Hildebrandt, A. F.

English

NASA Technical Reports Server

July 6, 1965 JAMES E. WEBB 3,192,730 
ADMINISTRATOR O F  THE NATIONAL AERONAUTICS 
AND SPACE ADMINISTRATION 
HELIUM REFINING BY SUPERFLUIDITY 
Filed Feb. 5, 1963 
G -I / 
(NASA CR OR TMX OR AD NUMBER) s 
https://ntrs.nasa.gov/search.jsp?R=19700025630 2020-03-17T02:03:55+00:00Z
3,192,730 United States Patent Office ,,,, , , ,,
-,-- - 7  - 
B%iEkiEUM R;%Pl&Ttiir.JG BY SUPERFLUIDITY 
3a:nes E. Webb. Administrator of ithe National Aeronau- 
tics and ~ ~ n c b  Admi.~Zstration, with respect to an inven- 
tion of Akin P. CIi?debwndt 
Piled Peb. 5, 1963, Ser. No. 25Qt484 
8 Claims. (C1. 62-15) 
The present invention relates to a process for the pro- 
duction of ultra-pure helium. More particularly, the 
present invention relates to a process for refining helium 
in which impurities such as hydrogen, nitrogen and oxy- 
gen are removed by filtering these substances from the 
helium while the helium is in a condition which renders 
it especially suitable for such filtration. 
In the past, helium has been purified by various tech- 
niques including diffusion, gettering procedures, and a 
variety of chemical means. These processes are costly 
and are incapable of producing helium of the purity ob- 
tained according to the practice of the present inven- 
tion. As is well known to those skilled in the art, a 
growing need has developed for highly refined or ultra- 
pure helium. For example, such helium is particularly 
useful in gas chromatography. 
Thus, it is a principal object of the present invention 
to provide a simple and economical process for produc- 
ing ultra-pure helium. 
It is another object of the present invention to pro- 
vide an apparatus and process wherein helium is puri- 
fied by filtration. 
It is a further object of the present invention to pro- 
vide an apparatus and process for producing ultra-pure 
helium wherein the helium is first brought to the lambda 
11 state, i.e., below the lambda point, and then passed 
through a suitable filter to remove impurities. 
Other objects and advantages of the present invention, 
it is believed, will be apparent from the following descrip- 
tion of specific embodiments thereof when read in con- 
nection with the drawings. 
Briefly, the present invention comprises bringing liq- 
uid helium to the lambda 11 state and then filtering this 
helium through a filter having pore sizes which permit 
the passage of substantially only helium. 
Helium in the lamba I1 state is often referred to as 
helium PI or superfluid helium. The latter designation 
will often be used in the following description. 
Superfluid helium is prepared by bringing helium to 
a temperature below the lambda point at 2.19' K. and 
extremely low pressures. At this point, the superfiuid 
form appears. Superfluid helium has an extremely low 
viscosity, less than about lo-" poise, as compared with 
the normal viscosity for liquid helium which is greater 
than 10-6 poise. This extremely low viscosity permits 
superfluid helium to pass through tightly packed filters 
with relative ease. Thus, since the major impurities pres- 
ent in superfluid helium are frozen solids having very 
low vapor pressures, these impurities may be removed 
by filtration. Furthermore, since superfiuid helium has 
a viscosity of practically zero, it will flow through a filter 
having extremely fine pores which filter will stop other 
gases or cause them to diffuse through the filter thousands 
of times slower than superfluid helium. 
A suitable filter for use in the present invention is 
a filter bed comprising a compacted means of iron oxide 
particles having a particle size of about 10-15 microns. 
As previously noted, almost all impurities are solids at 
superfluid helium temperatures, and are blocked by the 
extremely fine pores betvieen the iron oxide particles. 
5 Although the vapor pressures of the impurities are ex- 
tremely low, single atoms are occasionally liberated, but 
these atoms are arrested by the iron oxide filter particles 
when they collide therewith and this further reduces the 
flow of impurities through the filter. 
10 The present invention is further usefnl in separating 
isotopes of helium. For example, helium 3, which ex- 
ists in minute amounts together with the most common 
isotope, helium 4, may be separated by the process of 
this invention. Although helium 3 is a l i q ~ ~ i d  at  super- 
15 fluid helium temperatures and does not adhere to iron 
oxide particles, it is not superfluid, i.e., it has a rela- 
tively high viscosity, and AOWS through the filter much 
less rapidly than superfluid helium 4. In the present de- 
scription, all refirence to helium designates helium 4 un- 
20 less otherwise indicated. 
In one embodiment of the present invention, the fil- 
tering process is accelerated by use of the fountain effect 
by slightly heating the helium on the effluent side of 
the filter. 
25 Referring now to the drawings: 
FIGURE 1 illustrates, in partial section, the appa- 
ratus which may be used in the present invention. 
FIGURE 2 is a detailed illustration of the filtration 
and collection units of the apparatus of the present in- 
30 vention in which these units are provided with means 
for employing the fountain effect. 
The apparatus illustrated in FIGURE 1 comprises an 
outer shell 1 containing liquid nitrogen 2.  Shell 1 is 
35 supported by a cylindrical stand 3 which is filled with tar 4. An inner shell 5 is supported within shell 1 by 
bottom support 6 and is provided with a plurality of 
separating means 7. Inner shell 5 is substantially filled 
with liquid helium. A vent 9 is provided on shell 5. 
40 Cap 11 seals shell 5 in airtight relation therewith. Cap 
11 is provided with three port members 12, 13 and 14. 
Breaker rod 41 extends through port 14 in airtight rela- 
tion therewith. 
A filter apparatus including a glass fitting 15 having 
a vent 16 and a break-tip B7 is positioned within shell 
" 5. Fitting 15 is connected by tube 18 to a filter assem- 
bly indicated generally by numeral 19. 
Filter assembly 19, as illustrated in more detail in FIG- 
URE 2, comprises an outer shell 20 which contains a 
60 bed of fine grains of filter material, e.g., iron oxide, 
21. The bed of filter particles 21  is closed at each end 
by sintered iron plugs 22 and 23. The lower end of 
shell 20 is provided with tube 24. Preferably, tubes 18 
and 24 are welded to shell 20. Fitting 15 is prefer- 
55 ably fabricated from glass, tube 18 from a material hav- 
ing the same coefficient of expansion as glass such as 
ICovar, while shell 20 and tube 24 are preferably fabri- 
cated from steel. 
Optionally, the apparatus may be provided with a 
60 means indicated generally by numeral 36 for heating the 
hclium on the eftlnent side of filler 19. Heating means 
36 comprises a housing 34 which encloses a tnbe 38 which 
has a dark or heat absorbing surface. In this embodi- 
ment, housing 37 is preferably attached to tube 24 by a 
65 tube 39 which is preferably iabricated frcm Kovar. 
3,L,l",r.,^? 
'-t 
. 7  13 
Movsing 33 is preferably faSlicated from glass and pro- fluid without passing impu~ii :~s  may be uscd. Given lhc 
viikd with Kovar connecting tube 40 at its lower cnd. concspt of thc ljreserit isvention, only ronttne experimen- 
'c3dhea the 2nparatas of the present invention is provided t3iiaLl 1s rcquj-ed to cEctc2m;~~ cperaL$e fiiters. TIie irorl 
with heating nieans 56, a suitable heat source (not oxide filter bed 21 employed in the foregoing examlj!~ 
shown), e.g., a source of infrared light, may be posi- ~vas yrep?ed from Optical London Red Ro~ige, i.e., par- 
tioned outside shell I. In this embodiment, shells 1 and ticles having a sizc of about 10-15 lxicrons. However, 
5 ure pieferably fablicated from a transparent material it is io be understood that these din~cnsions are inc!icati~e 
such as ghss. Thils, the infrared light easily passes only of an order of magnitude and are not to be coil- 
through sLells 1 and 5 and housing 37 to heat coil 3%. sidered as limitations on the present invention. 
Thc beatin: of coil 33 causes the i~elislm in the coil lo The apparatus of the present invcniion may be fabri- 
become ~ :on-~ 'a~er i l~~id .  This, of cowse, lenders the cated from any suitclble mote~ials a d  niateriais other 
helium incnp:tblc oE flowing back through filter bed 21 than those inrlicatec! as being plefcrred in the foregoiilg 
2nd ih~,  process of d;Susion will force superfiuid helium dcscription may be i:sed. 
through SItsr 19 and into coil 38. Thus, the flow of Having fully described the present invention, it is lo  
he!iiim is acccleraied. be rinderstood that it is not to be limited to the specific 
Filler assembly 19 and, iL' present, heating means 36 details set forth, but is of the full scope of the appended 
are connected to acc~mnlation chamber 25 by tube 42. claims. 
Accum~llation vessel 25 is also provided with tube 26 I claim: 
which is provided with arms 27 and 28 at its upper end. I. A process for refining helium by separating inz~url- 
Arm 27 leads to a high pressure vessel 30 having a safety 29 ties which are solids under conditions at which said heii- 
valve 31. Aim 28 is provided with a pressure transfer um is superiluid comprising bringing helium to the lamb- 
dia;lirapm 32 and a pressure gauge 33. The diaphragm da II state; and passing said helium through a filter, said 
32 functions to i:olaie the interior of tube 26 from pres- filter having pore sizes suficienily largc to pass said heli- 
sure gause 33. Tube 25 is further provided with s top  urn in the lrlmbda I1 state but suf5cien:ly small to sub- 
coc!i 634 v/LL:e ti*be 27 is provided with stopcock 35. 2i  stantially prevent the passage of impurities. 
The operation of this apparatus is described in the 2.  k proccss For refinicg heli~im by separating irnpuri- 
lollcwing e7am;le. ties which are solids uncier conditions at which said heIi- 
Example um is superCuid con~prisicg snbjecting said h e l i ~ m  to a 
temperature 01 less than about 2.19" K. and rccluced 
i3eh-e assembly, filter apparatus 19 was thoroX>ghly ,, prezsure whereby ~ ~ p e ~ f i , ~ l d  hel i~~in s prodaced and pass- 
clearled to remove ail inipurities and heated to 360" C. ' iIig said mpelfl:~id 1;~lium through a filter, said filter hav- 
to remole moisture while stopcock 31 and vent 16 w e ~ e  ing a pole size which is sufiicient to permit snid soperfluid 
~ 0 n ~ e c l e d  io a vacunm. e~nnect ion of S ~ O ~ C C C ~  $4 and helium to pass therethrough, but inwficient to permit 
vent 16 to a vacuLin1 allows moisture on either side of the passage of iR3pri!ies. 
the filter bed 21 to be eliminated. After heating and 3 -  3. A process for refining helium by separating imp~iri- 
evacuating, stopcock 34 VJ2S closed and Vent IQd sealed ties which are solids under conditions at which said heli- 
by melting down its narrow neck. The entire filtering um is stlper-uid conlprising s~lbjecting said helium to re- 
system attached lo cap PI was then lowered into Dewar duced temperarure and pressure such that superfluid heli- 
shells 1 and 5. Shell 5 was filled with liquid helium to unl having a ~iiscosity of less than about 10-l1 poise is 
a level abcve accnmulaiion chamber 25, but below vent ,, and passing said sllperfluid helium through a 
9. The space between shell 5 and shell 1 had previous- filter having a pore size sufficient to permit the passage 
ly been substantially filled with liquid nitrogen. Cap 11 of said superfluid helium, but insuEcient to permit the 
was then scaled lo shell 5. passage of impvrities. 
The liquid h-liam was then made superfluid by reduc- 4. A proccss for refining helium by separating impuri- 
ing the temperature to below 2.19" K. and evacualing ,; ties which are solids under conditions at which said M i -  
shell 5 by connecting vent 9 to a vacuum pump. After urn is su,-.edcid comprising reducing said helium to super- 
thc helium hed been made superfiuid, breaker rod 41 was &jid heiiLln1 hzvirjz a viscosity of less than about 10-11 
pushed down to break breaktip 17. This pennittea poise and passiFg said superfluid helium through a filter 
superfluid I~el iun~ to enter glass 1'5 and flow through filter having a pore size on the older of abolrt 10-15 microns. 
19. Since substantially only superfluid helium is capa- 5. A process for refining helium by separating impnri- 
ble of passing through filter bed 21, which comprised ties which are solids under at which said heli- 
ieweler's rouge,  virtual!^ ali of the impurities in the heli- um is superfluid comprising reducing sai6 helium to super- kin wcre removed by filter 49. The hydro-static Pressure fluid helium having a viscosity of less than about 10-" 
of the helium in shell 5 caused the superfluid helium to poise and passing said heliunl through a fiber comprising 
flow into collection chamber 25. 100 CC. helium was col- 5? compacted pariicles of iron oxide, said particles having 
lected in chamber 25 after thirty minutes. The enlirc the particle size of about 10-1 j micro3s. body of helium in sheell 5 was then heated to above the 6. A process for refining helium by separating impuri- 
lambda point such that no superfluid helium remained. ties which are solids under conditions at which said heli- 
The helium in chamber 25 was thereby prevented flom um is superfluid comprising reducing said helium to super- 
leaving chamber 25 since, as normal helium, it was in- cQ fluid helium having a viscosity of less than abmt 10-11 
capable of flowing through filtcr bed 21. poise, passing said superfluid helium throingh a filter hav- 
&lap 11 and the attached filter apparatus was then re- ing a pole size sl;Ecienl to pats said superfiuid hsliunl 
moved as a unit fronl shell 5. Chamber 25 was then but insufficient to pass inlpurities and hsating said super- 
heated to vaporize the helium to Cause it to fill Pressure fluid lle]ivm after it passes through said filter to a degree 
vessel 30. Stopcock 35 was then closed to seal the pres- such it is not supera,,id. 
sure vessel 30 from the remainder of the apparatus. 7. A process for refining normal helium by separating As previously described, it has been found that the Bow ilnpuriiies which are solids under conditions a: which said 
of helium may be accelerated by providing the apparatus 
with heating means 36 and then heal means to helium is siiperfluid comprising reducing said normal M i -  
vm to superkid helium having a viscosity of less thzn 36. 
As will readily be apparent to those in the art, 70 aballt 10-11 poise, passing said superfluid helinm through 
the specific enlbodillzeslts of the present invention which a filtei., said filter having a pore size suscient to pass said 
has bten described in the folegoing example may be superfluid helium, but insuffcient to pass impurities, heat- 
modified in various manners without departing from the ing said superhid helium after it  asses through szid 
scope oC this invention. E j ~ i  exzmple, any micro-porous filter to a degree such that it is not superhid, and then 
Liter hating a pore size which is effective to pass super- 7 3  herting said helium to a degree such that it vaporizes. 
3,192,730 
5 6 
8. A process for refining normal helium containing im- 3,098,732 7/63 Dennis ----------------- 62-9 
purities selected from the group consisting of oxygen, 
nitrogen, hydrogen and mixtures thereof, comprising re- OTHER REFERENCES 
ducing said normal helium to superfluid helium having Helium Three, Daunt, Ohio State Univ. Press, 1960, 
ia viscosity of less than about 10-11 poise, and passing 5 empllasis on pp. 148, 149, QD 181.H4 ~ 9 .  
said superfluid helium through a filter having a pore size Low Temperature Physics and Chemistry, Dillinger, 
sufficient to pass said superfluid helium, but insufficient Univ. of wis. Press, 1958, particular emphasis pp. 29-32 
to pass said impurities. and 146-148. OC 278 25 1957. 
References Cited by the Examiner Liquid ~el i<m, Atkins, Comb. Univ. Press, 1959, with 10 particular emphasis pp. 9, 10, 94, 95, 291, 292. 
- - 
UNITED STATES PATENTS 
2,982,106 5/61 Ambler ----------------- 62-9 NORMAN YUDKOFF, Primary Examiner. 
3,057,167 10/62 Yendall ---------------- 62-11 


Helium refining by superfluidity Patent

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