# US 6,294,048 B1 · Method for regenerating sodium hydroxide by partial autocausticizing sodium carbonate containing smelt by reaction with a borate

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- Number: US 6,294,048 B1
- Document ID: US6294048B1
- Status: Granted
- Kind: B1
- Application number: 09/238,828
- Filed: 1999-01-28
- Granted: 2001-09-25
- Earliest claimed: 1998-06-01
- Assignees: U.S. Borax Inc.
- Inventors: Charles M. Bair; Robert B. McBroom; Honghi N. Tran
- Web page: https://patentgrep.com/patent/US6294048B1

## CPC

- D21C 11/0078: {Treatment of green or white liquors with other means or other compounds than gases, e.g. in order to separate solid compounds such as sodium chloride and carbonate from these liquors; Further treatment of these compounds (fractionating of spent liquors D21C11/0042)}
- D21C 3/02: with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
- Y02P 40/40: Production or processing of lime, e.g. limestone regeneration of lime in pulp and sugar mills
- D21C: PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A method is provided for the use of borates in the recausticization of alkali-containing liquors such as those produced in the chemical and semi-chemical pulping of wood and in the oxidation and bleaching of wood pulp. Sodium hydroxide is regenerated from sodium carbonate-containing smelts in such pulp processes by autocausticization through the addition of limited amounts of borate. Autocausticization may be carried out at boron to carbonate molar ratios below 2:1 and at sodium to boron molar ratios exceeding 3:1, resulting in high reaction efficiency. Partial autocausticization using borate may also be combined with conventional lime recausticization for the regeneration of sodium hydroxide from sodium carbonate-containing smelts.

## Claims

### Claim 1

A method for regenerating sodium hydroxide in a wood pulping process comprising the steps of:
(a) partially autocausticizing a sodium carbonate-containing smelt by reaction with borate, thereby producing a borate-containing partially autotcausticized smelt which includes a reacted portion and an unreacted portion;
(b) dissolving in aqueous solution said borate-containing partially autocausticized smelt, including said reacted and unreacted portions thereof, to form a borate-containing liquor, thereby regenerating sodium hydroxide and forming dissolved sodium carbonate from said reacted and unreacted portion, respectively, in said borate-containing liquor; and
(c) introducing lime into said borate-containing liquor so as to react said dissolved sodium carbonate with said lime, thereby regenerating additional sodium hydroxide from said borate-containing liquor in the substantial absence of calcium borate formation.

### Claim 2 (depends on 1)

The method according to claim 1 wherein said autocausticization reaction is carried out by adding a limited amount of borate sufficient to provide a boron to carbonate molar ratio of less than about 2:1 and a sodium to boron molar ratio of greater than about 3:1.

### Claim 3 (depends on 2)

The method according to claim 2 wherein the boron to carbonate molar ratio is in the range of from about 0.01:1 to 1:1 and the sodium to boron molar ratio is in the range of from about 4:1 to 400:1.

### Claim 4 (depends on 2)

The method according to claim 2 wherein the boron to carbonate molar ratio is in the range of from about 0.02:1 to 0.8:1 and the sodium to boron molar ratio is in the range of from about 5:1 to 200:1.

### Claim 5 (depends on 2)

The method according to claim 2 wherein the boron to carbonate molar ratio is in the range of from about 0.05:1 to 0.4:1 and the sodium to boron molar ratio is in the range of from about 10:1 to 100:1.

### Claim 6 (depends on 1)

The method according to claim 1 wherein said wood pulping process is a kraft process.

### Claim 7 (depends on 1)

The method according to claim 1 wherein said borate is added in the form of an inorganic borate compound.

### Claim 8 (depends on 7)

The method according to claim 7 wherein said inorganic borate compound is selected from the group consisting of boric acid, boric oxide and sodium borate.

### Claim 9 (depends on 7)

The method according to claim 7 wherein said inorganic borate compound is a sodium borate.

### Claim 10 (depends on 9)

The method according to claim 9 wherein said sodium borate is selected from the group consisting of sodium metaborate, sodium tetraborate and the hydrated compounds thereof.

### Claim 11 (depends on 9)

The method according to claim 9 wherein said sodium borate is sodium tetraborate pentahydrate.

### Claim 12 (depends on 1)

The method according to claim 1 wherein said borate is added in the form of sodium borate, the boron to carbonate molar ratio is in the range of from about 0.02:1 to 0.8:1 and the sodium to boron molar ratio is in the range of from about 5:1 to 200:1.