JPH076093B2 - Gas or liquid separation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating gas or liquid using polyvinyl alcohol fiber (hereinafter referred to as PVA fiber) as a raw material and using hollow activated carbon fiber.

Several types of activated carbon fibers are already well known. For example, natural fibers, recycled cellulose fibers, phenol fibers, PVA fibers and the like are used as raw materials. When activated carbon is made into fibrous form, compared with the widely used granular or powdery adsorbents, the macro contact area is much larger, so the adsorption speed is faster and there is no generation of dust and pressure loss. There are many advantages such as low.

However, by making the fibrous activated carbon hollow, the macroscopic contact area is further increased, and in addition, it exhibits a unique physical property having both the adsorptivity peculiar to activated carbon and the selective permeability of the hollow fiber wall. The present invention is a method for separating a gas or liquid component containing a plurality of components using hollow activated carbon fibers having a molecular sieving property that combines the adsorptivity of activated carbon and the properties of a semipermeable membrane.

[0004]

2. Description of the Related Art A method for producing carbon fiber using PVA fiber as a raw material is disclosed in JP-A-49-24897, 50-35431, 50-52320, and
No. 50-52321, the gist of which is to treat PVA fibers coated or impregnated with a dehydration catalyst by heat treatment at 180 ° C. to 300 ° C. in an oxidizing atmosphere to carbonize, and if necessary, treat at a higher temperature. Is a method of promoting graphitization and improving mechanical properties. All of them are intended for carbon fiber as a structural material and include common elements in terms of carbonization of PVA fiber, but they are neither hollow in shape nor activated carbon.

Japanese Patent Publication No. 54-3973 discloses a method for producing activated carbon fiber, in which 3 to 15% of a dehydration catalyst is added to a spinning dope, and the resulting PVA fiber is produced at 180 to 340 ° C. with a yield of 65 to
It is a method of heat-treating to 85% and carbonizing, and then activating in an inert gas containing steam at 600 ° C to 1,000 ° C to a yield of 10 to 35%. (Publication 1, page 1, column 1, 16-28
Line, claims). Furthermore, there is a close relationship between the method of adding the dehydration catalyst and the adsorptivity of the obtained activated carbon, and only when it has been added to the spinning dope in advance, activated carbon fibers with high adsorptivity (iodine adsorption amount 1600 to 1700 mg / g) It is stated that it can be obtained (page 3, table 1 and page 6, column 6, column 5 of the publication).
~ Line 8).

The activated carbon fibers are ordinary fibrous and are not hollow. A hollow activated carbon fiber having a thin fiber surface layer having a property of a semipermeable membrane, which is made of a polyvinyl alcohol resin, is not known.

In addition, hollow fibers having a diameter of 10 and several μ or less, which is the object of the present invention, cannot be produced at all by the extrusion molding technique of activated carbon powder.

[0008]

[Problems to be Solved by the Invention] Activated carbon having a large specific surface area and high adsorption ability is formed into a fiber having a hollow surface in the center portion, which has a very thin surface layer. The present invention aims to provide a method for separating a gas or a liquid containing a plurality of components by utilizing the semipermeable property of a thin film.

[0009]

Means for Solving the Problems In the step of soaking PVA fibers in an aqueous solution of a dehydrating agent and then heat-treating and carbonizing the same, the present inventors have studied the degree of penetration of the dehydrating agent, the heat treatment conditions and the shape of the obtained carbide. Researched. As a result, it was found that there is a close relationship between the two and that hollow carbides can be obtained under specific conditions. Further, they have found a method in which PVA fibers that have been wet-spun or dry-spun are used as a raw material for the carbides and other activation conditions are devised to remarkably enhance the adsorptivity of the activated carbon fibers. Further, they have found that the surface layer of the thin fiber thus obtained has a molecular sieving property and completed the present invention.

That is, after attaching a dehydrating agent to the surface layer of polyvinyl alcohol fiber, it is heat-treated until it becomes blackish brown or black so that the fiber does not melt, and further from 400 ° C. to 1,
A hollow activated carbon fiber prepared by heating to 000 ° C within 5 minutes, dry distillation, and activation is used to supply gas or liquid containing multiple components from the outside or inside of the fiber and pass through the fiber wall. It is a method for separating a gas or a liquid, characterized in that the contained components are separated by urging.

The present invention will be described in detail below.

The PVA fiber production method includes dry spinning and wet spinning. The dry spinning is a method in which a spinning solution containing polyvinyl alcohol in an aqueous solution is spun into air, dried and stretched into a fiber. The wet spinning is In this method, a spinning solution is spun into a concentrated electrolyte aqueous solution such as Na ₂ SO ₄ or NaOH, washed with water, dried, and stretched to form fibers.

The present invention is applicable to PVA fibers obtained by any method. In the case of the wet-spun PVA fiber, a yarn having a fine fineness can be obtained, and the hollow portion can be easily formed. In addition, the dry-spun PVA fiber produces thicker threads than the wet-spun method.
The diameter of the hollow portion can be increased.

The PVA fiber may be subjected to a crosslinking reaction with the addition of boric acid or MgSO ₄ for the purpose of improving its physical properties, or with a crosslinking agent such as an aldehyde for the purpose of improving the water resistance. It can also be applied to fibers. Fibers of a copolymer containing vinyl alcohol as a main component and another monomer such as ethylene or vinyl chloride may also be used. Further, in the present invention, a so-called PVA produced by mixing an aqueous solution of PVA into an emulsion mainly composed of polyvinyl chloride (PVC) and spinning the mixture in a sodium sulfate bath and producing it in the same manner as in the normal wet spinning of PVA fibers. -PVC fiber can also be used as a raw material fiber.

The dehydrating agent used in the present invention is preferably an inorganic acid having a strong acidity such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, metaphosphoric acid and the like, and a Lewis acid such as ZnCl ₂ AlCl ₃ and TiC.
l _{2 is} also valid. If there is a problem in terms of material due to acidity, ammonium salt can be used. It is considered that this is because the thermal decomposition in the next heat treatment step causes ammonia to scatter, and the generated inorganic acid acts as a dehydrating agent. As ammonium salts, ammonium sulfate, ammonium chloride, ammonium nitrate, ammonium phosphate, phosphoric acid 1
Diammonium hydrogen, diammonium dihydrogen phosphate, ammonium metaphosphate, ammonium polyphosphate and the like are effective.

The dehydrating agent as an aqueous solution can be uniformly attached to the surface layer of the PVA fiber by a dipping method using a mang roll or a nip method. Here, the surface layer is a portion close to the fiber surface, and when divided into a skin and a core, it means a region substantially corresponding to a skin.

[0017]

In the present invention, the dehydrating agent is not allowed to uniformly permeate to the center of the fiber, but is stopped only in the portion close to the surface layer and is dried rapidly. The core portion (hereinafter referred to as the central layer) that has not penetrated is melted and removed to form a hollow shape. Therefore, it is necessary that the dehydrating agent penetrates only to a certain depth of the surface layer, and does not penetrate into the central portion, resulting in a non-uniform permeation state. Although any method may be used as long as it can be attached in this way, as a result of examining the relationship between various immersion conditions and hollow formation, the concentration of the dehydrating agent aqueous solution is 2 to 40%, the immersion temperature is 40 ° C to 80 ° C, and the immersion is performed. It has been found that a method of rapidly drying with warm air after adhering with a time of 5 seconds to 2 minutes and an amount of adhering the dehydrating agent of 5 to 20% by weight is suitable.

That is, 5 to 20% by weight of the dehydrating agent adheres only to the surface layer of the fiber by the above-mentioned method, but if it is 2% or less, the dehydration reaction in the heat treatment step is insufficient and the fiber is easily deformed, which is good. It may not be possible to make a hollow shape,
If 20% or more is attached, the dehydration reaction easily proceeds and the inner diameter of the hollow portion tends to be small.

It is preferable that the PVA fiber is dried immediately after the attachment of the dehydrating agent. The drying method is not particularly limited,
Good results can be obtained by a method in which hot air at 120 ° C. is used for rapid drying in 3 to 4 minutes. It may melt if heated rapidly after drying, so it is appropriate to gradually heat from 180 ℃ to 300 ℃ to obtain blackish brown or black. Next, raise the temperature to 400 ℃ to 1,000 ℃. It is necessary to raise the temperature to ℃ within 5 minutes to complete the dry distillation. Then PV
A molecule becomes a polyene structure by the dehydration reaction and is infusibilized.

Although the rate of dehydration reaction due to heat treatment is higher at higher temperatures, the softening point of PVA is 220 ° C. to 240 ° C. Therefore, if the temperature reaches this region during insufficient dehydration reaction, PVA
The fibers are melted and shrunk and deformed remarkably, and a good hollow shape cannot be obtained. When the dehydration reaction by heat treatment progresses, PVA
The fibers change from brown to blackish brown or black and become infusible and the softening point gradually rises. Therefore, in order to form a good surface layer, the heat treatment temperature must be kept below its softening point depending on the progress of the dehydration reaction. If heated rapidly, it may be melted and deformed, and the hollow part may be clogged. Therefore, a method of gradually heating from 180 ° C. to 300 ° C. is preferable.

On the other hand, the central layer is not made infusible because it does not contain a dehydrating agent, and it is considered that when it reaches 220 ° C to 240 ° C or more, it gradually melts to form a hollow portion. However, the hollow part created at this stage is still incomplete in shape,
By increasing the temperature from 400 ℃ to 1,000 ℃ within 5 minutes and performing high-temperature dry distillation for a short time, the carbonization of the surface layer progresses further, the melting of the central layer also progresses, and the cross-sectional shape of the hollow part is also adjusted. It has a round shape and is completely black. It is considered that when the temperature rising rate is decreased, the central portion becomes poorly melted, and the hollow portion carbonized before being melted and removed is narrowed.

The heat treatment and carbonization are carried out in an inert gas,
The treatment time is not particularly limited, but it is 60 minutes from 180 ℃ to 300 ℃, 2
Good results are obtained when the temperature is between 20 ° C and 300 ° C for about 60 minutes. If dry distillation is carried out in any of carbon monoxide gas, hydrogen gas, nitrogen gas, or a mixed gas thereof, it is easy to obtain a regular hollow shape. The shape of the hollow portion may be a continuous type or an independent type.

As described in detail above, the heat treatment and the high temperature dry distillation step, together with the dehydrating agent attaching step, are important steps for forming the hollow shape which is the main part of the present invention.

Next, the hollow carbon fibers formed in the dry distillation step are activated to obtain hollow activated carbon fibers. Although the activation method is not particularly limited, generally, when the activation is promoted, the adsorption property is improved, but the strength property and the yield are lowered, and the property shows a dichotomy. In order to activate the two so that they have a relatively balanced property, the inside of the furnace is maintained at a relatively high temperature of 800 ° C to 1,100 ° C by the combustion gas of liquefied petroleum gas, and the PVA fiber that has been subjected to dry distillation is added thereto. Then 20-30
A rapid activation method that retains the amount of water is preferable, in which case the activation yield is 40
It will be ~ 60%.

The thickness of the hollow activated carbon fiber of the present invention is not limited as long as the surface layer shows semi-permeability, but the outer diameter is usually 5 to 20 μm and the thickness of the fiber wall of the surface layer is 4 μm. The volume of the hollow part is 10 to 70%. Therefore, the surface layer shows a unique physical property having both the adsorptivity peculiar to activated carbon and the property of a semipermeable membrane. Moreover, the hollow portion can be continuous or independent.

The characteristics of the hollow activated carbon fiber of the present invention are most exerted when the activated carbon fiber having continuous pores is bundled, cut into an appropriate length and enclosed in a glass tube, and only the outside of the fibers at both ends is bundled. It adheres to the inner wall of the glass tube with a thermosetting resin,
In this method, the hollow part of the fiber and the outside of the fiber are completely separated by the surface layer part.

The benzene adsorption amount of the hollow activated carbon fiber is 120.
〜130%, BET specific surface area reaches 1,600〜2,500m ² / g. Granular activated carbon has a specific surface area of 1,500-
Due to the limit of 1,700 m ² / g, the hollow activated carbon according to the present invention has a very large specific surface area and therefore exhibits a very high adsorptivity. Further, despite having a large surface area, it has excellent strength properties. This property is considered to have been imparted in the high temperature carbonization process.

As described above, the surface layer of the hollow activated carbon fiber is
Although it is made of activated carbon having a very high adsorptivity, the fiber wall in the surface layer is extremely thin and thus has a property of a semipermeable membrane, and these two functions are synergized to show a unique molecular sieving property. This is clearly seen from the results of Examples 6 and 7. Further, it can be used for highly accurate adsorption separation of organic compounds, separation of nitrogen and oxygen in the air, separation of ethanol and water, and the like. In the case of gas separation, it is possible to use two columns alternately and perform a continuous separation operation by the pressure swing method.

The discovery and use of the molecular sieving properties of hollow activated carbon fibers is a remarkable effect of the present invention which has hitherto been unknown.

Other hollow activated carbon fibers have extremely high adsorptivity even when used for ordinary activated carbon applications, and are therefore widely used for ozone decomposition, sugar solution decolorization purification, deodorization and the like.

[0031]

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

Example 1 PVA fiber for industrial materials (1800
d / 1000f, strength 10.5g / d, elongation 7%) (NH ₄ ) ₂ SO ₄ 70
70 g of each of g and (NH ₄ ) ₂ HPO ₄ was dissolved in 1,000 g of water, and the PVA fiber was squeezed by diple mangle at 70 ° C. for 10 seconds and dried at 105 ° C. for 3 minutes. The deposition rate of the dehydrating agent was 7.3 wt%. After heat-treating this fiber at 300 ℃ or less until it becomes blackish brown, 400 ℃ to 900 ℃ in 3 minutes
The temperature was raised in N ₂ and the mixture was dried and distilled. Then in steam at 1,050 ° C
Activation was carried out until the activation yield reached 50%.

Table 1 shows processing conditions and physical property values. The surface area was measured by Carlo Erba's Sorptomatic 1800 using the BET method (Brunauer Emmett & Teller method), which is the usual method for activated carbon.
It was measured by.

[0034]

[Table 1]

The shape of the hollow portion of the fiber cross section was observed with an optical microscope and a scanning electron microscope. A scanning electron micrograph (× 2000) of the fiber cross section is shown in Fig. 1 as a photograph instead of a drawing to show its shape.

In Example 1, the heat treatment was performed at 300 ° C. or lower until it became blackish brown, and then high temperature dry distillation was not performed. When activated under the same conditions as above, the hollow portion was narrow and did not become a continuous type. The shape was also extremely irregular.

Comparative Example 1 The same conditions as in Example 1 were used except that the temperature rising time from 400 ° C. to 900 ° C. was 10 minutes, but the inner diameter of the hollow portion was 0.6 μ, and the internal void ratio was 0.2%. Very small or hardly produced. When the temperature is gradually raised, the melted state of the central portion where the dehydrating agent has not penetrated becomes poor. This is probably because the core portion was melted and carbonized before being removed. When the temperature rising rate was further reduced and the temperature rising time was set to 20 minutes, no hollow part was observed. Table 2 shows the processing conditions and physical property values.

[0038]

[Table 2]

(Comparative Example 2) Dehydrating agents (NH ₄ ) ₂ SO ₄ and (NH ₄ ) ₂
The HPO ₄ deposition rate was increased to 12% and 13%, respectively, and the treatment was performed under substantially the same conditions as in Example 1. However, the inner diameter of the hollow part was 2.1 μ, the internal void ratio was 3.2%, and the hollow part was narrow. It was also an independent hole.

Table 2 shows processing conditions and physical property values.

(Examples 2 to 5) Sulfuric acid was used as a dehydrating agent,
Zinc chloride or phosphoric acid was used, and the high temperature dry distillation conditions were also changed. The treatment conditions and physical properties of Examples 2 to 4 are shown in Table 1, and Example 5 is shown in Table 2.

(Example 6) A tow of hollow activated carbon fiber having an outer diameter of 12 µ and an inner diameter of 7 to 8 µ having the treatment conditions and physical properties shown in Table 2 was inserted into a glass tube having an inner diameter of 5 cm and a length of 50 cm. Both ends of the fiber bundle and the inner surface of the glass tube were filled with an epoxy resin to separate the hollow portion of the hollow fiber from the outside of the fiber, and a port was provided for each.

When the outer side of the fiber is kept slightly pressurized at about 0.3 kg / cm ² and continuously blown with air,
Oxygen gas permeates the surface layer of the activated carbon fiber and flows into the hollow portion of the fiber, and a gas enriched with nitrogen gas continuously flows out from the outlet of the fiber on the outer side.

When air is aerated at the space velocity of the separator of 0.1 hr ^-1 , the oxygen concentration in the separated nitrogen gas is 0.1%.
Therefore, it was confirmed that oxygen and nitrogen in the air can be efficiently separated.

(Example 7) A column having the same size as in Example 6 was prepared using the hollow activated carbon fiber obtained in Example 3, and CHCl ₃ and CCl ₄ were added at 1% from the outside inlet of the fiber. The nitrogen gas containing the nitrogen gas was slightly pressurized and was continuously flowed at a space velocity of the separator of 0.1 hr ⁻¹ .

99.99% of the organic components contained in the gas that has permeated the surface layer of the fiber and flowed into the hollow portion are CHCl ₃ and CC
Almost no l ₄ was observed.

[0047]

EFFECTS OF THE INVENTION By utilizing the high molecular weight of the hollow surface activated carbon fiber having a high adsorptivity and the semipermeable property of the thin surface fiber wall, the separation of nitrogen and oxygen from the air and the organic compound It can be used for highly accurate adsorption separation, separation of ethanol and water, etc. Further, in the case of gas separation, a continuous separation operation is possible by the pressure swing method.

In addition, since the hollow activated carbon fiber has an extremely high adsorptivity even as activated carbon, it can be widely used for applications such as ozone decomposition, sugar solution decolorization and purification, and deodorization.

[Brief description of drawings]

FIG. 1 shows a scanning electron micrograph of a cross section of the hollow activated carbon fiber obtained in Example 1 (2,000 times).

Claims (2)

[Claims] 1. After applying a dehydrating agent to the surface layer of polyvinyl alcohol fiber, heat treatment is performed until it becomes blackish brown or black so as not to melt the fiber, and further heated from 400 ° C. to 1,000 ° C. within 5 minutes. It is possible to separate the contained components by supplying a gas or liquid containing multiple components from the outside or inside of the fiber by using the hollow activated carbon fiber prepared by dry distillation and further activation. Characteristic method for separating gas or liquid. 2. The separation method according to claim 1, wherein air is used as a gas containing a plurality of components, and the separation component is nitrogen gas.