IL29379A - Process for the preparation of aqueous alkali metal carbonate solutions from alkali metal hydroxide solutions - Google Patents

Description

PATENTS AND DESIGNS ORDINANCE SPECIFICATION Process for the preparation ofaqueous alkali metal carbonate solutions from alkali metal hydroxide solutions a German of 521 Germany do hereby declare the nature of this invention and in what manner the same is to to be particularly described and ascertained in and by the following statement The invention concerns preparation of alkali metal carbonate solutions alkali solutions by ion chemical processes yield dilute alkali hydroxide solutions whose concentration and possible further use involve as a rule considerable For an about alkali metal hydroxide solution is produced w a cation exchanger alkali metal ion is treated with a solution or suspension of slaked Highly dilute alkali metal hydroxide solutions are also obtained by the desalination aqueous salt solutions such solutions are firet passed through a strongly basic anion exchanger charged uith In this case the concentration of the alkali metal hydroxide solution produced varies with the salt content the starting aqueous salt solution within a few tenths of a per desalination of sugar solutions yields alkali metal hydroxide solutions of similar concentrations contain some residual nt of Diluted alkali metal hydroxide solutions in also contain are produced by the regeneration of strongly basic anion exchangers with an excess of alkali metal hydroxide the excess alkali metal hydroxide required for the regeneration remains in the spent regeneration If for the conversion a sodium chloride solution into a sodium hydroxide solution a strongly basic anion exchanger is the latter can subsequently be regenerated by means of a suspension of slaked She sodium chloride solution yields at best a about of sodium alkali hydroxide solutions also produced by the of occurring containing carbonate or which usually has a content of chloride and sulfate is with a of slaked Alkali metal hydroxide solutions containing alkali metal sulfite produced by tho reaction of alkali sulfite solutions calcium this is never seemingly of producing alkali metal solutions of higher concentrations the aforesaid solutions of low concentration would be the evaporation of dilute In this process any present in the solution precipitate and can be tho concentration those highly dilute even by means of a requires a very large quantity of whose cost as a much higher than the value of the alkali metal hydroxide solution actually is to bind the alkali ions of a dilute alkali octal hydroxide solution to a weakly acidic cation exchanger subsequently regenerate the latter tilth carbon process yields alkali metal bicarbonate it has the disadvantage that even w a carbon dioxide solution saturated under very high pressure is only very dilute product solutions are for a of gauge yields solutioi the bicarbonate solutions thus produced have only a very limited In addition the conversion According to a further already the alkali metal ions of dilute alkali metal hydroxide solutions are removed from these solutions means of a weakly acidic cation exchanger which can be hydrogen ions by means of an alkali metal bicarbonate the contact of this alkali metal bicarbonate solution with the ion exchanger an alkali metal carbonate solution is formed can be used for many purposes and whose conversion into an alkali metal hydroxide solutio requires only half amount of slaked lime necessary for the aforesaid even this process involves considerable since owing to the nature of the cation exchanger used the bound alkali metal ions are largely removed from the ion exchanger by use of water for displacing the alkali metal hydroxide solution is necessary in particular in those cases where the latter solution also contains salt which would otherwise pass into the alkali metal carbonate Xn order to produce an alkali metal carbonate solution of high concentration it is necessary that the alkali metal bicarbonate solution should also have a high so only a slightly higher concentration than that the starting solution is obtained in the first effluent Owing to the delayed even the first runnings of the effluent solution still contain considerable quantities of alkali metal g to which this process again shows the same disadvantages the one to The invention has the ob ect to eliminate the drawbacks The invention provides a process for the preparation of alkali metal carbonate solutions of medium concentration from dilute alkali metal hydroxide solutions by mesne of ion the term metal carbonate solutions of medium meaning to of a concentration of 5 to by weight in the case of sodium and 7 to by weight in the case of potassium The process is not only comparatively simpler and cheaper but has in addition further considerable advantage in that it enables the production of alkali metal carbonate solution and in most oases even free from the salts accompanying the alkali metal hydroxide in the starting and in that the alkali metal carbonate solution of medium concentration prepared in accordance with the invention can be converted into an alkali metal hydroxide solution of medium concentration which in most cases can be used as it for the regeneration of strongly or weakly basic anion In since the solution has already a medium it can readily be further concentrated by evaporation to commercial strength even to a solid under economic conditions and by means of comparatively small quantities of process according to the invention is characterized in that the alkali metal ions of a dilute alkali metal hydroxide solution are absorbed by a very weakly acidic cation exchanger and then recovered from the latter by exchange against hydrogen ions by treatment with four groups of eluent fraotions of which the first one consists of preferably two to higher than that of solution to produced and which contain decreasing amounts of alkali metal carbonate and increasing amoun s of alkali metal the third preferably by one single consists of a pure alkali aetal bicarbonate solution concentration is lower than that of the desired product solution and whose alkali ion content is equal to at least preferably three to six that of the desired product and the fourth group comprises at least preferably two to four fractions containing decreasing concentrations of alkali metal and further characterised in that last fraction of the fourth group is displaced by means of an amount of water larger than that which ultimately remains in and from the effluent solution there is separated first displaced the then the fractions of the group are returned to their storage thereafter the product solution containing the alkali aetal ions of the ion exchanger is subsequently fractions of the second to fourth groups are returned to their respective and finally the fractions of the third and preferably the first fraction of the fourth are prior to being in a exchange with carbon dioxide for converting the alkali metal carbonate alkali metal It is a particular advantage of the process according to the invention that several objects are achieved separately by means of different groups of fractions are has been neither their quantity nor their composition A further advantage of process according to the invention over hitherto known or proposed processes consists in that the amount of water contained in the product solution is charged the last fraction together with water of displaceaent serving for washing the ion Shis of water reaches the product the last three groups of of the four groups of fractions used in accordance with the invention and having different compositions fulfils a different task in this first group of fractions passed through the ion exchanger immediately after the dilute alkali metal s olution displaces the alkali metal hydroxide solution from the without loss of alkali This group consists of fractions which contain the alkali metal carbonate solution in increasing concentrations and addition they contain small amounts of alkali aetal which originates in part from the added dilute alkali metal hydroxide solution and in part from the hydrolysis of alkali metal ions absorbed by ion By the second group of fractions as high a concentration possible of the alkali metal carbonate solution to be produced is group comprises fractions whose total concentration is equal to or higher than the concentration of product solution and which contain in the first line alkali in addition to which they contain comparatively amounts of alkali metal bicarbonate whose concentration increase from fraction to and which react with the alkali metal These fractions come into contact with the ion exchanger fully charged with alkali metal ions are still capable of absorbing additional quantities of alkali metal ions from the exchanger despite their high In this manner the original dilute alkali metal metal hydroxide solution yields an solution of concentration which contains only a very small amount of alkali metal bicarbonat It is advisable employ in this group from two to five third group of fractions finally serves to recover as completely as possible the bulk of the alkali aetal ions absorbed by the ion exchanger from the dilute alkali metal hydroxide For this purpose it is constantly prepared and consists of pure alkali metal It is only because of their high content of hydrogen ions that the fractions of this group can take up the large amount of alkali metal In order to ensure this thoir hydrogen ion content should be equal to at least preferably from three to six the quantity of alkali metal ions to taken She product of the exchange is alkali metal carbonate which is converted into bicarbonate after each exchange In this process the alkali aetal ion concentration that can be achieved in product is only the concentration of the alkali ions in the fraction of the third since the fractions of the second group are obtained from the latter and can only take up many alkali metal ions as they have received hydrogen of the product is limited by the of the fraction of third upper limit of the concentration of this last fraction is the saturation with bicarbonate for is of the order of in the of sodium 2n order to achieve higher tions of the product the second group of fractions is preferably She first half is used described above bat the number of fractions is Into at least one fraction of other half so much carbon dioxide is introduced that this solution becomes saturated with alkali metal distinct from the fraction of the third group this solution still contains considerably amounts of unchanged alkali metal Owing to the added hydrogen ions these fractions can take up further of alkali metal ions whereby an alkali metal carbonate solution can be produced concentration is then twice that of the saturated alkali metal bicarbonate fourth group fractions has the task to separate the charged water from the bicarbonate solution of the third group of fractions and thus serves to keep the concentration of the product solution as as volume and concentration of the fractions of this group are than those of third group and decrease fractions too are capable of removing small amounts of alkali metal ion from the exchanger so that it can happen that the alkali metal carbonate content increases in the first can also be converted into alkali This group consists preferably of one to three As already mentioned water is charged into the exchanger after the fourth group of In the process according to the invention the water has not only the task to displace the solutions from the is the case in conventional but it also achieves the necessary result to introduce at this stage into the exchanger the quantity of which has to be subsequently with the product In conventional ion exchante processes the charged are used ia the form of aqueous solutions and the water introduced with these solutions is removed the product Against in the process according to the invention the reagen 9 namely the alkali metal is produced from alkali metal ions set free from the exchanger ia anhydrous form and from tho equally carbon introduced into the Consequently the water leaving with the product solution is introduced Only then follows ths further amount of water which remains in the exchanger and is referred to as water of Shis of particular advantage since the pH value of water is lower than that of the alkali metal bicarbonate solution owing to which fact the water can take up further amounts of alkali metal ions from the Since that of water which goes over into the product solution is charged first it carries over most of the absorbed alkali metal ions in the displacement so that the losses occurring at this stage are greatly reduced in the process according to the inven The invention is illustrated the following to ic it is not 1 The according to the invention is described the following with reference to 1 of the accompanying latter shows a complete exchange cycle with an exchanger bed of 140 The alkali metal hydroxide is represented without the alkali metal carboaate densely hatched and the alkali metal bicarbonate finely in the drawing correspond to 1 litre of dilute hydroxide solution is introduced between 0 and follow the fractions of the first group and consisting of of some hydroxide and increasing concentrations o sodium The following fractions having a total concentration of about form the second have concentrations of sodium bicarbonate of and Then follows the fraction of the third group which consists of pure Shis fraction contains tiaes hydrogen lone than the quantity corresponding to the amount of sodium lone absorbed by the She following fractions of the fourth group also contain pure sodium bicarbonate solutions and have concentrations of and The of water that is being charged is indicated by the 12 rate of throughput during operation of charging the dilute sodium hydroxide solution 25 volumes per volume of exchanger per hour and during charging of tho She effluent solution discharged from tho exchanger during the charging of dilute sodium hydroxide solution in its first litre about 6 of initial concentratio of charged sodium This concentration increases gradually of the initial value in the last half About half tho sodium ion content of the charged 4 litres of dilute sodium hydroxide is absorbed by the exchanger the first group of fractions is being into the first runnings of an effluent composition corresponds to the last portions of the solution from a previous are the fractions of the first grou and are recovered and unaltered in a following She volume of the next fraction has a concentration is chosen at Apart from minor losses it contains tho amount of sodium ions as had been removed from tho charged dilute sodium hydroxide fraction consists of of carbonate and of sodium It ie product solution sodium carbonate solution of medium which is from the She two following fractions and form the second group and are stored unchanged for the subsequent fraction constituting the third group contains considerable of sodium Of the fractions of the fourth fraction still contains sodium Fractions and are converted by means of into sodium bicarbonate before being In accordance with this embodiment of the according to the invention a hydroxide solution is thus converted into a carbonate solution containing of sodium bicarbonate in the concentration of sodium ions has thus increased by a factor of process illustrated in 1 may be combined with ion exchange further advantages can be for two exchanger beds may in series of at the beginning of a the had already been used while the second one has been charged with hydrogen supply of dilute metal hydroxide solution is continued until the first bed is nearly completely then the feed of the hydroxide solution is interrupted and first bed is end is charged with the various g of At the same time thG second exchanger bed is connected so as to become the one a fresh bed charged with hydrogen ions is connected as the second In this manner the exchanger beds can charged to a very high degree while at the same time the iono of the dilute hydroxide solution are largely withdrawn from this the described of this combination of result that of ions removed from two litres of a dilute sodiun hydroxide solution by of two exchangers of 140 ml e rate of throughput of the dilute solution 12 the exchanger g aggregate volume of both In the of the process according to invention it been found to be of advantage to saturate the fractions of the third and fourth groups with carbon dioxide so that they contain free carbon dioxide in addition to In this manner the absorption capacity of the solution for alkali metal ions is A further increase of the absorption capacity is achieved the saturation is effected under elevated preferably the same pressure which is anyhow required for charging circulating the solutions through the exchanger at the required certain circumstances it aay happen that the effect ic obtainable with the very weakly is insufficient for the of the alkali metal ions from the the above the use the process left ions in the In order to remove this residual slightly more cation exchanger has be used as secondary exchanger has still to be sufficiently acidic to permit metal ions absorbed by it by means of an aqueous carbon dioxide Owing the solubility the carbon dioxide the alkali metal bicarbonate solution is too It has been found that alkali bicarbonate solution obtained in the first place is saturated again with carbon dioxide and e further amounts of alkali ions taken This renewed saturation and recycling can be repeated several possible to operate with a series of solutions of which the firot one is to the highest degree the one to the lowest while the last solution of the series is water saturated with saturation can be carried out under preferably the pressure is as is anyhow required for and circulating the solution at the required rate through the exchanger The solution of alkali metal bicarbonate thus obtained is interposed the group of fractions of the third group of the exchanger the place corresponding to its In this manner the metal ions contained in this solution finally reach the discharged product an additional amount of water is added to the system this the amount of water added at the end of the to be correspondingly Xn the 1 thus the regeneration of the secondary exchanger yielded a solution whose concentration corresponded to that of the fraction and whose volume was half the volume of the product solutio i this solution was used instead of fraction Xa order to by the process according to the alkali metal ions from an alkali metal hydroxide solution contaminated with this solution is preferably charged into a y acidic cation which absorbs only alkali ions of tho hydroxide solution while the components of tho salts pass through tho In order to the salt from the fractions of the mentioned four of fractions with the product it is preferred to after introduction of separating fractions containing increasing amounts of alkali metal carbonate decreasing amoun of alkali metal hydroxide and of variant invention is illustrated in 2 reference to s 2n this bod of 1 amoun ing to 400 contained 1 potassium chloride and of potassium hydroxide per of throughput of solution and of tho fractions and that of the further fractions separating fractions introduction of solution contained potassium and potassium chloride in decreasing and potassium carbonate in She first of tho fractions and nearly potassium but the first of still contains some potassium the last already contains some potassium group consists of fractions and which in addition to potassium carbonate of fractions contains only a potassium bicarbonate fractions and of the fourth group contain potassium bicarbonate in decreasing water is In the drawing the alkali chloride has been represented by Of the effluent solution the 520 are in addition to potassium 1 of potassium hydroxide calculated on the separating and displacement fractions are returned unchanged to storage tanks and Fraction which is strong and contains of bicarbonate is the product its potassium chloride content is less than calculated on the total salt next fractions and are stored the following fractions and saturated with carbon dioxide and thus while the last fractions are again stored In this case the removal of the potassium ioaa dilute potassium hydroxide solution with a single exchanger bed so good that the arrangement of secondary exchanger was not From the initial hydroxide solution a solution was separation good since both products contaminated with only the other product contained of the potassium of the potassium hydroxide f Since in certain cases this very low contamination of the product solution is a further group of displacement fractions is advantageously used after the containing alkali metal hydroxide fractions contain alkali metal hydroxide in amoun s increasing to a concentration which must not the alkali hydroxide content of mixture to bo and decreasing amounts of alkali Af er these a fraction of only is follow va groups of fractions containing alkali metal carbonate and bicarbonate as described The effluent solution is treated a manner different from that described salt solution separated from the alkali is removed and the group of the further displacement fractions is She fraction volume corresponds to the volume of the added is Shis fraction contains small amounts of salt la addition to alkali metal hydroxide and is advantageously recycled to starting treatment of the following fractions corresponds to the description given If the salt solution is to be processed further it is as rule of advantage to pass it on with as high a concentration as In this case a further group of fractions is used has the taek to displace the water from the exchanger charging of this group precedes that of the starting solution the effluent thereof is equally collected before that of the starting and it is stored variant described in Example 3 with reference to 3 first group of and contains increasing amounts of sodium chloride and traces of sodium Then the chloride starting being in regard to sodium is Then follows the second group of fractions whose hydroxide content increases in steps while the chloride content the fraction consisting of pure water is whose volume corresponds to that of the neighbouring The third group contains fractions and having increasing concentrations of sodium carbonate but containing practicall no The fractions of the fourth group and are solutions of over and contain increasing amounts of sodium The fifth group consists in this of a single fraction of pure sodium The fractions of sixth group contain traces of sodium Finally the last fraction consisting of pure water is From the effluent solution the fractions of the first group and are collected and stored after tho rejection of the first runnings which contain small amounts of sodium Subsequently the chloride which is practically free of concentration has decreased to and which contains about of sodium is fractions of the second group a d are stored while the fraction of the third group with a chloride content of and a sodium hydroxide content The following fractions of the fourth group and are She fraction is the product solution with a total concentration of carbonate and sodium The following fractions and are stored while the fractions and are converted with carbon dioxide into a pure sodium bicarbonate The further fractions of the sixth group are again stored embodiment of the process according to the invention a increase in concentration of the from to was She sodium chloride solution had a slightly lower concentration and a content of sodium while the sodium hydroxide solution practically free desalting solutions by the process according to the where the anions of the solution are first replaced by ione and the alkali metal ions are then absorbed by a weakly acidic cation the cation be slightly more acidic than the one used the which referred to as being very weakly Preferably the secondary exchanger in the above as the main the regeneration of this exchanger about metal bicarbonate solution be produced by saturation of the water h carbon dioxide under high exchanger may be regenerated several fractions of a solution of which the first one has highest alkali metal bicarbonate concentration and the one a concentration of alkali metal bicarbonate charged into the ia which process pressure used is preferably tho as is anyway needed for the resistance of the ion exchange or a pressure is higher by 1 to 2 atmospheres than one which anyway needed for the introduction or the of the solution at the of flow exchanger In this vari sat of invention an alkali metal concentration of to can be anion exchanger used is regenerated with alkali metal hydroxide solutions which have to be used in ex but can be recovered from the spent re enerating solution in the described Preferably the alkali metal bicarbonate solution obtained in the regeneration of strongly acidic cation exchanger used as one of the group of employed in Since in this case this solution has a relatively high concentration it is instead of fraction this manner not only the alkali ions derived from the regeneration of the more strongly acidic cation exchanger are but also the bicarbonate ions derived from this regeneration are converted into carbonate ions and the water content of this is used for preparing the product solution of the regeneration of the weakly acidic cation A a very weakly acidic cation exchanger in the according to the invention there may be for those containing an active group hydroxy as as phosphoric acid and phosphorous acid acid sulfonic acid amide amino acid order to doorcase the time work for reaching the steady when the results achieved on a laboratory scale are translated into a or the same fractions are used and in both eases the ratio between the volume of each fraction and the of the exchanger the composition of the fractions is identical in both insufficientOCRQuality

Claims (1)

1. A process for the preparation of alkali metal carbonate of medium as herein from dilute alkali hydroxide solutions means of ion wherein the alkali ions of a dilute alkali metal hydroxide solution are by a very weakly acidic cation exchanger then recovered from the latter by exchange against hydrogen ions by treatment four groups of eluent fractions of which the first one consists of fractions preferably two to of alkali carbonate solutions of increasing the second roup of preferably two whose total centration is equal to or higher than that of the solution to be produced which contain decreasing amounts of alkali carbonate and increasing anounts of alkali the third preferably formed by one single consists of a alkali aetal bicarbonate solution whose concentration is lower than that of the desired product solution and whose alkali metal ion content is equal to at least preferably three to six that of the desired product and the fourth group comprises at least preferably two to fractions containing concentrations of alkali metal and w erein the last fraction of the fourth group is displaced by means of an amount of water larger than that which ultimately regains in the and from the effluent solution there is separated first the liquid displaced from the then the fractions of first group are returned to their storage thereafter the product solution containing the alkali respective and finally fractions of the third and preferably the first fraction of the fourth are prior to being in a subsequent exchange with carbon for converting the alkali metal carbonate into alkali metal A process according to wherein the fractions of the third and fourth groups are saturated with carbon dioxide preferably at an elevated process according to Claim wherein the saturation is carried out at a pressure which is equal or higher by 1 to 2 atmospheres the working pressure of the ion exchange A process according to any of Claims 1 to wherein a very weakly acidic cation exchanger has connected to it in series a second slightly more acidic cation the alkali metal ions absorbed by the latter are by of aqueous carbon dioxide solution and the aqueous alkali metal bicarbonate thus obtained nose water content is smaller or at most equal that of the alkali metal carbonate solution of medium concentration to be is interposed in the series of fractions of the third 1 process according to Claim wherein the second cation exchanger is charged successively with several fractions saturated with carbon which contain alkali metal bicarbonate in amounts decreasing to A process according to Claim wherein the saturation is carried out at a pressure which is equal or higher by 1 to 2 heres than the workin ressure of the ion exchan e A process according to a y of to being applied to the conversion of a solution containing alkali metal hydroxide and alkali metal salt into a alkali metal solution of A process according to Claim therein a further of fractionscontaining increasing amounts of alkali metal carbonate amounts of alkali metal hydroxide and of alkali salt is interposed between the hydroxide and the first group of alkali carbonate containing A process according to Claim wherein after the posed further group of a fraction of water only is charged into the cation exchanger and from the effluent there is after the recycling of the interposed group of a fraction whose volume corresponds to the water fraction A process according to Claim wherein the separated effluent fraction which contains alkali metal is added to the starting Δ process according to any of Claims 7 to wherein before the alkali metal hydroxide solution is charged into the cation a further group of fractions of an increasing concentration of salt is charged into the cation A process according to any of Claims 1 to 11 applied to the regeneration of a weakly acidic cation exchanger used for the desalting of sugar juices and the recovery of the utilised unutilized alkali metal hydroxide is the spent egeneration solution by of a weakly acidic cation and the dilute alkali bicarbonate solution produced by the regeneration of the acidic cation exchanger is used as fraction the series of fractions used for of the unutilised alkali Dated this 26th 1968 c For insufficientOCRQuality