JP2010137195A - Method and system for solvent recovery, and method and apparatus for freeze-dehydration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover a high-purity organic solvent with a water content lower than that of an azeotrope without adding or using a third component. <P>SOLUTION: A gas 1 containing an organic solvent is brought into contact with water in a gas absorbing column 20 to absorb the organic solvent with water. The obtained aqueous solution 2 of the organic solvent is distilled in a dehydration distillation column 30 so that the water content of the aqueous solution of the organic solvent is reduced to a water content equal to or higher than that of the azeotrope of the organic solvent and water. The obtained aqueous solution of the organic solvent is cooled in a freeze-dehydration apparatus 40 to separate the water contained in the solution by freezing. The water content of the organic solvent is thus reduced to a water content lower than that of the azeotrope of the organic solvent and water. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solvent recovery method and system, and a freeze dehydration method and apparatus.

  Tetrahydrofuran (THF) is widely used as an organic solvent. However, since it is an expensive solvent, if it can be recovered and reused, the economic merit is great. As a method for recovering THF from a gas containing THF, as described in Non-Patent Document 1, a method of dehydrating and distilling the water that has absorbed the THF after absorbing the THF in the gas into water is described. Has been. However, since THF azeotropes with water, this method can only obtain THF containing about 6 wt% of water having an azeotropic composition.

  Therefore, in Non-Patent Document 1, as a method for purifying THF to a higher purity, an extraction solvent such as pentane is added to the distillate having the above azeotropic composition, and three components of water, THF, and extraction solvent are added. A method is described in which water is separated from THF by performing purification distillation in a system and THF is purified to a higher concentration. Further, in this Non-Patent Document 1, as an alternative, the distilled liquid having the above azeotropic composition is passed through a tower filled with a water-absorbing agent such as sodium hydroxide or calcium chloride to absorb moisture in THF. How to do is described.

"Recovery of Tetrahydrofuran (THF)", Product Information, DuPont Terathane (R) Products, DuPont

  However, the method of purifying distillation by adding an extraction solvent such as pentane has a problem that the extraction solvent may be mixed in the recovered THF, and it is difficult to obtain high-purity THF. In addition, the method of using a water absorbing agent such as sodium hydroxide may cause the water absorbing agent to be mixed into the recovered THF, making it difficult to obtain high-purity THF, and a used water absorbing agent that has absorbed moisture. Since a large amount of water is generated, the treatment of the water-absorbing agent also becomes a problem. Such problems are not limited to THF, but azeotrope with water, such as ethanol, and are common in methods for recovering organic solvents that can reduce the water content only to the azeotropic composition by distillation alone. It is a problem.

  Therefore, in view of the above problems, the present invention provides a solvent recovery method and system capable of recovering a high-purity organic solvent having a lower water content than the azeotropic composition without adding or using a third component, It is another object of the present invention to provide a freeze dehydration method and an apparatus therefor.

  In order to achieve the above object, according to one aspect of the present invention, there is provided a solvent recovery system, wherein a gas containing an organic solvent is brought into gas-liquid contact with water, and the water absorbs the organic solvent. Gas absorption means and an organic solvent aqueous solution obtained from the gas absorption means are distilled, and the water content in the organic solvent aqueous solution is increased to a water content that is an azeotropic composition of the organic solvent and water or higher. A dehydrating distillation means for lowering the water content to a lower temperature, cooling the distillate obtained by the dehydrating distillation means, freezing water contained in the distillate, and allowing the water in the distillate to coexist with the organic solvent and water. And a freeze dehydration apparatus that further lowers the water content of the boiling composition.

  Another aspect of the present invention is a solvent recovery method, which comprises a gas absorption step in which a gas containing an organic solvent is brought into gas-liquid contact with water and the water absorbs the organic solvent, and the gas absorption step. Distilling the aqueous solution of the organic solvent obtained in step (b) to lower the water content in the aqueous solution of the organic solvent to a water content of the azeotropic composition of the organic solvent and water or higher, and the dehydration step. The distillate obtained by the distillation step is cooled to freeze the moisture contained in the distillate, and the moisture in the distillate is further reduced from the water content which is the azeotropic composition of the organic solvent and water. And a freeze-dehydration step for lowering.

  Another aspect of the present invention is a freeze dehydration apparatus, a cooling tank containing a processing target liquid containing an organic solvent and water, and a stirring means for stirring the processing target liquid in the cooling tank, The cooling target for cooling the processing target liquid in the cooling tank until the water in the processing target liquid freezes and becomes a sherbet shape, and the processing target liquid in the sherbet shape is kept in a liquid state. A filter for separating the organic solvent and the sherbet-like ice and means for heating and liquefying the separated sherbet-like ice are provided. The opening of the filter is preferably in the range of 0.15 mm to 1 mm.

  In another aspect, the present invention provides a solvent recovery method, in which a water in the liquid to be treated is frozen while the liquid to be treated containing an organic solvent and water is stirred, so that the liquid to be treated is a sherbet. A cooling step for cooling the processing target liquid until it becomes a shape, an organic solvent recovery step for separating and removing the sherbet-like ice from the processing target liquid in the sherbet shape by a filter, and the separated sherbet shape And the step of liquefying the ice.

  Thus, according to the present invention, a solvent recovery method and system capable of recovering a high-purity organic solvent having a moisture content lower than the azeotropic composition without adding or using a third component, and freeze dehydration A method and apparatus can be provided.

  Hereinafter, an embodiment of an absorption solvent recovery system according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an outline of an embodiment of an absorption solvent recovery system according to the present invention. Although the case where the solvent to be treated is tetrahydrofuran (THF) will be described, the present invention is not limited to THF, and is water-soluble such as ethanol, isopropyl alcohol, ethyl acetate, methyl ethyl ketone, dioxane, Similarly, an organic solvent having a property of azeotropically with water can be recovered with high purity.

  As shown in FIG. 1, the absorption solvent recovery system 10 includes a gas absorption tower 20 that absorbs and removes THF from a THF-containing gas 1, and an aqueous THF solution generated in the gas absorption tower 20 by distillation to azeotrope water. The dehydration distillation column 30 that can be removed to the composition, the freeze dehydration device 40 that freezes and separates the water in the hydrous THF solution obtained in the dehydration distillation column 30 and performs high dehydration, and the freeze dehydration device 40 It is mainly composed of a purification distillation column 50 that purifies and distills dehydrated THF to obtain high-purity purified THF.

  The gas absorption tower 20 is not particularly limited as long as it is a device that brings the THF-containing gas 1 into gas-liquid contact with water as an absorption liquid and absorbs and removes THF in the gas into the absorption liquid. In addition, in order to send the gas filter 11 which removes the fine particles contained in the THF-containing gas 1 and the THF-containing gas 1 to the gas absorption tower 20 upstream of the gas-absorbing tower 20 where the THF-containing gas 1 is introduced. A gas blower 12 and a gas cooler 13 for cooling the THF-containing gas 1 are installed.

  Between the gas absorption tower 20 and the dehydration distillation tower 30, a pipe for sending the THF aqueous solution 2 discharged from the bottom of the gas absorption tower 20 to the dehydration distillation tower 30 is installed. 2 and a preheater 22 for preheating the THF aqueous solution 2 are installed. An exhaust pipe 26 for exhausting the gas from which THF has been removed is installed at the top of the gas absorption tower 20.

  The dehydrating distillation column 30 is not particularly limited as long as it is an apparatus capable of distilling the THF aqueous solution 2 and removing water to an azeotropic composition (water content: about 6 wt%). In the dehydrating distillation column 30, a reboiler 31 for heating the aqueous THF solution 2 with steam is installed at the bottom of the column. Between the dehydration distillation tower 30 and the gas absorption tower 20, a pipe for sending water discharged from the bottom of the dehydration distillation tower 30 to the gas absorption tower 20 to be reused as an absorption liquid is installed. The pipe is provided with a pump 23 for sending the reused water, a preheater 22 for preheating the THF aqueous solution 2 with the heat of the reused water, and a cooler 24 for further cooling the reused water.

  A condenser 32 that condenses the gas discharged from the top of the dehydrating distillation column 30 is installed between the dehydrating distillation column 30 and the freeze dehydrating apparatus 40. In addition, piping for sending the hydrous THF solution 3 which is the condensate obtained by the condenser 32 to the dehydration distillation column 30 and the freeze dehydration apparatus 40 is installed.

  Although details of the freeze dehydration apparatus 40 will be described later, this is an apparatus that cools the water-containing THF liquid to freeze water in the liquid and separates ice and THF into solid and liquid. A pipe for sending the dehydrated THF liquid 4 obtained by the freeze dehydration apparatus 40 to the purified distillation tower 50 is installed between the freeze dehydration apparatus 40 and the purification distillation tower 50, and the dehydrated THF liquid is sent to this pipe. A pump 41 is installed. Further, the freeze dehydration apparatus 40 is provided with a pipe for sending the solution 6 in which the removed ice is dissolved to the dehydration distillation column 30.

  The purification distillation column 50 is not particularly limited as long as it is a device capable of lowering the water content than the azeotropic composition without adding the third component. The refining column 50 is provided with a reboiler 51 for heating the dehydrated THF solution with steam at the bottom of the column. A cooler 52 for cooling the purified THF 5 discharged from the bottom of the tower is installed at the bottom outlet of the purified distillation tower 50. A condenser 53 that condenses the gas discharged from the top of the tower and a condensate 7 obtained by the condenser 53 are sent to the purification distillation tower 50 and the freeze dehydration apparatus 40 at the top outlet of the purification distillation tower 50. Piping is installed.

  According to the above configuration, first, the THF-containing gas 1 discharged from a production facility (not shown) such as a coater is introduced into the gas absorption tower 20 by the gas blower 12 via the gas filter 11 and the gas cooler 13. . In the gas absorption tower 20, the THF-containing gas 1 comes into gas-liquid contact with the water that is the absorption liquid, and the THF in the gas is absorbed and removed by the water, and is discharged as a clean gas from the exhaust pipe 26 at the top of the tower. . On the other hand, the absorbing solution that has absorbed THF is discharged as a THF aqueous solution 2 from the bottom of the column.

  The THF aqueous solution 2 is sent to the preheater 22 by the pump 21, preheated by the preheater 22, and then introduced into the dehydration distillation column 30. In the dehydration distillation column 30, by distilling the THF aqueous solution 2, THF having a boiling point as low as about 64 ° C. is obtained from the column top, and water is recovered from the column bottom. Here, since THF obtained from the top of the column azeotropes with water, it cannot be completely dehydrated and contains at least a water content of about 6 wt% which is an azeotropic composition with water. The THF gas is condensed by the condenser 32 to become the hydrous THF solution 3.

The water content of the water-containing THF solution 3 thus obtained is preferably 6 wt% to 8 wt%. In order to obtain the moisture content in this range in the dehydrating distillation column 30, for example, the number of columns of the dehydrating distillation column 30 is in the range of 25 to 35, the pressure at the top of the column is almost the same as the atmospheric pressure, and the temperature at the bottom of the column is set. The range of 100 to 110 ° C. and the reflux ratio are preferably in the range of 7 to 15.

  Since the water recovered in the dehydration distillation column 30 is heated by the reboiler 31, it is sent to the preheater 22 by the pump 23, and heat is exchanged with the THF aqueous solution 2 to recover the heat. After the temperature is further lowered, the gas is introduced into the gas absorption tower 20 and reused as an absorbing solution.

  A part of the hydrous THF solution 3 obtained in the dehydration distillation column 30 is refluxed to the top of the dehydration distillation column 30, and a part is extracted and introduced into the freeze dehydration apparatus 40. In the freeze dehydrating apparatus 40, the hydrous THF solution 3 is cooled. Since water has a higher freezing point than THF, water in the hydrous THF solution 3 can be frozen. Under low temperature conditions, it is known that THF and water produce a solid called an inclusion compound. In the present specification, the formation of ice or a clathrate solid at a temperature below freezing is referred to as freezing. Since the amount of ice increases as the cooling temperature decreases, the water content in the water-containing THF solution 3 can be lowered accordingly. The cooling temperature is preferably in the range of -25 ° C to -60 ° C, more preferably in the range of -35 ° C to -50 ° C. Then, by discharging the THF maintained in a liquid state from the freeze dehydrating apparatus 40 by solid-liquid separation, a sherbet-like substance having a high water concentration can be separated and dehydrated. As a result, a dehydrated THF solution 4 having a highly dehydrated water content of 1 wt% to 3 wt% can be obtained.

  The dehydrated THF solution 4 is introduced into the purification distillation column 50 by the pump 41. On the other hand, the ice remaining in the freeze dehydration apparatus 40 is discharged from the freeze dehydration apparatus 40 after being melted by natural thawing or the like. Since this solution 6 contains THF, it is returned to the dehydration distillation column 30 and reprocessed.

  In the purification distillation column 50, the dehydrated THF solution 4 is purified and distilled to purify the THF concentration to the quality of the THF reagent level defined by JIS K9705. That is, the water content of the dehydrated THF solution 4 is lowered to 0.05 wt% or less. In order to perform such purification distillation, for example, the number of stages of the purification distillation column 50 is in the range of 25 to 35, the pressure at the top is almost the same as the atmospheric pressure, and the temperature at the bottom is 65 to 70 ° C. The range and the reflux ratio are preferably in the range of 3 to 7. Since the purified THF 5 obtained from the bottom of the purified distillation column 50 is heated by the reboiler 51, it is cooled by the cooler 52.

  On the other hand, since the vapor discharged from the top of the purification distillation column 50 contains THF, after condensing in the condenser 53, a part of the condensate 7 is refluxed to the top of the purification distillation column 50, and a part thereof Return to the freeze dehydration apparatus 40 for reprocessing.

  Thus, according to the present embodiment, the water mixed in the THF is frozen by the freeze dehydrating apparatus 40, and the THF and the water are separated by solid-liquid separation without adding any third component, Water mixed in THF can be removed to a moisture content lower than about 6 wt% which is an azeotropic composition. Therefore, THF can be easily purified to a water content of 0.05 wt% which is the reagent concentration level by the subsequent purification distillation column 50.

  In the present embodiment, the case where the organic solvent is THF has been described. However, when the organic solvent is ethanol, the water content of the azeotropic composition with water is about 4 wt%. By cooling to a range of 35 ° C. to −50 ° C., the water content can be dehydrated to a range of 1 wt% to 2 wt%. When the organic solvent is isopropyl alcohol, the water content of the azeotropic composition with water is about 12 wt%, and it is cooled to a range of −35 ° C. to −50 ° C. by the freeze dehydration apparatus 40, and 2 wt% to 6 wt%. Can be dehydrated to a moisture content in the range. When the organic solvent is ethyl acetate, the water content of the azeotropic composition with water is about 8%, and it is 2% to 4% by cooling in the range of −35 ° C. to −50 ° C. with the freeze dehydrator 40. Can be dehydrated to a moisture content in the range. When the organic solvent is methyl ethyl ketone, the water content of the azeotropic composition with water is about 11%, and it is 2% to 6% when cooled to −35 ° C. to −50 ° C. with the freeze dehydrator 40. It can be dehydrated to a moisture content in the range. When the organic solvent is dioxane, the water content of the azeotropic composition with water is about 18 wt%, and it is cooled to a range of −35 ° C. to −50 ° C. with the freeze dehydration apparatus 40 to 3 wt% to 9 wt%. It can be dehydrated to a moisture content in the range.

  Next, an embodiment of the freeze dehydration apparatus according to the present invention will be described in detail. FIG. 2 is a schematic diagram showing an outline of an embodiment of a freeze dehydration apparatus according to the present invention. This is also a detailed description of the freeze dehydration apparatus of the absorption solvent recovery system in FIG. 1, and the same components as those in FIG.

  As shown in FIG. 2, the freeze dehydration apparatus 40 includes a cooling tank 42 into which the hydrous THF solution 3 is introduced and accommodated, a stirrer 43 for stirring the hydrous THF solution 3 in the cooling tank, and a hydrous THF solution in the cooling tank. 3 is mainly composed of a refrigerator 45 for cooling 3 and a filter 47 for solid-liquid separation of ice frozen in water and THF maintained in a liquid state in a cooling tank.

  The cooling tank 42 is preferably formed of a material such as stainless steel. As the stirrer 43, a plurality of stirring blades 44 that rotate in the horizontal direction in the cooling bath 42 are installed. The stirring blade 44 is preferably made of stainless steel or stainless steel coated with a resin such as polytetrafluoroethylene. The stirrer 43 is not limited to such a mechanical stirrer, for example, by taking a part of the water-containing THF liquid from the cooling tank with a pump or the like and introducing the water-containing THF liquid into the cooling tank again, The inside of the cooling tank can be similarly stirred.

  A cooling pipe 46 through which the refrigerant supplied from the refrigerator 45 circulates is installed in the cooling tank 42 to indirectly cool the hydrous THF solution. In FIG. 2, the cooling pipe 46 is installed only in a part of the cooling tank, giving priority to easy viewing, but it is preferable to install the cooling pipe 46 on the entire surface of the cooling tank 42. Further, the cooled refrigerant can be circulated through a jacket (not shown) provided on the wall surface of the cooling tank 42. As the refrigerant, for example, a cooling medium oil or a solvent having a low melting point is preferably used.

  A discharge pipe 49 is attached to the bottom of the cooling tank 42, and a filter 47 is installed in the discharge pipe 49. In addition, an automatic valve 48 is installed in the discharge pipe 49, so that the discharge pipe 49 branches into a discharge pipe 49 a that discharges the dehydrated THF solution 4 and a discharge pipe 49 b that discharges the solution 6. Yes.

  According to such a configuration, first, the hydrous THF solution 3 is injected into the cooling bath 42. If the inside of the cooling tank 42 is filled with the water-containing THF solution 3, next, the cooled refrigerant is circulated in the cooling pipe 46 to cool the water-containing THF liquid 3 in the cooling tank 42. Cooling is performed while rotating the stirring blade 44 by the stirrer 43. By cooling the water-containing THF solution 3 while stirring in this way, the water in the water-containing THF solution 3 begins to freeze, and a part of the water adheres to the surface of the cooling pipe 46, but is peeled off from the surface by stirring and is in the liquid. Floating. And since water | moisture content freezes uniformly throughout the inside of the cooling tank 42, the water-containing THF liquid 3 can be made into a sherbet shape.

  In order to cool the hydrous THF solution 3 so as to form a uniform sherbet throughout the cooling bath 42, the cooling rate of the hydrous THF solution 3 in the cooling bath 42 is in the range of 0.2 to 1.0 ° C./min. In addition, it is preferable that the stirring speed of the stirring blade 44 in the cooling bath 42 be in the range of 30 to 120 rpm. In particular, the cooling rate is more preferably in the range of 0.4 to 0.6 ° C./min. The cooling temperature is preferably in the range of -25 ° C to -60 ° C, more preferably in the range of -35 ° C to -50 ° C.

  Once the inside of the cooling bath 42 has been cooled to a predetermined cooling temperature, the dehydrated THF solution 4 is then recovered from the inside of the cooling bath 42. In this case, the automatic valve 48a on the dehydrated THF side of the discharge pipe 49 is opened, and the automatic valve 48b on the solution side is closed. As a result, the THF maintained in the liquid state is discharged from the cooling tank 42 to the discharge pipe 49a through the filter 47. The THF is discharged by its own weight. The sherbet-like ice is trapped by the filter 47 and remains in the cooling bath 42, so that highly dehydrated THF 4 can be obtained.

  In order to properly separate THF and sherbet-like ice that are kept in a liquid state in the cooling bath 42, it is preferable that the opening of the filter 47 be in the range of 0.15 mm to 1 mm, and 0.2 mm to 0.2 mm. A range of 3 mm is more preferable.

  After the recovery of the dehydrated THF 4 is completed, the solution 6 in the cooling tank 42 is then discharged. In this case, the automatic valve 48a on the dehydrated THF side of the discharge pipe 49 is closed, and the automatic valve 48b on the solution side is opened. And the circulation of the refrigerant | coolant of the cooling pipe 46 is stopped, and the inside of the cooling tank 42 is returned to the temperature which ice melt | dissolves. As a result, the ice remaining in the cooling bath 42 is melted, and the solution 6 is discharged from the cooling bath 42 to the discharge pipe 49 b through the filter 47.

  A plurality of cooling tanks 42 may be provided as the freeze dehydrating apparatus 40. FIG. 3 shows an embodiment when two cooling tanks are installed in parallel. In addition, the same code | symbol was attached | subjected about the structure similar to FIG. FIG. 4 shows an operation schedule of the freeze dehydration apparatus in this embodiment.

  As shown in FIG. 3, in the freeze dehydration apparatus of the present embodiment, two cooling tanks, a cooling tank A 42a and a cooling tank B 42b, are arranged, and each cooling tank 42a, 42b has the same structure as FIG. In addition, stirrers 43a and 43b, cooling pipes 46a and 46b, and filters 47a and 47b are installed, respectively. The cooling pipes 46a and 46b are piped so that the refrigerant is supplied in parallel from the refrigerator 45. In addition, in each of the cooling tanks 42a and 42b, sensors 71a and 71b for detecting the injection amount of the water-containing THF liquid in the cooling tank and thermometers 73a and 73b for measuring the temperature of the water-containing THF liquid in the cooling tank are installed. Has been.

  Further, a stock solution tank 61 for injecting the hydrous THF solution 3 into the two cooling tanks 42 in parallel is installed. Between the undiluted | stock solution tank 61 and the cooling tank 42, the piping for sending the hydrous THF liquid 3 to the cooling tank 42 is installed, and the pump 62 for sending the hydrous THF liquid 3 to a cooling tank is installed in this piping. In addition, a cold heat recovery device 63 for exchanging heat with the dehydrated THF solution 4 is provided. Further, this pipe is provided with an automatic valve 72a for injecting the hydrous THF solution 3 into the cooling bath A42a and an automatic valve 72b for injecting the hydrous THF solution 3 into the cooling bath B42b. The cooling pipes 46a and 46b are also provided with automatic valves 74a and 74b for controlling the circulation of the refrigerant.

  The bottom surfaces of the two cooling tanks 42a and 42b are connected to a discharge pipe 49 via automatic valves 48c and 48d, respectively. The discharge pipe 49 is provided with an automatic valve 48 a for discharging the dehydrated THF solution 4 and an automatic valve 48 b for discharging the solution 6. In the discharge pipe 49a for discharging the dehydrated THF solution 4, a cold heat recovery device 63 for heat exchange with the hydrous THF solution 3 is installed.

  The discharge pipe 49b for discharging the solution 6 includes a solution tank 64 for temporarily storing the solution, a pump 65 for sending the solution to the cooling tank 42, and heating for heating the solution. 66, an automatic valve 48e for draining the lysate from the freeze dehydrating apparatus, an automatic valve 48f for supplying the lysate to the cooling tank A42a, and an automatic valve 48g for supplying the lysate to the cooling tank B42b. Is provided.

  According to such a configuration, first, as shown in FIG. 4, the water-containing THF liquid to be treated is injected into one cooling tank A. Accordingly, the operation of the pump 62 of the stock solution tank is started, and the automatic valve 72a on the injection side of the cooling tank A is opened. The remaining automatic valves are closed. Thereby, the water-containing THF liquid 3 in the undiluted | stock solution tank 61 is inject | poured in cooling tank A42a. When a predetermined amount of water-containing THF liquid is accumulated in the cooling bath A42a, the sensor 71a detects this and closes the automatic valve 72a for injection.

  When the injection of the water-containing THF liquid into the cooling tank A is finished, the water-containing THF liquid in the cooling tank A is then cooled. Therefore, the pump 62 of the stock solution tank is stopped, the automatic valve 74a of the cooling pipe on the cooling tank A side is opened, and the agitator 43a on the cooling tank A side is started. Thereby, the water-containing THF liquid in the cooling tank A42a is cooled by the cooling pipe 46a while being stirred by the stirrer 43a. When the water-containing THF solution in the cooling bath A42a reaches a predetermined cooling temperature, the thermometer 73a detects this and closes the automatic valve 74a of the cooling pipe.

  After the water-containing THF solution in the cooling bath A is cooled to a predetermined temperature, the dehydrated THF solution in the cooling bath A is then recovered. Accordingly, the automatic valve 48c on the discharge side of the cooling tank A and the automatic valve 48a for discharging the dehydrated THF liquid are opened. As a result, the dehydrated THF solution 4 in the cooling tank A 42a is discharged through the filter 47a, and further supplied into the cold heat recovery device 63 through the discharge pipe 49a.

  Simultaneously with the recovery of the dehydrated THF in the cooling tank A, the other cooling tank B is injected with a hydrous THF solution. Therefore, the operation of the pump 62 of the stock solution tank is started and the automatic valve 72b on the injection side of the cooling tank B is opened. Thereby, the hydrous THF solution 3 in the undiluted | stock solution tank 61 is inject | poured into cooling tank B42b after passing the cold-heat recovery device 63. FIG. At this time, in the cold heat recovery device 63, heat exchange is normally performed between the hydrous THF solution 3 that is about 30 ° C. and the dehydrated THF solution 4 that is cooled to a predetermined cooling temperature in the cooling bath A42a. Thereby, the cold heat of the dehydrated THF solution 4 can be recovered. When a predetermined amount of the water-containing THF liquid is accumulated in the cooling bath B42b, the sensor 71b detects this and closes the automatic valve 72b for injection.

  When the dehydrated THF solution in the cooling bath A is recovered, the solution in the cooling bath A is discharged. At the same time, in the cooling tank B, the water-containing THF solution is cooled. Therefore, the pump 62 of the stock solution tank is stopped and the automatic valve 48a for discharging the dehydrated THF solution is closed, while the operation of the pump 65 of the solution tank is started, and the automatic valve 48f for supplying the solution of the cooling tank A is started. Then, the automatic valve 74b of the cooling pipe on the cooling tank B side and the automatic valve 48b for discharging the solution are opened.

  As a result, the solution generated by the melting of the ice is discharged from the inside of the cooling tank A 42a and supplied to the solution tank 64 through the discharge pipe 49b. The solution in the solution tank 64 is sent to the heater 66 by the pump 65 and heated by the heater 66. In the heater 66, it is sufficient that the solution is heated to about room temperature, so that the working water 67 can be used as a heat source of the heater. And the heated solution is supplied and spread | dispersed in cooling tank A42a. As a result, it is possible to accelerate the thawing of the ice accumulated in the filter 47a and the thawing of the ice adhering to the surface of the cooling pipe 46a, thereby shortening the thawing time of the frozen ice. Although not shown in the figure, the thawing time can be shortened in the same manner even if the industrial water is supplied and dispersed in the cooling tank A.

  If all the solution discharged from the cooling tank A 42 a is supplied to the solution tank 64, an excessive amount of solution is accumulated in the solution tank 64. Therefore, when the discharge of the solution in the cooling bath A42a is finished, the automatic valve 48c on the discharge side of the cooling bath A and the automatic valve 48f for supplying the solution in the cooling bath A are closed, and the automatic valve for discharging the solution is discharged. 48e is opened, and a part of the solution in the solution tank 64 is discharged out of the freeze dehydration apparatus. The discharged solution 6 is sent to a dehydration distillation column and reprocessed.

  As described above, while the solution is being discharged in the cooling bath A42a, the water-containing THF solution in the cooling bath B42b is cooled by the cooling pipe 46b while being stirred by the stirrer 43b. When the water-containing THF liquid in the cooling bath B42b reaches a predetermined cooling temperature, the thermometer 73b detects this and closes the automatic valve 74b of the cooling pipe.

  When the solution is discharged from the cooling bath A, the aqueous THF solution is again injected into the cooling bath A. At the same time, in the cooling tank B, the dehydrated THF solution is recovered. Therefore, the pump 62 of the stock solution tank 61 is started, while the pump 65 of the solution tank is stopped, the automatic valve 72a on the injection side of the cooling tank A, the automatic valve 48d on the discharge side of the cooling tank B, and the dehydrated THF liquid. The automatic valve 48a for discharging the gas is opened. As a result, the dehydrated THF solution in the cooling bath B42b is supplied into the cold heat recovery device 63 through the filter 47b and the discharge pipe 49a. Further, the water-containing THF solution in the stock solution tank 61 is injected into the cooling tank A 42 a after heat exchange with the dehydrated THF cooled to the predetermined cooling temperature in the cold heat recovery device 63.

  When the hydrous THF solution is injected into the cooling tank A, the hydrous THF solution is cooled. At the same time, in the cooling bath B, the solution is discharged. In this way, the processing contents of the four types of cooling tanks for injection of water-containing THF liquid, cooling, recovery of dehydrated THF, and discharge of the dissolved liquid are shifted in the two cooling tanks and repeatedly performed, so that processing in the freeze dehydration apparatus Can be performed efficiently. Further, by further increasing the number of cooling tanks, a large volume of hydrous THF solution can be easily treated.

  A water-containing THF solution having a water content of 6 wt%, which is an azeotropic composition, was prepared, and the water-containing THF solution was cooled to freeze water in the solution to obtain a dehydrated THF solution. The cooling temperature of the dehydrated THF solution and the water content in the dehydrated THF solution at that time were measured. The results are shown in Table 1. As shown in Table 1, the lower the cooling temperature, the lower the water content in dehydrated THF.

It is a mimetic diagram showing one embodiment of an absorption type solvent recovery system concerning the present invention. It is a mimetic diagram showing one embodiment of a freeze dehydration device concerning the present invention. It is a schematic diagram which shows another embodiment of the freeze dehydration apparatus which concerns on this invention. It is a timing chart which shows the operation schedule of the freeze dehydration apparatus shown in FIG.

Explanation of symbols

1 THF-containing gas 2 THF aqueous solution 3 Hydrous THF solution 4 Dehydrated THF solution 5 Purified THF
6 Solution 7 Condensate 11 Gas filter 12 Gas blower 13 Gas cooler 20 Gas absorption tower 21, 23, 41 Pump 22 Preheater 24, 52 Cooler 26 Exhaust pipe 30 Dehydration distillation tower 31, 51 Reboiler 32, 53 Condenser 40 Freeze dehydrator 42 Cooling tank 43 Stirrer 44 Stirrer blade 45 Refrigerating machine 46 Cooling pipe 47 Filter 48 Automatic valve 49 Drain pipe 50 Purifying distillation column 61 Stock solution tank 62, 65 Pump 63 Cold heat recovery device 64 Dissolved liquid tank 66 Heater 71 Sensors 72, 74 Automatic valve 73 Thermometer

Claims (8)

Gas absorbing means for bringing a gas containing an organic solvent into gas-liquid contact with water so that the water absorbs the organic solvent;
Dehydration distillation means for distilling an aqueous solution of the organic solvent obtained from the gas absorption means to reduce the water content in the aqueous solution of the organic solvent to a water content that is an azeotropic composition of the organic solvent and water or higher. When,
The distillate obtained by the dehydration distillation means is cooled, the water contained in the distillate is frozen, and the water in the distillate is obtained from a water content that is an azeotropic composition of the organic solvent and water. A solvent recovery system equipped with a freeze dehydration device that lowers the temperature further. A gas absorption step in which a gas containing an organic solvent is brought into gas-liquid contact with water and the water absorbs the organic solvent;
Dehydration distillation step of distilling the aqueous solution of the organic solvent obtained in the gas absorption step to reduce the water content in the aqueous solution of the organic solvent to a water content that is an azeotropic composition of the organic solvent and water or higher. When,
The distillate obtained by the dehydration distillation step is cooled to freeze the water contained in the distillate, and the water in the distillate is obtained from the water content that is the azeotropic composition of the organic solvent and water. And a freeze-drying step that further lowers the solvent recovery method. A cooling tank containing a liquid to be treated containing an organic solvent and water;
Stirring means for stirring the liquid to be treated in the cooling tank;
A cooling means for cooling the processing target liquid in the cooling tank until the water in the processing target liquid freezes and becomes a sherbet,
A filter for separating the organic solvent and the sherbet-like ice in a liquid state from the liquid to be treated in the sherbet-like shape,
Means for heating and liquefying the separated sherbet-like ice.   The freeze dehydration apparatus according to claim 3, wherein the opening of the filter is within a range of 0.15 mm to 1 mm. While cooling the processing target liquid containing an organic solvent and water, the cooling step of cooling the processing target liquid until the water in the processing target liquid freezes and the processing target liquid becomes a sherbet,
An organic solvent recovery step of separating and removing the sherbet-like ice by a filter from the sherbet-like liquid to be treated;
And heating the separated sherbet-like ice to liquefy it.   The solvent recovery system according to claim 1, wherein the organic solvent is tetrahydrofuran, ethanol, isopropyl alcohol, ethyl acetate, methyl ethyl ketone, or dioxane.   The solvent recovery method according to claim 2 or 5, wherein the organic solvent is tetrahydrofuran, ethanol, isopropyl alcohol, ethyl acetate, methyl ethyl ketone, or dioxane.   The freeze dehydration apparatus according to claim 3 or 4, wherein the organic solvent is tetrahydrofuran, ethanol, isopropyl alcohol, ethyl acetate, methyl ethyl ketone, or dioxane.

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