromatographs used are Perkin-Elmer Models 154A and 154C Vapor Fractometers with a Leeds & Northrup LL5 mv. recorder. The H, analyzer consists of a Gow Mac Model 9677-AEL detector with its necessary circuitry. The cell is mounkd in a heavily insulated box with no temperaturc control facilities. For sample injection, a Burrell Kromatog glass gas sampling valve is used. All three detectors are wired through a selector switch to the one recorder. The Model 154A chromatograph is equipped with a 12-foot column of 30 wt. % Fluoroluhe grease (Type LG160), Hooker Electrochemical Co., on 30- to 50-mesh Chromosorb. The 154C is equipped with an 8-foot Molecular Sieve column, Type 13X, 30- to 50mesh, Linde Air Products Co. PROCEDURE
Calibrated, IO-ml. sample loops (Figure 1) are filled a t the sample point as follows: The gas is pulled from the cell t)y gravity displacement of an alkaline solution a t the end of the sampling apparatus. The gas passes through a water trap to collect any condensed moisture, a concentrated H,SO, scrubber for drying, a glass wool trap, and a Mg(ClO& tube for final drying before passing through the sample loops. The gas is confined in the loops by turning the stopcocks so
that the sample stream will bypass the loops. When the sample is injected at 1 (Figure Z), there are three He carrier gas streams flowing. The first flow passes through the 154A instrument, then through valve 7a to the PerkinElmer gas sampling valve, 8 (which is in inject position), and floas through one leg of the gas sample valve's loop connection so that i t goes directly through the column, sensing detector, rotameter, and then to vent. The second flow passes through regulator 4a, valve 7b, restrictor valve Sa, and then to vent. The third flow is to the Model 154C reference cell, 3c, and through the other loop connection leg of the gas sample valve to a restrictor valve, 9h, and to vent. The third flow only maintains a He atmosphere In the reference side of the detector. The two Perkin-Elmer instruments are operated at 40" C., primarily for stability of operation. The H, analyzer is operated at room temperature. The Fluorolube column separates the sample into three fractious. The first recorded on the chromatogram contains H,, O,, NP, and CO; the second CO,; and the third CI,. Under the operating conditions used, 5 minutes after the injection, the gases contained in the first recorded peak have passed the manifold s y s t m , but CIS, although separated and recorded, has not reached the manifold. At this point valve 7a is turned to vent so that C12 will not reach the Molecular Sieve column and valve Zb is turned so that the He carrier may transport the gases contained in the first peak on to the Molecular Sieve column for separation. At the point when the flow changes are made, the .Molecular Sieve column detector is also switched to record so that a continuous chromatogram is obtained. By the use of the pressure regulator 4a, the He carrier flow through the Molecular Sieve colnmn is not changed. For the HP determination, a second sample is injected into a Nz carrier gas stream and passed through the Gow Mac detector cell without column refiolution. One peak is obtained which is read frorn a calibration curve. DISCUSSION
A typical chromatogram of chlorine cell gas is illustrated in Figure 3. Good resolution of all components is obtained in less than 20 minutes, whereas the same analysis by wet chemical methods (8) requires much longer. When compared to values obtained by wet chemical methods, the analyses in volume %
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Figure 2.
obtained chromatographically are accurate within 10.02%. The chromatogram is read by measuring the peaks and applying predetermined correction factors to the measurements. Since the 0 2 , N2, and CO are measured by a different detector cell, the areas of these peaks are related to the one combination peak obtained from the Fluorolube column. It was found that Hz, in the concentration normally obtained, has little influence on the size of the combination peak; therefore, the three peaks obtained from the Fluorolube column are considered as being lOOyo minus Yo HP determined from the Gow Mac cell. The calibration factors used for calculation of the chromatograms are checked weekly. A very slow change in the characteristics of the Fluorolube column is probably due t o the action of the large (10 ml.) chlorine sample on the column packing. However, a column has lasted as long as 18 months before having to be replaced. The operation of the Hz detector is based entirely on the fact that the thermal conductivity of H2 is so far removed from any other components in the sample and from the WI carrier that the size of the one peak obtained is dependent on the concentration of H2 in the s~lmple. Most of the sample points for chlorine cell gas are at or near atmospheric pressure, are widely separated in the plant, and the gas is saturated with water. Also, chlorine is either soluble in or reacts with most confining solutions; therefore, sampling of the chlorine cell gas by liquid displacement cannot be used and pressure cylinder filling is not practical. For these reasons, the use of the constant volume sample loop was developed. Blight variations in sample size injected into the chromatograph are obtained due to slight pressure varia-
Flow diagram
tions during sampling; however, this has little effect on the calculated results. The sample loops, Figure 1, are covered with black tape to prevent the reaction of Hz in the sample with Clz to form HC1, which is catalyzed by sunlight. If HC1 is formed in the sample, then a low Hz value and a high COz value would be obtained because of the H2 decrease and because HC1 is resolved with COz from the Fluorolube column. The results obtained to date have never shown any evidence of this reaction taking place. When the loop is attached to the chromatograph for injection, there is a dead area between the four stopcocks which must be purged with He before the sample is injected. The gas in this area, usually air, is injected into the Fluorolube column and then vented. This requires about 5 minutes. However, this operation can be done while the 02, N2, and CO are being recorded from the previous sample.
No trouble with chlorine corrosion has been experienced because all samples injected are carefully dried. However, the equipment is checked often for leaks since, if chlorine does escape to the atmosphere, the point of leakage will increase rapidly due to the corrosive action of chlorine and atmospheric moisture. Figure 2 shows a 1-foot Molecular Sieve column placed in the carrier gas line outside the instrument. This column is used for two purposes. It was found that as the four gases, Hz, 02, Nz, and CO, travel from the Fluorolube column to the 8-foot Molecular Sieve column, they disperse into the carrier gas causing some overlapping of the peaks. This short column concentrates the gases enough before reaching the 8-foot column that a much better separation is obtained. This short column also traps any CO2 which may get pass the valve manifold, thus protecting the 8-foot column from contamination. This short column is regenerated weekly by heating to 350' C. under vacuum and remains efficient. The flows used in this analysis are set so that the best possible chromatogram is obtained in the shortest time. These flows are primarily dependent on the column characteristics and the length of tubing between the two instruments. LITERATURE CITED
(1) Dudley, W. G., Poetker, B. F. (to
The Dow Chemical Co.), U. S. Patent 2,850,640 (Sept. 2, 1958). (2) Murrav. R. L..Kircher. W. S..' Trans. Electroc6ek. floc.' 86, 7 (1944). (3) Spreckler, S. B., ZSA Journal 4, 514 (1957). '
RECEIVEDfor review April 14, 1960. Accepted July 22, 1960. Division of Analytical Chemistry 15th Southwest Regional Meeting, ACd, Baton Rouge, La., Dee. 3-5, 1959. XB
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Figure 3. Chlorine cell gas chromatogram
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VOL. 32, NO. 11, OCTOBER 1960
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