JPH0732861B2 - Activated carbon regeneration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is directed to desorbing a solvent adsorbed on activated carbon with water vapor by using water vapor having a desorption pressure, a pressure lower than temperature and temperature. (Hereinafter referred to as a coal bed) is replaced with steam after degassing, and after the desorption is completed, the coal bed is maintained at a pressure lower than the desorption pressure, and by the heat of vaporization and desorption of water contained in activated carbon, The present invention relates to a method for regenerating activated carbon in which a coal bed temperature is lowered to a steam saturation temperature at a pressure and then a solvent is adsorbed.

[Conventional technology]

In the activated carbon adsorption method for recovering the organic solvent contained in the exhaust gas generated by various operations such as the manufacturing process of various plastic products and various operations such as the magnetic tape industry, the activated carbon was filled with 2
A bed or more adsorption tanks are installed in parallel, and a fixed-bed solvent recovery device or a tray column is installed in which adsorption and desorption for regeneration of activated carbon are alternately repeated, and the activated carbon is continuously lowered from the top of the tower. A fluidized bed type adsorbing device, etc., which adsorbs a solvent while flowing the activated carbon by a mixed gas of air and a solvent (hereinafter referred to as raw gas) fed from the bottom, is known.

These adsorption tanks are generally operated under atmospheric pressure for both adsorption and desorption, and steam is used for desorption. Of these conventional methods, the two-layer fixed bed adsorption device will be described with reference to FIG. 2 and Table 1 (conventional method). Table 1 shows an example of operating conditions of the adsorption tank for the conventional method and the method of the present invention.

In FIG. 2, the raw gas 1 is absorbed by the blower 2 in the adsorption tank 3-
The solvent in the raw gas is adsorbed by the activated carbon forming the fixed bed, and the purified waste gas is released to the atmosphere. For example, if an adsorption operation is performed in the adsorption tank 3-1, the other adsorption tank 3-2
Ends adsorption and is switched from adsorption to desorption by a switching valve. The water vapor S is blown in and the adsorbed solvent is desorbed and discharged in a gaseous state together with the water vapor. This mixed vapor (desorption vapor) is guided to the condenser 5 and is wholly condensed by water cooling. At this time, when the water and the recovered solvent are mutually insoluble, the decanter 9 separates into two layers, a solvent layer and an aqueous layer, due to the difference in specific gravity, and the water is discharged and the solvent is recovered. When the two are partially or wholly soluble in each other, they are appropriately sent to a distillation column (not shown) to separate water and solvent. At this time, the condenser side of the condenser 5 communicates with the atmosphere through the vent pipe 10, so that desorption is performed under atmospheric pressure. In this system, the activated carbon temperature is at the adsorption temperature (generally around 30 ° C) at the initial stage when the adsorption process is switched to the desorption process, and the absorbed water vapor condenses and raises the coalbed temperature to reach 100 ° C. The stagnant raw gas is discharged, then the desorption vapor is discharged from the adsorption tank, and the desorption is continued at 100 ° C. After the desorption process is completed, the adsorption tank is switched to the adsorption process, and the raw gas is blown into the adsorption tank. At this time, the temperature of the coal bed after desorption is 100 ° C, and the water in the activated carbon (condensed steam)
When the gas is evaporated into the raw gas, the temperature of the coal bed is gradually lowered by the heat of evaporation, and the adsorption of the solvent in the raw gas proceeds.

By the way, in recent years, a large amount of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone or the like has been used as a ketone solvent in the magnetic tape manufacturing or the synthetic resin processing industry. During adsorption and desorption, these ketone solvents are apt to undergo reactions such as oxidation, decomposition and polymerization on the activated carbon, which poses safety problems with respect to the purity of the recovered product, the activated carbon adsorption capacity retention period and coal bed ignition. For example, methyl ethyl ketone is oxidized by the catalytic action of activated carbon to produce diacetylacetic acid and the like, and the recovered solvent is colored yellow to impair the product purity. Cyclohexanone is also oxidized to produce cyclohexanedione, adipic acid and the like. These oxides have high boiling points, are not easily desorbed in the desorption process, accumulate in the activated carbon pores, and gradually reduce the adsorption performance of the activated carbon. Furthermore, these ketone solvents generate peroxides by oxidation, which often causes ignition of coal layers. In this oxidation reaction, when the adsorption step is completed and the desorption step is started, air in the raw gas is present in the coal bed, and steam is blown into the coal bed, and the coal bed is heated to a high temperature by condensation of the steam. The solvent adsorbed in the activated carbon is violently generated by the catalytic action of the activated carbon in the presence of oxygen. In addition, when desorption is completed and adsorption starts, the coal layer is still at a high temperature, and if raw gas is fed into this, along with the solvent remaining in the activated carbon, high temperature and the presence of oxygen will be present as in the desorption initial stage. Below, it is considered that the oxidation of the solvent occurs violently due to the catalytic action of activated carbon.

Therefore, suppression of reaction of these solvents is strongly demanded.

[Problems to be Solved by the Invention]

The present invention has been made to solve the above problems, and its purpose is to desorb, further suppress the reaction such as decomposition of the solvent adsorbed on the activated carbon during adsorption, oxidation, polymerization, etc., the life of the activated carbon Is trying to lengthen.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present inventors have found that the reaction rate such as the oxidation of the solvent on the activated carbon changes depending on the temperature, and that the reaction rate greatly decreases as the temperature decreases, and low pressure low temperature at the initial stage of steam desorption. The air in the coal seam is expelled using the steam of, and then desorption is performed using the steam of a predetermined temperature, and after the desorption is completed, the steam remaining in the coal seam is condensed by water-cooling with a condenser in the adsorption tank. Since the boiling point of water is lowered by reducing the pressure, the water contained in the activated carbon after steam desorption is evaporated, and at this time, the coal layer temperature is lowered by the heat of evaporation of water. After the temperature of the coal seam has dropped to a predetermined temperature, the process proceeds to the adsorption step, and the raw gas is passed through the coal seam.

By this desorption-adsorption method, steam desorption is carried out without the activated carbon and the solvent contained therein contacting with air at high temperature.

[Embodiment and Action]

The method of the present invention will be described below with reference to FIG. 1 and Table 1 (method of the present invention).

FIG. 1 is a flow chart showing an embodiment of the present invention. In FIG. 1, the adsorption tank 3-1 is in the adsorption step, and the adsorption tank 3-2 is in the desorption step. Here, adsorption tank 3-2
In the initial stage after switching to the adsorption step, the adsorption tank was filled with the raw gas, and was at about atmospheric pressure. The gas in the adsorption tank 3-2 in such a state is sucked through the vent pipe 10 of the condenser 5 by the vacuum pump 6 when the desorption process is started, and the adsorption tank 3-2 is depressurized to a predetermined pressure. On the other hand, the sucked gas is connected to the conduit at the outlet of the raw gas blower 2.

After that, the steam S is depressurized to a pressure almost equal to that of the adsorption tank 3-2 by the depressurization valve PCV-1, and the steam becomes a superheated steam temperature state at the depressurized pressure. Therefore, the steam S is cooled to the saturated steam temperature at the pressure. Water W to do
Is sent into the steam through the temperature control valve TCV, and the steam having reached the saturated steam temperature by the evaporation of water is sent to the adsorption tank 3-2 to heat the coal bed 4-2. The temperature of the coal bed 4-2 rises from the temperature in the adsorption step (generally around 30 ° C.) to the reduced pressure heating temperature, that is, the saturation temperature at a predetermined pressure of the steam, due to the condensation of the introduced steam. This rise in the temperature of the coal seam reaches the steam temperature from the upper part of the coal seam, at the same time the condensation of steam in that part stops, and the air staying in the coal seam in that part is extruded downward due to the passage of steam, and this gradually becomes to the lower part of the coal seam. The air in the coal seam is almost completely discharged at the time when the temperature of the entire coal seam reaches the temperature equal to the steam temperature.

In the conventional method, the time required for the entire coal bed to reach the desorption temperature (100 ° C) was 0.5
It is ~ 1 hour, and the organic solvent is exposed to high temperature in the presence of activated carbon and air during this time, and the solvent causes the most vigorous oxidation reaction. It is self-evident that the oxidation reaction rate decreases as the temperature decreases, but when the air in the coal seam is exhausted at the initial stage of desorption, 100 ° C
Compared with the conventional method of heating the coal bed to 100 ° C to remove the air by using the above steam, the use of steam at low pressure and low temperature has a great effect on suppressing the oxidation of the solvent. .

After the entire coal bed reached the saturated steam temperature under a predetermined reduced pressure, the vacuum pump 6 was stopped, the desorption valve V-B was closed, and then steam S was sent to the adsorption tank 3-2 at a pressure of about 1 atm and a temperature of about 100 ° C. By entering the water, further condensation of steam occurs in the coal seam 4-2 and reaches about 100 ° C. After the coal layer reaches about 100 ° C. in this way, the desorption valve V-B is opened, and then steam at about 100 ° C. is fed for a predetermined time to desorb the solvent adsorbed on the activated carbon. The reason why desorption is not performed with low-pressure low-temperature steam at 100 ° C steam is that the amount of steam required for desorption increases as the temperature decreases, and after air is removed from the coal bed, solvent oxidation does not occur even at high temperatures. It depends.

After finishing the desorption process and stopping the feeding of water vapor to the adsorption tank 3-2, the coal bed 4-2 is cooled to a predetermined temperature lower than the desorption temperature before entering the adsorption process and feeding the raw gas 1 to the adsorption tank 3-2. The SV of the condenser vent pipe 10 is fully opened for cooling to the temperature. Adsorption tank 3
-2 and the condenser 5 are filled with steam,
By closing the vent pipe 10, as the water vapor passes through the cooling water W and is condensed by water cooling in the condenser 5, the adsorption tank 3-
The pressure in 2 drops. As the pressure decreases, the water (condensed water in the initial stage of desorption) contained in the coal seam 4-2 at the desorption temperature evaporates, and its heat of vaporization (desorption heat: about the latent heat of vaporization of water)
1.3 times), the temperature of the coal seam drops. After the coal bed 4-2 has reached a predetermined temperature by this reduced pressure cooling, the desorption process is completed, and the on-off valve SV and the pressure control valve PCV-2 are opened to open the adsorption tank 3-.
2 is returned to atmospheric pressure, the adsorption process is switched to, and the raw gas 1 is fed. At the same time, the adsorption tank 3-1 is switched to the desorption process,
Decompression-decompression heating-desorption-decompression cooling are performed.

In this depressurized cooling after desorption, if there is some leakage in the switching valve attached to the adsorption tank and there is air inflow during depressurized cooling, which may impede depressurization, the on-off valve SV is not used and the vacuum pump 6 is not used. The present invention also includes adjusting the set pressure of the driven pressure control valve PCV-2 to a pressure corresponding to the ultimate temperature of the coal seam, and maintaining a predetermined depressurization pressure while discharging the inflowing air. It is clear that this pressure also depends on the water temperature of the cooling water W.

By this reduced-pressure cooling, the solvent remaining in the coal bed after desorption is cooled at a high temperature without contacting with air, so that oxidation of the residual solvent is prevented. Furthermore, the oxidation of new adsorption solvent at the initial stage of adsorption is also prevented.

In addition, desorption may be performed using reduced pressure low-temperature steam in order to suppress polymerization due to heating of the solvent, but in that case as well, in order to prevent oxidation of the solvent, heating under reduced pressure before desorption of the coal bed (air from the coal bed Exclusion) than in desorption
Further, it is included in the present invention that it is performed by using low pressure and low temperature steam, and that the reduced pressure cooling after desorption is performed at a lower pressure than that in desorption.

[Example] Using two adsorption tanks filled with activated carbon from a gas containing cyclohexanone and toluene generated from a dryer, one is a cycle in which adsorption by the conventional method and regeneration of activated carbon by steam desorption at 100 ° C. at atmospheric pressure are repeated. By the method according to the present invention and the method by the cycle of repeating adsorption by the method of the present invention and steam heating under reduced pressure, steam desorption at 100 ° C., and regeneration of activated carbon by cooling under reduced pressure under the same specification conditions. Table 2 compares the operating time until the concentration of exhaust gas in the tank exceeds the specified value).

Operating conditions Gas flow rate containing solvent (cyclohexanone, toluene) 10,0
00Nm ³ / H Solvent concentration in gas 2360volppm Solvent recovery amount Toluene 50Kg / H Cyclohexanone 50Kg / H Adsorption tank exhaust gas solvent concentration Specified amount <100volppm Adsorption tank (cylinder wise type) 2 units Inner diameter 3.1m φ Height 3.0m Activated carbon 3,300Kg / Substrate switching time Adsorption 3 hours, desorption 3 hours Steam used 2Kg / cm ² G Cooling water 30 ℃ Note that FIG. 3 shows the time until the concentration of the exhaust gas solvent in the adsorption tank reaches 100 volppm.

〔The invention's effect〕

In the conventional method, the solvent exposed to high temperature in the presence of air is oxidized in the conventional method, and the raw gas fed in the initial stage of adsorption is heated, so that oxides are generated and accumulated in the activated carbon.
The life of activated carbon is short. On the other hand, in the method of the present invention, after decompressing the adsorption tank and feeding low temperature steam to discharge air,
Oxidation of the solvent is suppressed because desorption is performed by atmospheric pressure steam. After desorption, the coal layer is cooled by the heat of evaporation of water due to the reduced pressure, and the raw gas is fed in the adsorption step, so that the oxidation is suppressed.

Due to the effect of these oxidation suppression, the adsorption tank exhaust gas solvent concentration under constant adsorption and desorption conditions in the method of the present invention is 100 volppm
It takes about 3 times longer than that of the conventional method. This means that the activated carbon replacement cost will be less than 1/3 of the conventional cost, and the recovery cost of the solvent will be greatly reduced, so the economic effect is great.

Further, by suppressing the generation of oxides, the yield and quality of the recovered solvent can be improved.

[Brief description of drawings]

FIG. 1 is a flow chart of the reduced pressure heating, atmospheric pressure desorption and reduced pressure cooling system of the present invention. FIG. 2 is a flow chart of a conventional atmospheric pressure heating and atmospheric pressure desorption method. FIG. 3 is a diagram showing the relationship between solvent recovery operation period and adsorption tank exhaust gas solvent concentration transition (Example). 1 ... Raw gas, 2 ... Gas blower 3-1, 3-2 ... Adsorption tank, 4-1, 4-2 ... Activated carbon layer 5 ... Condenser, 6 ... Vacuum pump 7 ... Relay tank , 8 ... Liquid feed pump 9 ... Decanter, 10 ... Vent pipe S ... Steam, W ... Cooling water PCV-1 ... Steam pressure control valve PCV-2 ... Vacuum pump pressure control valve TCV ... Steam Temperature control valve SV ... Shut-off valve V-B ... Desorption valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01D 53/44 53/81 B01J 20/34 B 7202-4G

Claims (1)

[Claims] 1. A method for regenerating activated carbon by adsorbing a solvent gas using an adsorption tank filled with activated carbon and then injecting a predetermined vapor directly into the activated carbon layer to desorb the gas adsorbed on the activated carbon. Before blowing in, the pressure in the adsorption tank is reduced, then steam below the temperature of the steam is blown, the air in the activated carbon layer is replaced by steam at the saturation temperature of the reduced pressure, and then the steam is blown for desorption. After stopping the steam injection, the pressure inside the adsorption tank is reduced to the pressure at the time of desorption or less, and the temperature of the activated carbon layer is changed from the desorption temperature to near the steam saturation temperature at the depressurized pressure by the heat of vaporization of the water contained in the activated carbon. A method for regenerating activated carbon, characterized by moving to an adsorption step after cooling.