1 / 29

Purification of nitrogen (argon)

Purification of nitrogen (argon). Grzegorz Zuzel MPI-K Heidelberg. Outline. Motivation of this research Radioactive noble gases in the atmosphere Methods of analysis Purification of N 2 /Ar Measurements of 222 Rn content in argon gas Conclusions and planned activity. Motivation.

wylie
Télécharger la présentation

Purification of nitrogen (argon)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Purification of nitrogen (argon) Grzegorz Zuzel MPI-K Heidelberg IDEA Meeting, LAL-Orsay, 14-15 April 2005

  2. Outline • Motivation of this research • Radioactive noble gases in the atmosphere • Methods of analysis • Purification of N2/Ar • Measurements of 222Rn content in argon gas • Conclusions and planned activity IDEA Meeting, LAL-Orsay

  3. Motivation • Ultra-pure LN2/LAr will be used in the GERDA experiment - Cooling medium for Ge-crystals - Passive shield against external radiation - Active shield (LAr) • Developed techniques could be applied in other low-level projects IDEA Meeting, LAL-Orsay

  4. Outline • Motivation of the research • Radioactive noble gases in the atmosphere • Methods of analysis • Purification of N2/Ar • Measurements of 222Rn content in nitrogen and argon gas • Conclusions and planned activity IDEA Meeting, LAL-Orsay

  5. Radioactive noble gases in the atmosphere IDEA Meeting, LAL-Orsay

  6. Outline • Motivation of the research • Radioactive noble gases in the atmosphere • Methods of analysis • Purification of N2/Ar • Measurements of 222Rn content in nitrogen and argon gas • Conclusions and planned activity IDEA Meeting, LAL-Orsay

  7. Low-level proportional counters IDEA Meeting, LAL-Orsay

  8. Counter filling line • Sample purification • Mixing with counting • gas (P10) • Counter filling IDEA Meeting, LAL-Orsay

  9. Sensitivities • 222Rn: -only α-decays detected - 50 keV threshold (bkg: 0.2 – 2 cpd) - total detection efficiency ~1.5  abs. detection limit ~30 µBq (15 atoms) • 39Ar and 85Kr: - β-decays detected - 0.6 keV threshold (bkg: 1 – 5 cpd) - total det. efficiency ~0.5  abs. det. limit ~100 µBq (5x10485Kr atoms) IDEA Meeting, LAL-Orsay

  10. Measurements of 222Rn in gases – MoREx (Mobile Radon Extraction Unit) 222Rn detection limit: ~0.3 μBq/m3 IDEA Meeting, LAL-Orsay

  11. Ar and Kr: mass spectrometry Ar: 10-9 cm3 (1 ppb; ~1.4 nBq/m3 for 39Ar in N2) Kr: 10-13 cm3 (0.1 ppt; ~0.1 µBq/m3 for 85Kr in N2) IDEA Meeting, LAL-Orsay

  12. Outline • Motivation of the research • Radioactive noble gases in the atmosphere • Methods of analysis • Purification of N2/Ar • Measurements of 222Rn content in nitrogen and argon gas • Conclusions and planned activity IDEA Meeting, LAL-Orsay

  13. Different possibilities • Distillation - high costs and energy consumption • Sparging (e.g. with He) - boiling point for contaminants must be lower than for the gas to be purified - high purity carier gas needed • Adsorption - successfully used for 222Rn removal from nitrogen - a lot of experience at MPI-K IDEA Meeting, LAL-Orsay

  14. Henrys law • n = number of moles adsorbed [mol/kg] • p = partial pressure of adsorptive [Pa] • H = Henry constant [mol/(kg·Pa)] • H determines the retention volume: n = H  p VRet = HRTmAds IDEA Meeting, LAL-Orsay

  15. Purification in the column n = Hp IDEA Meeting, LAL-Orsay

  16. Adsorption models IDEA Meeting, LAL-Orsay

  17. Purification of N2/LN2 from 222Rn • Strong binding to almost all adsorbers • Easy trapping with activated carbon @ 77 K • Problem: 222Rn emanation due to 226Ra - Requires careful material selection - Activated carbon „CarboAct“: 222Rn emanation rate (0.3  0.1) mBq/kg, ~100 times lower than other carbons IDEA Meeting, LAL-Orsay

  18. Purification of N2/LN2 from Kr • Advanced models needed to describe adsorption of multi-component system N2/Kr – e.g. pore size of the adsorber and its internal polarity has to be taken into account • Henry coefficient is expected to be higher for pure gas phase adsorption (@ T > 77 (87) K for N2 (Ar)) - Cooling: LAr (for N2), pressurized liquid gases (for LAr) or gas phase cooling • Pores, low polarity and adsorption from gas phase should lead to H ~1 mol/kg/Pa IDEA Meeting, LAL-Orsay

  19. Henry constant and pore size IDEA Meeting, LAL-Orsay

  20. Considered adsorbers • Molecular sieves, polar (Si/Al ~ 1) 5/10 Å • Hydrophobic zeolite MFI-type: low internal polarity (Si/Al ~ 75), pores ~6.6 Å • Hydrophobic zeolite BEA-type: Si/Al ~ 200, pores ~5.3 Å • “Carbo Act” F3/F4: low 222Rn emanation rate, wide pore size distribution • Charcoal Cloth FM 1-250, fabric • Activated Carbon C38/2, optimized for solvent recovery IDEA Meeting, LAL-Orsay

  21. Experimental setup IDEA Meeting, LAL-Orsay

  22. Results Synthetic carbon, CarboAct ZEOCAT, 5.3Å, Si/Al  200 IDEA Meeting, LAL-Orsay

  23. Results IDEA Meeting, LAL-Orsay

  24. Purification of N2 – Summary • 222Rn removal rather easy, even from LN2 • Low 222Rn emanation rate of the adsorber required • Ar removal impossible (no Ar reduction observed) • Kr removal requires: • Low temperature gas phase adsorption • Activated carbons seem to be more suitable than zeolits • Pore size-tuning required IDEA Meeting, LAL-Orsay

  25. Purification of Ar • (Almost) no difference between Ar and N2 for adsorption on activated carbon • However higher temperatures have to be considered (~100 K for pure gas phase adsorption) • 222Rn removal is not a problem IDEA Meeting, LAL-Orsay

  26. Outline • Motivation of the research • Production of N2 and Ar • Radioactive noble gases in the atmosphere • Methods of analysis • Purification of N2/Ar • Measurements of 222Rn content in nitrogen and argon gas • Conclusions and planned activity IDEA Meeting, LAL-Orsay

  27. 222Rn 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 IDEA Meeting, LAL-Orsay

  28. Outline • Motivation of the research • Production of N2 and Ar • Radioactive noble gases in the atmosphere • Methods of analysis • Purification of N2/Ar • Measurements of 222Rn content in nitrogen and argon gas • Conclusions and planned activity IDEA Meeting, LAL-Orsay

  29. Conclusions and planned activity • Nitrogen purification intensively studied - Adsorbers selection based on the adsorption theory - Experimental tests are ongoing (zeolites already tested) - For Kr removal from nitrogen better suitable seem to be activated carbons - Adsorption from the pure gas phase has to be studied • First results of purity and purification tests for Ar available - 222Rn removal from Ar possible - 222Rn concentration in argon seems to be significantly higher than in nitrogen of similar quality • Purity tests for different supply chains are planned (N2/Ar) • Although the program was slightly extended it is progressing as scheduled IDEA Meeting, LAL-Orsay

More Related