| 摘要 |
Cellulosic materials are bleached with aqueous hypochlorite in the presence of a bromide, and the addition of the bromide to the bleaching liquor is spread over a great part or the whole of the time required for the bleaching. The bromide may be added as such or formed in situ by adding bromine and alkali hydroxide or carbonate simultaneously to the bleaching liquor. The hydrogen ion concentration of the liquor is preferably kept at about pH 7 to 8.2. The following examples are given: (1) wood pulp is bleached with bleaching powder and after one hour aqueous potassium bromide is added over a further period of an hour, the pH being brought to 7.5; (2) wood pulp is treated as in (1), but using a solution of bromine in sodium hydroxide instead of a solution of potassium bromide; (3) wood pulp is mixed with chloride of line and aqueous potassium bromide is added over a period of 45 mins.; (4) the process of (1) is modified by adding aqueous potassium bromide one hour after the beginning of the bleaching and spreading it over 75 mins.; (5) wood pulp is treated with hypochlorite as in (1) and, one hour after starting, solutions of sodium hydroxide and bromine are added over a period of an hour; (6) wood pulp is treated with hypochlorite and a solution of potassium bromide is added over 100 mins.; (7) cotton cloth is run continuously through boiling caustic soda, then through water and thereafter through a succession of bleaching vats containing hypochlorite at a pH of 7.0 to 8.0 to which potassium bromide and make-up hypochlorite are continuously added. The cloth is again washed and treated with caustic soda and passed through another series of bleaching vats containing hypochlorite without bromide; (8) Kraft pulp is treated with hypochlorite to which bromide is added in three portions over a period of 30 mins., and then washed in caustic soda and again bleached with hypochlorite containing a small amount of bromide; (9) sulphite pulp is chlorinated, washed with sodium hydroxide solution and bleached with bleaching powder. After 45 mins. the pH is brought to 7.0 to 7.5 and potassium bromide added over 30 mins.; (10) sulphite pulp is treated with bleaching powder at pH 9 and after 1 hour the pH is brought to 7.0 to 7.5 and potassium bromide is added during 30 mins. |
