as Chromatographic Determination of Ozone an ther Products from the Electrolysis f Fluoride J. A. DONOHUE and F. S. JONES Research and Development Department, American Oil Co., Whiting, Ind.
A gas-solid chromatography technique has been developed for determination of hydrogen, oxygen, oxygen difluoride, and ozone in gaseous products from the electrolysis of wet hydrogen fluoride. The gases are separated on a silica gel column ternperature-programmed from -75" to - 10" C. to minimize decomposition. This technique represents the first application of gas chromatography far the determination of ozone. the mechanism of the electrolysis of wet hydrogen fluoride requires accurate analyses of the gaseous product, which is a mixture of hydrogen from the cathode and oxygen, oxygen difluoride, ozone, and sometimes fluorine (4) from the anode. Initially, we separated ozone by adsorption on silica gel a t -78" C. (3, 6) and then determined ozone and oxygen difluoride separately by iodimetry (6) and fluoride ion colorimetry (8), However, this scheme was too slow to follow changes in yield with time, and gave no information on hydrogen and oxygen, R e have therefore developed an analysis for the gases by gas-solid chromatography on silica gel programmed from -75" to - 10" C. Detector responses are calibrated with individual components of known purity. Because the temperature is kept low, and because the column is no longer than necessary to separate hydrogen and oxygen, the decomposition of ozone is minimized. To our knowledge, this is the first time gas chromatography has been used to determine ozone. CERTAINING
EXPERIMENTAL
Apparatus. Figure 1 is a schematic diagram of the temperature - programmed gas chromatograph. All parts that come in contact with the sample are made of fluorocarbon plastic or of dry, degreased metals (nickel, copper, or stainless steel) passivated with oxygen difluoride and ozone. Gaseous products from the HF electrolysis cell are swept through the sampling loop and a flow counter (soap bubble meter) by a stream of ordinary helium. The helium carrier gas is purified by
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ANALYTICAL CHEMISTRY
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HELIUM SUPPLY
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VENT VIA FLOW COUNTER OR V A C U U M P U M P
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CONTROLLERS
k GASES FROM ELECTROLYSIS CELL OR F O R STANDARDIZATION
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passage through molecular sieves (Linde, 5A) cooled in liquid nitrogen, and then is divided into two streams, one for reference and the other for the sample, each kept at 40 cc./minute by its own controller (Moore Products Co., Model 63BU-L). The sample stream passes through a Perkin-Elmer 1.06-cc. sampling valve where i t is mixed with the gases to be analyzed. The two streams then pass through twin columns of silica gel (Davidson, Grade 923, 100200 mesh), 6 inch by inch in diameter, contained in an insulated can whose temperature is controlled by a stream of dry air precooled by liquid nitrogen. Effluent streams from the columns go to a thermal conductivity cell (Gow Mac-No. 9285) with matched filaments, operated by a Gow Mac 9999D d.c. power supply. The chromatograms are traced on a 10-mv. strip chart recorder. Detector upsets caused when samples at atmospheric pressure are introduced into the column at 30 p.s.i.g. are minimized by surge tanks in each gas stream, just downstream of the detector. The vacuum pump, the reference and sample stream, and gases in excess of those needed for analvses are vented into a hood. Calibration Materials. Hydrogen (NCG) and oxygen (Air Products) were used as purchased. The oxygen difluoride (Allied Chemicals) contained 1.5% oxygen, for which correction was made. The ozone was produced by a Wels-
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bach Ozonator (Model T-23) and was freed of oxygen by adsorption on silica gel at -78' C. (3). Ozone sample pressure was varied by changing the temperature of the silica gel from -78' to 0' C. Because some ozone decomposed to oxygen in the transfer from the silica gel to the sampling valve, the purity of the calibration samples ranged from 70 to 95% ozone, as determined by correcting for the oxygen peak. Calibration Procedure. The silica gel columns are cooled to -75' C. while the sample loop is filled t o a known pressure with the gas for calibration. The sample is then swept into the column which is allowed to warm to -10" C. (Warming requires about 5 minutes.) The calibration graphs of peak area us. sample pressure (corrected if impure) were obtained. Those for oxygen, oxygen difluoride, and ozone are linear over the range studied, but the one for hydrogen shows considerable curvature. Analysis of Sample. The sample is swept into the sampling loop by a stream of helium adjusted to keep the hydrogen concentration in the sensitive range (via. where curvature is small), and the analysis is carried out by the same procedure as described for the calibration. Because about 2 minutes are required to cool the columns, maximum sampling rate is one every 7 minutes. Electrolysis yields for each gas can be calculated as per cent of current
Table 1.
Gas 0 2
OF2 0 s H2
Estimation of Precision Rel. Sensitivity precision, % (relative t o 0 2 ) *1.9 1.00 h2.0 1.24 rt2.4 1.13 f2.4 NO. 03
if, in addition to the gas chromatographic. data, the electrolysis cell current and the gas flow rate from it are determined a t the time of sampling.
A typical chromatogram is shown in Figure 2, together with the range of retention times for the maxima of known peaks. The variation in retention times
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is caused by minor variations in the temperature program. However, such errors are no greater than the precision of the method. Thus, when the pro-
0 2
RESULTS AND DISCUSSION 0
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Figure 2.
TIME, S E C O N D S Typical analysis of gases from wet HF electrolysis Range of retention time for peak maximum [seconds): HZ 8-9, 0 2 = 20-35, OF2 85-1 20, 0 8 = 210-250
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Precision of the method and the sensitivity of the detector are given in Table I. Because preparation of known mixtures was not feasible, precision was estimated from the calibration data. As indicated, the relative sensitivity for hydrogen is low.
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Figure 3. Conditionr;
KF = 1.0 mole
TIME, M I N U T E S Continuous monitoring of the electrolysis of wet HF
?&,HzO
= 0.57 mole ?&, temp. = 12'-15' C., applied volts = 6.0, continuous operation, anode = Ni (1 0 cn2), cathode = Ni (26 am2)
VOL. 38, NO, 13, DECEMBER 1966
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gram was intentionally started a t -70" or -85' C. instead of the usual -75' C., the peak areas did not change by more than 3%. The small peak ( A ) at 0 seconds occurred in all samples because of pressure changes during sampling. The relatively small hydrogen peak is a consequence of poor sensitivity. Although the size of this peak can be increased somewhat by increasing the hydrogen concentration, this approach is limited because of the rapid change in the slope of the hydrogen calibration curve a t high concentration. Peaks ( B )and (C) occurred only when the hydrogen fluoride was approaching dryness and are believed to arise from fluorine reactions. They were seldom apparent when the water concentration was kept above 0.2 mole yo (4). The small displacement from the base line before the ozone peak is an indication of ozone decomposition. Such decomposition also occurred during the calibration, so it is not considered a source of serious error. An application of this analysis for monitoring an electrolysis experiment is shown in Figure 3. The rapid Sampling permitted changes in product yields to be followed closely-for example, the rapid increase in ozone during the first hour and the drop in oxygen difluoride
after about 3 hours. Moreover, the displacement of hydrogen from 100% indicates the extent of depolarization, and the discrepancy between anode and cathode (Hz) totals may indicate unidentified, probably nonvolatile, anode products. Such results are giving a more complete picture (4) of the reaction than was previously possible (I,fJ,Q).
is detectable only above 200-300 p.p.m. Presumably, the use of more sensitive detectors and/or larger samples would permit detection down to 1 p.p.m. or less. ACKNOWLEDGMENT
We thank J. Marlcovich for assisting with the experimental work. LITERATURE CITED
CONCLUSfONS
In our experiments, the formation of fluorine was a condition we wished to and could avoid (4). However, the fact that fluorine shows discrete peaks in the chromatograms indicates that the gas chromatographic technique might be extended to include this gas. Our attempts to passivate the equipment with fluorine were not successful; but we did not try extensive daily passivation ( 7 ) ,which may be effective for such studies as the reactions of fluorine with water or base (8). Alternatively, such reactions could be run with excess water or base to give complete fluorine conversion and thus avoid passivation problems. Another possible extension is to such important areas as the determination of ozone and other gases for air pollution studies. In our present setup, ozone
(1) Briner, E., Tolun, R., Helv. Chim. Acta. 31, 172 (1948). (2) Cady, G. H., J . A m . Chem. SOC.57, 246 (1935). (3) Cook, G. A,, et al., Advan. Chem. Ser. 21,44 (1959). (4) Donohue, J, A., Nevitt, T. D., Zletz, A., Ibid., 54, 192 (1966). ( 5 ) Donohue, J. A,, Wilson, W. A. (to Standard Oil Co., Ind.) U. S. Patent 3,134,656 (May 26, 1964). (6) Engelbrecht, A, Nachbaur, E., Monatsh. Chem. 90, 367 (1959). (7) Hamlin, A. G., et aZ., AXAL. CHEY. 35, 2037 (1963). (8) Hensley, A. L., Barney, J. E., Ibid., 32, 828 (1960). (9) Rodgers, H. H., Evans, S.,Johnson, J. H., J. Electrochem. Soc. 111, 701 (1964).
RECEIVEDfor review July 26, 1966. Accepted September 26, 1966. Work
~Research ~ ~ Office-Durham ~ e " c ' tunder " sE " eAsA ~ r~:$~ Contract DA-31-124-ARO(D)-78.
Quantitative Gas Chromatographic Analysis of Metals, Alloys, and Metal Oxides, Carbides, Sulfides, and Salts RICHARD S. JUVET, Jr. and RICHARD L. FISHER Deparfment o f Chemistry and Chemical Engineering, University o f Illinois, Urbana, 111.
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b This paper describes a
with CC1, in a sealed capillary, no studies of the quantitative gas chromatographic analysis of nonvolatile inorganic compounds have yet appeared. In this paper it is demonstrated that certain pure metals, alloys, carbides, oxides, sulfides, and metal salts may be fluorinated vith elemental fluorine and quantitatively determined in a rapid gas chromatographic procedure.
rapid, direct method for the quantitative analysis of alloys and certain metal oxides, carbides, sulfides, aceta tes, and nitrates by in sifu reaction with Fz in a specially designed reactorinjection system of a gas chromatograph followed by separation and analysis of the volatile metal fluorides on a chemically conditioned column. The reaction and elution properties of the elements: U, S, Se, Te, W, Mo, Re, Si, 8, Os, V, Ir, and Pt in various chemical forms have been evaluated. Quantitative determination of the first seven elements is reported.
c
INTEREST has developed recently in the quantitative determination of metal halides. Hamlin, Iveson, and Phillips (4) determined UFe in mixtures of UFa, Clz, ClK, ClF, and HF. Phillips and Timms (9) employed the quantitative ONSIDERABLE
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ANALYTICAL CHEMISTRY
gas chromatographic determination of silicon and germanium tetrachlorides produced by reaction of silanes and germanes with gold(II1) chloride as a measure of silicon and germanium in mixed hydrides. Dennison and Freund ( I ) described the analysis of SnCLAsCls mixtures, and Sie, Bleumer, and Rijnders (11), recently determined a number of metal chlorides in mixtures quantitatively. Juvet and coworkers (6, 14) described a sensitive and selective, corrosion-free, flame photometric detection system giving linear response for metal halides over four orders of magnitude. The present authors in a previous publication (6) showed that several volatile metal fluorides can be chromatographed on a chemically conditioned poly(tetrafluoroethy1ene) column coated with poly(trifluoromonochloroethylene). With the exception of Sievers, Wheeler, and ROSS' (1.9) interesting work on the determination of Tic14 following reaction of TiOz
EXPERIMENTAL
Chemicals. The chemicals used in this study were obtained from commercial suppliers as follows: W, Mo, Re, Os, UC2 (Research Inorganic Chemical Co.); UOZ, Mo&, WC, VC (Alpha Inorganics, Inc.); UOz(CzHs0z)z * 2Hz0, UOz(T'JOs)2 * 6Hz0, Mooa, VzOs, S (J. T. Baker Chemical Co.); Se (B. F. Drackenfelt and Co., N. Y.); Te (C. A. F. Kahlbaum, Berlin); Mo-W alloys (courtesy P. R. Mallory and Co., Inc., and Climax Molybdenum Coo of Michigan); MOSZ (native molybdenite crystals, A. D.
