US1945913A - Process for producing stable bleaching powder - Google Patents

Description

rr to PRGCESS FQR PRODUCING STLE BLEACG POWDER Adolf Remel, Bitterfeld, Germany, assignor to ll. G. Farbenindustric Aktiengesellschaft, Frankfort-on-the-Main, Germany No Drawing. Application July 8, 1930, Serial No. 466,611, and in Germany July 16, 1929 2 Claims. (Cl. 23-250) This invention relates to a process for the pmas it should be calculated on the basis of the duction of bleaching powder with greatly imextraction of water alone. In this operation 9. proved stability during storage. further rather considerable amount of the avail- In the manufacture of bleaching powder, it is able chlorine is converted into chloride or chlo- 5 known to be important that a product should be rate. In addition, these drying processes are fill obtained in which the content of available chloattended with the drawback that suitable measrine is as high as possible at the outset, and does ures must be taken for the separation and recovnot decrease during storage in warm air, for excry of the highly diluted escaping chlorine, and ample in the tropics. finally that, in the initial stage, the drying can Owing to its relatively high moisture content, only be performed at a moderate rate. 65 the bleaching powderproduced in the ordinary It has also been proposed that the small way is well known to be inferior in respect to its amounts of water still left in'the bleaching powbehavior during storage, and frequent attempts der after a drying process of this kind should have therefore been made to discover ways and be combined by means of quick lime and thus means of dehydrating the bleaching powder, or rendered innocuous. Quite apart, however, from 70 of rendering the moisture content harmless in the losses of available chlorine owing to the some other way. previous partial drying, and the further reduc- Experiments conducted by applicant with retion in the available chlorine content by introgard to the efiect of diminishing proportions of duction of quick lime, even this process does not contained moisture upon the storing qualities make the bleaching powder sufficiently stable ?5 of bleaching powder have revealed the fact, that during storage. with a moisture content of about 1 percent and It has now been observed that the losses of less, bleaching powder is particularly resistant to available chlorine, attending the drying of bleachthe action of elevated temperatures. ins pow r y the known Processes are largely From the works of various writers on the fordependent on the moisture content of the inimation of bleaching powder, it isalso known that, tial product, and it has been ascertained that in the course of reaction of chlorine on calcium notable losses of available chlorine occur whenhydroxide, the molecule of water combined with but only when-the moisture content of the the CaO is displaced by chlorine (and also by any bleaching p w to be tr a d is hi h r than 30 carbon dioxide present), and that both this wacorresponds to the theoretical" amount. In the terthe theoretical amount, which can be calcase of a bleaching Powder containing 36-37 P culated from the chlorine content-and also the cent of available chlorine, s ount is about free water introduced, as moisture, in the cal- 9.5 percent of water, when dry calcium hydroxide cium hydroxide can be combined in the manner has been used. On the other hand, it has been of water of crystallization with the resulting found that a bleaching powder with a lower conchlorine compounds of calcium. Since this loosetent of moisture can be freed from the latter, ly combined water has a certain vapour tension, without any appreciable loss of chlorine, by the it can be extracted from the chlorine compounds known processes either in a current of air free by the action of a vacuum or of a current of infrom carbon dioxide, or in vacuo, at progressively 40 ert gas. rising temperatures, and that this dehydration A number of so-called drying processes for can be carried to below the 1 percent limit of bleaching powder have been based on this fact, moisture-ascertained as decisive for the stabilwith the object of extracting a large portion of ity of the b ea powder-Without any ethe moisture content (about 10-14 percent) from worthy losses of available chlorine. In such case,

45 bleaching powder manufactured in the ordinary a product is obtained which, with a maximum manner, by drying it, at increasing temperatures, content of available chlorine, is storage-proof in a current of air free from carbon dioxide and to a greater degree than hitherto attainable. also, if necessary, in vacuo. It is known, how- The known processes for the production of ever, that in drying such bleaching powder by bleaching powder ordinarily furnish a product,

50 means of this process, considerable losses of the moisture content of which exceeds, to a not 1 available chlorine are always bound to oc ur at inconsiderable extent, the 9.5 percent ascertained the start, this liberated chlorine escaping with as the limit for drying without appreciable dethe water to be eliminated. The result of these composition; so that the requisite initial'drying losses is that the increase in the content of availto that limit is always attended with losses of 55 able chlorine in the final product is not as large available chlorine.

It has now been ascertained that also these losses can be prevented by adding to the bleaching powder produced by the ordinary processes, prior to drying, an amount of unslaked lime which is sufilcient to combine with at least the free water, that is such water as is present in excess of the theoretical moisture content which is the moisture displaced by chlorine in the manufacture of bleaching powder when moisture-free slaked lime is treated with chlorine. As a practical rule, it has been found that the amount of unslaked lime to be added should be 0.5-1 part for each part of water present in the bleaching powder. The addition of unslaked lime may, however, be carried so far that the finished product contains not less than 35 percent of available chlorine after drying. The bleaching powder treated with quick lime in this manner is left to stand for a few dayswith moderate heating, if desired-during which period the slaking of the quick lime takes place, and is then subjected to any of the known drying processes.

Example A bleaching powder containing 36.5 percent of available chlorine and 11.5 percent of moisture is intimately mixed with 6 percent of unslaked lime and left to stand for about three or four days. Owing to the addition of the unslaked lime, the percentage content in available chlorine of the product is reduced to 34.4 percent. The product is subsequently dried in a vacuum of about 30 mms. while heating slowly from normal temperatures up to about 100 C. until a bleaching powder containing 36.5 percent of available chlorine and 1 percent of moisture is obtained.

In order to test the storing qualities of the products obtained by the present process they were successively subjected to the following conditions ("quick storage test).

Stage 1 0., maintained during open air during 16 Stage 2 ((2) Slowly heated from to C. within two hours (b) Temperature of 70 six hours (0) Slowly cooled in hours.

0. maintained during the open air during 16 Stage 3 C. maintained'during Stage 4 (a) Exposed to a temperature of 80 hours.

After this treatment the products showed a decrease of their percentage of available chlorine not exceeding about 3 units (that is from 39 percent of available chlorine to 36 percent etc.)

I claim:

1. A process of converting undried bleaching powder into a condition in which it is stable during storage which comprises the steps of mixing the undried bleaching powder containing at least about 36 percent of available chlorine with an amount of unslaked lime which is at least sufficient to combine with the free water content of said bleaching powder,.exposing the mixture to temperature conditions leading to the slaking of said added unslaked lime, and finally drying the product.

2. A process of converting undried bleaching powder into a condition in which it is stable during storage which comprises the steps of first mixing the undried bleaching powder containing at least about'36 percent of available chlorine with between about 0.5 to 1 part of unslaked lime for each part of water present in said bleaching powder, then leaving the product to stand for a prolonged time until the lime added is converted into the slaked co dition and finally drying the product.

- ADOLF REMELE.

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