Agglomerates of zeolitic molecular sieves which are bonded with particles of generally spherical amorphous colloidal-sized silica particles having nominal diameters in the range of 40 to 800 nanometers are found to have increased adsorption capacity for many molecular species due to the development in the binder of a pore system created by the packing of the silica spheres. When the molecular sieves employed are highly siliceous and hydrophobic, the agglomerates are ideally suited for use in odor elimination applications in which unagglomerated molecular sieve particles create dusting and handling problems.

FIELD OF THE INVENTION 
The present invention relates in general to bonded agglomerates of 
crystalline zeolite particles, and more particularly to silica-bonded 
spray dried agglomerates of molecular sieves, especially high-silica 
hydrophobic zeolitic molecular sieve particles suitable for use in the 
elimination of odors. 
BACKGROUND OF THE INVENTION 
The suppression or elimination of odors, particularly undesirable odors, 
has been the objective of untold investigations over the period of many 
centuries. In general these investigations have been focused on either of 
two approaches, namely (a) odor masking, in which a substance of strong 
yet relatively pleasant odor is introduced into the proximity of a less 
pleasant odor source with the intent of overburdening the olfactory 
receptors with the dominant pleasant odor, or (b) sequestering the 
undesired odorous substance in a non-volatile form either by chemical 
reaction, adsorption or absorption on a sorbent material exhibiting a 
sorptive preference for the odorous substance. 
With respect to the latter approach, a very significant advance has been 
described in detail in U.S. Pat. No. 4,795,482, Gioffre et al, the entire 
disclosure of which is incorporated by reference herein. The discovery 
which is the basis for this advance is that a particular subclass of 
crystalline zeolitic molecular, i.e., those in which at least 90 percent 
of the framework tetrahedral oxide units are SiO.sub.2 tetrahedra and have 
a sorptive capacity for water, at 25.degree. C. and 4.6 torr, of less than 
10 weight percent, possess a remarkable capability to sequester vapor 
phase molecules of odorous organic materials. In some instances, the 
zeolitic materials are found to render odorless vapors phases in which 
concentrations of the odor-causing composition must be reduced to levels 
below 0.00000004 mg./liter, the threshold concentration for detection by 
the normal human olfactory system. It is apparent that much more than mere 
organophilic adsorptive selectivity is involved. Although the phenomenon 
is not fully understood at present, one theory is that a catalytic process 
is involved whereby the odor molecules are reacted inter se or with other 
available molecular species, such as oxygen, to form compounds or polymers 
which no longer stimulate the olfactory receptors. It is known that high 
molecular weight organic molecules are significantly less odorous than low 
molecular weight molecules of similar atomic content and structure, 
n-decyl and lauryl mercaptans have no more odor than their corresponding 
alcohols. Thus, polymerization or condensation reactions could be 
beneficial in the present process. It is another possibility that the 
adsorption isotherms for the odor molecules for the very highly siliceous 
zeolite adsorbents involved here have steeper slopes in the region of very 
low adsorbate partial pressures than has heretofore been appreciated. 
Since the partial pressures of odor molecules often encountered are 
frequently quite low, the high silica adsorbents would exhibit superior 
adsorptive performance for that reason. Still another factor may be van 
der Waals interactions between the odor molecules and the molecular sieve 
causing the odor molecules to be tightly bound and trapped within the 
adsorbent. There may also be a coadsorption of two or more different odor 
molecules resulting in a synergism that eliminates the odors of both. 
The crystalline zeolitic adsorbents, to be effective in the elimination or 
suppression of odors, must in most instances be applied topically to the 
odor source. Such topical application can involve the use of powders, 
aerosol sprays, lotion formulations and the like. For these procedures the 
powderous nature of the very small crystallite forms in which zeolitic 
compositions are conventionally synthesized is ideally suited since 
further size reduction by grinding will ordinarily not be required. There 
are, however, a considerable number of applications for which powders are 
not completely satisfactory. For example, it has been proposed to utilize 
the deodorizing properties of high-silica molecular sieves in a variety of 
fibrous absorbent articles such as diapers, catamenial devices, wound 
dressings, incontinence pads, and shoe inserts. These articles are 
disclosed in detail in U.S. Pat. No. 4,826,497 (Marcus et al). It is 
important that the molecular sieves be incorporated into these articles in 
a manner whereby they not only remain in a dispersed condition throughout 
the fibrous area to which they are initially imparted, but also that their 
deodorizing properties are not unduly diminished as a consequence of the 
means used to prevent their dislocation. It is virtually impossible to 
prevent powdered solids such as molecular sieve crystallites from 
separating from fibrous batting without the use of some type of adhesive 
adjunct. Such adhesives necessarily cover at least a portion of the 
surface of the adsorbent particles and thereby tend to decrease their 
deodorizing capacity. 
Another disadvantage of powders in general and molecular sieve powders in 
particular is the difficulty involved in the handling and dispensing 
operations carried out by the automated production apparatus used almost 
universally in the commercial scale manufacturing of articles which 
contain the powders. In addition to having the potential for creating 
harmful dust contamination of the air in the production area, the powders 
are difficult to transport and meter accurately and cause abrasive damage 
to machine parts in contact with the moving powder particles.

SUMMARY OF THE INVENTION 
It has now been found that zeolitic molecular sieve agglomerates, 
preferably highly siliceous molecular sieve agglomerates, having nominal 
diameters within the range of about 40 to 800 micrometers, preferably from 
100 to 600 micrometers, which are bonded with a bonding agent consisting 
essentially of amorphous silica particles having nominal silica particle 
diameters of from about 5 to 20 nanometers are readily incorporated into 
fibrous articles, are firmly retained within the fibrous article during 
packaging, transport and use thereof, and, in addition, exhibit increased 
effectiveness in sequestering at least some of the common constituents of 
unpleasant odors. On an anhydrous basis, the silica binder constitutes 
from about 10 to 20 weight percent, the crystalline molecular sieve 
adsorbent constitutes from about 50 to 90 weight percent and the 
optionally present constituents such as fillers, pigments, lubricants, and 
agents used to increase the hydrophobicity of the silica binder, and the 
like, can comprise from zero to about 40 percent of the weight of the 
overall agglomerate. Configuration, i.e., shape, of the agglomerates is 
not a critical factor, but it is preferred that the agglomerates have 
curved outer surfaces with a minimum of sharp edges and corners which tend 
to increase agglomerate attrition. Spherical or spheroidal shapes are much 
preferred configurations, and such shapes most frequently result from the 
manufacturing procedure. The preferred method of manufacture, spray 
drying, readily produces essentially spherical mini-beads. 
DETAILED DESCRIPTION OF THE DRAWINGS 
The molecular sieves suitably employed in the compositions of the present 
invention include any of the crystalline aluminosilicates well known in 
the art either as naturally occurring minerals or as synthetic species 
such as zeolite X, zeolite A, ZSM-5 or zeolite Omega. Preferably, however, 
the molecular sieves are hydrophobic crystalline siliceous molecular 
sieves in which at least about 90, and preferably at least 95, percent of 
the framework tetrahedral oxide units are SiO.sub.2 tetrahedra and which 
have a sorptive capacity for water at 25.degree. C. and 4.6 torr of less 
than about 10 weight percent, preferably less than about 6 weight percent. 
In the case of aluminosilicate molecular sieves, the framework SiO.sub.2 
/Al.sub.2 O.sub.3 molar ratio is at least 18 and is preferably at least 
35. Molecular sieve zeolites having framework molar Si/Al.sub.2 ratios of 
from 200 to 500 are particularly suitable. Many of the synthetic zeolites 
prepared using organic templating agents are readily produced in a highly 
siliceous form. In many instances the reaction mixtures can be essentially 
free of aluminum-containing reagents. These zeolites are markedly 
organophilic and include ZSM-5 (U.S. Pat. No. 3,702,886); ZSM-11 (U.S. 
Pat. No. 3,709,979); ZSM-35 (U.S. Pat. No. 4,016,245); ZSM-23 (U.S. Pat. 
No. 4,076,842); and ZSM-38 (U.S. Pat. No. 4,046,859) to name only a few. 
It has been found that the silica molecular sieves known as silicalite and 
F-silicalite are particularly suitable for use in the present invention 
and are thus preferred. These materials are disclosed in U.S. Pat. Nos. 
4,061,724 and 4,073,865, respectively. To the extent the aforesaid 
siliceous sieves are synthesized to have SiO.sub.2 /Al.sub.2 O.sub.3 
ratios greater than 35, they are ordinarily suitable for use in the 
present compositions without any additional treatment to increase their 
degree of hydrophobicity. Molecular sieves which cannot be directly 
synthesized to have both sufficiently high Si/Al and/or degree of 
hydrophobicity ratios can be subjected to dealumination techniques, 
fluorine treatments and the like, which result in organophilic zeolite 
products. High-temperature steaming procedures for treating zeolite Y 
which result in hydrophobic product forms are reported by P. K. Maher et 
al, "Molecular Sieve Zeolites," Advan. Chem. Ser. 101, Americal Chemical 
Society, Washington, D.C., 1971, p. 266. A more recently reported 
procedure applicable to zeolite species generally involves dealumination 
and the substitution of silicon into the dealuminated lattice site. This 
process is disclosed in U.S. Pat. No. 4,503,023, issued Mar. 5, 1985 to 
Skeels et al. Halogen or halide compound treatments for zeolites to 
increase their hydrophobicity are disclosed in U.S. Pat. Nos. 4,569,833 
and 4,297,335. 
In the case of the aluminosilicates or silica polymorphs produced using 
large organic templating ions such as tetraalkylammonium ions, it is 
frequently necessary to remove charge balancing organic ions and any 
occluded templating material in order to facilitate their use in 
adsorption processes. 
It should be pointed out that with respect to the hydrophobic 
aluminosilicates it is the framework SiO.sub.2 /Al.sub.2 O.sub.3 ratio 
which is important. This is not necessarily the same ratio as would be 
indicated by conventional wet chemical analysis. Especially is this the 
case when dealumination has been accomplished by high temperature steaming 
treatments wherein aluminum-containing tetrahedral units of the zeolite 
are destroyed, but the aluminum values remain, at least in part, in the 
zeolite crystals. For such zeolite products resort must be had to other 
analytical methods such as X-ray and NMR. One such steam-treated zeolite Y 
composition, known in the art as LZ-10, has been found to be particularly 
useful in the compositions of the present process, especially when 
utilized in combination with the silica polymorph silicalite. The process 
for preparing LZ-10 is described in detail in U.S. Pat. No. 4,331,694 and 
in U.S. application Ser. No. 880,561, filed Feb. 23, 1978. When applied to 
the sequestration of organic odors, a benefit appears to be obtained by 
such a combination of molecular sieves in all proportions, but each type 
of adsorbent is preferably present in an amount of at least 10 percent 
based on the total weight of the two adsorbents (hydrated weight basis). 
As synthesized the molecular sieve crystallites have, in general, sizes of 
about 1.5 to about 6.0 micrometers, but the crystallites are most 
frequently agglomerated into particles having sizes in the range of 10 to 
about 20 micrometers. Molecular sieve particles in this range, i.e., 1.5 
to 20 micrometers, are all suitably utilized in forming the present 
compositions. It is preferred, however, that the particles are within the 
size range of 1.5 to 6.0 micrometers, or even more preferably within the 
range of 2 to 4 micrometers. If it is necessary to reduce the molecular 
sieve particle size, the grinding techniques well known in the art are 
suitably employed. 
The silica binder is comprised of amorphous silica particles of colloidal 
dimensions. Such particles are readily available commercially in the form 
of silica sols, either aquasols or organosols. While the size of the 
colloidal silica particles is not narrowly critical, it is preferred that, 
in terms of nominal diameters, the particles are within the range of 5 
nanometers up to 80 nanometers. Silica particles having nominal diameters 
within the preferred range of 5 to 20 nanometers, however, provide the 
additional benefit of increasing the sorptive capacity of the bonded 
agglomerates for molecular species having kinetic diameters calculated 
from their minimum equilibrium cross-sectional diameter of less than about 
8 Angstroms. Such molecular species include many of the odor-causing 
organic substances of concern in odor elimination applications such as 
aliphatic amines, saturated or unsaturated aliphatic acids and aldehydes 
containing a single --COOH or --CHO group and the sulfur-containing 
compounds in which the valence of sulfur is less than 6. Triethylamine, 
isovaleric acid and methyl mercaptan are typical of compounds of these 
groups. The oxygen-adsorbing capacity of the preferred class of 
agglomerates is also increased, which may improve the effectiveness of the 
molecular sieve constituent of the agglomerates in suppressing odor. 
The agglomerated adsorbent particles can consist of only the crystallites 
or particles of molecular sieve and the silica binder described above. In 
such agglomerates, the content of the molecular sieve constituent active 
in odor elimination is maximized. Unlike other binder materials, the 
colloidal sized amorphous silica particles of the present binder do not 
cause what is sometimes referred to as "binderblinding" of the molecular 
sieve. Binderblinding is in effect an interference by the binder with 
access by the intended adsorbate to the pore system of the molecular 
sieve. To some extent binderblinding can be alleviated by the inclusion in 
the bound agglomerate of particles of an inert diluent material with a 
particle size equal to or somewhat smaller than the adsorbent particles. 
The binder becomes attached preferentially to the diluent rather than to 
the molecular sieve particles. In effect, the diluent becomes the binder 
for the zeolite adsorbent. Though not necessary constituents in the case 
of the agglomerates of the present invention, inert diluents such as 
non-colloidal silicas, aluminas and clays can be included if desired, 
preferably in amounts less than about 40, preferably less than 30, weight 
percent of the overall agglomerate, anhydrous basis. 
In preparing the agglomerates of this invention it is only necessary to 
combine the molecular sieve crystallites with the colloidal silica binder 
and any other optional and suitable constituents, form the resulting 
mixture into agglomerates of the desired size and configuration, and 
calcine the agglomerates at elevated temperatures, preferably in the range 
of 500.degree. to 750.degree. C., but in no event at a temperature high 
enough to destroy the crystal structure of the molecular sieve. According 
to the preferred procedure, the molecular sieve crystals are blended with 
a silica sol having colloidal suspended SiO.sub.2 particles having nominal 
diameters of at least about 5 nanometers, preferably in the range of 5 to 
20 nanometers, and containing from 16 to 40 weight percent silica. The 
dispersion medium for the sol can be either aqueous or organic. The 
processes for preparing such sols are well known in the art. Suitable sols 
are available commercially from several sources including Nalco Chemical 
Company, E. I. duPont de Nemours & Co. and Monsanto Chemical Company. The 
blended mixture is then dried to form agglomerates in the range of 40 to 
800 micrometers. 
With reference to the diagram of FIG. 1 of the drawings, the spray-dried 
agglomerates of this invention are prepared by metering an aqueous 
colloidal silica sol contained in holding tank 10 and molecular sieve 
adsorbent particles from bin 12 into a blending device, such as a Cowles 
mixer or dissolver 14. The thoroughly blended mixture from mixer 14 is fed 
to a spray dryer 18 through line 16 which produces a range of agglomerated 
particle sizes, the bulk of which are of the predetermined desired sizes. 
The two variables which have the greatest effect upon the particle size of 
spray-dried slurries are viscosity and flow rate to the spray nozzles. An 
increase in either or both of these parameters results in an increase in 
the average diameter of the product. The viscosity of the silica 
sol-zeolite blend fed to the spray drier can easily be increased by 
increasing the solids content of the blend, and is the preferred technique 
in forming the mini-beads of the present invention. An alternative, though 
not preferred, technique is to add a viscosity enhancer, such as 
carboxymethyl cellulose to the blend. The undersized particle (fines) are 
separated from the spray dried product, advantageously using a cyclone 
type separator, and recycled through lines 20 and 22 to the mixer 14. The 
remaining agglomerates are passed from the spray drier through line 24 to 
calcination means 26 wherein the calcination temperature can range from 
about 500.degree. C. to 750.degree. C., but is preferably about 
650.degree. C. The hardened and activated (dehydrated) particles are 
thereafter screened for size in screen 28 and the oversized agglomerates 
passed through line 30 to mill 32 wherein they are ground to particles of 
less than about 20 microns. The ground particles are recycled to blender 
14 through line 22 and the agglomerates of proper size are collected as 
product and removed from the system through line 34. 
The invention is illustrated by the following examples: 
EXAMPLE 1 
(a) Agglomerate compositions both within and without the scope of the 
present invention were prepared using as ingredients: 
(i) A silica polymorph known in the art as silicalite and having a bulk 
Si/Al.sub.2 ratio of &gt;130. 
(ii) a high silica form of zeolite Y (framework Si/Al.sub.2 &gt;17) prepared 
by high temperature steam extraction of framework aluminum from the 
ammonium-exchanged form of the zeolite. The water adsorption capacity was 
&lt;6 weight percent at 25.degree. C. and 4.6 torr water vapor pressure. 
(iii) a basic (ammonium ion stabilized) aqueous silica sol sold under the 
tradename Nalco 2326 (Nalco Chemical Co.) containing 16 weight percent 
SiO.sub.2 and having nominally spherical silica particles with diameters 
of about 5 nanometers; 
(iv) an acid stabilized aqueous sol commercially available under the 
tradename Nalco 1034A containing 34 weight percent SiO.sub.2 and having 
nominally spherical silica particles with diameters of about 20 
nanometers. 
(v) an ammonium ion stabilized aqueous silica sol available commercially 
from E. I. duPont under the tradename Ludox AS-40. This sol contains 40 
weight percent SiO.sub.2 and contains silica particles about 20 nanometers 
in diameter. 
(vi) a solid amorphous precipitated silica commercially available under the 
tradename "HiSil" having a nitrogen surface area of 150 m.sup.2 /g and 
average agglomerate size of about 8 microns. 
(vii) a kaolin type clay sold under the tradename "Altowhite" by the 
Georgia Kaolin Company. 
(viii) an haloysite-type mineral clay generally known as New Zealand China 
clay (NZCC). 
The HiSil, NZCC and Altowhite materials were employed as diluents or 
fillers. The N2326, N1034A and AS-40 silica sols were utilized as binder 
precursers. Mixtures of the silicalite and the high-silica form of zeolite 
Y were the molecular sieve constituent of some of the agglomerate 
products, and in others the zeolite Y material was used alone as the 
molecular sieve constituent. Hereinafter, the mixture of silicalite and 
high silica Y is identified as "S/Y" and the high silica Y alone is 
identified as "Y." 
In preparing the agglomerates, the well-blended mixtures of ingredients 
were spray dried and calcined in air at 650.degree. C. The products were 
variously analyzed for oxygen capacity, attrition resistance and 
triethylamine adsorption capacity. 
The particulars concerning the chemical composition of the agglomerates and 
their properties are set forth in Table I, below. 
TABLE I 
__________________________________________________________________________ 
Molecular Sieve 
Silica Sol Binder 
Filler Agglomerate Particle 
Agglomerate Oxygen 
Type Wt. % 
Type Wt. % 
Type Wt. % 
Size Range, Micrometers 
Capacity, Wt. 
__________________________________________________________________________ 
% 
S/Y 75 N2326 
15 HiSil 
10 250 .times. 600 
18.05 
S/Y 75 N2326 
10 HiSil 
10 150 .times. 250 
18.04 
S/Y 85 N2326 
15 None -- 250 .times. 600 
-- 
Y 85 N1034A 
15 None -- 250 .times. 600 
-- 
S/Y 80 N2326 
20 None -- 250 .times. 600 
18.89 
S/Y 80 N2326 
20 None -- 250 .times. 600 
18.57 
S/Y 50 N2326 
20 HiSil 
30 250 .times. 600 
13.93 
Y 80 AS-40 
20 None -- -- 19.05 
Y 80 AS-40 
20 None -- -- 18.57 
S/Y 50 N2326 
20 Altowht. 
30 -- 12.69 
S/Y 60 N2326 
20 Altowht. 
20 -- 14.79 
S/Y 50 N2326 
20 NZCC 30 -- 12.75 
__________________________________________________________________________ 
EXAMPLE 2 
(a) The unique aspect of the colloidal silica bonded agglomerates in which 
the adsorption of oxygen and odor-causing organics exceeds their expected 
capacities in this regard, is demonstrated by the following experimental 
procedures: Five agglomerated products were prepared by spray drying and 
calcining at 650.degree. C. the blended mixtures whose compositions are 
set forth in tabular form below: 
TABLE II 
______________________________________ 
Sample Sample Sample Sample 
Sample 
Ingredient 
A B C D E 
______________________________________ 
S/Y, wt. % 
75 80 50 50 60 
N2326 15 20 20 20 20 
HiSil 10 -- 30 -- -- 
Altowhite 
-- -- -- 30 20 
______________________________________ 
The S/Y mixture of molecular sieves alone was determined to have an 
adsorption capacity for oxygen at -183.degree. C. and 100 torr oxygen 
pressure of 21.3 weight percent. Both the HiSil and the Altowhite filler 
materials have essentially nil capacity for oxygen under the same 
conditions. Thus, Sample A would be expected to adsorb 75% of the amount 
of oxygen adsorbed by an equal weight of pure S/Y molecular sieve 
constituent. Similarly, Sample B should adsorb 80% as much, samples C and 
D 50% as much and Sample E 60% as much oxygen as pure S/Y. It was found, 
however, that the samples all adsorbed more than the expected amounts of 
oxygen, the surplus being attributable to the N2326 colloidal silica 
binder. The values for the oxygen capacities of the sample at -183.degree. 
C. and 100 torr oxygen pressure are shown graphically in FIG. 2 of the 
drawings. It appears that the silica sol N2326 upon drying develops a pore 
system in which the pores have diameters of about 9 Angstroms. This value 
is calculated based on the assumption that the pores are cylindrical and 
monodispersed and that the micropore volume of the N2326 is 0.079 cc/g. 
and using the equation 
EQU d=4V/SA 
wherein "V" is the micropore volume of the solid in terms of m.sup.3 /g and 
"SA" is the BET surface area in terms of m.sup.2 /g (342 m.sup.2 /g for 
the N2326). In view of the size of the colloidal silica particle, 50 
Angstroms, and their generally spherical configuration the cylinder 
circumscribed by the close packed spheres is approximately 0.16 times the 
diameter of the spheres, or about 8 Angstroms, a value in good agreement 
with the pore diameter calculated above using the micropore volume and the 
surface area. 
(b) The micropore system developed in the binder by the colloidal-size 
silica particles is also found to adsorb triethylamine quite strongly, 
thus adding to the effectiveness of the siliceous molecular sieve 
agglomerate constituent in odor elimination. Samples of silica bonded 
agglomerates of this invention, the unbonded molecular sieve constituent 
and the silica binder alone were tested for adsorptive capacity for 
triethylamine (TEA) under various conditions of TEA partial pressure and 
using the adsorbents in both the hydrated and anhydrous states. The 
adsorbents tested were as follows: 
Sample A: A silica-bonded S/Y agglomerate containing 80 weight percent 
molecular sieve, 0 weight percent HiSil filler and 20 weight percent 
colloidal silica binder. The silica binder was derived from the 
commercially available silica sol obtained from Nalco Chemical Company 
under the tradename Nalco 2326. The S/Y molecular sieve composition was a 
mixture of the same silicalite and the steam-treated form of zeolite Y as 
used in Example 1 above. 
Sample B: The same S/Y agglomerate composition of Sample A except when 
tested the agglomerate contained 20 weight percent water. 
Sample C: A pure sample of the Nalco 2326 silica binder used in the 
preparation of Sample A which had been calcined at 650.degree. C. for 1 
hour. 
Sample D: The same Nalco 2326 composition as Sample C except immediately 
prior to testing the sample was allowed to become hydrated to the extent 
that it contained 20 weight percent water. 
Sample E: A sample of the same S/Y molecular sieve mixture used in the 
preparation of Sample A. 
The TEA adsorption isotherms at 35.degree. C. for the various compositions 
are set forth in tabular form below: 
TABLE III 
______________________________________ 
TEA Partial Pressure 
Wt % TEA 
Sample No. P/Po at .degree.C. 
Adsorbed 
______________________________________ 
A 0.12 9.5 
A 0.1 .times. 10.sup.-2 
7.2 
B 0.1 .times. 10.sup.-1 
7.2 
B 0.27 8.8 
C 0.1 .times. 10.sup.-2 
7.2 
C 0.04 10.0 
D 0.12 6.5 
D 0.58 7.0 
E 0.65 11.0 
E 0.1 .times. 10.sup.-2 
5.8 
E 0.4 9.0 
E 0.28 7.5 
______________________________________ 
It is readily apparent from the data of Table III that upon hydration the 
adsorption capacities of both the silica binder composition and hence the 
agglomerates of the present invention decrease compared with their 
respective anhydrous forms. As expected from the known characteristics of 
the molecular sieve constituents, the decrease in TEA capacity for the 
binder alone was greater than for the bonded molecular sieve agglomerates, 
but the capacity for TEA of the bonded agglomerate remains higher after 
hydration than the calculated capacity based solely on the zeolite 
content. 
To limit the adverse effect upon adsorption characteristics resulting from 
hydration of the silica binder material, the surface of the silica 
particles can be treated to remove at least a portion of the terminal 
hydroxyl groups bonded to surface silicon atoms. Such treatments, using 
procedures well known in the art, can be either thermal or chemical. The 
thermal treatment comprises simply calcining the silica bonded agglomerate 
at temperatures in the range of 300.degree. C. to 800.degree. C. for 
periods of from about 3.times.10.sup.-4 to 2 hours in dry air to 
dehydroxylate the surface of the silica particles which form the binder 
without thermally destroying the crystal structure of the bonded siliceous 
molecular sieve particles. It will be understood by those skilled in the 
art that the calcination time and temperature are interdependent, the 
higher temperatures requiring the least time to accomplish 
dehydroxylation. 
Several chemical treatments are known in which the surface silanol groups 
are converted to other groups, such as methoxy or siloxy groups, which 
inhibit the adsorption of water on the silica surface. Other methods 
involve the "screening" of silanol groups by coating the silica particles 
with polymer such as a polysiloxane. In the methoxylation procedure the 
silica particles can simply be heated at an appropriate temperature and 
time in a methanol vapor until the degree of methoxylation has occurred. 
For complete methoxylation it is necessary to treat the silica particle 
several times with methanol vapor since water formed from the reaction of 
the methanol with the silanol groups of the silica causes some hydrolysis 
of the .tbd.Si--OH groups previously formed. It has also been proposed by 
M. J. D. Low et al, Journal of Catalysis,44, 300-305 (1976), to 
methoxylate silica with other methoxy-containing compounds of which 
trimethoxymethane (TMM) was the most efficient. TMM reacts readily and 
completely removes surface silanols in the relatively short time of less 
than 20 minutes at a temperature in the range of 300.degree.-400.degree. 
C. at TMM pressures of 10 to 30 torr. Low et al have also reported 
successful dehydroxylation of silica surfaces by reaction with 
trichlorosilane at 350.degree. C. See Journal of Catalysis, 54, 219-222 
(1978), in this regard. Other reactive silanes include alkyl, aryl 
(especially phenyl) and aralkyl halosilanes and silazanes. These reactants 
employed to accomplish silanization include dimethyl monochlorosilane, 
dimethyl dichlorosilane, hexamethyl disilazane and 
trichlorooctadecylsilane. Treatments of silicas involving these silanes 
are disclosed in U.S. Pat. No. 4,954,532, issued Sep. 4, 1990, to T. J. 
Elliott et al. In the Elliott et al patent it is also disclosed to 
polymerize a suitable siloxane monomer in the presence of the silica 
particles thereby coating the particles with a polysiloxane to render the 
particles hydrophobic. Suitable siloxane monomers for this purpose include 
methyl hydrogen polysiloxane and alkyl, aryl and aralkyl 
cyclotetrasiloxanes, especially octamethylcyclotetrasiloxane. 
Polymerization can readily be accomplished by heating.