US2145062A

US2145062A - Bleaching of cellulosic materials

Info

Publication number: US2145062A
Application number: US445196A
Authority: US
Inventors: Maurice C Taylor; James F White
Original assignee: Mathieson Alkali Works Inc
Current assignee: Mathieson Alkali Works Inc
Priority date: 1930-04-17
Filing date: 1930-04-17
Publication date: 1939-01-24
Anticipated expiration: 1956-01-24

Description

Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE 2,145,062 BLEACHING 0F CELLULOSIO MATERIALS Maurice C. Taylor and James F. White, Niagara Falls, N. Y., assignors to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation of Virginia 5 No Drawing. Application April 1''], 1930, 5 Serial No. 445,196 1 6 Claims. (Cl. 8-108) This invention relates to improvements in the material or without prejudice to the bleaching bleaching of cellulosic materials, more particularly of materials composed of cellulose or'of cellulose derivatives. The invention involves, broadly, a novel application of the salts of chlorous acid for this purpose.

Chlorous acid, HC1O2, forms salts with the alkali-metals, such as sodium chlorite, NaClOz, and the alkaline-earth-metals, such as calcium chlorite, Ca(ClO2) 2.

These salts, chlorites, as applied to the bleaching of cellulosic material, difier in important respects from the hypochlorites. The hypochlorites are among the agents more commonly used for the bleaching of cellulosic materials and they are effective agentsfor this purpose. The hypochlorites, however, tend to exert a destructive action upon the cellulosic material itself. This tendency has involved, in one aspect, critical control of the bleaching operation in which the hypochlorites are used, and, in another aspect, reduction of the strength of the cellulosic material as well as actual loss of the cellulosic material itself.

We have discovered that the chlorites in an acid aqueous solution are efiective bleaching agents but that, with the chlorites as distinguished from the hypochlorites, any tendency to exert such destructive action upon the cellulosic material itself either does not exist or is, for practical purposes, negligible. Consequently the application of the chlorites to the bleaching of cellulosic material involves neither necessity for critical control nor loss of or damage to the cellulosic material itself. In this application of the chlorites as distinguished from the hypochlorites, factors such as temperature, concentration and acidity either are not critical or are much less critical.

The bleaching of cellulosic material with the chlorites may be carried out under acid conditions without destructive action on the cellulosic material. The temperature is not critical; in general increasing the temperature accelerates the bleaching action. The bleaching of cellulosic material with the chlorites may be carried out at temperatures approximating 100 C. without destructive action on the cellulosic material and without appreciable loss of available oxygen. Higher temperatures may be used by carrying outthe operation under superatmospheric pressure. Since the chlorites are so inert with respect to cellulosic material the initial and final concentrations of the chlorite may be high or low, without destructive action on the cellulosic operation. The period of contact between the chlorite and the cellulosic material also is not critical. It is important that suflicient time be allowed for the bleaching operation to proceed 5 'to the desired point but the period of any continued contact beyond this point is unimportant. The bleaching operation may thus be carried out under the conditions best meeting the economic requirements in each particular'case. 10

According to our invention, cellulosic material is bleached by subjection to treatment with an aqueous solution containing a chlorite, a chlorite of the alkali-metals or a chlorite of the alkalineearth-metals for example. This improved meth- 0d of bleaching is applicable to; cellulosic materials generally, as will be apparent from the following examples:

Woon PULP The improved bleaching method of our invention is applicable generally to wood pulps intended for the manufacture of paper, including wood pulps produced by the kraft process, by. the soda process and by the sulfite process.

Hitherto, chlorine or a hypochlorite has usually been used in the bleaching of kraft pulp, but the use of these agents has usually involved appreciable losses of the cellulosic material of the pulp itself and a reduction of the strength of the pulp product. By the use of chlorites, instead of chlorine or hypochlorites, these difficulties are avoided although good colors are obtained. Moreover, when chlorites are used, these difficulties do not appear even though an excess of the bleaching agent be used or even though the temperature at which the operation is carried out be permitted to vary widely.

In applying the chlorites to the bleaching of kraft pulp, for example, the pulp is with advan 40 tage subjected to treatment with an aqueous solution containing a chlorite, sodium chlorite or calcium chlorite for'example, having a pH value approximating 3.4-5.0 at a temperature approximating 80-90 C. However, the temperature at which the operation is carried out may be lower or higher than the range indicated. The operation may be carried out over a temperature range including 20 C., C., C., C., etc. The concentration of the treating solution may vary widely as the salts are very soluble. The density of the pulp subjected. to treatment also may vary widely. The treatment also may be carried out in one stage or in a number of successive stages and it may be combined with other bleaching treatments. Successive bleaching treatments with a chlorite may with advantage be combined with an intermediate treatment with an aqueous solution of an alkaline hydroxide such as sodium hydroxide or of a peroxide such as hydrogen peroxide or sodium peroxide or of an acid such as hydrochloric acid or an acid salt such as sodium acid sulfite or sodium acid sulfate. Bleaching treatments with a chlorite may also be combined with preceding or succeeding treatment with chlorine or a hypochlorite or successive bleaching treatments with a chlorite may be combined with an intermediate treatment with chlorine or a hypochlorite.

The application of the bleaching method of our invention to wood pulps produced by the kraft process will be illustrated by the following examples:

Example I First step.2500 parts or disintegrated kratt pulp (bone dry weight) together with sufiicient water to bring the pulp density to about 5% is heated to 80 C. 152 parts of 50% NaOH, 570 parts of glacial acetic acid and 2000 parts of water are then added to the pulp. After the pulp mixture is again brought to 80 C., 231 parts of calcium chlorite and 4500 parts of water are added to the pulp mixture. This pulp mixture is maintained in agitation at a temperature approximating 80 C., for three hours. The bleach liquor is then separated fromthe pulp and the pulp is washed.

Second step-Water is then added to the washed pulp to bring the pulp density to about 4 50 parts of 50% NaOH are added, and this pulp mixture is maintained in agitation at a temperature approximating 17-20'C., for ten minutes. The alkaline solution is then separated from the pulp and the pulp is washed.

Third step.The first step is then repeated except that the NaOH and acetic acid are added before the pulp is heated to the bleaching temperature and only 154 parts of calcium chlorite, instead of 231 parts, are used.

Example II is separated from the bleach liquor and is washed.

Second step.-The washed pulp is brought to a pulp density of about 5% by the addition of water and 10 parts of 35% HCl and 150 parts of calcium chlorite are added. The pulp mixture is maintained at 65 C., for three hours. The bleach liquor is separated from the pulp and the pulp is washed.

Example III First step-2500 parts of disintegrated kraft pulp together with sufiicient water to bring the pulp density to about 5% is heated to 80 C. 10 parts of 35% H] are first added and 231 parts of calcium chlorite together with 4500 parts of water are then added and the pulp mixture is maintained in agitation at a temperature approx-' imating 80 C., for two hours. The bleach liquor is separated from the pulp and the pulp is washed.

Second step.-Same as in Example 1. Third step.-The washed pulp is brought to a pulp density of about and 25 parts of 35% HCl and 154 parts of calcium chlorite are added. The pulp mixture ismaintained in agitation at a temperature approximating 80 C., for two hours. The bleach liquor is separated from the pulp and the pulp is washed.

Example IV First step.Same as the first step in Example I except that the pulp mixture is maintained in agitation at a temperature approximating 90 C., or a somewhat higher temperature, for one and one-half hours.

Second step.-The washed pulp is brought to a pulp density of about 5% by the addition of water. 250 parts of NaHSOa are added and the pulp mixture is maintained at a temperature approximating 17-20 C., for one hour. The sulfite solution is separated from the pulp and the pulp is washed.

Third step.--Arter bringing the washed pulp to a pulp density of about 5% by the addition of -water, it is heated to a temperature of 80 C.,

The pulp mixture is maintained in agitation at a temperature approximating 90 C., or a somewhat higher temperature, for one and one-half hours.

' The bleach liquor is separated from the pulp and the pulp is washed.

' Example VI First step-2500 parts of disintegrated kraft pulp together with suflicient water to bring the pulp density to about 5% is heated to C., 250 parts of glacial acetic acid are added, the pulp mixture is then heated to 50 C., and 231 parts of calcium chlorite together with 2500 parts of water are added. This pulp mixture is maintained in agitation at a temperature approximating 50 C., for one and one-half hours. The bleach liquor is separated from the pulp and the pulp is washed.

' Second step-Same as the second step in Example V.

Third step.Same as the first step in this example except that 154 parts of calcium chlorite, instead of 231 parts, are used.

Example VII First tep.--Same as the first step in Example I except that the entire operation is carried out at a temperature approximating 17-20 C., and is continued for twenty-four hours, instead of three hours.

Second step.The washed pulp is brought to a pulp density of about 5% by the addition of water, 250 parts of NaHSOa are added and the pulp mixture is maintained at a temperature approximating 17-20 C., for sixteen hours. solution is separated from the pulp and the pulp is washed.

Third step.-Same as the first step in this example except that 154 parts of calcium chlorite, instead of 231 parts, are used and the bleaching operation is continued for only nineteen hours, instead of twenty-four hours.

It is intended and will be understood that the invention is not limited to the foregoing examples; they are illustrative merely. An equivalent amount of sodium chlorite, for example, may be substituted for calcium chlorite in any of these examples. The pulp density, again for example, may vary from less than 445% to 10-12% or more.

In applying chlorites to the bleaching of soda pulp or sulfite pulp, for example, the pulp is similarly subjected to treatment with an acid aqueous solution containing a chlorite, sodium chlorite or calcium chlorite for example. Neither the concentration of the solution, with respect to the chlorite, nor the density of the pulp is critical. The bleaching treatment with a chlorite may be carried out in successive treatments and may be combined with other treatments as described above in connection with kraft pulp.

The application of the bleaching method of our invention to wood pulps produced by the soda process will be illustrated by the following example:

Ercample VIII First step.-15 parts of 35% HCl and 231 parts of calcium chlorite together with 4000 parts of water are added to 2500 partsof disintegrated soda pulp (bone dry weight) previously brought to a pulp density of about 5% by the addition of water. The pulp mixture is heated to 50 C., and maintained in agitation at a temperature approximating 50 C., for four hours. The bleach liquor is separated from the pulp and the pulp is washed.

Second step.Sufilcient water is added to the washed pulp to bring the pulpdensity to about 5%, 125 parts of NaHSOa are added, and the pulp mixture is maintained in agitation at a temperature approximating 17-20 C., for sixteen hours. The sulfite solution is separated from the pulp and the pulp is washed.

Third step-Same as the .first step in this.

example except that 154 parts of calcium chlorite, instead of 231 parts, are used.

In bleaching soda pulp, it is advantageous to subject the pulp to treatment with an aqueous solution of an acid agent, hydrochloric acid or sodium acid sulfate for example, prior to treatment with the aqueous solution of the chlorite. For example, 2500 parts of distintegrated soda pulp (bone dry weight) together with sufiicient water to bring the pulp density to about 5% may be so treated with 15 parts of 35% H] at a temperature approximating 17-20 C., for sixteen hours.

The application of the bleaching method of our invention to wood pulps produced by the sulfite process will be illustrated by the following example:

- Example IX 2500 parts of disintegrated sulfite pulp (bone dry weight) together with suflicient' water to bring the pulp density to about is heated to a temperature of 50 C., or a somewhat higher temperature. parts of 35% HCl are first 'added and 231 parts of calcium chlorite together with 4000 parts of water are then added. The pulp mixture is maintained in agitation at a temperature approximating 50 C., or a somewhat higher temperature, for five hours, or a somewhat shorter period.

Rag pulp can be bleached satisfactorily by Example X 500 parts of blue rag pulp (air dry weight) are treated with 31 parts of calcium chlorite and 11.5 parts 'of 35% HO] together with 400 parts of water. The pulp mixture is gradually raised to a temperature approximating 100 C., during the course of two and one-quarter hours and maintained at that temperature for one and onequarter hours, replacing water evaporated during the bleaching operation. The bleach liquor is separated from the pulp and the pulp is washed.

,Cor'ron' TEXTILES In the bleaching of cotton textiles, according to our invention, the cotton material is subjected to treatment with an acid aqueous solution containing a chlorite, sodium chlorite or calcium chlorite for example. The bleaching operation may be carried out in conjunction with the kier boiling operation by adding the chlorite to the solution used in the boiling operation. A considerable economy with respect to time, equipment and labor may be so efiected.

RAYON Hitherto the bleaching of rayon has usually been effected by treatment with aqueous solutions of sodium hypochlorite; As commonly practiced, this bleaching operation has been critical to an extreme with respect to factors including concentration, alkalinity and temperature. We have discovered that equally satisfactory bleaching of rayon may be effected by treatment with aqueous solutions containing a chlorite, sodium chlorite or calcium chlorite for example, in an operation which, if critical at all, is much less critical. The concentration of the treating solution is not important, the temperature at which the operation is carried out may vary widely, from 20 C. to more than 100 C., for example, and the acidity of the treating solution may also vary widely. At low temperature, the treating solution may have, for example, a pH value approximating 1-3 and at higher temperature the solution may be less acid. The bleaching operation may with advantage be carried out by impregnating the rayon with a neutral or alkaline aqueous solution containing the chlorite and then subjecting the rayon while impregnated with this chlorite solution to treatment with an aqueous solution of an acid agent, such as hydrochloric acid or, if the chlorite used is a chlorite of an alkali metal, sodium acid sulfate. Rayon may thus be bleached in cake form, an operation impractical with conventional bleaching agents because of tendencies toward local fibre damage.

The application of the bleaching method of our invention to rayon will be illustrated by the following examples:

Example XI Rayon skeins are immersed in a solution containing 3.2 grams per liter of sodium chlorite and 3.6 grams per liter of HCl maintained at a temperature approximating l'7-20 C., for thirty minutes. withdrawn and allowed to drip for ten minutes, and then washed.

Example XII Rayon skeins are immersed in a solution containing 64 grams per liter of sodium chlorite and 1 gram per liter of phosphoric acid maintained at a tempeature approximating 17-20 (3., for thirty minutes, withdrawn and allowed to drip for ten minutes, and then washed.

Example XIII Woon SURFACES It is frequently desirable to lighten the color of wood surfaces, in the manufacture of veneers and furniture for example. This may be accomplished in an advantageous manner by treatment of the wood surface with an acid aqueous solution containing a chlorite, sodium chlorite or calcium chlorite for example. The operation may be carried out at ordinary temperature with a solution containing about 160 grams per liter of sodium chlorite and up to 1' gram per liter of acetic acid, for example. After drying, the strength of the wood is affected little if at all. The bleach extends beneath the surface far enough to maintain the desired color in the finished product yet not far enough to injure the wood in any serious respect.

Gxourm Woon The bleaching method of our invention is applicable with advantage to ground wood and ground wood pulp producing therefrom good yields of good quality.

Lnmnnymc The chlorites of the metals of the class comprising the alkali-metals and the alkaline-earthmetals are particularly useful in carrying out our invention. The chlorite radical is the component important with respect to our invention. It will be appreciated that the chlorite should be chosen for any particular purpose to avoid undesired reactions such as the precipitation, if that is undesirable, of calcium sulfate through the use of calcium chlorite, rather than sodium chlorite for example, in a solution also containing a sulfate. y

We claim:

1. In bleaching cellulosic material, the improvement which comprises subjecting the cellulosic material to treatment with an acid aqueous solution containing a chlorite of a metal of the class comprising the alkali metals and the alkaline earth metals without destructive action on the cellulosic material.

2. In bleaching kraft pulp, the improvement which comprises subjecting the kraft pulp without destructive action on the cellulosic material temperature approximating 80-90 C.

3. In bleaching kraft pulp, the improvement which comprises subjecting the kraft pulp to treatment with an aqueous solution containing a chlorite of a metal of the class comprising the alkali-metals and the alkaline-earth-metals and an acid agent without destructive action on the cellulosic material of the kraft pulp.

4 In bleaching wood pulp, the improvement which comprises subjecting the wood pulp without destructive action on the cellulosic material to successive treatments with an aqueous solution containing a chlorite of a metal of the class comprising the alkali-metals and the alkalineearth-metals and to a treatment intermediate said treatments with another aqueous solution of an acid agent.

5. In bleaching soda pulp, the improvement which comprises subjecting the soda pulp without destructive action on the cellulosic material first to treatment with an aqueous solution of an acid agent and then to treatment with an aqueous solution containing a chlorite of a metal of the class comprising the alkali-metals and the alkaline-earth-metals.

6. In bleaching rayon, the improvement which comprises subjecting the rayon without destructive action on the cellulosic material to treatment with a non-acid aqueous solution containing a chlorite of a metal of the class comprising the alkali-metals and the alkaline-earth-metals and then subjecting the rayon while impregnated with the chlorite solution to treatment with an aqueous solution of an acid agent.

MAURICE c. TAYLOR. JAMES F. WHITE.