Aug. 19, 2010  8  US 2010/0210871 Al  [0092]  It  has been found that the temperature has a great  influence on the extraction rate. The higher the temperature of  the aqueous ammonium salt solution, the more rapidly the  reactive extraction proceeds.  [0093]  In the case of use of a 10% aqueous 2-hydroxy-4- methylthiobutyric acid ammonium salt solution at 50°  C. with  isobutyl methyl ketone as the extractant and with 6 1 of  nitrogen per hour as the entraining gas, after 90 hours of  extraction time, 39% of the 2-hydroxy-4-methylthiobutyric  acid used was found (Example 2). A temperature increase by  30°  C. to 80°  C. under otherwise identical conditions also  increases the amount of 2-hydroxy-4-methylthiobutyric acid  extracted within the same period to 93% (Example 1, FIG.  7).  [0094]  It  has also been found that the concentration of the  ammonium salt used has an influence on the extraction rate.  The higher the concentration of the ammonium salt in the  aqueous solution, the more slowly the reactive extraction  proceeds.  [0095]  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 6 1 of  nitrogen per hour as the entraining gas, after 90 hours of  extraction time, 93% of the 2-hydroxy-4-methylthiobutyric  acid used was found (Example 1 ). When the concentration of  the ammonium salt is increased to 20%, under otherwise  identical conditions, 71 % of extracted 2-hydroxy-4-meth› ylthiobutyric acid is obtained within the same period (Ex› ample 3, FIG.  8).  [0096]  The reactive extraction is not restricted to the use of  isobutyl methyl ketone as the extractant.  It  is possible to use  all water-immiscible or only sparingly water-miscible  organic solvents, such as alcohols, ethers, ketones or hydro› carbons, or mixtures thereof.  [0097]  In the case of use of a 10% aqueous 2-hydroxy-4- methylthiobutyric acid ammonium salt solution at 50°  C. with  isobutyl methyl ketone as the extractant and with 6 1 of  nitrogen per hour as the entraining gas, after 90 hours of  extraction time, 39% of the 2-hydroxy-4-methylthiobutyric  acid used was found (Example 2). When, under identical  conditions, methyl tent-butyl ether is used as the extractant,  after 90 hours of extraction time, 38% of the 2-hydroxy-4- methylthiobutyric acid used is found in the solvent (Example  4, FIG.  9).  [0098]  In addition to 2-hydroxy-4-methylthiobutyric acid,  reactive extraction using a stripping medium or entraining gas  is also employable for other hydroxycarboxylic acids.  [0099]  Examples cited here include the commercially sig› nificant lactic acid, and 2-hydroxyisobutyric acid, which is  used in plastics production as a precursor for MMA.  [0100]  In the case of use of a 10% aqueous lactic acid  ammonium salt solution at 80°  C. with 1-butanol as the  extractant and with 61 of nitrogen per hour as the entraining  gas, after 21 hours of extraction time, 88% of the lactic acid  used was found (Example 8, FIG.  10).  [0101]  In the case ofuse ofa 10% aqueous 2-hydroxyisobu› tyric acid ammonium salt solution at 80°  C. with isobutyl  methyl ketone as the extractant and with 6 1 of nitrogen per  hour as the entraining gas, after 21 hours of extraction time,  49% of the 2-hydroxyisobutyric acid used was found (Ex› ample 7, FIG.  11).  [0102]  The invention cited is not restricted only to the  release ofhydroxycarboxylic acids from the ammonium salts  thereof, but also includes other substituted or unsubsubsti› tuted carboxylic acids, e.g. valeric acid, and sulphonic acids,  e.g. (+)-camphor-I 0-sulphonic acid, and phosphonic acids,  for example toluenephosphonic acid.  [0103]  In the case of use of a 10% aqueous valeric acid  ammonium salt solution at 80°  C. with isobutyl methyl ketone  as the extractant and with 6 1 of nitrogen per hour as the  entraining gas, after 21 hours of extraction time, 90% of the  valeric acid used was found (Example 9, FIG.  12).  [0104]  In the case of use of a 10% aqueous (+)-camphor› ! 0-sulphonic acid ammonium salt solution at 80°  C. with  isobutyl methyl ketone as the extractant and with 6 1 of  nitrogen per hour as the entraining gas, after 66 hours of  extraction time, 25% of the (+)-camphor- I 0-sulphonic acid  used was found (Example 12).  [0105]  In the case of use of a 10% aqueous toluenephos› phonic acid ammonium salt solution, it was possible at 80°  C.  with isobutyl methyl ketone as the extractant and with 61 of  nitrogen per hour as the entraining gas, after 46 hours of  extraction time, to find 43% of the toluenephosphonic acid  used (Example 13).  [0106]  The examples cited were performed in a specially  developed perforator (FIG.  1).  The extraction vessel of the  perforator was half-filled with an aqueous ammonium salt  solution of an organic acid and filled with an extractant until  there is overflow to the reservoir. The reservoir itself is like› wise half-filled with extractant. The extraction vessel is  equipped with an inserted distributor and a gas inlet tube with  frit. The distributor is rotated by means of magnetic coupling.  A stripping gas, for example nitrogen, is simultaneously  introduced via the gas inlet tube. The extractant supplied to  the distributor from the condenser above through a tube by  distillation out of the reservoir is accelerated into the aqueous  ammonium salt solution to be extracted as fine droplets out of  small holes of a distributor ring by centrifugal force. This  achieves fine distribution and intimate mixing of the extrac› tant with the material for extraction. At the same time, the gas  stream drives the ammonia out of the aqueous phase. Caused  by the co-rotation of the aqueous ammonium salt solution to  be extracted, the finely distributed extractant laden with the  free organic acid extracted reaches the deposition zone only  after prolonged residence time in the aqueous phase and runs  back into the reservoir (distillation flask), from which the  solvent is recycled into the extraction circuit by re-evapora› tion. The free organic acid collects in the reservoir. The  ammonia stream released is removed with the stripping gas  via the attached jacketed coil condenser and collected in an  aqueous sulphuric acid trap.  [0107]  An apparatus improvement is the countercurrent  extractor (FIG.  2).  In a reaction tube equipped with random  packings, the aqueous ammonium salt solution of an organic  acid at a controlled temperature is introduced from the top and  pumped in circulation. The extractant is pumped into the  reaction tube in countercurrent through a frit and the entrain› ing gas is introduced into the system. The finely distributed  droplets of the extractant absorb the organic acid released.  The lighter organic phase is removed via an outlet at the upper  end of the reaction tube. After the separation of extractant and  organic acid (for example crystallization, distillation, separa› tion by cooling, separation by back-washing with water), the  extractant is introduced into the circuit again. The entraining  gas and the released ammonia which has been driven out are  removed via the top. Series connection of a plurality of coun› tercurrent extractors makes the process even more efficient  and industrially employable. A cascade reactive extraction is  obtained (FIG.  3). 