JP2006218474A - Method for liquid-liquid extraction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for simply and efficiently carrying out liquid-liquid extraction for much quantity of the liquid flow, adaptable to a wide range of operating conditions, and particularly useful for the extraction of valuable components from the waste water over 50 t/hr from an apparatus for producing high-purity terephthalic acid. <P>SOLUTION: The liquid-liquid extraction method is characterized in that the waste water is mixed with an extract agent for extracting an objective component from the waste water in the piping structured for their mixture, and that the mixture is subsequently supplied into a vessel with its flowing speed decreasing caused by gravity in order to settle the mixture in it for the liquid-liquid extraction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for liquid-extracting a target component from waste water having a large flow rate exceeding 50 t / hr, for example.

  When the concentration of useful substances in the wastewater is low, the economical efficiency of recovery is low, and therefore, the wastewater is usually disposed of after being treated by the activated sludge method. For example, wastewater generated from an apparatus for producing high-purity terephthalic acid contains a large amount of a reaction intermediate product, paratoluic acid, but is usually treated by an activated sludge method because of its low concentration.

  However, the treatment by the activated sludge method not only loses useful materials but also consumes a large amount of energy such as electricity for operation. It also causes odors. As the terephthalic acid production apparatus becomes larger and the amount of wastewater becomes large, it is necessary to remove and recover useful materials from the wastewater from the viewpoint of economic efficiency as well as the global environment.

As a method for recovering useful materials in wastewater, for example, a method for extracting paratoluic acid contained in wastewater generated from an apparatus for producing terephthalic acid with paraxylene is disclosed in Japanese Patent No. 2899927. This method uses para-xylene, which is a raw material for terephthalic acid, as an extraction agent, and is an excellent method that does not require a regeneration step for the extraction agent. However, in an ordinary extraction apparatus, the apparatus cost is high and the economic efficiency is reduced. .
Japanese Patent No. 2899927

Techniques for extracting useful materials from wastewater are well known. For example, various methods are described in Chapter 11.5 of the Chemical Engineering Handbook 5th edition (Edited by Chemical Engineering Society).
However, for example, when the mixer settler extractor described in chapter 11.5.1 of the manual is used for multistage extraction, the apparatus becomes complicated and expensive. For this reason, a tower-type extraction device is used in the case of multiple stages. For example, the countercurrent differential extraction tower described in the chapter 11.5.2 of the manual has a drift in the simple structure. It is difficult to increase the size and is rarely used industrially. In order to avoid this, if the pulsation type is used, it is possible to suppress the drift, but the structure becomes complicated and expensive. In addition, the non-stirring type columnar extraction tower described in chapter 11.5.3 of the manual has a simple structure, but the operation range is not flexible. In order to improve this, the stirring type column type extraction tower described in chapter 11.5.4 of the handbook has been devised, but the apparatus becomes complicated and expensive. As described above, the tower type is complicated and expensive when it is attempted to avoid the drift and widen the operation range.

If there is an efficient and inexpensive extraction device, it is possible not only to recover dilute useful materials contained in wastewater and the like, but also to purify the wastewater and to reuse the water.
However, the method of extracting paratoluic acid contained in waste water generated from an apparatus for producing terephthalic acid with paraxylene disclosed in Japanese Patent No. 2899927 (Patent Document 1) is commercially available without an inexpensive extraction apparatus. Implementation is difficult.

Therefore, the present invention provides a method for performing high-flow liquid-liquid extraction by an efficient and simple method with a wide operating range, particularly from an apparatus for producing industrially important high-purity terephthalic acid. It is an object of the present invention to provide a method suitable for extracting useful components from wastewater exceeding 50 t / hr.

The present invention comprises an operation of mixing and static separation as in the conventional extraction operation, but provides an extraction method suitable for treating a large amount of waste water.
That is, the present invention, after flowing and mixing waste water and an extractant for extracting a target component from waste water through a pipe having a structure for mixing them, the mixture is decelerated using gravity. The present invention relates to a liquid-liquid extraction method, characterized in that the liquid-liquid extraction method is characterized in that the liquid is supplied to a container and left to stand to separate the liquid. The mixed solution is preferably supplied from the lower part of the container while being decelerated using gravity.

  Further, the present invention, after flowing and mixing the waste water and the extractant for extracting the target component from the waste water through a pipe having a structure for mixing them, the mixture is supplied from the lower part of the container, The present invention relates to a liquid-liquid extraction method characterized by standing and liquid-liquid separation.

  A static mixer is suitable as the pipe. Further, it is preferable that the pipes are arranged in the vertical direction so that the flow is from top to bottom when the light liquid is in the dispersed phase and the flow is from bottom to top when the heavy liquid is in the dispersed phase. Here, the light liquid means a liquid having a low density among liquids to be mixed, and is usually an organic liquid, and the heavy liquid means a liquid having a high density among the liquids to be mixed, and is usually water.

  As a method of decelerating the inflow speed of the mixed liquid, a method of supplying the lower portion of the container so as to decelerate using gravity is preferable because it does not disturb the flow in the container to be stationary and separated. As a method of decelerating by gravity, it may be put in a direction against gravity from the lower part of the container, or it may be supplied toward the bottom of the container and reversed at the bottom of the container, and then decelerated using gravity. Regardless of which method is used, it is desirable to confirm that the inflow velocity is decelerated in a short time without turbulence in the container by computer analysis of the flow state.

  Further, the present invention provides a liquid-liquid extraction method, wherein the container is under pressure, and the waste water and the extractant are each extracted using the pressure of the container, and the container is full, and the gas phase and liquid There is provided a liquid-liquid extraction method characterized by not having a liquid level control device and a pressure control device between phases.

It is preferable that the waste water and the extractant after stationary separation are each extracted by a flow rate control that is cascade-controlled based on the amount of waste water or extractant flowing into the container.
In the present invention, the container includes a partition plate having a height of 10 to 70% of the height of the container, and a heavy liquid (water) separated from the lower part on the side opposite to the side supplied with the mixed liquid. A liquid-liquid extraction method is provided, in which a light liquid (organic phase) separated from the upper part on the side opposite to the side supplied with the mixed liquid is extracted.

  It is possible to combine two or more stages of the liquid-liquid extraction method into multi-stage extraction. Moreover, waste water from a terephthalic acid plant can be used as waste water in the liquid-liquid extraction method.

The present invention provides a method for performing liquid-liquid extraction at a large flow rate by an efficient and simple method with a wide operating range.
Conventionally, the present invention has a large flow rate but a low concentration, so that the economical efficiency of recovery is low and it is discarded as wastewater. For example, useful components are extracted from wastewater exceeding 50 t / hr generated from an apparatus for producing high-purity terephthalic acid. Provided is a method that is particularly useful when extracting and reusing wastewater.

  In the present invention, for example, a lottery (a raw material to be subjected to solvent extraction, specifically waste water) and an extractant are mixed by flowing through a pipe having a structure in which the flow is mixed, and then the water is full and under pressure. A large flow rate is processed by extracting the extract and the extractant using the pressure of the static separator under pressure, based on the flow rate of the extract or extractant. A liquid-liquid extraction method suitable for the above can be provided.

  For the mixing of the extractant and the extractant, a stirrer is used in an ordinary mixer / settler extractor. However, in the case of multi-stage extraction, several expensive stirrers and stirring containers are required, which is not economical. In addition, the tower type without a mechanical stirring device is insufficiently mixed and has poor extraction efficiency. The present invention is characterized in that mixing is efficiently completed with a simple device by using a pipe having a structure in which flows are mixed.

  As a pipe having a structure in which a flow is mixed, for example, there is a static mixer called a static mixer. Although it is known to perform the extraction operation using a static mixer, when performing multistage extraction, a pump is required at each stage due to pressure loss in the static mixer. The present invention is characterized in that the problem that the pump is required for each stage is solved by making the stationary separator pressurize and drawing out the liquid using the pressure instead of the pump. Moreover, this invention solves the subject that the pressure control apparatus for pressurization is added by making a stationary separator full.

  In the case of a conventional static separator having an interface and a gas phase, two liquid level control devices are required. Further, since the liquid level is controlled, the residence time of the stationary separator becomes longer than the time necessary for the original liquid-liquid separation. The present invention is characterized in that the liquid level control device at the interface between the two liquids is not required by extracting based on the flow rate of the supplied extract or extractant. Furthermore, the present invention is characterized in that the liquid level control device at the gas-liquid interface is not required by filling the stationary separator with water.

  By eliminating the need for liquid level control in this way, in the present invention, the stationary separator is used only for the time required for the original liquid-liquid separation, not the residence time required for liquid level control. It is also a feature. In order to control the liquid level, the residence time of the liquid usually exceeding 10 minutes is required. If liquid level control is not required using the present invention, for example, in the case of paraxylene and an aqueous system, where liquid-liquid separation is easy, separation is possible within 1 minute if there is no flow. Only time to decelerate the flow is required.

  Specifically, this is achieved by cascade control of the inflow amount and the flow rate from the container. For example, when the extractant is para-xylene and the extract is waste water, the same value as the flow rate of the supplied para-xylene is extracted by cascade control as the amount of para-xylene extracted from the stationary separator, and the waste water becomes full in the container. Just pull out. Since the waste water is a heavy liquid, if the sealing operation is performed to raise the extraction pipe to a position higher than the container, the container can be extracted so that the container becomes full.

  When controlling the flow rate of wastewater, the same value as the flow rate of the supplied wastewater is extracted by cascade control as the amount of drainage from the stationary separator, and if the paraxylene is extracted from the upper part of the container by overflow, the container becomes full. Can be extracted. Since the flow rate of the inflow and the flow rate of the outflow are not exactly the same, it is necessary to fine-tune the wastewater in the paraxylene so that the paraxylene does not enter the wastewater. It can be extracted stably.

The present invention is characterized by minimizing the stationary separator by supplying the mixed liquid from the lower part of the stationary separator to reduce the supply speed using gravity. Furthermore, in order to reduce the supply speed, a filler may be put inside the supply pipe. However, in the case of a large-sized apparatus, a pipe having a sufficient diameter is used to increase the cross-sectional area of the supply pipe and / or Alternatively, it is possible to use a means such as a means for supplying a plurality of pieces and the like, and a means for reducing the supply speed.

  Furthermore, the present invention supplies the liquid from the lower part of the stationary separator and provides a partition plate between the supply port and the outlet of the heavy liquid, thereby completely reversing the direction of the heavy liquid flow and reducing the separation path time. It is characterized by maximizing. The height of the partition plate is preferably 10 to 70% of the height of the container. In this way, supplying the mixed liquid from the lower part can use not only gravity but also inertial force.Therefore, the flow rate of heavy liquid is larger than that of light liquid, and the flow rate of heavy liquid dominates the separation. Become useful. In the present invention, the light liquid means a low density liquid to be mixed, usually an organic liquid, and the heavy liquid means a high density liquid to be mixed, usually water. It is.

  In the present invention, as described above, mixing is performed by a pipe having a simple structure, and a stationary separator having no special structure is used, so that a stable extraction operation can be performed in a wide operating range. The lower limit of the operating range is that the flow rate drops and mixing in the pipes becomes insufficient, but the pipes are arranged vertically and preferably vertical, and the flow is higher when the light liquid is in the dispersed phase. If the heavy liquid is a dispersed phase from the bottom to the bottom, the operating range can be widened by changing from the bottom to the top. The upper limit of the operating range depends on the separation capacity of the stationary separator, but the time to drop the flow velocity in the stationary separator is not the time for liquid-liquid separation in the stationary separator. The operating range can be widened by simple means such as increasing the diameter of the pipe supplied to the separator and / or supplying the pipe with a plurality of pipes. The operating range means a flow range of light liquid and heavy liquid, and the upper limit and the lower limit of the operating range mean the maximum flow rate and the minimum flow rate, respectively.

The present invention can be applied to, for example, wastewater treatment during terephthalic acid production. Examples are described below.
Using a cobalt compound, a manganese compound and a bromine compound as a catalyst in an acetic acid solvent, paraxylene is oxidized with air at a reaction pressure of 0.4 to 5 MPa-G and a reaction temperature of 160 to 260 ° C. to produce crude terephthalic acid. . The main impurities in this crude terephthalic acid are the oxidation intermediates 4-carboxybenzaldehyde 500-5000 ppm by weight and p-toluic acid 100-1000 ppm by weight.

  The crude terephthalic acid thus obtained is dissolved in water by raising the temperature to 225 ° C. or more, preferably 250 to 310 ° C. under a pressure of 5 MPa-G or more, preferably 7 to 9 MPa-G. To do. At this time, the terephthalic acid concentration in water is adjusted to 10 to 40% by weight, preferably 20 to 35% by weight.

  Subsequently, after contacting with a catalyst such as palladium in the presence of hydrogen to reduce the oxidation intermediate 4-carboxybenzaldehyde, which is a major impurity in the crude terephthalic acid, to paratoluic acid that is easy to remove by crystallization, one step or Crystallization under reduced pressure in multiple stages, preferably 3 to 7 stages, followed by solid-liquid separation to obtain high purity terephthalic acid.

The waste water generated in the production process of such high-purity terephthalic acid and the paraxylene as the extractant are pressurized to 0.15 MPa-G or more, preferably 0.3 to 1.0 MPa-G, and flowed through a static mixer. Mix. The mixing ratio is 5 to 70 parts by weight, preferably 10 to 40 parts by weight of para-xylene with respect to 100 parts by weight of waste water. The number of times of inversion in the static mixer is 2 to 30 times, preferably 5 to 15 times.

Thereafter, the mixed liquid from the static mixer is separated by a partition plate of a stationary separator having a partition plate at the center under a pressure of 0.1 MPa-G or more, preferably 0.25 to 9.95 MPa-G. Supply from the lower part of one side partitioned, paraxylene and waste water are separated. The separated paraxylene is extracted from the upper part on the other side of the stationary separator and the waste water is extracted from the lower part by the flow rate control in the same amount as the supplied paraxylene. The extracted waste water is again mixed with para-xylene by a static mixer, and a stationary separator having a partition plate at the center under a pressure of 0.05 MPa-G or more, preferably 0.2 to 9.9 MPa-G. Is supplied from the lower part of one side partitioned by a partition plate, and paraxylene and waste water are separated.

  The wastewater from which impurities have been extracted twice with paraxylene is removed by steam stripping to remove and collect paraxylene in the mixed and dissolved portion, and then reused as water for purifying crude terephthalic acid. Depending on the type of wastewater, it may not be possible to remove impurities that adversely affect the quality of the product, high-purity terephthalic acid, simply by extraction with paraxylene. In this case, since these impurities are very small, they are reused as water for purifying crude terephthalic acid after removal by activated carbon or membrane separation. Paraxylene extracted from the upper part of the separator is used as a raw material for producing crude terephthalic acid.

[Example]
Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[Example 1]
FIG. 1 is an explanatory diagram illustrating one embodiment of the present invention. Waste water from the terephthalic acid plant 1 flowed through the waste water discharge passage S1, was pressurized to 0.6 MPa-G by the pump 6, and was mixed with paraxylene from the supply passage S5 by the static mixer 2. The para-xylene from the supply path S5 flows through the supply path S3 and is pressurized to 0.7 MPa-G by the pump 7, and then the flow rate is adjusted to 1 part by weight with respect to 4 parts by weight of the wastewater by the flow rate regulator 10. It was adjusted. The static mixer 2 is manufactured by Noritake, and the number of elements for reversing the flow is 12 and the residence time is 15 seconds.

  The liquid mixed by the static mixer 2 was supplied from the lower part of the stationary separator 3 through the supply path S6. The para-xylene after the liquid-liquid separation flows through the outlet path S7, the flow rate of which is adjusted by the flow rate regulator 8, and is extracted. The paraxylene is sent to the terephthalic acid plant 1 from the return path S8 and used as a raw material of terephthalic acid. The flow rate regulator 8 was cascade controlled so as to be the same as the flow rate of the flow rate regulator 10. The pressure of the stationary separator 3 was 0.55 MPa-G, and the residence time was 3 minutes.

  The waste water after the liquid-liquid separation flowed from the lower part of the stationary separator 3 through the outlet path S9 and was mixed with paraxylene from the supply path S11 by the static mixer 4. In the exit passage S9, the piping position is once higher than the stationary separator 3 so that the stationary separator 3 is filled with water. The para-xylene from the supply path S11 flows through the supply path S3 and is pressurized to 0.7 MPa-G by the pump 7, and then the flow rate is adjusted to 1 part by weight with respect to 4 parts by weight of the waste water by the flow rate regulator 11. did. The static mixer 4 is manufactured by Noritake Corporation, has 12 elements for reversing the flow, and has a residence time of 15 seconds.

  The liquid mixed by the static mixer 4 was supplied from the lower part of the stationary separator 5 through the supply path S12. The para-xylene after the liquid-liquid separation flows through the outlet passage S13, the flow rate is adjusted by the flow controller 9, and is extracted. The para-xylene is sent to the terephthalic acid plant 1 from the return passage S14 and used as a raw material of terephthalic acid. The flow rate regulator 9 was cascade controlled so as to be the same as the flow rate of the flow rate regulator 11. The pressure of the stationary separator 5 was 0.5 MPa-G, and the residence time was 3 minutes.

  The waste water extracted from the outlet passage S15 at the lower part of the stationary separator 5 is steam stripped to remove and recover the remaining paraxylene, and then the RO membrane removes impurities that could not be removed by paraxylene, and then terephthalic acid. In plant 1, the crude terephthalic acid was reused as water for purification. The outlet passage S15 has a piping position that is once higher than the stationary separator 5 so that the stationary separator 5 is filled with water.

  As described above, 90% by weight of paratoluic acid contained in the waste water of the terephthalic acid plant 1 can be recovered with an extremely small apparatus having a total residence time of 6 minutes 30 seconds without using a special stirring apparatus or packing. did it.

FIG. 6 is an explanatory diagram illustrating one embodiment of the present invention.

Explanation of symbols

1 terephthalic acid plant 2 static mixer 3 static separator 4 static mixer 5 static separator 6 pump 7 pump 8 flow controller 9 flow controller 10 flow controller 11 flow controller S1 terephthalic acid plant wastewater discharge path S2 Single-stage static mixer supply path S3 Para-xylene supply path S4 Para-xylene first-stage static mixer flow control meter supply path S5 Para-xylene first-stage static mixer supply path S6 First-stage static separator supply path S7 First-stage stationary Separator paraxylene outlet path S8 First stage static separator paraxylene return path S9 First stage static separator waste water outlet path S10 Paraxylene second stage static mixer Flow control meter supply path S11 Paraxylene second stage static mixer Supply path S12 Second stage stationary separator supply path S1 Second stage stationary separator paraxylene outlet passage S14 Second stage stationary separator paraxylene return path S15 Second stage stationary separator waste outlet passage

Claims (11)

  After flowing and mixing the waste water and the extractant for extracting the target component from the waste water through a pipe having a structure for mixing them, the mixture is supplied to the container while decelerating using gravity, A liquid-liquid extraction method characterized in that the liquid is separated by standing.   The liquid-liquid extraction method according to claim 1, wherein the liquid mixture is supplied from the lower part of the container while being decelerated using gravity.   After flowing and mixing the waste water and the extractant for extracting the target component from the waste water through a pipe having a structure that mixes them, the mixed liquid is supplied from the lower part of the container, and left to stand. A liquid-liquid extraction method characterized by separating.   The liquid extraction method according to claim 1, wherein the pipe is a static mixer.   The pipes are arranged in the vertical direction, and when the light liquid is in the dispersed phase, the flow is from top to bottom, and when the heavy liquid is in the dispersed phase, the flow is from bottom to top. 5. The liquid-liquid extraction method according to any one of 4 above.   The liquid-liquid extraction method according to claim 1, wherein the container is under pressure, and waste water and an extractant are extracted using the pressure of the container.   The liquid-liquid extraction method according to any one of claims 1 to 6, wherein the container is full and does not have a liquid level control device and a pressure control device between a gas phase and a liquid phase.   The waste water and the extractant after stationary separation are each extracted by a flow rate control that is cascade-controlled based on the amount of waste water or the amount of the extractant flowing into the container. Liquid extraction method   The container is provided with a partition plate having a height of 10 to 70% of the height of the container, and the heavy liquid separated from the lower part on the side opposite to the side where the mixed liquid is supplied is extracted and the mixed liquid is supplied. The liquid-liquid extraction method according to any one of claims 1 to 8, wherein a light liquid separated from the upper part on the opposite side to the dried side is extracted.   A liquid-liquid extraction method according to claim 1, wherein the liquid-liquid extraction method according to claim 1 is combined into two or more stages to form multi-stage extraction.   The liquid-liquid extraction method according to claim 1, wherein the waste water is waste water from a terephthalic acid plant.

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