Sulfite process for making pulp having a tactile softness from hardwood chips

• US 4,634,499 A
• Filed: 08/14/1985
• Issued: 01/06/1987
• Est. Priority Date: 05/02/1983
• Status: Expired due to Term

• Current Assignee: The Procter & Gamble Company
• Original Assignee: The Procter & Gamble Company
• Inventors: Ampulski, Robert S.
• Primary Examiner(s): Alvo, Steve
• Application Number:
  US06/766,063
• Time in Patent Office: 510 Days
• Field of Search: 162/19, 162/83, 162/84, 162/72, 162/63, 162/36, 162/16, 162/14, 162/86, 127/37
• US Class Current: 162/84
• CPC Class Codes: D21C 3/14 ammonium bisulfite

Abstract

Pulps having a tactile sense of softness which are made from hardwoods and processes for making such pulps. The process comprises the steps of: providing hardwood chips having specified sizes; introducing the chips into a digester; removing substantially all the free oxygen from the chips within the digester; providing a cooking liquor comprising from about 0.4% to about 3% ammonia and from about 9% to about 14% sulphur dioxide; completely submerging in cooking liquor all the chips within the digester; sulfonating the lignin within the chips at a temperature of less than about 110° C.; rapidly increasing the temperature to an appropriate hydrolysis temperature; hydrolyzing the lignin sulfonation products at a temperature of from about 140° to about 155° C. at a pH from about 2 to about 3; and rapidly reducing the temperature of the system following the hydrolysis. Pulps made by this process were made into useful tissue paper webs having enhanced softness properties.

Claims

1. A process for making pulp from hardwood having a tactile sense of softness comprising the steps of:

a. Providing hardwood chips having dimensions of from about 0.6 to about 2.5 centimeter;

b. Introducing said chips into a digester;

c. Removing substantially all the free oxygen from said chips;

d. Providing a cooking liquor comprising from about 0.4% to about 3% by weight ammonia and from about 9% to about 14% by weight sulfur dioxide;

e. Reacting the lignin in said chips by maintaining the temperature within said digester at less than about 110°

C. to form lignin products, wherein said chips are reacted under substantially oxygen-free conditions and substantially all of said chips are immersed in said cooking liquor;

f. Increasing the temperature within said digester to from about 140°

C. to about 155°

C. at a rate of from about 0.75°

C. per minute to about 3°

C. per minute under substantially oxygen-free conditions;

g. Hydrolyzing said lignin reaction products at a temperature of from about 140°

C. to 155°

C. at a pH of from about 2 to about 3;

h. Decreasing rapidly the temperature within said digester; and

wherein subsequent to step h, said pulp has a xylan content of between 6% and about 8% by weight on a dry pulp basis, a xylan to mannan weight ratio of between 2.5 and about 3.7 and a glucan content of between about 80% to 92%.

2. The process of claim 1 wherein said hydrolyzing continues for from about 30 to about 80 minutes.

3. The process of claim 2 wherein said hydrolyzing is accompanied by a side relief operation.

4. The process of claim 3 wherein said decreasing of temperature is accomplished by reducing the pressure on said chips to essentially atmospheric pressure in less than about 50 minutes.

5. The process of claim 2 wherein said decreasing of temperature is accomplished by reducing the pressure on said chips to essentially atmospheric pressure in less than about 50 minutes.

6. The process of claim 1 wherein said hydrolyzing is accompanied by a side relief operation.

7. The process of claim 6 wherein said decreasing of temperature is accomplished by reducing the pressure on said chips to essentially atmospheric pressure in less than about 50 minutes.

8. There process of claim 1 wherein said decreasing of temperature is accomplished by reducing the pressure on said chips to essentially atmospheric pressure in less than about 50 minutes.

9. The process of claim 1 wherein said xylan content is between about 6.5% and about 7.5%.

10. The process of claim 9 wherein said xylan content is between about 7.0% and about 7.5%.