Jan.  23,  2014  7  US  2014/0021404 Al  in reaction temperature decreased pKa value, increasing acid› ity and thus promoting decarbonation. Similar results were  obtained when ammonium acetate (Example 16) and acetic  acid (Example 17) were used.  [0112]  The present invention defined the reaction tempera› ture to fall within a range from 10°  C. or higher but not  exceeding 50°  C. The reasons why this temperature range was  selected are as follows: if temperatures of 50°  C. or higher are  selected, (1) there is a possibility that weight loss occurs by  dissolution depending on the type of acid, (2) heating opera› tion and cooling operation for preventing evaporation of alco› hol and acidic compounds are required, and (3) special heat› ing is unnecessary in many cases, and if no heating is  performed, it is more economical. However, if special advan› tages are ensured by increasing the reaction rate or acidity,  reaction temperatures of 50°  C. or higher may be adopted.  [0113]  The present invention selected 10°  C. as the lowest  temperature because commonsense room temperature is 10°  C. or higher. If advantages of selecting temperatures lower  than 10°  C., such as decrease in acidity, are ensured, causing  reactions to occur at lower temperatures are not excluded,  provided that the temperature is higher than the freezing  temperature of organic solvents not allowing the solution to  freeze.  [0114]  As described above, temperatures can be selected  arbitrarily or as required although optimum temperature  range varies depending on pKa value. Generally, however,  temperatures 10°  C. or higher and lower than 50°  C., more  preferably room temperatures (20°  C. or higher and up to 25°  C.) are desirable.  [0115]  In the process of decarbonation, carbonate ion-type  LDH is immersed in an organic solvent containing acidic  compound to allow protons (H+) and anions  (X-)  to contact  theLDH.  [0116]  As described above, the present invention allows a  carbonate ion-type LDH to contact an organic solvent con› taining an acidic compound, thereby converting the hardly  anion-exchanging carbonate ion-type LDH to highly anion› exchanging LD H by decarbonation at room temperatures and  in short time, without changing particle size or uniformity.  [0117]  The present invention will hereinafter be described  more specifically by referring to Examples, but the present  invention is not limited to the Examples shown.  [0118]  Commercially available hydrotalcite represented by  general formula MgsAl(OH)s(CO$_{3 }$ 2 -) $_{05}$.2H$_{2}$O  (DHT-6,  Kyowa Chemical Industry Co., Ltd.) was used. Particle size  distribution was approximately from 0.1 to 1 µm,  and Mg/ Al  molar ratio was 2.99 (–0.06). This LDH is designated as  CO$_{3 }$$^{2}$-MgAl-LDH3.  [0119]  100 mg of co/-MgAl-LDH3 was weighed and  placed in a three-neck flask, to which 45 mL of methanol was  poured to prepare suspension. Perchloric acid-methanol solu› tions of various concentrations were prepared by dissolving  perchloric acid (60%) to 5 mL of methanol.  [0120]  Perchloric acid-methanol solution was dropped  onto co/-MgAl-LDH3 suspension while the liquid was  being agitated with a magnetic stirrer in nitrogen gas flow (0.5  Umin.), and reaction was performed at room temperatures  (20 to 25°  C.) for one hour with continuous stirring.  [0121]  Then the solution was filtered in nitrogen gas flow  with a 0.2 µm  membrane filter, and the deposits were washed  thoroughly with methanol. The filtered out deposits were  collected and recovered, the pressure was decreased imme› diately, the deposits were dried in vacuum for one hour or  longer, and white powder was obtained.  [0122]  For comparison, experiment was conducted using  degassed water (obtained by boiling ion-exchanged water for  15 minutes or longer to remove carbon dioxide, hereinafter  referred to simply as water), instead of methanol.  [0123]  In this experiment, perchloric acid of the amounts  satisfying f=[W]/(2x[CO$_{3 }$$^{2}$-])=0.5, 0.75, 1.0, 1.25, 1.5, 2.0,  3.0, 4.0, 5.0, and 8.0 were used. For example, when f=l, the  amount of perchloric acid used was 56 mg.  [0124]  FIG.  2  shows the relation between the weight of  product and value f.  [0125]  In the case of methanol (FIG.  2  (a)),  the weight of  the product rarely changed even if value fwas changed from  1 to 8. In the case of water (FIG.  2  (b)),  dissolution ofCo/› MgAl-LDH3 started to occur when value fwas 2, and most of  the product had been lost by dissolution when f=8.  [0126]  The weight of the product increased when value f of  methanol was 0.5 to 1.0 because CO$_{3 }$ 2 - was substituted by  ClO$_{4}$ -,  and thus the molecular weight increased. Assuming  that CO$_{3 }$ 2 - is substituted by ClO$_{4}$ - completely, and assuming  the recovery rate to be 95%, the weight should be approxi› mately 116%. The weight reached this value when f=l or  larger when methanol was used, which coincides with this  assumed value.  [0127]  Infrared absorption profile obtained by Fourier  transform infrared spectroscopy (FTIR) was studied and the  following results were obtained: with methanol, when f=l  .O,  absorption due to carbonate ions (CO$_{3 }$ 2 -) remaining by as low  as several % was found at 1370 cm-1, but when f=l.25,  absorption by carbonate ions (CO$_{3 }$ 2 -) at 1370 cm- $^{1 }$was lost  and intense absorption characteristic of ClO$_{4}$ - was found in a  range from 1090 to 1100 cm-1, which confirmed that high› purity ClO$_{4}$ -MgAl-LDH3 had been prepared.  [0128]  FIG.  3  shows the Fourier transform infrared spec› trum (transmittance), where (a) and (b) respectively show the  FTIR profile of carbonate ion-type MgAl-LDH3 and that of  ClO$_{4}$ -type LDH3 obtained under f=l.25 conditions. In (b),  intense absorption due to perchlorate ions (1090 to 1100  cm- 1 )  was found, but absorption due to carbonate ions (1370  cm- 1 )  was not found, which confirms that there were no  residual carbonate ions.  [0129]  With methanol, ClO$_{4}$-MgAl-LDH3 was obtained in  a range where f= 1.25 to 8, and existence of other phases was  not found.  [0130]  Meanwhile, when water was used, even when f=2,  existence of residual carbonate ions by nearly 30% was  found, and when f=3 or higher, the residual carbonate ions  were lost, and generation of ClO$_{4 }$-MgAl-LDH3 was con› firmed. However, as shown in FIG.  2,  when f=3, weight loss  was approximately 20%, meaning that dissolution of LDH  itself was occurring. As described above, when water was  used as a solvent, there were no experimental conditions for  producing LDH without involving weight loss due to disso› lution and without existence of residual carbonate ions.  [0131]  Since there was a possibility that metal ions dis› solve, thus causing Mg/ Al ratio to change, Mg andAl analysis  was conducted by inductively-coupled plasma (ICP) spec› trometry to examine the Mg/Al ratio.  Example 1  Perchloric Acid-Methanol System; MgAl-LDH3 