Sodium sulfide pulping with hydrogen sulfide generation
First Claim
1. A process for pulping hardwood to produce cellulose pulp in good yield and of high quality, with a low requirement for causticized pulping liquor, which comprises in a first pulping stage, in the absence of added carbon dioxide, pulping the hardwood in an alkaline pulping liquor containing sodium sulfide at a pH within the range from about 10.5 to about 13 and at a temperature within the range from about 110°
- to about 170°
C for a time sufficient to consume at least 3%, based on the dry weight of the wood, of alkali in the pulping liquor, determined as titratable alkali, in chemical reactions with the wood, thereby forming a large proportion of soluble organic acids in the pulping liquor, and generating hydrogen sulfide in situ in the alkaline pulping liquor by reaction of sodium sulfide with said organic acids; and
then in a second pulping stage, following directly after the first pulping stage, continuing the pulping at a pH higher than said first stage pH, within the range from about 12.5 to about 14, and at a temperature higher than said first stage temperature, within the range from about 145°
to about 190°
C, in the presence of added alkaline pulping liquor comprising sodium hydroxide and sodium sulfide until cellulose pulp is produced.
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Abstract
A process for pulping hardwood to produce cellulose pulp in good yield and of high quality, with a low requirement for causticized pulping liquor, which comprises in a first pulping stage pulping the hardwood in an alkaline pulping liquor containing sodium sulfide at a pH of about 10.5 to about 13 and at a temperature within the range from about 110° to about 170° C while generating hydrogen sulfide in situ by reaction of sodium sulfide with organic acids liberated in the pulping; and then in a second pulping stage, following directly after the first pulping stage, continuing the pulping at a pH higher than said first stage pH, within the range of about 12.5 to about 14 and at a temperature higher than said first stage temperature within the range from about 145° to about 190° C, in the presence of added alkaline pulping liquor comprising sodium hydroxide and sodium sulfide until cellulose pulp is produced.
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Citations
23 Claims
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1. A process for pulping hardwood to produce cellulose pulp in good yield and of high quality, with a low requirement for causticized pulping liquor, which comprises in a first pulping stage, in the absence of added carbon dioxide, pulping the hardwood in an alkaline pulping liquor containing sodium sulfide at a pH within the range from about 10.5 to about 13 and at a temperature within the range from about 110°
- to about 170°
C for a time sufficient to consume at least 3%, based on the dry weight of the wood, of alkali in the pulping liquor, determined as titratable alkali, in chemical reactions with the wood, thereby forming a large proportion of soluble organic acids in the pulping liquor, and generating hydrogen sulfide in situ in the alkaline pulping liquor by reaction of sodium sulfide with said organic acids; and
then in a second pulping stage, following directly after the first pulping stage, continuing the pulping at a pH higher than said first stage pH, within the range from about 12.5 to about 14, and at a temperature higher than said first stage temperature, within the range from about 145°
to about 190°
C, in the presence of added alkaline pulping liquor comprising sodium hydroxide and sodium sulfide until cellulose pulp is produced. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
- to about 170°
Specification