Process for preparing ethylene polymer and catalyst used...

Details Process for preparing ethylene polymer and catalyst used... Process for preparing ethylene polymer and catalyst used...

1998-12-11

2001-12-04

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S154000, C526S352000, C502S104000, C502S150000

Reexamination Certificate

active

06326443

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a polymerization catalyst and a process for the production of an ethylene polymer in the presence thereof. More particularly, the present invention relates to a novel polymerization catalyst having a high activity and a good hydrogen response, which comprises a chromium compound, an organic aluminum compound and a carrier and which is prepared by a specific method, and to a process for the production of an ethylene polymer having a wide molecular weight range at a remarkably enhanced productivity using the polymerization catalyst.
BACKGROUND OF THE INVENTION
In the production of an ethylene polymer in the presence of a catalyst containing a transition metal, the use of a catalyst obtained by supporting a chromium compound on a carrier makes it possible to produce an ethylene polymer having properties which cannot be attained by other catalysts such as Ziegler catalyst. Thus, such a catalyst is generally known as a representative ethylene polymerization catalyst comparable to Ziegler catalyst.
It is known that the use of a so-called Phillips catalyst comprising chromium trioxide supported on a solid inorganic oxide such as silica makes it possible to produce a blow-moldable ethylene polymer having an excellent moldability. However, the Phillips catalyst is disadvantageous in that it undergoes no effect of a molecular weight modifier such as hydrogen as generally used for Ziegler catalyst and thus exhibits a poor hydrogen response. Thus, ethylene polymers which can be produced in the presence of Phillips catalyst are limited to those having a molecular weight falling within a relatively high range.
As described in JP-B-45-40902 (The term “JP-B” as used herein means an “examined Japanese patent publication”), a catalyst comprising chromocene supported on a solid inorganic oxide such as silica undergoes a good effect of hydrogen as a molecular weight modifier and thus exhibits a good hydrogen response that allows the production of ethylene polymers having a relatively low molecular weight. However, this catalyst is disadvantageous in that it has a low activity and hence gives a poor productivity.
As described in JP-B-44-2996, JP-B-47-1766, JP-B-47-20004 and JP-B-47-21574, a catalyst obtained by reducing a chromic acid ester supported on a solid inorganic oxide such as silica with an organic aluminum compound, too, undergoes the effect of hydrogen as a molecular weight modifier. However, such a catalyst is disadvantageous in that it exhibits a deteriorated hydrogen response as compared with the foregoing catalyst comprising chromocene supported in a carrier and an insufficient activity.
An object of the present invention is to provide a process for the efficient production of an ethylene polymer having a wide molecular weight range at a remarkably improved productivity given by eliminating the above-described difficulties and attaining a high activity and a good hydrogen response.
DISCLOSURE OF THE INVENTION
The inventors made extensive studies of solution to the foregoing problems. As a result, the foregoing problems were solved by a process for the production of an ethylene polymer comprising the use of a catalyst which comprises a chromium compound, an organic aluminum compound and a carrier and which is prepared by a specific method.
The present invention relates to:
1) A polymerization catalyst obtained using a chromium compound, an organic aluminum compound and a carrier by a method comprising the following steps (a) to (d):
(a) contacting a chromium compound with a carrier in the presence or absence of a solvent;
(b) adding an organic aluminum compound to said contacted substances at a temperature of not higher than 60° C. in an amount such that the mixing ratio of said organic aluminum compound to said chromium compound falls within the range of from 0.5/1 to 100/1 as calculated in terms of the ratio of aluminum atom/chromium atom (Al/Cr molar ratio) and that the following relationship (1) is satisfied:
log
10
t≦0.33log
10
C+0.35  (1)
wherein t represents the time (min) required until the organic aluminum compound is added to give an Al/Cr molar ratio of 10/1; and C represents the amount of the carrier used (Kg);
(c) after the addition of the organic aluminum compound, stirring at a temperature of from 0° C. to 60° C. for 0.5 to 4 hours; and
(d) removing the solvent used, unreacted matters and by-products at a temperature of not higher than 60° C. in such a manner that the following relationship (2) is satisfied:
log
10
T≦0.23log
10
C+1.10  (2)
wherein T represents the time required until the removal is completed; and C represents the amount of the carrier used (Kg); and
2) A process for the production of an ethylene polymer using a polymerization catalyst which is obtained using a chromium compound, an organic aluminum compound and a carrier by a method comprising the above-described steps (a) to (d).
Preferred embodiments of the above 1) are as follows.
(a) The polymerization catalyst according to the above 1), wherein said chromium compound comprises chromium carboxylate, chromium-1,3-diketo compound and chromic acid ester.
(b) The polymerization catalyst according to the above 1), wherein said organic aluminum compound is an organic aluminum compound represented by the following general formula (5) or an alumoxane:
R
1
n
Al (OR
2
)
3−n
  (5)
wherein R
1
and R
2
may be the same or different and each represent a C
1-18
hydrocarbon group; and n ranges from 0 to 3.
(c) The polymerization catalyst according to the above 1), wherein said carrier is a solid inorganic oxide.
(d) The polymerization catalyst according to the above 1), wherein said catalyst comprises a carrier having a specific surface area of from 50 to 1,000 m
2
/g, a pore volume of from 0.5 to 3.0 cm
3
/g and an average particle diameter of from 10 to 200 &mgr;m, and a chromium atom supported on the carrier in an amount of from 0.05 to 5.0 wt-% based on the weight of said carrier.
BEST MODE FOR CARRYING OUT THE INVENTION
Examples of the chromium compound (excluding chromium oxide) for use in the present invention include chromium carboxylate, chromium-1,3-diketo compound, and chromic acid ester.
Examples of the chromium carboxylate include compounds of chromium (II) or chromium (III), represented by the following general formulae (1) or (2):
wherein R
3
, R
4
, R
5
, R
6
and R
7
may be the same or different and each represents a hydrogen atom or C
1-18
hydrocarbon group, preferably a hydrogen atom or an alkyl or aryl group having 8 or less carbon atoms.
Specific examples of these chromium compounds include chromium formate (II), chromium acetate (II), chromium propionate (II), chromium butyrate (II), chromium pentanoate (II), chromium hexanoate (II), chromium 2-ethylhexanoate (II), chromium benzoate (II), chromium naphthenate (II), chromium oleate (II), chromium oxalate (II), chromium formate (III), chromium acetate (III), chromium propionate (III), chromium butyrate (III), chromium pentanoate (III), chromium hexanoate (III), chromium 2-ethylhexanoate (III), chromium benzoate (III), chromium naphthenate (III), chromium oleate (III), and chromium oxalate (III). Preferred among these chromium compounds are chromium acetate (II), chromium 2-ethylhexanoate (II), chromium acetate (III), and chromium 2-ethylhexanoate (III).
The chromium-1,3-diketo compound is a chromium complex (III) represented by the following general formula (3) having one to three 1,3-diketo compounds:
CrX
k
Y
t
Z
u
  (3)
wherein X is a 1,3-diketo type chelate ligand, preferably &bgr;-diketonate type chelate ligand; Y and Z may be the same or different and each represents a halogen atom (preferably fluorine, chlorine or bromine), alkoxy group (preferably C
1-6
alkoxy group, more preferably methoxy, ethoxy, isopropoxy or butoxy), aryloxy group (preferably aryloxy group having 10 or less carbon atoms, more preferably phenoxy or naphthoxy), alkyl group (preferably C
1-6
alkyl group, more preferably methyl, ethyl, propyl, butyl, pe

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