Olefin polymerization catalyst

Olefin polymerization catalysts are prepared by depositing an organophosphoryl chromium product and an aluminum compound on an inorganic support material, and heating the support material in a non-reducing atmosphere at a temperature above about 300.degree. C. up to the decomposition temperature of the support material.

BACKGROUND OF THE INVENTION 
The use of chromium compounds in the polymerization of olefins is 
well-known. U.S. Pat. Nos. 2,825,721 and 2,951,816 teach the use of 
CrO.sub.3 supported on an inorganic material such as silica, alumina or 
combinations of silica and alumina and activated by heating at elevated 
temperatures to polymerize olefins. When these catalyst systems are used 
in various polymerization processes such as the well-known particle-form 
process, the resins produced, while useful in many applications, are 
unsatisfactory for others because of a deficiency in certain properties 
such as melt index. 
Attempts to improve deficient properties of polyolefins produced using 
supported, heat-activated chromium oxide catalysts have been made by 
adding various metal and non-metal compounds to the supported chromium 
oxide prior to activation by heating. For example, in U.S. Pat. No. 
3,622,522 it is suggested that an alkoxide of gallium or tin be added to 
supported chromium oxide prior to heat activation. U.S. Pat. No. 3,715,321 
suggests adding a compound of a Group II-A or Group III-B metal to 
supported chromium oxide prior to heat treatment whereas U.S. Pat. No. 
3,780,011 discloses adding alkyl esters of titanium, vanadium or boron and 
U.S. Pat. No. 3,484,428 discloses adding alkyl boron compounds. 
In columns 5 and 6 and Table 1 of U.S. Pat. No. 3,622,522 the addition of 
aluminum isopropoxide to supported chromium oxide prior to heat activation 
is shown for purposes of comparison with the addition of an alkoxide of 
gallium or tin. The patentee concluded that the addition of the aluminum 
compound gave substantially the same or an increased HLMI/MI ratio of 
polymers produced as compares to the chromium oxide catalyst with no metal 
alkoxide added, whereas the addition of gallium or tin alkoxides produced 
polymers having a lower HLMI/MI ratio. 
It is also known to utilize other chromium compounds as catalysts for the 
polymerization of olefins. Such compounds include various silyl chromate 
and polyalicyclic chromate esters as described, for example, in U.S. Pat. 
Nos. 3,324,095; 3,324,101; 3,642,749; and 3,704,287. The use of 
phosphorus-containing chromate esters in olefin polymerization catalysts 
has also been disclosed in the aforesaid U.S. Pat. No. 3,704,287; and in 
U.S. Pat. No. 3,474,080 and copending application Ser. No. 532,131, filed 
Dec. 16, 1974 now U.S. Pat. No. 3,985,676. 
Use of the above chromium compound catalysts in Ziegler-type coordination 
catalyst systems has also been proposed. As is well-known in the art, such 
catalysts frequently additionally comprise organometallic reducing agents 
such as, for example, trialkyl aluminum compounds. Ziegler-type catalyst 
systems incorporating supported chromium compound catalysts and 
organometallic reducing agents, particularly organoaluminum compounds, are 
disclosed, for example, in U.S. Pat. Nos. 3,324,101; 3,642,749; 3,704,287; 
3,806,500; and in the aforesaid copending application Ser. No. 532,131. 
SUMMARY OF THE INVENTION 
It has been discovered in accordance herewith that olefin polymers, of 
suitable properties e.g. melt indexes and melt index ratios, may be 
secured at acceptable productivity levels by utilization of an olefin 
polymerization catalyst system prepared by depositing an organophosphoryl 
chromium product and an aluminum compound on an inorganic support material 
and heating the supported chromium containing product and aluminum 
compound at a temperature above 300.degree. C. up to the decomposition 
temperature of the support. The heat treated, supported chromium 
containing product and aluminum compound may be employed directly as an 
olefin polymerization catalyst. Polymers produced using the novel catalyst 
systems of the present invention have desirable flow properties and shear 
response. 
DETAILED DESCRIPTION OF THE INVENTION 
The novel catalyst systems of the present invention are prepared by 
depositing, on an inorganic support material having surface hydroxyl 
groups, an aluminum compound capable of reacting with the surface hydroxyl 
groups of the support material and an organophosphoryl chromium product. 
The supported chromium containing product and aluminum compound are then 
heated in a non-reducing atmosphere at a temperature above about 
300.degree. C. up to the decomposition temperature of the support 
material. 
It is believed that the chromium containing product and the aluminum 
compound may react with the surface hydroxyl groups on the inorganic 
support material during the course of preparing the novel catalyst systems 
of the present invention. However, the precise mechanism involved is not 
known and applicants do not wish to be restricted to the mechanism 
postulated above. 
The inorganic support materials useful in the present invention include 
those normally employed in supported chromium catalysts used in olefin 
polymerizations such as those discussed in U.S. Pat. No. 2,825,721. 
Typically, these support materials are inorganic oxides of silica, 
alumina, silica-alumina mixtures, thoria, zirconia and comparable oxides 
which are porous, have a medium surface area, and have surface hydroxyl 
groups. Preferred support materials are silica xerogels or xerogels 
containing silica as the major constituent. Especially preferred are the 
silica xerogels described in U.S. Pat. No. 3,652,214 which silica xerogels 
have a surface area in the range of 200 to 500 m.sup.2 /g, a pore volume 
greater than about 2.0 cc/g, a major portion of the pore volume being 
provided by pores having diameters in the range of 300 to 600 A. 
The chormium containing compounds useful in the present invention comprise 
the organophosphoryl chromium compounds disclosed in U.S. Pat. No. 
3,985,676 (incorporated herein by reference) which comprise the reaction 
product of chromium trioxide with an organophosphorus compound having the 
formula: 
##STR1## 
wherein R is alkyl, aralkyl, aryl, cycloalkyl or hydrogen, but at least 
one R is other than hydrogen. The preferred organophosphorus compounds are 
trialkyl phosphates such as triethyl phosphate. 
Aluminum compounds useful in the present invention are characterized as any 
aluminum compound capable of reacting with the surface hydroxyl groups of 
the inorganic support material. Preferred aluminum compounds may be 
represented by the formula: 
EQU Al(X).sub.a (Y).sub.b (Z).sub.c 
wherein X is R, Y is OR, and Z is H or a halogen; a is 0-3, b is 0-3, c is 
0-3, and a+b+c equals 3; and R is an alkyl or aryl group having from one 
to eight carbon atoms. 
Examples of such aluminum compounds include aluminum alkoxides such as 
aluminum sec-butoxide, aluminum ethoxide, aluminum isopropoxide; alkyl 
aluminum alkoxides such as ethyl aluminum ethoxide, methyl aluminum 
propoxide, diethyl aluminum ethoxide, diisobutyl aluminum ethoxide, etc.; 
alkyl aluminum compounds such as triethyl aluminum; triisobutyl aluminum, 
etc.; alkyl or aryl aluminum halides such as diethyl aluminum chloride; 
aryl aluminum compounds such as triphenyl aluminum, aryloxy aluminum 
compounds such as aluminum phenoxide and mixed aryl, alkyl and aryloxy, 
alkyl aluminum compounds. 
The novel catalysts of the present invention may be prepared by depositing 
the organophosphoryl chromium product and the aluminum compound on the 
inorganic support in any suitable manner such as by vapor coating or by 
impregnating the support with solutions thereof in a suitable inert 
solvent which is normally an anhydrous organic solvent. Such organic 
solvents include aliphatic, cycloalkyl, and alkylaryl hydrocarbons and 
their halogenated derivatives. A preferred organic solvent is 
dichloromethane. The chromium containing-product may be applied to the 
support first or the aluminum compound may be applied first or the 
chromium and aluminum compound may be applied together. In applicants' 
usual method of catalyst preparation, the support is impregnated first 
with the chromium-containing product and then the aluminum compound. 
Preferably the organoaluminum compound may be applied to the catalyst 
support under conditions similar to those utilized for deposition of the 
organophosphoryl chromium compound. 
The most effective catalysts have been found to be those containing the 
chromium in an amount such that the amount of Cr by weight based on the 
weight of the support is from about 0.25 to 2.5% and preferably is from 
about 0.5 to 1.25%, although amounts outside of these ranges still yield 
operable catalysts. The aluminum compound should be added in sufficient 
amounts to provide from about 0.1 to 10% of aluminum by weight based on 
the weight of the support and preferably from about 0.5 to 5.5% although 
other amounts outside of these ranges can be used to prepare operable 
catalysts. 
After the chromium containing product and the aluminum compound have been 
deposited on the inorganic support, the support is heated in a 
non-reducing atmosphere, preferably in an oxygen containing atmosphere, at 
a temperature above about 300.degree. C. up to the decomposition 
temperature of the support. Typically, the supported compositions are 
heated at a temperature of from 500.degree. to 1000.degree. C. The heating 
time may vary, for example, depending on the temperatures used, from 1/2 
hour or less to 50 hours or more. Normally the heating is carried out over 
a period of 2 to 12 hours. The non-reducing atmosphere which is preferably 
air or other oxygen containing gas should be dry and preferably should be 
dehumidified down to a few parts per million (ppm) of water to obtain 
maximum catalyst activity. Typically, air used in the procedure described 
in this application is dried to less than 2-3 ppm of water. 
The heat-treated supported chromium and aluminum materials of the present 
invention may be used directly as an olefin polymerization catalyst i.e., 
in the absence of a reducing agent as shown in the Examples. Such 
catalysts may also of course be employed in combination with metallic 
and/or non-metallic reducing agents as disclosed and claimed in U.S. Pat. 
No. 3,984,351. 
The catalyst compositions of this invention are amenable to use with 
conventional polymerization processes for olefins, in particular 1-olefins 
having 2-8 carbon atoms and are suitable for polymerization effected under 
temperature and pressure conditions generally employed in the art, e.g, 
temperatures of from about 40.degree. C. to about 200.degree. C. and 
preferably from about 70.degree. C. to 110.degree. C. and pressures of 
from 200 to 1000 psig and preferably from 300 to 800 psig, as are used in 
slurry or particule form polymerizations.

EXAMPLE 1 
I. CATALYST PREATION PROCEDURE 
A. Polypor silica xerogel having a pore volume of about 2.5 cc/g prepared 
in accordance with the disclosure in U.S. Pat. No. 3,652,215 is added to a 
2000 ml, three-neck round bottom flask equipped with a stirrer, nitrogen 
inlet and y-tube with water condenser. A nitrogen atmosphere is maintained 
during the coating operation. Dichloromethane is then added to the flask 
containing the silica gel and stirring is commenced to insure uniform 
wetting of the gel. A dichloromethane solution of the reaction product of 
CrO.sub.3 and triethyl phosphate prepared as described in U.S. Pat. No. 
3,985,676 is then added to the flask in sufficient quantity to provide a 
dry coated catalyst containing about 1% by weight of Cr The supernatant 
liquid is removed by filtration and the coated gel is dried in a rotary 
evaporator at 60.degree. C. and with 29 inches of Hg vacuum. 
B. Dichloromethane is added to a similar flask as used in step A and while 
maintaining a nitrogen atmosphere stirring is commenced. To the flask is 
added the supported chromium composition prepared in step A above. A 
solution of dichloromethane and aluminum sec-butoxide is prepared in a 
pressure equalizing dropping funnel and the funnel attached to the stirred 
flask. The aluminum sec-butoxide solution is gradually added to the flask 
at the rate of 10 grams of solution per minute. After the addition of the 
solution is complete the slurry in the flask is stirred for about 1 hour. 
The supernatant liquid is removed by filtration and the coated gel is 
dried in a rotary evaporator at temperatures up to about 60.degree. C. and 
29 inches Hg vacuum. The amount of aluminum compound added depends on the 
% aluminum desired for the production of olefin polymers having specific 
properties necessary for certain end use applications. 
C. To heat activate the catalyst composition prepared in step B, the 
supported catalyst is placed in a cylindrical container and fluidized with 
dry air at 0.20 feet per minute lineal velocity while being heated to a 
temperature of 900.degree. C. and held at this temperature for six hours. 
The activated supported catalyst is recovered as a powder. 
II. POLYMERIZATION 
The polymerization were carried out in a stirred autoclave using isobutane 
as a diluent. The supported organophosphoryl chromium reaction product and 
aluminum compound is added along with the isobutane solvent to a sitrred 
one gallon autocalve. The contents of the stirred autoclave are then 
heated to the polymerization temperature, i.e., 88.degree. to 108.degree. 
C. Hydrogen, if used, is added and then the ethylene is added to give 10 
mol% in the liquid phase at which time the total pressure will be from 
about 425 to 455 psig. Polymerization begins almost immediately as noted 
by the ethylene coming from the ethylene demand supply to the reactor. 
After approximately one hour of polymerization, the reaction is terminated 
by dropping the reactor contents into a pressure let-down system. The melt 
index (M.I.) and the high load melt index (HLMI) of the polymers prepared 
were determined using ASTM D-1238-65T (conditions E and F respectively). 
III. A series of polymerizations were carried out comparing catalysts with 
and without the aluminum compound present. The catalysts were prepared as 
in the Catalyst Preparation Procedure above, except that the aluminum 
compound of step B was omitted where indicated. The polymerizations were 
carried out at about 99.degree. C. and hydrogen was added to the reactor 
as indicated. No reducing agent catalyst component was employed. 
TABLE I 
______________________________________ 
Al % Productivity 
Wt./SiO.sub.2 
H.sub.2 (psi) 
(gm PE/gm cat./hr.) 
MI HLMI 
______________________________________ 
None 0 622 0.26 27.8 
3.7 0 1032 0.71 53.6 
None 30 190 0.58 43.9 
3.7 30 1399 0.75 58.2 
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EXAMPLE 2 
Catalysts prepared with and without the aluminum compound were compared in 
the following olefin polymerizations. The catalysts were prepared 
identically (except for the omission of the aluminum compound, as 
indicated) utilizing a spray coating technique substantially in accord 
with the Catalyst Preparation Procedure above except that minimum solvent 
is employed, about equivalent to one pore volume of solvent for the silica 
gel (2.2-2.4 cc/g). 
In these polymerizations (carried out in accordance with the procedure 
outlined in Example 1) no hydrogen was employed, and no reducing agent. 
The results were obtained as follows: 
TABLE II 
______________________________________ 
Al % Productivity 
Wt./SiO.sub.2 
(gm Pe/gm cat./hr.) 
MI HLMI HLMI/MI 
______________________________________ 
3.7 552 2.96 162 54.7 
None 390 1.11 66 59.5 
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