Adsorption of organic vapors on alkylammonium montmorillonites

Adsorption of Organic Vapors on Alkylammonium Montmorillonites M. S. STUL, L. VAN LEEMPUT, l M. RUTSAERT, 2 AND J. B. UYTTERHOEVEN Centrum voor Oppervlaktescheikunde en Colloidale Scheikunde, Katholieke Universiteit Leuven, De Croylaan 42, B-3030 Leuven (Heverlee), Belgium Received February 2, 1982; accepted June 15, 1982 Exchanging Moosburg montmorillonite with monoalkylammonium ions of varying chain length (MA-n), a,~o-diammoniumalkanes (DA-n), monotrimethylammoniumalkanes (MTM-n), and a,o~-bistrimethylammoniumalkanes (BTM-n) with n = 5 to l0 produces valuable monolayer sorbents. MA10- and MTM-10-clays contain 15 and 30% double-layer complexes, respectively. Sorption isotherms are obtained for two groups of single vapors: benzene, thiophene, ethanol, ethanethiol (group I); and hexane, l-hexene, cyclohexane, methylcyclopentane (group II). Adsorption of the first group of compounds results in a slight swelling (to 1.5 nm) at low P/Po values (< 0.1). Extensive swelling is observed beyond P/Po = 0.4 in the case of mono- and double-layer complexes of MA (ethanol) and doublelayer complexes of MTM (benzene and ethanol). Swelling is of minor importance with the adsorption of the second group of compounds. Micropore evaluation utilized the Dubinin-Radushkevich treatment. The micropore volumes accessible to the different organic vapors change in the order MA
INTRODUCTION

The interparticle porosity is more heterogeneous with micropores, supermicropores, Upon replacing the inorganic cations of and mesopores. smectites with small organic ones a perman-Alkylammonium and a,o~-alkyldiamnent interlamellar volume to both polar and monium cations containing less than 13 carnonpolar vapors is created (1, 2). The extent bon atoms (nc ~< 12) are sorbed with the chain of the internal volume depends on the inter- parallel to the basal surface (5). Alkyldiamlayer distance (A) and the intercation dis- monium ions cover only about half the intance (X) (3). Smectites of variable porosity terlamellar layer surface occupied by alkylmay be obtained by introducing monofunc- ammonium ions; consequently a greater uptional or bifunctional organic cations of vari- take of benzene was observed (5). able chain length. These complexes present In n-alkylammonium-bentonites with 12 mainly microporous sorbents with slit-shaped nc ~ 18 the cation area exceeds the area pores. The interlamellar porosity at P/Po available per exchange site resulting in bi< 0.1 consists of micropores (width < 0.7 layer complexes (6). In these complexes the nm) and for some vapors at P/Po > 0.4 a sorption of methanol from the vapor phase swelling of the adsorbent accompanied by a at P/Po > 0.8 produces a reorientation of the reorientation of the cations creates super- cations; the swelling is limited by the chain micropores (0.7 n m < width < 1.5 nm (4)). length of the alkyl chains oriented perpendicular to the silicate surface (7). For aromatic hydrocarbons the dool spacing of dil Present address: Janssen Pharmaceutica, 2340 Beerse, methyldioctadecylammonium-bentonite inBelgium. 2Present address: Upjohn, 2670 Puurs, Belgium. creases continually with P/Po (8, 9). 222 0021-9797/83/030222-10503.00/0 Copyright © 1983 by Academic Press, Inc. All rights of reproduction in any form reserved.

Journal of Colloid and Interface Science, Vol. 92, No. 1, March 1983

S O R P T I O N OF O R G A N I C VAPORS O N ORGANO-CLAYS

The influence of modifying the interlamellar space in montmorillonite on its sorption behavior is studied by comparing the adsorption of eight organic vapors in n-alkylammonium- and a,o~-alkyldiammonium-Moosburg clays, and their trimethyl quaternary ammonium analogs. The micropore volume will be determined by the Dubinin-Radushkevich method (4). MATERIALS A N D M E T H O D S

The montmorillonite used is from Moosburg (G.F.R.) further denoted as Mo. The fraction < 0.5 #m (e.s.d.) is obtained after sodium saturation using standard methods of centrifugation. Hydroxyaluminum compounds were removed by consecutive washing with acidified (pH -- 4) and neutral l N NaC1. The product was stored as 1.5% suspension. The monoammoniumalkanes further denoted as MA followed by the number of carbon atoms in the alkyl chain and the diammoniumalkanes (DA) are purchased from Fluka (Buchs, Switzerland) with the exception of DA-7 (Aldrich). DA-5 and -6 are purchased in their salt form and free bases are titrated with HC1 to their equivalence point. Monotrimethylammoniumdecane, MTM-10 (Eastman-Kodak), and the a,o~bistrimethylammoniumalkanes: BTM-5, -6, and -10 (Fluka AG) are used as obtained. MTM-5, -6, -7, and -8 and BTM-7 and -8 are synthesized by refluxing trimethylamine (Fluka) with the corresponding mono- or dihalogenoalkane (Fluka, Aldrich) in ethanol for 48 hr (10). The product is recrystallized three times and dried in high vacuum before use. The various adsorbents are obtained at 25°C by fourfold overnight exchange of 1 liter 0.01 N aqueous solutions of the organic cations with 50 ml clay suspension contained in dialysis membranes. Excess cations and physically adsorbed ammoniums are removed by four methanol washings, spread over a 36-hr period. The suspensions are dried in a 13.6 X 10-3 k g . m -2 vacuum at room temperature. The organosmectite is

223

ground to particles smaller than 0.1 mm and degassed at 60°C and 1.36 x 10-7 kg. m -2 to eliminate the remaining traces of solvent. The samples are stored at 80% RH. The chemical composition is evaluated from a calcination at 800°C and the nitrogen determination (Kjeldahl). The organic cation content is expressed as milliequivalents per gram of backbone. Adsorption isotherms for all vapors were obtained using a McBain balance except for ethanol adsorption which was recorded with a volumetric adsorption apparatus. The pressure is read with a 0.02-mm precision cathetometer. The adsorbents are outgassed at 60°C for 24 hr in a 1.36 × 10-7 kg. m -2 vacuum. Fresh samples are used for each isotherm. Benzene, cyclohexane, hexane, ethanol (UCB), ethylmercaptane (K & K), thiophene (Baker), methylcyclopentane (Aldrich), and l-hexene (Fluka) are purchased in high purity form and studied as organic adsorbates. They were dried over zeolite A (Linde) and distilled in vacuo. An equilibrium period of 12 hr is chosen for most adsorbates except ethanol (24 hr). The basal distances are recorded with a Debye-Scherrer camera. The samples are held in Lindemann capillaries which are connected to a vacuum line for outgassing and subsequent equilibration with the sorbate for 3 days. The capillaries are sealed by means of a small torch and irradiated. Swelling in organic liquids is studied after a prolonged contact (l week) of the outgassed samples, enclosed in a capillary. RESULTS

The average organic exchange capacity amounts to 0.97, 1, 0.98, and 1.04 meq/g for the MA-, DA-, MTM-, and BTM-clays, respectively. The basal spacings of the outgassed samples are given in Table I and in general correspond to a monolayer of ammonium cations in the interlamellar region: 1.33 nm for MA-, 1.31 nm for DA-, and 1.38 for M T M - and BTM-clays. MA-10Journal of Colloid and Interface Science, Vol. 92, No. l, March 1983

224

STUL ET AL. TABLE I

and MTM-10-Mo have spacings of 1.388 and 1.49 nm due to the formation of 15 and 30% bilayers (11). Benzene and thiophene. Figure I shows the benzene sorption isotherms on montmorillonite exchanged with ammonium cations of chain length nc = 5, 6, 7, and 8. The isotherms for nc = 10 can be found in Fig. 5. The isotherms are of the BET-IV type. The extent of adsorption increases as MA < MTM < BTM < DA for identical chain lengths except for MA nc = 6. The adsorption capacity is inversely proportional to the alkyl chain length of the DA cations, but less variant to nc for the other cation types. The difference between BTM and DA is most pronounced for the pentyl derivatives. The behavior of MTM-10-Mo deviates

The Changes in Basal Distances doo~ (nm) of A]kylammonium-Montmorillonite in Contact with Benzene at 20°C

p/Po

5

0.0 0.068 0.081

1.328 1.296

DA

0.0 0.068 0.081

1.295 1.508

MTM

0.0 0.056 0.061

1.358 1.405

0.0 0.056

1.374 1.449

MA

BTM

6

7

8

I0

1.337

1.388 1.377

1.364

1.322 1.381 1.364

1.307

!.309

1.317 1.442

1.329

1.374

1.385

! .390 1.398

1.493

1.412

1.383

1.374 1.446

1.377

1.381 1.419

1.381 1.403

1.336

1.488

1.449

i ~ , , , r l ,

%% mmollg.b.

A~ AI lJ &~"

,J

2.

i

°~

/

~

%= 5

/

e~ e~e~

vi'vi~ Ir

m' •2

J

A

,6

ncm 6 .2

.8

--1~'j

.4

i

:

.8

WPo

f .~'f-~" nc----7

i

.6

i

i

i

nc 8

i

I

i

i

i

i

i

FiG. 1. Adsorption isotherms of benzene at 20°C on M A - (I), D A - (1), M T M - (V), and B T M montmorillonite (O) for n~ = 5, 6, 7, and 8. Open symbols indicate desorption points. Journal of Colloid and Interface Science, Vol. 92, No. I, March 1983

225

SORPTION O F ORGANIC VAPORS ON ORGANO-CLAYS '2.4 .

.

.

.

.

.

J

'

' +~

C2HsOH

/

"doo'l(nm)

I

~

"2.0

"

..

•

-,6

"

• 1.4

.

_

,

.

.

.

,

C6H6

.4

,

.+

,

/

,

•

e'-~ e - e -

/

J~

-1.2 ,

.

l.6

d '/

•

•

,2.0

L2

.i:,?0

,

•

•

.

..4

,

;6

,

.8

RG. 2. Basal distances as a function o f ethanol and benzene relative pressures at room temperature o f M A - 5 - (+), M A - 8 - (rq), MA-10- (i), DA-5- (&), DA-10- (V); M T M - 8 - (x), M T M - 1 0 - (e), and BTM- 10-montmorillonite (B~).

from that of the other adsorbents (Fig. 5): 1.55 mmol/g is adsorbed byp/po = 0.55 comparable to the DA-10 sample but a loading of 3 mmol/g is reached near P/Po = 1. Desorption was studied in the case of MA-8 and BTM-8 (see Fig. 1). Hysteresis persists up to P/Po = 0 in both cases and can be attributed to interlamellar desorption and to structural reorganization upon contact with benzene (9, 12, 13). The basal spacing of the organosmectites change as shown in Table I and Fig. 2. Only the MTM-10 sample gradually expands to above 2 nm beyond P/Po = 0.4 (indicating

i

i

i

|

i

,

+

•

either a tilting of the stretched cations in an angle of at least 49 ° or formation of a quasicrystalline structure of benzene in the interlayer space with conformational changes of the alkyl chains (15)) but is accompanied by the occurrence of a second spacing which decreases to the value of the monolayer complex (1.38 nm). The apparent basal distance of the outgassed adsorbent (1.49 nm) is generally viewed as an interstratified system of 1.36-nm (monolayer) and 1.81-nm (bilayer) complexes. The enhanced swelling and adsorption in the case of MTM-10 may thus be attributed to that fraction of the interlay-

" 3 |,.L

'

'

l

,

i

~nrnol/g.b,

e~s

, / i

l

/

THIOPHENE

& ]

,

2

.17

./ .//'"

.,

nc= 5

f l

.2a

,

.4 J

i

.6 i

|

.,8

,

.?.

.4

,

p

,

:8

FIG. 3. Adsorption isotherms o f thiophene at 25°C on M A - (ll), D A - (A), M T M - (V), and B T M montmorillonite (O) for nc = 5 and 10. Journal of Colloid and Interface Science, Vol. 92, No. l, March 1983

226

STUL ET AL.

,,p /

ETHANOL

rnrncd/cab.

el/ .

.4 •~

ETHANETHIOL

3

"

p no= 5

nc= 5

.2

.4

.6

.8 P/I~

.2

~

..e

.

.p

.7

•

[]

/

:I/)/

,•~V ~''~'-

,

.2

,4,

./

":,,

nc 8 .6,

[]J

1 .8

,

nc~=lO ,

.2 .

.4.

.6

.8

,

FIG. 4. Adsorption isotherms on MA- (11), DA- (A), M T M - (V), and BTM-montmoriUonite (e) of ethanol (no = 5 at 25°C; nc = 8 and 10 at 20°C) and ethanethiol (n~ = 5) at 20°C. Open symbols indicate desorption points.

ers covered with double layers of MTM cations. The fact that the MA- 10 sample, which has also a fraction of double-layer complexes, does not show this swelling is a finding that points to the involvement of the nature of the ionogenic group. The extent of adsorption of the other organo clays is dictated by the sole presence of monolayer complexes of ammonium cations and is thus inversely proportional to the alkyl chain length. A slight expansion occurs upon incorporation of benzene, the order being MA < MTM < BTM < DA. The highest Journal of Colloid and Interface Science, Vol. 92, No. 1, March 1983

interlamellar distances are measured for DA5-Mo, in accordance with its important adsorption capacity. Basal distances of 1.461.51 nm are observed for benzene sorption on MA- and DA-bentonites with 2 ~< nc ~< 12 (5). These distances are in accordance with a single layer of benzene in the interlameUar space, if the plane of the aromatic rings is tilted to a nearly vertical position. Thiophene (Fig. 3) behaves in a similar way as benzene as regards its order of adsorption: MA ~ MTM < BTM < DA. Higher amounts of thiophene are adsorbed

227

SORPTION OF ORGANIC VAPORS ON ORGANO-CLAYS OA-IO

4

BTM- 10

/ mmollab.

/

&jj~A 3

A~ A j l

/ •2

' __ _.....

I

, ~

.2 I

,-~-~-~. - - - - ~

.4 I

I

I

.6 I

. ~ _

/ _

i _ " I_

7

~ ~

•

~

•" ~ i

--

~._~

•~

.8 I

I

I

/

-6

MA-IO

• ~.

MTM-IO -5

/ .

/,

,,

•

*/

-4

•

I i

I--

...._...i""

I

r

I

•

- - -_- -. . , . . l ~ . ~ ' -

i

a

I

I

i

n

- -

/

~--

/, -1, -~ ll" - , ~ ' - ~ -. ~ . ~ , ~ . ~.]r.-. ~ ~; ~l"~ "4"4"4"4~" I a i , , ,

¢¢"

P/Po

,

n

FiG. 5. Adsorption isotherms of ethanol (1), ethanethiol (It), benzene (O), 1-hexene (~), hexane (ll), cyclohexane (.) at 20°C and thiophene (i), methylcylcopentane (V) at 25°C on MA-, DAm MTM-, BTM-montmorillonite (no = 10).

compared to benzene as was also noticed in tetramethylammoniumbentonite (14). Ethanol and ethanethiol. The sorption isotherms o f ethanol on organoclays with n~ = 5, 8, and 10 are represented in Fig. 4; they have the BET-IV shape. The adsorption capacity increases in the order M T M < MA < BTM < DA. As in the case o f benzene the adsorption isotherms of the bifunctional adsorbents (DA, BTM) exceed those of the monofunctional at P/Po values below 0.4. Beyond P/Po = 0.4 crossing o f adsorption isotherms is noted: (i) a strong affinity and adsorption capacity is observed for MA in the

case of nc = 5, 8, and 10; (ii) the enhanced adsorption capacity in the M T M derivatives appears from nc = 10 on. The same pattern is observed in the adsorption o f ethanethiol for nc = 10 (see Fig. 5) but lower amounts of ethanethiol are adsorbed compared to ethanol. Primary alkylammonium samples exhibit a swelling in ethanol vapor (Fig. 2 and Table II). Double layers induce an expansion beyond P/Po = 0.4; when only monolayers o f a m m o n i u m cations are present as observed in MA-8 the expansion is deleted to P/Po = 0.5. This indicates that a stronger interJournal o f Colloid a n d Interface Science, Vol. 92, No. 1, March 1983

228

STUL ET AL. TABLE II

The Basal Distance dool (nm) of AlkylammoniumMontmorillonite in Contact with Ethanol at 20°C nc

p/Po

5

8

MA

0.0 0.086 Liquid

1.328 1.343 1.337

1.337 1.368 2.502

1.388 1.394 2.668

DA

0.0 0.086 Liquid

1.295 1.317 1.325

1.317 1.323 1.349

1.329 1.323 1.341

MTM

0.0 0.066 Liquid

1.358 1.385 1.401

1.390 1.398 1.418

1.493 1.451 2.914

10

distances while MTM-5-Mo swells little in hexane vapor (Table III). Small increments in the intedamellar distances were also proved for alkylammonium-bentonites (5). Upon desorption ofcyclohexane from MTM-5 and BTM-5 for which both external and interlamellar microporosity is expected, the hysteresis persists to zero relative pressure in contrast to bentone-34, in which case the interlamellar region is completely filled with the organic cations and for which hysteresis ends at P/Po = 0.30 (8). DISCUSSION

The adsorption capacity of an organosmectite may be considered as composed of BTM 0.0 1.374 1.381 1.381 (i) a permanent interlamellar adsorption vol0.066 1.407 1.413 1.401 ume; (ii) an additional internal volume, Liquid 1.405 1.414 1.403 made available by lattice swelling; and (iii) an external surface capacity. action with the ionogenic group adds to the The sorption capacity in the micropores swelling in the case of ethanol adsorption of the sorbent can be calculated by applying (compared to the benzene adsorption). In liq- the Dubinin-Radushkevich equation to the uid ethanol, the basal distances are known sorption isotherm in the low pressure region: to increase with nc (6). Swelling only occurs log W = log Wo - D (logpo/p) 2 in which 14/o if a minimum chain length, depending on = the limiting adsorption value (#l/g backthe mineral charge density, is exceeded (16). bone). The micropore volumes (W0) accesFrom P/Po = 0.6, a swelling of the MTM- sible to the different organic vapors are com10-Mo is noticed (Fig. 2), reaching 2.92 nm pared for the various sorbents in Fig. 6. The in the liquid (Table II). It is ascribed to the volumes change in the order MA < MTM organic bilayers, by analogy with the obser- < BTM < DA and nc 5 > 8 > 10 except for vations for benzene. ethanol adsorption on MA-10 and MTM-10 n-Hexane, 1-Hexene, cyclohexane, and and benzene and thiophene sorption on methylcyclopentane. The dependence of the MTM-10. adsorption capacity of these vapors on the One may now estimate the contribution cation type and chain length is shown in Fig. of the interlamellar porosity to the total vol5 for nc = 10. Both hexane and cyclohexane ume at low P/Po as follows. Assuming an invapor induce minor adjustments in the basal terlamellar surface area of 700 m2/g, the perTABLE III The Basal Spacing dooi (nm) of Alkylammonium-Montmorillonite in Contact with the Vapor of Cyclohexane or Hexane at 20°C P/Po

-C6H12 C6HI4

0.0 0.86 0.89

MA-10

DA-5

DA-10

MTM-5

MTM-10

1.388 1.392 1.414

1.295 1.311

1.329 1.323 1.343

1.358

1.493 1.488 1.496

Journal of Colloid and Interface Science. Vol. 92, No. 1, March 1983

1.493

BTM-10

1.381 1.414

SORPTION OF ORGANIC VAPORS ON ORGANO-CLAYS

229

FIG. 6. Dubinin-Radushkevich mieropore volumes accessible to the different organic vapors as a function of the cation type and the alkyl chain length on the Moosburg clay. Benzene (O), thiophene (XT), ethanol (A), ethanethiol (D), hexane (A), 1-hexene (,), eyclohexane (O), methyleyelopentane (11).

manent free interlamellar volume Vf equals 350 × (Ae - A c ) / A e × (doo~ - 0.96) ~l/g in which A~ = 0.465/2~ nm 2 = equivalent area or the area available per charge (6), ~ = 0.314 eq/(Si, A1)4Oi0 (10), and Ac = the area of a fiat-lying cation. The value for A~ is different according to the organic cation: (a) for MA and DA, A¢ = nc × 0.126 × 0.45 + k × 0.14 nm 2 (6) in which k = 1 and 2 for the MA and DA cation, respectively, (b) for MTM A¢ = (n¢ - 1) × 0.126 × 0.45 + 0.25 nm 2, (c) for BTM A~ = (n~ - 2) × 0.126 × 0.45 + 0.50 nm 2. Upon adsorption of an organic vapor d0ol increases by a factor fzx, relative to the outgassed state. The d0ol increase is too small to accommodate an adsorbate molecule between the ammonium cation and the silicate layer, so V~ -- Vf × f~ renders an estimate of the accessible free intedamellar volume. Table IV presents fa, V~, and the interparticle porosity Wo - V~ for benzene and ethanol. The free interlamellar volume V~ decreases with increasing cation chain length and is also accompanied by a smaller

change of the basal distance. The interparticle porosity changes with the type of adsorbate and cation. A certain constancy with chain length is observed in the benzene-MA and -DA combinations and in the ethanolDA combination. The higher interparticle porosity observed for DA-5 (benzene) and MA-10 (ethanol) may be caused by the contribution ofsupermicropores and mesopores. At higher relative pressure (P/Po > 0.40) there is a reorientation possible of monofunctional cations with the first group of adsorbates, e.g., ethanol, ethanethiol, benzene, and thiophene. Bifunctional cations with the chain length used seem to inhibit this behavior (Fig. 5). The adsorption can be viewed as the result of two processes: the interaction of the adsorbate with the functional group of the organic cation and the solvation of the alkyl chain (7). In general, however, the energy needed to expand the lattice against the electrostatic cohesion energy of the silicate layers is inversely proportional to the initial d0ol Journal of Colloid and Interface Science, Vol. 92, No. 1, March 1983

230

STUL ET AL. TABLE IV Microporosity of the Adsorbents for Benzene and Ethanol Vapor Benzene

Ethanol

f~

v~

wo- v~

f~

v~

.Io- v}

1.04

57.3

33.9

1.08 1.01

28.3 30.1

55.3 86.6

1.06

76.6

35.0

1.02 0.98

64.4 54.1

57.8 60.2

1.07

53.1

39.9

1.02

19.4

61.6

1.08

85.6

64.4

1.07 1.05

68.2 55.1

34.7

MA-5 6 7 8 10

1.18 1.07 1.16

65.0 48.2 40.4

24.6

0.97

29.0

33.2

DA-5 6 7 8 10

1.62 1.51 1.42 t.34 1.24

117.1 106.5 94.1 84.6 68.4

73.0 60.9 66.5 60.9 57.0

MTM-5 6 8

1.12 1.09 1.02

55.6 44.1 19.4

42.2 42.8 68.3

BTM-5 6 8 10

1.18 1.12 1.09 1.05

93.6 82.7 69.4 55.1

47.1 59.9 33.0

36.9

Note. fa is the ratio between the d0o~ value measured at P/Po < 0.10 to that of the outgassed state (see Tables I and II), ~ (el/g) = the total free interlamellar volume, and Wo - ~ is a measure of the interparticle porosity. The molecule volumes are obtained from the density of the liquids.

value. This is verified by the higher vapor pressure of ethanol (P/Po = 0.5) needed to expand MA-monolayer complexes in comparison with bilayer structures (P/Po = 0.40; Fig. 2). The present results are in conflict with literature data on the alcohol adsorption in MA-bentonites (12 < nc < 18). Notwithstanding the presence of bilayers in these cases one observes only a reorientation beyond P/Po = 0.8 (7). The smaller amount of organic cations and consequently of functional groups may be responsible for this phenomenon. By comparing MTM-10 and MA-10 samples which have double-layer complexes a different behavior upon ethanol adsorption is observed, MA-10 expanding more easily (P/Po = 0.4) than MTM-10 (P/Po = 0.6). This points to a weak ethanol-MTM interaction Journal of Colloid and Interface Science, Vol. 92, No. 1, March 1983

and is also corroborated by the absence of a reorientation of MTM-monolayer complexes. Benzene displays an interaction with the MTM group in double-layer complexes which is absent or of minor importance in the case of primary cations as shown for MA-10-Mo (this work) and MA-12-bentonite (5). The sorption mechanism is not yet clear since benzene compared to ethanol has a lower threshold pressure to expand MTM-10-Mo but nevertheless has a lower affinity (Fig. 5). Adsorption of benzene and ethanol on other MTM-double-layer complexes and of ethanol on MA-monolayer complexes may elucidate these problems. Larger adsorption capacities for this group of vapors can be obtained by changing the chain length of the modifying cations and the mineral charge density.

SORPTION OF ORGANIC VAPORS ON ORGANO-CLAYS CONCLUSION Organic derivatives of clay minerals are useful for s e p a r a t i o n o f o r g a n i c m o l e c u l e s . A t t e m p t s to c r e a t e selective s o r b e n t s h a v e b e e n m a d e in t h e d i r e c t i o n o f d e v e l o p i n g clays w i t h a p e r m a n e n t l y o p e n - p o r e system. T h i s w o r k shows t h a t use c a n also b e m a d e o f t h e swelling p r o p e r t i e s o f clays in o r d e r to o b t a i n c o m p o u n d s with h i g h - s o r p t i o n c a p a c ity a n d i n t e r e s t i n g selectivities. ACKNOWLEDGMENTS The authors thank Mrs. L. Lcplat for technical assistance. M.S.S. acknowledges the "Instituut voor Aanmoediging van het Wetenschappclijk Onderzoek in Nijverheid en Landbouw" for a research fellowship and the Belgian Government "Diensten Programmatie Wetenschapsbeleid," REFERENCES 1. Barrer, R. M., and McLeod, D. M., Trans. Faraday Soc. 51, 1290 (1955). 2. Barrer, R. M., and Rcay, J. S., Trans. Faraday Soc. 53, 1253 (1957). 3. Barrer, R. M., and Jones, D. L., J. Chem. Soc. (A) 16, 2594 (1971).

231

4. Dubinin, M. M., J. Colloid Interface Sci. 46, 351 (1974). 5. Barter, R. M., and Millington, A. D., J. Colloid Interface Sci. 25, 359 (1967). 6. Lagaly, G., and Weiss, A., in "Proceedings International Clay Conference, Tokyo, 1969," Vol. I, p. 61. Israel Univ. Press, Jerusalem, 1969. 7. Slabaugh, W. H., and Hiltner, P. A., J. Phys. Chem. 72, 4295 (1968). 8. Barfer, R. M., and Kelsey, K., Trans. Faraday Soc. 57, 625 (1961). 9. Vasofsky, R. W., and Slabaugh, W. H., J. Colloid Interface Sci. 55, 342 (1976). 10. Badow, R. B., and Zoller, A., Brit. J. Pharmacol. 23, 131 (1964). Verbruggen, A., PhD, Verb. Kon. Acad. Geneesk. Belg, 38, 261 (1976). I I. Stul, M. S., and Mortier, W. J., Clays Clay Miner. 22, 391 (1974). 12. Bailey, A., Cadenhead, D. A., Davies, D. H., Everett, D. H., Miles, A. J., Trans. Faraday Soc. 67, 231 (1971). 13. Greg~ S. J., and Sing, K. S. W., in "Surface and Colloid Science" (Matijevic, ed.), Vol. 9, Chap. 4, Wiley, New York (1976). 14. Barter, R. M., and Hampton, M. G., Trans. Faraday Soc. 53, 1462 (1957). 15. Lagaly, G., Stange, H., and Weiss, A., in "Proceedings International Clay Conference, Madrid" (Serratosa and Sanchez, cds.), p. 693 (1972). 16. Weiss, A., and Lagaly, G., KolloidZ. Z. Polym. 216, 356 (1967).

Journal of Colloidand InterfaceScience,Vo|.92, No. 1, March1983