US1662951A - Process of bleaching animal and vegetable materials - Google Patents

Description

Patented Mar. 20, 1928.

umrao STATES PATENT OFFICE.

man 0. mac, or snow rune, nnw YORK, mrenon m manur nnmomo ooaromnox, a oonrom'rxon or nmwau P100188 Oil BLELOEING ANNA]; AND VlGl'I-APLI lumen.

Io Drawing.

This invention relates tonew and useful improvements in processes of bleaching animal and vegetab e materials, but 1s designed more speciall for use in a process for bleaching groun wood pulp, and has for its principal objects:

First, to increase the efiiciency and speed with which such bleaching is carried out,.

particularly with reference to ground wood ul p S cond, to effect a reat increase in the degree of activity an effectiveness of the fundamental bleaching agents operative in the present bleaching processes, by a wholly different treatment.

Third, to roduce a bleached ground wood pulp of hig er quality than is 'obtamed by present methods.

Further objects, apparent to those skilled in the art, will appear from the following description.

The process of the present invention is suitable for use in bleaching substances other than ground wood pulp capable of being bleached by sulphurous acid such as, for example, palm leaf, straw, s lk, cane, wool,. etc.

In the following description and clalms, the term animal and-vegetable materials will be understood to include such substances, the bleaching of ground wood pulp being the preferable application of the lnventlon.

The existing methods of bleachlng ground wood pulp are carried out by applylng to the pulp, at densities from about 3 0% to 45% bone dry ulp, a solut1on of sodium or calcium bisulp ite and, at times, concentrated sulphuric acid. The pulp, in laps, is allowed to remain in the air for one or two days or longer, for the bleaching to become completed as far as possible, and the bleach-- ing chemicals are applied to the pulp on the couch roll of the wet press, or similar machine. I

The bleaching is presumably effected by both sulphonation of the colormg matter of the pulp to form soluble, colorless, coloringmatter sulphonates, and also by reduction."

The first reactions are made by the sulphurous acid itself and the second, by the nascent hydrogen evolved from the sulphurous 'acid.

The bleaching of ground wood pulp at present is done both with, and without, the use of sulphuric acid to speed up the bleach in by rapid evolution 'of free sulphurous acid from the bisulphite.

Application ma se arate: a, 1m. mm Io. 54,510.

These methods have serious disadvan including lrregularities in the ap licatlon of the blsulphite solution, due to inherent short-comm in the e uipment used, frequently resu ting in strea ed or incompletely bleached pulp. I

The s ace required for storin the pul whlle b caching moreover, is lar e, an costly, and interferes with other m1 atlons. The bleached pulp retains an, odor of sulphurous acid, due to chemical residues left 1n 1t, These residues causetrouble and expense in manufacturing paper from the pulp, such as decolorizing of aniline dyes, cp'rosion of equipment, acid in the paper, e

The labor necessary for for the storage period during bleaching, an for unpillng it or use, is considerable. The permanence of the color obtained is not sufliciently great for man urposes, and the degree of whiteness o tainable is often msuflicient. Usually, only new ground wood pul as it 1s belng manufactured, can be bleac ed, as the wet -lpresses or equivalent equipment are ordinari y an integral part of the ground wood pulp manufacturing process. Because of this last condition, the existing methods do not permit of being efliciently used with the other methods and equipment of the mill. Lastly, the bleaching is very slow.

A further object of the invention is to avoid the foregoing difficulties and disadvantages as well as to greatly increase the efiiciency, speed and quality of the bleaching. I have discovered that, if ground wood pulp be circulated in water at densities of from 4% to 40% bone dry pulp and at temperatures of from F. to 200 F., with a mixture of. a bisulphite or bisulphites, an acid other'than sulphurous acid, and free 1 operpiling the pul washed with water until e of acid and thfer undesired materials, the foregoing ob wer are attained, and the pulp is bleached free fr om the above disadvantages and in the most facile, economical and satifacto manner. It may be added that under ordlnary conditions the temperature above referred to should not be over 165 F. because of the danger of darkening the pulp. There are conditions where greater temperatures would not darken the pulp, but they would not usually be met with in practice.

' hydrosulphite, as reducing material.

I have further discovered that if nascent hydro en in larger amounts than is evolved from 518 amount of sulphurous acid used, be kept in contact with the (pulp while it is being bleached as describe above, the permanence and whiteness of the bleach is improved and the speed of the bleaching process is considerably increased.'

It should be understood, however, that the practice of my process, without the nas cent hydrogen as described, produces faster bleaching, and a better color and permanence to the bleach than resent methods, due to the fact that both t e sulphonation and re- "duction are greatly accelerated by the conditions of my process.

The details of carrying out my process a dmit of several variations, which will be apparent to those skilled in the art, without departure from the spirit of the invention, 'which resides in circulating the ground wood pulp with sulphurous acid, and then washing the pulp, so as to remove the acids and other undesirable material therefrom.

The following is given as an illustration of the method of the invention as applied to ground wood pulp.

Ground wood pulp and water are mixed in the proportions of about 7% bone dry pulp and about 93% water. To each 2,000 pounds of the bone dry pulp, there are added about 115 pounds of sodium bisulphite, 20 or 25 pounds of concentrated sulphuric acid (66 degrees Baum) and 10 pounds of sodium These chemicals are preferably dissolved in water. and then added to the pulp." p I The mixture is then circulated for one or two hours within a temperature range of from F. to 200 F., but usually'at a temerature of 130-150 degrees Fahrenheit. It 1s then washed withwater until free from acids and other undesired materials, and the pulp is bleached, cleansed and ready for use.

My invention is not limited to any particular bleaching or washing equipment, as any ap aratus of suitable construction and adapte to carrying out the process may be.

used. The invention is not limited moreover to any specific means for obtaining the nascent hydrogen in the material being bleached, nor to any particular temperature, density or thickness, or rate of circulation.

Nor is the invention limited to, any specific bisulphites, or acid (other than sulphurous) or reducing material. I

The amount of acid, other than sulphurous acid, used, can be varied within wide limits depending on speed of bleaching desired, cost limits, etc. It is advisable, however, to use enough sulphuric acid so that an excess thereof remains when bisulphites of metals whosesulphites are insoluble in neutral or alkaline solution, are used.

For example, sulphite pulp cooking acid,

which consists of a mixture of calcium bisulphite, ma esium bisulphite, and free sulhurous aci can be used as a source of both isglphites and some of the free sulphurous aci To furnish the nascent hydrogen any suitable sources'of nascent hydrogen, such as hydrosulphites, zinc, electrolysis, etc., can be used. In this event, the nascent hydrogen is formed in the presence of the nip.

H drosulphites, to be adde to the ulp, can e conveniently formed from bisulpiiites, such as sulphite ulp cooking acid or sodium bisulphite, by re uction, by zinc dust or foil, and also by electrolysis,

The amount of hydrosulphite used should be small as com ared with the amount of hisulphite, in or er to prevent the formation of free hydrosulphurous acid, which decomposes into sulphur dioxide and finely divided sulphur, and the presence of the latter may com licate the washing step.

T e formation of the hydrosulphite may be done either in the bleaching equipment during bleaching or previously, and then added to the mixture.

Temperatures between 80 degrees Fahrenheit and 200 degrees Fahrenheit can be used under different conditions; and densities or thicknesses of from 4% bone dry-material to 40% bone dry material. a

What I claim is:

1. The process ofbleachin ground wood pulp, which consists in circu ating the pulp 1n water having mixed therewith a bisul' than the sulp ,urous acid, and finally washing the mixture with water until free of acid and other undesired materials.

2. The process of bleach ground wood pulp, which consists in circu ating the phit'e, free sul hurous acid, and an acid other a in water having mixed therewith abi phite, free sulphurous acid, an acid other than sulphurous acid, and nascent h drogen in larger amounts than is given 0 the amount of sulphurous acid used, and

ally

washing the mixture with water until free of acid and other undesired materials.

3. The process of bleaching ground wood pulp, which consists in circulating the pulp in water, at, densities of from 4% to 40% and at temperatures between 80 F. and I 200 F., with a bisulphite', free sulphurous acid, an acid other than sulphurous acid, and nascent hydrogen in larger amounts than is 'given ofi by the amount of sulphurous acid used, and then washing the mixture with water until free of acid and other undesired materials.

4. The process of bleachin ground wood pulp, which consists in circu ating the pulp, at densities of form 4% to 40% and at temperatures between 80 F. and. 200 F., in water having mixed therewith a bisulphite, andan acid other than sulphurous Ill acid, and finally washing the mixture with water until free of acid and otherundesircd materials.

5. The process of bleaching ground wood pulp, which consists in circulating the pulp in water having mixed therewith sodium bisulphite, concentrated sulphuric acid, and sodium hydrosulphite, and finally washing the mixture until free from acid and other undesired materials.

6. The process of bleaching ground wood pulp, which consists in circulating the pulp in water and in contact with a bleaching agent at densities of from 4% to 40% and at tem eratures between 80 F. and 200 R, an then washing-the pulp with water until free of acid and other undesired materials.

7. The process of bleaching ground wood pulp, which consists in circulating the pulp in water in contact with a bisulphite, free pulp, which consists in circulating the pulp in water, at densities of from 4% to 40%, in contact with a bisulphite, free sulphurous acid, an acid other than sulphurous acid, and nascent hydrogen.

10. The process of bleaching ground wood pulp, which consists in circulatlng the pulp in water, at densities of from 4% to 40% and at temperatures between 80 F. and 200 F., in contact with a bisulphite, free sulphurous acid, and an acid other than sulphurous acid.

11. The process of bleaching ground wood pulp, which consists in circulating the pulp in water, at densities of from 4% to 40% and at temperatures between 80 F. and 200 F., in contact with a bisulphite, free sulphurous acid, an acid other than sulphurous acid, and nascent hydrogen.

12. The process of bleaching ground wood pulp, which consists in circulating the pulp in water, at densities of from 4% to 40% and at temperatures between 80 F. and 200 F., with a bisulphite, free sulphurous acid, an acid other than sulphurous acid, and finally washing the whole. with water until free from acid and other undesired materials.

In testimony whereof I have afiixed my signature.

ALFRED O. BRAGG.