WO2020159167A1 - Method for recovering amide-based compounds - Google Patents

Abstract

The present invention provides a method for recovering amide-based compounds, wherein, before a distillation step for separating and recovering amide-based compounds from waste liquid including amide-based compounds such as N-methyl-2-pyrrolidone generated in a polyarylene sulfide polymerization process and inorganic salts, the inorganic salts are removed from the waste liquid by using a decanter-type centrifuge at room temperature and normal pressure, and thus the occurrence of clogging by fine PPS powder, which may be generated in the distillation step, and the inorganic salts or distillation efficiency deterioration is prevented, and accordingly, amide-based compounds such as N-methyl-2-pyrrolidone in the waste liquid are efficiently recovered.

Description

Method for recovering amide compounds

Cross-citation with relevant application(s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0010742 filed on January 28, 2019, and all contents disclosed in the documents of the Korean patent applications are included as part of this specification.

The present invention efficiently recovers amide-based compounds such as N-methyl-2-pyrrolidone from waste liquids containing amide-based compounds such as N-methyl-2-pyrrolidone generated in the polyarylene sulfide production process. It's about how.

Polyarylene sulfide (PAS), typified by polyphenylene sulfide (PPS), is used in metals, especially aluminum or zinc, in automobiles, electrical and electronic products, machinery, etc. due to its excellent strength, heat resistance, flame retardancy, and processability. It is widely used as a material to replace the same die casting metal. Particularly, in the case of PPS resin, it is one of the Super EPs, and because it has good fluidity, it is advantageous to use as a compound by kneading with fillers or reinforcing agents such as glass fibers.

In general, a method of using an amide compound such as N-methyl pyrrolidone (NMP) as a solvent in a PAS polymerization process is widely known in the industry. Further, even after polymerizing the PAS, residual unreacted substances are removed by washing with an amide compound such as N-methyl-2-pyrrolidone (NMP) or water. Amide-based compounds such as N-methyl-2-pyrrolidone used in this way are not only more expensive than conventional organic solvents, but are also known to be the main cause of environmental pollution when discharged in aqueous solutions, and are generally recovered and purified to recycle. Is becoming.

However, amide-based compounds such as N-methyl-2-pyrrolidone have excellent compatibility with water as they have high organic solubility, so they are infinitely mixed with water, and a large amount of inorganic salts are dissolved, such as effluent from the PAS manufacturing process. If it is, it is difficult to distill as it is, various recovery methods have been tried.

For example, unreacted material remaining after PAS polymerization is removed by washing with NMP or water. At this time, most of the NMP used was recovered through a distillation process.

In addition, in order to remove particles such as NaCl generated after the PAS polymerization, a method of installing a filter in front of a waste liquid storage tank is currently used. However, the above method requires frequent maintenance by blocking filter holes in which inorganic salt particles such as NaCl and fine powder are installed in the front of the storage tank, and it is difficult to remove salts smaller than the filter mesh or salts dissolved in water.

As another method, a process for removing fine powder is added by using a general batch centrifuge, but there is a problem in that it is difficult to remove salts smaller than the mesh size because the inorganic salt is dissolved in water along with a problem in which the fine powder is removed.

Therefore, it is necessary to remove fine powders such as inorganic salts in order to effectively recover the amide compound.

The present invention to minimize clogging of the distillation column in the distillation process for treating the waste liquid generated in the conventional polyarylene sulfide production process and clogging of the filter in the front of the waste liquid tank and deterioration of efficiency, a specific centrifuge before the distillation process of the waste liquid By using, an amide compound such as N-methyl-2-pyrrolidone can be efficiently recovered from a waste solution containing an amide compound such as N-methyl-2-pyrrolidone generated in the polyarylene sulfide production process. It is possible to provide a method for recovering an amide-based compound.

In addition, the present invention is to provide a method for improving the recovery effect of the amide-based compound by lowering the water content of the fine powder such as inorganic salts that may be included in the waste solution.

In this specification, the step of recovering the waste solution containing water, amide-based compounds and inorganic salts generated in the polyarylene sulfide manufacturing process;

Removing the inorganic salt in the waste solution by supplying the waste solution to a decanter centrifuge; And

Collecting the waste solution from which the inorganic salt has been removed into a storage tank, and then recovering the amide compound from the waste solution using a distillation column;

It provides a method for recovering an amide-based compound comprising a.

Hereinafter, a method for recovering an amide-based compound from waste liquid generated in the process of manufacturing polyarylene sulfide according to a specific embodiment of the present invention will be described in more detail.

In the present invention, terms such as first and second are used to describe various components, and the terms are used only for the purpose of distinguishing one component from other components.

In addition, the terms used herein are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms “include”, “have” or “have” are intended to indicate the presence of implemented features, numbers, steps, elements, or combinations thereof, one or more other features or It should be understood that the existence or addition possibilities of numbers, steps, elements, or combinations thereof are not excluded in advance.

The present invention can be applied to various changes and may have various forms, and specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to a specific disclosure form, and it should be understood that all modifications, equivalents, and substitutes included in the spirit and scope of the present invention are included.

Hereinafter, the present invention will be described in more detail step by step.

According to one embodiment of the invention, the step of recovering the waste solution containing water, amide-based compounds and inorganic salts generated in the polyarylene sulfide manufacturing process; Removing the inorganic salt in the waste solution by supplying the waste solution to a decanter centrifuge; And collecting the waste liquid from which the inorganic salt has been removed into a storage tank, and then recovering the amide compound from the waste liquid using a distillation column.

The present invention relates to a method for recovering an amide compound such as N-methyl-2-pyrrolidone used as a solvent from waste liquid generated after washing the reaction mixture after polyarylene sulfide polymerization.

In the process of recovering the amide-based compound in the waste liquid in the conventional polyarylene sulfide production process, clogging problems of the distillation column occur because fines (solids) such as inorganic substances contained in the waste liquid are not effectively removed.

That is, the waste solution also contains various inorganic salts and impurities generated from a polyarylene sulfide (PAS) manufacturing process. The inorganic salt may include a halide of an alkali metal, and may further include finely divided PPS. More specifically, the inorganic salt contains a halide of an alkali metal having a particle size of 5 to 30um, such as brine containing fine PPS (<100um) and sodium chloride (NaCl) generated in the polymerization process of polyarylene sulfide. . Accordingly, when the waste liquid is directly distilled, clogging of the distillation column occurs due to the inorganic salt contained in the waste liquid, resulting in a problem that distillation efficiency is reduced, and there is a limit to recovering the amide compound from the waste liquid.

In addition, in the conventional method, a filter is installed at the front end of the waste liquid storage tank or a general centrifuge is used, but the filter of the front end tube of the storage tank for collecting the waste liquid may be blocked, and a solid material may be accumulated under the storage tank to block the discharge port. . In addition, when a general centrifugal separator is used, since solids are accumulated for each batch, there is a problem in that it must be continuously removed, which is inefficient.

In addition, there is a case where a centrifugal separator is used under high pressure and a high temperature condition of about 200 degrees or more when recovering a solvent from the waste liquid, which may be uneconomical due to a decrease in processability due to the addition of equipment.

Thus, in the present invention, the solid material of the inorganic salt contained in the waste liquid is removed before distilling the waste liquid by using a decanter centrifuge, and the amide compound contained in the waste liquid is increased by preventing the clogging of the distillation column and increasing distillation efficiency. It can increase the separation efficiency. In addition, since these processes can be continuously performed, the inorganic salt can be removed and separated from the waste solution more efficiently than in the prior art, thereby improving processability. In addition, when using the decanter-type centrifuge in the present invention, a small amount of impurities can be removed. The waste liquid supplied to the decanter-type centrifugal separator may be waste liquid generated in the process of synthesizing and washing polyarylene sulfide.

The present invention proceeds to a solvent recovery process after separation of the waste liquid, which is separately discharged after polymerization, so that the separation process of inorganic salts such as fine PPS and NaCl can be performed more efficiently than before.

Specifically, the method for recovering the amide-based compound may be performed according to the process shown in FIG. 1.

As shown in Figure 1, the present invention does not perform a distillation process to recover the amide-based compound by collecting the waste solution generated in the manufacturing process of polyarylene sulfide directly into the storage tank, decanter type before collecting into the storage tank Using a centrifuge (Decanter type centrifuge), it is characterized in that to remove the solid material, such as inorganic salts from the waste liquid. At this time, the solid material may include finely divided polyarylene sulfide.

According to one embodiment of this method, a step of removing the inorganic salt in the waste liquid by supplying a waste liquid containing water, an amide-based compound and an inorganic salt generated in a polyarylene sulfide manufacturing process to a decanter type centrifuge .

Subsequently, after removing the inorganic salt in the above method, the waste solution containing water and the amide compound is transferred to a storage tank for collection. Then, a step of recovering the amide-based compound from the waste liquid is performed using a distillation column. Through this, 99% or more of the amide compound can be recovered from the waste solution, and the recovered amide compound can be recycled to the polymerization process.

More specifically, the reaction mixture after polymerization in the polyarylene sulfide production process is subjected to a process of separating the main reactant, polyarylene sulfide, by washing and filtering in a conventional manner, and waste liquid is generated in this process. . The washing and filtration process is a step of washing with one or more of amide-based compounds and water to remove impurities such as an oligomer generated after polymerization in a reaction product or an alkali metal halide such as sodium chloride (NaCl). to be.

Through the above process, a part of the alkali metal halide may be removed, but since the particle size of the inorganic salt such as NaCl is about 5 to 10 μm and the fine PPS or unreacted alkali metal halide is 100 μm or less, it is generally The filter size used (for example, 300 um) has very low removal efficiency. In addition, when using a filter size of 10um or less, there is a problem that requires a regular cake removal process due to the clogging phenomenon. In addition, even when a centrifugal separator is used in general batch operation, the filter size (for example, 75 um) has very low efficiency or clogging, and solids are only accumulated under the centrifuge. As a result, the continuous process is impossible as a one-time operation.

Therefore, the present invention is characterized in that the separation and removal of inorganic salts from the waste liquid by using a decanter-type centrifugal separator that performs a specific horizontal rotation.

Accordingly, in the step of removing the inorganic salt in the waste solution, about 25% by weight or more or about 25 to 40% by weight of the inorganic salt may be removed based on the total weight of the waste solution.

In particular, the inorganic salt separated in the step of removing the inorganic salt in the waste solution may have a water content of 45% or less or 30 to 45% calculated by the following Equation 1.

[Equation 1]

Moisture content (%) = [(Weight before drying of separated inorganic salt-weight after drying of separated inorganic salt)/ Weight before drying of separated inorganic salt] × 100

If the water content of solids such as inorganic salts separated from the wastewater is too high, solids may stick to the centrifuge and a removal process is necessary, and continuous operation may not be possible.

According to an embodiment of the present invention, the present invention is a polyarylene sulfide after the polymerization reaction mixture of the polyarylene sulfide in a general method after the polymerization process of the polyarylene sulfide in the polymerization reactor (1) And it is possible to obtain a waste solution containing an inorganic salt. Then, the waste liquid (2) is supplied to the decanter-type centrifuge (3) through the separation process, inorganic salts such as NaCl can be removed through the stream (4).

Then, the waste liquid from which the inorganic salt has been removed may be supplied to the storage tank 6 through the stream 5, and the waste liquid discharged from the storage tank may be supplied to the distillation column 8 through the stream 7.

This process can be performed continuously, unlike the batch process of a typical centrifuge. Therefore, by using the above method, it is not necessary to periodically remove inorganic salts including finely divided solid materials such as NaCl, and the efficiency of a filter or mesh used as a filtering means for the conventional inorganic salts when a certain operation is performed Falling shortcomings can be overcome.

In addition, since there is no fine NaCl in the waste liquid collected in the storage tank, it is possible to prevent a clogging phenomenon such as a filter in a pipe in the front end of the storage tank and a clogging of the discharge port due to the accumulation of solids under the storage tank. In addition, the distillation column 8 may also overcome the clogging phenomenon due to inorganic salts such as finely divided NaCl or the limit of distillation efficiency.

At this time, the decanter-type centrifuge used in the present invention to remove the inorganic salt in the liquid, by using a centrifugal force, by creating a solid and liquid layer on the wall surface of the decanter-type centrifuge, it is possible to separate and remove the solid Device.

For example, the decanter-type centrifugal separator may have a structure in which a cylindrical cylinder and a conical cylinder are combined to provide a horizontally installed bowl and a screw conveyor in which shafts and screws are coupled. In addition, a pipe for supplying the waste liquid to be separated is provided inside the shaft, and can be connected to a device that performs a washing process. In addition, the decanter-type centrifugal separator may be separately provided with an outlet for removing inorganic salts from the waste liquid and an outlet from which the inorganic salts have been removed.

When the waste liquid is supplied to the decanter-type centrifuge, the bowl and the screw conveyor rotate at different speeds, and the solid having a high specific gravity and a liquid having a small specific gravity can be separated by the action of the centrifugal force due to the speed difference. Therefore, when the decanter-type centrifugal separator is used, a solid substance (solid content) containing inorganic salt in the waste liquid may be sedimented and discharged through a separate outlet after being settled to the lower portion inside the bowl. In addition, at the same time, the liquid having a small specific gravity separated from the decanter-type centrifuge can be discharged through a separate line and transferred to a storage tank. In the liquid, an amide compound and a small amount of polyarylene sulfide may be included, and then the amide compound can be separated and recovered through a distillation process.

At this time, the operating conditions of the decanter type centrifuge can be used by operating for 30 seconds to 5 minutes or 30 seconds to 2 minutes at 1500G to 3100G. Under the above operating conditions, if the speed is 1500 G or less, the separation speed becomes slower and the operation time becomes longer, and if it is 3100 G or more, even if the water content reaches a threshold value and increases the gravitational acceleration, the water content does not decrease. In addition, "G" in the speed of the centrifuge, as is well known, may mean G-force, and may be used that is adjusted within the range according to the radius of the rotor of the decanter type centrifuge. When using the decanter type centrifuge within 30 seconds, the inorganic salt in the waste liquid is not properly separated and removed, and if the operating time is 5 minutes or more, it may be inefficient.

In addition, when using a decanter type centrifuge, the step of removing the inorganic salt in the waste solution is preferably performed at room temperature and atmospheric pressure of 20 ℃ to 25 ℃.

Particularly, the present invention does not operate a decanter type centrifuge under high temperature and high pressure conditions by supplying a waste liquid to a general extraction column or a batch centrifugal separator, so that processability can be improved. In other words, in the present invention, after the above-described waste liquid is introduced into a decanter type centrifugal separator, and performed under normal temperature and normal pressure, process equipment under high temperature and high pressure conditions is unnecessary.

In addition, in the distillation column (8), the amide-based compound in the waste liquid is separated and recovered from the bottom of the distillation column in a series of distillation processes, and the recovered amide-based compound (10) is re-polymerized through the circulation pump (11) (1) And can be reused. In addition, water 9 may be separated and discharged to the top of the distillation column.

The specific type of distillation column that can be used in the recovery process of the amide-based compound is not particularly limited. In addition, in the distillation process, a general compressor, reboiler, and condenser may be included. For example, the distillation column may include a column including an extraction region and a distillation region.

Meanwhile, the manufacturing process of the polyarylene sulfide may be performed according to a method well known in the art, and after the polymerization of the polyarylene sulfide is completed, a washing process may be performed to collect waste liquid.

In addition, it is preferable that the fine liquid of the polyarylene sulfide is removed from the reaction mixture of the polyarylene sulfide production process through a pre-treatment process using a filtration means. In addition, the filtration means may be performed according to methods well known in the art, and the method is not limited.

In particular, the present invention effectively separates amide compounds such as N-methyl-2-pyrrolidone from waste liquids containing various inorganic salts and impurities generated from a process for manufacturing polyarylene sulfide (PAS). Is what you want. Accordingly, the composition of the waste liquid introduced into the distillation column through the decanter-type centrifuge and the storage tank may include a composition in which inorganic salts and impurities, which are halides of alkali metals, are removed. The impurity may include fine powders such as polyarylene sulfide.

The waste solution may further include at least one selected from the group consisting of a small amount of alkali metal hydrosulfide, alkali metal sulfide, dihalogenated aromatic compound, and polyarylene sulfide together with water and an amide compound. . Specifically, the waste solution is o-dichlorobenzene (o-DCB), m-dichlorobenzene (m-DCB), p-dichlorobenzene (p-DCB), sodium hydrogen sulfide (NaSH), sulfide together with water and amide compounds It may also include one or more selected from the group consisting of sodium (Na ₂ S), and polyphenylene sulfide (PPS).

In one example, the composition of the waste solution after washing in the polyarylene sulfide production process includes, as described above, an amide-based compound such as NMP from about 20% to about 70% by weight, or from about 30% to about 60% by weight And, the composition of brine containing sodium chloride (NaCl) may include about 30% to about 80% by weight, or about 40% to about 70% by weight. In addition, the waste solution may further include p-DCB, NaSH, Na ₂ S and other impurities including dispersed PPS microparticles within about 10% by weight, or within about 5% by weight, based on the total weight of the solution medium. have. Other impurities include 2-pyrrolidinone, 1-methyl-2,5-pyrrolidione (1-methyl-2,5-pyrrolidione) and 3-chloro-N-methylaniline (3-Chloro- N-Methylaniline) and the like, and may be one or more of them.

Then, when using the above-described decanter-type centrifugal separator, as described above, about 25 to 40% by weight of the inorganic salt is removed based on the total weight of the waste solution, and the inorganic salt can be removed more efficiently than before. In addition, the composition of the waste liquid collected in the storage tank contains an amide-based compound such as NMP from about 15% to about 65% by weight, or from about 20% to about 60% by weight, of sodium chloride (NaCl)-free water. The composition may be up to about 25% by weight or from about 20% to about 30% by weight. In addition, the waste solution may further include p-DCB, NaSH, Na ₂ S, and other impurities including dispersed PPS microparticles within about 5% by weight, or within about 3% by weight, based on the total weight of the solution medium. have.

Here, specific examples of the amide compounds include amide compounds such as N,N-dimethylformamide or N,N-dimethylacetamide; Pyrrolidone compounds such as N-methyl-2-pyrrolidone (NMP) or N-cyclohexyl-2-pyrrolidone; Caprolactam compounds such as N-methyl-ε-caprolactam; Imidazolidinone compounds such as 1,3-dialkyl-2-imidazolidinone; Urea compounds such as tetramethyl urea; Or a phosphoric acid amide compound, such as hexamethylphosphate triamide, etc. are mentioned, It can be one or more of these.

The specific production method of the polyarylene sulfide and the specific separation and recovery method of the amide compound may refer to Examples described later. However, the method for producing polyarylene sulfide or the method for separating and recovering an amide-based compound is not limited to the contents described herein, and the method for preparing and separating and recovering is generally employed in the technical field to which the present invention pertains. In addition, the step(s) of the above-described manufacturing method and separation and recovery method may be changed by the step(s), which is usually changeable.

As described above, according to the present invention, by removing the inorganic salt from the waste liquid generated in the polymerization process of polyarylene sulfide using a decanter centrifuge, clogging phenomenon caused by fine inorganic salts that may occur during the distillation process or It is possible to recover the high-purity amide-based compound by improving the performance of separation efficiency of the amide-based compound such as N-methyl-2-pyrrolidone from the waste liquid generated in the polyarylene sulfide production process by preventing a decrease in distillation efficiency.

1 is a schematic view showing a process for recovering an amide-based compound from the waste solution generated in the polymerization process of polyarylene sulfide according to an embodiment of the present invention.

Figure 2 is a schematic diagram showing a conventional process for recovering an amide-based compound from the waste solution generated in the polymerization process of polyarylene sulfide according to Comparative Example 1.

Figure 3 is a schematic diagram showing a conventional process for recovering an amide-based compound from the waste solution generated in the polymerization process of polyarylene sulfide according to Comparative Example 2.

Hereinafter, preferred embodiments are provided to help understanding of the present invention. However, the following examples are provided only for easier understanding of the present invention, and the contents of the present invention are not limited thereby.

<Production of polyphenylene sulfide>

Preparation Example 1

Manufacturing process of polyphenylene sulfide

Sodium sulfide was prepared by mixing 1 equivalent of 70% sodium hydrogen sulfide (NaSH) and 1.05 equivalent of sodium hydroxide (NaOH) (ie 1:1.05 ratio) to make a PPS polymer. At this time, 0.4 equivalents of sodium acetate (CH ₃ COONa) powder, 1.65 equivalents of N-methyl-2-pyrrolidone (NMP), and 4.72 equivalents of deionized water (DI water) were added to the reactor. Here, equivalent weight means molar equivalent weight (eq/mol). At this time, the solid reagent was first added and then added in the order of NMP and deionized water. Then, the reactor was stirred at about 150 rpm, and dehydrated by heating to 190° C. for 1 hour 40 minutes. Thereafter, the temperature was lowered to 175°C, and 1.02 equivalents of para-dichlorobenzene (p-DCB) and 1.35 equivalents of N-methyl-2-pyrrolidone (NMP) were added to the reactor. Thereafter, the reaction mixture was heated to 230°C to react for 2 hours, heated to 255°C to react for 2 hours, and then 3 equivalents of distilled water was added and stirred for 5 minutes to obtain a reaction mixture containing PPS polymer.

After the polymerization process was completed, in order to remove residual unreacted substances or by-products from the reaction product, each was rinsed once with DI water and NMP at about 90° C. and filtered. This washing and filtration process was repeated twice more, and the final product, linear polyphenylene sulfide (PPS), and the waste solution (aqueous medium containing NMP) after the washing were recovered.

At this time, the waste solution after washing contained NMP-containing aqueous medium, brine (NaCl aqueous solution), wherein the composition of NMP was 5 to 40% by weight and the composition of brine containing NaCl was 1 to 15% by weight, water 20 to 95% by weight was included. In addition, the waste solution contains about 10 weights of other impurities including microparticles such as p-DCB, NaSH, Na ₂ S, differential PPS, and 2-pyrrolidinone, relative to the total weight of the solvent of NMP and brine. %.

Preparation Example 2

Manufacturing process of polyphenylene sulfide

Sodium sulfide was prepared by mixing 1 equivalent of 70% sodium hydrogen sulfide (NaSH) and 1.05 equivalent of sodium hydroxide (NaOH) (ie 1:1.05 ratio) to make a PPS polymer. At this time, 0.4 equivalents of sodium acetate (CH ₃ COONa) powder, 1.65 equivalents of N-methyl-2-pyrrolidone (NMP), and 4.72 equivalents of deionized water (DI water) were added to the reactor. Here, equivalent weight means molar equivalent weight (eq/mol). At this time, the solid reagent was first added and then added in the order of NMP and deionized water. Then, the reactor was stirred at about 150 rpm, and dehydrated by heating to 190° C. for 1 hour 40 minutes. Thereafter, the temperature was lowered to 175°C, and 1.02 equivalents of para-dichlorobenzene (p-DCB) and 1.35 equivalents of N-methyl-2-pyrrolidone (NMP) were added to the reactor. Thereafter, the reaction mixture was heated to 230°C to react for 2 hours, heated to 255°C to react for 2 hours, and then 3 equivalents of distilled water was added and stirred for 10 minutes to obtain a reaction mixture containing PPS polymer.

After the polymerization process was completed, in order to remove residual unreacted substances or by-products from the reaction product, each was rinsed once with DI water and NMP at about 90° C. and filtered. This washing and filtration process was repeated twice more, and the final product, linear polyphenylene sulfide (PPS), and the waste solution (aqueous medium containing NMP) after the washing were recovered.

At this time, the waste solution after washing contained NMP-containing aqueous medium, brine (NaCl aqueous solution), wherein the composition of NMP was 5 to 40% by weight and the composition of brine containing NaCl was 1 to 15% by weight, water 20 to 95% by weight was included. In addition, the waste solution contains about 10 weights of other impurities including microparticles such as p-DCB, NaSH, Na ₂ S, differential PPS, and 2-pyrrolidinone, relative to the total weight of the solvent of NMP and brine. %.

< Separation and recovery of N-methyl-2-pyrrolidone>

[Example 1]

Recovery process of amide compound (NMP) from waste liquid

The waste solution obtained from the washing process after the PPS polymerization of Preparation Example 1 is supplied to a decanter-type centrifuge (3) before collecting it into a storage tank for distillation, as shown in FIG. 1, and the waste solution containing solids such as NaCl and PPS is used as a waste solution. Removed from. This process was performed as a continuous process.

That is, after filtering the reaction mixture obtained after the PPS polymerization and passing through a washing process of NMP, 100 g of the generated waste liquid is collected, and using a decanter type centrifuge, 1500 G and 50 ml at room temperature and normal pressure are 30 sec. As a result, when proceeding for 30 sec, the total amount of separated NaCl and fine PPS in 50 ml of waste liquid was 15.7 ml, and the waste liquid was 34.3 ml.

Subsequently, the liquid obtained from the decanter-type centrifuge contained 20% by weight of NMP and 80% by weight of water, and the mixed solution of this composition was collected into a storage tank (6), and then introduced into a distillation column through a stream (7), N The separation and purification recovery process of -methyl-2-pyrrolidone (NMP) was performed. That is, at a flow rate of 700 kg/hr, stream 7 was introduced into the mixed liquid supply port located at the first stage of the distillation column having 15 theoretical stages to perform the NMP separation process. In the distillation process, the temperature at the top of the column was 134°C and the temperature at the bottom of the column was performed at 183°C.

Through the above process, it was confirmed that the NMP recovered from the waste liquid was 99.9% by weight or more of pure (99.9%) NMP with respect to all components.

	Characteristics for each stream of FIG. 1 according to Example 1
	Stream 7	Stream 9	Stream 10
NMP (%)	20	>1	99
Water (%)	80	99	<1
Total flow rate (kg/hr)	700	558	142
Temperature (℃)	25	100	176

Example 2

When removing solids including fine powders such as NaCl and PPS, except that the operating time of the decanter centrifuge was changed from 120sec to 30sec, in the same manner as in Example 1, the waste solution obtained from the washing process after PPS polymerization was treated. , N-methyl-2-pyrrolidone was separated and recovered using the process of FIG. 1. The characteristics of each stream in Example 2 are also the same as in Example 1.

That is, after filtering the reaction mixture obtained after the PPS polymerization and undergoing a washing process of NMP, 100 g of the generated waste liquid is collected, and using decanter type centrifuge, 1500 G and 50 ml at room temperature and pressure are 120 sec. As a result, when proceeding for 120 sec, the total amount of NaCl and fine PPS separated in 50 ml of waste liquid was 20.7 ml, and the waste liquid was 29.3 ml.

Through the above process, it was confirmed that the NMP recovered from the waste liquid was 99.9% by weight or more of pure (99.9%) NMP with respect to all components.

Example 3

The waste solution obtained from the washing process after the PPS polymerization of Preparation Example 1 is supplied to a decanter-type centrifugal separator (3) before being collected into a storage tank for distillation as shown in FIG. 1, and the solid solution containing fine powders such as NaCl and PPS is used as a waste solution. Removed from. This process was performed as a continuous process.

That is, after filtering the reaction mixture obtained after polymerization of the PPS and undergoing a washing process of NMP, 37.5 ml of the resulting waste liquid is collected and put into a decanter type centrifuge, under conditions of 1500 G and 120 sec at room temperature and pressure. Was driven by.

As a result, the total amount (volume) of the solid content of NaCl separated from the 37.5 ml waste solution and the differential PPS was 5.5 ml, and the water content of the inorganic salt according to Equation 1 below was 43.53%. (The remaining content is liquid waste liquid)

[Equation 1]

Moisture content (%) = [(Weight before drying of separated inorganic salt-weight after drying of separated inorganic salt)/ Weight before drying of separated inorganic salt] × 100

At this time, the inorganic salt may contain a trace amount of finely divided PSS.

Comparative Example 1

After the PPS polymerization of Preparation Example 1, the waste solution obtained from the washing process after the PPS polymerization was tried to remove solids including fine powders, such as NaCl and PPS, by using a general filter before collecting them into a storage tank for distillation as shown in FIG. 2.

That is, after filtering the reaction mixture obtained after the PPS polymerization and NMP washing process, 100 g of the generated waste liquid was collected, and the waste liquid was filtered using a 25 mm syringe filter. As a result, when a 25 mm syringe filter was used, NaCl having a particle size of 5 to 30 μm passed through the filter, and the removal efficiency of inorganic salts from the waste solution was very low.

As a result, the total amount of NaCl and finely divided PPS separated in 50 ml of the waste liquid was 1 ml or less, and solids observable in the waste liquid were still present.

Comparative Example 2

It was intended to remove NMP from the waste solution in the same manner as in Comparative Example 1, except that a 0.45 μm syringe filter was used. However, when a 0.45 μm syringe filter was used, the filter was clogged and further experiments were impossible. As a result, the separated filtered waste liquid in 50 ml of waste liquid was 5 ml or less.

Comparative Example 3

The waste solution obtained from the washing process after the PPS polymerization of Preparation Example 1 was removed by using a general centrifugal separator that proceeds in a batch operation before collecting it into a storage tank for distillation as shown in FIG. 3 to remove solids including fine powders such as NaCl and PPS. .

That is, the reaction mixture obtained after the PPS polymerization was filtered and washed with NMP, and then 50 ml of the resulting waste liquid was collected in a conical tube, and treated at 4000 rpm (about 1500 G) at room temperature and pressure for 3 minutes with a centrifuge. As a result, the total amount of NaCl and fine PPS separated in 50 ml of waste liquid was 11.3 ml, and the waste liquid was 38.7 ml. However, in the case of using the above method, since solid matters accumulated in the centrifuge must be removed each time, continuous operation was impossible and processability was deteriorated.

Comparative Example 4

The waste solution obtained from the washing process after the PPS polymerization of Preparation Example 2 was attempted to remove solids including fine powders such as NaCl and PPS using a general filter before collecting the waste solution obtained in the storage tank for distillation as shown in FIG. 2.

That is, after filtering the reaction mixture obtained after polymerization of PPS and undergoing a washing process of NMP, 100 g of the generated waste liquid was collected, and the waste liquid was filtered using a 300 μm filter.

As a result, in the case of Comparative Example 1 using a 300 μm filter, NaCl passed through the filter. Therefore, the filtration efficiency of the solid content including the inorganic salt was low, and the waste solution still contained solids observable with the naked eye.

Comparative Example 5

It was intended to recover NMP from the waste liquid in the same manner as in Comparative Example 4, except that the 75 µm syringe filter of Preparation Example 2 was used. However, when a 75 μm syringe filter was used, the filter was clogged after about 2 minutes, so there was no filter effect and further experiments were impossible. That is, the waste liquid separated and filtered with a filter in 100 g of the waste liquid was only 5 ml or less.

Comparative Example 6

After collecting the waste solution obtained from the washing process after the PPS polymerization of Preparation Example 2, as shown in FIG. 3, using a general centrifugal separator that proceeds in a batch operation, the solids including fine powders such as NaCl and PPS are removed. I wanted to.

That is, the reaction mixture obtained after the PPS polymerization was filtered and washed with NMP, and then 50 ml of the resulting waste liquid was collected in a conical tube, and treated at a room temperature and a normal pressure in a batch centrifuge at 7000 rpm for 10 minutes.

As a result, the volume of NaCl separated in 50 ml waste liquid was 7.3 ml, and the water content of NaCl calculated by Equation 1 was 85.47%.

From the above results, as in Comparative Example 3, even if the inorganic salt in the waste liquid NaCl is removed, the removal efficiency is small, the water content is large, and it is difficult to remove when the batch centrifuge solids are accumulated. In particular, since the solid matters accumulated in the centrifuge must be removed each time using the above method, continuous operation was impossible and processability was deteriorated.

Claims (11)

1. Recovering waste liquid containing water, amide compounds and inorganic salts generated in the polyarylene sulfide production process;

   Removing the inorganic salt in the waste solution by supplying the waste solution to a decanter centrifuge; And

   Collecting the waste solution from which the inorganic salt has been removed into a storage tank, and then recovering the amide compound from the waste solution using a distillation column;

   Method for recovering an amide-based compound comprising a.
2. According to claim 1,

   The inorganic salt is a method for recovering an amide-based compound containing an alkali metal halide.
3. The method of claim 1, wherein in the step of removing the inorganic salt in the waste solution, 25 to 40% by weight of the inorganic salt is removed based on the total weight of the waste solution.
4. The method for recovering an amide-based compound according to claim 1 or 3, wherein the inorganic salt separated in the step of removing the inorganic salt in the waste solution has a water content of 45% or less calculated by Equation 1 below.

   [Equation 1]

   Moisture content (%) = [(Weight before drying of separated inorganic salt-weight after drying of separated inorganic salt)/ Weight before drying of separated inorganic salt] × 100
5. The method of claim 1, wherein the decanter-type centrifugal separator is operated at 1500G to 3100G for 30 seconds to 2 minutes.
6. The method of claim 1, wherein the decanter type centrifuge is separately provided with an outlet for removing inorganic salts from the waste liquid and a waste liquid outlet from which the inorganic salts have been removed.
7. The method of claim 1, wherein the step of removing the inorganic salt in the waste solution is performed at room temperature and atmospheric pressure of 20°C to 25°C.
8. According to claim 1,

   The step of removing the inorganic salt in the waste solution is a continuous process, a method for recovering an amide compound.
9. According to claim 1,

   The step of recovering the amide-based compound from the waste solution is a continuous process, the method for recovering the amide-based compound.
10. According to claim 1,

    The waste solution supplied to the decanter-type centrifuge is a waste solution produced in the process of synthesizing and washing polyarylene sulfide, and a method for recovering an amide compound.
11. According to claim 1,

    The amide compound is N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), N-cyclohexyl-2-pyrrolidone, N-methyl-ε -Caprolactam, 1,3-dialkyl-2-imidazolidinone, and at least one member selected from the group consisting of tetramethyl urea, a method for recovering an amide compound.

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