Composition for gas purification and method of preparing same

A composition for gas purification, comprising a reaction product of at least one metal selected from the group consisting of iron, manganese, chromium, nickel, zinc, aluminum, copper, tin and cobalt, and alloys containing these metal elements, with at least one oxypolybasic acid, wherein the metal co-exists therein while in an unreacted state.

TECHNICAL FIELD 
The present invention relates to a composition for gas purification, which 
composition can be used as an air purification material for purifying 
polluted air containing harmful gases such as nitrogen oxides (NOx), 
sulfur oxides (SOx), and ozone (O.sub.3) gas; and odorous gases including 
nitrogen compound type gases such as ammonia (NH.sub.3); sulfur compound 
type gases such as hydrogen sulfide (H.sub.2 S); carboxylic group type 
gases such as acetaldehyde; and carboxylic acid (lower fatty acid) type 
gases such as acetic acid; or as a purification material for a combustion 
exhaust gas or harmful gas. The composition of the present invention also 
can be used as a food freshness retaining agent. The invention also 
relates to a method of preparing the composition. 
BACKGROUND ART 
The concentrations of NOx gases, SOx gases, and O.sub.3 gas in the air must 
be lowered, and to prevent the generation of such gases, various 
combustion devices, gas purification devices, and chemical treatment 
devices are employed. Nevertheless, a method of efficiently removing these 
harmful gases with the use of simple equipment such as an air cleaner has 
not been generally realized. 
Nitrogen compound type gases and sulfur compound type gases in the air are 
accompanied by objectionable odors, which are usually eliminated by the 
adsorption method using activated charcoal, a masking method using 
perfumes, and a chemical method in which a chemical reaction among the 
odorous gases is carried out. These deodorants of the prior art, however, 
have a problem in that the deodorizing ability thereof is lost within a 
short time. 
Senigakkaishi (Seni to Kyoto) Vol. 42, No. 12 (1986), pages 18 to 26, 
states that a complex compound obtained by the reaction between an Fe (II) 
compound and ascorbic acid in the form of a solution is able to deodorize 
nitrogen compound type odorous gases. Nevertheless, to the knowledge of 
the present inventors, such a complex compound has a weak ability for 
deodorizing sulfur compound type odorous gases, and although nitrogen 
compound type odorous gases are deodorized by adsorption by the complex 
compound, the amount adsorbed is limited, and therefore, a problem arises 
in that the deodorizing ability is lost within a short time, and further, 
it can not be practically applied to a gas other than ammonia. Further, 
such a complex compound is powderized by distillation or vacuum drying, 
but the preparation steps are complicated and the cost is high, because 
such compounds as FeSO.sub.4, FeCl.sub.2, and Fe(NO.sub.3).sub.2 are 
employed as the Fe (II) compound. The powdery form must be carried on, for 
example, zeolite, and the method of using the same is also complicated. 
Further, although the adsorption type or chemical reaction type 
purification agent of the prior art can remove a part of the gases 
(depending on molecular size or readiness of the reaction), it cannot 
remove other gases, and thus it becomes necessary to use a plurality of 
purification filters to separately remove the respective gases. 
To purify air, there is a need to provide an air purification material 
which can remove harmful NOx gases, SO.sub.2 gas and O.sub.3 gas, and 
further can remove carboxylic group type gases, carboxylic acid type 
gases, nitrogen compound type gases, and sulfur compound type gases, which 
are accompanied by objectionable odors. Also, there is a need for the 
development of a purification material having a large absorption capacity 
when removing harmful gases contained in the exhausted gases of internal 
combustion engines, objectionable odors, and harmful gases generated by 
chemical plants, etc. In the present specification, the ability to remove 
all of these harmful gases and objectionable odors is hereinafter referred 
to as air purification power. 
There is also a need to develop an air purification material which can 
exhibit a strong air purification power even when used over a long term. 
Further, for example, an air purification material is needed which can 
remove harmful gases or objectionable odors without the need for 
complicated treatments such as distillation and vacuum drying, etc., and 
an air purification material which is not powdery is most preferable 
because it is easily handled. 
DISCLOSURE OF THE INVENTION 
An object of the present invention is to provide a composition for gas 
purification which can be used as an air purification material which 
solves the problems of the prior art and satisfies the respective 
requirements mentioned above. 
Therefore, according to the present invention, there is provided a 
composition for gas purification comprising a reaction product of at least 
one metal selected from the group consisting of iron, manganese, chromium, 
nickel, zinc, aluminum, copper, tin and cobalt, and alloys containing 
these metal elements, with at least one oxypolybasic acid, wherein said 
metal is not completely reacted and remains while co-existing therein. 
The present inventors further found that the composition of the present 
invention is excellent as a food freshness retaining agent, and thus the 
present invention provides a composition for gas purification which is not 
limited only to providing purified air.

BEST MODE OF CARRYING OUT THE INVENTION 
The present inventors found that, when the reaction between iron and 
ascorbic acid is carried out without the use of Fe (II) compounds such as 
FeSO.sub.4, FeCl.sub.2 or Fe(NO.sub.3).sub.2, and dried in the air, iron 
and ascorbic acid react with oxygen and moisture components in the air to 
give a reaction product having a strong gas or air purification power 
(hereinafter sometimes called air purification power) which can remove 
substantially all gases such as sulfur type compounds, nitrogen type 
compounds, lower fatty acids, SOx, NOx, and O.sub.3. The inventors also 
found that, if an excessive amount of iron is used, such that unreacted 
iron remains, the iron and the above-mentioned reaction product co-exist, 
and consequently, the purification power of the reaction product is 
regenerated through the reaction of the oxygen and moisture components 
with iron, whereby a strong air purification power can be exhibited over a 
long term. Further, when a large number of acids similar to ascorbic acid, 
oxypolybasic acids, and acids having an OH group and COOH group are used, 
the effects of the purification power were different. Particularly, it was 
found that citric acid, tartaric acid and gluconic acid form reaction 
products having a strong air purification power similar to that of 
ascorbic acid. As oxypolybasic acids other than the above, which can be 
used in the present invention, for example, there are included malic acid, 
mannonic acid, xylonic acid, and tartaric acid. The above-mentioned 
ascorbic acid, citric acid, tartaric acid, gluconic acid, and other 
oxypolybasic acids may be used as a mixture of two or more kinds thereof, 
to give reaction products having a strong air purification power. 
(Hereinafter, in the present specification, one or a mixture of acids 
selected from ascorbic acid, citric acid, tartaric acid and gluconic acid 
may be sometimes referred to as "ascorbic acid, etc.".) 
The present inventors further found that, when a reaction between manganese 
and ascorbic acid is carried out, in place of iron as the metal, a 
reaction product with an even stronger air purification power can be 
obtained. Particularly, by using manganese instead of iron, the 
deodorizing power with regard to hydrogen sulfide type odorous gases is 
markedly improved. When an alloy of iron and manganese is used, such as a 
mixture of iron particles and manganese particles, an improvement of air 
purification power corresponding to the manganese content is exhibited. In 
the present specification, although iron and manganese only are 
particularly disclosed any reference to other metals means alloys or 
mixtures thereof. 
The present inventors made a further investigation by varying the kinds of 
metals, and as a result, it appears that the metals of Cr, Ni, Zn, Al, Cu, 
Sn, and Co have an air purification power, and further, a purification 
power regeneration effect with air. Note, Ni and Al are equal to Fe and 
Mn, but Cr, Zn, and others are slightly inferior thereto. 
An example is shown in the following Table, in which the data was obtained 
by placing, in a 40-liter sealed box, 40 g of the co-existing product of 
the metal and the reaction product obtained by adding L-ascorbic acid to 
the respective metal powders having a size of 44.mu. at a molar ratio of 
0.2, and kneading with water followed by drying, measuring the NH.sub.3 
removal ratio each time the initial NH.sub.3 concentration became 2000 
PPM, and thereafter, leaving the co-existing product of the metal and the 
reaction product of the metal with ascorbic acid to stand in the air for 
10 hours and again performing similar tests, to investigate the activity 
regeneration effect of the co-existing product. 
______________________________________ 
After 5 After 10 After 20 After 30 
minutes minutes minutes minutes 
______________________________________ 
Ni after first 
76.8% 89.1% 97.5% 98.4% 
left to stand 
79.7% 93.5% 98.2% 98.8% 
Al after first 
82.6% 93.5% 98.2% 99.0% 
left to stand 
92.7% 96.7% 98.8% 99.5% 
Cr after first 
62.3% 74.6% 92.8% 96.4% 
left to stand 
41.3% 49.3% 63.0% 72.5% 
Zn after first 
85.5% 90.2% 93.1% 95.7% 
left to stand 
57.5% 58.4% 74.2% 80.0% 
Mn after first 
78.0% 90.5% 98.0% 99.0% 
left to stand 
80.0% 94.0% 98.5% 99.8% 
______________________________________ 
The present invention has been accomplished on the basis of the findings 
mentioned above, and the composition for gas purification of the present 
invention is a composition containing a reaction product of one or two or 
more metals of Fe, Mn, Cr, Ni, Zn, Al, Cu, Sn and Co, and alloys thereof, 
with an oxypolybasic group, wherein unreacted metal remains therein while 
co-existing therewith. 
The metal to be used in the present invention is not required to have a 
high purity, and metals containing usual impurities can be used. The 
composition of the present invention can be simply produced, because a 
complicated chemical engineering treatment such as distillation or vacuum 
drying is not required. In the present invention, if the metal is prepared 
in a shape that enables an easy practical purification operation, it is 
not required to be carried on zeolite, etc., and a composition having a 
shape enabling an easy use thereof can be formed. 
The air purification action of the composition of the present invention is 
described as follows. In the present specification, the description is of 
iron and/or manganese as representative examples of the metal (iron and/or 
manganese are hereinafter abbreviated as iron, etc.), but other metals 
give the same or similar effects. If the base material is iron and, for 
example, manganese, is plated or flame sprayed thereon, iron coated with 
manganese is obtained, and according to the same method, manganese coated 
with iron can be produced. In the present specification, "iron, etc." 
includes these double-layer moldings of iron and manganese. As described 
later, the composition of the present invention is prepared by, for 
example, bringing iron, etc., into contact with ascorbic acid, etc., 
followed by drying. Due to this contact, the surface and crystal grain 
boundary of iron, etc., are subjected to corrosion or grain boundary 
corrosion by the ascorbic acid, etc., to thereby generate fine 
unevennesses that enlarge the surface area thereof. Further, with an 
elapse of time, the reaction proceeds and the number of cracks increases, 
thereby increasing the surface area of the iron, etc. The corroded surface 
is covered with the reaction product of iron, etc., and ascorbic acid, 
etc., (assumed to exist in the state where [OH] is coordination bonded to 
Fe.sup.++ in a complex to form a chain). 
Namely, the reaction product may be assumed to be as follows: 
##STR1## 
FIGS. 1 (a) and (b) are photographs of the metal structure; FIG. 1 (a) is 
an electron microscope photograph (magnification: .times.1000) showing the 
state after a treatment of 100.mu. iron powder with 2M L-ascorbic acid, 
followed by drying, and FIG. 1 (b) is a photograph (magnification: 
.times.1000) showing the state after NH.sub.3 gas absorption and leaving 
in the air have been repeated 40 times. 
The composition of the present invention has a broad surface area between 
the iron, etc., and the reaction product, and therefore, the chemical 
reaction between the iron, etc. and the reaction product as described 
below proceeds smoothly. Further, the reaction product is inserted into 
the grain boundry, to thereby exhibit an anchoring effect, and the 
regeneration effect can be exhibited because the reaction product is kept 
in close contact with the iron, etc., and cannot be detached therefrom. 
The present inventors estimate the gas purification mechanism of the air 
according to the present invention to be as described below. 
(1) The nitrogen compound type gas (e.g. NH.sub.3) is primarily bonded to 
the reaction product on the metal surface through a coordination to 
Fe.sup.++ in the above-mentioned reaction product, to become an ammine 
complex. 
EQU Reaction product+NH.sub.3 .fwdarw.dehydroascorbic acid-Fe.sup.++ 
(NH.sub.3).sub.2 
(2) Regarding the NH.sub.3 adsorbed on the metal surface of the reaction 
product, with active iron existing immediately beneath the reaction 
product as the catalyst, the reaction of a part of Fe(OH).sub.2 in the 
complex and oxygen in the air with NH.sub.3 in the ammine complex occurs 
as follows, to partially regenerate the reaction product: 
EQU O.sub.2 +NH.sub.3 .fwdarw.N.sub.2 +H.sub.2 O 
(3) The active iron works as a reducing agent in the presence of oxygen and 
moisture components in the air, whereby the cyclic mechanism of a redox of 
dehydroascorbic acid becomes valid. 
EQU Dehydroascorbic acid+Fe reduction.fwdarw.Regenerated ascorbic acid 
(4) The ascorbic acid as generated above reacts with iron and oxygen and 
moisture components in the air, and acts as an oxidizing agent such as 
NOx, SO.sub.x, O.sub.3, etc., to decompose harmful gases while forming a 
new reaction product, to thereby form active oxygen. 
Regenerated ascorbic acid+oxidizing agent and moisture component.fwdarw.New 
reaction product+S and N+active oxygen 
(5) Carboxylic group type gases (e.g., acetaldehyde), NH.sub.3, and H.sub.2 
S are oxidatively decomposed by this active oxygen. 
EQU O+R--CHO, NH.sub.3, H.sub.2 S.fwdarw.R--COOH (e.g., acetic acid), N.sub.2, 
S, and H 
(6) The acetic acid formed as above (or other lower fatty acids) is fixed 
with a solid base. 
(7) A part of H.sub.2 S undergoes the following reactions, due to the 
catalytic reaction thereof with iron oxide in the presence of a solid 
base: 
EQU H.sub.2 S.fwdarw.HS.sup.- +S.degree., HS.sup.- .fwdarw.H.sup.+ +S.degree.. 
As long as metal iron precipitated by the decomposition exists, this 
regeneration mechanism remains valid, and ascorbic acid causes a corrosive 
reaction toward the central portion of the metal while persistently 
maintaining the purification effect, and thus it can be considered that 
corrosion cracking proceeds microscopically in the metal, to thereby 
increase the surface area of the reaction product, and thus the gas 
purification effect of air, etc., can persist over a long term. 
According to the second embodiment of the present invention, a composition 
further comprising a solid base incorporated in the above-described 
composition is provided. Here, the solid base includes, for example, CaO, 
Ca(OH).sub.2, Na.sub.2 CO.sub.3, NaHCO.sub.3, MgO, Mg(OH).sub.2, and 
MgCO.sub.3, and refers to one which does not become an aqueous solution 
when formulated in the composition according to the first embodiment as 
described above. According to the knowledge of the present inventors, 
since the reaction product is dissolved if the base becomes an aqueous 
solution, to thereby lower the effect, a solid base is added to fix the 
place of the reaction of the composition according to the above-described 
embodiment, whereby the deodorizing power with regard to hydrogen sulfide 
type odorous gases can be markedly improved, and the fixing ability of low 
fatty acids is also improved. The addition of the solid base can be made 
by, for example, directly spraying powder of the above-mentioned solid 
base or spraying (or dipping) the same as a mixture with a rapid drying 
organic solvent when the constituents of the composition of the first 
embodiment of the present invention are almost dry or after the drying. 
This stage is shown in the photograph of FIG. 2 (electron microscope 
photograph of the reaction product of iron and ascorbic acid sprayed with 
Ca(OH).sub.2 powder, impregnated with ethyl alcohol, followed by drying, 
magnification +1000). The amount of the solid base formulated is 
preferably an amount sufficient to fix the place of the reaction, as the 
best effect is obtained if the place of the reaction is fixed (PH&gt;7.0). 
Since the reaction product has a pH of 4.0 to 5.5, the amount added is 
preferably 1% to 10% of the weight of the contacted product. 
The present inventors have prepared the compositions of the first and 
second embodiments of the present invention by using the various metal 
powders and oxypolybasic acids shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Metal powder 
Average Oxypolybasic acid 
Method 
particle 
Metal Mole of mixing 
Addition mixing 
No. 
Kind size components 
Kind rates *1 
contact *2 
of solid base 
__________________________________________________________________________ 
1 pig iron powder 
10.mu. 
Fe: 93% 
L-ascorbic acid 
0.01 A Mg(OH).sub.2 powder 10% *3 
2 scale reduced 
30.mu. 
Fe: 95% 
Tartaric acid 
0.01 B Ca(OH).sub.2 powder 30% *3 
iron powder 
3 Fe--Mn alloy 
50.mu. 
Fe: 30% 
Citric acid 
0.10 C -- 
powder Mn: 65% 
4 Manganese are 
5.mu. 
Fe: 10% 
L-ascorbic acid 
0.10 A -- 
reduced powder 
Mn: 80% 
Citric acid 
5 FeSO.sub.4 powder 
50.mu. 
Fe: 32% 
L-ascorbic acid 
0.10 D Mg(OH).sub.2 powder 10% 
__________________________________________________________________________ 
*3 
*1: mole ratio of ascorbic acid, etc., to metal 
*2: A . . . metal powder added to aqueous solution of ascorbic acid, etc. 
mixed and dried 
B . . . metal powder sprayed onto aqueous solution of ascorbic acid, 
etc., mixed and dried 
C . . . mixed powder of ascorbic acid, etc. and metal powder dried at 
80.degree. C. and 100% humidity. 
D . . . aqueous solution of ascorbic acid added to FeSO.sub.4 powder 
and dried 
*3: amount of solid base added based on ascorbic acid, etc. (% by weight) 
sprayed in mixture with alcohol and dried 
The deodorizing powers of the respective compositions were measured by the 
deodorizing measuring device shown in FIG. 3. In FIG. 3, 1 is an odorous 
gas holder, 2 a sample capsule, and 3 a flowmeter. An NH.sub.3 gas or 
H.sub.2 S gas was employed as the odorous gas. In FIG. 3, each 1 g of the 
respective powders in the above Table 1 was charged into the sample 
capsule 2, the flow of the NH.sub.3 gas or H.sub.2 S gas 4 was controlled 
at a rate that provided a concentration of 100 ppm, and the equilibrium 
adsorption amount was measured from the analytical value of the sample 
capsule outlet gas 5. The results are shown in Table 2. In Table 1 and 
Table 2, No. 5 is a Comparative example, which is a complex compound 
obtained by the reaction between FeSO.sub.4 and ascorbic acid as a 
solution. As shown in Table 2, the composition of the present invention 
has a life 10- to 100-fold greater than that of the Comparative example. 
Regarding the H.sub.2 S gas, Examples No. 1 and No. 2 of the second 
embodiment of the present invention have a stronger deodorizing power than 
Examples No. 3 and No. 4 of the first embodiment of the present invention. 
TABLE 2 
______________________________________ 
Equilibrium adsorption amount (wt, %) 
No. NH.sub.3 gas 
H.sub.2 S gas 
Remarks 
______________________________________ 
1 10.0% 8.0% Composition of 2nd embodiment 
2 10.0% 6.0% Composition of 2nd embodiment 
3 15.0% 3.0% Composition of 1st embodiment 
4 20.0% 5.0% Composition 1st embodiment 
5 1.0% 0.1% Comparative Example 
______________________________________ 
Next, ascorbic acid was added to 10.mu. iron powder at a molar ratio of 
0.2, then water was added followed by drying by evaporation. Each 5 g of 
the powder and a mixture of the powder mixed with 3% by weight of powdery 
Ca(OH).sub.2 was coated onto defatted cotton, for a deodorizing test of 
NH.sub.3 and H.sub.2 S. The results are as shown in the graphs in FIG. 4 
and FIG. 5. The deodorizing test was carried out by introducing the gas 
into a 40-liter sealed box, and then placing the defatted cotton in the 
box, and circulating the air in the box by a fan. 
In the preferred embodiment of the present invention, for example, the 
co-existing product of the reaction product and the iron, etc., is formed 
together with the ascorbic acid, etc., at a mole ratio of 0.005 to 0.5 
relative to the iron, etc. 
The present inventors prepared various compositions according to the 
present invention, while using different ratios of iron and ascorbic acid, 
by adding ascorbic acid having a 3 mole concentration to iron powder of 
10.mu. in various amounts and at mole ratios of between 0 and 0 followed 
by evaporation drying 100.degree. C. Each 1 g of the respective 
compositions was charged into the sample capsule 2 in FIG. 3, and a flow 
of a 100 ppm ammonia gas was directed into the capsule, to determine the 
amount of ammonia removed. The results are shown in FIG. 6. When the mole 
ratio of (ascorbic acid weight parts)/(iron part weight parts) exceeds 
0.5, less ammonia is removed, but as shown in the photographs in FIG. 7 
(a) and (b), when the ratio is 0.5 or more, the composition assumes the 
form in which iron powder is embedded in the ascorbic acid (see FIG. 7 
(a), whereby any contact with the gas becomes difficult. On the other 
hand, when the mole ratio is 0.5 or less, a reaction product is formed 
around the iron powder (see FIG. 7 (b)), whereby the composition has a 
form in which a good contact with the gas can be obtained. The composition 
has a required ammonia removing power even if the mole ratio of (ascorbic 
acid weight parts)/(iron powder weight parts) is 0.005. This tendency 
shown in FIG. 6 also occurs in the case of the composition according to 
the second embodiment of the present invention. 
The present inventors determined the air purification power of the present 
invention by using the device shown in FIG. 8, wherein 6 is the 
composition of the present invention formed into a filter, which is 
prepared from a sintered product of a three-dimensional network with a 
void diameter of 2 mm comprising 80% of iron and 20% of manganese by using 
3 parts by weight of ascorbic acid based on 100 parts by weight of said 
sintered product, and the total weight of the filter 6 is 40 gr, and 7 is 
a polluted air chamber having a volume of 1 m.sup.3. Various polluted airs 
are introduced into the polluted air chamber 7, as described later, 
through the introducing inlet 8, and after the introducing inlet 8 is 
closed the polluted air within the polluted air chamber 7 is circulated in 
the direction indicated by the arrows 10 by a circulation pump 9 having a 
capacity of 1 m.sup.3 /min. Note, 11 is a gas sample collecting outlet. 
FIGS. 9 (a) to (d) are graphs showing the results of the above tests. FIG. 
9 (a) shows an example of polluted air containing 23 to 36 ppm of SO.sub.2 
before the treatment; FIG. 9 (b) is an example of polluted air containing 
10 to 20 ppm of NO.sub.2 ; FIG. 9 (c) is an example of polluted air 
containing 1 to 3 ppm of acetaldehyde; and FIG. 9 (d) is an example of 
polluted air containing 1 to 3 ppm of O.sub.3. As can be seen from FIGS. 9 
(a) to (d), SO.sub.2, NO.sub.2, acetaldehyde, and ozone in polluted air 
were decomposed after 10 to 30 minutes, to a residual ratio of 0, to thus 
provide clean air. 
The present inventors also determined the deodorizing performance of 
ammonia gas and hydrogen sulfide gas, by using the device shown in FIG. 8. 
As the filter 6 in this case, the employed composition 6-1 was obtained by 
treating the sintered product of iron in the form of a three-dimensional 
network with ascorbic acid, and further, formulating Ca(OH).sub.2 therein 
by using ethanol, and the employed composition 6-2 was obtained by 
treating a double-layered sintered product of a sintered iron in the form 
of a three-dimensional network covered by sintering with manganese, with 
ascorbic acid, and formulating Ca(OH).sub.2 therein by the same method. 
The Comparative Example is a filter of activated charcoal having the same 
size. The results are shown in Table 10. FIG. 10 (a) shows an example 
where NH.sub.3 gas was used, and FIG. 10 (b) shows an example where 
H.sub.2 S gas was used. The deodorizing ratio was calculated as (gas 
concentration before treatment--gas concentration after treatment)/(gas 
concentration before treatment). Compared with the filter of the 
Comparative Example, the filters 6-1 and 6-2 of the present invention 
exhibited a stronger deodorizing ratio. It is also obvious that the filter 
6-2 using manganese has a stronger deodorizing power than the filter 6-1 
using iron alone. 
The present inventors exposed the above-mentioned filters (6-1, 6-2, 
activated charcoal) to 100% NH.sub.3 or 100% H.sub.2 S for 24 hours, and 
then the air, to bring them into contact with oxygen and moisture 
components in the air, for 24 hours to regenerate the reaction product, 
followed by the same deodorizing test by using the same device. The 
results are shown in FIG. 11 (a) and (b). The filters 6-1 and 6-2 of the 
present invention were regenerated with air to an extent such that they 
showed a better deodorizing power than initially shown but the deodorizing 
power after regeneration of the activated charcoal was zero. 
Therefore, the composition of the present invention is also useful as a 
material for cleaning exhausted gases and harmful gases. When a test was 
conducted by setting the three-dimensional network iron-manganese sintered 
porous body (30 mm.phi..times.50 mm) at the rear end of an automobile gas 
exhaust system, NOx and SOx in the exhausted gas were substantially 
completely removed. 
When a test was conducted by setting a porous body of the same quality as 
described above at the exhaust vent of a denitrification plant (NH.sub.3 
gas/V.sub.2 O.sub.5 catalysis type) of a boiler-discharge gas disposal 
equipment in a power plant, the term of use of the V.sub.2 O.sub.5 
catalyst was extended from 2 years to 4 years, because undecomposed 
NH.sub.3 was absorbed by the porous body. 
The composition of the present invention is also useful as a food freshness 
retaining agent, and as evidence of this, the present inventors sprayed 
the compositions of examples No. 1 to 5 in Table 1 over the inner walls of 
a 20-liter corrugated box, placed samples inside the corrugated box, and 
compared the freshness retainment of the samples at room temperature 
(20.degree. C.). The results are shown in Table 3. Material No. 5 is a 
Comparative example, and is a prior art material considered to have a food 
freshness retaining power. 
TABLE 3 
______________________________________ 
Freshness Food freshness 
Sample material 
retaining agent 
retentivity 
______________________________________ 
Spinach No. 1 in Table 1 
Discolored partially 
brown on day 10 
No. 5 in Table 1 
Discolored partially 
brown on day 9 
-- Discolored partially 
brown on day 4 
Strawberry 
No. 2 in Table 1 
Mold partially generated 
on day 5 
No. 5 in Table 1 
Mold partially generated 
on day 6 
-- Mold partially generated 
on day 2 
Pork No. 3 in Table 1 
Rotten odor generated 
on day 4 
No. 5 in Table 1 
Rotten odor generated 
on day 4 
-- Rotten odor generated 
on day 2 
Saurel No. 4 in Table 1 
Gloss disappeared 
on day 3 
No. 5 in Table 1 
Gloss disappeared 
on day 3 
-- Gloss disappeared 
on day 1 
______________________________________ 
As can be seen from Table 3, Examples No. 1 to No. 4, which are composition 
of the present invention have a food freshness retaining power equal to 
that of Example No. 5, and can extend the freshness retaining term of the 
samples by about 2-fold, compared with the case when they are not used. 
The reason why the composition of the present invention has a food 
freshness retaining ability is not clear, but it can be considered that 
the generation of active oxygen, etc., as mentioned above, may make a 
contribution thereto. 
The gas purification composition according to the present invention can be 
prepared by using a molded product of iron, etc., prepared by plastic 
working, or a worked product of iron, etc., obtained by further subjecting 
the molded product to a secondary working. Plastic working refers to the 
plastic working generally employed in a hot or cold working such as hot 
rolling, cold rolling, extrusion, drawing, and forging, etc. The secondary 
working is a working in which a further plastic working, cutting or 
bonding is applied to these molded products, i.e., preparing, for example, 
a vessel, net, honeycomb, or fiber. The use of these methods enables 
products shaped as a plate, foil, wire, tube, net, honeycomb, fiber, or 
fine strip to be obtained inexpensively and easily. Specific methods of 
causing a contact with ascorbic acid, etc., are described in detail below. 
The present inventors subjected an iron foil having a plate thickness of 
30.mu. to hardening by tempering at a temperature of 800.degree. C., to 
once extinguish the rolled composition and make it susceptible to grain 
boundary corrosion, then acid washed the surface layer with an aqueous 10% 
HCl solution for 30 minutes, and thereafter, dipped the foil in an 
ascorbic acid solution of 1 mole concentration for 30 minutes, followed by 
drying in the air at 100.degree. C., to form a reaction product on the 
surface of the iron foil. Further, a mixture of methanol and Na.sub.2 
CO.sub.3 was sprayed onto the surface to prepare a composition comprising 
an iron foil with a surface pH of about 8, as the base material. Using 
this composition as the honeycomb material shown in FIG. 12, a deodorizing 
cylinder shown in FIG. 12 with a diameter of 10 cm and a length of 10 cm 
was prepared and stood in a toilette for domestic use for one year, in 
which period no odor was found. In FIG. 12, 12 is the composition of the 
present invention shaped in a honeycomb, and 13 the holding board thereof. 
The present inventors also dipped a metal net made of iron and having a 
mesh size of 1 mm in a solution of ascorbic acid of 2 mole concentration 
for 10 minutes, to form a reaction product on the surface of the metal 
net, which was then dried at room temperature to form a composition in the 
shape of a net. The net-shaped composition was placed as a lining on the 
inner surface of a 20-liter volume corrugated box and fresh foods shown in 
Table 4 were placed inside the box, and maintained at room temperature, to 
determine the freshness retaining power. 
TABLE 4 
______________________________________ 
Spinach Strawberry 
Pork Saurel 
______________________________________ 
Ascorbic 
Discolored 
Mold Rotten odor 
Gloss 
acid treated 
partially partially generated 
disappeared 
wire net 
brown generated on day 4 on day 3 
on day 10 on day 5 
-- Discolored 
Mold Rotten odor 
Gloss 
partially partially generated 
disappeared 
brown generated on day 2 on day 1 
on day 4 on day 2 
______________________________________ 
As can be seen from Table 4, the corrugated box lined with the net-shaped 
composition of the present invention was found to have a freshness 
retaining power about 2-fold that of conventional deodorizers and 
freshness-retainers. 
Next, the method of preparing the composition of the present invention by 
using a powder of iron, etc., or a molded product using a powder of iron, 
etc., is explained. According to this method, the powdery iron, etc., is 
allowed to react with ascorbic acid to obtain a powdery co-existing 
product wherein the surface of powder is the reaction product and the 
inner material of the powder is unreacted iron. FIG. 13 shows an example 
of a co-existing product prepared by mixing iron powder, etc., having an 
average particle size of 50.mu., and 0.10 mole of ascorbic acid, followed 
by natural drying. In FIG. 13, 14 is a reaction product formed in the 
shape of a tortoise shell on the inner portion 15 of iron. 
When powdery iron, etc. having a different particle size is employed, a 
finer powder will become the reaction product also of the inner material, 
but the inner material of a coarse powder will be unreacted iron, etc., 
and therefore, a powdery co-existing product is obtained. The compositions 
of the present invention of Examples No. 1 to No. 4 shown in Table 1 and 
Table 3 are examples of the powdery compositions prepared according to 
this method. 
Further, the powder of iron, etc., can be kneaded by an appropriate binder 
to form a kneaded product, to thereby provide molded products having 
various shapes. As the binder to be used for this purpose, there can be 
employed inorganic binders such as water glass, cement, and bentonite, and 
organic binders such as CMC, polyacrylate, and methylcellulose. As the 
molding method, there can be employed an extruder, rolls, pelletizer, or 
injection molding machine. According to this method, rod-shaped products, 
such as spherical, cylindrical, hollow, and polygonal shapes, strip-shaped 
products, particle-shaped products, and mass-shaped products can be 
prepared. In the above-mentioned method, these molded products are placed 
in contact with the ascorbic acid, etc., to prepare co-existing products 
of the reaction product of the iron, etc., with the ascorbic acid. 
The powder of iron, etc. also can be carried on a metallic or non-metallic 
carrier by using a binder to form a molded product. For example, the 
powder of iron, etc., can be coated on the surface of glass spheres or 
organic polymeric spheres to form a spherical molded product. As the 
organic polymeric sphere, organic polymeric spheres subjected to a foaming 
treatment, for example, styrene expanded foam (manufactured by Sekisui 
Kagaku K.K.), Expancellplastic fine hollow sphere (manufactured by Japan 
Ferrite K.K.), Epoxyballoon (manufactured by Emerson Cumming Co.), etc., 
can be subjected to a foaming treatment (heating treatment with vapor and 
hot water) before use to provide organic polymeric spheres with an 
apparent specific gravity of 0.30 or less. The use of the organic 
polymeric spheres subjected to the foaming treatment enables the provision 
of lightweight and spherical molded products. These molded products can be 
brought into contact with the ascorbic acid, etc., to provide the 
co-existing product of the present invention. 
FIG. 14 shows an example of the spherical composition of the present 
invention prepared according to this method, in which 18 is an organic 
polymeric sphere, 16 is the reaction product of ascorbic acid, etc., with 
iron, etc., and 17 is unreacted iron, etc. 
As the carrier, for example, a porous body having three-dimensionally 
communicating pores, such as urethane foam, etc., can be used. For 
example, when the iron powder, etc., is coated on the skeleton of urethane 
foam, a porous molded product having three-dimensionally communicating 
pores wherein the skeleton is covered with the iron powder, etc., is 
obtained, and the porous product also can be brought into contact with 
ascorbic acid, etc., to prepare a co-existing product. The use of an 
organic three-dimensional fabric (manufactured by Kabushiki Kaisha Arisawa 
Seisakusho), instead of the urethane foam, enables a porous molded product 
having three-dimensionally communicating pores to be similarly obtained. 
As other carrying methods, those having metal powder carried on synthetic 
resins, such as metal mixed spun fibers, metal mixed foamed materials of a 
synthetic resin starting material (e.g., polyurethane, polyester, 
polystyrene) supplemented with a metal and subjected to a mixing synthetic 
treatment to form fibers and foams also can be used and treated with 
ascorbic acid, etc., to give the desired co-existing product. 
The co-existing product which is a rod-shaped product, strip-shaped 
product, particle-shaped product, or mass-shaped product, as previously 
mentioned, or the co-existing product prepared by using spherical bodies 
of, for example, organic polymeric spheres coated on the surface with the 
powder of iron, etc., also can be housed in an air permeable housing 
vessel to be used as the filter for air purification, but the composition 
using the co-existing product produced from the porous molded product 
having three-dimensionally communicating pores requires no housing vessel, 
and thus has an advantage in that it can be used as such as a filter for 
air cleaning. 
The molded products of the compositions of the present invention which may 
be carried on carriers include all molded products and molded products 
carried on carriers. 
Further, as a method of carrying the iron, etc., the iron, etc. can be 
carried on organic and inorganic materials by electrolytic, electroless 
plating. The molded product can be treated with ascorbic acid, etc., to 
obtain the co-existing product of the present invention. As such an 
organic material, a synthetic or fibrous urethane foam, etc., can be used, 
and as the inorganic material, glass, etc., can be used. 
The composition of the present invention can be prepared by molding powder 
or particles of iron, etc., placed in contact with ascorbic acid, etc., 
such as the powdery product or the particulate product shown in FIG. 13, 
by using a binder, or by molding the same when carried on a metallic or 
non-metallic carrier. The same binder, molding method, and carrier as 
described above can be used as the binder, the molding method, and the 
carrier in this method. FIG. 15 shows an example of the co-existing 
product in FIG. 14 when carried on organic polymeric spheres, wherein 21 
is an organic polymeric sphere, 19 unreacted inner material of iron 
powder, etc., and 20 the reaction product. The composition prepared by 
using the co-existing product prepared in the example shown in FIG. 14 has 
a broad active surface area, and therefore, when the spherical composition 
is filled in a large number of air-permeable housing vessels and used as a 
filter for air cleaning, a filter with a high air purification efficiency 
can be obtained. In FIG. 15, 22 is an example of the flow passage of 
polluted air in the above case. 
The composition of the present invention can further form a sintered 
product of iron, etc., which is brought into contact with ascorbic acid, 
etc., to prepare a co-existing product. Namely, a molded product having a 
large unevenness, large surface area, and many micro- and macro-voids with 
which gases can be easily and completely brought into contact can be 
readily obtained by sintering. When a co-existing product is prepared by 
using such a molded product, the area at which the reaction product comes 
into contact with the iron, etc. is broad and has micro- and macro-voids 
which exhibit an anchoring effect, and thus the reaction product is 
brought into close contact with the metal such that it is not easily 
detached therefrom, and further, the area of contact between polluted air 
and the composition is broad, and therefore, the activity of the gas 
purification material is maintained and a superior carrier is provided. 
An iron powder to be used for the sintered product and containing, for 
example, 2.0 to 4.5% by weight of carbon, can be readily pulverized, and 
an iron powder with an average particle size of 50.mu. or less can be 
prepared easily and economically by a dry process pulverization or wet 
process pulverization. 
The iron-manganese alloy powder can be prepared by, for example, 
pulverizing ferromanganese. 
The manganese powder can be obtained by pulverizing metallic manganese or 
reducing manganese ore. 
The oxidized iron powder can be obtained by boiling iron powder containing 
2.0 to 4.5% of carbon, in boiling water, to produce an oxidized iron 
powder having an oxidized surface and further, as the oxidized iron powder 
per se a powder obtained during, for example, the iron steel steps in an 
iron plant can be used. 
The oxidized manganese powder can be obtained by pulverizing manganese ore, 
or treating a powder of manganese carbonate. 
The carbon powder can be obtained by, for example, pulverizing a graphite 
electrode, or by using a fine powdery coke. 
The composition of the present invention can be prepared by further adding 
Si, Ni, Cr, Mo, Cu, and Al, etc., thereto, which elements may be added as 
a metallic powder, or iron containing these metals can be pulverized and 
added. Si, Ni, Cr, Mo, Cu, and Al, etc. are added to improve the strength, 
heat resistance, and corrosion resistance of the sintered product. 
In accordance with the present invention, the respective powders as 
mentioned above are blended and kneaded with a binder. As the binder, 
inorganic binders such as water glass, cement, and bentonite, etc., or 
organic binders such as CMC and polyacrylate, etc., can be used. By 
controlling the particle size of the respective powders to 50.mu. or less, 
the kneaded product obtained by kneading can be easily molded as is or 
molded when carried on a carrier. 
The kneaded product can be molded into a molded product having the same 
shape as mentioned above, by using an extruder, rolls, pelletizer or 
injection molding machine. The kneaded product also can be molded into a 
molded product by being coated on and carried at the surface of the same 
organic polymeric spheres as mentioned above. 
According to the present invention, the molded product is subsequently 
sintered. Conventionally, the molded product obtained by working molding 
can be subjected to a sintering heat treatment to provide a sintered 
product corresponding to the shape of the molded product. In the molded 
product carried on organic polymeric spheres, the organic polymers will be 
eliminated by pyrolysis at 400.degree. C. during the sintering, and will 
become a hollow spherical sintered product. 
The temperature and time for sintering must be controlled in accordance 
with the mixing ratio of the starting material metals such as Fe and Mn, 
but the macro-void ratio in the sintered composition after sintering has a 
great influence on the air purification efficiency. According to tests by 
the present inventors, as shown in FIG. 16, this efficiency is greatly 
lowered at a void ratio (void area/whole area of field of vision 
.times.100 at a microscope magnification of .times.200) of 15% or less. 
This is considered to be due to the fact that sufficient acid is not 
carried on the sintered product, and that the surface area becomes 
smaller. The void ratio can be freely controlled by controlling the 
above-mentioned sintering temperature and adding a pyrolyzable powder, as 
described later, to the kneaded product. Note, it is a specific feature of 
a sinterable metal that the void ratio thereof can be controlled. 
According to the present invention, when preparing powdery starting 
materials, the carbon and oxygen therein can be controlled as shown in the 
following formula, to prepare a sintered product: 
EQU [C]&gt;2.1% 
EQU 4/3 ([C]-2)&lt;[O]&lt;4/3 ([C]+7) 
where 
[C]: carbon content in powdery starting material (wt.%) 
[O]: oxygen content in powdery starting material (wt.%). 
If [C] in the powdery starting material is greater than 2.1%, co-crystals 
of iron and Fe.sub.3 C will be formed and the liquid phase sintering 
easily effected. 
FIG. 17 is a graph showing the influences of [O] and [C] in the powdery 
starting material on the properties of the sintered product. By 
controlling the components as shown in the above-mentioned formula, the 
sintered product prepared is free from heat distortion cracking, and 
further, a sintered product with a high toughness can be obtained. 
Further, the sintered product using the powdery starting material 
containing [C] and [O] of the above-mentioned formula generates CO gas and 
CO.sub.2 gas from [C] and [O] through a self-reduction reaction during 
sintering, and a large number of micro-bubbles remain after the degassing 
of CO gas and CO.sub.2 gas in the sintered product. The sintered product, 
therefore, has a large surface area having macro- and micro-bubbles, and 
when later brought into contact with ascorbic acid, etc., the ascorbic 
acid, etc. penetrates the small pores to further broaden the contact area 
with the reaction product, to thereby provide a composition with a good 
reactivity. The composition also has large area in contact with polluted 
air, and this is an efficient air purification material. 
FIGS. 18 (a) and (b) show the surfaces of the sintered product of the 
sintered product where the [C] and [O] has been thus controlled, in which 
23 is a small bubble after degassing of CO gas and CO.sub.2 gas, and 24 is 
a matrix after sintering. 
According to the present invention, when preparing the thus sintered 
product, a pyrolyzed product which generates a gas during sintering is 
added to the powdery starting material. Therefore, by increasing the 
surface area of the sintered product, increasing the contact area between 
the iron, etc., and the reaction product, or increasing the contact area 
between the composition and the polluted gas, an air purification material 
with an even stronger air purification power can be obtained. To increase 
the surface area of the sintered product, an organic material such as 
plastic powder and sawdust, etc., or a carbonate such as limestone powder 
and dolomite powder, etc., are effective when added. In the case of an 
organic material, a pyrolysis occurs at 200 to 400.degree. C., but a 
carbonate powder is pyrolyzed at 900.degree. to 1100.degree. C. and traces 
of the liberated gases remain as voids on the surface of the sintered 
product. FIG. 19 shows an example of a sintered product having such voids, 
in which 24 is the matrix after sintering, and 25 is a void. When the 
sintered product is brought into contact with the ascorbic acid, etc., due 
to the large surface area thereof, a composition having a higher activity 
can be obtained. 
According to the present invention, the above-described sintered product 
can be formed as a plate, tube, hollow particle, or mass, etc. 
As described above, when molding the kneaded product with a binder to form 
the powdery starting material, a plate-shaped product can be obtained by, 
for example, roll molding, a tube-shaped product can be obtained by, for 
example, extrusion molding, and a particle-shaped molding can be obtained 
by, for example, pelletizing, and when sintered these molded products are 
produced as sintered products having the shape of a plate, a tube, or 
particles. A hollow particulate sintered product, as already described, 
can be obtained by sintering the kneaded product on the surface of organic 
polymeric spheres; a mass product can be obtained by preparing and then 
crushing a large sintered product. 
In another example of the present invention, the co-existing product can be 
prepared by bringing the sintered product into contact with the ascorbic 
acid, etc., but if the substrate is a sintered product it is not easily 
broken, and therefore, is most suitable as an air purification element 
which purifies polluted air by passing the air through a large number of 
elements housed in an air-permeable housing vessel. 
In another example of the present invention, the composition can be 
prepared as the shaped sintered products described above, while obtaining 
a sintered product having three-dimensionally communicating pores. 
The composition using a porous sintered product having three-dimensionally 
communicating pores does not require an air-permeable housing vessel, and 
can be arranged as such in, for example, a polluted air pathway, and by 
passing polluted air therethrough, for example, NOx, SOx and odorous 
components contained in the polluted air can be decomposed during the 
passage therethrough and the air made clean. 
An example of the method of preparing such a sintered product having 
three-dimensionally communicating pores is specifically described as 
follows. 
The first example comprises a kneaded product of the powdery starting 
material and a binder coated on the skeleton of an organic 
three-dimensional porous body. As the organic three-dimensional porous 
body, a urethane foam or an organic three-dimensional fabric as mentioned 
above can be employed. It is difficult to coat the powdery starting 
material with an average particle size of 50.mu. or more on the skeleton 
of the organic three-dimensional porous body, and thus the coating of the 
kneaded product is performed by a roll squeeze method, the spraying method 
or dipping method. By heating the organic three-dimensional porous body 
coated with the kneaded product at 300.degree. to 350.degree. C. for 2 to 
3 hours, the organic polymer will be eliminated by pyrolysis, to effect 
defatting. Further, by heating to 800.degree. to 1200.degree. C. for about 
60 minutes, the coated kneaded product is sintered to obtain a sintered 
product comprising a sintered skeleton having three-dimensionally 
communicating pores. The carbon contained in the powdery starting material 
reduces the metal oxides during the sintering. 
The present inventors prepared an iron powder (C: 4.0%, O: 6.4%, Mn: 0.38%, 
Si: 0.1%, P: 0.01%, S: 0.02%, balance: Fe) having an oxidized surface and 
an average particle size of 10.mu., by pulverizing a powdery iron (C: 
4.3%, Si: 0.1%, Mn: 0.4%, P: 0.01%, S: 0.02%, balance: Fe) by the wet 
process, and boiling the powder in boiling water. The iron powder was 
kneaded with CMA and water, and coated onto a urethane foam with a void 
diameter of 2 mm, by the spraying method, and subjected to heat treatments 
for drying (100.degree. C.), defatting (200.degree. C.), self-reduction 
(800.degree. C.), and sintering (1100.degree. C.) in a nitrogen 
atmosphere, to prepare a sintered porous body having three-dimensionally 
communicating pores. An enlarged view of the appearance thereof is shown 
in FIG. 20. 
The present inventors also formed a kneaded product similar to that 
described above and coated the same on urethane foam, and after drying, 
further applied another coating of a kneaded product obtained by kneading 
metallic manganese powder having an average particle size of 5.mu., a 
plastic powder having an average particle size of 10.mu., at a volume 
ratio of 50% with CMC and water. Thereafter, the same heat treatment as 
described above was applied to form a double-layered sintered porous body 
having three-dimensionally communicating pores, with the inner layer 
comprising iron and the outer layer comprising a highly porous manganese. 
FIG. 21 shows an enlarged view of the appearance of this product. 
In FIG. 20 and FIG. 21, 26 is the skeleton of the sintered product, 27 is a 
pore formed after a degassing of CO and CO.sub.2 gases, 28 is a void 
formed after pyrolysis of the pyrolyzing agent, and a metallic powder gap, 
and 29 is the three-dimensionally communicating pore. 
The porous body having the three-dimensionally communicating pores shown in 
FIG. 20 and FIG. 21 was dipped in a 30% tartaric acid solution to prepare 
the co-existing product of the present invention, and together with the 
co-existing product as the final composition, it was employed as the 
deodorant in the device shown in FIG. 8. FIG. 10 and FIG. 11 are graphs 
showing the results, and as shown in FIG. 10 and FIG. 11, the composition 
was found to have a strong deodorizing power. In FIG. 10 and FIG. 11, 6-1 
is an example in which the sintered product in FIG. 20 is employed, and 
6-2 an example in which the sintered product in FIG. 21 is employed. 
As a three-demensional example, the sintered product having 
three-dimensionally communicating pores also can be prepared according to 
the method as described below. FIG. 22 illustrates the preparation steps 
thereof, wherein a mold frame 31 is filled with a large number of organic 
polymer spheres 30 and pressure applied to the upper portion thereof. This 
pressure brings the organic polymer spheres 30 into mutual contact with 
each other, and thus while under pressure at the upper portion, the 
kneaded product is permitted to flow into the voids within the mold frame 
31 and heat treated as such. This heat treatment causes the organic 
polymer spheres to be eliminated by pyrolyzation, to thereby form voids 
which are three-dimensionally communicating at the plane contact portion, 
whereby the kneaded product becomes a sintered product. 
FIG. 23 shows an example in which the organic polymer spheres 30 are 
mutually bonded with a pyrolyzable adhesive 32. In this case also, the 
kneaded product of the powdery starting material and the binder is 
permitted to flow into the voids and is heat treated, and the organic 
polymer spheres 30 and the adhesive 32 are eliminated by pyrolyzation to 
thereby form three-dimensionally communicating pores, whereby the kneaded 
product becomes a sintered product. According to the example shown in FIG. 
23, a sintered product having three-dimensionally communicating pores with 
quantitated voids can be obtained. Note, the sintered product having 
three-dimensionally communicating pores as mentioned above also includes 
the sintered products prepared in the examples shown in FIG. 22 and FIG. 
23. 
According to the present invention, when bringing the ascorbic acid into 
contact with the iron, preferably an aqueous solution of ascorbic acid 
having a concentration of 0.1 to 5 mole is used, and an aqueous solution 
of the iron is dipped in the aqueous solution and taken out and dried, or 
the aqueous solution is sprayed onto the iron and then dried, to prepare 
the composition of the present invention. 
In this case, when the aqueous solution of ascorbic acid has a 
concentration of less than 0.1 mole, the formation rate of the reaction 
product is slow, and further, the amount of reaction product becomes 
smaller. Conversely, when it exceeds 5 moles, a large amount of unreacted 
ascorbic acid will remain in the reaction product, whereby the reaction 
product is covered with unreacted ascorbic acid and the gas purification 
effect may be undersirably reduced. For example, if the ascorbic acid 
having a concentration of 5 moles or higher is placed in contact with the 
above-mentioned porous sintered product, the pores of the porous material 
may be clogged with the ascorbic acid. In this case, preferably the 
contact reaction is carried out with an aqueous solution having a molar 
ratio of 0.05 to 0.5 relative to the metal, followed by evaporation drying 
as such, to cause the reaction product to co-exist with the powder. 
According to the knowledge of the present inventors, products having a 
relatively large shape are preferably coated at a mole ratio of 0.1 to 5 
moles of the ascorbic acid relative to the metal, by the dipping method or 
the spraying method, and products with small shapes such as the powder are 
mixed at a mole ratio of 0.005 to 0.5 of the ascorbic acid, and dried as 
such, and the ascorbic acid placed in contact by such methods provides a 
co-existing product in which the reaction product is closely attached to 
the iron, etc. 
In accordance with the present invention, a composition shaped as a 
non-woven fabric is also provided. As already described, as the 
co-existing product of the iron and the ascorbic acid, products shaped as 
particles, foils, and fibers can be obtained. In these embodiments, by 
using the existing product and one or more fibers selected from synthetic 
fibers, glass fibers, natural fibers, cellulose, and carbon fibers, these 
fibers can be mixed to form a composition shaped as a non-woven fabric. 
Alternatively, after mixing or adhering these fibers to form a non-woven 
fabric, a solid alkali can be formulated on the surface to form a 
composition shaped as a non-woven fabric. The composition shaped as a 
non-woven fabric can be used as a filter for a simple air cleaning and 
dust collection, and further, as a food freshness retaining agent when 
coated on the inner surface of a corrugated board. 
According to another embodiment of the present invention, the product 
shaped as powders, foils, and fibers, which is a co-existing product of 
the iron and the ascorbic acid, can be formulated with a solid base and 
then mixed with one or more of synthetic fibers, glass fibers, natural 
fibers, cellulose fibers, and carbon fibers, to form a composition shaped 
as a non-woven fabric, and can be used for the same purposes as described 
above. 
According to another embodiment of the present invention, a composition 
shaped as a non-woven fabric can be obtained by a different preparation 
method. Namely, in this embodiment, one or more elements selected from a 
metal powder, a foil, fibers of the iron, and one or more fibers selected 
from synthetic fibers, glass fibers, natural fibers, cellulose fibers, and 
carbon fibers are bound together to form a non-woven fabric, the non-woven 
fabric is placed in contact with the ascorbic acid, and the metal powder, 
foil or fibers of the iron will form a co-existing product of the reaction 
product and the iron, by contact with ascorbic acid, to thereby provide an 
air purification product and food freshness retaining agent. In these 
embodiments, the diameter of the metal powder, the thickness of the foil, 
and the diameter of the fibers is preferably 1.mu. to 1 mm, and this 
dimension is particularly preferable for the formation of a non-woven 
fabric. By placing the ascorbic acid in contact with the non-woven fabric, 
and further, formulating a solid base on the surface thereof, the 
deodorizing power is strengthened against odorous gases such as sulfur 
compounds and lower fatty acids. The composition shaped as a non-woven 
fabric also can be used for the same purposes as described above. 
Industrial Applicability 
As described above, the composition having the gas purification power of 
the present invention can effectively remove harmful NOx gases, SOx gases, 
and O.sub.3 gas, and can be used for removing nitrogen compound type 
gases, sulfur compound type gases, and lower fatty acids, which are a 
source of objectionable odors. 
The composition having the gas purification effect of the present invention 
also retains a strong gas purification effect even when used over a long 
term. 
The composition having the gas purification effect of the present invention 
can be easily and simply prepared, at a low cost. 
The purification composition having the gas purification effect of the 
present invention further can be used as a food freshness retaining agent.