Process for the electrochemical reductive bleaching of lignocellulosic pulp

Abstract

Reductive bleaching of lignin containing pulps employing polydentate ligand complexes of dipositive vanadium, chromium and titanium. High brightness pulps with good reversion stability are obtained. The process is essentially polution free as the reduced complexes can be repeatedly regenerated electrochemically.

We claim: 
     
       1. .[.A continuous.]. .Iadd.An .Iaddend.electrochemical reductive process for increasing the brightness of lignocellulosic pulp which comprises reacting said lignocellulosic pulp with a polydentate ligand complex of Cr ++  or V ++  formed by the electrochemical reduction of the complexed trivalent chromium or vanadium metal ion having a concentration from about 0.1 millimole to the upper limit of solubility of the complex wherein the lignocellulosic pulp is brightened during the reaction. 
     
     
       2. A process is defined in claim 1 wherein the lignocellulosic pulp is mechanical wood pulp. 
     
     
       3. A process as defined in claim 1 wherein the lignocellulosic pulp is chemical wood pulp. 
     
     
       4. A process as defined claim 1 wherein the polydentate ligand complex is of Cr ++ . 
     
     
       5. A process as defined in claim 1 wherein the polydentate ligand complex is of V ++ . 
     
     
       6. A process as defined in claim 1 wherein the polydentate ligand is an aminopolycarboxylic acid. 
     
     
       7. A process as defined in claim 6 wherein the aminopolycarboxylic acid is ethylenediamine tetraacetic acid. 
     
     
       8. A process as defined in claim 6 wherein the aminopolycarboxylic acid is 1, 2-diaminocyclohexanetetraacetic acid. 
     
     
       9. A process as defined in claim 6 wherein the aminopolycarboxylic acid is diethylenetriaminopentaacetic acid. 
     
     
       10. A process as defined in claim 1 wherein the polydentate ligand is 8-hydroxyquinoline or a substituted 8-hydroxyquinoline. 
     
     
       11. A process as defined in claim 10 wherein the substituted 8-hydroxyquinoline is 8-hydroxyquinoline-5-sulfonic acid.