Process for alkaline peroxide bleaching of wood pulp using a quaternary amine as additive

DETAILED DESCRIPTION OF THE INVENTION According to the process of the present invention, a quaternary amine or salt thereof is added to the peroxide bleach solution.
The hydrogen peroxide bleach may be stabilized in any manner known to the art, i.
e.
with soluble silicates, aminocarboxylic acids, polyphosphates, aminophosphonic acids or combinations thereof.
The quaternary amines of the invention are represented by the structural formula: ##STR1## wherein R is an alkyl group containing 1-3 carbon atoms and R' is hydrogen, a halogen, hydroxyl, R or -N.
sup.
+ R.
sub.
3 (together with X.
sup.
-) and X.
sup.
- is a negatively charged counter-ion.
If R' is halogen, an epoxy group may be formed by the elimination of hydrogen halide by reaction of the hydroxyl and halogen substituents on adjacent carbon atoms under basic pH conditions.
Such epoxy compounds can be formed in situ in the presence of the alkaline solution of bleach or the epoxy derivative of the halohydrin can be used in its place as the additive.
The quaternary amines exemplified in the following experiments have the structures: ##STR2## The invention is illustrated by the following description of the process conducted in the laboratory which simulates the alkaline peroxide bleaching of mechanical wood pulp in a refiner process.
EXPERIMENTAL PROCEDURE Wood pulp is (1) pretreated with diethylenetriaminepentaacetic acid in an aqueous bath and heated to a temperature of ca.
100.
degree.
C.
and digested for 15-20 minutes and (2) an aqueous solution containing NaOH, a quaternary amine compound and a stabilizer* are added to the pulp followed by aqueous H.
sub.
2 O.
sub.
2.
The same temperature used in the pretreatment is used throughout the bleaching period of 20-25 minutes.
After the bleaching step, H.
sub.
2 SO.
sub.
4 is added to the pulp to reduce the pH to about 4.
5.
* The stabilizer is an aqueous solution containing about 30 wt.
% diethylenetriaminepenta(methylenephosphonic acid) and about 10 wt.
% sodium salt of polyacrylic acid.
The bleach liquor is made to contain 2