Molecular sieve abstract
A closable container in which is enclosed brominated carbonaceous
molecular sieve having micropores within the range of 4 to 6 Angstrom
units in diameter and a method for prolonging the shelf-lives of
green perishable foods and flowers by the use of said container.
Molecular sieve claims
What is claimed is:
1. A closable container in which is enclosed carbonaceous molecular
sieve which carries bromine as adsorbed thereon and has micropores
within the range of 4 to 6 Angstrom units in diameter.
2. A closable container according to claim 1 wherein said closable
container is made of material whose permeability to carbon dioxide
gas at 25.degree. C. is in the range of 5000 to 100000 ml/m.sup.2
/24 hours.
3. A closable container according to claim 1 wherein said carbonaceous
molecular sieve contains no less than 90% of carbon, no more than
3% of oxygen and no more than 1l % of hydrogen, and has a surface
area of 400 to 900 m.sup.2 /g, and no less than 80% of the total
volume of said micropores is accounted for by micropores of diameters
within the range of 4 to 6 Angstrom units.
4. A closable container according to claim 3 wherein the amount
of bromine adsorbed on said carbonaceous molecular sieve is 2 to
30 weight %.
5. A method for prolonging the shelf-lives of green perishable
foods or flowers which comprises enclosing a green perishable food
or flower and a carbonaceous molecular sieve, which carries bromine
as adsorbed thereon and has micropores within the range of 4 to
6 Angstrom units in diameter, in a closable container.
6. A method according to claim 5 wherein said closable container
is made of material whose permeability to carbon dioxide gas at
25.degree. C. is in the range of 5000 to 100000 ml/m.sup.2 /24
hours.
7. A method according to claim 5 wherein the amount of said carbonaceous
molecular sieve is in the range of 0.5 to 30 grams per kilogram
of said green perishable food or flower.
8. A method according to claim 5 wherein said carbonaceous molecular
sieve contains no less than 90% of carbon, no more than 3% of oxygen
and no more than 1% of hydrogen, and has a surface area of 400 to
900 m.sup.2 /g, and no less than 80% of the total volume of said
micropores is accounted for by micropores of diameters within the
range of 4 to 6 Angstron units.
9. A method according to claim 8 wherein the amount of bromine
adsorbed on said carbonaceous molecular sieve is 2 to 30 weight
%.
Molecular sieve description
This invention relates to a closable container in which is enclosed
carbonaceous molecular sieve which carries bromine as adsorbed thereon
and has micropores within the range of 4 to 6 Angstrom units (hereinafter
referred to as brominated carbonaceous molecular sieve) and to a
method for prolonging the shelf-lives of green perishable foods
or flowers by the use of said container.
The term "prolonging the shelf-lives of green perishable foods
and flowers" or any term equivalent thereto as used herein
means retarding the post-harvest ripening or spoiling of green perishable
foods, and maintaining freshness of them, and retarding the unfolding
of a flower bud as well as keeping the flower life as long as possible.
It has been a conventional practice to enclose a green perishable
foodstuff in a closed packaging material for the purpose of keeping
the foodstuff fresh during the storage or transit thereof. Since
the supply of endogenous oxygen into the package is then depressed,
the respiration of the green perishable foodstuff is suppressed
and, hence, the spoilage or staling thereof is somewhat retarded.
However, this method is not satisfactory altogether, for the ethylene,
which is known to be a promoter of the post-harvest ripening of
plant life, emanates from the green perishable foodstuff itself
to fill the internal space of the package and, thereby, to accelerate
changes in the color and a further ripening of the foodstuff. An
attempt has also been made to remove the ethylene by adsorption
by enclosing activated carbon within said closed package or container.
However, this method is not fully satisfactory, either. Moreover,
because in this method, the aromatic substances emanating from the
green perishable foodstuff are also removed by adsorption, the foodstuff
does not give off its characteristic aroma upon unpackaging, thus
detracting from the salability of the foodstuff.
The research undertaken by us for overcoming the above disadvantages
led us to the finding that by allowing a special carbonaceous molecular
sieve to be present in a closed package or container housing a green
perishable foodstuff or a flower, the over-ripening promoter ethylene
can be selectively removed by a process of adsorption without loss
of the intrinsic aroma of the foodstuff and flower, thus ensuring
a better prolongation of the shelf-life of the foodstuff and flower
than any of the prior art methods.
The brominated carbonaceous molecular sieve employed according
to this invention is prepared by causing bromine to be adsorbed
on a carbonaceous molecular sieve having micropores in the range
of 4 to 6 Angstrom units in diameter.
The aforesaid cabonaceous molecular sieve contains no less than
90 percent of carbon, no more than 3 percent of oxygen and no more
than 1 percent of hydrogen, has a surface area of 400 to 900 m.sup.2
/g and includes micropores such that no less than 80 percent of
the total volume of said micropores is accounted for by micropores
of diameters within the range of 4 t 6 Angstrom units. Such a special
carbonaceous molecular sieve can be prepared, for example by the
method described in Japanese Pat. No. 49-37036 that is to say by
adsorbing starting materials capable of polymerizing and/or condensing
to yield a phenolic resin or furan resin on a carbonaceous adsorbent
material, causing said starting materials to polymerize and/or condense
in situ and heating the thus-treated carbonaceous adsorbent material
at a temperature between about 400.degree. C. and about 1000.degree.
C.
While said carbonaceous adsorbent material may be any porous carbonaceous
material having an adsorptive capacity, normally activated carbon
and other materials having the like properties are preferably employed.
Thus, it is desirable to employ a carbonaceous material which has
a high adsorptive affinity for the starting materials, has a porosity
distribution such that micropores of not more than 20 Angstrom units
in diameter account for a large proportion of the total porosity,
and comprises tough granules having a high grain hardness. The starting
materials to be adsorbed on said carbonaceous adsorbent material
are the materials which will polymerize and/or condense to yield
phenolic resins, i.e. phenol and analogs, such as phenol, cresol,
xylenol, etc., on the one hand and aldehydes such as formaldehyde,
acetaldehyde, benzaldehyde, furfural, etc., or the materials which
will polymerize and/or condense to yield furan resins, i.e. furfuryl
alcohol or furfural. These materials may be used alone or in suitable
combinations. The amounts of those starting materials are preferably
selected in such a manner that the carbon fixation by the resin
produced from the starting materials adsorbed on the carbonaceous
adsorbent material will be within the range of about 0.1 to about
1.0 gram and, for still better results, about 0.3 to about 0.7 g
per cubic centimeter of the micropores of not more than 300 Angstrom
units. For this purpose, it is normally desirable to employ about
0.1 to 2.0 grams, preferably 0.3 to 1.5 g., of said starting materials
per cubic centimeter of micropores of not more than 300 Angstrom
units in said carbonaceous adsorbent material.
These starting materials may be used after admixing with carbon
sources such as lignin, pitch, carbohydrates, etc. and/or carbon
fixatives such as aromatic nitro compounds. A catalyst is preferably
employed in polymerizing and/or condensing said starting materials
onto activated carbon. The catalyst may be any of the catalysts
commonly employed. Thus, with respect to starting materials for
the production of a phenolic resin, there may be mentioned alkaline
catalysts such as sodium hydroxide, potassium hydroxide, barium
hydroxide, ammonia, etc. or acid catalysts such as hydrochloric
acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, oxalic
acid, succinic acid, etc. With respct to starting materials for
the production of a furan resin, there may be mentioned acids such
as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid,
oxalic acid, succinic acid, boric acid, or acidic salts such as
zinc chloride, magnesium chloride, etc. With respect to phenolic
resins, alkaline catalysts are preferred. The amount of the catalyst
is desirably selected from within the following range, with respect
to the starting materials for the resin.
Phenolic resins:
Alkali catalysts: 1 to 10%
Acid catalysts: 2 to 30%
Furan resins:
Acid catalysts: 10% or less
The starting materials for said phenolic resin or furan resin are
diluted with a suitable solvent such as water, methanol, benzene
or creosote oil and the carbonaceous adsorbent material is sprayed
with, or dipped in, the resultant solution to cause the starting
materials to be adsorbed and supported on the adsorbent. Alternatively,
said starting materials may be adsorbed and supported in gaseous
phase on the carbonaceous adsorbent. When a catalyst is employed,
the catalyst may be first adsorbed and supported on the adsorbent
and the starting materials next adsorbed and supported. The procedure
may be reversed so that the adsorption of the starting materials
will take place first. As a further alternative, both the starting
materials and catalyst may be simultaneously adsorbed and supported.
It is, however, most desirable that the catalyst and starting materials
be supported in the order mentioned. The supporting operation may
be carried out in two or more steps and, in doing so, the starting
materials and catalyst may be adsorbed in an optional sequence and
in optional combinations. In the method of this invention the heat
of adsorption evolved in the course of adsorption of starting materials
on the carbonaceous adsorbent sets off a polymerization and/or condensation
reaction of the starting materials, but the polymerization and/or
condensation reaction may be hastened, if necessary, by heating
the system to a temperature not exceeding 200.degree. C.
By this heating, the solvent and some of unreacted components are
desorbed and evaporated off. The carbonaceous adsorbent thus treated
is then subjected to a carbonization treatment. This carbonization
treatment is carried out in the same manner as the usual carbonization
of activated carbon. Thus, the substrate adsorbent may be carbonized
either directly or after it has been pre-oxidized. The pre-oxidation
treatment may be carried out by treating the adsorbent in an oxygen-containing
atmosphere at low temperature. The carbonization treatment may be
carried out, for example, by heating the adsorbent by means of a
heater in streams of an inert gas, e.g. N.sub.2 H.sub.2 He, CO,
CO.sub.2 or SO.sub.2 or in vacuo at a temperature between 400.degree.
to 1000.degree. C.
The atmosphere may contain a minor amount of oxygen. To retard
the degradation rate of the resin, the heating rate is preferably
about 50.degree. C./hr. to 400.degree. C./hr. in most instances.
The carbonaceous molecular sieve thus obtained has micropores, the
large majority of which have pore diameters within the range of
4 to 6 Angstrom units. A typical relation of micropore diameters
with the total volume of micropores may be represented by the curve
MSC-A in the drawing. As shown by the curve for Activated Carbon-B,
the prior art activated carbon has larger pore diameters and a broader
pore diameter distribution.
The carbonaceous molecular sieve prepared as above may be put to
use, for example in such forms as spherical or cylindrical molded
pellets, irregular crushed fragments or other granulated forms,
powdery forms and other forms and particle sizes suited for the
intended applications.
The carbonaceous molecular sieve may be directly used in the process
for bromine adsorption. Or, prior to the adsorption of bromine,
a small amount of phosphoric acid, boric acid or a salt thereof
may be previously adsorbed and supported. By this prior treatment
with such acid or salt, the aging loss of the property of the brominated
carbonaceous molecular sieve of this invention to maintain the green
perishable foodstuffs and flowers can be further retarded.
To support such additional substances, the carbonaceous molecular
sieve is sprayed with or immersed in an aqueous solution containing
such a substance in a suitable concentration. The amount supported
of such additional substances is normally 0.02 to 2 weight % and
preferably 0.05 to 1 weight percent. The amount of bromine to be
adsorbed on the carbonaceous molecular sieve is 2 to 30 weight %
and preferably 5 to 20 weight %.
The adsorption of bromine on the carbonaceous molecular sieve may
be achieved by any of such known procedures as (1) the gas-phase
adsorption process in which a carrier gas containing bromine gas
is contacted with the carbonaceous molecular sieve, (2) the liquid-phase
adsorption process in which the carbonaceous molecular sieve is
immersed in aqueous bromine and (3) the spray adsorption process
in which the carbonaceous molecular sieve is directly sprayed with
liquid bromine, although the gas-phase adsorption process is most
desirable.
In the above-mentioned gas-phase adsorption process, the carrier
gas may for example be air, nitrogen or carbon dioxide gas. As to
the mixing ratio of bromine gas to such a carrier gas, the concentration
of bromine gas is normally not more than 30 volume % and preferably
0.05 to 2 volume %. The contacting temperature is not more than
150.degree. C. and preferably not more than 80.degree. C. Since
the heat of adsorption is evolved in the course of adsorption, the
contacting procedure and the temperatures of the gas and of the
adsorption vessel are preferably selected so that the temperature
of the system will not rise beyond 150.degree. C. An exemplary procedure
may thus be a continuous gas-phase adsorption process in which a
bromine-containing gas is circulated through a fluidized bed, moving
bed or jet bed of said carbonaceous molecular sieve. Preferably,
the brominated carbonaceous molecular sieve obtained by the above
bromine-adsorption process is further treated with the passage of
a bromine-free carrier gas therethrough at a temperature not exceeding
100.degree. C. so that unadsorbed bromine will be stripped off.
In the liquid-phase adsorption process, the carbonaceous molecular
sieve is immersed in an aqueous solution of bromine containing about
2 to 3% of bromine at a temperature not exceeding 50.degree. C.,
preferably below 30.degree. C., for about 1 to 10 hours and, after
this adsorption process, the brominated carbonaceous molecular sieve
is separated by filtration or other procedure and dried. In this
manner, also, there is obtained the brominated carbonaceous molecular
sieve to be employed according to this invention.
In the process comprising spraying the carbonaceous molecular sieve
with liquid bromine, the desired brominated carbonaceous molecular
sieve can be prepared by spraying the carbonaceous molecular sieve
directly with liquid bromine under constant stirring and, if necessary,
drying the treated molecular sieve. The temperature at which liquid
bromine is sprayed is preferably not more than 50.degree. C.
The closable container mentioned hereinbefore may be formed by
a material having a carbon dioxide gas permeability at 25.degree.
C. of 5000 to 100000 ml/m.sup.2 /24 hrs., preferably 10000 to
70000 ml/m.sup.2 /24 hrs. and an oxygen permeability at 25.degree.
C. of 2000 to 50000 ml/m.sup.2 /24 hrs., preferably 3000 to 30000
ml/m.sup.2 /24 hrs. As examples of such a material there may be
mentioned films and sheets of polyethylene, polypropylene, EVA(ethylene-vinyl
acetate copolymer) and other plastics. While such films and sheets
may vary in thickness according to various conditions of use, e.g.
foodstuffs or flowers to be protected, the quantities thereof, etc.,
the range of about 10 to 100.mu. is suitable and about 15 to 70.mu.
is more suitable. To produce a container, the material may be formed
into a bag and the opening thereof closed with a rubber band or
cord or heat-sealed or, alternatively, the material may be folded
by the so-called handkerchief method. From a shipping point of view,
it is advantageous to employ such a material in conjunction with
a corrugated board box, or a corrugated board box fabricated by
laminating said material to a board material in the manner of surfacing
or interlining.
In the practice of the method of this invention, the atmosphere
within the closed container has an appreciable influence upon the
retention of freshness of the green perishable foodstuff and the
flower contained therein. Although it depends upon the kind of foodstuff
and flower, the internal atmosphere of the closed package desirably
has a carbon dioxide concentration of 2 to 13%, preferably 4 to
7%, an oxygen concentration of 1 to 15%, preferably 3 to 8%, a relative
humidity of 70 to 99%, preferably 75 to 95% and a temperature of
0.degree. to 35.degree. C., preferably 0.degree. to 10.degree. C.
If the carbon dioxide gas concentration of the closed container
is low and the oxygen gas concentration thereof is high, there will
be obtained no adequate CA effect (the effect of retaining the freshness
of a green perishable foodstuff and flower through a slowdown in
their respiration which can be caused by adjusting the concentration
of oxygen and carbon dioxide in the ambient atmosphere.)
Conversely, if the carbon dioxide concentration in the closed container
is high and the oxygen concentration thereof is low, there are caused
the so-called gas injuries such as browning as well as such troubles
as alcohol fermentation. Therefore, in consideration of the kind
and amount of green perishable foodstuff and flowers, the type and
thickness of the container material are selected from the ranges
indicated hereinbefore so that the atmosphere in the closed container
will satisfy the conditions set forth above.
While the amount of the brominated carbonaceous molecular sieve
in the closed package should vary with such variables as the kind
and quantity of the green perishable foodstuff, it is normally within
the range of 0.5 to 30 grams and preferably 1 to 10 grams per kilogram
of the foodstuff. There is no limitation on the form in which the
brominated carbonaceous molecular sieve is present in the closed
container. Thus, for example, it is an expedient procedure to include
about 1 to 50 grams of the brominated carbonaceous molecular sieve
in a container made of an air-permeable material such as paper,
cloth, nonwoven fabric or the like, or fix the brominated carbonaceous
molecular sieve securely to the internal wall of a closable container.
While this invention is applicable to all varieties of green perishable
foodstuffs and flowers, it is particularly useful for prolonging
the shelf-lives of fruits such as apple, pear, mandarin orange,
persimmon, loquat, peach, banana, grape, cherry, etc., and vegetables
such as bamboo shoots, mushrooms (Cortinellus shiitake), spinach,
leek, lettuce, cabbage, tomato, cucumber, strawberry, green pepper,
etc., and flowers such as carnations, tulips, chrysanthemums, orchids,
roses, etc.
In accordance with this invention, because the brominated carbonaceous
molecular sieve enclosed in the closed container selectively adsorbs
low molecular weight substances inclusive of ethylene, among the
substances, emanated from green perishable foodstuffs and flowers,
which include not only ethylene but aldehydes, alcohols and so forth,
the effect of adsorptive removal of ethylene lasts a long time even
when the molecular sieve is used in a small amount. Moreover, because
esters and other aromatic components are not adsorbed, the characteristic
aromas of green perishable foodstuffs and flowers remain unabated
or otherwise unaffected until the time when the packages are opened. |