Patent GB-641786-A (GB)
Title: Improvements relating to the production of potassium bitartrate
IPC: B01J41/00
Filed: 1946-08-01
Abstract: Potassium bitartrate is prepared from aqueous acid tartrate solutions by a process in which some of the tartrate anions present in the initial solution are taken up by anion-exchange material and are subsequently displaced from it as tartaric acid by an aqueous solution of an acid of higher ionization constant than tartaric acid and other tartrate anions present in the initial solution are taken up by anion-exchange material and subsequently displaced from it as potassium tartrate by an aqueous solution of potassium alkali, and the resultant solutions of tartaric acid and potassium tartrate are combined to yield potassium bitartrate.  The concentrations of these solutions are selected so that the average tartrate concentration of the mixture exceeds that of a saturated solution of potassium bitartrate at 0 DEG  C. or other convenient temperature, whereby on mixing the solutions, crystalline potassium bitartrate forms. Suitable aqueous acid tartrate solutions for use as starting materials are obtained from grape waste; still slop may be used directly but grape pomace and other solid residues require to be extracted with water.  In one method of carrying out the process of the invention, the aqueous acid tartrate solution is passed through a bed of cation-exchange material charged with hydrogen ions and then through a bed of anion-exchange material, the anion-exchange material charged with tartrate anions then being treated with potassium alkali in one run and with a displacing acid in the next run, the respective effluents being thereafter combined to yield potassium bitartrate; following the acid-treatment, the anion-exchange material is regenerated by alkali.  Regeneration of the cation-exchange material is effected by acid in the usual way.  The preferred process comprises passing aqueous acid tartrate solution containing free tartaric acid through a bed of anion-exchange material whereby the free tartaric acid is taken up, then through a bed of cation-exchange material which substitutes hydrogen ions for metallic cations and finally through another bed of anion-exchange material which takes up the tartaric acid formed in the preceding step.  Then one bed of anion-exchange material is treated with potassium alkali and the other with displacing acid and subsequently with regenerating alkali. The effluents are combined as above.  It is immaterial which of the beds of anion-exchange material is treated with potassium alkali and which is treated with the acid; the recovery process may be alternated, the first anion exchange bed being treated with potassium alkali in one run and with displacing acid and regenerating alkali in the next run or the same regeneration order may be used for any given number of runs and then reversed in the following series of runs. Alternatively, for one or more runs both beds of anion-exchange material may be treated with potassium alkali and then for one or more runs both may be treated with the displacing acid; the effluents from the respective runs are bulked and eventually the two are combined to yield the desired bitartrate.  In another variation, two sets of ion-exchange materials may be used, in the one set the anion-exchange materials are treated with potassium alkali and in the other set with displacing acid and then with regenerating alkali. The treatment with the displacing acid is the same as that described in Specification 627,702.  The effluent from the displacing acid treatment may be collected in fractions and a fraction containing tartaric acid and displacing acid may be passed in a subsequent cycle through anion-exchange material charged with tartrate anions prior to the acid-treatment; similarly, the effluent from the potassium alkali treatment may be collected in fractions and a fraction containing potassium tartrate and potassium alkali may be passed in a subsequent cycle through tartrate-charged anion-exchange material prior to the potassium alkali treatment.  Instead of passing the various solutions through the ion-exchange materials, the granular material may be added to the solutions, agitated and then separated by decanting, filtering or centrifuging.  In typical examples: (1) dry grape pomace is treated with water, filtered and the filtrate having 46.4 meq./1 of acidity is passed successively through an aliphatic amine anion-exchange resin, a cation-exchange material of the sulphonated coal type and then through a second anion-exchange resin, the first anion-exchanger is treated with aqueous potassium hydroxide and the second with aqueous sulphuric acid, the respective effluents are collected in fractions and the four most concentrated fractions of each are decolourized by charcoal, cooled to 20 DEG  C. and combined yielding crystals of potassium bitartrate; (2) the extracted pomace of (1) is further extracted with water and the extract obtained used to treat fresh pomace giving a final extract which is passed through three ion-exchange materials as in (1); the first anion-exchange resin is then treated however, with aqueous sulphuric acid and the second with aqueous potassium hydroxide, the effuents collected in fractions, the more concentrated fractions used to prepare potassium bitartrate and the weaker fractions recycled in a subsequent run as indicated above.