IL29714A - Process for the crystallization of inorganic salts - Google Patents

Description

P Process for the crystallisation of inorganic salts Λ 863394 This invention relates to procoos obtaining from their aqueous Tho manu of line is ono of the difficult problems in mercial ealt Up to one only in obtaining a precipitate in processes wherein the salt precipitation is carried out by or In the crystallization by solubility changes with an organic precipitant which up to 10 has more and more there generally obtained only a very crystalline in which the deh drying is rather Contrary to the evaporation ami cooling crystallization it is not t in displacement crystallization to effect the lization in the range and to avoid a spontaneous Even adding the organic precipitant in various to the salt solution to be spontaneous crystallization will prevail in any such as in and a groat number of vory 20 small crystals will be According to tho etate of the prior a directional crystallization is not neither discontinuous addition of the organic precipitant nor with its continuous The production of ed crystals from an organic aqueous solution can only be obtalnod when the alcohol portion is slowly increased by using and by mixing the salt solution and organic precipitants solely by diffusion Both ciples being in laboratory technique cannot be roalized economically on industrial the recovory 30 of aqueous by crystallization out organic ants has to now found a United range of application in field of rate the displacement duction of a cryctalline precipitate leads to siderable cf tho organic since sufficient recovery is not possible unless the crystalline precipitate ie well washed out and with low residual moisture the expenses encountered during the tallization depend to a high degree on the condition of the crystalline and the possibility of a tional displacement crystallization has a determining influence on the economy of tho its competitive pared to other crystallization The purpose of the invention is to avoid the high losses of organic precipitant which not economically It is on object of the invention to make directional displacement crystallization possible in order to produce crystalline easily washable and euscoptiblo to centrifugation on centrifugal another object of the invention t avoid the above especially the high and economically not tolerable losses of organic It has been found that coarse crystals may be obtained by mixing solutions having various contents of salt and organic component instead of mixing salt solution and organic For coarse crystalline precipitate is obtained when mixing a saturated aqueous sodium sulfate solution with a solution saturated with respect to sodium sulfate and containing methanol and water and having a methanol content of from 20 to instead of mixing it with puro Coarse crystalline precipitate can also be obtninod by mixing solutions saturated with to su fato arid having 20 and or and 863394 On the other a sulfate solution methanol always only very fine even with very careful For the production of a sufficient coarse crystalline direct mixing of an aqueous salt solution and of an organic precipitant must be avoided and replaced by a dual mixing of solutions of suitable should be pointed out that the concentrations the mixing should be selected to avoid spontaneous crystallization and should not be increased at any stage of the crystallization process The acceptable difference the concentrations of solutions to be mixed is very easily determined by mixing testo on saturated solutions having variouo contents organic It is then possible to the composition of the solution for which tho eatuiation produced during mixing is just maintained for a tain without spontaneous While tho hitherto known for displacement crystallization are based on the fact that crystallization is initiated by the direct mixing of aqueous solution the crystallization process according the sont invention avoids such direct mixing and replaced it by a gradual mixing of solutions only little differences with respect to their concentration of organic The extent of the suporsaturatlon zone determines the number of mixing stops into the difference of tion between the salt solution and tho precipitant should be At this it must considered that the way of such the agitator determines in a certain way tho extent of tho as it is also known to bo the in directional nd oration 863394 The intermediate solutions obtained in the mixing processes are fed into corresponding mixing stages either as as the solution to be precipitated to cause on tho whole a for the solution leaving tho The superoaturation ed during the mixing process remains within the limits able in order to avoid spontaneous and the crystallization can be directed at During the lization supersaturation ia reduced by the growth of grains already present in the and by the crystals which are in small according to tho well known crystallization principles on cooling or There are produced largo crystals or crystal which are easily separated from the solution taining the organic The crystallization according to tho present invention may be carried out in any The apparatus of tho type developed for the are Simple mixing vessels provided with an agitator may also be The lity of the crystalline precipitate can be improved by ifying and recycling tho fines the suporsaturated zone of the crystallization apparatus similarly as in the known The crystalline precipitate obtained in the various orystallizatlon steps is from the crystallization ratus at the particular point which 3hows the lowest tion with respect to the organic component and which the fresh salt solution is It is theroforo pos ible to the fresh solution in to tho crystalline precipitate which leaven the apparatus and to wash the lattor in order to remove tho This 86339 effect may be combined with In the following examples tho invention io deocribod more and with particular reference to the drawings which Figure 1 ie a representation of an tus used for the crystallization of sodium and Figure 2 is a schematic representation of an tus uaod for the crystallization of amiiionium Example 1 crystallization of sodium sulfate A saturated sodium sulfate solution io continuously introduced into stirrer 1 along with tho underflow of the thickener 2 and the filtrate of centrifugo The tiono of tho materials oro so adjusted that the stirrer J vessel 1 con bains approximately methanol with respect to the The underflow of 2 has a methanol concentration of The concentration differences from 0 to and from to remain below tho 20 oaturation limit for oodium culfate The content of the stirror vessel 1 is passed via pump 4 to a hydrocyclone The cyclone underflow containing chiefly coarse crystal grain is passed to centrifuge The contrifuged salt is washed and the of the trifuge flows into stirror vessel The upper flow in hydrocyclone containing the finer grain io paosed into a second stirrer veoocl 6 there it is continuously mixed with methanol containing overflow from stirrer vessel quantities are adjusted that the methanol 30 in 7 at Tho to and 45 to both whereby 863394 taliization is also avoided in stirrer The overflow from 6 clarified in thickener 2 and passed to the storage tank there it is passed and in adequate proportions via pump 9 into vescel 7 and tification column The distillate leaving at the top is condensed and introduced into vessel There it mixed with tho mothanol containing partial stream to give a The maximum concentration differences are again 310 kg dehydrated sodium sulfate from 1000 kg sodium sulfate solution saturated at 64ft out this quantity crystallize in vessel 674 kg water and 17 kg sodium sulfate the sump of the distillation The yield of the crystallization oess is in the neighborhood of with respec to the initial i sodium sulfate Example 2 Directional crystallization of ammonium sulfate Owing to the smaller metastable the directional crystallization of ammonium sulfate has to be carried out with lower concentration differonoes those of sodium In a classifying 11 a saturated ammonium sulfate is mixed with a suspension consisting of a methanol containing solution and of ammonium sulfate The resulting solution reduces supers by crystal growth of the already existing A olassified devoid of the organic component by withdrawn at tho outlot and centrifuged 16 and The of cryotallizor 11 is passed into 12 and there it is mixed with a solution containing part of the of ammonium in 863394 solution 12 adequate proportion cd into and tho part is into 13 where it mixed w h a The euepended sulfate again in two partial metered into stirrer 12 and In the tho colution vcjocl 15 io to a con taininc in throe partial ie panoed to 13 and 15 and a clarifior 16 to the latjon tho methanol rccovorcd to 15 in form of a 1000 a total of 395 sulfate product io of the tity introduced ia from the with the colution loavinc the of the either for production of the oulfato tion rejected containing disturbing insufficientOCRQuality

Claims (5)

1. A process for the production of inorganic salts by direct crystallization from solutions thereof and organic precipitants therefor, wherein the crystallization is carried out while the solutions and precipitant are mixed in the meta-stable solubility range, which range is maintained by mixing only solutions which do not produce spontaneous crystallization during the mixing step.

2. Process according to Claim 1, wherein the solutions and organic precipitants are mixed with each othe by mixing intermediate solutions containing the salts and the organic precipitant in suitable concentration ranges.

3. · Process according to Claims 1 or 2 wherein a f esh solution is introduced into the mixture at a particular point in which the mixture has the lowest content of organic precipitant,

4. Process according to Claims 1, 2, or 3, wherein the total crystalline precipitate is extracted at a point in which the mixture has the lowest content of organic precipitant.

5. Process according to any one of Claims 1 to 4, wherein the extracted crystalline precipitate Is passed in oounter-current to the fresh solution to remove the adhering organic precipitant and entrained fine grain particles. For the Applicants DR. PARTHERS RCied