JP2011125799A - Method for recovering low boiling point organic solvent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently recover a solvent from a gas containing a low boiling point organic solvent with a boiling point of 40-110°C by using cleaning air as a purging gas. <P>SOLUTION: To recover the low boiling point organic solvent with a boiling point of 40-110°C contained in exhaust gas by using a pair of adsorption-desorption vessels charged with an adsorbent, a process of switching from adsorption to desorption and vice versa in the pair of adsorption-desorption vessels in 5-20 minutes, a process of feeding the gas containing the organic solvent to the adsorption side of the adsorption-desorption vessels, a process of feeding a purging gas feeding cleaning air in a vacuum state as the purging gas for desorption to the adsorption-desorption vessels, and a process of recovering a solvent by liquefying the desorbed solvent in the purging gas are included. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to the technical field of a method for recovering a low-boiling organic solvent contained in exhaust gas and having a boiling point in the range of about 40 to 100 ° C.

Generally, this kind of low boiling point organic solvent (volatile organic solvent) includes dimethyl ether, methyl ethyl ether, diethyl ether, acetone, methyl ethyl ketone, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, dimethyl ethylene, n-hexane. Organic solvents such as cyclohexane, benzene, and toluene are exemplified, and when these organic solvents are vaporized and contained in the air to become organic solvent-containing air, they are not allowed to be released into the atmosphere as they are and must be recovered. is there.
Such a low boiling point organic solvent has a low boiling point and is difficult to recover by simply cooling the air containing the organic solvent.
Therefore, an organic solvent is adsorbed using an adsorbent such as silica gel or alumina, and the adsorbed organic solvent is desorbed under reduced pressure and recovered (see Patent Document 1).

JP-A-5-337323

However, the conventional one uses nitrogen which is an inert gas as a purge gas for desorption. By the way, when nitrogen gas is used as a purge gas, when a nitrogen gas cylinder or liquid nitrogen is used, it is not suitable for continuous organic solvent recovery. Therefore, when nitrogen in the air is taken out and used, there is a problem that a nitrogen gas taking out device is required. Therefore, the above-mentioned conventional one collects and reuses the nitrogen gas used for desorption, but this one is provided with a nitrogen gas adsorption / desorption tank for collecting nitrogen gas and adsorbed here. Since nitrogen is used after being desorbed, there is still a problem that the apparatus itself becomes complicated and large.
Accordingly, if the adsorption / desorption conditions when using purified air instead of such nitrogen gas as the purge gas are considered, the idea is that the device itself can be reduced in size and size, and here is the problem to be solved by the present invention. There is.

The present invention was created with the object of solving these problems in view of the above-mentioned circumstances, and the invention of claim 1 is an exhaust gas using a pair of adsorption / desorption tanks charged with an adsorbent. A method of recovering a low-boiling organic solvent having a temperature of 40 to 110 ° C. contained in the adsorption / desorption switching step in which the adsorption / desorption switching of the pair of adsorption / desorption tanks is performed for 5 to 20 minutes; A contained gas supply step for supplying the gas containing the organic solvent to the adsorption side adsorption / desorption agent tank, a purge gas supply step for supplying purified gas to the desorption side adsorption / desorption tank in a vacuum state as a purge gas for desorption, and a solvent A method for recovering a low boiling point organic solvent, comprising: a solvent recovery step of liquefying and recovering a solvent from a desorbed purge gas.
The invention according to claim 2 is the method for recovering a low-boiling organic solvent according to claim 1, wherein the adsorbent is a hydrophobic silica gel having a pore diameter of 5 to 60 mm and a specific surface area of 400 to 1000 m ² / g. It is.
The invention according to claim 3 is the low boiling point organic solvent recovery method according to claim 1 or 2, wherein the degree of vacuum is -0.080 to -0.095 MPa and the adsorbent is not overheated. .

According to the first aspect of the present invention, efficient recovery of the low boiling point organic solvent can be continuously performed while using purified air as the purge gas.
By making the invention of claim 2 or 3, further efficient recovery of the low boiling point organic solvent can be continuously performed.

It is a block circuit diagram in a solvent recovery device. 6 is a table showing experimental conditions and results of Experimental Example 1. FIG. 10 is a table showing experimental conditions and results of Experimental Example 2. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Reference numeral 1 denotes a suction channel for air containing a low-boiling organic solvent, and the suction channel 1 is branched into first and second branched suction channels 1a and 1b. It is connected to the. Both adsorption / desorption tanks 2 and 3 are charged with hydrophobic silica gel.
Reference numeral 4 denotes an exhaust passage provided with an adsorption blower 5. The exhaust passage 4 joins branch exhaust passages 4a and 4b connected to the first and second adsorption / desorption tanks 2 and 3, respectively. It is composed of that.

  Branch desorption channels 6a and 6b through which desorption gas desorbed from the first and second adsorption / desorption tanks 2 and 3 flow are connected to the branch suction channels 1a and 1b, respectively. The channels 6a and 6b merge to form a desorption channel 6 and reach the condenser 7. The desorption channel 6 is provided with a vacuum pump 8, and the first and second adsorption / desorption tanks 2 are provided. 3 is desorbed in a vacuum state. The refrigerant cooled by the refrigerator 9 is supplied to the condenser 7, and the desorption gas is cooled to liquefy the desorption solvent and collect it in the recovery container 10 as a recovery liquid. The gas to be condensed discharged from the condenser 7 is returned to the suction flow path 1 via the trap tank 11 and the reduction flow path 11a.

  On the other hand, reference numeral 12 denotes a purge gas supply passage through which purge gas (purified air) is supplied. The purge gas supply passage 12 serves as a branch purge gas supply passage and is connected to the branch exhaust passages 4a and 4b. Yes.

  The branch suction channels 1a and 1b, the branch exhaust channels 4a and 4b, the branch desorption channels 6a and 6b, and the branch purge gas supply channels 12a and 12b are respectively provided with on-off valves 13, 13a, 14, 14a, 15, 15a, 16 and 16 a are provided, and a vacuum pressure adjusting valve 17 is provided in the purge gas supply flow path 12. Reference numeral 19 denotes a filter provided in the purge gas supply flow path 12.

  Next, the repetition of adsorption / desorption in the first and second adsorption / desorption tanks 2 and 3 is continuously performed by the opening / closing control of the on-off valves 13, 13a, 14, 14a, 15, 15a, 16, 16a. The procedure will be described. The opening / closing control of each opening / closing valve is automatically performed by a control command from a controller (not shown).

  When adsorption is performed in the first adsorption / desorption tank 2 while the adsorption blower 5 and the vacuum pump 8 are driven and desorption is performed in the second adsorption / desorption tank 3, the on-off valves 13, 14, 15a and 16a are opened and opened / closed. The valves 13a, 14a, 15, 16 are closed. Thus, the organic solvent-containing air sucked from the suction channel 1 is exhausted via the branch suction channel 1a, the first adsorption / desorption tank 2, the branch exhaust channel 4a, and the exhaust channel 4. The organic solvent is adsorbed in the first adsorption / desorption tank 2. On the other hand, the purge gas includes a purge gas supply channel 12, a branch purge gas supply channel 12b, a second adsorption / desorption tank 3, a branch desorption gas supply channel 6b, a desorption gas supply channel 6, a condenser 7, a trap tank 11, The second adsorption / desorption tank 3 is subjected to desorption action of the adsorbing material by the purge gas while being in a vacuum state, and the desorption gas is condensed into the condenser 7. The solvent condensed and liquefied in step 1 is recovered in the recovery container 10.

  On the other hand, when the adsorption blower 5 and the vacuum pump 8 are driven and desorbed in the first adsorption / desorption tank 2 and adsorbed in the second adsorption / desorption tank 3, the on-off valves 13, 14, 15a and 16a are provided. It closes and the on-off valves 13a, 14a, 15, 16 are opened. As a result, the organic solvent-containing air sucked from the suction channel 1 is exhausted via the branch suction channel 1b, the second adsorption / desorption tank 3, the branch exhaust channel 4b, and the exhaust channel 4. The organic solvent is adsorbed in the second adsorption / desorption tank 2. On the other hand, the purge gas includes a purge gas supply channel 12, a branch purge gas supply channel 12a, a first adsorption / desorption tank 2, a branch desorption gas supply channel 6a, a desorption gas supply channel 6, a condenser 7, a trap tank 11, The first adsorbing / desorbing tank 3 is desorbed by the purge gas while being in a vacuum state, and the desorbing gas is supplied to the condenser 7. The solvent condensed and liquefied in step 1 is recovered in the recovery container 10.

In carrying out the present invention using such an apparatus, the organic solvent to be recovered is a low-boiling organic solvent in the range of about 40 to 100 ° C., which is dimethyl ether, methyl ethyl ether, diethyl ether, acetone, methyl ethyl ketone. , Methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, dimethylethylene, n-hexane, cyclohexane, benzene, toluene and the like.
As the adsorbent used in the present invention, commonly known adsorbents such as silica gel, zeolite, alumina, activated carbon and the like can be used, but hydrophobic silica gel is preferred. The hydrophobic silica gel is preferably a silica gel having a pore size of 5 to 60 mm and a specific surface area of 400 to 1000 m ² / g.
The degree of vacuum performed in the desorption step of the present invention is preferably in the range of -0.080 to -0.095 MPa, and the adsorbent is preferably left at room temperature without overheating.

<Experimental example 1>
As an adsorbent, 21.3 kg of “Q6” hydrophobic silica gel (average pore diameter: 60 mm, specific surface area: 628 m ² / g) manufactured by Fuji Silysia Chemical Co., Ltd. was charged into both adsorption / desorption tanks 2 and 3 each. The flow rate of the adsorption blower was adjusted so that isopropyl alcohol was used as the adsorption solvent and the treatment air volume was 2 m ³ / min. Both the first and second adsorption / desorption tanks 1 and 2 were left in the room temperature condition where the apparatus was installed. When the adsorption / desorption treatment experiment was conducted under the conditions of adsorption conditions, desorption conditions, cycle time for switching between adsorption / desorption and the number of operation cycles (number of adsorption / desorption times) shown in the table of FIG. 2, the exhaust concentration shown in the table of FIG. Became. When the recovered solvent was trapped and identified by gas chromatography, the presence of a small amount of water was confirmed in isopropanol.
According to this, when the cycle time is 20 minutes, it is confirmed that the exhaust gas contains 68 ppm of isopropyl alcohol at the maximum, and there is discharge of the organic solvent that is not recovered at a cycle time longer than this, which is not preferable. It can be said.

<Experimental example 2>
Next, the adsorbent, the adsorbing solvent, and the treatment air volume are the same as those in Experimental Example 1. When the adsorption / desorption treatment experiment was conducted under the conditions, the exhaust concentration shown in the table of FIG. 3 was obtained. When the recovery material was trapped and identified by gas chromatography, the presence of a small amount of water was confirmed in isopropanol. According to this, it was confirmed that the higher the degree of vacuum, the higher the desorption efficiency, and the one with a degree of vacuum of -0.0080 MPa confirmed that the exhaust gas contained 25 ppm of isopropyl alcohol at the maximum. It can be said that it is not preferable to desorb at the above degree of vacuum.

  INDUSTRIAL APPLICABILITY The present invention has industrial applicability for efficiently recovering an organic solvent from air containing a low-boiling organic solvent while using air as a purge gas.

DESCRIPTION OF SYMBOLS 1 Suction flow path 2 1st adsorption / desorption tank 3 2nd adsorption / desorption tank 4 Exhaust flow path 5 Intake blower 6 Desorption flow path 7 Condenser 8 Vacuum pump 10 Recovery container 12 Purge gas supply flow path 17 Vacuum pressure control valve

Claims (3)

A method of recovering a low boiling point organic solvent at 40 to 110 ° C. contained in exhaust gas using a pair of adsorption / desorption tanks loaded with an adsorbent,
An adsorption / desorption switching step in which the adsorption / desorption switching of the pair of adsorption / desorption tanks is performed for 5 to 20 minutes;
A containing gas supply step of supplying a gas containing the organic solvent to the adsorption side adsorption / desorption agent tank;
A purge gas supply step of supplying purified gas to the desorption side adsorption / desorption tank in a vacuum state as purge gas for desorption;
A solvent recovery process for liquefying and recovering the solvent from the purge gas desorbed;
A method for recovering a low-boiling organic solvent, comprising the steps of: The method for recovering a low-boiling organic solvent according to claim 1, wherein the adsorbent is hydrophobic silica gel having a pore diameter of 5 to 60 mm and a specific surface area of 400 to 1000 m ² / g.   The method for recovering a low-boiling organic solvent according to claim 1 or 2, wherein the degree of vacuum is -0.080 to -0.095 MPa and the adsorbent is not overheated.

Images