Pulping with quinones and hydroquinones

Abstract

A process for the delignification of .Iadd.softwood .Iaddend.lignocellulosic material is described wherein the lignocellulosic material is cooked with .[.an alkaline or.]. .Iadd.a .Iaddend.neutral sulphite pulping liquor, and there is added to the pulping liquor at least 0.001% by weight of an additive compound or mixture of additive compounds selected from quinones and hydroquinones.

We claim: 
     
       1. In a process for the delignification of .Iadd.softwood .Iaddend.lignocellulosic material wherein the .Iadd.softwood .Iaddend.lignocellulosic material is cooked with a neutral sulphite pulping liquor, the improvement comprising adding to the pulping liquor 0.001% to 10% by weight of an additive compound selected from the group consisting of anthraquinone, phenanthrenequinone, naphthoquinone, anthrone, anthrahydroquinone, naphthohydroquinone, phenanthrahydroquinone, the alkyl-, alkoxy-, hydroxy-, amino-, halo- or carboxy derivatives of said quinones or hydroquinones, the tautomeric form of said additive compounds and mixtures of said additive compounds. 
     
     
       2. A process as claimed in claim 1 wherein the tautomeric form of the additive compound is selected from the group consisting of 10-hydroxyanthrone, 1- and 2-alkyl-10-hydroxyanthrone, 1- and 2-amino-10-hydroxyanthrone, 1- and 2-hydroxy-10hydroxyanthrone, 1- and 2-halo-10-hydroxyanthrone and mixtures thereof. 
     
     
       3. A process as claimed in claim 1 wherein the additive compound is selected from the group consisting of 9,10-anthrahydroquinone and 1- and 2-alkyl-9,10-anthrahydroquinone. 
     
     
       4. A process as claimed in claim 1 wherein the additive compound is pre-mixed with the cooking liquor and the .Iadd.softwood .Iaddend.lignocellulosic raw material before introduction to a digester for cooking. 
     
     
       5. A process as claimed in claim 1 wherein the additive compound is added to the cooking liquor and to the .Iadd.softwood .Iaddend.lignocellulosic raw material in the digester. 
     
     
       6. A process as claimed in claim 1 wherein the hydroquinone compound is generated in situ during cooking by reaction of the corresponding quinone compound with a reducing agent. 
     
     
       7. A process as claimed in claim 6 wherein the reducing agent is an inorganic agent selected from the group consisting of sodium dithionite, zinc dithionite, sodium borohydride, zinc powder and sodium hydroxide. 
     
     
       8. A process as claimed in claim 6 wherein the reducing agent is an organic agent selected from the group consisting of glucose, xylose, mannose, sucrose, cellobiose, maltose, raffinose, starch, xylan, amines, alkanolamines, aldehydes and spent cooking liquor. 
     
     
       9. A process as claimed in claim 6 wherein the quinone compound is 9,10-anthraquinone and the reducing agent is sodium dithionite. 
     
     
       10. A process as claimed in claim 6 wherein increments of the reducing agent are periodically added during cooking in order to maintain a sufficient amount of the hydroquinone compound in the cooking liquor. 
     
     
       11. A process as claimed in claim 1 wherein the cooking occurs at a temperature in the range of 50° C. to 250° C.; and the cooking period is in the range of 480 minutes to 0.5 minutes. 
     
     
       12. A process as claimed in claim 11 wherein the cooking temperature and the cooking period consists of a first stage of 30 minutes to 120 minutes in reaching a temperature of 100° to 130° C.; a second stage of 15 minutes to 50 minutes held at the temperature of 100° to 130° C.; and a third stage of 30 minutes to 300 minutes at a temperature from the 130° C. to a maximum temperature of 180° C. 
     
     
       13. A process as claimed in claim 1 wherein the .Iadd.softwood .Iaddend.lignocellulosic material is subjected to a pretreatment in a soaking liquor containing a soluble quinone or hydroquinone compound for a preliminary impregnation of said .Iadd.softwood .Iaddend.lignocellulosic material with said compound before the introduction of the .Iadd.softwood .Iaddend.lignocellulosic raw material into a digester for delignification. .[. 
     
     
       14.  In a process for the delignification of lignocellulosic material wherein the lignocellulosic material is cooked with an alkaline pulping liquor, the improvement comprising adding to the pulping liquor 0.001% to 10% by weight of a hydroquinone selected from the group consisting of 9,10-anthrahydroquinone, phenanthrahydroquinone, the alkyl-, alkoxy-, halo-, hydroxy-, amino-, or carboxy-derivatives of said hydroquinones and the tautomeric form of said hydroquinones and mixtures thereof..]. .[.15. A process as claimed in claim 14 wherein the additive compound is pre-mixed with the cooking liquor and the lignocellulosic raw material before addition to a digester for cooking..]. .[.16. A process as claimed in claim 14 wherein the additive compound is added directly to the cooking liquor and to the lignocellulosic raw material during the cooking..]. .[.17. A process as claimed in claim 14 wherein the hydroquinone compound is generated in situ by reaction of the corresponding quinone compound with a reducing agent..]. .[.18. A process as claimed in claim 17 wherein the reducing agent is an inorganic agent selected from the group consisting of sodium dithionite, zinc dithionite, sodium borohydride, zinc powder and sodium hydroxide..]. .[.19. A process as defined in claim 18 wherein increments of the reducing agent are periodically added during cooking in order to maintain a sufficient amount of the hydroquinone compound in the cooking liquor. .[.20. A process as claimed in claim 17 wherein the reducing agent is an organic agent selected from the group consisting of glucose, xylose, mannose, sucrose, cellobiose, maltose, raffinose, starch, xylan, amines alkanolamines, aldehydes and spent cooking liquor..]. .[.21. A process as claimed in claim 14 wherein the cooking occurs at a temperature in the range of 50° C. to 250° C.; and the cooking period in in the range of 480 minutes to 0.5 minutes..]. .[.22. A process as claimed in claim 14 wherein the lignocellulosic raw material is subjected to pretreatment in a soaking liquor containing a soluble hydroquinone compound for a preliminary impregnation of the lignocellulosic raw material with said compound before the introduction of the lignocellulosic material into a digester for delignification..]. .[.23. A process as claimed in claim 14 wherein the hydroquinone compound is selected from the group consisting of 1- and 2-hydroxy-9,10-anthrahydroquinone..]. .[.24. A process as claimed in claim 14 wherein the hydroquinone compound is selected from the group consisting of 1- and 2-alkyl-9,10-anthrahydroquinone and mixtures thereof..]. .[.25. A process as claimed in claim 14 wherein the amount of the hydroquinone compound is in the range of 0.001 to 5% by weight based on the lignocellulosic material; the cooking temperature is in the range of 130° C. to 180° C.; and the cooking period is in the range of 480 minutes to 0.5 minute..].