US1923292A

US1923292A - Purification of cellulose material

Info

Publication number: US1923292A
Application number: US560521A
Authority: US
Inventors: Harry P Bassett
Original assignee: Individual
Current assignee: Individual
Priority date: 1931-08-31
Filing date: 1931-08-31
Publication date: 1933-08-22
Anticipated expiration: 1950-08-22

Description

Patented Aug. 22, 1933 UNITED STATES PATENT OFFICE No Drawing. Application August 31,1931 Serial No. 560,521

6 Claims.

This invention relates to a process of purifying cellulosic material and more particularly to a pretreatment of cellulosic material containing coloring matter to facilitate a more complete removal of the coloring matter by a subsequent digesting process, such as an alkali boil-out.

As is well known, certain cellulose base materials such as kraft pulp contains a large proportion of coloring matter so that such product is 10 adapted for use as a base material only when the products to be prepared therefrom are satisfactofy if colored, .such as wrapping paper and the like. However, in so far as I am aware, no commercially practical process has been developed for treating highly colored cellulose material so as to render it suitable for making light colored or white products. The processes which have been produced either have been too expensive for commercial utilization or have not been efflcient in removing the color from the material treated. The principal purpose of the present invention is to provide a commercially practical process for removing coloring matter from highly colored cellulose material.

As indicated above, the present process is particularly designed for use in connection with the removal of color from kraft pulp. However, it is suitable for use in, removing coloring matter from any other form of pulp andis also suitable for treating cotton linters containing coloring matter and for removing coloring matter from screenings from the kraft process. tice of the process the material to be treated is intimately contacted with a weak mineral acid solution. The intimate contact of the material to be treated with the weak acid solution may be effected by thorough agitation of the materials together, or, as is preferable, by subjecting the material to the action of a boiling weak mineral acid solution. The strength of the acid solution employed and the time of treatment will vary according to the material worked upon; the

time will also vary according to the temperature of the treating solution. For example, a longer 4-5 period of time will be required when intimate contact is effected by agitation of the materials in the cold than in the case where the material is subjected to a boiling treating solution. After intimately contacting the material with the weak acid solution the acid is removed, the product washed and subjected to a conventional digesting treatment, such as an alkali boil-out. The digesting treatment removes the major amount of coloring matter present and a subsequent wash ing of the material with hot water whitens it In the 'prac- I appreciably. To whiten the material completely it is advisable to follow the hot water wash with a light chlorine bleach.

In the preferred practice of the process the cellulosic material. to be treated is subjected to Go the action of a weak nitric acid solution as hereinafter described in detail; However, I may employ weak solutions of other mineral acids in place of the nitric acid solution. For example,

a hydrochloric acid solution of from .035 to 2.0 5 per cent. strength maybe employed. Where kraft pulp is to be treated the hydrochloric acid solution is preferably of .075 per cent. strength. A sulphuric acid solution of from .015 to 2.0 per cent. strength may also be optionally employed, a 79 solution of about .03 per cent. strength being preferred when kraft pulp is being treated. However, the use of a sulphuric acid solution is not recommended because of its marked tendency to lower viscosity. Phosphoric acid solutions of from .025 to 5 per cent. are also suitable, a solution of about .075 per cent. strength being suggested for usewhen kraft pulp is to be treated. Moreover, sulphurous acid solutions of from .015 to 2 per cent. strength may be used in the praca0 tice of the invention, a solution of .05 per cent. strength being preferred for treating kraft pulp. In addition to the foregoing other weak mineral acid solutions which are suitable will suggest themselves to those skilled in the art.

While it seems most expedient to prepare the weak solutions of mineral acids by adding the acids directly to water'and. the material under treatment, I have found that substantially the same, and in some cases slightly better, results can be obtained by adding a mineral salt and a weak organic acid and forming the mineral acid in situ. For example, a final product of superior fiber strength is obtained by treating the cellulosic material with a weak nitric acid solution formed by reacting sodium nitrate and acetic acid-in the treating bath. Among other mineral salts which may be usd'in place of sodium nitrate in conjunction with acetic acid are sodium chloride, sodium phosphate, potassium sulphate, sodium bisulphite, or the like. These are typical of the salts which may be used. While sodium and potassium salts are preferred because of the solubility of their compounds, sim ilar salts of other metals may be employed in cases where the precipitation of a mineral on the cellulosic material is not harmful. Besides acetic acid other weak organic'acids may be employed. Among such acids which are suitable no be found to produce best-results.

I effect on theflber. that after the acid solution has once been colare oxalic, tartaric, and citric acids and fatty acids such as oleic, stearic and palmitic acids.

As stated above, I prefer to employ in the practice of my process a weak nitric acid solution and, according to the material under treatment, I have found it advisable to employ a nitric acid solution of from .05 to 5 per cent. strength. In treating linters containing coloring matter a .05 to 1 per cent. nitric acid solution is satisfactory. For treating kraft pulp from .05 to 2 per cent. nitric acid solution will Where kraft screenings are to be treated a stronger solution, say from 4 to 5 per cent. nitric acid solution, is

recommended. The time of treatment also varies, as stated above, according to the material under treatment. For example, when a cold solution is used, linters are agitated in the acid solution for about one hour only. For kraft pulp, an agitation of 3 hours is recommended. If hot solutions are used, it is sufficient to bring the mass to the boiling point only with linters, while for kraft pulp, hour at boiling is recommended. Kraft screenings should be boiled for an hour and, in some instances, boiling for a longer period will be found desirable.

The first use of a fresh acid solution tends to make the fibers tender but I have found that after the acid solution has once been used in the process it does not thereafter have any adverse Moreover, it has been noted ored by use in the process the color does not deepen when the acid solution is reused. Moreover, there does not appear to be any substantial loss of acid, except for mechanical losses, in the practice of the process. Thus, these last two features indicate that the acid does not react chemically with the coloring matter so as to render it more easily removable by a subsequentdigest. However, regardless of what may be the real action of the acid on the coloring matter present it has been definitely ascertained that the coloring matter is more readily and washed material is then subjected to a conventional hot alkali trfltment, either an open boiling or a digestitng opreation being suitable. Generally, the treatment consists of boiling the material in an 8 to 10 per cent. caustic soda solution for about one hour in a digester. Following the alkali treatment the material is preferably subjected to the washing action-of an excess of hot water and it may be further subjected to the action ofa light bleach as set forth above.

The term rendering active as applied to the weak mineral acid solution in the appended claims is intended to include both the substantial agitation of the acid solution in'contact with the cellulosic material as described above in connection with one embodiment of the invention and also heating the acid solution to boiling condition as disclosed in connection with the preferred embodiment of the invention.

7 By the term weak solution of a mineral acid". as employed in the appended claims is meant 9.

mineral acid solution having a strength not materially in excess of 5 per cent., the particuar strength of a given acid solution depending upon the particular mineral acid present. For example, a nitric acid solution of from .05 to 5.0 per cent. strength, a hydrochloric acid solution of from .035 to 2.0 per cent. strength, a sulphuric acid solution of from .015 to 2 .0 per cent. strength, a phosphoric acid solution of from .025 to 5.0 per cent. strength and a sulphurous acid solution of from .015 to 2 per cent. strength are considered weak mineral acid solutions in connection with the practice of the present invention and are intended to be included within the meaning of the term in question.

While I have described in detail the preferred embodiment of my invention it is to be understood that the details of procedure may be variously modified without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

1. The process of treating cellulosic material containing coloring matter to be removed therefrom which comprises contacting such material with a solution of nitric acid of from .05 to 5 per cent. strength, rendering such solution active with respect to said cellulosic material, removing the acid, washing the thus treated material, thereafter subjecting the thus pretreated material to a hot alkali purifying treatment, washing the resulting product with hot water, and subjecting the resulting product to the action of a bleaching agent.

2. The process of removing coloring matter from kraft pulp which comprises contacting such kraft pulp for a period of up to approximately 3 hours with a nitric acid solution of about .05

to 2 per cent. strength rendered active with respect thereto, removing the acid, washing the thus treated material, subjecting the washed product to a purifying hot alkali treatment, washing the resulting product with hot water, and subjecting the thus washed product to a light bleach.

3. The process of removing coloring matter from kraft pulp which comprises contacting such pulp for a period of up to approximately 3 hours with a nitric acid solution of from .05 to 2 per cent. strength rendered active with respect thereto, pressing out the excess of acid, washing the thus treated material, digesting the washed material for approximately 1 hour in a caustic soda solution of from approximately 8 to 10 per cent. based on dry weight of pulp, washing the digested material with hot water, and subjecting the thuswashed product to a light bleach of approximately 8 per cent. chlorine strength, based on dry weight of pulp.

4. The process of treating cellulosic material containing coloringmatter to be removed therefrom which comprises subjecting such material to a pretreatment including contacting such ma terial with a solution of nitric-acid of frem .05 to 5 per cent. strength, rendering such solution active with respect to said cellulosic material, removing the acid solution, and washing the thus treated material, and thereafter subjecting the pretreated material to the action of a bleaching agent.

5. The process. of treating cellulosic n; containing coloring matter to be removed from which comprises subjecting such material to a pretreatment including contacting the material with a solution of nitric acid of from .05

treating steps including subjecting such kratt pulp to the action of a solution of nitric acid of approximately .05 to 2 per cent. strength rendered active with respect thereto, removing the acid solution, and washing the resulting material, and thereafter subjecting the pretreated material to the action of a bleaching agent.

HARRY P. BASSETI.