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US4295929A
Expired / Lapsed
US
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Process for acid sulfite digestion of wood
Assignee: Rayonier Inc
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Filing: 1980-03-19
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Granted: 1981-10-20
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Expires: 2000-03-19
Abstract
Abstract The production of chemical pulp by the acid sulfite digestion process is improved by increasing the ratio by weight of combined SO2 to wood to a range of from 4 to 12 (based on one part of combined SO2 to 100 parts of dry wood) and by increasing the minimum average rate of heating to the substantially maximum cooking temperature to 40 DEG C. per hour.
Inventors
- 👤 Phyllis C. Leithem
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 12:25
CPC Classifications
D; D21; D21C; D21C3/00; D21C3/04; D21C3/06
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
139 words
In a process of digesting wood to produce chemical pulp by the acid sulfite digestion process in which the ratio by weight of total SO 2 to combined SO 2 is at least 4 to 1 comprising heating in a closed vessel wood chips in an acid sulfite cooking liquor having a concentration of free SO 2 no greater than 16% to a maximum cooking temperature no greater than 180° C. and at a maximum pressure no greater than 170 psig for a period of time sufficient to defiber the wood, the improvement in which the ratio by weight of one part of combined SO 2 to 100 parts of dry wood is from 4 to 12 and the minimum average rate of heating to a temperature which is the substantially maximum cooking temperature is 40° C. per hour.
Claim 2
Dependent Claim
139 words
In a process of digesting wood to produce chemical pulp by the acid sulfite digestion process in which the ratio by weight of total SO 2 to combined SO 2 is at least 4 to 1 comprising heating in a closed vessel wood chips in an acid sulfite cooking liquor having a concentration of free SO 2 no greater than 16% to a maximum cooking temperature no greater than 180° C. and at a maximum pressure no greater than 170 psig for a period of time sufficient to defiber the wood, the improvement in which the ratio by weight of one part of combined SO 2 to 100 parts of dry wood is from 4 to 12 and the minimum average rate of heating to a temperature which is the substantially maximum cooking temperature is 40° C. per hour.
Claim 3
Dependent Claim
30 words
The process of claim 1 in which the temperature is raised to substantially the maximum temperature from an ambient temperature cooking liquor in a time of less than 21/2 hours.
Claim 4
Dependent Claim
29 words
The process of claim 1 in which the temperature is raised to substantially the maximum temperature from a heated cooking liquor in a time of less than 2 hours.
Claim 5
Dependent Claim
16 words
The process of claims 2 or 3 in which the time is less than 11/2 hours.
Claim 6
Dependent Claim
19 words
The process of claim 1 in which the ratio of combined SO 2 to wood is 4.5 to 9.
Claim 7
Dependent Claim
19 words
The process of claim 1 in which the ratio of combined SO 2 to wood is at least 5.
Claim 8
Dependent Claim
18 words
The process of claim 1 in which the average minimum rate of heating is 50° C. per hour.
Claim 9
Dependent Claim
20 words
The process of claim 1 in which the initial pH of the cooking liquor ranges from about 1 to 2.
Claim 10
Dependent Claim
24 words
The process of claim 1 in which the ratio by weight of total SO 2 to combined SO 2 ranges from 4 to 12.
Claim 11
Dependent Claim
15 words
The process of claim 1 in which the process is a single stage digestion process.
Claim 12
Dependent Claim
15 words
The process of claim 1 in which the process is a soluble base digestion process.
Claim 13
Dependent Claim
29 words
The process of claim 1 in which the concentration of free SO 2 ranges from 4 to 12% and does not exceed 10% at cooking temperatures above 120° C.
Claim 14
Dependent Claim
13 words
The process of claim 1 in which the maximum pressure is 150 psig.
References Cited (Backward Citations)
US1880042A
Cited
US3523060A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-10-19 | 1985-04-20 | 1985-10-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-10-19 | 1989-04-20 | 1989-10-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-10-19 | 1993-04-20 | 1993-10-20 | $7700.00 | Window Closed / Lapsed |