Glycol ether compounds for the production of polyolefin catalysts and supports

A method of making chromium containing oxide gel-based catalyst wherein an oxide hydrogel is convened to a xerogel by azeotropic distillation of a mixture of said hydrogel and an organic solvent, the improvement comprising impregnating the gel with a chromium compound during azeotropic distillation by incorporating said chromium compound into said mixture before azeotropic distillation and wherein the organic solvent used is selected from the group consisting of ethoxy ethyl acetate, tert-butyoxy propanol, methoxy propyl acetate, n-butoxy propanol, ethoxy ethyl propionate and mixtures thereof.

BACKGROUND OF THE INVENTION 
Oxide gel based materials (e.g. silica gels) are widely used as catalyst 
supports for the polymerization of olefins. Silica gel has been used as a 
support per se or has been used in the form of a cogel or tergel with 
metals such as chromium and titanium. 
Oxide gels (including cogels and tergels) are most often commercially 
prepared by a gelation from an aqueous system to form a porous hydrogel 
containing water in its pores. For use in polymerization processes, it is 
generally necessary to remove the water from the hydrogel. Unfortunately, 
simple drying cannot be used to remove the water since shrinkage of the 
desired porosity will occur. 
In order to overcome the water removal problem, several techniques have 
been attempted in the prior art. Many of these methods are discussed in 
numerous patents assigned to Phillips Petroleum Company. U.S. Pat. Nos. 
3,900,457, 4,081,407, 4,152,503 and 4,436,883 discuss the use of 
azeotropic distillation techniques for removal of water from the gel while 
avoiding pore collapse. U.S. Pat. No. 4,169,926 discusses a process where 
the gel is given a one time impregnation with certain organic liquids 
followed by drying. 
While azeotropic distillation has proven to be effective, there are various 
disadvantages associated with the known processes. For example, certain 
preferred organic solvents such as those described in U.S. Pat. No. 
3,900,457 take a long time to achieve the desired distillation owing to 
their limited miscibility with water. On the other hand, the organic 
solvents used in U.S. Pat. Nos. 4,081,407 and 4,152,503have resulted in 
more rapid water removal, but these various organic distillation liquids 
are relatively expensive in the quantities needed for commercial 
production. For Ti--Cr--SiO.sub.2 systems, these azeotropic processes can 
result in excessively high melt index capability. 
These problems have led to use of alternative techniques such as those 
described in U.S. Pat. Nos. 4,169,926 and 4,436,883. While these other 
techniques may be more economical than azeotropic distillation, the 
resulting catalyst is generally not as good can be obtained by azeotropic 
techniques. 
Accordingly, there is a need for an economical azeotropic distillation 
technique for use in production of silica gel based materials for catalyst 
applications. 
SUMMARY OF THE INVENTION 
The invention provides improved methods of making oxide gel based materials 
for catalyst applications using azeotropic distillation. Particularly, it 
has been discovered that certain classes of organic compounds, namely 
glycol ethers and glycol ether esters, can be used to permit effective and 
economical production of oxide-containing gels (including cogels and 
tergels) for catalyst applications. The invention also provides improved 
gel based catalysts useful in polyolefin manufacture. 
In one aspect, the invention encompasses a method of producing an oxide 
xerogel by removing water from an oxide hydrogel, the method comprising: 
(a) contacting a water-containing oxide hydrogel with an organic liquid 
selected from the group consisting of glycol ethers, glycol ether esters 
and mixtures thereof, 
(b) removing water from the hydrogel resulting from step (a) by azeotropic 
distillation to form a gel containing the organic liquid, 
(c) removing the organic liquid from the gel resulting from step (b) to 
produce an oxide xerogel. 
Preferred hydrogels are silica-containing hydrogels. If desired, the gel 
can be impregnated with catalytic species such as chromium before step (c) 
or after step (c). Preferably, the oxide xerogel is subsequently calcined. 
The method of the invention is especially suitable for use in the 
formation of polyolefin catalysts. 
These and other aspects of the invention will be described in further 
detail below. 
DETAILED DESCRIPTION OF THE INVENTION 
The invention encompasses processes where organic liquids selected from the 
group consisting of glycol ethers, glycol ether esters, and mixtures 
thereof are used in the removal of water from oxide hydrogels by 
azeotropic distillation. 
The starting oxide hydrogel may be prepared by virtually any known method. 
Preferably, the hydrogel is prepared by a method known to be suited for 
the production of supported polyolefin catalysts. U.S. Pat. Nos. 
4,436,883, 4,152,503, 3,900,457 or 3,887,494 describe various methods for 
making hydrogels, however it should be understood that the invention is 
not limited to any particular oxide hydrogels nor any particular method of 
hydrogel production. 
The oxide hydrogel may be of any known oxide hydrogel composition. While 
silica-containing hydrogels are preferred, the invention may also be used 
for other gel materials such as aluminum phosphate gels. The process can 
also be used with cogels (e.g. silica-titania or chromium-silica) and 
tergels (e.g. chromium-silica-titania). At least when used in connection 
with chromium-silica-titania systems, the invention method yields a 
product whose melt index potential can be varied as a function of the 
catalyst activation temperature. 
If desired, the hydrogel may be impregnated with catalytic species such as 
chromium by any conventional technique before, during or after use of the 
method of the invention. U.S. Pat. No. 4,152,503 discloses various 
chromium compounds useful for such impregnation as well as suitable 
impregnation techniques. The amount of chromium in the final catalyst is 
preferably about 0.1-2.0 wt. %, more preferably about 0.5-1.5 wt. %. If it 
is desired to perform the impregnation during or after the method of the 
invention, then it is preferred to avoid the use of water as a carrier 
medium. 
The hydrogel may be contacted with the organic liquid (i.e. glycol ether 
and/or glycol ether ester) by any conventional means to form a slurry. 
Preferably, the hydrogel is recovered from any aqueous washing or aging 
medium by filtration before contacting with the organic liquid. However, 
if desired, the organic liquid may be added to an aqueous slurry which 
contains the hydrogel. Agitation may be employed to facilitate mixing. 
In azeotropic distillation, any conventional azeotropic distillation 
apparatus may be used. Thus, the organic liquid-hydrogel slurry would be 
placed in a container where the water-organic liquid mixture is then 
evaporated, and the effluent is cooled to separate the water from the 
organic liquid. The recovered organic liquid is then preferably circulated 
back to the slurry. Alternatively, fresh organic liquid may be added to 
the slurry during the course of distillation. If desired, the distillation 
can be conducted under reduced pressure to facilitate evaporation. 
The amount of organic liquid in the initial slurry is preferably about 
100-300 vol % based on the volume of hydrogel. Preferably, the slurry is 
heated to about 90.degree.-110.degree. C. during the distillation, more 
preferably about 100.degree.-105.degree. C. Once the water is removed, the 
temperature in the distillation apparatus may be raised to boil off the 
organic solvent. The pressure used during distillation is preferably 
ambient pressure. The distillation is preferably conducted until no water 
remains in the gel. The time needed to achieve complete water removal may 
depend on the distillation conditions used. Preferably, the distillation 
conditions are selected such that complete water removal is achieved in 
about 30 minutes-4 hours more preferably about 30-120 minutes. 
The organic liquid used in the invention is selected from the group 
consisting of glycol ethers, glycol ether esters, and mixtures thereof. 
Preferred organic liquids are ethoxy ethyl acetate, tert-butoxy propanol, 
methoxy propyl acetate, n-butoxy propanol, and ethoxy ethyl propionate. 
Where the method of the invention is used to make a polyolefin catalyst, 
catalytic species such as chromium may be added to the oxide gel before, 
during or after use of the method of the invention. The invention 
encompasses the discovery that chromium actually can be added to the 
catalyst support during the azeotroping step by use of a compatible 
chromium compound which is added directly with the organic azeotroping 
solvent. Most chromium compounds used for non-aqueous post-impregnation of 
xerogels can be used during the azeotroping step of the invention. 
Preferred chromium compounds are chromium acetylacetonate, chromium 
acetate, and chromium nitrate. 
Once the water removal has been completed, the azeotroping solvent is 
preferably removed by evaporation followed by calcining. If desired, 
catalytic species may be added to the xerogel after calcination by any 
known method. To the extent that the catalytic species on or in the 
xerogel have not been activated, the catalyst may be activated by any 
conventional treatment. 
Where chromium is used as a catalytic species, preferably activation of the 
chromium is avoided until the catalyst is ready to be used so that 
handling of toxic chromium VI (hexavalent) in minimized. Avoidance of 
chromium activation during the calcining to remove residual glycol 
compound can be achieved by use of the mild oxidizing calcination 
technique (at 425.degree.-760.degree. C.) described in U.S. patent 
application Ser. No. 08/066,368 filed on May 24, 1993, the disclosure of 
which is incorporated herein by reference, or by heating in nitrogen at 
about 400.degree.-800.degree. C. 
When activation is desired, the catalyst may be treated according to any 
suitable known activation procedure. Typically, activation is accomplished 
by heating in air to about 650.degree.-870.degree. C. 
(1200.degree.-1600.degree. F.). Chromium-silica-titania catalyst products 
obtained by the invention advantageously exhibit a melt index capability 
which can be varied as a function of the activation temperature. Thus, 
1200.degree. F. activation results in a lower melt index capability than 
1600.degree. F. activation. 
These and other aspects of the invention are further illustrated by the 
following examples. It should be understood that the invention is not 
limited to the specific details of the examples.

EXAMPLE 1 
A silica-titania Hydrogel containing about 2.5 wt. % (dry basis) titanium 
97.5 wt. % SiO.sub.2 (dry basis) and a water content of about 80 wt. % was 
prepared. 
100 g of the hydrogel were combined with 250 g of ethoxy ethyl acetate to 
form a slurry in a flask of Buchi Rotavapor.RTM. distillation apparatus. 
Chromium acetylacetonate was added with the ethoxy ethyl acetate in an 
amount to give about 1 wt. % Cr in the resulting dry catalyst. The mixture 
was heated to about 100.degree. C. by immersing the flask in a 185.degree. 
C. hot oil bath and distilled at ambient pressure until all the water was 
removed from the gel (about 60 minutes). During the distillation, the 
effluent containing a mixture of water and ethoxy ethyl acetate was 
treated to recover the organic phase which was then recirculated into the 
slurry. On completion of water removal, the temperature of the mixture 
approached the boiling point of the solvent. 
The resulting Cr-containing silica-titania xerogel was then dried to remove 
the ethoxy ethyl acetate solvent. The resulting catalyst was then calcined 
at about 650.degree. C. (1200.degree. F.) in nitrogen. The catalyst was 
then milled and classified to an average particle size of about 150 
microns. 
The resulting catalyst was then used to polymerize ethylene after 
activating for 5 hours at 1500.degree. F. in dry air. The polyethylene 
polymerization was done at. 109.degree. C. in a two-liter stirred 
autoclave. The temperature was controlled and held constant to within 
0.5.degree. C. by adjusting the pressure of boiling methanol in the jacket 
surrounding the reactor. After the autoclave was filled with nitrogen and 
heated to about 102.degree. C., about 0.05 gm of activated catalyst was 
transferred under nitrogen blanket into the autoclave, followed by about 
one liter of liquid isobutane. The isobutane was prepurified by passing it 
through beds containing activated charcoal and alumina. Stirring was 
started and ethylene was supplied on demand to maintain 550 psig. Under 
these conditions the polyethylene produced does not dissolve in the 
isobutane, but reamins in slurry form. After the reactor was pressurized, 
the reaction was allowed to proceed at 109.degree. C. until about 4000 
grams of resin were made per gram of catalyst. The reaction was terminated 
by venting off isobutane and excess ethylene from the reactor. The 
resulting polyethylene had a melt index of about 6.5 measured according to 
ASTM D1238-79, Condition E, Procedure B. The surface area and pore volume 
measured by nitrogen BET method are listed in Table I along with the 
catalytic activity. 
EXAMPLES 2-5 
The procedure of example 1 was followed identically except using different 
glycol ether compounds as listed in Table I below. The melt indices of the 
resulting polyethylene produced using the catalysts is also given in Table 
I. 
TABLE I 
______________________________________ 
Surf. Area 
Pore Vol. 
Activity 
Melt 
Ex. Solvent (m.sup.2 /g) 
(cc/g) (g/g/hr) 
Index 
______________________________________ 
1 EEA 535 2.47 8490 6.5 
2 PTB 530 2.62 7770 6.7 
3 PMA 527 2.57 7830 6.6 
4 ProB 530 2.64 7480 6.8 
5 EEP 532 2.55 7710 6.1 
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EEA = ethoxy ethyl acetate 
PTB = tertbutoxy propanol 
PMA = methoxy propyl acetate 
ProB = nbutoxy propanol 
EEP = ethoxy ethyl propionate