and dissolution started to occur due to excessive amount of acid, the maximum weight value became lower than that exhibited when organic polar solvents were used. These results show that the decarbonation caused by adding an acid occurs quantitatively in organic polar solvents, and that dis› solution of LDH itself is suppressed in organic solvents. 

## Ammonium Salt-Methanol System; MgAl-LDH3 

[0202] Using ammonium salt, a type of amine acid salt, specifically, using ammonium chloride (NH$_{4}$Cl), ammonium perchloride (NH$_{4}$ ClO$_{4}$ ) and ammonium nitrate (NH$_{4}$NO$_{3}$), decarbonation was performed in methanol solution. These are salts respectively made up of ammonia, which is weak base, and hydrochloric acid (HCl), perchloric acid (HC1O$_{4}$ ), and nitric acid (HNO$_{3}$ ), which are a strong acids. As LDH, CO 3 2 - MgAl-LDH3 was used as a starting material. The amount of addition was represented by value f. For example, assuming that only one His protic, of the 4 Hs ofNH$_{4}$Cl, one proton is considered to be supplied from NH$_{4}$Cl. Consequently, value f is represented as follows: f=[H+]/(2x[CO$_{3 }$$^{2}$-])=[NH$_{4}$ Cl]/(2x [Co/-]). 100 mg of co/-MgAl-LDH3 and 50 mL of methanol were used. 

[0203] Ammonium salt was dissolved in 10 to 20 mL methanol, and the remaining methanol was used to suspend CO$_{3 }$$^{2}$-MgAl-LDH3. The experimental method was the same as Example 1. Reaction was performed by adding the metha› nol solution of ammonium salt in nitrogen gas flow while the solution was being agitated. The same procedure was fol› lowed with other ammonium salts. Although a large amount of CO$_{2 }$was found in outlet nitrogen gas due to decarbonation in all of them (peak of discharged CO$_{2 }$ concentration: 2 to 5 minutes after addition), discharge of slight amount of CO$_{2 }$ was also found even after one hour. The reaction time was therefore defined as 1.5 hours. 

[0204] As in Examples 1 to 4, the obtained products were identified by FTIR and powder X-ray diffraction measure› ment, and MgAl-LDH3 containing anion of ammonium salt was confirmed to have been prepared in all of them. 

[0205] FIG. 20 shows the relation between the amount of ammonium salt added and the residual carbonate ion content, and change in weight, of the products obtained. [0206] In FIG. 20, (la), (lb), and (le) are curves respec› tively showing the change in weight ofNH$_{4}$ ClO$_{4}$ , NH$_{4}$ Cl, and NH$_{4}$NO$_{3}$ , and (2a), (2b ), and (2c) are curves respectively showing the change in the content of residual carbonate ions ofNH$_{4}$ClO$_{4}$ , NH$_{4}$Cl, and NH$_{4}$NOy 

[0207] As shown in FIG. 20, the residual carbonate ion content in the obtained products decreased to 5% or lower by the addition of ammonium salt of the amount of f=2 to 3, except when ammonium nitrate was used. The residual car› bonate ion content was 12% or lower when ammonium nitrate was used. If value f was increased to 3 or higher, no significant change in the residual amount was found. 

[0208] The weight of the products obtained increased until value f reached 3, because molecular weight increased due to substitution of anions. No change in weight was found even if the amount of addition was 3 or higher and up to 6, and thus weight loss considered to result from dissolution was not found at all. 

[0209] From the above, it was found that the residual car› bonate ions were mostly lost, and that no weight loss occurred 

## Example 9 

due to addition of excessive amount of ammonium salt, when the amount of addition was f=2 or larger. 

[0210] To examine the change in weight in long-time reac› tion, reaction was made to occur in nitrogen gas flow under f=5 condition for 1.5 hours using NH$_{4}$ Cl, NH$_{4}$ ClO$_{4}$ , and NH$_{4}$NO$_{3}$ , and after sealing in nitrogen for 5 days, the prod› ucts were taken out and their weight was measured. No dif› ference was found between the weight of the product taken out in 1.5 hours and that of the product taken out in 5 days. Weight loss by dissolution was thus not found. 

[0211] Experiment was conducted by mixing ammonium salt and hydrochloric aid. The amount ofHCl was f=0.7 5, and that ofNH$_{4}$Cl wasf=l. WhenHCl (f=0.75) andNH$_{4}$Cl (f=l) were used independently, carbonate ions were found to be remaining by 25% and 50% respectively. However, when they are used in combination, the amount of residual carbon› ate ions was 3% or lower. 

[0212] Experiment was conducted using ethanol, instead of methanol. NH$_{4}$Cl (f=3) was added and reaction was per› formed for 2 hours, and the same results were obtained as in the case of methanol. 

[0213] For comparison, decarbonated water was used, instead of methanol, to conduct experiment of causing reac› tion to occur using NH$_{4}$Cl under f=S condition, the largely excessive addition condition, for 3 hours. The amount of residual carbonate ions was 91 %, meaning that they had rarely been substituted by c1-, decarbonation was not found, and CO$_{2 }$ was not found in outlet nitrogen gas. 

[0214] Experiment was conducted using NH$_{4}$Br, whose anion is Br-, as another ammonium salt. Reaction was made to occur for one hour in methanol (f=3). A large amount of CO$_{2 }$ was found in outlet nitrogen gas due to decarbonation, and the amount of residual carbonate ions in the product Br-MgAl-LDH3 was as low as 3%. 

## Alkylamine Hydrochloride-Methanol System; MgAl-LDH3 

[0215] Using alkylamine hydrochloride represented as R$_{1}$NH(3-J)•HC1, a compound of alkylamine, which is weak base, and hydrochloric acid, decarbonation was made to occur in a methanol solution. R in the alkylamine hydrochlo› ride used represents methyl group and ethyl group. Specifi› cally, methylamine hydrochloride ((CH$_{3}$)NH$_{2}$ .HC1), dim› ethylamine hydrochloride ((CH$_{3}$ ) $_{2}$NH.HC1), trimethylamine hydrochloride ((CH$_{3}$ ) $_{3}$N.HC1), ethylamine hydrochloride ((CH$_{3}$CH$_{2}$)NH$_{2}$ .HC1), diethylamine hydrochloride ((CH$_{3}$CH$_{2}$) $_{2}$NH.HC1), and triethylamine hydrochloride ((CH$_{3}$CH$_{2}$ ) $_{3}$N.HC1) were used. 

[0216] CO$_{3 }$$^{2}$-MgAl-LDH3 was used as the starting mate› rial, and the amount of addition was represented by value f. For example, since H, one of the components ofHCl, is only protic molecule, one proton was considered to be supplied from the acid salts represented by these chemical formulae. Value f is represented as follows: f=[H+]/(2x[CO$_{3 }$$^{2}$-])= [R$_{1}$NHC3:1)•HC1]/(2x[CO$_{3 }$ 2 -]). 

[0217] 100mgofCO$_{3 }$$^{2}$-MgAl-LDH3 and 50mLofmetha› nol were used. Amine acid salt was dissolved in 10 to 20 mL of methanol, and the remaining methanol was used to suspend CO$_{3 }$$^{2}$-MgAl-LDH3. The experimental method was the same as Example 9, but the experiment was conducted at f=3. 

[0218] As a result, in all the experiments conducted using the amine acid salt shown above, the carbon dioxide concen- 

## Example 10 

