US1848780A - of stockholm - Google Patents

Description

Patented Mar. 8, 1932.

UNITED STATES PATENT OFFICE GUSTAF EAGLUND, OF STOCKHOLM, SWEDEN, ASSIGNGR '1"O PATENTAKT'IEBOLAGEI." GBfiNDAL-RAMEN, OF STOCKHOLM, SWEDEN S'U'LPHITE CELLULOSE DIGESTION No Drawing. Application filed March 31, 1931, Serial No. 526,762, and in Germany April 15, .1980.

In the usual sulphite cellulose digestion where a solution containing bi-sulphite of lime or alkali and a surplus of sulphur diox ide over and above that required to combine with normal sulphite to form bi-sulphite is used as cooking liquor, which surplus the following is called free sulphur dloxide, and where'the digestion is made under pressure at a temperature of 120? C. or above, it has appeared that the free sulphur dioxide content of the liquor rapidly diminishes even at the beginning of the digestion and before the chips that are to be digested have been the chips at softened or their lignin substances dissolved.

This isdue to the fact that the pores of the chips "(gas and air cavities) get filled with sulphur dioxide, because the free sulphur dioxide escapes from the digesting liquor even at temperatures below the boiling. point of the liquor and consequently enters into the chips before these have been penef trated'by the liquor. Lignin and other noncellulose components that are to be dissolved from the chips, have a strong inclination to take up sulphur dioxide at an early stage of the digestion and forsaid reason there is a strong concentration of sulphur dioxide in dioxide content of the liquor at the beginning of the digestion and before the liquor has completely penetrated the chips. p

This rapid entry of sulphur dioxide into the beginning of the digestion has an unfavorable influence on the further progress of the digestion because the sulphur dioxide collected in the pores of the chips is a hindrance to thepenetration of the .liquor into the chips and also because the concentration of sulphur dioxide in the chips eifects a too ra id reaction with the. lignin content of the chips whereby lignin sulphonic acids diflicult to dissolve and of an unstable character are formed.

The bi-sulphites of the liquor should react with the lignin-sulphonic acids formed through the sulphur dioxide reaction so as to form lignin-sulphonic salts whichsalts are more easily dissolved and more stable than the sulphonic acids primarily formed and it results from this that if the liquor cannot diminishing of the sulphur penetrate into the chips freely or if the sulphur dioxide reaction in the chips takes place too rapidly before the penetration of the liquor the consequences as regards the digesportions of the chips, dark coloring of the cellulose and an incomplete digestion.

To prevent these lnconveniences, in the usual sulpliitedigestion process, care is taken when starting the digestion to have the temperature rise slowly which causes a slackening up of the reaction speed of sulphur dioxide, providing at the same time an opportun-- ity' for the liquor to enter with its contents of bi-sulphite into the chips.

If the digestion is carried out with alkalibi-sulphite, therecovery of the alkali is facilitated by keeping the waste liquors at a high degree of concentration and for that purpose varying quantities of wast-e liquors from previous digestions are added to that c'oooking liquor. WVhen using such a liquor in the digestion another inconvenience will present itself, namely that the liquor penetrating into, the chips carries with it large quantities of organic materials which are easily influenced by the sulphur dioxide concentrated in the chips in the same way as the organic contents of the chips themselves. It has consequently proven to be a diflicult thing to carry out digestions of sulphite cellulose with cooking liquors containing waste liquors from previous digestions.

The. present invention aims to improve the digestion process by removing the causes of an irregular digestion process, and also to.

render it possible to addwaste liquors to the liquor used for digestion of sulphite cellulose.

In the usual digestion processes where bisulphite and sulphur dioxide are j0intly introduced into the digester in' the same liquor,

' bility factors, it is preferable to use alkali bi-sulphite in these cases. The second solution is prepared by introducin sulphur dioxide gas from a digester or from another source preferably into waste liquors or weak liquors obtained when washing cellulose from earlier digestions, and introducing it in such a quantity that the solution will have a high content of free sulphur dioxide or is saturated with sulphur. dioxide at the temperature of the solution. A

This solution contains the free sulphur dioxide that is required for the reaction and the presence of bi-sulphite in this solution is immaterial.

' The above two solutions form the real digestion liquor but they are not introduced simultaneously.

The process may be suitably carried out in the following way: To the digester which is filled with chips the bi-sulphite solution is added. After the chips have been saturated with the solution the major part of it is tapped oil so that only a smallquantity remains.

After this, the digester is filled up with the solution prepared from waste liquor or washing water containing a high concentration of free sulphur dioxide, and the digestion is started.

As the temperature of the digester rises the sulphur dioxide gas is set free in the usual way, but it is prevented from penetrating too rapidly into the chips, for the same are already saturated with bi-sulphite solution and no abnormal concentration of sulphur dioxide gas is possible which would give rise to a premature influence on the lignin substances by the sulphur dioxide.

The bi-sulphite of the solution with which the chips are saturated before the sulphur dioxide reactions can occur, immediately reacts with the lignin-sulphonic acid formed by the penetrating sulphur dioxide, and the reactions will therefore take a regular and normal course even when no precautions are taken as regards a rapid rise of the temperature when starting the digestion.

As dry chips can take up their own weight of bi-sulphite liquor, the alkali bi-sulphite used for the preliminary soaking of the chips, may be provided with such a high concentration of bi-sulphite that before the addition of S0 solution, the chips contain'the quantity of bi-sulphite required for carrying out the digestion process.

The solution of sulphite added to the digester may be made so concentrated that for instance a quantity of solution corresponding to one fourth only of the free Volume of the digester will contain enough alkali metal sulphites for carrying through the reactions noted. In using such a solution, the quantity introduced into the digester may either correspond approximately 'to one fourth of the free volume of the digester, in which case there will be no subsequent removal of the solution, orif desired the digester may be filled more or less completely with such solution. In the latter case, however, after the soaking with the concentrated sulphite solution has been completed, the excess solution should be tapped off from the digester, at least to the extent that sufficient space .will be provided for the succeeding solution of sulphur dioxide, and to a further extent if desired.

While in the foregoing I have indicated the use of a solution of sulphur dioxide in waste liquor and/or washing water from previous digestions, and in practice it is more expedient to use such a carrier for the sulphur dioxide, the solution may if desired consist simply of an ordinary water solution of the sulphur dioxide without any complement of waste liquor and/or washing water.

I claim as my invention:

1. The sulphite cellulose -digestion process which comprises, first intimately contacting the cellulose-containing material with-a solution of a sulphurous acid salt of the group: alkali metal, alkaline earth, then adding a solution of sulphur dioxide, and digesting the cellulosecontaining material in said solutions.

2. The sulphite cellulose digestion process which comprises, first intimately contacting the cellulose-containing material with a solution of an alkali metal salt of sulphurous acid, then adding a solution of sulphur dioxide, and digesting the cellulose-containing material in said solutions.

3. The sulphite cellulose digestion process which comprises, first intimately contacting the cellulose-containing material with a solution of an alkaline earth salt of sulphurous acid, then adding a solution of sulphur dioxide, and digesting. the cellulose-containing material in said solutions.

4. The sulphite cellulose digestion process which comprises, first intimately contacting the cellulose-containing material with a so lution of an alkali metal salt of sulphurous acid, then adding a solution of sulphur dioxide in waste liquorand/or wash water from a similar digesting operation to obtain a'h1gher concentration of organic matr ter' 1n the waste liquor of the instant operation, and digesting the cellulose-containing material in said solutions.

5'. The sulphite cellulose digestion process which comprises, first soaking the cellulosecontaining material in a solution of a sulphurous acid salt of the group: alkali metal, alkaline earth, until the materiali's suitably saturated with said solution, then adding a solution of sulphur dioxide, and digesting the cellulose-containing material in said solutions. i

6. The sulphite cellulose digestion process which comprises, first intimately contacting the cellulose-containing material with a solution of a sulphurous acid salt of the group: alkali metal, alkaline earth, said solution being provided in excess of that capable of being absorbed by said material, removing a substantial portion of the excess solution after absorption, then adding a solution of sulphur dioxide, and digesting the cellulosecontaining material in said solutions.

7. The sulphite cellulose digestion process which comprises, first intimately contacting the cellulose-containing material in a solution of a sulphurous acid salt of the group: alkali metal, alkaline earth, said solution having such concentration of the sulphurous acid salt that the quantity of solution absorbed by said material will contain suflicient sulphurous acid salt for carrying out digestion, then adding a solution of sulphur dioxide, and digesting the cellulose-containing material in said solutions.

8. The sulphite cellulose digestion process which comprises, first soaking the cellulosecontaining material in a solution of the group: alkali metal, alkaline earth, bi-sul-.

phite, then adding a solution of sulphur dioxide, and digesting the cellulose-containing material in said solutions.

9. The sulphite cellulose digestion process 7 which comprises, first soaking the cellulosecontaining material in a solution of alkali metal bi-sulphite until said material has substantially reached its 'abso tion limit as regards said solution, said i-sulphite being provided in such concentration in said solution that the quantity of bisulphite conv tained in the solution absorbed is sufiicient for carrying out the digestion, then adding a solution of sulphiir dioxide, and digesting the cellulose-containing material in said solutions.

10. The sulphite cellulose digestion process which comprlses, first soaking the cellulosecontaining material with a solution of a sulphurous acid salt of the group: alkali metal,

alkaline earth in a di ester, removing from the digester such portlon of the. unabsorbed solution as .is necessary to accommodate the quantity'of a sulphur dioxide solution to be used for the digestion process, said firstnamed solution containing said salt in such concentration that the portion remainingin said digester provides a sufiicient quantity