US727798A - Process of making tanning extracts. - Google Patents

Description

UNITED STATES Patented May 12, 1903.

QATENT OFFICE.

PROCESS OF MAKING TANNING EXTRACTS.

SIECIFIGATION forming part of Letters Patent No. 727,798, dated May 12, 1903;

' Application filed November 5, 1901. Serial No. SL253. (No specimens.)

To all whom it may concern:

Be it known that I, MAX Home, a subject of the Emperor of Austria-Hungary, residing at Briinn, in the Province of Moravia, inthe Empire of Austria-Hungary, have invented certain new and useful Improvements in Processes of Making Tanning Extracts; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention has relation to the production or formation of a tanning agent from the Waste lyes resulting from the manufacture of cellulose by the sulfite process.

In the production of tanning agents from I the waste sulfite lyes referred to by the processes made use of prior to my invention the tanning condensate obtained is of a very dark color, the leather being of agray-black color, which is, commerciallyspeaking, undesirable, while on the other hand the leather is rendered very brittle. This is especially the case when the waste lyes are neutralized before concentration by means of milk of lime for the purpose of eliminating the combined and free sulfurous'acid, as it is well known that solutions of tannin or tannic acid in the presence of alkaline carbohydrates undergo rapid changes and become very dark. I have found that even where strong mineral acids are used for eliminating the sulfurous acid, removing the latter by evaporation or by blowing air through the lye, it is practically impossible to prevent or solimit the changes above referred to as to obtain a tanning agent soluble in water and forming light -colored clear solutions wherewith leather can be tanned and the tanned leather possess the usual light yellow-brown color. I came to the conclusion that if it were possible either to prevent or sufliciently counteract the changes in color which the tanning constituent undergoes in the lye, and thereby prevent its becoming so deeply colored as to render its use for tanning leather practically of little value, a product could be obtained of great con1- mercial value. I have discovered that this result can be attained and the disadvantages known processes and above referred to entirely obviated. This resultl attain by bleaching the lye before concentration, and as hydrosulfurous acid is a well known and powerful bleaching agent I make use of the combined and free sulfurous acid present in the lyes byconvertingitinto hydrosulfurous acid, whereby the lye is sufficiently bleached to obtain a condensate of the desired depth of color and one that is soluble in Water.

That my invention may be fully understood, I will describe the same in detail.

Broadly speaking, the process consists, essentially, in reacting upon the waste sulfite lye with an acid capable of liberating the combined sulfurous acid and the acetic acid in the lye without injnrionsly afiecting the tanning constituents therein and with a sufficiency of zinc to convert the whole or substantially the whole of the sulfurous acid in the lye into hydrosulfurous acid.

In practice I prefer to proceed as follows: The percentage of free and combined sulfurous acid in the lye is determined, a quantity of zinc in the form of dust sufficient to convert both the free and combined sulfurous acid into hydrosulfurous acid is added to the lye while being stirred, and then the acid capable of liberating the combined sulfurous and acetic acid-as, for instance, sulfuric, phosphoric,or oxalic acid-is preferably gradually added to gradually liberate the combined acetic and sulfurous acid, the latter to be gradually reacted upon by the zinc and, together with the free sulfurous acid, converted into hydrosulfurous acid, the lye being agitated until the conversion is completed, the process being carried out at normal temperatures and, if necessary, under the influence of a cooling agent to keep the temperatu re of the lye down-to about 30 centigrade.

To convert sulfurous acid into hydrosulfurous acid, one molecule of Zn for every two molecules of S0 is required, the reaction being a well-known one. Taking, for instance,

a waste cellulose sulfite lye containing, per liter, sulfurous and acetic acid in the 'following proportions: sulfurous acid, free, 1.928

(C H O QH so 1406 a: 2.153 grams sulfuric acid. 1; "00 2 z 4 9 2.013 x 1.644 grams.

3.797 grams sulfuric acid.

Hence to convert the whole of the sulfurous acid (1.928+1.4@O6) 1.693 grams zinc powder will be required according to the conversion equation. An additional quantity of acid can of course be added to the lye if the remainder of the lime, which is chiefly combined with organic acid, is to be precipitated. This can, however, also be effected by using a sufficient quantity of a salt that Will combine and form Withthe lime an insolublecompound bydouble decomposition as, for instance, a sulfate, phosphate or oxalate, and the like-the insoluble lime compound being removed by filtration-as, for instance, in a filter-pressthe lye being then concentrated to the proper degree by evaporation. The concentration may be carried out in a single-efiect evaporator; but in this case the separation of the crystalline sulfate, phosphate, or oxalate of lime takes place, resulting in hammering, while the insoluble lime compound deposits upon the heating-pipes, which is of course undesirable. To avoid this, I effect the concentration in a double-effect evaporator by first evaporating the lye to from 16 to 18 Baum, after which I remove the insoluble calcium compounds by filtration and finally condense the lye in vacuum to from 28 to 30 Baum.

Although phosphoric acid has the same property as sulfuric acid and oxalic acid in that, like the last-named two acids, it will liberate the combined acetic and sulfurous acids in the lye, yet it has not the property of precipitating calcium, so that when phosphoric acid is used the removal of the calcium can be effected by converting it into an insoluble salt, as hereinabove described.

It is of course evident in carrying out my invention that it is immaterial whether the sulfite lye is first reacted upon with an acidreversed and the solution first treated with zincand then with the acid.

Having thus described my invention, what I claim as new therein, and desire to secure by Letters Patent, is-

1. The process, which consists in reacting upon a waste lye, resulting from the manufacture of cellulose by the sulfite process,with zinc to convert the sulfurous acid present into hydrosulfurous acid, and liberating the combined sulfurous acid and the combined acetic acid in the lye by means of an acid indifiercut to the tanning constituents present, for the purpose set forth.

2. The process, which consists in reacting upon a waste lye, resulting from the manufactu re of cellulose by the sulfitc process,with zinc to convertthe sulfurous acid into hydrosulfurous acid, and with an acid indifferent to the tanning constituents and capable of liberating the combined sulfurous acid as Well as the combined acetic acid present, and precipitating the calcium, for the purpose set forth.

3. The process, which consists in reacting upon a Waste lye, resulting from the manufacture of cellulose by the sulfite process,with zinc to convert the sulfurous acid present into hydrosulfurous acid, and treating the lye, during conversion, with sulfuric acid to liberate the combined sulfurous acid, as well as the combined acetic acid, for the purpose set forth.

4. The process, which consists in reacting upon a waste lye, resulting from the manufacture of cellulose by the sulfite process,with zinc to convert thesulfurous acid present into hydrosulfurous acid, treating the lye, during conversion, with an acid indifierent to the tanning constituents and capable of liberating the combined sulfurous acid as well as the combined acetic acid present, and reacting upon the lye with a salt capable of combining and forming with the calcium present an insoluble calcium compound, for the purposes set forth.

In testimony that I claim the foregoing as my invention I have signed my name in presence of two subscribing witnesses. U

' MAX l-IONIG.

Witnesses:

W. DRAHOKOUPIT, WOLF DREW.