Ammoniated silica-alumina gel and catalyst containing the same and processes for producing same

This invention relates to hydrothermal treatment of silica-alumina cogels resulting in a reduction in the NH.sub.4 content of the gel and the generation of a beta crystal phase and the employent of such gels as cracking catalysts.

Prior to the introduction of the exchanged crystalline zeolites of the 
faujasite type, as a catalyst for cracking of hydrocarbons, a commonly 
used catalyst was composed of a silica-alumina cogel containing from about 
3 to about 25 percent by weight of Al.sub.2 O.sub.3 on a volatile free 
basis. 
Because of the substantially higher activity of the catalyst formed from 
crystalline zeolite, they have replaced to a large measure the 
silica-aluminum cogels as the primary component of a hydrocarbon 
conversion catalyst. 
The literature relating to a silica-alumina gels and their catalytic 
properties is extensive (see Iler, "The Colloid Chemistry of Silica and 
Silicates", Chapter VI, Cornell Press [1955] Ed.) and citations there 
given. Milliken, et al., "Discussions Faraday Society" No. 8, 
"Heterogeneous Catalysis" p. 279, etc. (1950) Mills, et al., Journal of 
the American Chemical Society, vol. 72, pp. 1554-1556 (1950). See also: 
Erickson, U.S. Pat. No. 2,872,410; Winyall, U.S. Pat. No. 2,886,512; 
Wilson, U.S. Pat. No. 3,124,541; Magee, et al., U.S. Pat. No. 3,433,748; 
Haden U.S. Pat. No. 3,065,054; Maher, et al, U.S. Pat. No. 3,423,332; 
Lussier, et al, U.S. Pat. No. 3,974,099. 
STATEMENT OF THE INVENTION 
We have discovered that the catalytic cracking activity of the 
silica-alumina cogels which are substantially free of sodium or other 
alkali or other alkali metal cations may be materially improved by 
digesting the cogel at an elevated temperature in the presence of 
solutions containing hydrogen, ammonium or polyvalent cations such as rare 
earth or alkaline earth cations. 
Gels so treated may, depending on the gel and the reaction system and the 
conditions of treatment, remain in the amorphous state or develop a 
crystalline phase. 
Gels which have ammonium cations associated with the gel are herein 
referred to as ammoniated gels. Such gels for example may contain 
substantial concentrations of ammonium cations. 
Gels may also be formed substantially free of ammonium cations by reacting 
sodium aluminate with an aluminum salt and maintaining the mixture on the 
acid side. The sodium content of the acid gel may be similar to that of 
the ammoniated gel. We refer to such gels as acid gels. 
While hydrothermal treatment of the acid gel according to the process of 
our invention produces a gel of substantial catalytic activity, supeprior 
activity is obtained by treatment of the ammoniated gel. 
In the case of the ammoniated gels the improvement in catalytic activity 
obtained by the hydrothermal treatment is increased by treatment at a 
temperature in excess of about 150.degree. F. In such ammoniated gels, 
preferably those containing SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 
less than about 3, substantially free of sodium cations, the catalytic 
activity of the gel is increased to a degree which is dependent on the 
concentration of the ammonium cations associated with the treated gel. 
Preferably the NH.sub.4 content of the gel, expressed as NH.sub.3, is in 
the range from less than about 0.3 and preferably less than 0.2 
equivalents of ammonium ion per mole of Al.sub.2 O.sub.3. 
The activity produced from such gels depends on the conditions of the 
hydrothermal treatment and the ionic system. A crystalline phase may 
develop or the gel may remain amorphous and a reduction in the ammonium 
content of the gel and an increase in the catalytic activity of the gel 
may be obtained in both cases. 
The activity may be measured by the microactivity cracking test described 
in the Oil and Gas Journal of Sept. 16, 1966; page 48, etc,; and Nov. 22, 
1975; page 60, etc. 
In the following examples the conditions in carrying out the above tests is 
as follows. The calcined pelleted catalyst was first steamed at 
temperatures and for times specified below and then used in cracking of a 
petroleum fraction under the following conditions. The oil charge is a 
wide boiling range high sulfur feed stock (boiling range about 430.degree. 
to 1000.degree. F.). The catalyst to oil ratio is 4. The weight hourly 
space velocity is 16.45 grams of oil per gram of catalyst per hour. The 
temperature of the reactor is 910.degree. F. The percent conversion is 
reported as the volume of liquid condensate product of boiling point range 
of up to 421.degree. F. based on the volume of liquid charge. The percent 
conversion when the catalyst is tested after calcination of the catalyst 
in air for two hours at 1450.degree. F. is termed M activity. When the 
calcined sample is steamed at 1500.degree. F. for two hours, prior to 
testing it is termed the S activity. When the calcined sample is first 
steamed for two hours at 1550.degree. F., prior to testing, it is termed 
S+ activity. 
The process of our invention includes the treatment of a silica-alumina 
cogel containing less than about 1% of Na.sub.2 O based on the cogel on a 
volatile free basis by a hydrolytic treatment of the gel. The treatment 
may be carried out in the presence of monovalent cations other than alkali 
metal cations such as hydrogen or ammonium or polyvalent cations such as 
rare earth cations or alkaline metal cations. We prefer to carry out the 
hydrothermal treatment under acid conditions rather than at higher pH as 
for example under alkaline conditions. A superior amplification in the 
activity by reductions in ammonium content in the gel is obtained by 
treatment under acid conditions. 
Under relatively mild and controlled hydrothermal conditions of 
temperatures below about 300.degree. F., the reaction of the gel having 
low Na.sub.2 O content, results in an amorphous gel which exhibits 
superior catalytic activity as compared with the original gel. At 
temperatures above about 350.degree. F. and at suitable concentrations of 
cations and time of digestion a crystalline phase develops. 
The nature of the crystalline phase as evidenced by its x-ray spectrum 
depends on the nature of the cations employed in the hydrothermal 
treatment. The product of this application is produced by employing an 
acid solution of rare earth cations. The characteristic of the crystal 
phase developed in the gel depends on the conditions of the reaction for 
example, the ratio of the rare earth to the gel and the time of digestions 
at the above temperatures under autogenous superatmospheric pressure 
according to the invention of this application. A crystal phase is 
generated in the gel which acts as a host for the crystalline phase. For 
purposes of distinguishing the gel and the crystal phase from others which 
may be generated by variations in the hydrolytic treatment of the cogel, 
we have designated the crystal phase as "beta" and the gel which contains 
the "beta" phase as "beta" cogel. 
The crystalline phase is characterized by an x-ray spectrum in which 
characteristic peaks occur. Excessive exposure of the gel for prolonged 
periods of time particularly at the higher temperatures may deliteriously 
affect the catalytic activity of the deammoniated gel although a 
successful reduction in ammonium content is achieved. 
For purposes of describing the result of the process of treating the 
ammoniated gel with water or a solution of a salt, whereby the NH.sub.4 
content of the gel is reduced, we refer to the process as an "exchange" 
and the cation as "associated" with the gel. 
The cogel, which we prefer to treat by the process of our invention to form 
the catalyst of our invention may be produced by any of the methods used 
in the prior art to form such cogels in which the treatment results in a 
gel having an ammonium ion associated with gel as in the ammoniated gel 
referred to above. 
The cogel, which may be hydrothermally treated according to our invention, 
may be formed by treating a mixture of silica hydrosol with aluminum salt 
in the ratios to produce a gel of the desired SiO.sub.2 /Al.sub.2 O.sub.3 
ratio and exchanged with ammonium cation to reduce the sodium content of 
the gel. 
We prefer to coprecipitate the silica-alumina hydrosol to form the gel from 
a mixture of sodium silicate and aluminum salt, e.g. aluminum sulfate, or 
aluminum nitrate or aluminum chloride made alkaline with ammonium 
hydroxide to reduce the sodium content as is more fully described below. 
We have found that the improvement in the catalytic activity of a gel 
treated according to our invention depends on the silica to alumina ratio 
of the cogel. The ammonia content of the ammoniated gel of our invention 
depends on the silica to alumina ratio of the gel. The catalytic activity 
attainable by our invention is substantially greater as the molar weight 
ratio of SiO.sub.2 to Al.sub.2 O.sub.3 is less than about 3 and preferably 
about 1 to about 2. 
Our preferred embodiment of our invention is to employ an ammoniated 
silica-ammonia cogel having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio in 
the range of about 1.25 to about 2.5, and an ammonium ion content of less 
than about 0.3 equivalents of ammonium cation per mole Al.sub.2 O.sub.3 to 
form a catalyst having a M activity in excess of 60%. 
The preferred embodiment of the process for producing the "beta" cogel is 
to hydrothermally treat an ammoniated cogel with an acid solution of rare 
earth cations in amount of about 10% of the weight of the gel on a 
volatile free basis, at an elevated temperature to reduce the ammonia 
content of the gel to less than about 1% by weight of the treated gel to 
produce a beta crystal phase as set forth below. 
We prefer to employ the gel formed when using the ammoniated cogel formed 
from aluminum sulfate.

EXAMPLE 1 
5,017 grams of sodium silicate (28% SiO.sub.2 -8.9% Na.sub.2 O by weight) 
equivalent to 1,440 grams of SiO.sub.2 is dissolved in water. The slurry 
solution is acidified to a pH of 11 with sulfuric acid; 26,896 grams of an 
aluminum sulfate solution (equivalent to 1,560 grams of Al.sub.2 O.sub.3) 
is added gradually to the acidified slurry with constant agitation. 
The pH at the end of the addition of the aluminum sulfate should be in the 
range of about 3 to about 3.5. The solution is passed through a colloid 
mill to be well homogenized. The homogenized solution is made alkaline 
with ammonium hydroxide with constant and vigorous agitation to adjust the 
mixture to a pH of about 8.5 to about 9. 
The mixture is vigorously stirred and the pH is maintained in the range of 
about 8.5 to about 9 by suitable adjustment for about 1 hour to insure 
uniformity of the mixture. It is then heated to a temperature of about 
75.degree. to 80.degree. C. for about 30 minutes and then immediately 
filtered and the filter cake washed with hot distilled water of about 
80.degree. C. The wash filter cake is then slurried to a solid content of 
about 5% in distilled water which contained about 2% of ammonium nitrate 
and then filtered. The filter cake is then again slurried with ammonium 
nitrate solution as in the last previous step. The filter cake from the 
last step is again reslurried in an ammonium nitrate solution as above and 
filtered. The filter cake from the last filtration above is washed with 
distilled water. 
The silica-alumina gel thus produced is preferably maintained in a sealed 
container prior to use in the catalyst of our invention. It should be used 
as promptly as possible since aging of the gel will impair its properties 
in producing a good attrition resistant catalyst. 
The ammoniated cogel is amorhpous to K alpha copper radiation at 500 counts 
per second on the counter of the strip chart x-ray spectrum so produced. 
The gel produced as above, was employed in the following examples, except 
in Example 19 where the acid gel was used. In all examples and except as 
is indicated in Example 7, where zerogel was employed, all of the examples 
employed the hydrogel. 
The above cogel was pelleted and tested by the microactivity test 
identified above after steaming at 1450.degree. F. for two hours (M 
activity) and again another sample after steaming at 1500.degree. F. for 
two hours (S activity) and a third sample after steaming for two hours at 
1550.degree. F. (S+ activity). The results are reported as volume percent 
conversion. The results obtained were as follows: 
______________________________________ 
M S S+ 
______________________________________ 
Volume % conversion: 
43 36.5 46 
______________________________________ 
The gel was also mixed with acid treated halloysite (see Secor, 2,935,463 
and 3,446,727) in the ratio of 90% by weight of the dried gel and 10% by 
weight of the dry halloysite. The mixture was tested as above with the 
following results: 
______________________________________ 
M S+ 
______________________________________ 
Volume % conversion: 
47 44 
______________________________________ 
EXAMPLE 2 
1,600 grams of the cogel prepared as in Example 1 (calculated on a volatile 
free basis) was mixed gradually with 18.4 liters of rare earth sulfate 
solution containing 1.96% of rare earth oxides ReO while the mixture was 
maintained for about an hour at a pH of 5 by adjustment during the mixing. 
The composition of the rare earth sulfate expressed as oxides and 
symbolized as ReO was: 
______________________________________ 
La.sub.2 O.sub.3 = 57% by weight 
CeO.sub.2 = 16% by weight 
Nd.sub.2 O.sub.3 = 21% by weight 
Other rare earth oxides 
= 7% by weight 
______________________________________ 
100 grams of Reo (volatile free) is equal to 1.896 equivalents of ReO, 
i.e., 52.7 grams per equivalent. 
The ReO was determined by the standard oxalate method. See Roden, 
"Analytical Chemistry of the Manhatten Project", McGrawHill Co., Chapter 
22. In all examples, ReO was similarly determined and had the above 
equivalent value. 
The above mixture was held at the temperature of about 180.degree. to 
200.degree. F. for about 2 hours at atmospheric pressure. During the 
reactions, the pH of the mixture was adjusted to hold a pH in the range of 
5.2 to 5.4. 
The filter cake was analyzed on a volatile free basis as follows. 
______________________________________ 
SiO.sub.2 
= 48.8% by weight 
Al.sub.2 O.sub.3 
= 45.6% by weight 
ReO = 4.15% by weight 
NH.sub.3 = 0.3% by weight 
Na.sub.2 O 
= 0.06% by weight 
SO.sub.3 = 0.67% by weight. 
______________________________________ 
The x-ray spectrum obtained as in Example 1, showed lines having the "d" 
spacings and intensities as in the following Table 1. 
TABLE 1 
______________________________________ 
d I 
______________________________________ 
6.39 6 
6.26 24 
4.58 3 
3.57 3 
3.49 3 
3.41 2 
3.24 2 
3.14 3 
3.00 10 
2.86 3 
2.43 2 
2.21 6 
______________________________________ 
We have designated the above crystal phase as "alpha" and the host gel as 
"alpha" gel. 
The cogel treated as above was slurried in water with 10% of acid treated 
halloysite and 90% of the cogel all measured on a volatile free basis in 
Example 1 and subjected to the above test as set forth in Example 1 with 
the following results: 
______________________________________ 
M S S+ 
______________________________________ 
Volume % conversion 
77 62 56 
______________________________________ 
EXAMPLE 3 
The procedure of Example 2 was repeated except the ReO was used in the 
ratio of 10% by weight of the gel. The exchanged gel had the following 
composition: 
______________________________________ 
SiO.sub.2 = 44% 
Al.sub.2 O.sub.3 
= 47.6% 
ReO = 6.81% 
NH.sub.3 = 0.75% 
Na.sub.2 O = 0.06% 
______________________________________ 
Examined by x-ray as in Example 1, the pattern showed that the gel 
contained a crystalline phase substantially different from the product of 
Example 2. The following Table 2 states the "d" spacings of the 
reflections. 
TABLE 2 
______________________________________ 
d (Angstroms) I 
______________________________________ 
8.44 44 
4.75 4 
4.47 5 
4.24 4 
4.16 3 
3.96 3 
3.76 3 
3.26 4 
3.04 3 
2.33 2 
______________________________________ 
This crystal phase is designated as "beta" and the host gel as "beta" gel. 
The exchanged gel when formulated as in Example 1 had the following 
results: 
______________________________________ 
M = 68.4% 
S+ = 61.6% 
______________________________________ 
The M activity of the alpha gel is substantially greater than the M 
activity of the "beta" gel but the hydrothermal stability of the "beta" 
gel as reflected by the larger S+ activity is substantially superior to 
the "alpha" gel. 
In employing rare earth sulfate for the exchange salt in the hydrolytic 
treatment of the gel, the improvement in activity obtained by the 
generation of the beta phase may be depreciated if the temperature or the 
ratio of the cations to the gel or the time of digestion or both are made 
excessive. Reference is had to our copending application, Ser. No. 3,879; 
filed Jan. 16, 1979, and Ser. No. 9,487; filed Feb. 5, 1979 for further 
details. The acid applications are incorporated herein by this reference. 
While we do not wish to be bound by any theory of why the facts are as 
observed, the data tends to indicate that the hydrolytically treated gel 
forms, whether it be a crystalline or amorphous, a catalytically active 
structure which is a metastable form. Continued treatment or excessive 
temperatures transform the gel and depreciates its activity. 
The preferred embodiment of our invention is as stated in Example 3. 
Modifications of the temperature, ratios of reactants, pH, time and time of 
digestion may be adjusted to produce the "beta" gel. Departures from the 
conditions as set forth in said examples may be made and the deammoniated 
gel x-rayed as described above. Such variations following the above guides 
will permit those skilled in the art to produce the "beta" gel of this 
invention. 
It will be understood by those skilled in this art, that the exact values 
of the "d" spacings of the "beta" crystal phase may vary, for example, 
plus or minus about 1 or 2% from those of Table due to experimental 
artifacts and uncertainties in the production of x-ray spectra. 
Those skilled in the art will understand from the above disclosure how to 
determine temperatures, time, cation concentration and ratios to the gel 
to obtain the desired level of activity. The examples illustrate the 
procedure and result effective parameters and may act as a guide to those 
who wish to determine these parameters for their particular conditions and 
desired result. 
The treated gel may be employed with or without a matrix, i.e. alone if 
desired as for example, as a microsphere obtained by spray drying the 
slurry of the exchanged product by dispersing the washed filter cake in 
water and spray drying. 
Instead of using the exchanged gel either alone or mixed with a relatively 
catalytically inactive constituent acting as a matrix such as clay, silica 
gel or alumina gel or other inorganic oxide such as gel or cogel, the 
exchanged gels produced according to our invention may be combined with an 
exchanged zeolite. Such as the ammonium or the rare earth or rare earth 
and ammonium exchanged zeolites or alkaline with exchanged zeolite either 
of the faujasite type such as the X or Y zeolite or other crystalline 
alumino-silicate zeolites such as mordenite, chabazite, erionite, and 
zeolite A. 
The mixture may be in the ratio in the range of about 1% to less about 50% 
by weight of the zeolite suitably exchanged, if necessary, to a sodium 
content as in the case of catalysts of the prior art and the above 
exchanged silica-alumina gel. In the case of an ammonium or a rare earth 
exchanged Y or exchanged with both NH.sub.4 and ReO, with a Na.sub.2 O 
ratio of less than 5% by weight on a volatile free basis, we may use a 
minor proportion of about 1 to less then 50% of zeolite based on the 
mixture of gel and zeolite. A suitable mixture is about 20% by weight of 
the zeolite to 80% by weight of the cogel all on a volatile free basis. 
Such mixtures may suitably be combined with matrix material for zeolites 
in the prior art. 
When using the exchanged "beta" gel with a zeolite, we prefer to use the 
exchanged gel to be mixed with the rare earth exchanged zeolites of the 
prior art with an Na.sub.2 O content of less than about 4-5%, for example 
3.5% and preferably the so-called A type pseudoboehmite (see U.S. Pat. No. 
4,100,108). We prefer to employ the Y zeolite of an SiO.sub.2 /Al.sub.2 
O.sub.3 ratio of above 4 for example, 4.5. The percent of the zeolite in 
the gel zeolite mixture on a volatile free basis may be about 5% to 25% of 
the mixture. 
Instead of mixing the exchanged gel with the exchanged zeolite as above, we 
may combine the zeolite either in the sodium form or exchanged as above 
with the gel such as the gel of Example 1. (See our applications Ser. Nos. 
769,118, filed Feb. 6, 1977; now U.S. Pat. No. 4,142,995 and 874,755, 
filed Feb. 3, 1978 now U.S. Pat. No. 4,198,319.) The zeolite may be 
partially exchanged for example with NH.sub.4 or rare earth or with both 
for example to reduce the Na.sub.2 O to about 3 to about 6% of the 
exchanged gel on a volatile free basis. The spray dried zeolite and gel 
may then be exchanged, preferably with an acid solution of rare earth 
salts as is described in the above examples. 
Our invention includes the use of the hydrothermally treated gel of our 
invention either alone or combined with a matrix as above, and whether or 
not combined with a zeolite as described above, in catalytic process other 
than straight catalytic cracking as described above. Such processes 
include other hydrocarbon conversion process such as, fore example, 
hydrocracking, hydroforming and hydrodesulfurizing process. Promoters 
employed in the prior art in catalysts for such process may be employed 
with the hydrothermally treated gels of our invention.