# US 4,397,769 A · Olefin polymerization catalyst

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- Number: US 4,397,769 A
- Document ID: US4397769A
- Status: Granted
- Kind: A
- Application number: 06/250,446
- Filed: 1981-04-02
- Granted: 1983-08-09
- Earliest claimed: 1981-04-02
- Assignees: Phillips Petroleum Company
- Inventors: Max P. McDaniel; John A. Sanbrano; Marvin M. Johnson
- Web page: https://patentgrep.com/patent/US4397769A

## CPC

- B01J 23/26: Chromium
- C08F 10/00: Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- B01J: CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS

## Abstract

A supported chromium oxide polymerization catalyst is prepared by a process which includes the steps of heating silica-supported chromium oxide or a substance oxidizable to chromium oxide in a nonoxidizing atmosphere in the presence of formaldehyde or a compound thermally decomposable to formaldehyde, and then heating the thus-treated catalyst in an oxygen-containing atmosphere. The temperatures of the respective heating steps can vary depending upon the properties desired in the polymer to be produced with the invention catalyst; however, the invention catalyst preparation method enables the production of a catalyst having a high melt index potential at relatively low treatment temperatures, e.g. no higher than about 600.degree. C.

## Claims

### Claim 1

A process for preparing a supported chromium oxide polymerization catalyst comprising the steps of
(a) heating at a temperature within the range of about 300.degree. to about 600.degree. C. a catalyst comprising silica-supported chromium in a nonoxidizing atmosphere in the presence of a treating agent selected from formaldehyde and substances thermally decomposable to formaldehyde and
(b) heating the thus-treated catalyst in an oxidizing atmosphere at a temperature within the range of about 300.degree. C. to about 600.degree. C.

### Claim 2 (depends on 1)

The process of claim 1 wherein the chromium treated in step (a) is present in the form of a compound selected from the group consisting of chromium oxide and compounds convertible to chromium oxide.

### Claim 3 (depends on 2)

The process of claim 2 wherein the treating agent comprises paraformaldehyde.

### Claim 4 (depends on 3)

The process of claim 3 wherein the nonoxidizing atmosphere is nitrogen.

### Claim 5 (depends on 2)

The process of claim 2 wherein step (b) is carried out at a temperature in the range of about 500.degree. to about 595.degree. C.

### Claim 6 (depends on 2)

The process of claim 2 wherein the silica-supported chromium further comprises titanium.

### Claim 7 (depends on 6)

The process of claim 6 wherein the silica support is a silica-titania cogel containing from about 0.1 to about 20 weight percent titanium, based on the weight of the polymerization catalyst.

### Claim 8

A process for activating a chromium oxide polymerization catalyst comprising the steps of
(a) fluidizing an unactivated silica-supported chromium catalyst in a nonoxidizing gas stream;
(b) heating the fluidized catalyst to a temperature of about 300.degree. to about 600.degree. C. for at least about 0.2 hour;
(c) during step (b), adding to the nonoxidizing gas stream, upstream from the activator, a treating agent comprising the products of heating paraformaldehyde to a temperature of at least 165.degree. C., and allowing the treating agent to flow in contact with the fluidized catalyst;
(d) cooling the fluidized catalyst to a temperature within the range of about 400.degree. C. to about 500.degree. C.; and
(e) fluidizing the thus-treated catalyst in an oxygen-containing gas for at least about 0.5 hour at a temperature within the range of about 400.degree. C. to about 500.degree. C.

### Claim 9 (depends on 8)

The process of claim 8 wherein the temperature of heating step (b) is within the range of about 400.degree. C. to about 595.degree. C.

### Claim 10 (depends on 8)

The process of claim 8 in which the nonoxidizing gas is nitrogen and the oxidizing gas is air.

### Claim 11 (depends on 1, 2, 7)

A polymerization catalyst prepared by the process of claim 1, 2, 7, or 8.

### Claim 12 (depends on 8)

The process of claim 8 in which the silica support comprises silica-titania cogel.