Patent ID: 8641863
Filing Date: 2014-02-04
Classification: C08B,D21C,D21H,Y02P

Abstract:
1. A method of making a stable fibrous carboxylated cellulose, the method comprising: carboxylating cellulose wood pulp fibers in an aqueous alkaline suspension by catalytically carboxylating the fibers in at least two catalytic carboxylation stages in which the catalytic carboxylation stages are in series and each later catalytic carboxylation stage further catalytically carboxylates the carboxylated fibers from the previous catalytic carboxylation stage; wherein the first catalytic carboxylation stage is provided with a precursor of primary oxidant, the active oxammonium salt catalyst, selected from the group consisting of heterocyclic nitroxides, their corresponding hydroxyl amines or their corresponding amines, stable under aqueous alkaline conditions in which the carbon atoms adjacent the nitroxide nitrogen lack hydrogen substitution, and mixtures thereof; a secondary oxidant to regenerate the active catalyst; and a sufficient amount of alkaline material to cause the fibers to be at an alkaline pH of 8-11 at the beginning of the catalytic carboxylation stage to carboxylate the cellulose fibers; wherein each subsequent catalytic carboxylation stage is provided additional amounts of the active catalyst precursor, the secondary oxidant, and alkaline material to adjust the pH to 8-11 to further carboxylate the cellulose fibers from the previous catalytic carboxylation stage; and wherein the catalytically carboxylated cellulose fibers have a carboxylation level of 18 to 100 meq. per 100 g of oven dry pulp.