Composition containing divalent manganese ion and method for preparing the same

Abstract: There is provided a composition containing divalent manganese and a method for preparing the compound. The compound is stable but has good activity and reactivity to be able to use as a deodorizer.

Description: BACKGROUND OF THE INVENTION (1) Field of the Invention This invention relates to a composition containing a divalent manganese ion and a method for preparing said composition. (2) Description of the Prior Art Manganese takes several oxidation forms, such as divalent, trivalent, tetravalent, hexavalent, and heptavalent. In particular, permanganate, in which manganese takes a heptavalent state, exhibits high oxidation power, resulting in it being extensively utilized as an agent for chemical synthesis, analysis, and the like. Unfortunately, permanganate involves colored property and some safety concerns, due to its high oxidation power. Accordingly, it is disadvantageous in that when it is to be used in the home, it must be carried on a substrate, such as activated carbon. The most stable of the manganates contain a divalent manganese ion. However, the reactivity of the divalent manganate is low, so that its use range is quite restricted. For example, in a fixing reaction, due to the formation of manganese sulfide by reacting sulfide in the category of an odorous material such as hydrogen sulfide, methyl mercaptan, methyl disulfide, or the like with a divalent manganese compound, the ion-dissociation of the sulfide is increased as its pH changes from neutrality to alkalinity, such that it is necessary to provide the sulfide with a base effect. However, this causes its divalent manganese ion to be insoluble, leading to the formation of manganese hydroxide while exhibiting a chelate effect, which thereby does not contribute to its reactivity. JP-A-63.12 723 discloses an aqueous solution comprising a divalent metal ion such as manganese and an organic acid such as malic acid. The known solution is used for deodorising a synthetic acrylic fibre. Further, CA-A-1 186 425 concerns an aqueous medium comprising, for example, 1 ppm Mn II and 100 ppm isoascorbic acid and ascorbic acid, respectively. The known medium is used for scavenging dissolved oxygen from boiler feed water. Finally, EP-A-0 147 464 discloses an aqueous solution or a solid substance comprising Fe II and ascorbic acid for use as a deodorant or functional food. There has, however, still been a need for an improved oxidation resistant divalent manganese composition. BRIEF SUMMARY OF THE INVENTION The object of the present invention is to provide a novel manganese composition capable of exhibiting improved stability and safety and high reactivity while eliminating the above-described disadvantage of a conventional manganese compound. The above and other objects, features, and advantages of the invention will become apparent in the following detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graphic representation showing relationships between a manganese (II)-ascorbic acid composition and its ammonia-adsorption capability (Comparative Example), and Fig. 2 is a graphic representation showing relationships between a manganese (II)-citric acid composition and its ammonia-adsorption capability. DETAILED DESCRIPTION OF THE INVENTION The inventor, in working to achieve the above-described object, found that the addition of ascorbic acid to manganese (II) at an optimum ratio followed by the addition of citric acid, which readily forms a water-soluble complex in cooperation with manganese (II), thereto for the purpose of further improving a chemical reactivity of manganese (II) and maintaining stability of a manganese (II) composition, leads to a composition that exhibits better reactivity and can be effectively used for removing odor. The present invention has been made in view of the above facts. The problem underlying the invention is solved by an oxidation resistant divalent manganese composition comprising divalent manganese ion and ascorbic acid and citric acid or their salts, wherein the mole ratio of ascorbic acid and citric acid or their salts to the divalent manganese ion is in the range of 0.1:1.0 to 1.0:1.0. Preferred embodiments are covered by claims 2 to 8. The problem underlying the invention is further solved by a method for preparing a composition containing divalent manganese comprising mixing ascorbic acid or their salts and citric acid or their salts in an aqueous solution of divalent manganese ion, wherein the mole ratio of ascorbic acid and citric acid or their salts to the divalent manganese ion is in the range of 0.1:1.0 to 1.0:1.0. Prefered embodiments are covered by claims 10 to 15. The molar ratio of the acid ingredient ((L,D-) ascorbic acid and citric acid to the manganese (II) salt or compound is preferably 0.25 : 1.0 to 0.75 : 1.0. Preparation of such a composition may be carried out by adding a suitable amount of the acid ingredient to an aqueous solution of the manganese (II) and dissolving the former in the latter. The manganese (II) compounds suitable for use in the present invention include both inorganic and organic manganese (II) compounds. Water-soluble manganese (II) salts such as, for example, manganese (II) chloride, manganese (II) nitrate, manganese (II) sulfate, manganese (II) acetate or manganese (II) thiocyanate may be used for this purpose. A concentration of an aqueous solution of the manganese (II) salt is not limited to a specific range as long as the concentration is included in the range of its solubility. However, it is preferably in the range of 10 to 25% by weight. Ascorbic acids that may be used as the acid ingredient added to the aqueous manganese (II) solution in the present invention include L-ascorbic acid, which is generally known as vitamin C. D-ascorbic acid is referred to as D-araboascorbic acid or D-erythrobic acid, and it is often used for various purposes because it is readily synthesized, although it exhibits poor physiological activity compared with vitamin C. D-ascorbic acid likewise may be used as the acid ingredient in the present invention. These ascorbic acids each may be used in the form of its alkali metal salt, such as sodium and potassium ascorbate, or its ammonium salt. Further, citric acid may be used in the form of, for example, its alkaline metal salts or its ammonium salts. Citric acid forms coordinate bonding or chelate bonding with manganese (II), resulting in a composition stable in an aqueous solution. Such use of the citric acid in combination with the ascorbic acid causes a solution of the manganese (II) composition to satisfactorily react with sulfide ions in a gas-liquid contact reaction for contacting the solution with odorous gas in air, even when the pH of the solution is in the acid region, resulting in the removal of a sulfur-containing material. Such function of the solution is promoted corresponding to neutral fixing of ammonia. In the present invention, when NaCℓ or KCℓ is added in an amount of, for example, 3% to 7% by weight to the solution, the ion dissociation is retarded by being accompanied with the increase of ion density, and the oxidation of ascorbic acid due to the dissolved oxygen in the aqueous solution is also retarded to improve the stability of the solution. Further, the addition of a reducing agent such as Na₂S₂O₄, Na₂SO₃, and Na₂S₂O₃ in an amount of, for example, 0.1% to 0.2% by weight to the solution of the present invention is effective to prevent its stability from deterioration which is caused by the presence of an oxidative material. In particular, the reducing agent is excellent in preventing the oxidation of ascorbic acid. The amount of addition below 0.1% is less effective, and when it exceeds 0.2% a negative effect such as generation of gas occurs. Use of the manganese (II) composition of the present invention is not limited to any specific form. It may be used in the form of its solution. Alternatively, it may take a solid form, which may be obtained by spray-drying or lyophilization. The solid composition may be used in a manner to be mixed with resin or carried on a porous substrate such as paper, activated carbon, or the like by impregnation. The amount of the composition to be carried on the substrate by impregnation may be suitably varied depending on its application. The amount of the composition used in the form of a solution is generally in a range of 10-70% by weight, although it is varied depending on its application. The mechanism of the reaction by the manganese (II) compound of the present invention has not been made clear. However, it is supposed that, for example, a reaction of the compound with sulfide would be carried out in such a manner that a chelate compound of manganese (II) takes in an oxygen molecule from air and then converts it into active oxygen, so that sulfide caught by the manganese (II) may be oxidized with the active oxygen. A composition free of manganese (II) and consisting of only the acid ingredients, fails to exhibit such a function because of its weak acidity. In the composition of the present invention, it is not necessary that the manganese (II) ion component bonds with the acid components from the beginning as long as they bond to each other when the composition is used. Thus the composition of the present invention embraces a sole mixture of the components not bonded to each other. In order to cause the composition of the present invention to more efficiently carry out the reaction, water preferably coexists. For the same purpose, a small amount of alcohol may be added. The manganese (II) composition of the present invention exhibits satisfactory stability, activity, and reactivity. Such featured properties of the composition permit it to be used most preferably as a deodorizer capable of removing, for example, ammonia, trimethylamine, sulfides, such as hydrogen sulfide, methyl mercaptan and methyl disulfide. It is known that a certain metal complex is substantially colored and deteriorated in stability due to oxidation by oxygen molecules in the air. However, the composition of the present invention is substantially free from discoloration and deterioration in performance, even when it is left standing in the form of a solution for as long as about two months. Also, it does not cause any change in color, even when it is dried. Further, the composition is not substantially colored even after it reacts with a smelly material. Thus, it will be noted that the composition of the present invention exhibits the noteworthy advantage that it is free from coloring even when it is used as an impregnating material or substrate. The manganese (II) composition of the present invention that exhibits such properties as described would be extensively used as not only a substrate for removing odors, but as a culture medium for bioindustries, as a functional food agent for human consumption, as a catalyst for oxidation of organic substance, and as a material for an industry in which manganese (II) is used as a raw material. In such applications, the adjustment of the pH of the composition of the present invention from 2 to 6 by the addition of weak alkali causes the advantage of the composition to be more promoted, because the dissociation of sulfide may be readily carried out. The invention will be described in further detail referring to examples. Comparative Example 1 A manganese (II) sulfate solution containing 11.5 g of MnSO₄·4-5H₂O in 200 mℓ of the solution was prepared and L-ascorbic acid was dissolved in the solution in amounts of 0 to 8.80 g,based on 200 mℓ of the solution, to prepare various solutions containing differing manganese (II) composition. A water-absorbent paper (20 g) of size 255 mm x 80 mm x 13 mm and a honeycomb-like structure was impregnated with each of the so-prepared solutions to obtain impregnated papers. Then the impregnated papers were air-dried to cause the composition to be carried on the paper in an amount of 43 to 52 percent by weight based on the weight of the paper and the dry solids content. Each impregnated paper was suspended in a test box having a volume of 0.12 m³, and then gas having an ammonia concentration of about 200 ppm was circulated in the box at a rate of 1.2 m³/min. The concentration of ammonia in the box after ten minutes was measured as an initial concentration, and that after thirty minutes was measured as a residual concentration. The results are shown in Fig. 1 . As is apparent from the results in Fig.1 , it is indicated that the composition consisting of only manganese (II) sulfate failed to exhibit a satisfactory reactivity to ammonia, but the composition in which ascorbic acid coexists was increased in reactivity. More specifically, the addition of ascorbic acid in an amount as small as 0.1 mol caused the ammonia-removing function of the composition to be improved. Such improvement was noteworthy when ascorbic acid was added in an amount of 0.25 to 0.75 mol. Example 1 A manganese (II) sulfate solution containing 11.5 g of MnSO₄·4-5H₂O in 200 mℓ of the solution was prepared as in Comparative Example 1. Then, L-ascorbic acid was added to the solution in an amount of 0.5 mol, based on mol of manganese, to prepare a solution (Solution A). To Solution A was added citric acid, which is an oxypolybasic acid, in amounts 0-1.25 mol based on manganese to prepare a series of solutions varying citric acid-concentration (A series). Concurrently, an aqueous solution containing only manganese (II) sulfate (Solution B) was prepared, and then citric acid was added thereto in amounts of 0-1.25 mol, based on manganese to prepare another series (B series) of solutions of varying concentration of citric acid. Then a honeycomb-like water absorbent paper was impregnated with each of the so-prepared solutions and air-dried, to obtain impregnated papers as in Comparative Example 1. A deodorizing test was carried out using an apparatus and under conditions similar to Comparative Example 1, except that the initial ammonia concentration was set at 400 ppm which is twice that used in Comparative Example 1, because it was expected that more amount of ammonia would be adsorbed compared with Comparative Example 1. The results are shown in Fig. 2 , which clearly indicates that the coexistence of ascorbic acid exhibited satisfactory effects at a region in which the amount of addition of the complex-forming agent to manganese (II) is small, resulting in the ammonia-removing ratio of the composition to be highly improved compared with that obtained due to the ammonia-neutralizing effect of citric acid. Example 2 11.5 g of manganese (II) sulfates tetra- or hepta-hydrate and 4.4 g of ascorbic acid (a molar ratio of 0.5 to manganese) were added to and dissolved in 200 mℓ of water, and then 5.25 g of citric acid was added thereto to obtain a 20% active manganese (II) aqueous solution. The solution was stored, in place of water, in an ultrasonic humidifier (100V, 45W, manufactured by Koshin Co. (Japan)) so that the humidifier was used as an atomizer for atomizing the active manganese (II) solution. Then the atomizer was placed in a closed container of size 500 mm x 900 mm x 480 mm and volume 0.22 m³ equipped with an internal agitating fan, and then hydrogen sulfide gas of a predetermined concentration was fed into the container at a rate of 1.8 m³/min to carry out a contact reaction between the atomized active manganese (II) solution and the hydrogen sulfide gas in the container, during which treated gas was discharged from the container through an outlet, and the concentration of hydrogen sulfide in the gas was measured. The operation was carried out while setting the indicator of the humidifier at a maximum value "9" on the scale, which means that the rate of consumption of the solution was about 40 mℓ/hr. The operation was continuously carried out for eight hours, wherein the initial concentration of hydrogen sulfide was set at 1800 ppm, 900 ppm, and 350 ppm, and the concentration of hydrogen sulfide at the outlet is shown an average value. Initial Concentration of H₂S (ppm) Outlet Concentration of H₂S (ppm) Removal Ratio (%) 1800 67.5 96.1 900 20.1 97.7 350 0.0 100.0 Thus, it will be noted that the composition of the present invention substantially completely treat hydrogen sulfide gas having an initial concentration as high as 500 ppm.

Claims: An oxidation resistant divalent manganese composition comprising divalent manganese ion and ascorbic acid and citric acid or their salts, wherein the mol ratio of ascorbic acid and citric acid or their salts to the divalent manganese ion is in the range of 0.1 : 1.0 to 1.0 : 1.0. The composition as claimed in claim 1, wherein the divalent manganese ion comes from the compound selected from the group consisting manganese (II) chloride, manganese (II) nitrate, manganese (II) sulfate, manganese (II) acetate, and manganese (II) thiocyanate. The composition as claimed in claim 1, wherein the composition is in the form of solution. The composition as claimed in claim 3, wherein the concentration of divalent manganese compound in the solution is in the range of 10 to 25% by weight. The composition as claimed in claim 1, wherein the composition is a solid form. The composition as claimed in claim 5, wherein the composition is mixed with resin. The composition as claimed in claim 5, wherein the composition is carried on a porous substrate. A chemical product selected from a deodorant, a culture medium, a functional food and a catalyst for oxidation of organic substance which comprise the composition according to claim 1. A method for preparing a composition containing divalent manganese comprising mixing ascorbic acid or their salts and citric acid or their salts in an aqueous solution of divalent manganese ion, wherein the mol ratio of ascorbic acid and citric acid or their salts to the divalent manganese ion is in the range of 0.1 : 1.0 to 1.0 : 1.0. The method as claimed in claim 9, wherein the aqueous solution of divalent manganese ion is prepared by dissolving one or more water-soluble inorganic or organic divalent manganese compound in water optionally comprising a small amount of alcohol. The method as claimed in claim 10, wherein the divalent manganese compound is selected from a group consisting manganese (II) chloride, manganese (II) nitrate, manganese (II) sulfate, manganese (II) acetate, and manganese (II) thiocyanate. The method as claimed in claim 10, wherein the concentration of divalent manganese compound in the solution is in the range of 10 to 25%. The method as claimed in claim 9, wherein citric acid is used in the form of an alkaline metal or ammonium salt thereof. The method as claimed in claim 9, wherein one of compound of NaCℓ or KCℓ is added to the aqueous solution to prepare the composition. The method as claim in claim 9, wherein a reducing agent is added to the aqueous solution to prepare the composition.

Inventors: IKARI YOSHIKATSU, IKARI, YOSHIKATSU
Applicants: BIOX CORP, IKARI YOSHIKATSU, BIOX CORPORATION, IKARI, YOSHIKATSU
Application year: 1989
Main classification: C01G45
IPC codes: C01G45, A61L9, C07C51, B01D53, C07D307, C07F13, C07C59, C07C67