JPH0223208B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an activated carbon fiber for dehumidification and a method for producing the same, and more particularly to an activated carbon fiber with improved hygroscopicity under low humidity and a method for producing the same. Activated carbon has been industrialized for a long time and has been widely used as an adsorbent for removing impurities from liquids and gases, for recovering useful substances, and as a carrier for catalysts. Activated carbon that has long been used in these applications has been in the form of powder or granules, but in recent years, activated carbon in the form of fibers has been developed, and the uses of activated carbon have expanded due to its form and distinctive performance. Conventionally available carbon-based adsorbents such as activated carbon and activated carbon fibers are so-called hydrophobic adsorbents, and have relatively large pores and are suitable for use in low relative humidity regions such as 20%. The amount of water vapor adsorbed was extremely small. Further, as a moisture absorbing material used in a dehumidifier, a material that absorbs a large amount of moisture in a low humidity region is necessarily required in order to obtain air with a low relative humidity. The moisture absorbing material unit to be incorporated into the dehumidifier preferably has a shape such as felt or cardboard, which has a high rate of adsorption and desorption of moisture and a small pressure loss, and the moisture absorbing material constituting these is preferably fibrous. Until now, no satisfactory fibrous moisture absorbing material has been obtained which absorbs a large amount of moisture in such a low relative humidity region. In view of these circumstances, the inventors of the present invention have conducted intensive research and have discovered a carbon-based fibrous adsorbent with excellent hygroscopicity at low humidity and a method for producing the same, and have arrived at the present invention. That is, the present invention has a benzene adsorption amount of 2 to 20% by weight.
, and a hydrophilic functional group is added to the surface,
The activated carbon fiber has a moisture absorption of 10% by weight or more at a relative humidity of 20%, and the activated carbon fiber has a benzene adsorption amount of 2 to 20% by weight as determined by the following method, and is treated in air at 260 to 350°C. Manufactured by Benzene adsorption amount; JIS-K-
1474 "4.4 1/n Equilibrium adsorption performance of solvent vapor" The value obtained by setting the concentration of solvent vapor to 1/10 of the saturated concentration. The present invention will be explained in detail below. According to the moisture absorption isotherm of conventional carbon-based adsorbents, moisture absorption exceeding several tens of percent is observed at high humidity, but the amount of moisture absorption at low humidity is low. This is thought to be because the pore diameter of conventional carbon-based adsorbents is too large and/or the surface is hydrophobic. Furthermore, even if hydrophilic functional groups are added to the surface of these conventional carbon-based adsorbents simply to increase their affinity for water, there is a limit to the amount of hydrophilic functional groups that can be added to the surface of these conventional carbon-based adsorbents to improve their hygroscopicity at low humidity. This is due to misfortune. The present inventors have discovered that by creating activated carbon with a small pore size and adding hydrophilic functional groups to it, it is possible to obtain a carbon-based adsorbent of a certain quality with excellent hygroscopicity in a region of low relative humidity. I found it. In other words, as a base activated carbon fiber before adding hydrophilic functional groups, the benzene adsorption amount ( (hereinafter simply referred to as benzene adsorption amount) is 30% by weight
When using a carbon-based adsorbent with a large pore size,
Although hygroscopicity is improved in a region with relatively high relative humidity, it is difficult to obtain a material that absorbs a high amount of moisture at a relative humidity of 20%, which is the object of the present invention. Excellent hygroscopicity at a relative humidity of 20% can only be obtained by using a carbon-based adsorbent having a benzene adsorption amount of 2 to 20% by weight as the base carbon material.
More surprisingly, it was found that when activated carbon fibers in this range are used as a base carbon material, variations in hygroscopicity due to differences in benzene adsorption amount are eliminated, which is extremely advantageous in industrial production. This method of producing activated carbon fibers having a benzene adsorption amount of 2 to 20% by weight can be carried out by appropriately selecting activation treatment conditions. Next, air oxidation is essential in the present invention as a method for imparting hydrophilic functional groups.
In general, known methods for imparting hydrophilic functional groups to carbon materials include wet oxidation using nitric acid, chromic acid, etc.; dry oxidation using ozone, air, and oxygen; however, air oxidation is the easiest to implement and is less polluting. This is a great way to avoid using or releasing . When performing air oxidation, the processing temperature is extremely important.
If it is lower than 260°C, it is not sufficient to impart a functional group, and if it is higher than 350°C, there will be more consumption due to oxidation, and the hygroscopicity at low humidity will become even lower. As described above, the activated carbon fiber of the present invention has a much improved moisture absorption capacity at low relative humidity compared to conventionally known carbon-based adsorbents due to the appropriate pore diameter and the introduction of hydrophilic functional groups. Therefore, there is an advantage that the moisture absorbent unit can be made compact and the amount of adsorbent used can be reduced. Furthermore, since the activated carbon fibers of the present invention are in the form of thin fibers with a diameter of about 10 μm, they have the advantage that they have a higher moisture adsorption rate than powdered silica gel, which has a diameter of several tens of μm, and can shorten the adsorption/desorption time. Also, since it is fibrous, it can be used for paper, cardboard,
Since it can be easily molded into a non-woven fabric or the like having a certain shape, it has the great advantage of having a small air pressure loss and being able to construct a compact moisture absorbing unit (element). Furthermore, since the activated carbon fiber of the present invention is carbonaceous, it is free from not only moisture but also corrosive gas.
It has the advantage that it is stable against organic gases and does not necessarily undergo alteration or deformation. Furthermore, since it is heat resistant, it does not deform or deteriorate in performance even when exposed to high temperatures. In the present invention, the amount of moisture absorption is measured and calculated by the following method. That is, the activated carbon fiber of the sample is
It is dried for 2 hours at a temperature of 120°C under a reduced pressure of 1 mmHg or less, and the weight is accurately weighed before use. Pure air is created by removing organic substances, sulfur dioxide gas, nitrogen oxides, ozone, and moisture, and then passed through distilled water to saturate the created moisture.The air is then diluted with the above pure air to maintain a specified relative humidity. The above-mentioned sample is placed in this airflow, and moisture is adsorbed until there is no change in the weight of the sample, and the amount of moisture absorbed is calculated in weight percent. Measurements are carried out at a temperature of 30°C. Also, unless otherwise specified, the value is for the suction side. EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited by these Examples. Reference example: A 1.5 denier regenerated cellulose fiber was impregnated with 10% by weight of diammonium phosphate, dried, brought to 300°C from room temperature at a rate of 60°C per hour in an inert gas, and kept for 1 hour. Subsequently, the temperature was raised to various temperatures from 650 to 800°C at a heating rate of 400°C per hour, and water vapor was introduced to produce six types of activated carbon fibers as shown in Table 1 with different amounts of benzene adsorption. Table 1 shows the amount of benzene adsorbed by these six types of activated carbon fibers.

[Table] Example 1 Activated carbon fiber C obtained in Reference Example was oxidized in air at various temperatures of 250 to 375°C for 1 hour, and H, I,
Six types of modified activated carbon fibers, J, K, L, and M, were obtained.
Table 2 shows the amount of moisture absorbed by these activated carbon fibers at a relative humidity of 20%. As can be seen from Table 2, the appropriate treatment temperature is 275 to 350°C; if it is lower than this, it is difficult to obtain the oxidation effect, and if it is higher than this, the pore size will increase due to loss due to oxidation, and the It can be seen that the hygroscopicity decreases.

[Table] Example 2 Five types of activated carbon fibers (A, B,
D, E, and F) were oxidized in air at 300° C. for 1 hour to obtain five types of modified activated carbon fibers, P, Q, R, S, and T, respectively. The moisture absorption of these five types of activated carbon fibers at a relative humidity of 20% is 13.2%, respectively.
They showed 13.8%, 12.4%, 10.0%, and 11.0%. Example 3 70 parts of the activated carbon fiber J obtained in Example 1, 30 parts of softwood pulp, and 7 parts of polyvinyl alcohol fiber were mixed in a beater in the usual manner, and the paper was made at a speed of 15 m/min in a fourdrinier paper machine. A mixed paper was produced. The weight of the obtained paper was 40 g/m ² and the thickness was 0.25 mm. The moisture absorption amount of this paper at 20% relative humidity is 9.3% by weight.
Since the expected value of moisture absorption based on the amount of activated carbon fiber contained was 9.1% by weight, almost no decrease in moisture absorption due to paper making was observed. Examples 4 to 8 Activated carbon fiber paper (dehumidifying material) obtained in Example 3
was formed into a corrugated hole shape using a corrugator, and this was rolled up to form a honeycomb rotor. The step shape was 2.1 mm in height and 2.8 mm in interval. While rotating this honeycomb rotor, outside air (dehumidifying air) was passed through 3/4 of its cross section to perform dehumidification. On the other hand, use a duct for the remaining 1/4 part.
The dehumidifying material was regenerated by passing hot air at ℃ to desorb moisture adsorbed from the outside air. The diameter of the honeycomb rotor is 50cm, the thickness is 40cm, and the amount of activated carbon fiber is
It weighed 4.0Kg. Tests were conducted by changing the honeycomb rotor rotation speed, the dehumidifying air volume, and the ratio of the regenerating air volume to the dehumidifying air. The test results are shown in Table 3.

[Table] Here, air volume Kg is the weight per dry air equivalent (Kg)
The amount of dehumidification refers to the amount of moisture adsorbed and removed by the activated carbon fibers when passing through the honeycomb rotor once. The outside air was 25°C and relative humidity was 50%.

Claims (1)

[Claims] 1. The benzene adsorption amount is 2 to 20% by weight, a hydrophilic functional group is added to the surface, and the relative humidity is
Activated carbon fiber for dehumidification whose moisture absorption amount at 20% is 10% by weight or more. 2. A method for producing activated carbon fiber for dehumidification, which comprises air-oxidizing activated carbon fiber having a benzene adsorption amount of 2 to 20% by weight at 260 to 350°C.