Treatment of pulp
View Patent ↗The present invention relates to a method of treating an aqueous suspension of bleached pulp derived from an alkaline pulping process comprising dewatering and drying said suspension, wherein the pH of the suspension to be treated ranges from about 6.5 to about 12.
1. A method of treating an aqueous suspension of bleached pulp derived from an alkaline pulping process prior to papermaking, wherein the bleached pulp has a final pH in the range from about 7.5 to about 12, said method consisting of subjecting said bleached pulp to a dewatering step and dewatering said bleached pulp to a dry content of from about 20 to about 60 wt %, forming said dewatered pulp into a pulp web or pulp sheet, and drying said pulp web or pulp sheet to a dry content of from about 50 to about 100 wt % prior to papermaking, wherein the pH of the suspension during said dewatering and drying prior to papermaking is maintained in the range from about 7.5 to about 12, wherein the step of maintaining pH optionally includes adding at least one pH-adjusting chemical to the pulp before or during dewatering and/or drying, and wherein, optionally, at least one drainage chemical is added to the pulp before dewatering.
2. The method according to claim 1 , wherein at least one drainage chemical is added to the pulp before dewatering.
3. The method according to claim 1 , wherein the pH of the suspension ranges from about 9.5 to about 10.5.
4. The method according to claim 1 , wherein at least one pH-adjusting chemical is added to the pulp before or during dewatering and/or drying.
5. The method according to claim 2 , wherein at least one drainage chemical is added in an amount from about 0.01 to about 10 kg/ton dry pulp.
6. The method according to claim 1 , wherein said at least one drainage chemical is a) a cationic starch or a cationic polyacrylamide-based polymer; and b) anionic silica-based particles or an anionic water-soluble or water-dispersible polyacrylamide-based polymer.
7. The method according to claim 1 , wherein the bleached pulp has a hexenuronic acid content ranging from about 1 to about 100 mmol/kg dry pulp.
8. The method according to claim 1 , wherein the pulp is a kraft pulp.
9. The method according to claim 1 , wherein a pH-adjusting chemical is added in an amount from about 0.001 to about 50 kg/ton dry pulp.
10. The method according to claim 1 , wherein the pH of the suspension ranges from about 8.5 to about 12.
11. The method according to claim 1 , wherein the drying is not performed by means of a flash-dryer.
12. The method according to claim 1 , wherein pulp sheets are formed during the dewatering stage.
13. The method according to claim 1 , wherein the pH of the suspension ranges from 10.5 to 12.
14. The method according to claim 1 , wherein the bleached pulp is dewatered to a dry content of from about 30 to about 60 wt %.
15. The method according to claim 14 , wherein the pulp web or pulp sheet is dried to a dry content of from about 50 to about 98 wt %.
16. A method according to claim 7 , wherein the bleached pulp has a hexenuronic acid content ranging from about 30 to about 80 mmol/kg dry pulp.
17. The method according to claim 14 , wherein the bleached pulp is dewatered to a dry content of from about 40 to about 60 wt % and the pulp web or pulp sheet is dried to a dry content of from about 60 to about 95 wt %.
18. The method according to claim 17 , wherein the pulp web or pulp sheet is dried to a dry content of from about 90 to about 95 wt %.