Enzymatic treatment of pulp for lyocell manufacture
Bleached and unbleached pulps are treated with an enzyme in one or more stages of the bleaching process to yield a low DP pulp suitable for lyocell manufacture. This allows higher throughput of fiber an economy of manufacture.
1 . A method for making a lyocell pulp comprising the steps of
providing an unbleached pulp;
wherein said pulp has a IV of from 10 to 5 dl/g;
contacting said pulp in a bleaching sequence;
wherein said bleach sequence has at least one stage of an enzyme treatment;
wherein said bleach sequence having at least one enzyme treatment reduces said pulp by 8 to 2 IV units;
and wherein said bleached pulp is suitable for lyocell manufacture.
2 . The method of claim 1 wherein the enzyme treatment is immediately after the oxygen delignification stage.
3 . The method of claim 1 wherein the enzyme treatment is after the last bleaching stage.
4 . The method of claim 1 wherein the enzyme treatment is immediately after the oxygen delignification stage and after the last bleaching stage.
5 . The method of claim 1 wherein the enzyme is added at 0.045 to 4.5 kg/MT pulp.
6 . The method of claim 1 wherein the enzyme is added at 0.136 to 3.27 kg/MT pulp.
7 . The method of claim 1 wherein the enzyme is added at 0.227 to 1.3 kg/MT pulp.
8 . The method of claim 1 wherein the IV is reduced to 2 to 4 IV units
9 . The method of claim 1 wherein the IV is reduced to 2.5 to 3.5 IV units.
10 . The method of claim 1 wherein the pH is adjusted after the oxygen delignification stage and before the bleaching stage.
11 . The method of claim 10 wherein the pH is adjusted in the range of a pH of 3 to a pH of 10.
12 . The method of claim 1 wherein the pH is adjusted after the last bleaching stage.
13 . The method of claim 12 wherein the pH is adjusted in the range from a pH of 3 to a pH of 10.
14 . The method as in any one of claims 10 or 12 wherein the pH is adjusted with carbon dioxide.
15 . The method as in any one of claims 10 or 12 wherein the pH is adjusted with a mineral acid.
16 . The method as in any one of claims 10 or 12 wherein the pH is adjusted with an organic acid.
17 . The method of claim 1 wherein the enzyme is selected from the group consisting of xylanases, cellulases, hemicellulases, peroxidases, mannases, laccases, lipases and combinations thereof.