JPH07143843A - Freshness keeping in refrigerator - Google Patents

Abstract

PURPOSE:To obtain a freshness keeping agent for vegetables and fruits in a freshness-keeping box, effectively applicable in a narrow space on behalf of a board shape and capable of exhibiting high activity as an ethylene oxidation catalyst even at normal temperature or low temperature. CONSTITUTION:A carbonaceous raw material is activated in an atmosphere containing <=15vol.% of steam, then cooled to <=300 deg.C in the same atmosphere to obtain an active carbon. 100 pts.wt. of the active carbon made to carry 0.1-10wt.% of palladium chloride is incorporated with 1-20 pts.wt. of an organic fiber having diameter of 1-50 p m as a binder to obtain a molded board-shaped article. In the additional case, an active carbon obtained by the conventional process or an active carbon whose activity as an oxidation catalyst is lowered is subjected to a heat treatment at >= about 500 deg.C in an atmosphere of nitrogen and/or carbon dioxide gas essentially free from oxygen and/or steam, then cooled to <=300 deg.C in the same atmosphere. The treated active carbon is molded after incorporated with palladium chloride and the organic fiber in the same way as in the above case to obtain an active-carbon board carrying palladium chloride for keeping freshness in a refrigerator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a freshness method for a refrigerator or a vegetable box, and more specifically, it utilizes activated carbon formed into a plate shape by impregnating palladium chloride and the oxidation catalytic activity of the activated carbon, This is a method of maintaining the freshness of fruits and vegetables such as a vegetable box in a refrigerator.

[0002]

2. Description of the Related Art The reaction of oxidizing carbon monoxide and ethylene by using activated carbon loaded with palladium chloride as a catalyst is well known. However, they are often used in the form of powdered or granular activated carbon as a carrier. It was almost [Journal of the Chemical Society of Japan (1
972) p.1092-1097, JP-B-60-10776, JP-A-56-55147
Issue bulletin]. The applicant previously applied for activated carbon impregnated with palladium chloride (Japanese Patent Application No. 60-10776 and Japanese Patent Application Laid-Open No. 56-5).
No. 5147), the activated carbon carrying palladium chloride is granular, and therefore, it must be put in a pouch or packed in a column for use. When used in this way, there was a problem in using it effectively in a narrow space such as a refrigerator.

In addition, in the conventional method of impregnating palladium chloride on honeycomb-shaped activated carbon, it is difficult to increase the amount of palladium chloride impregnated because the strength of the honeycomb-shaped activated carbon as a carrier is small and the specific surface area is small. No active palladium chloride-supported activated carbon was obtained. In addition, there are many problems such as the expensive honeycomb activated carbon and the necessity of forced ventilation using a fan or the like.

For example, when used in a refrigerator, a fan is required at the same time as a conventional deodorizing method in which gas is circulated through the entire chamber to remove ethylene, and at the same time, adsorption of harmful gas generated from other foods is required. Also occurs, the catalytic performance of ethylene decomposition may be significantly reduced. In order to effectively achieve the purpose of keeping freshness, it is preferable to remove ethylene only at a place where ethylene is generated, that is, a portion such as a vegetable box. The conventional granular activated carbon impregnated with palladium chloride cannot achieve this purpose. This is because it is necessary to use activated carbon packed in a column or a container in the case of granular coal, and it has been difficult to effectively use it in a narrow place such as a refrigerator.

Therefore, in such a case, there has been a demand for a plate-shaped molded palladium chloride-impregnated activated carbon which has high performance and is inexpensive as an oxidation catalyst and can be easily used in a narrow space.

Further, there is a method using a liquid resin binder as a method of forming the activated carbon into a plate shape, but with this, the performance of the activated carbon is remarkably deteriorated, and the original performance of the activated carbon cannot be exhibited.

[0007] Further, a method for producing an oxidation catalyst by impregnating plate-like activated carbon with palladium chloride can be considered, but in this case, the performance of the plate-like activated carbon used is limited, and activated carbon having a large specific surface area can be used. Can not. because,
Since plate-like activated carbon has problems of cracking, strength reduction, deformation, etc. when activated for high performance, it is usually 1000 m ²
It is difficult to make a plate-like activated carbon having a specific surface area of 1200 m ² / g or more at about / g.

[0008]

In view of the above-mentioned problems, the present invention removes dilute ethylene at a low temperature, so that the gas can quickly contact with the oxidation catalyst and be sufficiently removed.
An object of the present invention is to provide a method of maintaining freshness of fruits and vegetables in a refrigerator freshness-keeping box by molding palladium chloride-impregnated activated carbon having a high catalytic property so as not to deteriorate the performance.

[0009]

In order to remove dilute ethylene at a low temperature, the present inventor can be used in a narrow space such as a vegetable box in a refrigerator and has an excellent catalytic property. Various studies were conducted.
As a result, by impregnating activated carbon produced through a specific process with palladium chloride and then forming it into a plate by a specific method, the low concentration ethylene gas of about 10 ppm at 0-40 ° C was sufficiently oxidized and removed. It has been found that a plate-like palladium chloride-impregnated activated carbon having a very high activity can be obtained, and based on this, the present invention has been accomplished.

That is, after activating the carbonaceous raw material in an atmosphere having a water vapor content of 15% by volume (hereinafter simply referred to as%) or less, it is cooled to 300 ° C. or less in the same atmosphere, and palladium chloride is added in an amount of 0.1 to 10% by weight. % (Hereinafter, simply referred to as%) loaded on 100 parts by weight of activated carbon (hereinafter, the weight of parts is omitted), as a binder, a diameter of 1 to 50 μm
1 to 20 parts by weight of organic fiber is added, and molded palladium chloride-impregnated activated carbon formed by molding into a plate shape, and further, activated carbon obtained by a conventional method or activated carbon having a reduced function of an oxidation catalyst is treated with substantially oxygen or / And steam-free nitrogen gas and / or carbon dioxide gas heat treated at about 500 ℃ or more, cooled to 300 ℃ or less in the same atmosphere, and 100 parts of activated carbon loaded with 0.1-10% palladium chloride. As a binder, 1 to 20 μm diameter organic fibers 1 to 20
A method of maintaining freshness of a refrigerator, characterized in that palladium chloride-impregnated activated carbon, which is added to a part by weight and formed into a plate shape or put in a non-woven bag, is inserted into a fruit and fruit storage box in the refrigerator for use.

The term "substantially free of oxygen and / or water vapor" as used herein means an atmosphere in which oxygen atoms bonded to the surface of activated carbon do not exist in the heat treatment of activated carbon after activation, and oxygen and water vapor are It means a state of 1 to 2% or less.

The present invention will be described in detail below.

The activated carbon used in the present invention is obtained by carbonizing a carbonaceous raw material such as coconut shell coal or coal as a carbonaceous raw material and activating it by the method of the present invention.

At this time, the activating gas contains not only water vapor but also carbon dioxide gas, but the water vapor content must be 15% or less. The composition of the activated carbon activating gas that is usually used is 40-60% of steam, and in many cases it is higher than that. Since the activation rate of carbonaceous matter by water vapor is considerably faster than that of carbon dioxide gas, the composition of the activation gas is set so that the water vapor partial pressure is as high as possible. Therefore, the conditions of the present invention are mild conditions in which the activation rate is remarkably slower than in the conventional method. As shown in Example 10 and Comparative Examples 12 to 13 in Table 5, when activated under the condition that the water vapor content is high, it is found that the oxidation catalytic property of ethylene is significantly reduced. The details of the mechanism by which the activation condition with a low water vapor content improves the oxidation catalytic ability of the activated carbon are not clear, but the plate-shaped activated carbon obtained under such conditions has a state in which oxygen atoms bound to its surface are not present. It is pointed out that there is.

Ordinary plate-like activated carbon is produced by activating a plate-shaped carbonaceous raw material with steam, combustion gas, etc., but even if such activated carbon is used in the present invention, it has sufficient oxidation catalytic properties. Not shown. The effect of the present invention, after being activated with a gas having a specific composition as described above, is obtained only by using, as a raw material, activated carbon impregnated with palladium chloride, a plate-shaped activated carbon formed by a specific method. is there.

The plate-like activated carbon thus obtained has a high catalytic property for rapidly oxidizing ethylene. However, the raw material activated carbon of the present invention is taken out of the system at a high temperature after activation,
If it is left in an atmosphere containing a large amount of water vapor, hydrogen gas or oxygen gas, its ability as an oxidation catalyst is significantly reduced.

After activation, the activated carbon of the present invention must be cooled to a temperature of 300 ° C. or lower under the same gas as the activation gas, and then taken out of the system. The cooling atmosphere may be an atmosphere of nitrogen gas, carbon dioxide gas, or a mixed gas thereof (oxygen, hydrogen, and water vapor content is not more than a specified amount) used during activation, and a gas used for activation and a gas used for cooling Do not necessarily have the same composition. In the present invention, "cooling as it is" means an atmosphere having the above composition.

The specific surface area of the activated carbon of the present invention obtained as described above is preferably 1200 m ² / g or more.
More preferably, it is m ² / g or more.

Further, in the present invention, waste granular activated carbon whose surface has been oxidized by contact with air or the like to reduce its oxidation catalytic property or activated carbon obtained by a conventional method in a gas having the same composition as the above-mentioned activating gas, The granular activated carbon obtained by treating at a temperature of 500 ° C. or higher and cooling it to a temperature of 300 ° C. or lower in the same atmosphere also shows a high oxidation catalytic property to ethylene gas, like the above-mentioned granular activated carbon. In other words, this heat treatment gives the granular activated carbon a high oxidation catalytic ability. The granular activated carbon to which this heat treatment is applied may be obtained from any raw material such as coal and palm shell coal, and its shape is not particularly limited.

The activated carbon obtained by the conventional method means activated carbon activated in an atmosphere having a high water vapor content as described above and contacted with air without being sufficiently cooled in the atmosphere after activation. When activated in an atmosphere with a high water vapor content, the activated carbon tends to have a larger pore size, and when it is brought into contact with air without sufficient cooling in an atmosphere after activation, oxygen bound to the surface of activated carbon The amount increases.

In other words, the granular activated carbon obtained by the usual method can also be treated by this method to obtain the granular activated carbon carrier usable as the oxidation catalyst of the present invention. At this time, the processing temperature must be 500 ° C or higher. The treatment time varies depending on the temperature, but in the case of 500 ° C., it is usually preferably 20 to 180 minutes, and at 800 ° C., the effect can be sufficiently obtained by treating for several minutes. The effect of the heat treatment temperature on the oxidation catalytic property is shown in Example 2 and Comparative Example 1 in Table 1.

The activated carbon carrier used in the present invention must be impregnated with palladium chloride in an amount of 0.1 to 10%. To impregnate palladium chloride on activated carbon, a predetermined amount of palladium chloride is dissolved in an aqueous hydrochloric acid solution having a hydrochloric acid concentration of 0.1 to 3 N, preferably 0.5 to 1 N, and the activated carbon is added to this solution and stirred to remove palladium chloride. After sufficient adsorption, drain and drain
Dry at 0 ° C. Palladium chloride loading is 0.1-10%
However, it is more preferable that the supported amount is 0.5 to 2%.

When the supported amount of palladium chloride is 0.1% or less, the catalytic activity is insufficient, and when it is 10% or more, the catalytic activity is not improved despite the large amount of the impregnated metal, and palladium is expensive. Considering economy, the amount of impregnation is 10%
Must be: The amount of palladium chloride supported is adjusted by changing the ratio between the amount of palladium chloride and the amount of activated carbon in the aqueous hydrochloric acid solution. Usually, the palladium chloride in the solution is almost completely adsorbed on the activated carbon.

In order to form the palladium chloride-impregnated activated carbon thus obtained into a plate shape, the particle size of the activated carbon depends on the particle size.
Various particle sizes ranging from 0.1 μm to 6 mm can be used and can be selected according to the purpose of use.

The organic fiber used as a binder can be widely used as long as it can form a molded product when mixed with activated carbon powder and pressed at a high temperature. For example, a thermoplastic resin, a thermosetting resin, a hydrophilic resin, a conductive resin, or the like formed into fibers, which can be heated and fused without using water or an organic solvent, is suitable.

Examples of the thermoplastic resin include polyethylene, polypropylene, ABS (acrylonitrile-butadiene-styrene resin), PET (polyethylene terephthalate), nylon, PBT (polybutylene terephthalate), ethylene-acrylic resin, PMMA (polymethylmethacrylate). Acrylate) resin, mesophase pitch, etc. can be used.

As the thermosetting resin, furan resin, phenol resin and the like can be used. Further, as the hydrophilic resin, polyvinyl alcohol resin, Eval resin or the like can be used.

The diameter of the organic fiber used as the binder must be 1 to 30 μm. Preferably 5-20μ
m. When the diameter of the organic fiber is 1 μm or less, the bulk specific gravity becomes large, and it is difficult to mold with high strength and high density. Further, when the diameter exceeds 30 μm, the adhesive strength becomes small and a plate-like sheet having high strength cannot be obtained. The influence of the diameter of the organic fiber on the strength of the molded product is shown in Examples 4 and 5 and Comparative Examples 4 and 5 in Table 2.

The amount of organic fiber used should be 1 to 20 parts per 100 parts of activated carbon. It is preferably 2 to 15 parts. When the amount of the organic fiber used is 1 part or less, the strength of the molded body is insufficient, and when the amount of the organic fiber used is 20 parts,
Since the surface of the activated carbon is covered with the fiber plastic, the catalytic property is lowered. The effects of the amount of organic fibers used on the strength and catalytic properties of the molded article are shown in Example 7 and Comparative Example 7 in Table 2.

The organic fiber used as the reinforcing material of the present invention is
Organic fibers such as polypropylene, vinylon, polyester, nylon polyester-polyethylene, and polypropylene-polyethylene conjugate fibers are preferable for improving the strength of the molded product.

Further, by using metal fibers and inorganic fibers in combination with the polymer fine powder, it is possible to use them as a binder.

The form of the inorganic fiber is 0.2 mm to 20 m in length.
A monofilament or multifilament fiber having m and a diameter of 3 μm to 50 μm is preferable.

In the case of molding into a plate shape, as a method of mixing activated carbon, binder fibers and the like, a usual industrial mixing method such as a mixer, a ribbon mixer, a static mixer, a ball mill, a sample mill and a kneader can be used. At the time of mixing, the organic fibers can be attached to the surface of the activated carbon only by mixing, but it is preferable to perform simple heating in advance in order to strengthen the adhesion between the organic fibers and the adsorbent. Microwaves, infrared rays, far infrared rays, high frequencies, etc. can be used as the heat source, but the organic fibers can be more firmly attached to the surface of the activated carbon by further heating while generating static electricity during mixing.

After filling a mixture of the above-mentioned adsorbent and organic fibers into a desired mold and heating the mixture above the softening point of the organic fibers,
The plate-like activated carbon sheet of the present invention can be obtained by compressing by applying a pressure of 0.1 to 10 kg / cm ² and then cooling.

It is well known that when a trace amount of ethylene generated from vegetables or fruits coexists, it promotes the growth and maturation of these plants. By removing ethylene generated from vegetables or fruits, It is known to suppress the growth and maturation of these plants and exhibit the effect of maintaining freshness. The freshness-keeping sheet of the present invention has a high function of oxidizing and removing a trace amount of ethylene gas existing in air, and can be effectively used in a narrow space because of its plate shape, and has a high function as an oxidation catalyst not only at room temperature but also at low temperature. Therefore, it is excellent as a freshness-keeping agent for fruits and vegetables in a vegetable box of a refrigerator.

[0036]

EXAMPLES The present invention will be described in more detail below with reference to examples.

In Example 1, coal crushed to 10 to 30 mesh was dry-distilled at 800 ° C., and then propane combustion gas (gas composition: nitrogen 80%, oxygen 0.2%, carbon dioxide gas 9.8%, steam 10
%) At 900 ° C. until a specific surface area of 1300 m ² / g is reached, and then the activated carbon is taken out into a container purged with nitrogen.
It was cooled to 300 ° C. or lower in the nitrogen gas to obtain an activated carbon carrier.

In Comparative Example 1, the activated carbon activated in the same manner as in Example 1 until the specific surface area reached 1300 m ² / g was taken out in nitrogen, cooled to 500 ° C., and taken out in air. Then, it was left to cool to obtain an activated carbon carrier. Comparative Example 1
Activated carbon carrier of 10% in a stream of N ₂ 50%, CO ₂ 50% at 700 ℃
After treating for minutes, the product was taken out in nitrogen and cooled to room temperature to obtain an activated carbon carrier of Example 2. The activated carbon carrier of Comparative Example 1 was treated in nitrogen at 900 ° C. for 5 minutes and then cooled to room temperature in nitrogen to obtain the activated carbon carrier of Example 3. Palladium chloride was attached to these activated carbons as follows.
Add 50 g of activated carbon carrier to 200 ml of 0.5N hydrochloric acid solution containing 500 mg of palladium chloride, stir well, let stand for 3 hours, drain water, wash with 100 ml of pure water, dry at 200 ° C, and impregnate palladium chloride at 1.0%. To obtain activated carbon impregnated with palladium chloride.

The palladium chloride-impregnated activated carbon thus obtained was crushed to 0.1 to 1 mm, then mixed well with 100 parts of activated carbon and 10 parts of polyethylene fiber having an average diameter of 20 microns, and pressed to a thickness of 3 mm. Molded into plates.

10 g of this molded plate was put in a vegetable box of a commercial refrigerator with a volume of 40 liters together with 8 kg of apple Fuji, and a freshness retention test was conducted.

Table 1 shows the results of ethylene concentration measurement after 14 days and the quality evaluation results of apples. Here, the hardness of the apple is measured by a method commonly used in the fruit and vegetable industry, which is obtained as a load when the epidermis of the apple is broken from the strain-stress curve when the plunger is brought into contact with the apple at a constant speed. Yes Further, the sugar content indicates the total content rate (%) of sucrose, fructose and glucose, which is determined according to the food analysis method.

Individual apples were evaluated by a 5-step evaluation method in which the excellent taste was 5 and the poor taste was 1, and the average value was shown. Density, burn disease, browning of fruit and browning in fruit core showed their respective ratios (%) to the total number.

[0043]

[Table 1]

In Comparative Example 2, palladium chloride was not impregnated on the commercially available activated carbon carrier obtained by a conventional method having a specific surface area of 1500 m ² / g,
It was used in the same state, and in Comparative Example 3, 1.0% of palladium chloride was impregnated and used on a commercially available plate-like activated carbon.

Each of the plate-like palladium chloride-impregnated activated carbons (Examples 1 to 3) of the present invention completely removed ethylene in a short time and showed excellent removal ability. On the other hand, comparative examples (1 to
As shown in 3), when the activated carbon carriers other than the present invention and the commercially available activated carbon carriers obtained by the conventional method were used, the harmful gas removal rate was slow in all cases. In particular, the commercially available plate-like activated carbon with palladium impregnated had a low oxidation catalytic property probably because of its small specific surface area.

Then, the kind of the activated carbon raw material, the particle size of the plastic powder as the binder and the mixing ratio were changed, and palladium chloride was impregnated in the same manner as in Example 1 to obtain a plate-shaped activated carbon. 10 g of these plate-like activated carbons
Mounted on the ceiling of a 40-liter plastic box,
Put 5 kg of apple apple trees, 500 g of spinach and 3 kg of grape Kyoho into the box, put these boxes in a cool room kept at 5 ° C, open and close the box lid 3 times in the morning, 3 lunch in the afternoon.
And 10 times at night, and the ethylene concentration in the box was measured. Table 2 shows the measurement results and the quality evaluation results. In Comparative Example 8, SB was used as a binder instead of plastic particles.
R (Styrene-Butadiene-Rubber) Latex is used.

In Table 2, Kyoho's natural shedding rate is shown by the ratio (%) of the weight of the grape particles shed during the storage period to the weight of the whole grape, and the simple shedding rate is a constant amplitude and cycle at the end of the storage period. Shake left and right 10 times with, and the ratio of the weight of the dropped grape particles to the weight of the whole grape (%)
Indicated by.

[0048]

[Table 2]

As shown in Table 2, the plate-like palladium chloride-impregnated activated carbon of the present invention has a large oxidation catalyst ability and plate strength.
If the diameter of the binder is larger than 30 μm, the strength of the plate molded product will be reduced and it will not be practical, and if 20 parts or more of the binder is used, the ethylene removal rate will be greatly reduced.
The effect of keeping freshness was small.

Further, activated carbon obtained by activating the activated carbon was taken out into the air at different take-out temperatures,
Palladium chloride was impregnated in the same manner as in Example 1 to obtain a diameter
Five parts of 15-micron PE / PP fiber was molded into an indenter plate, and this was put into a 50-liter plastic box together with 10 kg of fresh water, and the change in ethylene concentration and quality after 3 weeks were measured. The results and the properties of the activated carbon used are also shown in Table 3.

Here, the pear color of each pear was evaluated by a five-level evaluation method in which the mature yellow color was 5, and the blackish brown color was 1, and each pear color was evaluated and shown as an average value.

[0052]

[Table 3]

As shown in Table 3, the performance of the plate-like palladium chloride-impregnated activated carbon of the present invention depends on the temperature at which it comes into contact with air for the first time after cooling, and at 300 ° C. or higher, the removal capacity drops significantly.

Activated carbon obtained by changing the composition of the activating gas was impregnated with palladium chloride in the same manner as in Example 1, and was molded into a plate shape by using 10 parts of PP / PET fiber having a diameter of 10 microns as a binder to obtain an activated carbon. 5g of Sudachi from Tokushima Prefecture was filled in the vegetable box of the refrigerator using 10g of the plate and stored for 3 months, and then the ethylene concentration and quality were measured.

The results and the properties of the activated carbon used are shown in Table 4.
Are also shown. Here, the color of Sudachi was evaluated by a 5-step evaluation method in which fresh green was changed to 5 and yellow was changed to 1, and the color of each Sudachi was evaluated and shown as an average value.

[0056]

[Table 4]

As shown in Table 4, it is recognized that the performance of the plate-like palladium chloride-impregnated activated carbon of the present invention depends on the water vapor concentration at the time of activation, and shows a high catalytic property when the water vapor concentration is 15% or less.

[0058]

EFFECTS OF THE INVENTION The shaped palladium chloride-impregnated activated carbon of the present invention has a plate-like shape and can be effectively used in a narrow space. Since it has a high function as an oxidation catalyst even at room temperature or low temperature, it has an excellent ability to remove and oxidize ethylene. There is.

Utilizing this property, it is excellent as a freshness-retaining agent for the fruit and vegetable preservation section in the freshness-retaining box.

Claims (2)

[Claims] 1. Activated carbonaceous material in an atmosphere having a water vapor content of 15% by volume or less, then cooled to 300 ° C. or less in the same atmosphere, and 100 parts by weight of activated carbon loaded with 0.1 to 10% by weight of palladium chloride. As a binder, diameter 1
Activated carbon formed by adding 1 to 20 parts by weight of 30 μm organic fiber into a plate shape, or activated carbon obtained by a conventional method or activated carbon with reduced oxidation catalyst function, substantially containing oxygen and / or steam. Heat treatment at 500 ℃ or higher in nitrogen gas and / or carbon dioxide gas, then in the same atmosphere
Cool to below 300 ° C and add palladium chloride to 0.1-10
To 100 parts by weight of activated carbon supported by weight%, 1 to 20 parts by weight of organic fiber having a diameter of 1 to 30 μm as a binder is added,
A method of maintaining freshness of a refrigerator, characterized in that the activated carbon formed into a plate shape is inserted into a fruit and vegetable storage box in the refrigerator for use. 2. Activated carbonaceous raw material in an atmosphere having a water vapor content of 15% by volume or less, then cooled to 300 ° C. or less in the same atmosphere, and 100 parts by weight of activated carbon supporting 0.1 to 10% by weight of palladium chloride. As a binder, diameter 1
Activated carbon formed by adding 1 to 20 parts by weight of 30 μm organic fiber into a plate shape, or activated carbon obtained by a conventional method or activated carbon with reduced oxidation catalyst function, substantially containing oxygen and / or steam. Heat treatment at 500 ℃ or higher in nitrogen gas and / or carbon dioxide gas, then in the same atmosphere
Cool to below 300 ° C and add palladium chloride to 0.1-10
To 100 parts by weight of activated carbon supported by weight%, 1 to 20 parts by weight of organic fiber having a diameter of 1 to 50 μm is added as a binder,
A method for maintaining freshness of a refrigerator, characterized in that an activated carbon sheet formed into a plate shape is placed in a non-woven bag having gas permeability and inserted into a fruit and fruit storage box in the refrigerator for use.