US2193301A - Bleaching cellulose - Google Patents

Description

' March 12, 1940.

BLEACI-IING CELLULOSE Filed July 19, 1958 M. STEINSCHNEIDER ET AL Patented Mar. 12, 1940 use r'iilil" G @ELLULQSE Max Stelnschneider and Erich Knopf, rlin,

Germany, assignors to Aschafienburger Zell stoflwerke Aktiengesellschatt, Ber, Germany Application duly 19, 1938, Serial No. 220,116 In Germany July 23, 1937 3 Claims.

This invention relates to a method of bleaching cellulosic fibers with chlorine and more particularly with chlorine gas.

Quite a number of methods of bleaching cellulosic fibers are already known, in whichuse is made oi chlorine, and especially chlorine gas or other substances containing or yielding chlorine.

The defect of known methods consists essentially in that it is not possible to dose the chicrine so accurately, in respect of its time of action on the fibers, and to bring it so intimately into contact with the fibers, at the moment of the reaction, as to prevent the cellulose itself from being also attacked. Losses of and injuries to the cellulose consequently result.

It has now unexpectedly been ascertained in accordance with the present invention that these disadvantages can be reliably avoided by forcing a slurry of the celiulosic iibers to be bleached under pressure through a jet apparatus, for example by means of a pump, and drawing in chlorine gas, supplied in any desired manner, by the reduced pressure thus produced in the jet apparatus. In consequence of the resulting flowing and whirling, very thorough mixing of the slurry and chlorine gastakes place, in such a way that the chlorine is absorbed extremely quickly and completely by the fibers, in fact so quickly that the chlorine has no time to have an oxidizing action on-the cellulose itself, but only chlorinates the lignin, the latter being converted into a form in which it is readily soluble in water'cr dilute alkali and can easily be removed from the cellulose by simple washing out, while the cellulose itself remains entirely unafiected. The result attained by the present invention is evidenced by the constant molecular weight of the cellulose before and after bleaching. r The action of the chlorine on the fibers can be regulated in various ways for example by varying the concentration of the stufi mixture, or by varying the speed of the pump feeding the jet apparatus.

The following is an example of the manner in which the process is carried out.

The fibers to be bleached, e. g., wood pulp, are forced in suspension in a, carrier liquid, e. g., water, by a pump through a jet apparatus, its concentration being from 1 to 3%, and the amountoi chlorine gas required for the chlorination is drawn into the jet apparatus under the action of the resulting reduced pressure. After a relatively short time of reaction between the fibers and the chlorine, the chlorinated lignin is 6 removed by washing with water or dilute alkali.

In order more clearly to understand the invention, reference is made to the accompanying drawing, which illustrates diagrammatically and by way of example one embodiment of apparatus it) suitable for carrying the inventioninto practical efiect, and in which The fibers to be. treated pass in the form of a suspension, from the container i into the suction line 2 of a centrifugal pump t driven, for example, 15

by the electric motor 3, which pump forces the suspension through the pipe 5 into and through a jet apparatus 5 of known construction. A supply line 8 is connected at l to the jet apparatus for the chlorine gas which is drawn by'suctlon go into the jet apparatus. The latter, strictly speaking its diffusor, is containued by a pipe line 9. The action of the chlorine gas drawn in by the jet apparatus on the fibers starts in the diffuser and in this pipe line 9. tion chamber (not shown) may be connected to the line it.

The suspension may be forced into and through the jet apparatus by a different device or arrangement, instead of a pump. In addition, chlorine- 30 containing liquids or other substances containing or yielding chlorine may be drawn in with the aid of the jet apparatus, instead of chlorinegas.

1. In the method of bleaching cellulose pulp suspension with chlorinating agent the steps comprising, forcing the pulp through a jet apparatus, drawing the chlorinatingagent into the jet apparatus solely by the suction resulting therein, whereby intimate contact and mixture takes place in the diffusor of said jet apparatus between the 'chlorinating agent and the pulp.

2. Method as defined in claim 1 in which the chlorinating agent comprises gaseous chlorine.

3. Method as defined in claim 1 in which the chlorinating agent consists of gaseous chlorine.

MAX s'rnmscr an more.

However a special reac- 5

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