Jan., 1961
SEPARATIOK OF HS,HD
values recorded in Table I11 should be regarded as a necessary condition, but not as a proof of accuracy, for the curves from which 4v0,Aa and A, were read had been carefully constructed to ensure additivity of th'ese quantities, as well as temperature smoothing. The definition'l and calculation (11) Ref. 7. p. 387.
BY GAS CHROMATOGRAPHY
AND
87
of Aa make this an additive quantity, and it follows from equation 2 that A , must also be an additive property of the ions. The application of this principle was very helpful in limiting the positions of the curves in Fig. 1, because it had the effect of increasing the number of data points which had to be considered simult~aneously.
THE SEPARATION OF HYDROGEN, DEUTERIUM AND HYDROGEE DEUTERIDE MIXTURES BY GAS CHROMBTOGRAPHY BY PAULP. HUNTAND HILTOX A. SMITH Department of Chemastry, Universaty o j Tennessee, Knoxcalle, Tennessee Receiued June $0, 1960
The resolution and analysis of t h e components of hydrogen-deuterium mixtures have been accomplished by gas chromatography a t 77°K. Neon was employed as the carrier gas, and the column was chromia deposited on alumina. Orthohydrogen and parahydrogen did not separate on the chromia-alumina column. The separation factor for hydrogen deuteride and deuterium was much greater than that for hydrogen and hydrogen deuteride. The complete separation of deuterium and hydrogen deuteride was also obtained on a silica gel column with hydrogen as the carrier gas, whereas a charcoal column produced very little separation.
Gas chromatography affords a simple method for t'he analysis of t'he hydrogen isotopes. Various degrees of separation have been reported by several investigators.l--B A recent preliminary communications describes the first complete separation of hydrogen, hydrogen deuteride and deuterium by this method. The resolution was accomplished by means of a chromia-alumina column operated at 77'K. with neon as the carrier gas. Details of this separation. as well as experiments with other columns are given in the present contribution. Experimental
A double-acting, piston-type pump furnished sufficient pressure differential for gas flow. The construction of the gas pump was similar to those previously described.7~8with the following modifications. The piston barrel, a proximately 5 in. long, was constructed from 12-mm. yrex glass tubing. A Teflon-covered magnetic plunger, 1.5 in. in length, was fitted inside the chamber. The outlet and inlet connections t o the piston barrel were made of Pyrex tubing with an outside diameter of 6 mm. Valves were constructed from sections of 9-mm: glass tubing approximately in. in length, fitted over 1/2-in. sections of 6-mm. capillary tubing. The capillary tubing was ground on the end, and a section of a microscope cover glass was seated in the narrow space between the capillary end and the connection between the 6- and 9mm. tubing. Indentations were made at the taper seal Apparatus .-The chromia-alumina column consisted of a between the 9- and 6-mm. tubing just above the cover g!ass single piece of copper tubing 12 ft. in length and with an to prevent the cover glass from turning edgewise and stickoutside diameter of 5/16 in. Grade F-1, 8-14 mesh, acti- ing during the pumping process. The inlet leads from each vated alumina, obtained from the Aluminum Company of end of the pump were connected together with glass tubing, America, was crushed and screened through a series of as were also the outlet leads. standard screens. The column packing was prepared from The plunger was moved by two doughnut-shaped Indox 225 g. of 20-40 mesh alumina to which 6.7y0by weight magnets obtained from the Indiana Steel Products Comchromium trioxide was added in 350 ml. of water. The pany of Valparaiso, Indiana. The magnets were clamped mixture was agitated for three hours and the excess liquid in a brass carrier. The magnet carrier was connected by was removed b y filtration. The residue was dried and the means of a string across a pulley to a disc attached to a chromic acid reduced in a stream of hydrogen at 360". motor to furnish reciprocal movement of the plunger. The yellow material turned green upon reduction. Small A slot cut in a disc allowed the stroke length to be properly dust particles were removed by screening following the re- adjusted. The motor speed was 45 r.p.m. duction process. After the column was packed and coiled The system was prepared for operation by evacuation and in a spiral 4 in. in (diameter, water was added to the column flushing with hydrogen and neon. The entire apparatus in order to obtain partial deactivation. Considerable evolu- was then filled with neon to a pressure slightly greater than tion of heat was noted as the water was added. The column that of the atmosphere. When the column was immersed was reactivated when desired by passing a stream 2f nitro- in liquid nitrogen, it was necessary to add more neon to maingen through the column for three hours a t 140-150 . pressure. -4circulatory gas flow system with neon as the carrier tain thishydrogen and deuterium samples were oxidized in a gas was employed with the chromia-alumina column. hotThe copper tube after the samples had passed through the katharometer. The resulting water was adsorbed in silica (1) E. Glueckauf and G. P. Kitt, in D. H. Desty, "Vapor Phase gel and charcoal traps. The flow rate was measured bv a Chromatography," Butterworths Scientific Publications, London, 1957, soap-film meters placed in the circulatory system. Neon pp. 422-427; E. Glueckauf and G. P. Kitt, in the "Proceedings of the was conserved between a series of runs by absorbing the exInternational Symposium on Isotope Separation," Interscience Pubcess from the column in the charcoal trap immersed in liquid lishers, Inc., New York, N. Y.,1958, pp. 210-226. (2) C. 0. Thomas and H. A. Smith, J . Phys. Chem., 63, 427 (1959). nitrogen. Silica gel columns, 6 and 10 ft. in length, were prepared (3) W. R . Moore and H. R. Ward, J . A m . Chem. Soc., 80, 2909 from 40-60 and 60-80 mesh material obtained from the (1958). Davison Chemical Company. The packing was activated (4) W.A. \'an Hook and P. H. Emmett, J . P h y s . Chem., 64, 673 at 140-150° before being placed in the column. Hydrogen, (1960). (5) 9.Ohkoshi, Y. Fujita and T. Kwan, Bull. Chem. SOC.Japan, 31, 770 (1958); S. Ohkosbi, S. Tenma, Y.Fujita and T. Kwan, ibid., 31, 772 ( 1 9 5 8 ) ; S. Ohkoehi, S. Tenma, Y.Fujita and T. Kwan, ibid., 81, 773 (1958). (6) H. A. Smith and P. P. Hunt, J . P h p . Chem., 64, 383 (1960).
5
(7) J. C. Balabaugh, R. G. Larsen and D. .4. Lyon, Ind. EnQ.Chem.. cis2 (1936). (8) F. D.Rosen, Rev. Sd.Inetr., 84, 1061 (1953). (9) C. 0. Thomas and H. A. Smith, J . Chem. Educ, 86, 527 (1953).
as,
PAULP. HUNTAND HILTONA. SMITH
88
2.0 r
HD
100 120 140 160 Time (min.) since introduction of gas sample. Fig. 1.-Elution curves for hydrogen isotopes on chromiaalumina column with neon carrier a t 77%. and 35 cc. per min. flow rate. (A) Deuterium peak with an activated column after introduction of a mixture of Hz, H D and Ds The H* and H D peaks appertred after 114 and 133 minutes, respectively. (B) H,, H D and Dt overlapping peaks when the column is deactivated. (C) H2, H D and De eaks from mixture introduced into partially deactivated cofumn.
neon and helium were employed as the carrier gases a t 77OK.
The hydrogen and helium carriers were vented directly to the atPosphere. Silica gel columns were also employed a t -161 This temperature was obtained with boiling methane. The chamber for the preparation of the mixtures of hydrogen deuterium and hydrogen deuteride consisted of a 100ml. glass bulb carrying two tungsten leads, which were brazed to a coiled nichrome wire. The flask was connected to a capillary manometer through a three-way stopcock. The samples of hydrogen, deuterium and hydrogen deuteride were prepared by e uilibrating mixtures of h dro en and deuterium over thezeated nichrome wire. Lmpfes were injected into the column throu h a by-pass cell. The detection and the recorfing apparatus have been previously described .%e Gases.-Neon was obtained from the Matheson ComOrdinary commercial tank hydrogen was purchased f E z ' t h e National Cylinder Gas Company. Deuterium, reported to be 99.5% pure, was obtained from the Stuart Oxygen Company. Commercial nitrogen and argon were used. All gases were employed without further purification.
.
Results and Discussion Alumina columns' are effective in separating hydrogen and deuterium a t 77'K., but orthohydrogen and hydrogen deuteride overlap. A substance which haa different adsorption a5nitiee for the iso-
Vol. 65
topes' and *catalyzes the conversion of ortho- and parahydrogen but does not catalyze the hydrogendeuterium exchange should make the complete separation of the species possible. Chromia very effectively catalyzes the orthohydrogen-parahydrogen conversion at low temperatures and subsequently no separation of the ortho- and parahydrogen was noted with the chromia-alumina column. The hydrogen peak was effectively sharpened in comparison to the hydrogen deuteride and deuterium peaks. Elution curves for this system with activated and partially deactivated columns are shown in Fig. 1. The leading parahydrogen is equilibrated with orthohydrogen, and likewise the slower moving orthohydrogen is equilibrated with the parahydrogen a t the tail of the peak. For this reason the movement of the peak front should be slowed, while that of the tail should be accelerated. Pure samples of hydrogen produced only one peak indicating that orthohydrogen and parahydrogen were not separated. Freshly mixed samples of hydrogen and deuterium gave only two peaks, and thus ruled out the possibility of hydrogendeuterium exchange as the sample passed through the column. This separation can be very easily adapted to the determination of unknown quantities of the isotopes without either having an equilibrium mixture or a knowledge of the orthohydrogen-parahydrogen ratio. Calibration plots may be obtained for hydrogen, hydrogen deuteride and deuterium from equilibrated mixtures or from samples also subjected to mass spectrographic determination. The percentage composition for unknown mixtures can then be determined from the calibration plots. Neon gives sufKcient recorder deflection for small samples and does not require the oxidation of the isotopes befoi'e detection. Samples of pure hydrogen and pure deuterium of constant volume but varying pressures were passed through the columns. When the areas under the peaks shown in the recorder traces (as determined by the product of peak width a t half height and peak height) were plotted against the pressure of hydrogen or deuterium, straight lines were obtained for each isotope. When a mixture of hydrogen, deuterium and hydrogen deuteride of the same volume and a t a known total pressure were swept through the column, the pressures of hydrogen and deuterium were obtained from the areas under their peaks and the calibration curves. The pressure of hydrogen deuteride was then obtained by subtracting the partial pressures of the hydrogen and deuterium from the total pressure. A mixture of hydrogen and deuterium of known composition was placed in the equilibration bulb and the nichrome wire heated to approximately 1000OK. The equilibrium constant for the reaction H,
+ D2 --ic 2HD
is 3.895 a t this temperature.'O An error of 100' in the temperature of the wire makes such a small change in the equilibrium constant that variation in (10) H. W. Wooley. R. B. Scott and F. G . Brickwedde, J . Reaearch Noll. Bur. Standards, 41, 379 (1948).
Jan., 1961
::c.---
SEPARATION OF Hz, HD AND Dz BY GAS CHROMATOGRAPHY
89
the calculated percentages of hydrogen, deuterium and hydrogen cleuteride in a mixture are within experimental error. A mixture in which the calculated percentages of hydrogen, deuterium and 0.0 0.5 hydrogen deuteride were 17.7, 34.0 and 48.4 gave experimental vahes of 18.1, 33.4 and 48.6,with standard deviations of approximately 1%. The times involved in the analyses could be greatly reduced by increasing the flow rate above 1.o the value of 25-35 cc. per minute used in this research. Helium could undoubtedly be used as a 4 0.0 0.5 1 . 5 carrier gas if the hydrogen were oxidized between the column exit and the katharometer.S However, the thermal conductivity of mixtures of hydrogen and helium exhibits a minimum at certain gas k 1 . 5 concentrations*l so that direct quantitative anal- 3a 1.0 ysis without the oxidation process is not feasible. 8 A column was prepared by depositing chromia % 0.5 -a on flint quartz and the retention times for hydro8 0.0 gen and deuterium studied under conditions similar to those which resulted in successful isotope separa1.5 tions when chromia-alumina columns were employed. The retention times for pure samples were slightly less than four minutes, and indicated that no separation could be obtained. Thus the 0.5 0.0 chromia alone is not responsible for the separation achieved when the alumina was treated with chromia. Materials similar to chromia may also be deposited on the alumina for ortho-parahydrogen 1.0 conversion, and molecules other than water may be employed to deactivate the column. Moore and 0.5 Ward12 have now reported separations similar to * 5 S0.0 l 30 40 50 60 70 80 1that reported here with ferric oxide as the coating for the alumina and carbon dioxide as the deactiTime (min.) since introduction of gas sample. vating agent. Fig. 2.-Elution curves for hydrogen isotopes on silica The results obtained with silica gel columns are gel and charcoal columns. (A) Hn, HD and Dt on silica column at 77°K. Hydrogen carrier at flow rate of shown in Fig. 2. The separation of deuterium gel 144 ml./min. (B) H2 and Dz on silica gel column at 112'K. and hydrogen deuteride a t 77OK. with hydrogen Helium carrier at flow rate of 58 ml./rmn. (C) Hs, HD, and as a carrier gas is comparable to that which has D1on silica gel column at 112OK. Helium carrier at 60 been reported when a column containing molecular ml./min. (D) H2 and D2on silica gel column at 112'K. (E) Hx, HD and sieves is employed.6 Under these conditions, Neon carrier at flow rate of 25 &./mine 2 on charcoal column at 77OK. Hydrogen carrier at helium and neon failed to elute the isotopes from D flow rate of 75 ml./min. the silica gel column. The isotopes could be eluted by these carriers a t -161" (boiling methane), but deuteride was obtained with hydrogen carrier and a the overlapping of peaks prevented quantitative charcoal column at 77OK. This is also shown in Fig. 2. determination of the components of the mixture. Partial resolution of deuterium and hydrogen Acknowledgment.-The authors are grateful to the United States Atomic Energy Commission for (11) J. J. Madison, Anal. Chen., 30, 1859 (1968). (12) W. R. Moore:md H. R. Wrtrd.,J. Phys. Chem., 64,832 (1960). support of this research.
1
zl*o Q
