| 摘要 |
Wool pulp is bleached by contacting it with an aqueous hydrogen peroxide solution to produce a partially bleached material and a partially spent aqueous hydrogen peroxide solution, adding an organic carboxylic acid anhydride, e.g. formic, acetic, propionic, n butyric, isobutyric, malonic or succinic acid anhydride, to the partially spent aqueous hydrogen peroxide solution to yield a solution having further bleaching action and further bleaching the partially bleached material with this solution the wood pulp may be contacted with the original hydrogen peroxide solution having a concentration of 1-10% by weight of the wood pulp and a pH of 6.5-9 and preferably containing sodium hydroxide in the presence of stabilizers, e.g. sodium silicate and magnesium sulphate, at a temperature of 250 DEG -100 DEG C. for 10-45 minutes. The acid anhydride is then added, preferably in an amount of 0.5-2.5 moles per mole of hydrogen peroxide in the partially spent solution, if desired together with an acid, e.g. acetic sulphuric, hydrochloric or phosphoric acid or an excess of the anhydride, to adjust the pH value and bleaching continued at 30 DEG -70 DEG for a further 2-15 minutes. The hydrogen peroxide may be added as such or may be produced from an inorganic peroxide, e.g. sodium, potassium, lithium or barium peroxide which yields hydrogen peroxide on contact with water or from a percarbamate. The wood pulp may be ground wood pulp, chemi-ground wood pulp or semi chemical wood pulp. When bleaching hardwood pulp the process may comprise a number of steps e.g. chlorination, caustic extraction, hypochlorite bleaching, chlorine dioxide, hydrogen peroxide or additional hypochlorite bleaching followed by either a one-stage or two-stage-final hydrogen peroxide bleach. |
