investigation and improvement of cryogenic adsorption purification of argon from oxygen

8/8/2019 Investigation and Improvement of Cryogenic Adsorption Purification of Argon From Oxygen

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Gas Sep. Purif Vol. 9, No. 2, pp. 137-145, 1995Copyright % 1995 Elsevier Scien ce Ltd

Printed in Great Britain. All rights reserved0950-4214/95 $10.00 + 0.00

Investigation and improvement of cryogenicadsorption purification of argon from oxygen

A. N. Fedorov

NPO Cryogenmash , Balashiha-7, Mosco w Region, Russia

The intensification of argon purification from oxygen by cryoadsorption is feasible bycooling the adsorbent in an argon medium and by dehydration under decreased temperature.A modified NaA zeolite is used as an adsorbent. The argon purification process has beeninvestigated at an oxygen concentration of 3% at 90 K and at a degree of purificationof 1 ppm. The conditions of the occurrence of argon capillary condensation have beenconsidered. The zeolite modification with the best adsorption performance has been definedand an improved method of argon purification from oxygen has been developed.

The calculated relations for defining the value of the adsorbent dynamic capacitance asa function of the rate of flow, and the argon preadsorption as a function of the adsorbentcooling time have been obtained and a plot has been constructed for defining the coefficientof dynamic capacitance decrease under decreased temperature of dehydration. As a result,a calculation formula is proposed for defining the adsorber protective action time underargon p urification from oxygen with allowance for the rate of flow, the argon preadsorptionvalue and the temperature of dehydration.

Keywords: cryogenic purification; adsorption; argon; oxygen; zeolite

Nomenclature

a Constant value (cm3 g-i) T Temperature (K)a0 Equilibrium adsorption value (cm3 g- ) t a Adsorption layer value (nm)a cap Value of argon capillary condensation wo Ultimate volume of adsorption space

(cm3 gg) (cm3 g- )adyn Dynamic capacity (%) (cm3 g-)Calreads Ultimate value of adsorption (cm g- )

Amount of preadsorbed argon (cm3 g- )

Greek lettersspreads4, Amount of adsorbed argon (cm3 g- ) e Coefficient of affinityB Structural constant (Ke2) A Mean effective mass transfer coefficientC Breakthrough concentration of oxygen (%) (1 min - )co Initial concentration of oxygen (%) PO Mass transfer coefficient (1 min-)D Diffusion coefficient (m min- ) Aa Constant value (cm3 g- )a Mean diameter of adsorbent grains (m) P Dynamic viscosity (Pa s)K Coefficient (cm3 g-l min m-i) P Gas density (kg m-)K deer Coefficient of dynamic capacitance decrease o Surface tension of liquid argon (mH m- )K preads Coefficient of preadsorption

ET,,Cooling time (min)

(cm gg min-) Ultimate cooling time (min)L Adsorbent layer length (m) V Molar volume of adsorbed oxygenLO Length of heat exchange zone (m) (cm3 mmoll )P Gas pressure (MPa) VCI, Specific volume of liquid argon

PS Saturated vapour pressure (kPa )(m3 tt)

r Capillary radius (m) w Rate of flow (m min- )

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Cryogenic adsorption purification of argon from oxygen: A. N. Fedorov

Table 1 Investigation results of modified zeolite samples

Zeolite sample no.

Parameter 1 2 3 4 5 6 7 8

Grain mean diameter (m x 10m3)Mixture flow rate (m min-)Pressure (M Pa)

Oxygen volumetric fraction (%)Perio d of protective effect (min)Saturation period (min)Ultimate cleaning degree (% x 1 Om4)

Dynamic capacity before breakthrough (%)Mass transfer coefficient (I min )Mea n effective mass transfer c oefficient (I min-)Mass transfer zone lengt h (m)Equilibrium adsorption rate (cm3 g-)Ultimate volume of adsorption space (cm3 g-)Structural constant ( Km 2 x 10-e)Degree of utilization of zeolite equilibrium

capacity (%)

2.4 2.3 2.30.94 1.04 0.97

0.122 0.127 0.1322.5 2.92 2.99

215 255 255540 360 420

1.5 1.7 1.96.26 11.9 11.4

26.4 30.52 28.47

5.5 30.42 23.440.315 0.12 0.144

136.5 139.1 131.40.16 0.163 0.1565.2 4.72 5.69

36.8 68.4 69.5

2.30.734

0.1253.06

12 022 5

14.75

21.54

20.470.145

31.2

2.31.12

0.123.1716 0

0.67.48

-

15 20.1825.16

41.6

2.4 21.06 0.98

0.122 0.125 -3.29 3.9218 15031 5 24 0 -

1.4 1.2 -11.85 7.96 -31.1 28.1320.95 28.13

0.18 0.125 -149.2 168.3 91.2

0.179 0.204 0.1054.05 4.84

61.1 36.7

from Figure 2,a small-size front of an adsorption waveis generated at a specified flow rate. The init ial portionsof the isographs are linear and characterize the distribu-tion of the oxygen volumetr ic fraction by the layer lengthwithin the smal l breakthrough concentration range. It isevident from these linear portions that external diffusionprevails at the steady-state stage of the process withinthe range of small relative concentrations.

The end portions of the adsorption isographs definethe equilibrium onset in the adsorbate-adsorbent sys-tem: at c/c0 > 0.7 the internal differential resistancestarts to have an effect on the adsorption process.

The dynamic capacity adyn of the adsorbent samples

and the mean effective mass transfer coefficient fi, werefound from the calculation of the flow material balances.

The external mass transfer coefficient & for the experi-mental conditions was determined from Equation (1)using a similar theory for the conditions of purifyingargon from oxygen on synthetic NaA zeolites, whengoverned by the effect of external diffusion kinetics:

p. = 0.04D cop~ - d- l (1)

The heat exchange zone length L, is defined on the basisof plotting the experimental isographs (Figure 3) with thecoordinates log(c/c, ) and r and on the basis of the

adsorption poles Pd which correspond to the ordinatelog(cpreadsco 1.

1.0

0.8

o 0.6

-s 0.4

0.2

010 0 200 300 40 0 50 0

T (min)

Figure 2 lsographs of oxygen adsorption

Table 1 lists the results of the calculations andgraphical plottings.

Figure 3 shows plots of the adsorption graphs P,,and Pa z and definition of the heat exchange zone lengthL,,; Lo2 for the zeolite samples 1 and 2 which havethe maximum and minimum length of the heat exchangezone length, respectively.

The statics of oxygen adsorption on NaA zeolite mod-ified samples has been investigated concurrently with adynamic study of oxygen adsorption to reveal a mostpromising sample of the adsorbenP. The investiga tionswere performed using a volumetric method at 90 K withprecooling of the adsorbent in vacuum.

-r(h)0 1 2 3 4 5 6 7 8

Breakthrough

0.1 0.2 0.3 0.4 0.5

L Cm)Figure 3 lsographs and poles of oxygen adsorption

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18 0

7 + +-+-160 - -+------+

- 140

(51mE 120

t 100

80

600 10 20 30 40 50 60 70 80 90 100

P(kPa)

Figure 4 Isotherms of oxygen a dsorption

1.0

0.8

0.60

B

0.4

0.2

t I I I I I

0 10 20 30 40 50 60

T (min)

Figure 5 Kine tic curves of oxygen adsorption

Figures 4 and 5 illustrate the isotherms and the kinet iccurves of oxygen adsorption on zeolite samples. Al l thezeolite modifications under study have convex isothermsand kinetic curves. Almost complete filling of the zeoliteadsorption volume occurs at about 15 kPa.

The analysis of the kinetic curves shows that thevelocity of internal diffusion of the oxygen moleculeswithin the crystal cavity of the modified zeolite understudy is high and the majority of oxygen is adsorbedwithin l&15 min.

In compliance with the theory of volumetric filling ofmicropores, the equation for the adsorption isotherm ata temperature of T < T, has the form

(2)

Figure 6 illustra tes the oxygen adsorption isothermsof a zeolite sample with the coordinates log a and[log(pJp)] of Equation (2). The constants IV, and Band the oxygen ultimate adsorption rate were determinedfrom the results of the static investigations (see Tubk I).

A comparison of the result s of the dynamic and staticinvestigations, when cooling the adsorbent in vacuum,made it possible to establish that the modified zeolitesamples 2, 3, 6 and 7 had a high adsorption capacity,

0. 8

0. 6

0. 2

I I I I 1 I

0 1 2 3 4 5 6

[log (P,lPl12

Figure 6 Isotherms of oxygen adsorption in the coordinates of

Equation (2)

high mass transfer coefficient and high degree of equilib-rium capacity utilization (see Table I).

Thus, in the first stage of the investigat ions, the tech-nology was studied which would allow for almost com-plete removal of the adsorbed mixtures and preventionof their adsorption when cooling. However, the processof heating and cooling the adsorbent in a vacuum takesa long time since the heat transfer over a layer ofgranular, low-heat-conductive material is of low effi-ciency. Enhancement of the heat exchange eff iciency ispossible when the adsorbent is cooled by an argon how.However, as reported in ref. 1, a decrease in the adsorbentdynamic capacity may occur due to argon preadsorption.

In the second stage the argon adsorption was studiedwhen cooling the adsorbent7 on the zeolite samples ofhigh oxygen adsorption capacity which were revealed inthe first stage of the investigations.

It may be assumed that when cooling the adsorbentin an argon medium, argon adsorption (a,,) would takeplace on the surface of the crystals and on their defectsup to the temperature at which the molecular sievebecomes effective in r zeolite micropore spaces (spreads);it is also possible that argon cap illary condensation (a,,,)takes place in the secondary porosity of the zeolite grains.Thus, the total amount of the adsorbed argon is given by

%I + %I + apreads + %sp (3)

It seem like ly that the argon preadsorbed in the zeolitemicropores upon reaching the temperature when amolecular sieve becomes effective will be blocked withinthem since the dimensions of the inlet windows in the c1spaces become sm aller than the crit ical diameters of theargon molecules. It may be assumed that this pre-adsorbed argon wil l influence the intradiffusion kinet icsof oxygen adsorption in the purification process. Theextradiffusion kinet ics of oxygen adsorption may beinfluenced by the capil lary condensation in the secondaryporosity of the adsorbent grains formed by the zeolitecrys tals and the binder. The capil lary condensation ispreceded by polymolecular adsorption on the mesopore

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0.6

m

% 0.3a

0. 2

0.1

0

85 90 95 100 105 110

T(K)

Figure 7 Argon saturated vapour pressure p, as a function of(1) temperatu re T and (2) the adsorption pressure p, define d byEquation (4)

surface. Thus, before the capil lary condensation developsin the mesopores, the polymolecular adsorption rate wil lbe characterized by u,~ in Equation (3). The capillarycondensation takes place after the adsorbent forms aconcave meniscus in a capillary, and the pressure aboveit is lower than that of the saturated vapour above a flatsurface. and condensation occurs at p/ps < I.At p/p, = 1the mesopores are filled with adsorbate. Figure 7 showsthe dependence (Curve 1) of argon saturated vapour

pressure on temperature within the period of themolecular sieving effect of the NaA zeolite.

The effect of the capi llary condensation is best de-scribed by the Kelvin equation

P 2a v

~ = expPS ( 1RT

Solving this equation for p makes it possible todefine the pressure at which capil lary condensation mayoccur. In commercial zeolite samples the effective radiiof mesopores are characterized by a peak at 230 nm8. Asan example, Figure 7 illustra tes the results of defining pfrom Equation (4) at Y = 230 nm (Curve 2).

Thus, the working pressure in the process of purifyingargon from oxygen under the experimental conditionsconcerned (90 K) must not exceed 0.12 MPa. Specificpressure values (see Figure 7) correspond to differenttemperatures of the purification process. The absence ofcapi llary condensation in the samples under study, mod-ified at high partial argon pressures, was confirmed bythe static investigations of oxygen and argon adsorption.The adsorption isotherms are of a rectangular nature andthe capacity, close to equilibrium, is achieved at lowpartial pressures when the conditions for capil lary con-densation are absent.

Equation (4) was derived without considering that thelayer of molecules adsorbed on the mesopore surface

could result in the pore dimensions being smaller thanthose actually calculated and the capi llary condensationoccurring at a lower partial pressure. The adsorptionlayer t, may be estimated from the De Boure formuladerived for nitrogen at 77 K:

0.4584

td = [log(p,~p)] (5)

The calculations on the basis of Equation (5) showthat f, = I .28 nm. The results agree well with Aultonsdata (t, = 1.3 nm) obtained under similar conditions.Thus, any possib le decrease in the mesopore dimensionsdue to argon adsorption is insignif icant and has no effecton the development of capil lary condensation.

With regard to the above-mentioned considerations,Equation (3) may be presented in the form

%t = %I + spreads (6)

When cooling the adsorbent in vacuum and on itssubsequent saturation with argon at a fixed adsorptionpressure and temperature, Equation (3) has the form

Hence, having determined a,, from the adsorbent pre-cooling in vacuum, and having defined atot when coolingin the argon medium, we can find the value for argonpreadsorption from Equation (6).

The studies were carried out in the experimental plant(Figure I) using the volumetric method under the condi-

tions of cooling the adsorbent in an argon medium, inan argon flow and in vacuum followed by its saturationwith argon at 0.12 MPa.

Figure 8 shows the plots of argon adsorption versuscooling time when cooling the adsorbents in an argonflow. The plots are linear, showing an increase in theadsorption rate with cooling time. Samples 2, 3, and 6would be preferable for the conditions of cooling with

m,Ej 60 t;0

I I I 1 I I I I

0 IO 20 30 40 50 60 70 80

r(min)

Figure 8 Argon adsorption when cooling zeolite specimens in anargon flow

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Table 2 Calculation results of argon adsorption when cooling in argon medium and in vacuum

Cooling in argon m edium Coolin g in vacuum for 3 h

Zeolite Coolin g period Capacity for argon Capacity for argonsample no. (min) (N m3 g-l) (N m3g-)

7 84 119.5 59.66 40 38 22.32 35 36.2 233 35 31.3 24.3

argon. With a decrease in the cooling period the differ-ence in the argon adsorption rate for these samplesdecreases to a minimum.

Table 2 presents the values of argon adsorption whencooling the adsorbent in an argon medium and whencooling it in vacuum with its subsequent saturation withargon for 1 h.

It follows from Table 2 that cooling the adsorbent invacuum would be preferential from the point of view ofensuring a minimum rate of argon adsorption. In thiscase the adsorbent cooling period amounts to about 3 h,whereas when cooling the adsorbent in an argon mediumit is shorter by a factor of 4.5. However, when coolingthe adsorbent by an argon flow, the cooling period maybe reduced significantly (see Figure 8) although thiswould require a large amount of pure argon, or provisionshould be made for a special circulation system. It ispossible, however, to cool the adsorbent in an argonmedium quite rapidly for which purpose no additionalequipment is needed and the argon flow rate is aminimum. Hence, this cooling method would bepreferable provided the argon-from-oxygen purificationprocess is not influenced by preadsorbed argon.

Figure 9 shows the characteristic curves obtained whencooling the modified zeolite samples by differentmethods.

Table 3 lists the argon preadsorption rates found fromEquation (6).

For the determination of the preadsorption argoninfluence on the process of purification from oxygen, thetests on zeolite specimens were performed under dynamic

30 0

25 0

2- 200L

15 0

10 0

0 30 60 90 120 150 180

T (min)

Figure 9 Characteristic curves for cooling zeolite specimens: 1, 2,4, argon flow cooling (T = 15, 30. 60 min); 3, argon mediu mcooling; 5, vacuum cooling

conditions, cooling the adsorbents in an argon mediumusing the experimental plant shown in Figure 1. Table 4presents the results of the defined adsorption values foroxygen and argon. The value for argon preadsorption isdefined by Equation (6).

The comparison of the values obtained for the oxygencapacitance of the zeolite specimens with the test results,when cooling the adsorbents in vacuum (see Table I),shows some decrease in the dynamic capacitance whencooling the adsorbents in the argon medium.

The argon capacitance and the argon preadsorptionvalues obtained are in agreement with the data given inTable 3, when cooling the adsorbents in the argonmedium. Thus, the adsorption values presented in Table2 may be considered as constant under evaluation of theargon preadsorption value, when cooling the argonmedium for the appropriate zeolite specimens.

The data on the argon adsorption values for the zeolitespecimens, Figure 8, may be used for a graphicaldetermination of the argon preadsorption value as afunction of cooling time, as shown in Figure 10. Theconstruction reduces to the determination of thepreadsorption pole position PPreads, at the point ofintersection of the straight line CD, characterizing theargon adsorption value as a function of time, and thestraight line parallel to the time axis, intersecting thecoordinate axis at the level of a,,. Then, for instance, the

Table 3 Argon preadsorption rates for zeolite samples w hencooling in argon flow or argon medium

Argon preadsorption rate (cm3 g-)

Zeolitesample no. Cooling in argon flow Cooling in argon medium

7 51.76 22.3 15.72 15.5 13.23 8.2 7

Table 4 The results o f the defined adsorption values for oxygenand argon using zeolite specimens under dynamic conditions

Capacitance value under Amou nt ofdynamic conditions preadsorbed argon

No. of Oxygenzeolite (cm3 g-l) Argon Argonspecimen (% weight) (cm3 g-) (cm3 g-)

7 59.1 (7.83) 110.2 60

6 81.4 (10.77) 3 9.7 17.42 85.9 (11.37) 38.5 15.53 85.1 (11.42) 33.7 9.4



7/9

0 4 aIII r

I;lplead;p ~i7ial!

preads ? oI st *I I I b

[T1lt T

Figure 10 Argon preadsorption as a function of cooling time

argon preadsorption value at zB may be defined accord-ing to the following formula

a preads = Kprcads TB + Aa (8)

where Kpreadss the coefficient of preadsorptioncorresponding to the tangent of the angle y.It may be assumed that for a particular adsorbent

there is a maximum allowable time of adsorbent coolingC~lub when the preadsorption argon [alpreads wil lsignif icantly affect the process of argon purification fromoxygen.

Table 5 presents the results of the test data processing,when cooling the adsorbents by argon flow. It followsfrom the Table 5 that specimen 3, which has theminimum value of argon preadsorption and a highoxygen capacitance under dynamic conditions, is thepreferred modification of zeolite for the argon cooling

conditions.Thus, the introduction of the preadsorption poleconcept a llows one to illustra te readily the preadsorptionprocess under argon cooling. The construction ofpreadsorption poles for various modifications of zeoliteunder specified conditions of the cooling process allowsone to choose the adsorbent with the minimumpreadsorption value.

Taking Equation (8) into consideration, Equation (6)for defining the total adsorption value may be written inthe following form

alo1 a,, + &reads Llol + Aa (9)

The studies performed in the first and second stageshave been carried out with zeolite specimens subject todehydration at 673 K, which permits the exclusion of theinfluence of preadsorbed water on the process of argon

Table 5 The results of the test data processing under cooling

zeolite specimens with argon flow


purification from oxygen, but results in increased powerconsumption and metal content of the equipment.

In the third stage the work was devoted to the studyof the dehydration influence of zeolite specimen 3 on theprocess of argon purification from oxygen at decreasedtemperature. The studies were again performed at theexperimental plant shown in Figure 1.

The dehydration was carried out by a method whichinvolved heating the zeolite by gas flow to the desorptiontemperature of the basic mass of water (393423 K) withsubsequent cooling and saturation of the adsorbent withpure oxygen at the temperature of the process of argonpurification from oxygen (about 90 K) and desorption ofadsorbed oxygen at the cost of heating. The desorbedoxygen was analysed for the water content. Figure 11shows the adsorbent temperature variation (curve 1) inthe course of saturation with oxygen and desorption andthe charac teristic outlet curves for water (2) under oxygendesorption.

Thus, it is established that zeolite dehydration iscarried out at the cost of water removal with thedesorbed oxygen.

When performing the dehydration, a check of theadsorption properties of zeolite specimen 3 was carriedout under the dynamic conditions of argon purificationfrom oxygen with the parameters of the previous studies.As a result, a value of 75 cm3 g- for the dynamiccapacitance of oxygen was obtained and the oxygencapacitance decreased by 12% compared with dehydra-tion at 673 K. Thus, it is shown that the adsorbentdehydration is possible according to the proposedmethod. The decrease in the dynamic capacitance ofoxygen at the cost of dehydration under decreasedtemperature may be taken into account by the decreasecoefficient KdeCr Figure 12 shows the decrease coefficientas a function of dehydration temperature on the basis ofthe obtained results, assuming the linear character of theadsorption capacitance reduction under temperaturedecrease and assuming that Kdecr = 1 at 673 K.

In the final stage of the adsorption studies the influenceof the argon flow rate on the purification process wasdefined. The studies were performed within the range ofthe working rates of the industrial process.

Figure 13 shows the results of defining the dynamiccapacitance and mass transfer coefficient. The relation

- 100

-2

-50k-0

I

No. of zeolitespecimen

K(cm3g~ta~in-l)

Aa(cm3 g-)

7 0.296 11.56 0.114 5.29

2 0.096 3.563 0.044 3.34

90 I 00 60 120 18 0

T (min)

Figure 11 The adsorbent temperature variation in the course ofoxygen saturation (curve 1) and characteristic outlet curves of water(2) under oxygen desorption



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500 600

T(K)

Figure 12 The coefficient of zeolite dynamic capacitancedecrease as a function of dehydration temperature

30 - 60

- 50

20 - 40

- 30

10 20

0 0.4 0.8 1.2 1.6 2.0

-1w(m min )

Figure 13 The dynamic capacitance (1) and mass transfercoefficient (2) as a function of the rate of flow

for defining the dynamic capacitance has been obtainedon the basis of the test data processing:

a dyn=f(o) = a - Kc0 (10)

Figure 13 shows the relations ad,,,, =f(w) calculated byusing Equation (10) and /II0 Z:(W) constructed accordingto Equation (1) on the basis of calculat ion of the externalmass exchange coefficient. Good agreement of theexperimental and calculated data confirms the decis iverole of the external diffusion kinet ics of the process ofargon purification from oxygen under the consideredconditions.

Using the known equation for calculat ion of theadsorption duration, with allowance for the relation (10)and the external mass exchange coefficient /IO, a formula

c.-E

P

0 0.5 1 .o 1.5 2.0

-1w(mmin )

Figure 14 The test adsorber protective action time as a function ofthe rate of flow: (-) calculated by Equ ation (11); (0) experim entalvalues

is obtained for defining the adsorber protective actiontime for argon purification from oxygen:

7=~~-~[~ln(~-l)+ln~-l]j (11)

wherep, = c,/y, and y1 is the mass concentration of theadsorbing component in the gas flow equal to the halfthe maximum amount, adsorbed by the zeolite at a giventemperature (kg me3).

Figure 14 shows the dependence of the protectiveaction time of the test adsorber on the flow rate, definedby Equation (1 ), and the experimental points. As seenin Figure 14, good agreement between the test data andthe calculated relation is observed.

To take account of the influence of argon and waterpreadsorption, Equation (11) may be supplemented byEquation (8) for defining the preadsorption value spreadsand the coefficient of the dynamic capacitance decreaseKdeer, defined according to Figure 12. Then, the relationfor defining the protective action time takes the followingform:

The relation obtained allows one to perform thecalcula tions of the adsorbers of the systems for argonpurification from oxygen, taking into account the flowparameters, the adsorption properties of the zeolite andthe conditions of the adsorbent preparation for thepurification process.

The results of this work are at the stage of industrialadoption.

References

1 Golovko, G.A. Cryogenic production of inert gasesMash-inostroene (1983) 416

2 Barron, R.F. Cryogenic systemsEnergoizdat (1989) 408



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3 Fedorov, A.N., Davidov, I.A. and Golovko, G.A. The plant for thestudy of adsorbents under cryogenic dynamic conditions for theprocess of argon purification from oxygen Khim Nsft Mnshinostr(1990) 6 16

4 Fedorov, A.N. Golovko, G.A. and Davidov, LA. Investigation ofmodifie d zeolites for cryogenic purification of argon from oxygenKhim Neft Mashinostr (1990) 11 20

5 Fedorov A.N. The experimental and calculated data on cryogenicadsorption purification of argon from oxygen by modifie d zeolites

Khim Neft Mushinostr (1990) 12 146 Chelishev, V.Yu., Golovko, G.A. and Fedorov, A.N. The

experimenta l and theoretical study of statics of oxygen adsorptionwith modified specimens of zeolite NaA Kh im Ne/i Mashinostr(1992) 9 18

7 Fedorov, A.N. The investigation of argon adsorption by modifie dspecimens of zeolite NaA under cryogenic purification of argonfrom oxygen in the shell-and-tube adsorber Cryogenic processesand technology: Proc NPO Cryogenmash (1990) 127-136

8 Keltsev, N.V. Fundam entals of adsorption technology Khimiya(1984) 592

9 Fedorov, A.N. The investigation of argon preadsorption oncooling modifie d specimens of zeolite NaA Cryogenic processesand technology: Proc NPO Cryogenmash (1990) 137714 0

10 Fedorov, A.N. The increase of the efficiency of cryogenicadsorption purification of argon from oxygen for large-capacityplants Thesis: NPO Cryogenmash (1991) 135


investigation and improvement of cryogenic adsorption purification of argon from oxygen

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