Aug. 19, 2010  9  US 2010/0210871 Al  [0108]  The advantage of these two apparatuses (FIGS.  2  and  3)  over the perforator is that it is firstly possible here to  use significantly higher entraining gas flows and there is  secondly continuous removal of the organic acid released. In  this way, the extractant can always be reused unburdened and  thus dissolve more organic acid released. Redissolutionofthe  organic acid by the water in the ammonium salt solution is  thus prevented. The extraction can thus be conducted with  high extraction rates.  [0109]  One example cited here is a reactive extraction with  2-hydroxy-4-methylthiobutyric acid and isobutyl methyl  ketone. In the case of use of a 10% aqueous 2-hydroxy-4- methylthiobutyric acid ammonium salt solution at 80°  C. with  isobutyl methyl ketone as the extractant and with 30 1 of  nitrogen per hour as the entraining gas, after 90 hours of  extraction time, 73% of the 2-hydroxy-4-methylthiobutyric  acid used was found (Example 6, FIG.  13).  [0110]  High influence is possessed here not only by the  temperature in the extraction colunm and the amount of  entraining gas introduced but also by the flow rates of the  extractant and of the aqueous ammonium salt solution. The  temperature is guided by the extractant used and should be  below the boiling point of a possible azeotrope.  [0111]  In the case of use of a 10% aqueous 2-hydroxy-4- methylthiobutyric acid ammonium salt solution at 80°  C. with  isobutyl methyl ketone as the extractant and with 60 1 of  nitrogen per hour as the stripping medium, after 90 hours of  extraction time, 95% of the 2-hydroxy-4-methylthiobutyric  acid used was found (Example 10, FIG.  14).  [0112]  Means oflndustrial Implementation  [0113]  An apparatus used on the industrial scale in a liquid› liquid extraction by the countercurrent principle is a mixer› settler apparatus. In countercurrent extraction, in a mixer› settler, the carrier and the extractant are conducted through  the mixing battery in opposite directions. Thus, in the first  stage, the highly laden carrier stream is contacted with  already enriched extractant, which results in a first refining  step. With each stage, the loading of the carrier stream  decreases. The loading of the extractant stream contacted  therewith decreases in the same direction, such that, ulti› mately, the already highly depleted raffinate is dispersed with  fresh unladen extractant in the last stage. In the countercur› rent process, a high depletion of the raffinate is achieved with  small amounts of extractant, which makes this variant very  economically viable.  [0114]  The apparatuses shown (FIG.  4  for high boilers as  the extractant and FIG.  5  for low boilers) serve to dissociate  ammonium salts of organic acids into ammonia and the cor› responding organic acids, it being possible for this thermal  dissociation to take place under mild conditions, such that  there is no decomposition of the organic acids.  [0115]  The apparatus consists of a column with n trays, the  trays of which are preferably configured as bubble-cap or  valve trays, such that there is only a very minor degree of, if  any, direct trickle of liquid phases from the upper trays  through to the trays below. A stripping medium flows through  the colunm from the bottom upwards, which is preferably  introduced into the bottom of the colunm or below the low› ermost tray. The stripping medium may preferably be steam,  which is obtained by the heating of the aqueous phase passed  downwards, or the stripping medium or entraining gas may  also consist of an inert gas, for example nitrogen or another  gas which forms a mixture with ammonia by interactions,  which is readily convertible to the gas phase.  [0116]  The configuration of the trays is preferably such that  the aqueous and organic phases are conducted together from  the entry to the tray to the exit by suitable baffles, in order to  prevent back-mixing or short-circuit flows. On the trays, by  virtue of the gas entering at the bottom, good mixing of all  three phases takes place, such that the ammonia released by  thermal decomposition, owing to the large phase interface, is  converted easily to the gas phase and the organic acid which  forms can be extracted rapidly out of the aqueous phase into  the organic phase.  [0117]  Thus, the aqueous phase comprising the ammonium  salt and the organic phase which absorbs the organic acid are  firstly introduced together to the uppermost tray (No. 1) of the  column and mixed. In the case of an extraction in countercur› rent, the aqueous phase with the greatest ammonium salt  loading is combined on the uppermost tray with the organic  phase which absorbs the organic acid downstream of the  separation process belonging to the tray below (No. 2). As a  result of the thermal elimination of ammonia, by virtue of the  contact with the gas phase, it passes into the gas phase at each  tray, and the organic acid passes from the aqueous phase into  the organic phase. If ammonium salt is present in the aqueous  phase, no thermal equilibrium will exist between the concen› tration of the organic acid in the aqueous phase and in the  organic phase, and as a result there is always transfer of the  organic acid which forms after the elimination of ammonia  into the organic phase. After the aqueous and organic phases  have left the uppermost tray, the two phases are separated  from one another in a suitable separation process. In the case  oflow mutual solubility of organic and aqueous phases, this  separation process may be a phase separator. In order to  promote the phase separation, a temperature change can be  effected before the separation process. Further separation  processes, such as a distillation, rectification, membrane pro› cess, crystallization, adsorption, chromatography, etc., are  likewise possible. Thus, at the uppermost tray, the organic  phase with the highest loading of the organic acid is obtained.  The organic acid can be separated from the solvent by one or  more further separation processes such as a distillation, rec› tification, membrane process, crystallization, adsorption,  chromatography, etc. The solvent released can then be fed  back into the colunm for extraction.  [0118]  After the separation process on the uppermost tray  (No. 1), the aqueous phase passes to the tray below (No. 2)  and is in turn combined with the organic phase which absorbs  the organic acid downstream of the separation process  belonging to the tray below (No. 3). The fresh organic solvent,  or that recycled from preceding separation processes, is com› bined on the lowermost tray (No. N) together with the aque› ous phase from the tray above.  [0119]  To operate such a reactive extraction, it is necessary  to decide whether water or the organic solvent possesses a  higher boiling temperature. In the case of water as the lower› boiling component at the operating pressure of the colunm,  and of utilization of steam as the entraining medium, the  water is collected in the lower part of the colunm and evapo› rated by means of a heat exchanger operated in circulation.  This evaporator may also be configured as a natural circula› tion evaporator. The excess water is conducted out of the  column under fill level control. The steam is introduced again  below the lowermost tray (No. N). Steam, ammonia and  optionally a further gas and small amounts of solvent vapours  are passed out at the top of the column and can optionally be  separated in a downstream separation process. 