Jan.  23,  2014  5  US  2014/0021404 Al  (3) Metal salt (MX$_{2 }$ or MX$_{3}$ )  generating the protic acid (HX)  by hydrolysis.  [0080]  The anion (X-) is preferably chlorine ion (Ci-),  bromine ion (Br-), nitrate ion (NO$_{3 }$ -),  perchlorate ion  (ClO$_{4}$-), chlorate ion (ClO 3  -), and acetate ion (CH $_{3}$Coo-). X  in general formula (2) represents corresponding atom, which  is released as anion (X-) in aqueous solution, and protic acid  (HX) is desirably HCl, HBr, HNO$_{3}$ ,  HC1O$_{4}$ ,  HC1O$_{3}$ ,  or  CH$_{3}$COOH. However, it is only necessary that the protic acid  is monovalent anion, and anions other than those listed above  are not excluded regardless of whether they are organic or  inorganic.  [0081]  R, R’, and R" of the amine acid salt (NRR’R".HX)  are groups respectively represented by composition formula  C,HpOq  (t=0 to 6, p=l to 13, q=0 to 2).  [0082]  Of the amine acid salt used in Examples, three are  selected to show how they are represented by this composi› tion formula.  [0083]  When all ofR, R’, andR" satisfyt=q=0and p=l, the  formula becomes NH$_{3}$ .HX, which represents ammonium salt  such as NH$_{4}$Cl and NH$_{4}$ClO$_{4}$ .  [0084]  When R satisfies t=2, p=5, and q=0, and both R’ and  R" satisfy t=q=0 and p=l, the formula becomes C$_{2}$H$_{6}$NH$_{2}$ .  HX, which represents diethylamine hydrochloride, one of  amine acid salts, when X=Cl.  [0085]  When both Rand R’ satisfy t=2, p=5, and q=l 1, and  R" satisfies t=q=0 and p= 1, the formula becomes C$_{2}$H$_{5}$ONH.  HX, which represents diethanol hydrochloride, one of amine  acid salt, when X=Cl.  [0086]  Specifically, R, R’, and R" are hydrogen, hydroxyl  group or organic group. Here, organic group means alkyl  group having carbon number of 1 to 6 substituted by alkyl  group or hydroxyl group having carbon number of 1 to 6.  [0087]  Metal salt Mis one of the following metals: divalent  Zn, Mg, and Ca, and trivalent Fe and Al. However, metal salts  other than those listed above are not excluded, provided that  they generate acid in an aqueous solution.  [0088]  Substituting carbonate ions contained in LDH by  anions means that value b in formula (1) becomes larger than  value b of the starting material. When all the carbonate ions  have been substituted by anions  ex-) completely, the obtained  anion-exchanging LDH is represented by general formula (3)  shown below:  [0089]  In formula (3) shown above, a represents numeric  value range of 1.8sas4.2, z is 2(a+l),  Q represents divalent  metal. T represents trivalent metal, X represents an atom that  turns into monovalent anion, and n represents the amount of  water existing between layers. n changes within the following  range depending on the humidity of the atmosphere: 0sns5.  [0090]  The anion-exchanging LDH represented by general  formula (3) has high anion-exchanging property. General  formula (3) is a chemical formula typically representing a  case where ion exchange into anions (X-) has been completed  most perfectly. By relaxing reaction conditions, partial sub› stitution into anions ex-) occurs, thus naturally generating a  chemical compound containing residual carbonate ions.  [0091]  A case where complete substitution product is prac› tically not required and a case where partial substitution is  practically necessary are included in the scope of the present  invention. Specifically, it is only necessary that in formula (1 ),  b increases to become larger than value b of the starting  material and reach the desired value, and  Qa  T(OH)$_{2}$ ex-).  nH$_{2}$O need not be strictly maintained.  [0092]  Supplemental description of anion-exchanging  LDH will be given below. Generally, in an aqueous solvent,  ions having large valence number (multivalent anions such as  divalent and trivalent anions) or small-size ions have low  anion-exchanging property. On the contrary, monovalent  anions are known to have high anion-exchanging property.  The larger the size of the ions, the higher the anion-exchang› ing property. In the present invention, X of the anion-ex› changing LDH represents one of the following anions: chlo› rine ion (Ci-), bromine ion (Br-), nitrate ion (NO$_{3 }$ -),  perchlorate ion (ClO$_{4 }$-), chlorate ion (ClO 3  -), and acetate ion  (CH$_{3}$Coo-). Since all of these are monovalent anions and  large in size, affinity to LDH is low, and the LDH containing  these has high anion-exchanging property. Consequently,  anions other than those described above are not excluded,  provided that they satisfy the similar conditions.  [0093]  Organic solvents having carbon number of 1 to 4,  such as alcohols, acetone, tetrahydrofuran, are desirable.  [0094]  As alcohols, methanol, ethanol, n-propanol, i-pro› panol (2-propanol), n-butanol, and t-butanol can be used  desirably. Since organic solvents having carbon number of 1  to 4 can be handled easily, are easily available, have high  volatility and low boiling points, solvents can be removed  easily after reaction. In addition, since there is no possibility  that carbon dioxide in the air dissolves, thereby generating  carbonate ions, secondary incorporation of carbonate ions  between LDH layers does not occur.  [0095]  In an organic solvent containing an acidic com› pound, the amount of the acidic compound is calculated based  on the amount of carbonate ions (CO$_{3 }$ 2 -) existing in carbon› ate ion-type LDH as the starting material. Since CO$_{3 }$ 2 - has a  valence of -2, the amount of H+ (proton) required to com› pensate it completely is twice the molar quantity of the car› bonate ions, namely f=[H+]/(2x[CO$_{3 }$ 2 -]), which is inter› preted as valence-to-valence conversion.  [0096]  In the case of amine acid salt, value f was deter› mined, assuming that one proton was released from NRR’R".  HX. In the case of acidic metal salt, value fwas determined,  assuming that HX of a number of m were generated from  MXm by hydrolysis. Since the minimum requisite for 100%  substitution of co/- is f=l not only with the amount of  protons but also with the amount of anions ex-) existing in the  system, theoretically f must be 1 or higher to achieve com› plete substitution.  [0097]  In an aqueous solvent, weight loss starts to occur  before carbonate ions are substituted by other anions com› pletely. Meanwhile, since dissolution of LDH is suppressed  more in an organic solvent than in an aqueous solvent, ion  exchange occurs before weight loss starts to occur.  [0098]  In the case of decarbonation using protic acid and  alcohol, acidic compound of f=l or higher is necessary for  complete substitution. However, if the amount of acid is  excessive, LDH dissolves even in alcoholic solvent, thus  causing weight loss. The degree of weight loss varies depend› ing on the type of the alcohol and the acidic compound and  water content, but generally, when f=l to 2, decarbonation is  completed successfully without dissolution of LDH. In the  case of decarbonation using amine acid salt and alcohol, f=2  to 3 is required, but since acidity is low, weight loss due to  dissolution is not observed even if excessive amount of f=6 is  added.  (3)  [Chemical formula 10] 