# US 4,689,117 A · Thermomechanical digestion process for enhancing the brightness of cellulose pulp using bleachants

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- Number: US 4,689,117 A
- Document ID: US4689117A
- Status: Granted
- Kind: A
- Application number: 06/772,575
- Filed: 1985-09-04
- Granted: 1987-08-25
- Earliest claimed: 1980-11-24
- Assignees: Process Evaluation and Development Corporation
- Inventors: Eduardo J. Villavicencio
- Web page: https://patentgrep.com/patent/US4689117A

## CPC

- D21H 11/10: Mixtures of chemical and mechanical pulp
- D21B 1/12: by wet methods, by the use of steam (beaters D21D1/00)
- D21B 1/16: in the presence of chemical agents
- D21B 1/36: Explosive disintegration by sudden pressure reduction
- D21C 3/22: Other features of pulping processes
- D21C 9/1026: {Other features in bleaching processes}
- D21H: PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21B: FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
- D21C: PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR

## Abstract

The brightness of a thermomechanical pulp can be improved if a serial multiple blowdown technique is used and a bleachant is present at an effective concentration throughout the thermomechanical pulping process.

## Claims

### Claim 1

An improved method for enhancing the brightness of a cellulose fiber pulp undergoing digestion in a thermomechanical process comprising the steps of:
(a) providing a fiber source in a form suitable for input into a digester;
(b) conveying the fiber source into a first chamber of a digester and contacting said fiber source with steam and a first quantity of a bleach solution at an autogenous pressure of 2 kg/cm to 15 kg/cm for a first period of time;
(c) removing said fiber source from said first chamber, and rapidly decreasing the pressure on said fiber source at least 0.5 kg/cm to a first lower pressure; wherein water within said cellulose fiber source flashes to steam opening the fibers; and
(d) inputing said fiber source at said first lower pressure into a second chamber of said digester for contact, with steam at said first lower pressure for a second period of time;
the improvement comprising adding a second quantity of a bleach solution to said fiber source after removing said fiber source from said first chamber and prior to rapidly reducing the pressure on said fiber source to said first lower pressure, wherein part of the water of dilution of said second quantity of bleach solution converts to steam thereby concentrating said second quantity of bleach solution on said fiber source.

### Claim 2 (depends on 1)

A method for improving the brightness of cellulose fibers undergoing thermomechanical digestion as in claim 1 wherein the pressure on said fiber source at said first lower pressure is further decreased to atmospheric pressure.

### Claim 3 (depends on 1)

A method of improving the brightness of cellulose fibers undergoing thermomechanical digestion as in claim 1 wherein said fiber source is selected from the group consisting of wood, bamboo, bagasse, straw and eucylyptus.

### Claim 4 (depends on 3)

A method for improving the brightness of cellulose fibers undergoing thermomechanical digestion as in claim 3 wherein said bleachant is selected from the group consisting of hydrogen peroxide, sodium peroxide, oxygen, ozone, sodium hydrosulfite and zinc hydrosulfite.

### Claim 5 (depends on 4)

A method for improving the brightness of cellulose fibers undergoing thermomechanical digestion as in claim 4 wherein the bleach solution contains a buffering agent selected from the group consisting a sodium hydroxide and potassium hydroxide.

### Claim 6 (depends on 1)

A method for improving the brightness of cellulose fibers undergoing thermomechanical digestion as in claim 1 wherein the autogenous pressure of steam in contacting said fiber source is about 2.5 kg/cm.sup.2 to 10 kg/cm.sup.2.

### Claim 7 (depends on 6)

A method for improving the brightness of cellulose fibers undergoing thermomechanical pulp as in claim 6 wherein said autogenous pressure is decreased at least 1 kg/cm.sup.2 to the first lower pressure and at least 1 kg/cm.sup.2 to the first lower pressure.

### Claim 8 (depends on 7)

A method as in claim 7 for improving the brightness of a thermomechanical pulp wherein said bleach is slected from the group consisting of hydrogen peroxide, sodium peroxide, oxygen, ozone, sodium hydrosulfite and zinc hydrosulfite.