Description
Class D21C : PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE- CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
Subclass 3/10: Pulping cellulose-containing materials (digesters D21C 7/00) with acids, acid salts, or acid anhydrides sulfur dioxide; sulfurous acid; bisulfites magnesium bisulfite