idea meeting, lal-orsay, 14-15 april 2005 purification of nitrogen (argon) grzegorz zuzel mpi-k...

IDEA Meeting, LAL-Orsay, 14-15 April 2005IDEA Meeting, LAL-Orsay, 14-15 April 2005

Purification of nitrogen (argon)Purification of nitrogen (argon)

Grzegorz ZuzelGrzegorz ZuzelMPI-K HeidelbergMPI-K Heidelberg

Grzegorz ZuzelGrzegorz Zuzel IDEA Meeting, LAL-OrsayIDEA Meeting, LAL-Orsay 14-15 April 200514-15 April 2005

Motivation of this researchMotivation of this research Radioactive noble gases in the atmosphereRadioactive noble gases in the atmosphere Methods of analysisMethods of analysis Purification of NPurification of N22/Ar/Ar

Measurements of Measurements of 222222Rn content in argon gasRn content in argon gas Conclusions and planned activityConclusions and planned activity

OutlineOutline


Ultra-pure LNUltra-pure LN22/LAr will be used in the /LAr will be used in the

GERDA experimentGERDA experiment

- Cooling medium for Ge-crystals- Cooling medium for Ge-crystals

- Passive shield against external radiation- Passive shield against external radiation

- Active shield (LAr)- Active shield (LAr)

Developed techniques could be applied in Developed techniques could be applied in other low-level projectsother low-level projects

MotivationMotivation


OutlineOutline

Motivation of the researchMotivation of the research Radioactive noble gases in the atmosphereRadioactive noble gases in the atmosphere Methods of analysisMethods of analysis Purification of NPurification of N22/Ar/Ar

Measurements of Measurements of 222222Rn content in nitrogen Rn content in nitrogen and argon gasand argon gas

Conclusions and planned activityConclusions and planned activity


Radioactive noble gases in the Radioactive noble gases in the atmosphereatmosphere

SourceSource Concentration (STP)Concentration (STP)

222222RnRn Primordial Primordial 238238UU 10 - ?00 Bq/m10 - ?00 Bq/m33 air air

8585KrKr235235U fission (nuclear fuel U fission (nuclear fuel

reprocessing plants)reprocessing plants)1.4 Bq/m1.4 Bq/m33 air air

1.2 MBq/m1.2 MBq/m33 Kr Kr

3939ArAr CosmogenicCosmogenic 17 mBq/m17 mBq/m33 air air1.8 Bq/m1.8 Bq/m33 Ar Ar

4242ArAr CosmogenicCosmogenic0.50.5 µµBq/mBq/m33 air air50 50 µµBq/mBq/m33 Ar Ar


OutlineOutline





Low-level proportional countersLow-level proportional counters


Counter filling lineCounter filling line

Töpler pump

PusherHg diff.pump

P10Ar

Charcoal trap for He purification

with flowmeter

He

Getter pump

Molecular sieve trap

Si-Getrap

Chromo-sorb trap

Radon transport

trap

NaOHtrap

To the pump

To the bubbler

Counter flange

Mai

n li

ne

Pressure gauge

• Sample Sample purificationpurification

• Mixing with Mixing with counting counting gas (P10)gas (P10)

• Counter fillingCounter filling


222222Rn: Rn: -- only only α-α-decays detected decays detected

- 50 keV - 50 keV threshold (bkg: 0.2 – 2 cpd)threshold (bkg: 0.2 – 2 cpd) - total detection - total detection efficiency ~1.5efficiency ~1.5 abs. detection limit ~30 abs. detection limit ~30 µBq µBq (15 atoms)(15 atoms)

3939Ar and Ar and 8585KrKr: : - - ββ-decays detected -decays detected - 0.6 keV threshold (bkg: 1 – 5 cpd) - 0.6 keV threshold (bkg: 1 – 5 cpd)

- total det. efficiency ~0.5 - total det. efficiency ~0.5 abs. det. limit ~100 µBq abs. det. limit ~100 µBq

(5x10(5x1044 8585Kr atoms)Kr atoms)

SensitivitiesSensitivities


Measurements of Measurements of 222222Rn in gases – Rn in gases – MoRExMoREx ( (MoMobile bile RRadon adon ExExtraction Unit)traction Unit)

222Rn detection limit: ~0.3 μBq/m3


Ar and Kr: mass spectrometryAr and Kr: mass spectrometry

Ar: 10Ar: 10-9-9 cm cm33 (1 ppb; ~1.4 nBq/m (1 ppb; ~1.4 nBq/m33 for for 3939Ar in NAr in N22) )

Kr: 10Kr: 10-13-13 cm cm33 (0.1 ppt; ~0.1 µBq/m (0.1 ppt; ~0.1 µBq/m33 for for 8585Kr in NKr in N22))


OutlineOutline





Distillation Distillation - high costs and energy consumption- high costs and energy consumption

Sparging (e.g. with He) Sparging (e.g. with He) - boiling point for contaminants must be - boiling point for contaminants must be

lower than lower than for the gas to be purified for the gas to be purified - high purity carier gas needed- high purity carier gas needed

AdsorptionAdsorption - successfully used for - successfully used for 222222Rn removal from Rn removal from nitrogen nitrogen - a lot of experience at - a lot of experience at MPI-KMPI-K

Different possibilitiesDifferent possibilities


Henrys lawHenrys law

n = number of moles adsorbed [mol/kg]n = number of moles adsorbed [mol/kg] p = partial pressure of adsorptive [Pa]p = partial pressure of adsorptive [Pa] H = Henry constant [mol/(kgH = Henry constant [mol/(kg··Pa)]Pa)]

H determines the retention volume:H determines the retention volume:

n = H p

VRet = HRTmAds


Purification in the columnPurification in the column

C0

CN

VPVRet H ()

CN

= ½

C0

ads

t

RTm

VH Re

n = Hp


Adsorption modelsAdsorption models

GasGas TTC C [K][K] PPC C [bar][bar]TTCC··PPCC

-0.5-0.5

[K[K··barbar-0.5-0.5]]

H [mol/(kgH [mol/(kg··Pa)]Pa)]

@ 77 K@ 77 KPore size [Pore size [ÅÅ]]

ArAr 151151 4949 21.621.6 22××101022 6.8 6.8

NN22 126126 3434 21.621.6 22××101022 77

KrKr 209209 5555 28.228.2 22××101055 77

RnRn 377377 6363 47.647.6 10101414 ~8~8


Strong binding to almost all adsorbersStrong binding to almost all adsorbers Easy trapping with activated carbon @ 77 KEasy trapping with activated carbon @ 77 K Problem: Problem: 222222Rn emanation due to Rn emanation due to 226226RaRa

- Requires careful material selection- Requires careful material selection

- Activated carbon „CarboAct“:- Activated carbon „CarboAct“: 222222Rn emanation rate (0.3 Rn emanation rate (0.3 0.1) mBq/kg, 0.1) mBq/kg,

~100 times lower than other carbons~100 times lower than other carbons

Purification of NPurification of N22/LN/LN22 from from 222222RnRn


Advanced models needed to describe adsorption of Advanced models needed to describe adsorption of multi-component system Nmulti-component system N22/Kr – e.g. pore size of the /Kr – e.g. pore size of the adsorber and its internal polarity has to be taken into adsorber and its internal polarity has to be taken into accountaccount

Henry coefficient is expected to be higher for pure Henry coefficient is expected to be higher for pure gas phase adsorption (@ T > 77 (87) K for Ngas phase adsorption (@ T > 77 (87) K for N22 (Ar)) (Ar))

- Cooling: LAr (for N- Cooling: LAr (for N22), pressurized liquid gases ), pressurized liquid gases

(for LAr) or gas phase cooling (for LAr) or gas phase cooling

Pores, low polarity and adsorption from gas phase should Pores, low polarity and adsorption from gas phase should lead to H ~1 mol/kg/Palead to H ~1 mol/kg/Pa

Purification of NPurification of N22/LN/LN22 from Kr from Kr


Henry constant and pore sizeHenry constant and pore size

0 .01

0.1

1

10

100

1000

10000

100000

1e+06

1e+07

1e+08

1e+09

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Hen

ry c

oeffi

zien

t H

[ m

ol/(

kg*P

a)

]

Pore size b [ Angstroem ]

N itrogen

Krypton


Molecular sieves, polar (Si/Al ~ 1) 5/10 Molecular sieves, polar (Si/Al ~ 1) 5/10 ÅÅ Hydrophobic zeolite MFI-type: low internal polarity Hydrophobic zeolite MFI-type: low internal polarity

(Si/Al ~ 75), pores ~6.6 (Si/Al ~ 75), pores ~6.6 ÅÅ Hydrophobic zeolite BEA-type: Si/Al ~ 200, pores Hydrophobic zeolite BEA-type: Si/Al ~ 200, pores

~5.3 ~5.3 ÅÅ ““Carbo Act” F3/F4: low Carbo Act” F3/F4: low 222222Rn emanation rate, wide Rn emanation rate, wide

pore size distributionpore size distribution Charcoal Cloth FM 1-250, fabricCharcoal Cloth FM 1-250, fabric Activated Carbon C38/2, optimized for solvent Activated Carbon C38/2, optimized for solvent

recoveryrecovery

Considered adsorbersConsidered adsorbers


Experimental setupExperimental setup

gas

liquid

600-L dewar with Kr-enriched (100 - 400 ppt)

liquid nitrogen

Mass spectr.

N2

6.0

Samplepurif ication

LN2, LAr

100/300-cm3 column filled w ith adsorber

bubbler

VRet H ()VP

C0

CN


ResultsResults

0 2 4 6 8 10Vmadsm3kg0

0.2

0.4

0.6

0.8

1

nCoC

0 10 20 30 40Vmadsm3kg0

0.2

0.4

0.6

0.8C NC 0ZEOCAT, 5.3Å, Si/Al ZEOCAT, 5.3Å, Si/Al 200 200

Synthetic carbon, CarboActSynthetic carbon, CarboAct


ResultsResults

Adsorber descriptionAdsorber description NN

HH

[mol/Pa/kg][mol/Pa/kg]

Molecular sieve 5Molecular sieve 5Å, Si/Al Å, Si/Al 1 1

(Carl Roth GmbH)(Carl Roth GmbH)

no purification observedno purification observed

Molecular sieve 10Molecular sieve 10Å, Si/Al Å, Si/Al 1 1

(Carl Roth GmbH)(Carl Roth GmbH)

≥ ≥ 11 >> 2 2 10 10-4-4

Zeolite, ZEOCAT, 5.3Å, Si/Al Zeolite, ZEOCAT, 5.3Å, Si/Al 200 200

(Südchemie(Südchemie))

4 4 ± 1± 1 (6 (6 ± 1± 1) ) 10 10-3-3

Zeolite, MFI-Type (powder), 6.6Å, Si/Al Zeolite, MFI-Type (powder), 6.6Å, Si/Al 75 (Zeochem)75 (Zeochem)

1 1 ± 1± 1 (6 (6 ± 2± 2) ) 10 10-3-3

Synthetic carbon, CarboActSynthetic carbon, CarboAct

(CarboAct)(CarboAct)

1 1 ± 1± 1 (6 (6 ± 2± 2) ) 10 10-2-2


222222Rn removal rather easy, even from LNRn removal rather easy, even from LN22

– Low Low 222222Rn emanation rate of the adsorber requiredRn emanation rate of the adsorber required

Ar removal impossible (no Ar reduction observed)Ar removal impossible (no Ar reduction observed)

Kr removal requires:Kr removal requires:– Low temperature gas phase adsorptionLow temperature gas phase adsorption– Activated carbons seem to be more suitable than zeolitsActivated carbons seem to be more suitable than zeolits– Pore size-tuning required Pore size-tuning required

Purification of NPurification of N22 – Summary – Summary


Purification of ArPurification of Ar

(Almost) no difference between Ar and N(Almost) no difference between Ar and N22 for for adsorption on activated carbonadsorption on activated carbon

However higher temperatures have to be However higher temperatures have to be considered (~100 K for pure gas phase considered (~100 K for pure gas phase adsorption)adsorption)

222222Rn removal is not a problemRn removal is not a problem


OutlineOutline

Motivation of the researchMotivation of the research Production of NProduction of N22 and Ar and Ar

Radioactive noble gases in the atmosphereRadioactive noble gases in the atmosphere Methods of analysisMethods of analysis Purification of NPurification of N22/Ar/Ar




222222Rn in nitrogen and argonRn in nitrogen and argon

LN2 class 4.0, usually ~ 50 m3 (STP) of gas taken

CRn ~ 50 µBq/m3

Two measurements performed for Ar, class 4.6

Sample Sample No.No.

DescriptionDescription CCRnRn in trap 1 in trap 1

[mBq/m[mBq/m33]]CCRnRn in trap 2 in trap 2

[mBq/m[mBq/m33]]

11 117 m117 m33 of gas taken of gas taken 2.9 2.9 ± 0.2± 0.2 ––

22 141 m141 m33 of gas taken of gas taken 0.20 0.20 ± 0.02± 0.02 < 0.0005 (90% CL)< 0.0005 (90% CL)


OutlineOutline

Motivation of the researchMotivation of the research Production of NProduction of N22 and Ar and Ar

Radioactive noble gases in the atmosphereRadioactive noble gases in the atmosphere Methods of analysisMethods of analysis Purification of NPurification of N22/Ar/Ar




Nitrogen purification intensively studiedNitrogen purification intensively studied - Adsorbers selection based on the adsorption theory- Adsorbers selection based on the adsorption theory - Experimental tests are ongoing (zeolites already tested)- Experimental tests are ongoing (zeolites already tested) - For Kr removal from nitrogen better suitable seem to be - For Kr removal from nitrogen better suitable seem to be activated carbonsactivated carbons - Adsorption from the pure gas phase has to be studied- Adsorption from the pure gas phase has to be studied

First results of purity and purification tests for Ar available First results of purity and purification tests for Ar available - - 222222Rn removal from Ar possibleRn removal from Ar possible - - 222222Rn concentration in argon seems to be significantly higher than in Rn concentration in argon seems to be significantly higher than in nitrogen of similar qualitynitrogen of similar quality

Purity tests for different supply chains are planned (NPurity tests for different supply chains are planned (N22/Ar)/Ar) Although the program was slightly extended it is Although the program was slightly extended it is

progressing as scheduled progressing as scheduled


idea meeting, lal-orsay, 14-15 april 2005 purification of nitrogen (argon) grzegorz zuzel mpi-k...

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