Process for the conversion of lignocellulosic material to cellulose pulp by alkaline preoxidation followed by alkaline oxygen-free digestion both in the presence of a redox additive

摘要

A two-stage process is provided for the conversion of lignocellulosic material, for instance, wood, to cellulose pulp, first oxidizing the lignocellulosic material to form aldonic acid end groups, preferably bound with 1,4-glycosidic bonds, in the polysaccharides, in an alkaline medium in the presence of the oxidized form of a redox additive which is converted into a reduced form in reaction with the wood and/or products formed from the wood, withdrawing the alkaline medium and then reoxidizing the reduced form of the redox additive in the absence of the lignocellulosic material at a rate to maintain the oxidized form of the redox additive in a major proportion in the alkaline medium during oxidation of the lignocellulosic material by contacting the withdrawn alkaline medium with oxygen-containing gas, and then continuing the digestion in an alkaline medium at a temperature within the range from about 160° to about 200° C., also in the presence of a redox additive, but without any addition of oxygen.