US2161045A - Bleaching - Google Patents

Description

Jun 6, 1939.

w. HlRscvHKlND ET A1. 2,161,045

BLEACHING Original Filed June 1, '1937 6 Sheefs-Sheet 1 ATTOR'NFV June 6, 1939. w. HIRSCHKIND ET AL. 2,161,045

BLEACHING original Filed June 1, 1957 e sheets-sheet 2 ATTORNEY June 6, 1939. w. HlRfscHKlND ETYAL v i 2,161,045

BLEACING Original Filed Jung l, 1957 6 SheretsSheetv 3' 96C/7/0r/'ns consumed V/'scos//y A mmv-roei l o zo no @o 'l so 100 120 l/W//ze/m //rfc/v/'nd Wma /n mma/es Far/ 6. Thompson BY M ATTORNEY.

' June 6, 1939.1

w. HlRscHKlND ET Al.

BLEACHING `Original.Filed June l, 1937 6 Sheets-Sheet l4.

pramman/'z/m w's casi/g .D o S d a ,677/0/- 'ne /N VE N TOE 5 ATTORNEY.

June 6, 1939. w. HlRscl-n/ND ET Al. 2,161,045

` BLEAJHING Original Fild June 1, 1937 6 Sheets-Sheet 6 FILE- Q Patented June 6, 1939 UNITED' STATE p nLEAcmNG wilhelm Hir'sehkina, Berkeley, Davia J. Pye,

Pittsburg, Calif.,

and Earl G.

Thompson,

Seattle,'Wash., assignors, by mesne assignments, tol The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application June 1, 1931, serial Ne.145,sos

- Renewed November 7, 1938 12 Claims..

This invention relates to improvements in the use of oxidizing materials, particularly materials which are used to effect oxidizing bleaches. Such materials include chlorine,hypochlorous acid, the hypochlorites, water solutions of chlorine, hydrogen peroxide, peroxides, 'and per salts as perborates, persulphates, and permanganates. The invention is broadly applicable to the bleaching of materials generally, but it will be described in connection with the bleaching of cellulose materials, particularly wood pulps such as sulphite, soda and kraft pulps. However, it is to be understood that this is only disclosed as a typical application of the invention which is also useful on other materials as well as pulps, for example, to the bleaching of cloths, rags, wool and other,

materials. v '1 .Cellulose pulps are ordinarily bleached with chlorine water, hypochlorous acid, or hypochlorites. The initial portion of the bleaching treatment, whether the treatment be conducted in a single or a plurality of stages, if analyzed, will be found to be a chlorination step. That is, materials in the pulp are chlorinated by the available chlorine or by -the hypochlorite to form chlorinated addition and substitution products. Further treatment of the pulp is thereafter conducted to oxidize coloring material. Between the chlorination and oxidizing treatment, the pulp may or may not be washed to remove the soluble chlorinated materials with acid, alkaline or plain water washes.

The action of light upon the bleaching of cellulose has previously been studied by various invest-3f.

tigators, including Escourrou. He reported (Congres de la Papeterie, June, 1928, and Chimie et4 Industrie, June, 1928) that while the ultra violet light sensibly diminished the time of bleaching, it resulted in a greater consumption of chlorine and, because the chlorine became more active, a cellulose attack occurred which lowered the yield. Further, Escourrou found that the .bleached cellulose was rich in oxy and hydroxy celluloses. the presence of which was revealed by an appreciable elevation in the copper'number. Escourrou reported an undesirable decrease in the alpha cellulose content and an increase in the formation of beta and gamma celluloses. These ndings led him vto advise against the use of light bleaching, particularly if. the pulp was destined for the manufacture of viscose silk. As .a resultof investigations hereinafter set forth, we have arrived at the conclusion that the reason Escourrou did not find the use of lightA advantageous was that while he used light from a quartz mercury arc, reporting that its spectrum contained a group ofl particularly intense rays in the neighborhood of 365 millimicrons, this light source also contains light rays of a shorter length, as lovlr as 180 millimicrons, which Escourrou did not eliminate. We have secured excellent results by confining the light to a wave length not substantially beyond 300 millimicrons. vIn fact, the broad effective band which we prefer is between 300 land 420 millimicrons. Beyond 420 millimicrons, the visible light present is not of any appreciable value'. The eiective light band is that passed by a boro-silicate glass such as Crown glass or Pyrex. Apparently light rays shorter than about 300 millimicrons have a detrimental eifect upon cellulose, and hence the reason for Escourrous finding. The specific preferred light for use on wood pulp is that having a wave length of 365 millimicrons. f

It is in general the broad object of the present invention toprovide a bleaching process in which lightcan be used eifectively to improve the quality of the bleached product.

Another object of the inventionis to provide an improvement in bleaching wherein a selected light band is eiiectively used to improve the color without damage to the bleached material.

The invention includes other objects and fea` tures of advantage some of which, together with the foregoing, will-'appear hereinafter wherein the present preferred practice is disclosed.

A further object of the invention is to improve -the 4oxidizing ability, of oxidizing materials used for bleaching, as measured by color improvement. In the drawings accompanying and vforming a part hereof Figure 1 illustrates the decomposition rate of various solutions when subject to light for the time indicated.

Figure 2 illustrates the chlorine consumption rate of a pulp treated with a 3% chlorine water with and without light.

Figure 3 illustrates the relative chlorine consumption'of the same pulp treated initially in the dark and thereafter divided and treated with and without light.

i Figures 4` and 5 illustrate the chlorine consumption, the viscosity, copper number and percent of alpha cellulose in a pulp treated with and without light. Figure 4 shows the first stage treatment and Figure 5 shows the second stage treatment.

Figure 6 illustrates the same factors as in Figures 4 and 5 applied to the second stage, of another pulp.

Figures 7 and 8 indicate second stage chlorine consumption values onA a sulphite pulp.

Figure 9 illustrates diagrammatically the ab- 18% hydrochloric acid solution, and a solution of chlorine in water. The results, as set forth in Figure 1, indicate that the light is much more effective on the hypochlorous acid than on the chlorine. It is to be noted that the sodium hypochlorite is relatively stable under the light. 'I'he conclusion drawn from this is that any improved results` are due to something other than an increase in the rate of decomposition of the hypochlorite.

Escourrou subjected the pulp undergoing treatment to the action 'of ultra violet light during the chlorination stage. We have investigated the comparative value of light during the chlorination stage and during the oxidation stage in various chlorine bleaches and we have determined that the light is not particularly effective durf ing the chlorination stage treatment of the cellulose.

Referring to Figure 2, it is to be noted that the chlorination stage is indicated by a high percentage chlorine consumption in the rst five minutes at the particular chlorine concentration. Thereafter, in the presence of light, the chlorine consumption proceeds at a second very definite rate, while, in case light is absent, some few minutes elapse before the second rate of chlorine consumption is definitely established. There is an interval of secondary reaction which cannot be definitely explained but which is eliminated by the use of light, Aduring the chlorination operation. The value o f this secondary reaction will be discussed hereinafter in connection with Figure (i.

The pulp tested inthis instance (Figure 2), a sulphite pulp, was placed in a ve gallon crock at a 2% consistency. A 400 watt G. E. mercury vapor lamp was placed in the center of the crock and was shielded from the pulp by a suitable boro-silicate glass which eliminated substantially all light shorter. than 300 millimicrons. A cooling water jacket was provided to keep the temperature of the pulp below 30 C. The annular ring of pulp surrounding the light was about 3 inches in thickness, with a minimum radius of 3 inches from the light pencil as the center.

We have separated the encrusting material from a cellulose pulp, making an extract or infusion thereof. This material, when subject to light, was found to selectively absorb light between 300 and 420 millimicrons. The material particularly absorbed the 365 millimicron band. This means that in subjecting material to an oxidizing bleach, one should determine the light band selectively absorbed by the material to be treated. Thereafter, this light band can be used to enhance the action of the oxidizing bleaching agent, and any detrimental effects can be obviated by limiting the light to the band effectively absorbed by the material to be treated. This will be further discussed hereinafter in connection with Figure 9.

We have subjected pulp and lother materials to the action of various oxidizing chemicals while irradiating with light selectively absorbed substantially only by the encrusting or color imparting material. In some cases we used light containing bands shorter than 300 millimicrons and in these instances poor results were obtained as manifested by high reagent consumption, degradation of the material treated and little color improvement. This confirmed Escourrous lindings. In other cases we restricted the light substantially to that selectively absorbed by the encrusting or coloring material and in these instances the reagent economy. was increased, degradation was eliminated or at a minimum,

while material color improvement was observed. The irradiating light should be restricted to that selectively absorbed by the encrusting material, that light selectively absorbed by the other material, cellulose, for example, being substantially absent.

Hereinafter We have disclosed the application of the invention to various materials and various oxidizing chemicals.

We have used light of 300 millimicrons and above effectively in treating cellulose, both in single stage and in multi stage operations. In Figure 3 is shown the chlorine consumption on a sulphite pulp in the first stage. The sample was treated with 3% of chlorine for thirty minutes. This is equivalentto a chlorination operation. After this, the light was turned on and the increase in chlorine consumption is plainly indicated upon that portion of the sample which was subject to the light, as compared to that which Was permitted to remain me ely in the original condition. The color of the pulp treated under the light was very much brighter than that run under normal conditions, that is without the use of the light during the last portion of the single stage treatment.

In multi stage bleaching (Figures 4 and 5), chemical tests were made on vsamples taken at intervals from two bleach batches, run with light and without light. The original pulp was a sulphite pulp. The rst stage operation consisted of the 3% chlorine water bleach and 2% consistency for a total of sixty minutes (Figure 4). After washing, a second stage (Figure 5) of one hundred and twenty minute treatment was given with 1.5% of C12 as hypochlorite at a 2% pulp consistency. The temperature was kept below 30 C. at all times. Viscosity, copper number and alpha cellulose values were run upon each of the pulps during the bleaching operation, during both the first and second stages. It is to be noted in Figure 4 that the viscosity of the unradiated pulp dropped to a much lower value with the increased degree of chlorination. The increase in viscosity thereafter is connected with some secondary reaction which causes the chlorine consumption rate to proceed at a practically constant value between the ten and forty minute points before the reaction rate falls off to nearly zero (see Curve D, Figure 2). The secondary reaction does not seem to take place in the irradiated pulp, this being indicated by the constant decrease in viscosity which signifies a substantially pure oxidation process. The copper number shown in Figure 4, indicative of the degree of degradation of the pulp (approximately proportional to the reciprocal of the viscosity) docs not -indicate'any detrimental action upon the pulp. Likewise the alpha cellulose value shown in Figure 4 indicates the selected light band does not have any detrimental effect.

The second stage viscosity shown in Figure 6 shows a marked increase. This is followed by a decrease in viscosity directly correlated with the,

oxidation of the pulp. The slight drop in the viscosity is inconsequential in view of the tremendous improvement in color.

To determine further whethenor not light has any harmful effect upon the pulp, twelve liters of a 2% pulp were treated for a half hour using 3% chlorinein the first stage. The pulp was then washedand bleached for a half hour using 1.5% chlorine as NaOCl. After the initial half hour period, the pulp was subjected to the Pyrex glass 'screened light (above 300l millimicron that the long treatment of the irradiated pulp did not harm the pulp.

Another sample of the pulp bleached in the rst stage for thirty minutes was washed and then treated for ten minutes at a 3% consistency with 0.5% NaOH solution and then washed again. The second stage was then carried out by treating' with 1.5% chlorine as, NaOCl at a 2% consistency. The pulp was treated for thirty minutes without irradiation and then with radiation over a period of four hours. The resulting bleached pulp was of a very high order of brightness. This maximum practical brightness was reached after only two hours and was of the same brightness as the eight hour sheet ofthe previous two stage bleach.

The invention is applicable to the materials generally. It can be used to advantage in any case wherein an oxidizing bleach is employed. Cellulosic materials as the aforementioned pulps are most advantageously treated. Some pieces of unbleached muslln were treated in a single stage CaOClz bleach using 6% available chlorine. One sample was radiated directly with ultra violet light from the quartz lamp, the secondwas radiated with light from the same u source but filtered through Pyrex glass and the third sample was treated without light as a control. The bleach was somewhat slower and the chlorine consumption in the unradiated sample was more constant than in pulp bleaching but the v general eiect of the light is identical with that on the wood pulp. The speeds-up the bleach and results in a higher color while the direct radiated bleach is ineilicient from a chlorine consumption standpoint. The brightness and chlorine consumption are shown below:

v Brigh t- Percent Cl;

sample ness consumed No'light 84. 6 60 Direct ultra violet 8l. 5 98 Filtered ultra violet--- 85. 5 05 The utility of 'other bleach materials, for example, a peroxide, has been established. In one instance, a sulphitel pulp was treated inthe first stage chlorination in a manner similar tothat hereinbefore set forth, using 5% chlorine as the chlorinating material and following this with an alkaline wash. The second 'stage samples were treated with 1.0% H2O2 (on the weight of pulp) after being made alkaline with calcium hydroxide. The hydrogen peroxide, in the concentration `employed,.was equivalent in oxidizing power` to 2% available chlorine. Samples were radiated immediately upon addition of the hydrogen peroxide, one sample being radiated with a Pyrex filtered light and the other was kept in the dark in the control. rllheperoxide bleach was extremely slow, so' the bleach was prolonged 1 for four hours until 50% of the oxidizing -power had been consumed. The samples were treated the same Y length of time, but the radiated samples showed a brightness of 89.3 as against 86.5 for theA unradiated samples. The details of the apparatus and the treatment employed arel given hereinafter in connection with the investigation on sulte pulp.

bleaching of filtered light greatly .which is more ieactive than radation of the cellulose in the presence of effective oxidizing agents, `and that this presents the reason why Escourrous investigation failed, is amply established by the investigation conducted by us upon suliite pulps.

Sulflte pulp was treated in each case with a thirty minute first stage chlorine bleach at 4% consistency using 5% C12 on the weight of stock. The bleached pulp was then washed and the soluble chlorinated lignin extracted with a 0.2% NaOH wash. The second stage bleach was run at 2.5% consistency using 1.5% C12 as CaOClz.

The first thirty minutes of the bleach was performed without light for all tests. One sample was then treated in a crystallizing dish 4" below the direct radiation of aG. E. quartz vmercury vapor lamp, theseco'nd sample was treated simllarly but the light was screened through a 5 mm. sheet of Pyrex glass and the third sample was left as acontrol using nov light. Figure 7 shows the chlorine consumption for the three samples and the brightness and copper numbers are given below.

Bright- Copper Percent Cl; Sample tml'tmmt ness number consumed No light 86.5 2.08 18.5 Direct ultra violet. 89.0 2.0 53 Pyrex filtered ultra violer 90. 5 l. 8 43 A second test identical with the previous one was run using 3% C12 in the second stage to induce overbleaching to a more marked degree. The chlorine consumption curves are shown in Figure 8 and the brightness, copper number, etc., areshown below.

v llright- Copper Alpha- Percent C12 .Sample t'ratment ness number cellulose cnn-uuml o liebt sas 1. 23 x9. 2 11 Direct ultra violet.. 90. 5 2.0i 85.5 72 Pyrex lterell ultra violet 9i. S 88. 5 12 Itv can be seen Ifrom the comparison of the chlorine consumed in each case with the color obtained that the efliciency o`f the'direct radiated pulp bleach is lower than that' of the ltered ultra violet bleach due to the fact that the chlorine in the former bleach went partially to forming oxycellulose and was very likelydecomposed directly by the short ultra ciency here used refers to the ratio of brightness increase to chlorine consumed.

Light absorption' by cellulose starts somewhat below 360 millimicrons. On the other hand, the bleachable lignin or discoloring matter, the encrusting matter in pulp, starts absorbing light in the region of 420 millimicrons, and extends at least on to 300 millimicrons and perhaps farther. Apparently the longer or near ultra violet light of less energy is suicient to activate the lignin,

the cellulose, but the olecule requires the the suggested 365 millimicrons for lignin containlng materials of the character heretofore dealt with, then effective and improved-.bleaching of the pulp is readily obtained Without degrading the cellulose due to the radiation of thel pulp.

Upon other materials the effective light band may be found to have other limits but the determination of these is a simple matter of determining the bands selectively absorbed by the ma terial to be oxidized and that to be unaffected. The irradiations are then restricted to that absorbed by the material to be oxidized so that it valone is activated. This is illustrated in'Figure 9 wherein the absorption characteristics of vthe coloring matter and of a bleached sulte pulp are shown. The lcoloring matter absorption is indicated by line A and that of the bleached pulp by line B. To activate the coloring matter selectively while avoiding thev degradation of the pulps one should restrict the irradiation so that little, if any, effective radiations below line C are included. Practically, the only effective radiations for the coloring matter which are not harmful to the cellulose are those included in the shaded area of Figure 9.

With other wood pulps and with other materials the relative positions of lines A and B may shift, and it may be necessary to use light having other effective wave lengths. The determination.

and selection is a simple matter of determining the absorption of the coloring matter and the absorption of the other matter present which is not to be affected. With these -measurements available one eliminates from the irradiations passed to the material that light harmful to the other material. This is a simple matter of light absorption measurement readily made by one skilled in the art.

The light source utilized in some of the present work was a mercury vapor General Electric lamp designated as H-L This lamp has an inherent emission ycapacity for the 365 m. m. band, furnishing this radiation at comparatively high intensity. The only shorter band emitted is the 334 band. 'I'he intensity of this emission is low and the band is readily elimil ated by a suitable lter.

Because the present invention enables bright pulps to be secured, activating the oxidizable coloring material, low temperature operation is made feasible and we have successfully bleached pulps at 20"25V C. and below. This means an increase in steam economy with even increased brightness. At high temperatures` the present invention enables the time of treatment -to be shortened, thus avoiding pulp degradation due to heat.

Because of the desirability of uniform pulp radiation low pulp density is a factor for consideraticn. We have successfully worked at high and low densities but we prefer about a 5% density.

Reference has heretofore been made to measurement of the light absorption characteristics of the bleached pulp, as distinguished from cellulose. This has been done because after all the pulp is mainly cellulose and the two, in this sense, are synonomous. Another consideration is that in fact one does not wish to degrade the pulp and, therefore, if other components are present, besides the cellulose, these are not to be activated.

The process of the present invention is applicable. to oxidizing operations generally as performed on cellulose materials. It is particularly useful in producing high alpha cellulose pulps.

We claim:

l. The step of improving a cellulosic material undergoing an oxidizing bleach which consists in irradiating the material with only those light waves longer than 300 millimicrons and below 420 millimicrons.

2. The step of improving a cellulosic material undergoing an oxidizing bleach with a material selected from the group. consisting of chlorine, hypochlorous acid and a hypochlorite, which consists in irradiating the material with only,

those light waves longer than 300 millimicrons and below 420 millimicrons.

3. Irradiating a cellulose material, undergoing a treatment with a material selected from the group consisting of chlorine, hypochlorous acid of a material selected from the group consisting of chlorine, hypochlorous acid and a hypochlorite, to the action of effective light all of a wavelength substantially longer than 300 millimicrons.

5. A process of improving the quality of a cellulose pulp which includes subjecting the pulp, 'in aqueous suspension, to the action of effective light all of a wavelength substantially longer than 300 millimicrons while said pulp is undergoing an oxidizing phase of a bleaching operation.

6. The step of improving a cellulosic material undergoing an oxidizing bleach which consists in irradiating the material with light waves all substantially longer than 300 millimicrons.

'7. The step of improving a cellulosic material undergoing an oxidizing bleach with a material selected from the group consisting of chlorine, hypochlorous acid and a hypochlorite, which consists in irradiating the material with light waves all substantially longer than 300 millimicrons.

8. In a process of single stage bleaching of an aqueous suspension of a cellulose pulp, the steps of subjecting saidk pulp to the action of a hypochlorite for a portion of the normal operating time in said stage and then irradiating said pulp with light waves all substantially longer than 300 millimicrons.

9. In a multi-stage bleaching operation, the steps of subjecting an aqueous suspension of a pulp to chlorination, and subjecting 'said pulp to the further action of a material selected from the group consisting of chlorine, hypochlorous acid and a hypochlorite to bleach said pulp while irradiating said pulp with light rays all substantially longer than 300 millimicrons.

10. Bleaching a wood pulp withv an oxidizing bleach agent while irradiating said pulp with light of 365 millimicrons as the only substantially effective irradiating light.

1l. The step in improving the quality of a cellulosic material which consists in irradiating said material with only `those light waves longer than 300 millimicrons and shorter than 420 millimicrons while subjecting said material to an oxidizing bleach with a per compound.

12. The step in improving the quality of a cellulosic material which consists in irradiating said material with only those light waves longerthan 300 millimicrons and below 420 millimicrons while subjecting said material to an oxidizing bleach with a material selected from the group consisting of a peroxide, a perborate, a persulfate, a permanganate and hydrogen peroxide.

WILHELM HIRSCHKIND. DAVID J. PYE. EARL G. THOMPSON.

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