Fusion Engineering and Design 49–50 (2000) 855–861

Analysis of hydrogen isotopes with a micro gaschromatograph

Yoshinori Kawamura *, Yasunori Iwai, Toshihiko Yamanishi,Satoshi Konishi, Masataka Nishi

Tritium Engineering Laboratory, Department of Fusion Engineering Research, Japan Atomic Energy Research Institute,Shirakata Shirane 2-4, Tokai-mura, Naka-gun, Ibaraki-ken 319-1195, Japan

Abstract

In the fuel cycle system of fusion reactors, analysis of hydrogen isotopes is very important from the view point ofsystem control. The gas chromatograph (GC) with cryogenic separation column (cryogenic GC) is one of the mostextensively used methods for the analysis of hydrogen isotopes. The micro GC with cryogenic column is expected toimprove analysis time, that is a major disadvantage of conventional GC. The present authors have modified the microGC to use its separation column at cryogenic temperature for H2, HD and D2 mixture analysis. Obtained retentiontime of H2, HD and D2 was about 85, 100 and 130 s, respectively. Peak resolution between H2 and HD, these arenearest each other, was about 1.0. These result suggests that the column developed in this work attained the practicallevel for the separation of hydrogen isotopes without tritium. Present detection limit of hydrogen isotopes was about100–200 p.p.m., and it can be improved further by adjustment of separation column. © 2000 Elsevier Science B.V.All rights reserved.

Keywords: Hydrogen isotope; Micro gas chromatograph; Fusion fuel cycle; System control; Retention time; Tritium

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1. Introduction

In the fuel processing system of the fusionreactor, quick and accurate analysis of hydrogenisotopes is very important for system control andtritium accountancy. The gas chromatograph(GC) is one of the most reliable methods for the

analysis of hydrogen isotopes from the viewpointof accuracy and reproducibility, and the gas chro-matograph with cryogenic separation column(cryogenic GC) has been used for analysis ofhydrogen isotope mixture gas in general [1,2]. The‘cryogenic’ separation column used is based onthe fact that difference of sorption rate amonghydrogen isotopes becomes larger at lower tem-perature. However, the cryogenic GC has thedisadvantage of long retention time, that is to say,time taken to complete the analysis is long, typi-cally tens of minutes. Particularly, it is not suit-

* Corresponding author. Tel.: +81-29-2826393; fax: +81-29-2825917.

E-mail address: kawamura@tpl.tokai.jaeri.go.jp (Y. Kawa-mura).

0920-3796/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.

PII: S0 920 -3796 (00 )00302 -1

Y. Kawamura et al. / Fusion Engineering and Design 49–50 (2000) 855–861856

able for the application that requires quick re-sponse such as monitoring of rapid compositionchange or controlling the system using analyticalresults.

On the other hand, the micro gas chro-matograph (micro GC) that has small thermalconductivity detector (TCD) utilizing semiconduc-tor processing technology has been recently devel-oped commercially. As a result of using smallTCD, the amount of sample gas needed for analy-sis became smaller, and sample gas was separatedenough even if flow rate became large, and theretention time became shorter finally. The microGC with cryogenic separation column (cryogenicmicro GC) is expected to improve analysis timefor hydrogen isotopes as mentioned above. In thiswork, the micro GC is modified to immerse itsseparation column into liquid nitrogen, and was

attempted to obtain separation performance inpractical uses.

2. Experimental

For analysis of hydrogen isotopes, a separationcolumn must be kept at cryogenic temperatureusing refrigerant such as liquid nitrogen. How-ever, a separation column of the regular microGC commercially distributed is integrated into thecolumn module with a reference column. In thiswork, separation column was excepted from theinside of the column module, and connectors wereattached to tips of residual separation columnducts inside of the column module. Another edgeof connector faced the outside of module. Hand-made separation column with ducts was attachedto these connectors at the outside of module. So,the separation column was immersed into refriger-ant out of column module as shown in Fig. 1. Amicro GC used in this work was P200 made byMTI Analytical Instruments Inc., and was pur-chased from AERA JAPAN Ltd.

Fig. 2 shows a schematic diagram of experimen-tal apparatus. Sample gas used in this work wasH2, HD and D2 mixture gas balanced with he-lium. It was made by mixing H2/D2 mixture, H/Dratio was 1.0, and He in the mixing tank. Theconcentration of total hydrogen isotopes in thesample gas was adjusted between 200 p.p.m. and100% by adding He. HD was produced by passingthe sample gas through the catalyst bed. Thecatalyst packed into the bed was platinum-styrenedivinyl benzene (Pt-SDB) which can generate HDfrom H2 and D2 at room temperature by equi-librium reaction. Micro GC has an internal pump,which is used to transfer the sample gas fromprocess gas stream to the gas injector. In thiswork, sample gas in the mixing tank was trans-ferred to micro GC via the catalyst bed by inter-nal pump of micro GC. The carrier gas of microGC used in this work was neon gas, which isusually used for the cryogenic GC when hydrogenisotopes and helium mixed gas is analyzed, be-cause difference of thermal conductivity betweencarrier gas and sample gas is large [1,2].

Fig. 1. A photograph of the cryogenic micro gas chro-matograph. (A micro GC was modified to be able to immerseits separation column into liquid nitrogen).

Fig. 2. A schematic diagram of experimental apparatus.

Y. Kawamura et al. / Fusion Engineering and Design 49–50 (2000) 855–861 857

Fig. 3. A photograph of cryogenic separation column madeand tested. (packing: Al2O3+MnCl2, 0.5 mmf×50 cml).

Separation column used in this work was hand-made packed column. Alumina with MnCl2 coat-ing or alumina with FeCl3 coating is used for thepacked material of a cryogenic separation columnfor analysis of hydrogen isotope mixture gases[1,2]. In this work, separation column that waspacked with MnCl2 coated alumina was preparedas shown in Fig. 3. Packed material of which 19w/w of the ratio of MnCl2 to alumina haveenough capability for separation [3]. However, itwas not clear how much MnCl2 was held onalumina in this work, because some amount ofalumina and MnCl2 were lost during the process-ing and not all MnCl2 were held on alumina. Startmaterials were 25 g of activated alumina and 100cm3 of 1.0 N of MnCl2 aqua. This column wasused for analysis at liquid nitrogen temperature(77 K). The retention times of each species in thecolumn and peak resolution were observed in thiswork. Specification of this column and experimen-tal conditions were listed in Table 1.

3. Results and discussions

Fig. 4 shows a typical chromatogram that wasthe result of analysis for 1.3% of H2, 2.4% of HDand 1.3% of D2 mixture balanced with He. Reten-tion time of H2, HD and D2 were 85, 100 and 130s, respectively, and that of He was 15 s. Thosewere much shorter in comparison with the case ofconventional cryogenic GC. Micro GC used inthis work can change the amount of sample gasused for analysis between 1.0×10−7 cm3 and2.55×10−4 cm3. When total hydrogen isotopesconcentration is higher, smaller amount of samplegas is preferable. The peak for H2 are usuallymuch close to that of HD, and these two peaksare hardly separated when the amount of samplegas used for analysis is large. For example, in thecase of analysis for 26.3% of H2, 47.4% of HDand 26.3% of D2 mixture (no He), amount ofsample gas needed to separate H2 peak from HDpeak was only about 5.0×10−7 cm3. On theother hand, in the case of analysis for 131 p.p.m.of H2, 237 p.p.m. of HD and 131 p.p.m. of D2

mixture balanced with He, peaks of three hydro-gen isotopes were not sharp even if 2.55×10−4

Table 1Specification and experimental condition for the column madein this work

GC carrier gas Ne (99.99% pure)Pressure (primary) 559 kPaFlow rate 0.95–3.2 cm3/min(Head pressure) (166–393 kPa)

Column Packed columnAl2O3/MnCl2Packed materials

Packed weight 0.12 gParticle size 100–120 meshLength 50 cm

0.5 mmInner diameterTemperature 77 K (LN2)

Sample gas H2, HD, D2/HeConcentration of totalHydrogen isotopes 250 p.p.m.�100%

Fig. 4. Typical chromatogram of H2, HD and D2 mixturebalanced with He.

Y. Kawamura et al. / Fusion Engineering and Design 49–50 (2000) 855–861858

cm3 of sample gas, which is maximum with thepresent system, was injected to the separationcolumn. Signal-to-noise (SN) ratio for H2 and HDof above latter case were about 3.0 and 2.3,respectively and a peak of D2 was not able to bedetected. From these results, it is considered thatthe detection limit of hydrogen isotope in this caseis between about 100 p.p.m. and about 200 p.p.m.because 2.0 and above of SN ratio are needed tocount a signal as a peak. During the series ofexperiment, deterioration of column, such as de-crease of retention time and peak resolution, wasobserved for a few hours. Column performancerestituted by purge of the separation column atroom temperature or baking. The reason ofcolumn deterioration is considered adsorption ofwater vapor in the column, and it is consideredthat water mainly penetrate from the connectionbetween the separation column and column ductby leak. Residual moisture in/on the inner surfaceof the experimental apparatus is also probable(but, not mainly). Since the amount of adsorbent

in this column is much smaller than conventionalcryogenic separation column, capability ofcolumn is more sensitive to the existing watervapor even if amount of water vapor is verysmall. Leak tightness and elimination of watervapor from sample gas are strongly requested forthe cryogenic micro GC.

When the separation capability and practicalityof column are evaluated, the height equivalent toa theoretical plate and the peak resolution areused. The height equivalent to a theoretical plateis defined as

HETPi=LNi

��Ni=16

�VRi

Wi

�2

, (i=1, 2, . . . , n)�

,

(1)

where HETP is the height equivalent to a theoret-ical plate [cm], L is the column length [cm], N isthe number of theoretical plate, VR is the reten-tion volume in time [s] which is same as theretention time and W is the peak width in time [s].In addition, (n) means number of peaks and (i)means the peak number. Fig. 5 shows an exampleof the relationship between HETP and carrier gasflow rate. Generally, HETP decreases with flowrate of carrier gas, but it increases with decreaseof flow rate in case when flow rate is too small,that is to say, HETP indicates the minimumvalue. This is because mass transfer resistancebetween gas phase and adsorption phase on thepacking material becomes smaller with decreasingof flow rate and the influence of molecular diffu-sion of adsorbate becomes larger at smaller flowrate. For the column used in this work, HETPdecrease with carrier gas flow rate, but it can beseen that HETP increase with decrease the flowrate at lower flow rate region. Under this experi-mental condition, minimum of HETP for H2, HDand D2 were 0.058, 0.049 and 0.048 cm, respec-tively. These are corresponding to 862, 1020 and1041 of the numbers of plate. A column, whichhas smaller HETP or larger N, shows better sepa-ration capability. Capability of the column madeand used in this work was fairly good in compari-son with the conventional packed column (typicaldiameter: 3.0 mm, length: 2.0 m).

The peak resolution between peak 1 and peak 2is defined asFig. 5. Change of HETP with change of carrier gas flow rate.

Y. Kawamura et al. / Fusion Engineering and Design 49–50 (2000) 855–861 859

Fig. 6. Change of peak resolutions among H2, HD and D2

with change of carrier gas flow rate.

case that tritium (HT, DT and T2) are containedin the sample gas, it is expected that HT is hardlyseparated from HD or D2. Then, it is also ex-pected that peaks of DT and T2 become broaderthan that of D2, that is to say, detection limit oftritium becomes larger. More improvement forseparation column is needed to analyze all hydro-gen isotopes.

The partial pressure of hydrogen isotopes in aseparation column is considered to be low. There-fore, it is assumed that adsorption isotherm ofhydrogen isotope on MnCl2 coated alumina at 77K is expressed with Henry law. The retention timefor each hydrogen isotope is expressed using thedispersion model modified with moment method[3,4] as follows:

tR’ −

toi

2ep

eb

−ep

=rpK ’ep

zeb

u, (3)

tR’ = tR− (tR)inert, (4)

(tR)inert=�

1+ep

eb

−ep� zeb

u, (5)

where tR is the mean residence time of adsorbategas in the column [s], (tR)inert is the mean residencetime of inert gas in the column [s], toi is the timerequired for injection of adsorbate[s]. Void frac-tion of adsorbent particle [-] and that of column[-] are op and ob, respectively. Then, rp is apparentparticle density of the adsorbate [g/cm3], z iscolumn length [cm] and u is superficial velocity ofcarrier gas [cm/s]. K % is Henry law constant ofhydrogen/alumina system in neon carrier [cm3/g].Fig. 7 shows chromatographic parameters for H2,HD and D2 on alumina obtained by the momentmethod (Eq. (3)). As shown in Eq. (3), datashould be expressed with the line that is passingon the origin and its slope is equal to K %, but thegaps between data and expected lines are large. Itis understood as follows: value of the void frac-tion of column is difficult to estimate becausemicro packed column is so fine that the packingcannot be confirmed to be complete, and thedensity and void fraction of alumina particle areused for calculation in place of the values ofMnCl2 coated alumina. Retention time can be

R12=2�VR2−VR1

W1+W2

�, (2)

where R12 is the peak resolution between peak 1and peak 2 [-]. VR1 and VR2 are the retentionvolume for peak 1 and peak 2 in time [s], respec-tively. Then, W1 and W2 are the peak width ofpeak 1 and peak 2 in time [s], respectively. Fig. 6shows the peak resolution among H2, HD and D2.The peak resolution for each combination de-creases with increase of carrier gas flow rate,because adsorbate does not move between gasphase and adsorption phase sufficiently at largerflow rate. As derived from Eq. (2), 1.0 and aboveof the value of peak resolution is needed to attainthe separation capability of column to the practi-cal level. In this work, the peak resolution be-tween H2 and HD, these are the nearest peak todistinguish, scarcely exceed 1.0. Therefore, it isconcluded that separation capability of thiscolumn has attained the practical level for analy-sis of hydrogen isotopes without tritium. In the

Y. Kawamura et al. / Fusion Engineering and Design 49–50 (2000) 855–861860

estimated using Eq. (3) with K % obtained fromFig. 7. Fig. 8 shows the estimated retention timefor each hydrogen isotope at 0.3 of ob. Retentiontime becomes small with increase of flow rate, butdistance among peaks also becomes small. Asknown from Fig. 8, drastic improvement of sepa-ration capability can not be expected about thismicro packed column, because minimum of voidfraction is 0.28. It may be needed to change thepreparation technique of column to improvecolumn capability.

4. Conclusion

The cryogenic micro GC was developed for theanalysis of hydrogen isotopes by modifying amicro GC. Fine packed column with aluminacoating with MnCl2 was made and tested usingcryogenic micro GC at 77 K. Typical retentiontime of H2, HD and D2 were 85, 100 and 130 s,

Fig. 8. Estimated retention time for the column with MnCl2coated alumina. (0.5 mmf×50 cml, void fraction of column:0.3).

Fig. 7. Chromatographic parameter for H2, HD and D2 onMnCl2 coated alumina obtained from Eq. (3).

respectively, and those were much shorter in com-parison with the case of conventional cryogenicGC. Minimum of peak resolution exceeded 1.0.The capability of cryogenic micro GC developedand tested in this work attained the practical levelfor analysis of hydrogen isotopes without tritium.Analysis of separation characteristics in thepresent study suggests the cryogenic separationcolumn prepared has adequate performance.However, application of the column having otherfiguration, e.g. capillary column, for the cryogenicseparation column should be also studied to im-prove detection limit of cryogenic micro GC.

For further improvement of the micro GC forhydrogen isotope analysis, use of alternative pack-ing that works at higher temperature is expectedto be advantageous. For instance, modified mor-denite has been reported to work at 172 K byEngelmann et al. [5] that suggests possible elimi-nation of liquid refrigerant. Preliminary experi-

Y. Kawamura et al. / Fusion Engineering and Design 49–50 (2000) 855–861 861

ment to use mordenite in micro GC exhibitedpoor separation at dry ice temperature. Moremodification for the column preparation will beneeded to attain its separation capability to thepractical level.

References

[1] W.R. Moore, H.R. Ward, Gas-solid chromatography ofH2, HD and D2. Isotopic separation and heats of adsorp-tion on alumina, J. Phys. Chem. 64 (1960) 832.

[2] T. Uda, et al., Gas chromatography for measurement ofhydrogen isotopes at tritium processing, J. Chromatogr.586 (1991) 131–137.

[3] T. Yamanishi, H. Kudo, Adsorption equilibrium ofhydrogen isotopes on alumina adsorbents for gas-solid chromatography, J. Chromatogr. 475 (1989) 125–134.

[4] P. Schneider, J.M. Smith, Adsorption rate constants fromchromatography, AIChE J. 14 (1968) 762–771.

[5] U. Engelmann, et al., Mordenite Columns for HydrogenIsotopes Gas Chromatography, Proceedings of the FourthInternational Symposium on Fusion Nuclear Technolol-ogy, FT-P11, Tokyo, Japan, 1997.

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