US2477631A - Catalytic bleaching with chlorites - Google Patents

Description

CATALYTIC BLEACHING wr'rn on oarras Robert and James E Brennan, Brevard,

N. 0., assignors to Ecusta Paper Corporation, a corporation of Delaware No Drawing.

7 Claims.

chlorites of alkali metals or alkaline earth metals.

It is directed more particularly to this type of bleaching process and in which the action of the chlorites is catalyzed by water soluble salts of certain metals.

One of the features of our catalytic process is that it permits carrying out of the bleaching operation at substantially neutral or alkaline pH values. In accordance with our discovery the catalytic salts permit eficient bleaching with the chlorites at a pH range of about to 8.5. Within this range we have found a commercially advantageous pH range ,of about 7 to 8.

The use of these catalysts in accordance with ourinvention markedly increases the activity of the chlorite bleaching compounds in neutral and alkaline reaction solutions and enables the bleaching to be carried out in equipment which is not acid-proof, such as for example, that normally used in the soda or kraft processes for producing paper pulp. c

The chlorites that we may'employ in the process of our invention include the alkaline chlorites, such as, sodium chlorite, and the alkaline earth chlorites, such as, calcium chlorite.

The catalyst which we used to catalyze the action of the chlorites and thereby render them eifective bleaching agents in a neutral or alkaline medium, include the water soluble salts of cobalt, nickel, copper, and manganese. The catalytic effectiveness of these salts varies somewhat although they are in the same general category from the standpoint of catalyzing the chlorite bleaching agent. The amounts required for efiective use of these salts for catalyzing the chlorites are relatively very small as compared with the amount of the chlorite compound itself. In other words, the amounts of the catalytic salts required are in the order of characteristic amounts for catalyst, such as for example 0.01% to 0.5%.

Although we do not wish to be limited to any specific theory for explaining the eilfectiveness of our invention, we believe that the chlorite is decomposed by our catalyst to provide an adequate amount of chlorine dioxide; C102, which bieaches the cellulose. While itis' relatively easy to obtain the chlorine dioxide gas from the chlorite salt,

Application February 21, 1945, Serial No. 579,150 I such as for example, sodium chlorite, NaCl0z, by treatment with acid, it is much more dificult to effect the decomposition and rapid formation of the C102 gas at the higher pH values, especially above a pH of 5. We have found that this desired result can now be obtained by catalyzing the chlorite salt in aqueous solution with salts of the above mentioned metals. Typical examples of satisfactory catalytic salts are cobalt chloride and cobalt nitrate.

The cellulosic materials to be bleached by the method of our invention include textiles, wood pulp and vegetable fiber pulp; typical examples being kraft wood pulp, flex fiber pulp and cotton. The process is applicable generally to pulps produced by the conventional kraft, soda, sulfite 0 neutral sulfite processes.

Amounts of the chlorites and catalyst that may be. used satisfactorily in accordance with our invention vary widely. In general, it is not necessary to use more than about 0.5% of the catalyst salt based on the weight of the pulp to be bleached;

and often-times this percentage of the catalyst bleaching may be carried out in conventional.

non-acid-proof equipment. For a further and more complete understanding of our invention,

the following illustrative but non-limiting examples of the bleaching operations are given.

' Escample I Chlorinated kraft pulp, in the amount of about 60 grams, oven dry weight, was added to 940 cc.

additions of suitable alkali, such as caustic soda, as necessary. The formation of some insoluble cobalt pigment gives a slight discoloration, which is removed by a reducing compound, hydrosulflte. Following this treatment, the-pulp was washed,

and showed the following characteristics in com- The treatment described above under Example I was repeated in this case, using diiferent materials', as indicated below:

Grams Chlorinated flax pulp (O. D. weight) 60 Water 940 Sodium chlorite 1.65

Nickelous nitrate Ni(NOa):6H2O 0.09

\ The results obtained in this example are as follows:

Original Bleached Pulp Pulp Total available chlorine used percent 3. Total nickel used ..d0. 0 0.03 Brightness (G. E. meter) 40 85 Viscosity (Tappi standard) I 100 100 Example III The process given in Example I above was again carried out, in this case using materials similar to those in Example I, except for a change in the catalyst Grams Chlorinated kraft pulp 60 Water 940 Sodium chlorite 1.4

Mn(SO4).H:O 0.06

At the end of the bleaching process in this example, the dark colored manganese compound.

that was present was removed by washing the bleached pulp'with acidified water. The results obtained in this example as shown by the following values I I Original Bleached Pulp Pulp I gvglable chlorine ap iligd...' .per:1 eut. 3 036g 0 manganeseapp e o Brightness G. E. meter)..-r 41. 5 84.0 Viscosity appi standard) 38L 35 The brightness and viscosity values in the above three examples show good bleachingand high retention of viscosity which means that little or no degradation has resulted, from the bleaching operation. The insoluble and somewhat discolored compounds that may be formed in the bleaching operations, such as the cobalt pigment mentioned above, are easily removed by washing with acidified water or decolorized by treatment with a reducing compound-e. g. sulfur dioxide, a soluble'metal bi-sulflte or hydrosulflte.

The above described process and chemicals may housed in accordance with our invention for eiiecting complete bleaching of the pulp, that is, without the use of previous or other bleaching steps. However, the invention appears to offer the best advantages, at the present time, when applied to pulp that has been partially bleached in the usual manner using chlorine or hypochlorites. It is when the pulp has reached the partially bleached stage and requires complete bleaching to a high brightness that it is most susceptible to degradation. In other words, the cellulose is more likely to become degraded'durlng the latter stages of the bleaching operation, and in these stages we have found our catalytic chlorite bleaching process to work most eil'ectively.

Various other modifications and changes may be made in the materials and process described hereinabove without departing from the scope of our invention, some of the novel features of which are deflned in the appended claims.

We claim 1. In bleaching textiles, the improvement which comprises treating the textiles with an aqueous solution containing a chlorite of a metal of the ,class consisting of the alkaline metals and the alkali earth metals, and a catalyst for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel and manganese, and maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5.

2. In bleaching vegetable fiber pulp, the 'im-- provement which comprises treating the vegetable fiber pulp with an aqueous solution containing a chlorite of a metal of the class consisting of'the alkaline metals and the alkali earthmetals, and a catalyst for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese, and maintaining the pH during the bleaclging operation at a value of about pH5 to pH 8.

3. In bleaching wood pulp, the improvement which comprises treating the wood pulp with an aqueous solution containing-a chlorite of a metal of the class consisting of the alkaline metals and the alkali earth metals, and a catalyst for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese, and

maintaining the pH during the bleaching operation at a value ofabout pH 5 to pH 8.5.

4. In bleaching cellulosic material, the improvement which comprises treating the cellulosic material with an aqueous solution.containing a chlorite of a metal ot-the class consisting of the alkali metals and the alkaline earth metals, and a catalyst for said chlorite comprising a relatively small amount of a water soluble salt of a metal of the class consisting of cobalt, nickel, and manganese, and maintaining the pH during the bleaching operation at a value of about pH 5 to PH 8.5. r

5. In bleaching kraft pulp, the improvement which comprises treating the kraft pulp with an aqueous solution containing a chlorite of a metal of the class consistingof the alkali metals and the alkaline earth metals, and a catalyst for said chlorite comprising a relativelysmall amount of a water soluble salt of a metal of theclass consisting of cobalt, nickel, and manganese, and maintaining the pH during the bleaching operation at a value of about pH 5 to pH 8.5. I

6. In bleaching flax pulp, the improvement which comprises treating the flax pulp with an chlorite comprising a relatively small amount of Number ame mu:

a water soluble salt of a metal of the class con- 1,904,190 Becher- Apr. 18, 1933 sisting of cobalt, nickel, and manganese. and 2,193,173 Jellinek -L Mar. 12,1940

maintaining the pH during the bleaching oper- 2,249,646 Bragg July 15, 1941 ation at a value of about p35 to pH 8.5. 5 2,353,823 Hampei July 18, 1944 7. In bleaching soda pulp, the improvement 2,367,771 Hampel Jan. 23, 1945.

which comprises treating the soda pulp with an aqueous solution containing a chlorite of a metal FOREIGN PATENTS of the class consisting of the alkali metals and the Number ry D e alkaline earth metals, and a catalyst for said 10 260,190 Great Britain 00h 1 6 chlorlte comprising a relatively small amo t r 311,435 Great Britain May 7, 1929 :18 water soluble salt of a metal 01 the class con- 2, France 2 1932 ting of cobalt. nickel, and manganese, and

maintaining the pH during the bleaching opera- OTHER REFFRENCES m t, a value of about pH 5 to pH 85. M Hall, Monthly Review, Textile Colorist, Jan. ROBERT M. LEVY. 1 page 39.

JAMES BRENNAN. Taylor et 8.1., Sodium Chlorite, Properties and f Reactions, Industrial and Engineering Chem- REFERENCES CITED istry. July 1940, pages 899-903.

J. F. White et ai., "Chlorite vs. Hypochlorlte The following references are oi record in the 90 Bleaching... Technical Association of the Pulp me this patent; and Paper Industry, September 1940, pages UNITED STATES PATENTS 1591:0314. a1 U 1 ch! rue in mm E yor et se 0 Sodium o 1 Name me Bleaching," Tech. Ass'n. Papers. 1940, pages 32 2 Pond July 1885 M 251-256 page 253 esp pertinent 1,163,438 Muller Dec; 7, 1915 1,777,751 Franz Get. 7, 1930