U.S. patent application number 10/084299 was filed with the patent office on 2003-03-27 for powders of silica-oxide and mixed silica-oxide and method of preparing same.
Invention is credited to Auburn, Pamela R., Chan, Ignatius Y., Percoraro, Theresa A., Whaley, Darryl K..
Application Number | 20030060582 10/084299 |
Document ID | / |
Family ID | 22028896 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030060582 |
Kind Code |
A1 |
Percoraro, Theresa A. ; et
al. |
March 27, 2003 |
Powders of silica-oxide and mixed silica-oxide and method of
preparing same
Abstract
Silica powders and mixed silica-oxide powders and methods of
preparing such powders for use as catalyst supports for
polymerization processes.
Inventors: |
Percoraro, Theresa A.;
(Danville, CA) ; Chan, Ignatius Y.; (Novato,
CA) ; Whaley, Darryl K.; (Vallejo, CA) ;
Auburn, Pamela R.; (Houston, TX) |
Correspondence
Address: |
Chevron Phillips Chemical Company LP
Room 3447
1301 McKinney
Houston
TX
77010
US
|
Family ID: |
22028896 |
Appl. No.: |
10/084299 |
Filed: |
February 27, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10084299 |
Feb 27, 2002 |
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09557437 |
Apr 25, 2000 |
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6372685 |
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09557437 |
Apr 25, 2000 |
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09060340 |
Apr 14, 1998 |
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6107236 |
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Current U.S.
Class: |
526/129 ;
502/232; 502/240; 502/256; 526/348.2; 526/348.5; 526/348.6 |
Current CPC
Class: |
B01J 35/1047 20130101;
B01J 35/1061 20130101; B01J 35/002 20130101; B01J 21/12 20130101;
C01B 33/126 20130101; B01J 35/1019 20130101; B01J 35/1023 20130101;
B01J 21/08 20130101; B01J 35/1042 20130101 |
Class at
Publication: |
526/129 ;
526/348.5; 526/348.2; 526/348.6; 502/232; 502/240; 502/256 |
International
Class: |
C08F 004/44; C08F
010/14; B01J 021/08 |
Claims
What is claimed is:
1. An amorphous SiO.sub.2 or mixed oxide silica base composition
comprising: (a) a non-particulate, dense, continuous network
matrix; and (b) encapsulated, less dense, non particulate regions
with true macropores.
2. The composition of claim 1, wherein the gel matrix further
comprises a sheetlike microstructure.
3. The composition of claim 1, wherein the composition has surface
areas in a range of from 150 to 600 m.sup.2/gm.
4. The composition of claim 1, wherein the composition has a mean
mesopore diameter in a range of from 60 to about 250 .ANG..
5. The composition of claim 1, wherein the composition has a
measured pore volume in a range of from about 0.5 to 1.5 cc/gm.
6. The composition of claim 1, wherein the composition has a
macropore volume of at most 0.5 cc/gm.
7. The composition of claim 1, wherein the composition is a mixed
metal silica oxide selected from the group consisting of silica
alumina, silica titania, silica zirconia and silica vanadia.
8. Powders produced from the composition of claim 1.
9. The powders of claim 8, wherein the powders are spray dried.
10. The powders of claim 8, wherein the powders are vacuum
dried.
11. The spray dried powders of claim 9, wherein fragmentation
potentials are in a range of from about 20 about 30.
12. A catalyst comprising the composition of claim 1 impregnated
with a catalytic amount of at least one transition metal-containing
compound.
13. The catalyst of claim 12, wherein the at least one transition
metal-containing compound is a chromium compound.
14. The catalyst of claim 12, wherein the at least one transition
metal-containing compound is present in an amount of 0.1 weight
percent or greater based on the total catalyst weight.
15. The catalyst of claim 14, wherein the at least one transition
metal-containing compound is present in an amount in the range of
from about 0.1 weight percent to about 10 weight percent.
16. A polymerization process comprising contacting the catalyst of
claim 12 with at least one alpha-olefin under polymerization
conditions.
17. A method for preparing a silica gel composition which is a
precursor material for a silica powder material with a
microstructure comprising a non-particulate, dense, continuous,
network matrix and encapsulated, less dense, non-particulate
regions with true macropores, the method comprising: (a) forming a
first aqueous solution comprising silica ions; (b) forming a second
aqueous solution capable of neutralizing said first aqueous
solution; and (c) contacting said first and second aqueous
solutions in a mixer-reactor under mixing conditions with shear
forces to form the silica gel composition.
18. The method according to claim 17 further comprising aging the
silica gel composition in acidic or basic conditions for up to one
hour.
19. The method of preparing the silica powder composition from the
silica gel composition prepared by the method of claim 17,
comprising the steps of: (a) washing the silica gel with solutions
of ammonium acetate, bicarbonate or nitrate; (b) washing the silica
gel composition in deionized water to further replace
salts-contaminated water in the composition with fresh water; and
(c) drying the washed composition to remove substantially all
water.
20. The method of claim 19, further comprising calcining the dried
composition for up to 8 hours at a maximum temperature of
450.degree. C.
21. The method according to claim 17, wherein said first aqueous
solution is an acidic solution comprising sodium silicate and acid
wherein the second aqueous solution has a pH above 8.
22. The method according to claim 17, wherein said second aqueous
solution is an ammonia based material selected from the group
consisting of ammonium hydroxide; ammonium carbonate; ammonium
bicarbonate and urea.
23. The method according to claim 17, wherein said first aqueous
solution is a basic solution of sodium silicate and wherein the
second aqueous solution has a pH below 6.
24. The method according to claim 17, wherein said second aqueous
solution is sulfuric acid.
25. The method according to claim 17, wherein the apparent average
shear rate in said mixer-reactor is greater than about
0.5.times.10.sup.4 sec.sup.-1.
26. The method according to claim 17, wherein said neutralization
step is conducted in such a manner that the pH of the combined
first aqueous solution and the neutralizing medium is controlled in
the range of about 3.5 to about 11.
27. The method of claim 17, wherein said catalyst is activated by
being heated to a temperature in the range of 300.degree. C. to
900.degree. C. for from 2 to 16 hours.
28. The method of claim 21 further comprising the steps of: (a)
preparing an aqueous slurry of amorphous silica gel by continuously
feeding an acidic solution comprising sodium silicate and acid to
an emulsifier mixer while simultaneously and continuously feeding
to said mixer an alkaline solution; (b) operating said mixer with
sufficient shear so that the precipitated silicate has sheets of
silica in its microstructure; (c) recovering said silica from said
aqueous slurry using a vibrating filtration membrane to a solids
content from 8 to 20 wt. %, after washing; (d) drying the silica
from (c); (e) calcining the silica from (d); (f) dispensing a
chromium compound substantially uniformly onto said silica from (d)
or (e) to form a catalyst having from 0.01 to 4 wt. % chromium; (g)
drying said catalyst; and (h) activating said dry catalyst from (f)
by heating to a temperature from 300.degree. C. to 900.degree. C.
for from 2 to 16 hours.
29. An olefin polymerization catalyst prepared by the method of
claim 17.
30. An olefin polymerization catalyst prepared by the method of
claim 28.
31. A polymerization process according to claim 15 comprising
contacting at least one mono-1-olefin having from 2 to 8 carbon
atoms per molecule under polymerization reaction conditions in a
polymerization reaction zone with a catalyst comprising an active
catalytic component on a silica support comprising (a) a
non-particulate, dense, gel matrix; and (b) encapsulated regions
with true macropores.
32. A process according to claim 31, wherein said catalytic
component comprises a chromium component on the silica support.
33. A process according to claim 31, wherein said at least one
mono-1-olefin is selected from ethylene; propylene; butene-1;
hexene-1 and octene-1.
34. A process according to claim 33, wherein said at least one
mono-1-olefin comprises ethylene and from 0.5 to 2 mole percent of
one additional mono-1-olefin is selected from propylene; butene-1,
hexene-1 and octene-1.
35. A method for preparing silica alumina powder material with a
microstructure comprising a non-particulate, dense continuous
network matrix, encapsulated regions with true macropores, and
sheets, the method comprising: (a) preparing an acid aqueous
solution comprising aluminum and silicon ions; (b) preparing a
basic aqueous solution comprising ammonium hydroxide; (c) mixing
the acidic aqueous solution and the basic aqueous solution in a
mixer with shear forces to obtain a gel slurry with a
microstructure comprising a non-particulate, dense, continuous
network matrix, encapsulated regions with true macropores and
sheets; (d) maintaining the gel slurry at approximately pH 8.0 for
up to one hour before washing the gel; (e) washing the gel slurry
first with aqueous acetate solution, then with water to obtain a
gel conductivity below 1,000 mmhos; (f) acidifying and
concentrating the gel slurry by adding acid to the gel slurry to
achieve a pH below 6.0 while gradually removing water from the gel
slurry; and (g) drying and calcining the gel slurry to form the
silica-alumina powder material.
Description
FIELD OF THE INVENTION
[0001] This invention relates to silica powders and mixed
silica-oxide powders and methods of preparing such powders for use
as catalyst supports for polymerization processes.
BACKGROUND OF THE INVENTION
[0002] The use of amorphous gels and precipitates as support
material for polymerization catalysts is known. For example,
aluminophosphate gels and precipitates have often been used for
such support materials. In some cases, the support was improved by
incorporating silica into the aluminum phosphate support.
[0003] While aluminophosphates have long been known, along with
their methods of preparation, such aluminophosphates have not as
yet achieved commercial success. Part of this is believed to be
that the prior art aluminophosphates lacked a combination of
physical properties which have been found to characterize superior
polymerization catalysts. It is the combination of a high macropore
volume of at least 0.1 cc's per gram plus a fragmentation potential
(to be defined below) of preferably 30 to 60 plus a preferred
mesopore volume of 0.3 to 0.8 cc's per gram which particularly
characterize the superior polymerization catalysts. In two prior
inventions of Applicants (Pecoraro and Chan, U.S. patent
application Ser. No. 08/742,794; Auburn and Pecoraro, U.S. patent
application Ser. No. 08/741,595), which are incorporated herein by
reference, a new aluminophosphate with both high macropore volume
and a fragmentation potential about 30 was developed which was also
both physically and thermally stable. It is believed that the
presence of sheets of aluminophosphate in the microstructure
results in the packing of the microstructures in such a way that a
high macropore volume and a high fragmentation potential are
achieved along with physical and thermal stability.
[0004] In another related invention by Applicants (U.S. application
Ser. No. 08/961,825, Auburn, Pecoraro and Chan), which is a
continuation-in-part of 08/741,595 and 08/742,794 discussed above,
and which is also incorporated by reference herein, a
silica-modified, amorphous aluminophosphate composition which like
the previous inventions exhibits a microstructure of sheets and
exhibits spheres of silica-modified aluminophosphate as well.
[0005] The use of silica alone or the combination of silica with
other oxides such as alumina or titania or vanadia to form such
amorphous compositions for use as polymerization catalyst support
material is also known. Previously, the microstructure of such
supports primarily contained small particles. As a result of this
small particle structure, it was difficult to tailor the materials
over a wide range of pore sizes, distributions and volumes, and of
acceptable fragmentation characteristics.
[0006] It would be desirable to find silica support materials which
could be used over a wide range of pore sizes, distributions and
volumes and of acceptable fragmentation characteristics.
[0007] The present invention has achieved such materials. The
present invention has achieved high surface area, amorphous silicas
which surprisingly form a continuous network matrix, rather than
the typical small particles found in conventional amorphous
silicas. Furthermore, the pore size and the distribution and volume
of the pore size can be tailored over a wide range. Surprisingly,
also, the present invention achieves an amorphous SiO.sub.2 base
composition with a non-particulate, dense, network matrix and
encapsulated less dense, non particulate regions with true
macropores. In one embodiment, the present invention also comprises
a sheet-like microstructure.
SUMMARY OF THE INVENTION
[0008] One object of the present invention is to provide an
amorphous SiO.sub.2 or mixed oxide silica base composition
comprising:
[0009] (a) a non-particulate, dense, continuous network matrix;
and
[0010] (b) encapsulated, less dense, non particulate regions with
true macropores.
[0011] Another object of the present invention is to provide such
an amorphous SiO.sub.2 or mixed oxide silica base composition in
which the gel matrix further comprises a sheetlike
microstructure.
[0012] Still another object of the present invention is to provide
such an amorphous SiO.sub.2 or mixed oxide silica base composition
in which the composition has surface areas in a range of from 150
to 600 m.sup.2/gm.
[0013] Yet another object of the present invention is to provide
such an amorphous SiO.sub.2 or mixed oxide silica base composition
in which the composition has a mean mesopore diameter in a range of
from 60 to about 250 .ANG..
[0014] An additional object of the present invention is to provide
such an amorphous SiO.sub.2 or mixed oxide silica base composition
in which the composition has a measured pore volume in a range of
from about 0.5 to 1.5 cc/gm.
[0015] Still another object of the present invention is to provide
such an amorphous SiO.sub.2 or mixed oxide silica base composition
in which the composition has a macropore volume of at most 0.5
cc/gm.
[0016] Yet another object of the present invention is to provide an
amorphous mixed oxide silica base composition selected from the
group consisting of silica alumina, silica titania, silica vanadia
and silica zirconia.
[0017] An additional object of the present invention is to provide
powders produced from such an amorphous SiO.sub.2 or mixed oxide
silica base composition.
[0018] A further object of the present invention is to provide such
powders which are spray dried.
[0019] Yet a further object of the present invention is to provide
such powders which are vacuum dried.
[0020] Still a further object of the present invention is to
provide such spray dried powders having fragmentation potentials in
a range of from about 20 to about 30.
[0021] Another object of the present invention is to provide a
catalyst comprising such a SiO.sub.2 base composition, the
composition being impregnated with a catalytic amount of at least
one transition metal-containing compound.
[0022] Yet another object of the present invention is to provide
such a catalyst in which the at least one transition
metal-containing compound is a chromium compound.
[0023] Still another object of the present invention is to provide
such a catalyst in which the at least one transition
metal-containing compound is present in an amount of 0.1 weight
percent or greater based on the total catalyst weight.
[0024] An additional object of the present invention is to provide
such a catalyst in which the at least one transition
metal-containing compound is present in an amount in the range of
from about 0.1 weight percent to about 10 weight percent.
[0025] Yet an additional object of the present invention is to
provide a polymerization process comprising contacting such a
catalyst with at least one alpha-olefin under polymerization
conditions.
[0026] Still an additional object of the present invention is to
provide a method for preparing a silica gel composition which is a
precursor material for a silica powder material with a
microstructure comprising a non-particulate, dense, continuous
network matrix and encapsulated, less dense, non particulate
regions with true macropores, the method comprising:
[0027] (a) forming a first aqueous solution comprising silica
ions;
[0028] (b) forming a second aqueous solution capable of
neutralizing said first aqueous solution; and
[0029] (c) contacting said first and second aqueous solutions in a
mixer-reactor under mixing conditions to form the silica gel
composition.
[0030] An additional object of the present invention is to provide
an olefin polymerization catalyst prepared from a silica gel
composition obtained by such a method.
[0031] Yet another object of the present invention is to provide
such a method in which the first aqueous solution is an acidic
solution comprising sodium silicate and acid and in which the
second aqueous solution has a pH above 8.
[0032] Still an object of the present invention is to provide such
a method in which the second aqueous solution is an ammonia based
material selected from the group consisting of ammonium hydroxide;
ammonium carbonate; ammonium bicarbonate and urea.
[0033] An additional object of the present invention is to provide
such a method in which the first aqueous solution is a basic
solution of sodium silicate and in which the second aqueous
solution has a pH below 6.
[0034] Yet an additional object of the present invention is to
provide such a method in which the second aqueous solution is
sulfuric acid.
[0035] Still an additional object of the present invention is to
provide such a method, in which the apparent average shear rate in
the mixer-reactor is greater than about 0.5.times.10.sup.4
sec.sup.-1.
[0036] Another object of the present invention is to provide such a
method in which the neutralization step is conducted in such a
manner that the pH of the combined first aqueous solution and the
neutralizing medium is controlled in the range of about 3.5 to
about 11.
[0037] Yet another object of the present invention is to provide
such a method in which the catalyst is activated by being heated to
a temperature in the range of 300.degree. C. to 900.degree. C. for
from 2 to 16 hours.
[0038] Still another object of the present invention is to provide
such a method further comprising the steps of:
[0039] (a) preparing an aqueous slurry of amorphous silica gel by
continuously feeding an acidic solution comprising sodium silicate
and acid to an emulsifier mixer while simultaneously and
continuously feeding to said mixer an alkaline solution;
[0040] (b) operating said mixer with sufficient shear so that the
precipitated silicate has sheets of silica in its
microstructure;
[0041] (c) recovering said silica from said aqueous slurry using a
vibrating filtration membrane to a solids content from 8 to 20 wt.
%, after washing;
[0042] (d) drying and calcining the silica from (c);
[0043] (e) dispensing a chromium compound substantially uniformly
onto said silica to form a catalyst having from 0.01 to 4 wt. %
chromium;
[0044] (f) drying said catalyst; and
[0045] (g) activating said dry catalyst from (f) by heating to a
temperature from 300.degree. C. to 900.degree. C. for from 2 to 16
hours.
[0046] Yet another object of the present invention is to provide an
olefin polymerization catalyst prepared by such a method.
[0047] Another object of the invention is to provide such a method
further comprising aging the silica gel composition in deionized
water for up to one hour.
[0048] Yet another object of the present invention is to provide a
method of preparing the silica powder composition from such a
silica gel composition comprising the steps of:
[0049] (a) washing the silica gel with solutions of ammonium
acetate, bicarbonate or nitrate;
[0050] (b) washing the silica gel composition in deionized water to
further replace salts-contaminated water in the composition with
fresh water; and
[0051] (c) drying the washed composition to remove substantially
all water.
[0052] Still another object of the present invention is to provide
such a method further comprising calcining the dried composition in
a fixed fluid bed type calciner for up to 8 hours at a maximum
temperature of 450.degree. C.
[0053] Another object of the present invention is to provide a
polymerization process comprising contacting at least one
mono-1-olefin having from 2 to 8 carbon atoms per molecule under
polymerization reaction conditions in a polymerization reaction
zone with a catalyst comprising an active catalytic component on a
silica support comprising (a) a non-particulate, dense, gel matrix;
and (b) encapsulated regions with true macropores.
[0054] Still another object of the present invention is to provide
such a polymerization process in which the catalytic component
comprises a chromium component on the silica support.
[0055] Yet another object of the present invention is to provide
such a polymerization process in which the at least one
mono-1-olefin is selected from ethylene; propylene; butene-1;
hexene-1 and octene-1.
[0056] An additional object of the present invention is to provide
such a polymerization process in which the at least one
mono-1-olefin comprises ethylene and from 0.5 to 2 mole percent of
one additional mono-1-olefin selected from propylene; butene-1,
hexene-1 and octene-1.
[0057] A further object of the present invention is to provide a
method for preparing silica alumina powder material with a
microstructure comprising a non-particulate, dense, continuous
network matrix and encapsulated regions with true macropores and
sheets, the method comprising:
[0058] (a) preparing an acid aqueous solution comprising aluminum
and silicon ions;
[0059] (b) preparing a basic aqueous solution comprising ammonium
hydroxide;
[0060] (c) mixing the acidic aqueous solution and the basic aqueous
solution in a mixer to obtain a gel slurry with a microstructure
comprising a non-particulate, dense, continuous network matrix,
encapsulated regions with true macropores and sheets;
[0061] (d) maintaining the gel at approximately pH 8.0 for up to
one hour before washing the gel slurry;
[0062] (e) washing the gel slurry first with an aqueous ammonium
acetate or ammonium bicarbonate solution, then with water to obtain
a gel conductivity below 1,000 mmhos;
[0063] (f) acidifying and concentrating the gel slurry by adding
acid to the gel slurry to achieve a pH below 6.0 while gradually
removing water from the gel slurry; and
[0064] (g) drying and calcining the gel slurry to form the
silica-alumina powder material.
DESCRIPTION OF THE DRAWINGS
[0065] FIG. 1 is a side view of a mixer-reactor.
[0066] FIG. 2 is a top view of a mixer reactor.
[0067] FIG. 3 is a TEM Photomicrograph of Example Sample
C1936-20-13 (EM 2829) taken at magnification 30 KX. It shows the
particulate nature of the sample.
[0068] FIG. 4 is a TEM Photomicrograph of Example Sample EP-50 (EM
3309) taken at magnification 50 KX. It shows the gel network and
small TiO.sub.2 particles.
[0069] FIG. 5 is a TEM Photomicrograph of Example Sample C1935-23B
(EM 3821) taken at magnification 5 KX. It shows pockets and
sheets.
[0070] FIG. 6 is a TEM Photomicrograph of Example Sample C1935-44B
(EM 3735) taken at magnification 50 KX. It shows the pore size in
the matrix.
[0071] FIG. 7 is a TEM Photomicrograph of Example Sample C1935-47B
(EM 3728) taken at magnification 50 KX. It shows the pore size in
the matrix getting bigger than in FIG. 6.
[0072] FIG. 8 is a TEM Photomicrograph of Example Sample C1935-48B
(EM 3743) taken at magnification 50 KX. It shows the pore size in
the matrix getting even bigger than in FIG. 7.
[0073] FIG. 9 is a TEM Photomicrograph of Example Sample C1252-36B
(EM 0331) taken at magnification 10 KX. It shows the pore matrix
without sheets.
[0074] FIG. 10 is a TEM Photomicrograph of Example Sample C1934-45
(EM 2269) taken at magnification 10 KX. It shows the dense matrix
with many sheets.
DETAILED DESCRIPTION OF THE INVENTION
[0075] The present invention relates to high surface area,
amorphous silicas which form a continuous network matrix, rather
than the typical small particles found in conventional amorphous
silicas. Furthermore, the pore size and the distribution and volume
of the pore size can be tailored over a wide range so that the
silicas have unique microstructures and varied physical properties,
such as surface area, pore volume, mean mesopore size, mesopore
size distribution, macropore volume and acceptable fragmentation
potentials and methods of making such silicas.
[0076] An especially significant aspect of the present invention is
the achievement of "true" macropores in the amorphous silica
material. These macropores are "true" in the sense that their
existence is verified and their structure observed and measured by
TEM techniques, differing from "apparent" macropores which are
observed and measured by mercury porosimetry.
[0077] Mercury porosimetry is the common technique for measuring
the amount of macropores in a catalyst sample. The technique
involves subjecting the sample which was immersed in Hg to
increasing pressure. The pressure change starts from atmospheric
(14 psi) to about 60,000 psi. The volume change in the Hg level is
monitored and plotted against the pressure change. The change in Hg
level was assumed to be the result of the Hg penetrated into the
pore spaces of the catalyst. The plot of the Hg volume change
against the applied pressure can then be presented as the pore size
distribution of the catalyst.
[0078] However, when the skeletal framework structure of the
catalyst departs significantly from being infinitely rigid, some of
the volume change in Hg level recorded by the instrument comes
about because the porous catalyst particle was compressed or
"squeezed" and not Hg penetrated into the pores. Hence, the
instrument could report the existence of macropores while in
reality there were none present, especially in the case of silica
based catalysts. A detailed discussion of this phenomenon has been
published by Vittoratos and Auburn. (E. S. Vittoratos and P. R.
Auburn; "Mercury Porosimetry Compacts SiO.sub.2 Polymerization
Catalysts", J. of Catalysis, 152, 415-418 (1995)). TEM is the only
technique to verify the existence of true macropores. However, the
usefulness of TEM to quantify the amount of macropores is at best
quite limited, because of the difficulty of visually identifying
and counting each macropore in a TEM micrograph.
[0079] It is thus clear that the mercury porosimetry instrument
practically always overestimates the amount of macropores. The true
value matches the apparent (reported) value only for the limiting
case of an infinitely rigid sample. The apparent value can be
positive even when the true value (verified by TEM) is zero. EP-50
is an example of a commercially available silica material which has
been tested with the mercury porosimetry method and apparent
macropores were found but were not verified by the TEM method.
[0080] The invention also relates to mixed silica-oxides in which
the oxide is alumina, titania, zirconia, vanadia, etc., and
combinations thereof, with unique microstructures, unique catalytic
performance and varied physical properties and methods of making
such materials. Such mixed silica-oxides also have continuous,
tightly packed, gel network which routinely contain the unique
sheet structures. Furthermore, the mixed oxides are homogeneous
(i.e., no individual separate oxide phases are observed), and the
pore size, pore size distribution, and volume (meso) of these
materials can be tailored also.
[0081] These silicas and mixed-oxide silicas are prepared via
gelation of sodium silicate alone or in combination with the
precursors of the other oxides. The gelation can proceed from
either the acid or the base side. but it must be done with a high
rate of mixing with shear forces. The gel slurry can be washed at
different pH's via a batch or via a V*Sep process to remove
contaminant salts and to dewater the gel slurry. The washed gels
may be aged at various pH's, temperatures and times to alter the
meso and macropore characteristics. Spray drying is the preferred
method of forming and drying.
[0082] There are, of course, various types of mixing techniques and
apparatus which generate varying levels of shear delivery mixing.
See for example, "Scaleup and Design of Industrial Mixing
Processes" by Gary B. Tatterson, McGraw-Hill, Inc. (1994) and
especially FIG. 2.9 which illustrates the shear level of various
types of mixers and impellers. Referring to FIG. 2.9 of Tatterson,
which is incorporated herein by reference, the colloid mills, saw
blade type impellers; homogenizers and stator rotor mixers provide
the highest level of shear while the hydrofoil and propeller
provide the lowest shear. The newer jet stream mixers can also be
employed with sufficient shear as taught herein.
[0083] Shear in this specification means shear rate which is a
change in velocity (.DELTA.V) divided by a change in distance
(.DELTA.d). For example, in a rotor shear mixer, the fluids to be
mixed usually are pumped into the rotor stator chamber through
concentric tubes. The rotor stator chamber consists of a rotor
revolving at some desired rate and a "stator" or surrounding wall
close to the tips of the revolving rotor. The wall is provided with
openings to permit the mixed fluids to be removed or withdrawn
quickly and continuously from the rotor-stator chamber.
[0084] Using the rotor stator mixer as an example, the velocity of
the fluid is highest at the tip of the rotor impeller and is zero
at the wall. Thus, the .DELTA.V is taken as the velocity at the tip
which can be calculated by multiplying the revolutions of the rotor
per second times the radius of the rotor, i.e.:
.DELTA.V=ND/2
[0085] where N=revolution of the rotor per second; D=diameter of
rotor.
[0086] The "change in distance", .DELTA.d, is equivalent to the
distance over which one measures the change in velocity over the
change in distance and is calculated by the equation: 1 Apparent
Average Shear Rate = .PI. ND W .PI. = pi = 3.1416
.pi.=pi=3.1416
[0087] where
[0088] N is the revolutions of the impeller per second;
[0089] W is the distance between the tip of the impeller and the
wall of the mixer; and
[0090] D is the diamieter of the rotor (in the case of rotor-stator
mixer) or can be the thickness of the impeller blade for other
mixers.
[0091] It will be obvious to those with ordinary skill in the art
that shear rates can be increased by increasing .DELTA.V or
decreasing .DELTA.d.
Gelling Silica Salts
[0092] It is possible to form gel from silica salts by either
adding an acid such as sulfuric acid to sodium silicate or adding a
base such as ammonium hydroxide (sodium silicate plus acid). It is
also possible to form gels from an acidic mixture of oxide
precursors and a sodium silicate plus acid by adding a base such as
ammonium hydroxide. In a preferred embodiment of making silica,
adding acid to sodium silicate solutions was used. The acid and
base solutions were mixed with high-shear, continuous gelation
(CHSG) using a two-stream feed system pumped directly into a Ross
mixer (reactor). For gelling to occur in the high shear reactor, it
was necessary to determine the acceptable concentrations of the
reacting silica salt, the pH, the temperature, the mixing rate, and
the stator configuration. Removing the residual salts is
important.
[0093] Achieving the right degree of washing with a batch (i.e.,
repulping and filtering) or a continuous (i.e., V*Sep difiltration)
process has a significant effect on both the performance of the
finished catalyst and the outcome of any subsequent aging steps.
The amount of residual salt influences the type and degree of
aggregation of the primary particles subsequently affecting the
pore size and pore size distribution of the dried powder. In
addition, an aging step definitely can be used to vary physical
properties of resultant SiO.sub.2 bases.
Preparation of SiO.sub.2 Powders
"General Procedure"
Step 1--Preparation of Solution of Silicate Anions
[0094] (A) Add the desired amount of sodium silicate to DI water
with mixing.
[0095] (B) Dilute the sulfuric acid with DI water by weight.
Step 2--Gelation
[0096] The silicate solution formed in Step 1 and sulfuric acid
solution were simultaneously pumped into the mixing chamber of a
Ross-In-Line Laboratory Emulsifier (obtained from Charles Ross and
Son Company, Hauppauge, N.Y., Model ME 300L) shown diagramatically
in FIG. 1 (sideview) and FIG. 2 (topview). Referring to FIGS. 1 and
2, the basic solution silicate anions prepared in Step 1A is pumped
into the mixing chamber 10 through the outer 1/4" inside diameter
tube 12 and the sulfuric acid prepared in Step 1 B is pumped into
mixing chamber 10 through the inner, 1/8" inside diameter, tube 14.
The mixing chamber 10 is fitted with a rotor impeller 16 having
four arms and a stationary cylindrical wall 18 surrounding the
rotor impeller 16 and in relatively close proximity to the tips of
the impeller arms. The stationary wall 18 is provided with slots 20
through which the fluids and produced hydrogel pass into the
annular portions 22 of mixing chamber 10 and then out of the mixing
chamber 10 through outer housing 24 and line 26. The acid and base
solutions react in the mixing chamber 10 while the rotor impeller
16 operates at the desired revolutions per minute to provide the
apparent average shear rate as taught above. The distance between
the tip of one arm of impeller 16 and wall 18 is the "W" for use in
the shear rate equation set forth earlier in this specification.
The specific "W" for the mixer-reactor used in the working examples
below was 0.01 inches and the diameter "D" of the rotor was 1.355
inches. The rate of addition of the acid and base solutions into
the mixing chamber 10 is set to achieve desired pH at the outlet
24.
Step 3--Washing
[0097] The hydrogel was washed either by a batch process or by
diafiltration. In one case, Examples 14 and 15, the same hydrogel
was washed both ways.
Batch Washing
[0098] The hydrogel was blended with the desired wash solution in a
Waring blender, mixed for about 15 minutes with a marine impellar
mixer, and then filtered. This was done until the conductivity of
the filtrate equaled the conductivity of the wash solution. Then
the hydrogel was blended with DI water and filtered to yield a gel
cake.
Diafiltration
[0099] The hydrogel in the holding tank was diluted with hot
(50.degree. C.) DI water to about 4 to 10 weight percent solids as
measured by an LOM instrument (CEM AVC 80).
[0100] This dilute hydrogel was washed on a vibrating filtration
membrane machine (New Logic International V*SEP machine (Series P)
where V*SEP stands for Vibratory Shear Enhanced Processing). This
washing process known as difiltration involves dewatering the
hydrogel and adding fresh DI water at the same rate at which the
filtrate or permeate containing the contaminated salts is removed.
The washing is continued until the desired conductivity of the
permeate as measured by a conductivity meter (Yokogama Model SC400
conductivity converter) is achieved.
[0101] Once the desired conductivity was achieved, the hydrogel
solution was concentrated to the maximum "pumpable" weight percent
solids (by LOM).
[0102] This was done by dewatering the hydrogel solution by not
adding fresh DI water.
Step 4--Aging
[0103] The washed hydrogel was filtered to yield a filter cake. The
filter cake was diluted with DI water to allow for mixing with a
marine impellar mixer. The pH of the slurry was adjusted with
either acetic acid to a pH equal to about 5.6 or with ammonium
hydroxide to a pH equal to about 9.6. The pH adjusted slurry was
heated to 50.degree. C. over about 15 minutes and then held at
50.degree. C. for about 15 minutes. The hot aged slurry was then
pumped to the feed system of the spray dryer.
Step 5--Drying
Vacuum Drying
[0104] The gel cake was dried in a vacuum oven at 80.degree. C.
overnight.
Spray Drying
[0105] The hydrogel from Step 3 or 4 was pumped to the feed system
of a Stork Bowen BE 1235 spray dryer and dried. The spray dryer
conditions were varied, by means well known to those having
ordinary skill in the art, to achieve a desired particle size, LOM
moisture weight percent and other desired characteristics.
Step 6--Calcination
[0106] The spray dried from Step 5 was calcined in a muffle furnace
for one hour at 400.degree. C.
[0107] The vacuum dried hydrogel was calcined in a muffle furnace
for one hour at 400.degree. C.
[0108] In some Examples below, the uncalcined (as vacuum dried or
spray dried) silica was impregnated with a chromium salt to deposit
about 1 weight percent chromium on the support on an LOI basis,
done at 1000.degree. F. for one hour. Chromium impregnation is done
using a Buchi rotovap. A maximum of 50 g of powder is added to a
500 ml rotovap flask. About 75 to 100 g of the solvent methanol or
DI water is added to the powder (solvent to powder ratio is always
approximately 2 to 1 by weight). Swirl the flask to achieve uniform
wetting of the powder. Weigh the chromium (III) acetate hydroxide
and dissolve in the solvent (approximately 15-30 ml). Add the
chromium solution to the powder slurry and swirl to evenly coat the
powder. Attach flask to the Buchi and spin the flask for
approximately 5 minutes without vacuum to mix the slurry. Using a
vacuum regulator and vacuum pump, set the vacuum to approximately
200 to 400 mm Hg, and lower the flask into an 80.degree. C. water
bath when water is the solvent or a 40.degree. C. water bath when
methanol was the solvent. Maintain these conditions until
approximately 80% of the solvent was evaporated. Slowly increase
the vacuum to approximately 600 mm Hg as necessary to remove the
last of the solvent without "bumping" any of the slurry/powder
over. When the powder appears completely dry, increase the vacuum
to maximum for approximately 5 minutes. After the last vacuum
adjustment is complete, release the vacuum and shut off the
Buchi.
[0109] Such silicas and mixed silica-oxides have a wide variety of
uses, especially as supports for ethylene polymerization. Also,
because of the catalytic and physical properties, the mixed
silica-oxides can be tailored for use as FCC catalysts or for use
in hydroprocessing such as hydrodenitrification,
hydrodesulfurization, hydrodewaxing, hydrocracking or
hydrogenation.
[0110] The physical properties such as surface area and pore size
and pore size distribution can differ significantly not only
between hydrogels and precipitates of silicas and mixed oxide
silicas, but even between various types of precipitates depending
on the treatment of the precipitates both during and after
preparation, i.e., hot washing; hot aging, etc.
[0111] Certain silica and mixed oxide silica precipitates have now
been discovered which have excellent thermal and physical
stability, together with a relatively high amount of macroporosity
so that these materials are particularly suited for use as catalyst
support materials, especially for use in reactions involving
relatively large molecules (e.g., residua) in order to allow the
molecules easy ingress and egress.
[0112] The silica and mixed oxide silicas are characterized by
being amorphous; having a non-particulate, dense, continuous
network matrix, and having encapsulated regions with true
macropores. Some of the silica and the silica-alumina precipitates
have also been found to have sheet-like microstructures.
[0113] The new silicas and mixed oxide silicas have, in addition,
certain characteristics in their preferred form as set forth below.
These characteristics were determined after drying and calcining
the silicas at 400.degree. C. for 1 hour and mixed oxide silicas,
i.e., silica-aluminas, at 593.degree. C. for 2 hours.
[0114] (1) Surface area by the BET Method
[0115] Typically, the surface area of the new silicas and mixed
oxide silicas is from about 150 to 600 m.sup.2/gm.
[0116] (2) Macropore Volume by the Mercury Technique
[0117] By "macropore volume" in this specification is meant the
volume occupied by pore sizes in excess of 1000 .ANG.. It is
particularly desirable for some end uses such as the polymerization
of olefins to have a macropore volume in excess of 0.1 cc's per
gram. The problem in the past was obtaining supports with a "true"
macropore volume in excess of 0.1 cc's per gram along with physical
stability. The silicas and mixed oxide silicas of this invention
have a high macropore volume and are physically stable as shown by
the fact they were successfully used in a fluid bed gas phase
polymerization of ethylene.
[0118] The macropore volume is taken by the mercury porosimetry
test (by ASTM Designation: D4284-88 where gamma is taken to be 473
dynes per cm and the contact angle is taken to be 140 degrees).
[0119] The macropore volumes of the new silicas and mixed oxide
silicas are at most 0.5 cc's per gram.
[0120] (3) Mean Mesopore Diameter by the BET Method
[0121] The mean mesopore diameter of the silicas and mixed oxide
silicas can be from 60 to about 250 .ANG..
[0122] (4) Fragmentation Potential and Sonication Number
[0123] The testing of catalysts so as to determine attrition
characteristics is recognized in the art. These tests typically
involve introduction of catalyst particles into a vessel and
subsequent agitation of the particles. In such an arrangement,
attrition results primarily from abrasion caused by particles
impacting with each other as well as with the wall of the
vessel.
[0124] For example, in processes where particles are subjected to
fluidized bed conditions, fluidized tests such as air-jet testing
are common in as far as they can be considered directly relevant to
the performance of particles under such conditions.
[0125] While such tests can be effective in testing attrition under
certain conditions, they have largely proven ineffective with
respect to predicting the effectiveness of catalysts in processes
where the attrition is related to the fractionation of the
catalyst.
[0126] Moreover, such techniques fail to accurately report that
polymerization catalysts, unlike catalysts employed in other
processes, e.g., catalytic cracking, are subject to attrition at
two different stages, i.e., activation and polymerization. Thus,
while traditional techniques, e.g., air-jet testing, may provide an
effective model for attrition occurring during activation, such
techniques are not an effective model for attrition occurring
during polymerization and thus are not sufficient to deal with such
catalysts.
[0127] One particular process in which fractionation of the
catalyst occurs is the polymerization of olefins. Olefin
polymerization processes are well recognized in the art. Typical
examples of such processes include slurry batch, e.g., slurry loop
and gas phase olefin polymerization processes.
[0128] Although each of these processes utilize catalysts in the
production of polyolefins such as polyethylene, they differ
significantly with respect to the dynamics of particle growth
therein. For example, gas phase processes include as much as 85%
ethylene while slurry loop type processes have a much lower
ethylene solubility, e.g., typically 8% maximum. Accordingly,
catalysts which may be effective in one olefin polymerization
process may not be found effective in another process. The new
silica supported polymer catalysts of this invention are effective
in batch polymerization processes. One aspect of the present
invention is based upon the surprising discovery that the
"fragmentation potential" of catalysts, such as olefin
polymerization catalysts, as determined by sonication, can be used
in determining the expected efficiency of a catalyst in a process
where fragmentation will occur.
[0129] The sonication process for use in the present invention can
effectively be employed within any sonication environment with
sonication baths, and in particular sonication baths employing
water, being preferred.
[0130] This sonication test can then typically take on one of two
forms. The material can be sonicated for a predetermined period of
time, e.g., 30 minutes, and the increase in fines, e.g., percent
increase, subsequent to sonication can be determined. This test
directly provides what is called the "fragmentation potential".
[0131] Alternatively, the material can be sonicated for a period of
time sufficient to reach a preselected mean particle size. The
result of this particular test is called the "Sonication Number".
Although this specification will typically make reference to the
fragmentation potential, the concepts and advantages are the same
for both of these basic tests.
[0132] In fact, as is readily apparent, these tests are basically
analogous with the numerical results being inversely related. That
is, a catalyst which has a small increase in fine production over a
predetermined period of time will typically require a longer time
to reach the preselected mean particle size. The inverse is also
true; a catalyst having large percent increase in fine production
will have a smaller relative period of time to reach the
predetermined mean particle size.
[0133] The particular sonication test employed is not critical to
the present invention and the selection of test and equipment is
largely determined by practical considerations such as time
allotted to perform the test.
[0134] For purposes of this specification, the "fragmentation
potential" is defined as the percent increase in the percentage of
particles which are smaller than 40 microns after sonication for 30
minutes in the aqueous medium, plus a dispersant using an Horiba LA
900 instrument. Calculation of the fragmentation potential, of
course, involves taking the percent of particles which are smaller
than 40 microns after 30 minutes and subtracting the percent of
particles smaller than 40 microns in the sample before sonication.
It was recognized that the initial sample could have some spheres
of less than 40 microns agglomerated with somewhat larger spheres.
A preferred variation is to initially degglomerate the sample by
sonicating the sample for one minute to obtain a base value for the
percent of particles smaller than 40 microns before sonicating for
30 minutes as described herein. In this instance, the fragmentation
potential is calculated by taking the percent of particles smaller
than 40 microns after 30 minutes and subtracting the percent of
particles smaller than 40 microns in the sample after an initial
one-minute sonication. The fragmentation potential using the
preferred technique is lower, as expected. In the data to be given
below, the fragmentation potential is given as (30-0) or (30-1),
the "0" indicating no pre-sonication, and the "1" indicating a
pre-sonication of one minute. In an analogous test, the sonication
number is determined as the time for the mean particle size of a
test sample to fall to 40 microns.
[0135] Preferably, the fragmentation potential is from 10 to 84
percent, more preferably above 30 percent, and most preferably
above 30 to 60 percent.
[0136] Similarly, the Sonication Number is preferably from 5 to 200
minutes, more preferably from 10 to 150 minutes, and most
preferably from 20 to 100 minutes. These numbers are obtained when
using a Molvern Particle Size Analyzer with a 300 mm focal length
and an active beam length of 2 mm.
[0137] The fragmentation potential and sonication numbers set forth
above are for the silicas and mixed oxide silicas of this invention
after calcining at 400.degree. C. for 1 hour. The fragmentation
potential and sonication number will, of course, vary depending on
whether the catalyst base is tested before or after calcining;
before or after the addition of chromia, etc. Likewise, the optimal
fragmentation potential will differ from other bases such as
silica.
[0138] While not wishing to be bound by any theory, it is believed
the sonication technique is a unique tool for providing a
fingerprint of an improved ethylene polymerization catalyst because
of the shattering of the particles as shockwaves move through the
internal pore structure. Accordingly, it is believed that such a
process closely resembles the fracturing process which can occur
during polymerization, i.e., the catalyst particle breakup due to
the accumulation of polymer and pressure within the pore
structure.
[0139] (5) Microscopy
[0140] The new silica and mixed oxide silica compositions of this
invention possess very unique and important characteristics over
the silicas and mixed oxide silicas of the prior art, i.e., the new
silicas and mixed oxide silicas have a microstructure of
encapsulated regions with true macropores within a non-particulate,
dense, continuous network matrix. And in one embodiment, they also
exhibit sheet structures.
[0141] Physically, the new silicas and mixed oxide silicas are
spray dried to form a non-particulate, dense, continuous network
matrix with encapsulated regions of true macropores. The mean
mesopore diameter is in a range of from 60 to 250 .ANG.. The
microscopic examination of these regions is done using standard
transmission electron microscope (TEM) techniques. For example, to
observe the TEM specimen in the bright field imaging mode, it is
necessary to prepare the TEM specimen by the microtomy
technique.
[0142] The microtomy technique is a well established specimen
preparation technique in the field of transmission electron
microscopy. Its description can be found in standard reference
published literature, for example, T. F. Malis and D. Steele,
"Ultramicrotomy for Materials Science", in "Workshop on specimen
preparation for TEM of materials II", ed. R. Anderson, vol. 199,
Materials Research Symposium Proceedings (MRS<Pittsburgh, 1990)
and N. Reid, "Ultramicrotomy", in the "Practical methods in
electron microscopy" series, (ed. A. M. Glauert, publ.
Elsevier/North Holland, 1975). Briefly, it involves embedding the
sample in a resin, form a pellet by polymerizing the resin in a
mold, then cut thin sections using a microtome equipped with a
diamond knife. In the work for this specification, the resin used
was L.R. White resin. The typical thin section would have a
thickness of about 0.06 microns. Care needs to be taken to embed
whole encapsulated regions in order that views of the entire random
cross sections of the true macropores are presented. Furthermore,
it is important that prudent sampling techniques be used to collect
the sample to be used for the TEM specimen preparation step. The
portion of encapsulated regions that were embedded should be
selected from a sample by sequentially dividing the originally
collected sample into quarter portions until the desired amount of
material suitable for the embedding process is reached.
[0143] In the TEM examination of specimens, it is always a balance
between the amount of details to be observed and the amount of
material to be examined to ensure representativeness. To observe
the increasing details of relevant microscopic features requires
higher magnifications while this decreases the filed of view and
the amount of material examined. However, a modern microscope
allows the operator to easily change magnifications from 100.times.
to 1,000,000.times.. It is standard practice to survey the sample
at low magnifications, identify and confirm the views that are
typical and representative of the sample, then increase the
magnification as necessary to examine the details. Images will then
be recorded to illustrate the characteristics of the sample. The
recorded images (which usually are on a 3.25".times.4" negative)
are then printed and usually further magnified.
[0144] Such further magnification occurs by printing, for example,
to an 8.5.times.11" print.
[0145] For the purposes of this specification, the images of
photomicrographs have destination magnifications between
3000.times. and 150,000.times.. The term "destination
magnification" refers to the final magnification of the printed
image.
EXAMPLES
[0146] The invention will be further illustrated by the following
examples, which set forth particularly advantageous method
embodiments. While the Examples are provided to illustrate the
present invention, they are not intended to limit it.
[0147] The following are non-limiting examples of experiments
involving the making and testing of both silicas and mixed silica
oxides.
[0148] Tables 1 and 1A summarize the key process variables and the
resulting physical properties of the formed and calcined SiO.sub.2
powder resulting from the CHSG experiments. Examples 1 through 13
SiO.sub.2 powders were formed by vacuum drying the gel-cake, and
crushing and sizing. Examples 14 through 17 were spray dried with
the Stork Bowen spray-dryer.
[0149] Both sets of samples were calcined at 400.degree. C. for one
hour prior to characterization.
[0150] Tables 2 and 3 summarize the observations associated with
each of the CHSG, continuous, high shear, experiments.
1TABLE 1 Summary of the Preparation Conditions for the
SiO.sub.2-bases of This Invention 8 Example No 1 2 3 4 5 6 7 C1935-
Notebook No C1935-23A C1935-23B C1935-23N C1935-31 C1935-38A
C1935-38A C1935-38B 38B(3) I) Solutions
Na.sub.2O:SiO.sub.2,1:3.22,Kg 0.6831 0.6831 0.6831 1.591 1.75 1.75
1.75 1.75 (Banco Sodium silicate 41 Be 2.5 2.5 2.5 7 7 7 7 7 DI
H.sub.2O, Kg. 11.8 11.8 11.8 12.2 12.2 12.2 12.2 12.2 pH 3 to 1 3
to 1 3 to 1 6 to 1 6 to 1 6 to 1 6 to 1 6 to 1 w/w DI
H.sub.2O/H.sub.2SO.sub.4 1.1 1.1 1.1 1.01 1.2 1.2 1.2 1.2 pH II)
Gelation Stator configuration Slot Slot Slot Slot Screen Screen
Screen Screen RPM of Rotor 7563 7563 7563 7723 7700 7700 7700 7700
Apparent Average Shear 5.36 5.36 5.36 5.48 5.46 5.46 5.46 5.46 Rate
x (10).sup.4 pH Range 2 to 10 2 to 10 2 to 10 5 to 7 5 to 7 5 to 7
5 to 7 5 to 7 Acid Rate gm/min 72 to 220 72 to 220 72 to 220 100 67
67 67 67 Base Rate, gm/min 630 to 670 630 to 670 630 to 670 548 351
351 351 351 pH at outlet -- -- -- 7.5 9 9 9 9 Gel T, C. 21 21 21 21
20 20 20 20 III) Washing Batch Yes Yes Yes Yes Yes Yes Yes Yes Wash
Solution NH.sub.4 Acetate NH.sub.4 NH.sub.4 Nitrate NH.sub.4
Acetate NH.sub.4 Acetate NH.sub.4 Acetate NH.sub.4 NH.sub.4
Bicarbonate Bicarbonate Bicarbonate pH of Wash Solution 7.3 8.4 5.3
7.3 7.3 7.3 8.4 8.4 Wash Temperature, C. Ambient Ambient Ambient 50
Ambient 50 Ambient 50 Conductivity of Water Wash (1)
Initial,mmhos/cm.sup.2 8400 -- 9250 8000 7000 10000 6800 7250 (2)
Final 2300 1200 2600 2400 1950 2600 1350 500 Water Wash
Temperature, C. Ambient Ambient Ambient 50 Ambient 50 Ambient 50
Diafiltration No No No No No No No No Dilution,Wt % Solids(LOM)
Wash Solution pH of Wash Solution Conductivity of Water Wash (1)
Initial (2) Final Water Wash Temperature, .degree. C. Wt % Solids
of Concentrate IV) Aging pH Acid/Base Time, Min Temperature V)
Drying 80.degree. C. in 80.degree. C. in 80.degree. C. in
80.degree. C. in 80.degree. C. in 80.degree. C. in 80.degree. C. in
80.degree. C. in Vacuum Vacuum Vacuum Vacuum Vacuum Vacuum Vacuum
Vacuum VI) Physical Properties(2) Surface Area(BET),m.sup.2/gm 177
476 468 503 501 464 426 445 Pore Volume(BET) cc/gm 0.521 0.939
0.924 1.004 0.929 0.998 0.949 0.985 MMPD,A 128 100 96 81 96 115 117
119 Particle size, microns AASR = Apparent Average Shear Rate,
reciprocal seconds (2) Measurement made after calcination for 1 hr
at 400.degree. C.
[0151]
2TABLE 1A Summary of the Preparation Conditions for the
SiO.sub.2-Bases of This Invention Example No 9 10 11 12 13 14 15 16
17 Notebook No C1935-43 C1935-42 C1936-50A C1936-50B C1936-50N
C1935-44B C1935-44B C1935-47 C1935-48 I) Solutions
Na.sub.2O:SiO.sub.2, 1.75 1.75 0.683 0.683 0.683 4.098 4.098 4.098
1:3.22,Kg (Banco Sodium silicate 41 Be DI H.sub.2O, Kg. 7 7 5 5 5
15 15 15 pH 12.2 11 11 11 11 11.2 11.2 11.2 w/w DI H.sub.2O/ 6 to 1
6 to 1 3 to 1 3 to 1 3 to 1 6 to 1 6 to 1 6 to 1 H.sub.2SO.sub.4 pH
1.2 <0 1.3 1.3 1.3 <0 <0 <0 II) Gelation Stator Screen
Screen Screen Screen Screen Slot Slot Slot configuration RPM of
Rotor 7700 7800 2729 2729 2729 10200 9923 9923 Apparent Average
5.46 5.53 1.93 1.93 1.93 7.23 7.04 7.04 Shear Rate x (10).sup.4 pH
Range 5 to 7 6.9 to 8.5 5 to 7 5 to 7 5 to 7 2.3 to 4.8 5.5 5.5
Acid Rate, 67 145 50 50 50 127 150 150 gm/min Base Rate, 351 692
680 680 680 450 to 639 650 650 gm/min pH at outlet 9 7.3 -- -- --
6.5 4.1 4.1 Gel T, .degree. C. 20 23 24 24 24 30 28 28 III) Washing
No Yes No No Batch Yes Yes Yes Yes Yes Wash Solution NH.sub.4
NH.sub.4 NH.sub.4 NH.sub.4 NH.sub.4 Nitrate NH.sub.4 Bicarbonate
Bicarbonate Acetate Bicarbonate Bicarbonate pH of 8.4 8.4 7.3 8.4
5.3 7.9 Wash Solution Wash 50 50 Ambient Ambient Ambient 50
Temperature, .degree. C. Conductivity of Water Wash (1) Initial,
7250 7250 -- -- -- 6700 mmhos/cm.sup.2 (2) Final 500 500 2300 1400
4000 1233 Water Wash 50 50 Ambient Ambient Ambient 50 Temperature,
.degree. C. Diafiltration No No No No No Yes Yes Yes Dilution,Wt %
2 3 3 Solids(LOM) Wash Solution NH.sub.4 NH.sub.4 NH.sub.4
Bicarbonate Bicarbonate Bicarbonate pH of 7.9 8 8 Wash Solution
Conductivity of Water Wash (1) Initial 9360 -- -- (2) Final 300
2000 2000 Water Wash 50 50 50 Temperature, .degree. C. Wt % Solids
of 9 8.84 8.84 Concentrate IV) Aging Yes No No Yes Yes pH 5.1 5.6
9.6 Acid/Base Acetic acid Acetic acid NH.sub.4 Hydroxide Time, Min.
10 30 30 Temperature 38 50 50 V) Drying 80.degree. C. in 80.degree.
C. in 80.degree. C. in 80.degree. C. in 80.degree. C. in Spray Dry
80.degree. C. in Spray Dry Spray Dry Vacuum Vacuum Vacuumn Vacuum
Vacuum Vacuum VI) Physical Properties(2) Surface Area 417 476 570
475 515 538 to 561 378 471 to 487 454 to 474 (BET),m.sup.2/gm Pore
Volume 1.128 0.844 0.815 0.842 0.787 1.02 to 1.3 0.956 1.1 to 1.2
1.3 to 1.4 (BET) cc/gm MMPD, A 162 79 67 82 71 101 to 140 114 140
to 167 151 to 167 Particle size, 63 49 60 microns AASR = Appar- ent
Average Shear Rate, reciprocal seconds (2) Measurement made after
calcin- ation for hr at 400.degree. C.
[0152]
3TABLE 2 Comparison of the Physical Properties and the
Microstructure of this Invention to Other Sources of SiO.sub.2
Bases SiO.sub.2- Commerical Commercial CHSG-Invention Source of
SiO.sub.2 Dispersion SiO.sub.2 SiO.sub.2 1 2 5 14 16 17 Example
Comparative Comparative Comparative C1935- C1935- C1935- C1935-
C1935- C1935- Sample ID C1936-20-13 EP-30x EP-50 23A 23B 38A 44B
47B 48B Surface Area(BET) 166 309 451 177 476 501 564 487 474 Pore
volume, PV,(N.sub.2) 0.417 1.63 2.096 0.523 0.94 0.929 1.02 1.21
1.318 Mean Meso Pore Diameter,A 113 206 183 128 100 96 101 140 151
Geometric Pore Diameter,A 88 -- 161 104 72 66 64 88 97 Pore
Volume(N.sub.2) > 100A 0.2505 -- 2.06 0.423 0.264 0.2199 0.2387
0.7187 0.88 Pore Volume(N.sub.2) > 200A 0.0082 -- 0.395 0.0079
0.0319 0.04 0.0729 0.1554 0.188 Pore Volume(N.sub.2) > 500A
0.0029 -- 0.0157 0.0021 0.0083 0.0083 0.0133 0.0275 0.037
Fragmentation Potential -- -- 39 -- -- -- 28 22 22 (30-1 min)
"Apparent" Macro Yes Yes Yes -- -- -- Yes Yes Yes PV(Hg) > 1000A
Macro PV(Hg),cc/gm 0.529 0.15 0.492 -- -- -- 0.215 0.38 0.44 "True"
Macro PV(TEM) No No Yes Yes Yes Yes Yes Yes Microstructures(TEM)
Particulates X X Continuous network X X X X X X X matrix Pockets
(Lower density than X X X X X X matrix) Sheets X X
[0153]
4TABLE 3 TEM Characterization of SiO.sub.2, Bases of the Prior Art
and of this Invention Commercial SiO.sub.2- Commercial SiO.sub.2
CHSG-Invention Source of SiO.sub.2 Dispersion SiO.sub.2 Comparative
16 17 Example Comparative Comparative EP-50 1 2 5 14 C1935- C1935-
Sample ID C1936-20-13 EP-30x (SiO.sub.2/TiO.sub.2) C1935-23A
C1935-23B C1935-38A C1935-44B 47B 48 Particulates X X None None
None None None None Size of 17 N.A. Particulates, nm Size of Pores
10 (estimated) Continuos X X X X X X X network matrix Density of
Matrix 3.sup.+ 1 3 2 2 4 Size of Matrix 20 8 7 10 10 25 Pores, nm
Pockets X X X X X X Density of Pockets 5 1 2 2 2 Size of Pockets 1
2 3 3 3 Size of Pockets .about.15 Microns .about.10 Microns <10
Microns <10 Microns <10 Microns Porosity of Pockets 3 1 3 2 2
Size of Pocket 70 85 20 30 80 Pores,Typical,nm Size of Pocket 30 to
120 24 to 250 10 to 24 20 to 200 25 to Pores,Range,nm 200 Sheets X
X Quantity of sheets Only Only occasionally occasionally observed
observed Size of sheets About 0.02- About 0.1 0.15 microns microns
thick and thick and 5- several 10 microns microns length long
[0154] The General Procedure set forth above using the high shear
mixer was employed with specific amounts of reactants; shear rate,
etc. as set forth in Tables 1 and 1A above. The characteristics of
the silica are summarized in Tables 1, 1A and 2.
[0155] Referring to Table 2, the silica possessed "true" macropore
volume as observed by TEM. It also possessed a continuous network
matrix, with pockets of less density and occasional "unique" sheet
microstructures.
[0156] Table 3 summarizes the characteristics of the matrix,
pockets and sheets as observed by TEM.
Examples 1-2-3
[0157] Example 1 was split in thirds. Example 2 was washed
initially with an ammonium bicarbonate solution as noted in Tables
1 and 1A. Example 3 was washed initially with an ammonium nitrate
solution as noted in Tables 1 and 1A. Both were then washed with DI
water.
[0158] Referring to Tables 1 and 1A, Examples 2 and 3 had higher
surface areas than Example 1; they had higher pore volumes; they
had lower mean meso pore diameters. This shows that washing affects
the physical properties of the silica.
[0159] Referring to Table 2, Example 2 possessed "true" macropore
volume as observed by TEM. It also possessed a continuous network
matrix with pockets of less density and occasional "unique" sheet
microstructure. The "true" macropore volume of Example 2 was less
than that of Example 1.
[0160] Table 3 summarizes the characteristics of the matrix,
pockets and the sheets observed the TEM of Example 2. TEM showed
that the density of the matrix of Example 2 was less than that of
Example 1. However, the density of the pockets was higher. Example
2 had smaller pockets which contained smaller pores.
[0161] Chromium (III) acetate hydroxide was deposited onto the
silica to result in 0.7 weight percent chromium. The silica was
first calcined at 400.degree. C. for 1 hour. The chromium compound
was dissolved in methanol.
Example 4
[0162] Example 1 was repeated except for the differences noted in
Tables 1 and 1A.
Examples 5-8
[0163] Example 1 was repeated using a screen stator and the
differences noted in Tables 1 and 1A. All the silica powders were
high surface area, 428 to 501 m.sup.2/gm. These examples illustrate
the effects the washing solution, washing conditions and degree of
washing have on the physical properties.
[0164] Referring to Table 2, Example 5 possessed a continuous
network matrix, pockets, but no sheets. It also possessed "true"
macropore volume.
[0165] Table 3 summarizes the characteristics of the matrix and the
pockets observed in the TEM of Example 5. Example 5 had the least
dense matrix, compared to Examples 1 and 2. Example 5 had the most
porous pockets with pores ranging from 24 to 250 nm (240 to 2500
.ANG.).
Example 9
[0166] Example 5, 20 grams, was blended with 400 grams of DI water
and acetic acid in a Waring Blender. The pH was about 5.1. The
mixture was blended for about 12 minutes. The final temperature was
38.degree. C. The blend was filtered. The gel-cake was vacuum dried
at 80.degree. C. overnight. It was then calcined at 400.degree. C.
for one hour and then ground and sized. Compared to Example 5,
Example 9 had a lower surface area, 417 m.sup.2/gm versus 501
m.sup.2/gm. But Example 9 had both a larger pore volume, 1.128
cc/gm versus 0.929 cc/gm, and a bigger MMPD, 182 .ANG. versus 96
.ANG..
Example 10
[0167] Example 10 was essentially a repeat of Example 8 except for
the differences noted in Tables 1 and 1A.
Examples 11-13
[0168] The General Procedure set forth above using the high shear
mixer was employed with the specific amounts of reactants; shear
rate, etc., as set forth in Tables 1 and 1A above. These silicas
were prepared at a low AASR employing the screen stator.
[0169] Referring to Tables 1 and 1A, which summarizes silica
characteristics, all these silicas were high surface area, greater
than 470 m.sup.2/gm.
[0170] Examples 14, 16 and 17 were washed by difiltration and
formed by spray drying.
Example 14
[0171] The General Procedure set forth above using the high shear
mixer was employed with the specific amounts of reactants, shear
rate, etc., as set forth in Tables 1 and 1A above.
[0172] Referring to Tables 1 and 1A, this silica powder had higher
surface area, more pore volume, and a larger MMPD than the previous
examples, illustrating the impact of washing by difiltration and
forming by spray drying.
[0173] Referring to Table 2, the silica powder possessed macropore
volume as measured by mercury porosimetry, about 0.215 cc/gm. It
also possessed "true" macropore volume as observed by TEM. It was
comprised of a continuous network matrix and pockets of less dense
material. The fragmentation potential of this powder was 28.
[0174] Table 3 summarizes the characteristics of the matrix and
pockets as observed by TEM.
[0175] Chromium (III) acetate hydroxide dissolved in methanol was
deposited onto the silica powder to result in 1.0 weight percent
chromium catalyst. Chromium (III) acetate hydroxide dissolved in DI
water also was deposited onto Example 14 to result in a second 1.0
weight percent chromium catalyst.
Example 15
[0176] A portion of Example 14 was batch washed as set forth above
in the General Procedure, and formed after vacuum drying by
grinding the gel-cake as set forth in Tables 1 and 1A above.
[0177] Referring to Tables 1 and 1A, this silica powder, compared
to Example 14, had a lower surface area, 378 m.sup.2/gm versus
.about.550 m.sup.2/gm, a lower pore volume, 0.958 cc/gm versus
about 1.2 cc/gm, and smaller MMPD.
Example 16
[0178] Example 14 was repeated using the differences noted in
Tables 1 and 1A above. Acetic acid was added to the gel and enough
DI water to allow for mixing with a Marine impeller mixer. (The pH
of the slurry adjusted to 5.6.) The mixture was heated to
50.degree. C. over 15 minutes and held at that temperature for
about 15 minutes. The slurry was spray dried.
[0179] The characteristics of the silica powder are summarized in
Tables 1, 1A, and 2.
[0180] Referring to Table 2, Example 16, compared to Example 14,
had a lower surface area, 487 m.sup.2/gm compared to 564
m.sup.2/gm, but the pore volume was larger, 1.21 cc/gm versus 1.02
cc/gm, and the MMPD was bigger, 140 .ANG. versus 101 .ANG.. The
"apparent" macropore volume was also larger, 0.38 cc/gm compared to
0.215 cc/gm. Example 16 had "true" macropore volume as observed by
TEM. This clearly illustrates the benefit of hot aging in acid
conditions. The fragmentation potential of this powder was 22.
[0181] Table 3 summarizes the characteristics of the matrix and the
pockets. The hot aging in acid pH changed the characteristics of
the pockets. Compared to Example 14, Example 16, after aging as
described above, had more porous pockets with larger typical pores,
300 .ANG. versus 200 .ANG., and a wider range of pores in the
pockets, 200 .ANG. to 2000 .ANG. versus 100 .ANG. to 300 .ANG..
Example 17
[0182] Example 14 was repeated using the differences noted in
Tables 1 and 1A above. Ammonium hydroxide was added to the material
of the gel and enough DI water to allow for mixing with a marine
impeller mixer. The pH was adjusted to about 9.6. The mixture was
heated to 50.degree. C. over 15 minutes and held at 50.degree. C.
for 15 minutes. The slurry was spray dried.
[0183] The characteristics of the silica powder are summarized in
Tables 1, 1A, and 2.
[0184] Referring to Table 2, Example 17 compared to Example 14, had
a lower surface area, 474 m.sup.2/gm to 564 m.sup.2/gm, but the
pore volume was larger, 1.318 cc/gm versus 1.02 cc/gm, and the MMPD
was bigger, 151 .ANG. versus 101 .ANG.. The "apparent" macropore
volume was also larger, 0.44 cc/gm versus 0.215 cc/gm. Example 17
had "true" macropore volume as observed by TEM. This clearly
illustrates the benefit of hot aging in base conditions. The
fragmentation potential of this powder was 22.
[0185] Table 3 summarizes the characteristics of the matrix and the
pockets. The hot aging in base pH changed the characteristics of
both the matrix and the pockets. The density of the matrix
decreased and the size of the matrix pores increased to 250 .ANG.
compared to 100 .ANG. for Example 14. Compared to Example 14,
Example 17, after aging as described above, had more porous pockets
with larger typical pores 800 .ANG. versus 200 .ANG., and a wider
range of pores in the pockets, 250 to 2000 .ANG. versus 100 to 300
.ANG..
[0186] Chromium (III) acetate hydroxide dissolved in methanol was
deposited onto Example 17 to result in 1.0 weight percent
chromium.
[0187] Silicas of this invention, such as Examples 1, 2, 7 and 14,
made via gelation of sodium silicate (base side) by sulfuric acid
under shear conditions contain the microstructures described above.
This is in contrast to a commercial silica base used for ethylene
polymerization described in Example 19 which contain neither the
sheets nor the encapsulated, non particulate regions with true
macropores.
[0188] This is also in contrast to experimental materials made from
commercial dispersions and blends of those dispersions.
Comparative Example 18
Gelling Commercially Available SiO.sub.2 Dispersions
[0189] Two dispersions and mixtures thereof were used, with the
SiO.sub.2 in each dispersion having a different microstructure.
They were (1) Nyacol colloidal silica, 40 Wt. % SiO.sub.2
(amorphous) with a spherical structure; and (2) Snowtex-UP, 20-21
Wt. % SiO.sub.2 (amorphous) with a fiber structure. In order to
achieve the gelling of each dispersion, it was necessary to
determine the acceptable concentrations of the reacting SiO.sub.2s,
the pH, the temperature, and the type of mixing to achieve gelation
in a reasonable time. This was accomplished by using a heated glass
reactor fitted with a marine-impeller mixer or polytron mixer and a
means to gradually adjust the pH of the reaction. Because the
dispersions contained minimal amounts of residual salts, washing
the resulting gel was not necessary.
[0190] Comparative Table 4 summarizes the key process variables and
the resulting microstructure of the formed and calcined SiO.sub.2
powders resulting from the experiments done with the commercial
SiO.sub.2 dispersions. All the gel slurries were formed by spray
drying with the Yamato spray dryer, Model DL41 and the resulting
powders were calcined in a muffle furnace at 400.degree. C. for one
hour. The experimental SiO.sub.2's (comparative examples) made from
commercially available dispersions are as follows:
[0191] (1) 1936-21-32, made from 100 Wt. % Snowtex (fibers);
[0192] (2) 1936-45, made from a 50/50 blend of Snowtex (fibers) and
Nyacol (spheres);
[0193] (3) 1936-20-13, made from 100 Wt. % Nyacol (spheres).
5COMPARATIVE TABLE 4 Sample 1936-21-32 1936-45 1936-20-13 Gel pH
4.93 5.6 5.13 Temp. .degree. C. 58 50 38 Gel time Overnight 6 min
39 min Mixer Polytron Marine impellar Polytron Blend 100% 50%
Snowtex/50% Nyacol 100% Nyacol Snowtex Particulate <100 .ANG.
>100 .ANG. .about.170 .ANG. size: MMPD, .ANG. 144 78 113
Packing: Densely Densely packed with large Densely packed packed
cracks in about 1/3 of the with uniformly larger formed particles
formed spheres
Comparative Example 19
Physical and Microstructural Characteristics of the Silicas of this
Invention Compared to Commercially Available Silicas and Silicas
made from Silica Sols
[0194] SiO.sub.2 powders of Comparative Table 4 were characterized.
The characterization can be broken down into three categories:
commercial SiO.sub.2 (commercial dispersions and blends), and
experimental SiO.sub.2 (commercial dispersions and blends), and
experimental SiO.sub.2 (silica salt/CHSG). The commercial materials
are EP 30x and EP-50. The experimental SiO.sub.2's (comparative
examples) made from commercially available dispersions are as
follows:
[0195] (1) 1936-21-32, made from 100 Wt. % Snowtex (fibers);
[0196] (2) 1936-45, made from a 50/50 blend of Snowtex (fibers) and
Nyacol (spheres);
[0197] (3) 1935-11, made from a 25/75 blend of Snowtex (fibers) and
Nyacol (spheres); and
[0198] (4) 1936-20-13, made from 100 Wt. % Nyacol (spheres).
[0199] The experimental SiO.sub.2's made by gelling sodium silicate
with acid via CHSG are 1, 2, 5, 14, 16 and 17. The TEM data for
several of these bases is summarized below.
[0200] The matrix of EP-30x was mostly made up of individual
particles of irregular shapes and sizes. There were some areas
where the particles appeared to be sintered together and resembled
the appearance of the continuous network. These areas were only a
small fraction of the total volume of the sample.
[0201] EP-50 was made up of a continuous porous network of
amorphous SiO.sub.2. The pores appear to be about 200 .ANG.. This
is consistent with the value obtained via BET, about 100 .ANG..
EP-50 contains TiO.sub.2. The TEM analysis suggests that the
TiO.sub.2 is present as a second phase in the form of fine
particles of about 10 .ANG. and less in size.
[0202] The SiO.sub.2 bases made from the dispersions and spray
dried via the Yamato appeared as smooth rounded macroscopic
particles of uniform density. The larger spray dried particles,
5-20 microns, are made up of smaller, densely packed individual
particles.
[0203] The different microstructures of the starting dispersions
affect the size of the particulates present in the microstructure.
In fact, it looks like the ratio of the fibers to spheres affects
size and the packing of the particulates in the microstructure: the
amount of cracking in the spray dried particles increases with the
amount of fibers, Snowtex, present in the blend.
[0204] The spray-dried SiO.sub.2's made from CHSG exhibit different
microstructures from the preceding materials. They consist
primarily of a non-particulate, dense, continuous-network matrix
and not individual, fundamental particles. The secondary structure
is composed of pockets of less density, non-particulate regions
with true macropores. The size of these pockets, ranging from 2
.mu.m to 15 .mu.m, varies with the preparation conditions. The
density of the non-particulate, dense, continuous-network matrix
also varies with the preparation conditions. Examples 1, 2, 5 and
14 (V*SEP) have the microstructures described above.
[0205] However, Examples 1 and 2 display a "unique" sheet structure
also. They contain a few sheets which are 0.02 to 0.1 microns thick
and about 5-10 microns long.
Example 20
Physical Properties of the Dried/Calcined Powders made from Sodium
Silicate under Mixing with Shear
[0206] The range of the key physical properties achieved with the
above-described methods of the present invention described in
Examples 1-17 were measured as:
[0207] (1) surface areas from 150 to 600 m.sup.2/gm;
[0208] (2) mean mesopore diameter (MMPD) from 60 to about 250
.ANG.;
[0209] (3) varying modality of the pore size distribution from
mono-modal to multi-modal;
[0210] (4) measured pore volume (N.sub.2) from 0.5 to 1.5
cc/gm;
[0211] (5) macropore volumes (Hg) up to 0.5 cc/gm;
[0212] (6) median particle size from 7 to 63 microns; and
[0213] (7) fragmentation potential from about 20 to about 30.
Example 21
TEM Characterization of SiO.sub.2 Bases
[0214] The microstructure of SiO.sub.2 base samples was evaluated
with respect to:
[0215] (a) the presence of pockets of different densities in the
matrix;
[0216] (b) the density of packing in the matrix; and
[0217] (c) the presence of sheet structures.
[0218] Specifically, the typical sizes of the pores in the pockets
and in the matrix were estimated. An assessment of whether there
were true macropores was also made. As a comparison to the
SiO.sub.2 bases of this invention, experimental SiO.sub.2 bases
(e.g., 1936-20-13) made from commercially available dispersions and
commercial SiO.sub.2 bases (EP-30x and EP-50) were also
examined.
[0219] The comparison results are summarized in Tables 2, 2A and 3.
EM 2829 (1936-20-13) (FIG. 3) clearly showed that the experimental
SiO.sub.2 base made from silica dispersion was made up of
particulates, while EM 3309 (EP-50) (FIG. 4) showed that the matrix
of EP-50 was made up of a continuous network. For EP-30x, its
matrix was made up of mostly individual particulates. However, the
shape and size of these particulates were not as homogeneous as
those in 1936-20-13. In some areas, the particulates appeared to be
partially sintered and resembled the continuous network. The
matrices of all of the examples in this invention were made up of
continuous networks. In addition, they all contained pockets where
the density of packing was lower than the surrounding matrix. The
number density of the pockets in the matrix (frequency of
occurrence), the size of the pockets, and the porosity of the
pockets were evaluated in a numerical relative ranking from 1 to 5.
It should be noted that the ranking scale was neither linear nor
proportional. It only served to indicate an observable relative
difference. Furthermore, sheet structures were observed in the
Examples 1 and 2 samples 1935-23A and 1935-23B: A photomicrograph
of Example 2 1935-23B, EM 3821, is included as FIG. 5. The true
macropores were typically located in the pockets. They can be
recognized as empty spaces in the silica framework in the low
magnification images.
[0220] The difference in the effects between aging in acid and
aging in base was clearly observed and illustrated by comparing
Example 1935-44B (EM 3735) (FIG. 6), Example 1935-47B (EM 3728)
(FIG. 7), and Example 1935-48B (EM 3743) (FIG. 8). Aging in acid
did not change the microstructure of the matrix but increased the
pore size in the pockets slightly. Aging in base increased the pore
sizes significantly in both the matrix and the pockets.
Example 22
Batch Reactor Evaluation of Large Pore Silica Catalyst Bases
[0221] Three experimental catalysts were evaluated for their
reactivity (activity compared to a Benchmark EP-30X 1.0% chromium
catalyst) at constant ethylene maximum consumption, temperature,
reactor volume, heptane addition, agitation via stirring, ethylene
pressure, and aluminum to chrome ratio. The catalysts were
activated at either 600.degree. C. or 800.degree. C. as indicated
in Table 5 below which summarizes the reactor results. EP-30X, a
commercial catalyst discussed above in Example 21, was the
benchmark catalyst. The experimental catalysts 1935-48B (a catalyst
of the present invention discussed above in Example 21), 1935-44 (a
catalyst of the present invention also discussed above in Example
21), 1934-44 (also a catalyst of the present invention) were
compared to it. The activity of the catalyst on a gram of polymer
per gram of chromium varied with the catalyst.
[0222] The catalyst activations were performed on a bench-scale 28
mm diameter fluidized bed under a stream of dry air at either
600.degree. C. or 800.degree. C. for 8 hours. The activator tube is
constructed from a 28 mm diameter quartz frit, and a 67 mm diameter
quartz disengaging section. The fluidization section is 300 mm long
from the frit to the half angle transition, and the disengaging
section is 400 mm tall. The transition incorporates an 11.degree.
half angle for ideal transition in fluidized bed design. The whole
activator tube is enclosed in a Lindberg furnace and can be purged
with argon or low dew point air, typically .about.1L/minute. Gas
flow direction is from the bottom to the top, and a cyclone trap is
connected to the outlet to collect fines, which might otherwise
escape into the atmosphere. This scaled-down activation protocol
mirrors that used in the 4" and 6" activators at the Orange, Tex.,
pilot plant.'
[0223] Polymerizations were performed in 2L autoclave reactors
equipped with Genesis control systems. A dried 316ss 2L Autoclave
Engineers Zipperclave reactor system is heated at 80.degree. C. in
vacuo until a pressure of <50 mtorr is achieved. The reactor is
then charged with a solution of 0.2885 M 0.65 IBAO in 100 ml of
heptane and a slurry of experimental catalyst in 100 ml heptane.
The IBAO and catalyst amounts vary in .mu.L and grams respectively
to give an Al to Cr proportion of 8.4 indicated in Table 5 below.
The IBAO solution and Catalyst slurry were contained in a 500 ml
glass addition funnel that is fitted with a Kontes vacuum valve.
The Kontes valve is connected to the reactor on a Cajon Ultra-Torr
fitting, and the mixture is introduced into the reactor in-vacuo.
The reactor is stirred at 550 rpm and ethylene is introduced to an
internal setpoint pressure of 300 psi. The reactor temperature is
maintained at the setpoint temperature of 80.degree. C. with a
Neslab RTE-100 silicone or water-bath circulator. The reactor is
allowed to proceed to a given productivity, typically depletion of
80 L of ethylene, after which the reactor is vented and purged
three times with argon and shut down. The reactor is opened while
it is still hot and the contents are quickly removed. The reactor
is cleaned and prepared for the next reaction..sup.1
[0224] .sup.1 The description of the activation technique and batch
reactor setup and conditions are similar to previous work completed
by Ed Vega for Pamela Auburn and Theresa Pecoraro in "Alpo Catalyst
Batch Screening Studies", April 1994 and are reprinted here with
permission from Pamela Auburn.
[0225] Referring to Table 5, it can be seen that activity of the
experimental catalysts are superior to the commercial
benchmark.
6TABLE 5 Experimental Batch Reactor Runs for Large Pore Silicas
Prior Weight IBAO Run Run oxi- Activation % co-cat. Catalyst Al/Cr
Polymer Time Liter C.sub.2= Activity Activity Reactivity Sample ID
number dation (degrees C) Cr soln. (.mu. l) (g) ratio Yield (g)
(hr) consumed (g/g/hr) (g/mol/hr) EP30X 8 III 800 1.0 590 0.150 5.9
109.16 1.15 80.10 632.8 26.5 1.0 EP30X 15 III 800 1.0 590 0.150 5.9
114.03 1.07 80.10 710.5 29.8 1.1 C1935-48 16 III 600 1.0 700 0.125
8.4 108.30 0.76 81.68 1140.0 39.1 1.8 MEOH C1934-44 22 III 600 1.0
700 0.125 8.4 95.17 0.67 80.64 1136.4 39.5 1.8 MEOH C1935-44
H.sub.2O 23 III 600 1.0 700 0.126 8.3 180.27 0.88 96.40 1625.8 47.6
2.6 Constants: 80 L C.sub.2 = consumption 2 L reaction vessel 80
degree Celsius reaction vessel 300 psi initial C.sub.2 = addition
550 rpm agitation via stirring 200 ml heptane (100 ml soln w/ IBAO
and 100 ml slurry w/ catalyst) 0.2885 molar IBAO co-catalyst
standard solution
Gelling Mixed Silica-oxide Salts
[0226] It is also possible to form gels from an acidic mixture of
oxide precursors and a sodium silicate plus acid by adding a base
such as ammonium hydroxide. In this case the acidic solution
contained both a silica and an alumina precursor. The basic
solution was ammonium hydroxide. The acid and base solutions were
mixed with high-shear, continuous gelation (CHSG) using a
two-stream feed system pumped directly into a Ross mixer (reactor)
as described above. This resulting silica-alumina contained a
unique sheet-like structure.
Example 23
Procedure for Preparing SiAl of Prior Art
[0227] The following is a description of the procedure by which
Example 1252-36B, a conventional silica alumina, 60:40 wt ratio,
was prepared. Some of the process steps described below were used
to prepare the silica-alumina samples of the present invention. The
difference was that the materials of the present invention were
prepared in the presence of mixing with shear forces.
I--Starting Materials
[0228]
7 Material Source Key Concentration Aluminum Chloride 32 BE Reheis
10.8% Al.sub.2O.sub.3 Glacial Acetic Acid JT Baker 99.9% Sodium
Silicate 41 BE VWR 40% w/v Sodium Silicate Ammonium Acetate
Solution Amresco Inc. 65% solution
II--Chelation
[0229] 1. Add 22.2 lb. of DI water to a 55-gallon tank and turn on
the mixer (Nettco Model NSP 050 mixer).
[0230] 2. Add 53.92 lb. of aluminum chloride solution to the DI
water.
[0231] 3. Add 4.05 lb. of acetic acid to the aluminum chloride
solution and record the pH. It should be <0.
[0232] 4. In a separate tank make up a sodium silicate solution by
mixing 23.34 lb. of sodium silicate with 126.4 lb. of DI water.
Record the pH. it should be around 12.
[0233] 5. Pump the sodium silicate solution into the aluminum
chloride solution at approximately 5 lb./min. with a Masterflex
magnetic drive vein pump. NOTE: If the silicate solution is added
too quickly, it may come out of solution. The resulting solution
should be clear. Measure and record the pH. It should be around
2.8.
[0234] 6. Make up a solution of ammonium hydroxide which is 1 part
NH.sub.4OH and 3.205 parts DI water w/w. It will take approximately
90 lb. of the ammonium hydroxide solution to do the titration. Make
an excess of ammonium hydroxide. Record the pH.
[0235] 7. Begin the titration by pumping the ammonium hydroxide
solution into the acid solution (from step 3) at 918 ml per minute.
Titrate to a pH of 8.0. The titration was done in a 100-gallon tank
using a Lightnin Model XD-43 mixer running at about 1788 RPM.
[0236] The following titration table is typical:
8 Time min. Base Added lb. pH 0 0 2.8 7 9.2 3.06 19 23.1 3.42 35
42.7 3.92 56 64.8 4.9 66 75 6 72 81.6 8 80 89.1 8.03
[0237] 8. At the end of the titration, add ammonium hydroxide as
necessary to maintain a pH of 8.0 for 3 hours. It should take about
1.6 lb. of base over 3 hours to keep the pH at 8.0. The pH will
drift the most during the first hour. After 2 hours, the pH should
be fairly stable.
[0238] 9. At the end of three hours, begin washing the
gel-slurry.
III--Quenching: Not applicable
IV--Washing: Difiltration
[0239] The gel-slurry was washed with an ammonium acetate solution
consisting of 1.8 liters of 65% ammonium acetate solution in
approximately 55 gallons of DI water followed by a DI water wash.
Used New Logic's V*SEP difiltration equipment.
[0240] On day one, the gel was washed with 256 liters of acetate
solution for one hour. The conductivity went from 51,300 mmhos to
29,000 mmhos. The next day, the gel was washed with 398 liters of
the acetate solution over 2 hours. The conductivity decreased to
11,000 mmhos. At 11,000 mmhos, the wash liquid was changed to DI
water. The gel was washed with 719 liters of DI water over 4.5
hours to a conductivity of 958 mmhos. On day three, the wash
continued using 183 liters of DI water over 1 hour to decrease the
conductivity to the target of 600 mmhos.
Acidification/Concentration
[0241] The gel-slurry was acidified in a 20-gallon tank with mixing
by an air driven mixer with a marine impeller. Approximately half
of the slurry was acidified to a pH of 5.6 with 96.3 grams of
acetic acid. The acid was added in two increments of 71.3 and 25
grams. The first acid addition was dumped in all at once. The
second addition was added slowly until the pH reached 5.6.
[0242] The acidification process takes about 20-30 minutes. During
that time, the gel is being de-watered. Once a stable pH of 5.6 is
reached, the dewatering goes on for another 5-10 minutes before the
gel gets too thick to pump out of the mixing tank. The final
concentration was 8.6% solids by LOM.
[0243] The other half of the gel-slurry was acidified the following
day to a pH of 5.6 with 106 grams of acetic acid. The acid was
added in increments of 35.5 g, 28.3 g and 42.2 g. The first two
acid additions were dumped in all at once. The last addition was
added slowly until the pH reached 5.6.
[0244] Again, the gel-slurry was dewatered during the process to a
final concentration of 8.6% solids by LOM.
V--Aging: None
VI--Spray Drying
[0245] The slurry was spray dried separately with a Stork Bowen
Model BE 1235 Spray Dryer.
Calcination
[0246] The powder was calcined in air in a fixed fluidized bed
reactor. The calcination is an automated process which follows the
following program:
Program
[0247] 15 minute ramp to 213.degree. F. 1 hour hold.
[0248] 20 minute ramp to 482.degree. F. 1 hour hold.
[0249] 20 minute ramp to 762.degree. F. 1 hour hold.
[0250] 20 minute ramp to 1100.degree. F. 2 hour hold.
[0251] Cool to room temperature.
[0252] Table 6 summarizes the key process variables and the
resulting physical properties of the formed and calcined silica
alumina powders resulting from the CHSG experiments. Example 23
represents the prior art. Examples 24 and 25 represent material of
this invention, 1934-45 and 1935-13AF. Tables 7 and 8 summarize the
observations associated with each of the CHSG, continuous, high
shear, experiments.
Example 24
This Invention
[0253] The same starting materials were used as above.
[0254] 26.96 lbs of AlCl.sub.3 solution was added to 14.4 lbs of DI
water. The acetic acid, 918 grams, was added to the aluminum
solution. The pH was less than zero. 11.18 lbs of the sodium
silicate was added to 63.2 lbs of DI water with mixing. The
silicate solution was pumped into the aluminum-acetic acid solution
over a period of fifteen minutes with mixing. The pH was about 2.3.
An ammonium hydroxide: DI water solution was prepared by a 1 3.205
w/w dilution. The pH was 11.6. The acid and the base solutions were
pumped into the Ross high-shear mixer-reactor. The specifics are
summarized in Table 6. The gel from the reactor was collected in a
tank of DI water with mixing. Acetic acid was added to keep the pH
at 8.0. The pH was maintained at 8.0 for one hour before
washing.
[0255] The remaining process steps were similar to Example 23.
Table 6 contains the specifics.
Example 25
This Invention
[0256] The same starting materials were used as above.
[0257] 26.96 lbs. of AlCl.sub.3 solution was added to 16.69 lbs of
DI water. The acetic acid, 918 grams, was added to the aluminum
solution. The pH was less than zero. 11.18 lbs of the sodium
silicate was added to 63.2 lbs of DI water with mixing. The
silicate solution was pumped into the aluminum-acetic acid solution
over a period of fifteen minutes with mixing. The pH was about 2.3.
An ammonium hydroxide: DI water solution was prepared by a 1 to
3.205 w/w dilution. The acid and the base solutions were pumped
into the Ross high-shear mixer-reactor. The specifics are
summarized in Table 6. The remaining process steps were similar to
Example 23. Table 6 contains the specifics.
9TABLE 6 Preparation Conditions for the Silica/Alumina Bases of
this Invention Prior Art This Invention Example No Comparative: 23
24 25 Notebook No 1252-36B 1934-45 1935-13AF I) Solutions A) Al
solution 32 Be AlCl.sub.3, Lb. 53.92 26.96 26.96 Glacial Acetic
Acid(99.9%),Lb 4.05 2.025 2.025 DI H.sub.2O,Lb 22.2 14.1 16.7 pH
<0 <0 <0 B) Si Solution Na.sub.2O. SiO.sub.2, 1:3.22,Lb
23.34 11.18 11.18 (Banco Sodium silicate,41 Be) DI H.sub.2O,Lb
126.4 63.2 63.2 pH 12 11.6 11.5 C) NH.sub.4OH Solution NH.sub.4OH:
DI NH.sub.4OH: DI NH.sub.4OH: DI H.sub.2O = 1:3.205 w/w H.sub.2O =
1:3.205 w/w H.sub.2O = 1:3.205 w/w II) Gelation: High Shear No Yes
Yes Stator configuration Screen Screen RPM of Rotor 2785 2680
Apparent Average Shear 1.97 1.9 Rate(1),x (10).sup.4 pH Range 5 to
9 7.7 to 8.5 Acid Rate, gm/min 1947 to 2231 1468 to 2793 Base Rate,
gm/min 883 to 1016 420 to 690 pH at outlet 8.8 7.7 to 8.5 Gel T,C
26 28 III) Quench No Yes No IV) Washing Batch No No No Wash
Solution pH of Wash Solution Wash Temperature, .degree. C.
Conductivity of Water Wash (1) Initial,mmhos/cm.sup.2 (2) Final
Wash Temperature, .degree. C. Dilution ,Wt % Solids (LOM) Wash
Solution NH.sub.4 Acetate NH.sub.4 Acetate NH.sub.4 Acetate pH of
Wash Solution 7.3 7.3 Conductivity of Water Wash (1) Initial 11000
9000 12000 (2) Final 600 455 518 Wash Temperature, .degree. C.
Ambient Ambient 50 Acidified, pH 5.6 5.6 5.62 Wt % Solids of
Concentrate 8.6 5.4 1 to 7 V) Aging No No No VI) Drying Spray
Drying Spray Drying Spray Drying VII) Physical Properties(2)
Surface Area(BET),m.sup.2/gm 249 422 319 to 340 Pore Volume(BET)
cc/gm 0.865 0.527 0.524 to 0.644 MMPD, .ANG. 173 81 90 to 105
Particle size, microns 94 30 9 (1)AASR = Apparent Average Shear
Rate, reciprocal seconds (2)Measurement made after calcination for
2 hrs at 593.degree. C., in a fixed fluidized bed reactor.
Example 26
TEM Characterization of Silica/Alumina Samples
[0258] The microstructure of the silica/alumina bases was evaluated
with respect to:
[0259] (a) the presence of pockets of different densities in the
matrix;
[0260] (b) the density of packing in the matrix; and
[0261] (c) the presence of sheet structures.
[0262] Specifically, the microstructures of the samples of this
invention Examples 24 and 25 (for example, 1933-45 and 1934-13AF)
were compared to a sample prepared without shear Example 23
(1252-36B). The typical sizes of the pores in the pockets and in
the matrix were also estimated. The results are summarized in
Tables 7 and 8 below. They showed that only the samples made by the
CHSG method contained sheet structures. These samples also have a
much denser matrix framework. This is illustrated by comparing EM
0331 (1252-36B) (FIG. 9) and EM 2269 (1934-45) (FIG. 10).
[0263] A Silica/Alumina catalyst base, Example 25 (C1935-13A) made
by high shear continuous gelations was also analyzed.
[0264] The material contains the unique sheet structure discussed
above. The material is amorphous with no evidence of any kind of
phase separation.
[0265] Tables 7 and 8 below summarize and compare the physical
properties and TEM characteristics of Silica/Alumina bases of the
present invention to the prior art.
10TABLE 7 Comparison of the Physical Properties and the
Microstructure of the Si/Al Bases of This Invention to the Prior
Art Prior Art This Invention Example Comparative: 23 24 25 Sample
Id 1252-36B 1934-45 1935-13AF Surface Area,m.sup.2/g(BET) 249 422
319 Pore Volume(N.sub.2) 0.865 0.527 0.524 Mean Meso Pore 173.4 81
90 Diameter XRD Amorphous Amorphous Amorphous "True" Macro PV(TEM)
No Yes Yes Microstructures(TEM) Particulates No No No Continuous
network X X X matrix Pockets X X X Sheets No X X
[0266]
11TABLE 8 TEM Characterization of Silica/Alumina Bases of the Prior
Art and of this Invention Prior Art This Invention Sample ID
1252-36B 1934-45 1935-13A Fines Example Comparative: 23 24 25
Amorphous Yes Yes Yes Particulates No No No Size of Particulates
Size of Pores Continuos network X X X matrix Density of Matrix --
-- -- Size of Matrix Pores, 50 to 100 5 5 nm Pockets No X X Density
of Pockets 5 5 (relative ranking) Size of Pockets, 2 to 5 5 microns
Porosity of Pockets 4 4 (relative ranking) Size of Pocket Pores, 30
70 Typical,nm Size of Pocket Pores, 10 to 60 30 to 500 Range,nm
Sheets No X X Size of sheets Thickness, nm 20 to 100 20 to 100
Length, microns 1 to 3 1 to 3
[0267] While the present invention has been described with
reference to specific embodiments, this application is intended to
cover those various changes and substitutions that may be made by
those skilled in the art without departing from the spirit and
scope of the appended claims.
* * * * *