PROCESS FOR PREPARING CELLULOSE PULP BY ALKALINE DIGESTION WHILE INHIBITING EXTRACTION OF HEMICELLULOSE
First Claim
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2. A process as in claim 1 wherein the alkaline cooking liquor contains at least about 2 percent by weight of substantially nondegraded hemicellulose.
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Abstract
A process is provided for preparing cellulose pulp by the alkaline digestion of lignocellulosic material while inhibiting extraction of hemicellulose by employing an alkaline cooking liquor having a high concentration of substantially nondegraded hemicellulose having a degree of polymerization of at least 80. The cellulose pulp product thus contains within its fibers much or substantially all of the hemicellulose present in the natural lignocellulosic material.
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Citations
16 Claims
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2. A process as in claim 1 wherein the alkaline cooking liquor contains at least about 2 percent by weight of substantially nondegraded hemicellulose.
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3. A process as in claim 1 wherein the alkaline cooking liquor containing dissolved hemicellulose is prepared by heating an alkaline cooking liquor and a lignocellulosic material to a digestion temperature within the range from about 100 to about 190* C. to extract hemicellulose from the lignocellulosic material and dissolve the hemicellulose in the alkaline cooking liquor.
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4. A process as in claim 3, wherein the alkaline cooking liquor is cooled to a temperature below about 120* C. before it is employed in cooking lignocellulosic material.
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5. A process as in claim 3 wherein a stabilizer which inhibits degradation to hemicellulose to a degree of polymerization below 80 is admixed with the alkaline cooking liquor containing dissolved hemicellulose prior to employing the cooking liquor to cook lignocellulosic material.
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6. A process as in claim 5 wherein the stabilizer is added to the cooking liquor at a temperature below about 120* C.
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7. A process as in claim 5 wherein the stabilizer is selected from the group consisting of alkali metal and ammonium polysulfides, alkali metal borohydrides and hydrazine.
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8. A process as in claim 5 wherein from about 0.1 to about 3 percent stabilizer based on weight of lignocellulosic material is added to the alkaline cooking liquor.
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9. A process as in claim 1 wherein the alkaline cooking liquor containing dissolved substantially nondegraded hemicellulose is recycled from a previous lignocellulosic material digestion carried out under conditions to maintain a degree of polymerization of the dissolved hemicellulose of at least 80.
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10. A process as in claim 1 for digesting lignocellulosic materials while retaining hemicellulose within the resulting cellulose pulp material, which comprises heating a lignocellulosic material in an alkaline cooking liquor at a digestion temperature within the range from about 100* to about 190* C. to extract substantially nondegraded hemicellulose from the lignocellulosic material and dissolve the hemicellulose in the alkaline cooking liquor, so that the liquor contains at least about 1 percent hemicellulose having a degree of polymerization of at least 80, withdrawing at least a portion of the alkaline cooking liquor containing such dissolved substantially nondegraded hemicellulose, cooling the withdrawn liquor to a temperature below about 120* C., recycling the cooled liquor, with addition of alkali if necessary, and digesting a fresh portion of lignocellulosic material in accordance with the digestion process of claim 1 in the presence of such substantially nondegraded hemicellulose.
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11. A process as in claim 10 wherein the amount of cooking liquor remaining after a portion of the cooking liquor is drawn off, is sufficient for completing the digestion of the partially cooked lignocellulosic material.
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12. A process as in claim 11 wherein the amount of cooking liquor remaining is at least 1.5 liters per kg. lignocellulosic material.
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13. A process as in claim 10 wherein the lignocellulosic material is birch wood and the alkaline cooking liquor containing dissolved hemicellulose is drawn off at a temperature within the range from about 130* to about 170* C.
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14. A process as in claim 10 wherein the lignocellulosic material is pinewood and the alkaline cooking liquor containing dissolved hemicellulose is drawn off at a temperature within the range from about 120* to about 170* C.
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15. A process as in claim 10 wherein the digestion process is carried out continuously.
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16. A process as in claim 10 wherein the digestion process is carried out batchwise.
Specification