DE737505C - Process for the production of a highly concentrated solution of a stable, highly viscous, partially saponified cellulose acetate - Google Patents

Description

A method of a stable, hochviscosen for producing a highly concentrated solution, partially saponified cellulose acetate subject of the main patent 720 109o a process for preparing a highly concentrated solution of a stable, hochviscosen partially verseiften- cellulose acetate using acetic anhydride for acetylation in the presence of sulfuric acid as catalyst, which essentially consists in the fact that the acetylation of the cellulose at 15 to. 20 ° started in the presence of the smallest possible amounts of concentrated sulfuric acid and acetic acid and part of the acetic anhydride, continued after the addition of acid sulfates and further acetic anhydride at about 20 to 30 ° and after the addition of acids or compounds that split off the sulfuric acid of the acid sulfate in Set freedom, is terminated at elevated temperature and that the then carried out between 40 and 5o ° in the usual way with water partial saponification of the cellulose acetate is carried out in the presence of any salts to be added of those metals whose sulfates are insoluble in concentrated acetic acid, in water or dilute Acetic acid are soluble. In the further development of the process, considerable simplifications were found, which primarily have a positive effect from an economic point of view. One change is that. that in the second acetylation stage the acidic sulfate to be added is allowed to develop in the reaction mixture by adding sulfuric acid and the required amount of alkali metal chloride. The acetylation is then terminated in the third stage, as in the main patent, after the addition of an acid or an acid-releasing compound. According to the invention, the amount of acid should preferably be 1 to 20/6, based on the amount of cellulose originally used.

A further simplification of the procedure can be achieved by that the second and third stages of the acetylation are combined in such a way that that the acid or acid-splitting compound otherwise added in the third stage is added at the beginning or in the course of the second stage. The partial saponification of the cellulose acetate as well as the stabilization is then, no matter what modification was also made, in each case as in the main patent, namely by adding water as well as: salts, which react with sulfuric acid to form sulphates convert which is insoluble in concentrated acetic acid, in water or diluted Acetic acid are soluble. The stabilizing salts can be used, as with the Process of the main patent, even before saponification, e.g. B. during the second or third stage of acetylation, add.

Example i For 100 parts of cellulose z. B. in the form of pulp, expediently at room temperature, i 50 parts of concentrated acetic acid, 0.5 parts of concentrated sulfuric acid and ioo parts of acetic anhydride are added and the esterification is initiated. Acetylation is then carried out in the second stage at 25 ° to 30 ° with the addition of a mixture of 160 parts of acetic anhydride, 70 parts of concentrated acetic acid, 5.9 parts of concentrated sulfuric acid and 3.5 parts of ammonium chloride.

As soon as et <va q.o to 6o% acetic acid is introduced into the cellulose molecule the acetylation ends in the third stage at et <va q.o to 5o ° performed after the addition of 1.6 parts of acetyl chloride and io parts of glacial acetic acid, whereby the sulfuric acid bound to the bisulfate formed is set free. The partial saponification and stabilization of the acetyl cellulose is at a Temperature from about .1o to 5o "with the usual amount of water in the form of hydrous Acetic acid causes, but contains a salt, in the present case t o parts Magnesium chloride, which forms a sulfate with sulfuric acid, that in acetic acid difficult and easily soluble in water and dilute acetic acid. The amount of the salt is approximately dimensioned so that the reaction mixture after the esterification contains about 5o to 8o% of the mineral acid last present as free acid. the obtained solution can, for. B. be spun in a known manner without further ado; However, you can also precipitate the acetyl cellulose from the solution and then for plastic Masses or, dissolved in suitable solvents, for the production of films, synthetic threads and the like.

Example 2 The acetylation of 100 parts of cellulose, e.g. B. in shape of cotton is mixed with a mixture of i 50 parts of concentrated acetic acid, 0.5 parts of concentrated sulfuric acid and 100 parts of acetic anhydride at about 20 ° initiated; for the second stage, a mixture is as follows at about 20 to 30 ° Composition added: i 60 parts acetic anhydride, 70 parts concentrated Acetic acid, 6.5 parts concentrated sulfuric acid, 4.2 parts sodium chloride.

A mixture of is then used for the last stage of the aoetylation i part of acetyl chloride and io parts of concentrated acetic acid were added.

The partial saponification and stabilization take place accordingly the procedure given in Example i, but with a further saponification The addition of acetic acid can be omitted.

Example 3 The esterification of 100 parts of cellulose is carried out at room temperature by adding a mixture of i 50 parts of concentrated acetic acid, 0.5 Parts of concentrated sulfuric acid and 100 parts of acetic anhydride were initiated. The second and third stages are contracted into one in such a way that the at Hydrogen chloride determined itself for the third stage as early as the second stage is initiated. However, the hydrogen chloride can also be added separately in the third Add step. In addition, the stabilizing salt, here magnesium carbonate, not, in the previous examples, at the beginning of the saponification, but added before the same.

For the second and third stages of the acetylation, the following is accordingly Mixture added and the Acetyli; tion at .1o to 50 ° to the end led: 170 parts of acetic anhydride, 70 parts of concentrated acetic acid, 6.5 parts concentrated sulfuric acid, 1.6 parts sodium chloride, 1.86 parts magnesium carbonate, 2.1 parts of hydrogen chloride.

This is done in the usual way at a temperature of about 4o to 5o ° with the necessary amount of water in the form of hydrous acetic acid which partially Causes saponification of the gelulose acetate. The magnesium salt used for stabilization was added before the saponification. It formed with the existing sulfuric acid Magnesium sulfate, which is difficult in acetic acid, but in water and dilute acetic acid is easily soluble. The solution obtained after completion of the saponification can on can be processed further in the manner given in example i. Example 4 Acetylation 100 parts of linters are started in the first stage, as indicated in Example 3 and then in the second stage at about ¢ 5 ° with the addition of the following mixture continued: 180 parts acetic anhydride, 70 parts concentrated acetic acid, 7 Parts concentrated sulfuric acid, 1 part lithium chloride, 14 parts zinc chloride.

Already at the second stage or only after it has expired introduced as the third stage 0.5 parts of hydrogen chloride. Because that's for stabilization zinc chloride was added in the second stage, the saponification, as indicated in Example 3, only with no further addition of salt or acid the necessary water: to be carried out in quantity.

Claims (1)

PATENT CLAIMS: i. Further development of the process according to patent 720 iog for the production of a highly concentrated solution of a stable, highly viscous, partially saponified cellulose acetate, characterized in that the acid sulfate to be added is formed in the reaction mixture in the second acetylation stage by adding sulfuric acid and the required amount of alkali metal chloride. a. Process according to Claim i, characterized in that the acid or acid-splitting compound which is otherwise to be added in the third stage is already added in the second stage.