JPS6210221B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering N-alkylamide from an aqueous N-alkylamide solution containing inorganic chloride and heavy metal ions. The purpose is to provide a method for recovering N-alkylamide from an aqueous N-alkylamide solution containing inorganic chloride and heavy metal ions in a stable process, at low cost, in good yield, and with high purity. In recent years, there has been a strong demand in the industry for organic materials that have heat resistance, flame retardance, high strength, chemical resistance, and dimensional stability.
2. Description of the Related Art So-called organic heat-resistant polymers such as polyamide hydrazide, polyamideimide, and polyimide are being actively produced. These materials have already been formed into fibers, films, papers, tapes, etc. and used as various industrial products. However, these polymers are extremely poorly soluble and do not dissolve in ordinary inexpensive organic solvents.
In order to polymerize and mold polymers, expensive solvents called N-alkylamides such as N・N-dimethylacetamide and N-methylpyrrolidone, and inorganic solvents such as lithium chloride and calcium chloride are used as solvent aids. A mixture of chlorides is used. Polymers polymerized using N-alkylamides containing inorganic chlorides and molded articles are usually washed with water and isolated. On the other hand, N
- The alkylamides together with the inorganic chlorides are separated from the polymers and moldings in the form of aqueous solutions. and,
Since N-alkylamides are expensive, they must be recovered and reused, and the challenge in this industry is how to recover high-purity N-alkylamides from this aqueous solution at a high yield and at low cost. It is said to hold the key to success. There is a well-known method for extracting and recovering N-alkylamides from an aqueous solution of N-alkylamides and inorganic chloride (calcium chloride) used for polymer molding with dichloromethane or other extracting agent (Tokuko-Sho).
48-23415, Special Publication No. 49-48432). However, when used in polymerization, such as the reaction of aromatic dicarboxylic acid chloride and aromatic diamine to obtain aromatic polyamide, N It has been found that when extracting and recovering -alkylamides using this method, there are problems both in terms of the quality of the N-alkylamides obtained by recovery and in the process of extraction and recovery. That is, the problem with the quality of the recovered N-alkylamide is the phenomenon that when polymerization is carried out using this solvent again, the degree of polymerization of the resulting polymer is no longer sufficient. Although the cause of this is not clear, it is presumed that the recovered N-alkylamide contains impurities that inhibit polymerization, and we are investigating the identification of these impurities by means such as gas chromatography and mass spectroscopy. However, it has not yet been elucidated. Further, process problems in extraction and recovery are caused by solid matter (so-called "slag") that occurs when the aqueous solution and extractant come into contact during the extraction operation. According to the investigation by the present inventors, this solid substance is due to heavy metal ions mixed in the N-alkylamide aqueous solution, and is a combination of N-alkylamide or its decomposition products with heavy metals and inorganic substances in some way. It was estimated that This solid matter is generated during the extraction operation, adheres to the inside of the extraction device, reduces the contact area for liquid-liquid extraction, gradually reduces the extraction rate, and finally makes the extraction operation impossible.
In addition, this solid substance has a floating property, so it mixes into the extraction waste water and the extraction phase, and even in the recovery process after the extraction process, it can cause various problems such as adhering to heat exchangers etc. and impairing heat conduction. cause trouble. The contamination of heavy metal ions that cause this trouble is due to those originally contained in certain inorganic chlorides and due to corrosion of equipment materials by hydrochloric acid generated during polymerization. As is well known, hydrochloric acid corrodes iron and SUS materials that are generally used as equipment materials, and in order to completely eliminate corrosion, it is necessary to use very expensive materials or to take measures such as Teflon or glass lining or coating. There must be. However, it is economically difficult to make all devices that come into contact with these compounds using such materials, and it is also physically difficult due to the mechanical strength required for the devices and the workability during device manufacturing. In most cases it is possible,
It is an unavoidable fact that heavy metal ions are mixed into the aqueous solution of N-alkylamide used as a polymerization solvent to be recovered. The present inventors have discovered that in the extraction and recovery of N-alkylamides from such N-alkylamide aqueous solutions containing inorganic chlorides and heavy metal ions, the extraction operation can be performed smoothly and can be recovered with high purity and good yield. As a result of studying to develop an improved method, we succeeded in preventing the generation of solids during extraction by adjusting the aqueous solution to a specific pH range. Furthermore, by performing an extraction operation on the aqueous solution in a specific pH range, it is possible to reduce the polymerization-inhibiting impurities in the recovered N-alkylamide to an amount that does not actually participate in polymerization, and the recovered N −
It was discovered that quality problems with alkylamides could be solved all at once. The present invention has been completed based on the above findings and has achieved the intended purpose. That is, the present invention uses 1 to 50% by weight of inorganic chloride and
Extraction of N-alkylamide by adjusting the pH of the aqueous solution to 2.5 to 5.5 and extracting with an extractant when recovering N-alkylamide from an N-alkylamide aqueous solution containing 5 ppm or more of heavy metal ions. This is a collection method. Conventionally, when extracting an N-alkylamide aqueous solution, keeping the aqueous solution acidic meant that N-
This was considered undesirable due to the stability of alkylamides against hydrolysis. However, in the method of the present invention, by adjusting this aqueous solution to a specific pH range and performing extraction, it has become possible to recover N-alkylamide at low cost, in good yield, and with high purity in a stable process. is surprising. Why is it that in the PH range found by the present invention, the solids generated in the conventional technology are not generated, and impurities that inhibit polymerization are removed from the N-
Although it is not clear whether they are no longer included in alkylamides, it is presumed that the extraction rate of these substances changes depending on the pH of the aqueous solution. The present invention can be applied not only to an aqueous N-alkylamide solution used in polymerization, but also to an aqueous N-alkylamide solution used in molding. In other words, N-alkylamides containing inorganic chlorides used as coagulation liquids for long-term molding corrode equipment and materials due to the corrosivity of inorganic chlorides, contain non-negligible amounts of heavy metal ions, and This is because the polymer also contains impurities that inhibit the reaction during polymerization due to decomposition of alkylamides, etc. In such cases, the effects of the present invention are exhibited. N-alkylamide as used in the present invention means N.N.
It refers to solvents such as -dimethylacetamide, N-methylpyrrolidone, tetramethylurea, N-acetylpyrrolidine, and N-acetylmorpholine, which may be used singly or in a mixture of two or more. In the present invention, the inorganic chloride contained in the N-alkylamide aqueous solution refers to chloride which is known to be advantageous when coexisting when polymerizing or molding a polymer using N-alkylamide. Refers to inorganic chlorides added during polymerization or molding of lithium, magnesium chloride, calcium chloride, zinc chloride, etc., and also refers to the above inorganic chlorides produced by neutralizing hydrochloric acid produced as a by-product during polymerization using dicarboxylic acid chloride. Also included are chlorides and by-product inorganic chlorides such as sodium chloride and ammonium chloride. These inorganic chlorides may be used alone or in a mixture of two or more without impairing the effects of the present invention, and the concentration in the aqueous solution may be 1 to 1 by weight.
Applies to the invention in 50% of cases. In the present invention, the pH of the N-alkylamide aqueous solution is
Any value between 2.5 and 5.5 may be taken. However, studies conducted by the present inventors have revealed that the upper limit of the pH range suitable for recovering N-alkylamides in a stable process is correlated with the concentration of heavy metal ions contained in the aqueous solution. In other words, the heavy metal ions used in the present invention are metal ions of the elements that constitute various iron materials and SUS materials that are used as general equipment materials, and that constitute the fourth period of the periodic table. , iron, nickel, chrome,
Each type of manganese ion is included, and a mixture of two or more types may be used, but if the total of these heavy metal ions exceeds 5 ppm, solid matter will precipitate during extraction, and to prevent this, the pH of the aqueous solution must be below 6.0. It was necessary to do so. By the way, heavy metal ions
The upper limit of PH value suitable for 50 ppm is 5.2, and depending on the concentration of heavy metal ions, the pH value below these upper limits may be
Process troubles can be avoided by taking the PH value. On the other hand, preventing impurities that inhibit polymerization from being mixed into the recovered solvent can be achieved by adjusting the pH of the aqueous solution to 2.5 to 5.5. More favorable PH
The range is 3.0-5.0. Any method may be used for extraction when the pH of the N-alkylamide aqueous solution is 2.5 to 5.5. An easily adopted method is to adjust the pH to the range of the present invention before carrying out the extraction operation of an N-alkylamide aqueous solution containing inorganic chloride and heavy metal ions. That is, this is a method of adjusting the pH by adding a small amount of an acid such as hydrochloric acid to a neutralized aqueous solution. In addition, in cases where hydrochloric acid is produced as a by-product during polymerization using N-alkylamides, in addition to the above-mentioned method of adding acids to an already neutralized aqueous solution, it is possible to Any method may be used to neutralize only a portion of the by-produced hydrochloric acid, or to maintain the pH within the range of the present invention without performing any neutralization operation. In some cases, a method may be adopted in which acids are added to the extraction agent to substantially adjust the pH of the aqueous phase during extraction to 2.5 to 5.5. It is also recommended to prevent decomposition of the agent. The extraction agent used in the extraction of the present invention may be the extraction agent used for the extraction of N-alkylamides from ordinary aqueous solutions, such as halogenated hydrocarbons such as dichloromethane and chlorobenzene, hydrocarbons such as benzene, etc.
Higher alcohols such as amyl alcohol, ester compounds such as diethyl oxalate, and nitrile compounds such as adiponitrile and benzonitrile are known. According to the studies of the present inventors, halogenated hydrocarbons are preferable as extractants of the present invention, and more preferably dichloromethane, 1,2-dichloroethane, chloroform, 1,1,2-trichloroethane, These may be used alone or in combination of two or more. It has been found that these halogenated hydrocarbons not only have excellent extraction efficiency, but also that the decomposition of the extractant itself is suppressed by contact with the acidic aqueous solution, which is a feature of the present invention, resulting in good results. Conditions for extracting N-alkylamide using this extractant, ie, extraction temperature, amount of extractant, etc., can be arbitrarily selected depending on the type of N-alkylamide, the concentration in the aqueous solution, and the type of extractant. Also, the equipment used for this extraction is not particularly limited,
Regardless of continuous type or batch type, use a tower with built-in rotary vanes, a packed type tower, a tray type tower, an extraction device using centrifugal force, an extraction device using baffles, or a mixing tank with a normal stirring function. Extraction equipment etc. can be used effectively. Also, from the extracted phase extracted according to the present invention, N
- The method for recovering the alkylamides is not limited, and various methods for separating general N-alkylamides and extractants may be used. An easy method is conventional separation distillation, which can be used either continuously or batchwise. N- to be collected
The purity of the alkylamide can be arbitrarily selected depending on the conditions for reuse. Moreover, in the case of the present invention, since there is no contamination of solid matter, the amount of N-alkylamide to be removed as a distillation residue is reduced, and the recovery rate of N-alkylamide can be dramatically increased. Furthermore, since there are no solids present during distillation, there is no reduction in heat conduction due to solids adhering to the heat exchanger, and no flooding phenomenon occurs, resulting in stable quality recovered N-alkylamide. can be obtained. Any method may be used to treat the extracted waste water generated by carrying out the present invention. That is, the extraction water obtained by the present invention exhibits acidity,
It is optional to neutralize and slowly release the inorganic chloride, or to recover the contained inorganic chloride, and the cost of the inorganic chloride and
This is determined to be the cost required for recovery. Generally, it is advantageous to recover the higher the concentration of inorganic chloride;
The method for this may also be freely chosen. That is, the recovery method conditions, equipment, etc. are determined in consideration of the purity required for the recovered inorganic chloride. For example, if the required purity of the inorganic chloride to be recovered is not so strict, the extraction waste water may be concentrated as is or after neutralization.
Alternatively, a method such as removing a portion of the heavy metal ions as hydroxide and then concentrating it may be used. If even higher purity inorganic chlorides are required, methods such as treating extracted wastewater with an ion exchange resin or chelate resin that selectively adsorbs heavy metals to completely remove heavy metals and concentrate recovery can be used. . In the practice of the present invention, organic substances and inorganic substances other than inorganic chlorides and heavy metal ions may be contained in the N-alkylamide aqueous solution, and stabilizers and the like contained in the extraction agent are not included in the present invention. does not impair the effect of As detailed above, according to the method of the present invention, N-alkylamides, which are preferably used in the polymerization and molding of organic polymers having heat resistance, flame retardancy, high strength, and chemical resistance, can be recovered from aqueous solutions. , with virtually no process troubles and a stable process, it is possible to recover inexpensively and in high yields, and it is also easy to recover with high purity, making the quality of N-alkylamides extremely stable. It can be done. Furthermore, the effects of the present invention are not only remarkable in improving the recovery rate and quality of N-alkylamides as described above, but also suppressing the decomposition of extractants, and reducing the basic unit of extractants. It also has a remarkable effect in making it easier to recover high-purity inorganic chlorides. Examples and comparative examples of the present invention are listed below to more specifically illustrate the embodiments and effects of the present invention. In addition, the quantitative determination of heavy metal ions in the examples was determined by spectrophotometry (JIS-K-0102, etc.), and the ppm unit is expressed in mg/. In addition, the content of substances other than heavy metal ions is expressed in terms of % and weight %. The logarithmic viscosity (ηinh) used as a parameter representing the degree of polymerization of the polymer in the examples is defined by the following formula. ηinh=ln ηr/0.5 (where ηr is the polymer concentration in 98% by weight sulfuric acid
It exhibits a relative viscosity of 0.5 g/100 ml, which is the ratio of the number of seconds of fall between the polymer solution and 98% by weight sulfuric acid, measured with a capillary viscometer at 25°C. ) Example 1 N/N- was placed in a SUS304 container equipped with a stirrer.
Dimethylacetamide (hereinafter abbreviated as DMA)
1.0 kg of lithium chloride was charged and 50 g of lithium chloride and 108 g of metaphenylenediamine were dissolved. After these were dissolved, 203 g of isophthalic acid chloride was added all at once in powder form and stirred. The power load required for stirring increased with the viscosity of the liquid, and after 30 minutes, the load became constant and polymerization was completed. The resulting viscous liquid should be mixed with water containing 48 g of lithium hydroxide in a small mixer to solidify the polymerized poly-metaphenylene isophthalamide, and the polymer should be separated and recovered using a glass filter. An aqueous solution of DMA was obtained. This aqueous solution had a pH of 6.7, contained 23% DMA, 3% lithium chloride, and contained heavy metals such as 15 ppm iron ions, 2 ppm chromium ions, 1 ppm nickel ions, and 1 ppm manganese ions. 100 g of this DMA aqueous solution was collected, adjusted to PH = 4.0 with 0.1N aqueous hydrochloric acid solution, placed in a separatory funnel, added with 100 g of dichloromethane, shaken, and allowed to stand still. The liquid was completely separated into two phases, no foreign matter was generated at the interface, etc., and the two phases could be easily separated. The concentration of DMA in the extracted phase was 10%, and the concentration in the extracted water phase was 19%. Comparative Example 1 100g of the DMA aqueous solution used in Example 1 was added to dichloromethane in the same manner as in Example 1 without adjusting the pH.
100g was added and separation was attempted using a separatory funnel. The liquid was separated into two phases, and the distribution of DMA into the extraction phase and extracted water phase was the same as in Example 1, but a brown floating solid was precipitated near the interface. It was difficult to separate the two phases. Example 2 500g of N-methylpyrrolidone (hereinafter abbreviated as NMP) was placed in a SUS 316 container equipped with a stirrer.
and dissolved 25 g of lithium chloride, 15.5 g of terephthalic acid dihydrazide, and 2.2 g of paraphenylene diamine. The system was cooled and 20.3 g of terephthalyl chloride was added in powder form all at once while stirring was continued. A rapid increase in viscosity was observed and a clear polyamide hydrazide solution was obtained after 1 hour. Add 4.8 lithium hydroxide to this solution.
The polymer was coagulated with water containing g, and the polymer was filtered off to obtain an aqueous solution of NMP. This aqueous solution had a pH of 7.5, contained 25% NMP and 1.7% lithium chloride, and contained 10 ppm of iron ions and 1 ppm each of chromium and nickel ions as heavy metals. Collect 100g of this NMP aqueous solution and pH it with 0.1N hydrochloric acid.
= 3.5 and placed in a separatory funnel, 100 g of chloroform was added, shaken, and allowed to stand still. The liquid was completely separated into two phases, and the two phases could be easily separated. Note that the concentration of NMP was 14% in the extraction phase and 12% in the extracted water phase. Comparative Example 2 100 g of the NMP aqueous solution used in Example 2 was mixed with 100 g of chlorophoform in the same manner as in Example 2 without adjusting the pH.
g was added and separation using a separatory funnel was attempted. The liquid is separated into two phases: the extraction phase and the extracted water phase.
Although the NMP concentration was the same as in Example 2, a yellow-brown floating solid was precipitated near the interface, making it difficult to separate the two phases near the interface. Example 3 Poly-metaphenylene isophthalamide was dissolved in DMA containing 5% calcium chloride to create a stock solution for molding with a polymer concentration of 20%, and SUS
We conducted an experiment to spin poly-metaphenylene isophthalamide using wet spinning equipment manufactured by 316.
The coagulation bath composition was an aqueous solution of 25% calcium chloride and 30% DMA, and a study was conducted to recover DMA from this coagulation bath. This liquid had a pH of 7.8 and contained 45 ppm of iron ions, 2 ppm each of chromium ions and manganese ions as heavy metals. After adjusting the pH of this liquid to 3.0, an experiment was conducted in which it was extracted and recovered using a continuous extraction device. The extraction device is made of glass with a diameter of 25 mm and a pipe with a height of 1.5 m and SUS.
The equipment consists of a packed column with a Raschig ring made of 316, a metering pump, and a tank, and the DMA aqueous solution is continuously fed at a flow rate of 180 g/min from the bottom of the column, and the extractant 1,1,2-tochloroethane is continuously fed at a flow rate of 200 g/min from the top of the column. I washed it away. It can be operated continuously for 8 hours,
There were no occurrences that would interfere with subsequent driving. Furthermore, the DMA concentration in the extracted waste water was undetectable by gas chromatography (less than 50 ppm), and complete extraction operations were possible. Comparative Example 3 The DMA aqueous solution used in Example 3 was extracted using the same apparatus and under the same conditions without adjustment.
Approximately 30 minutes after the start of operation, brown solids were clearly generated inside the packed column, and after one hour, uneven flow was observed throughout the column due to adhesion to the packed column. The DMA concentration in the extracted wastewater at this point can be determined by gas chromatography.
It was 300ppm. After a further 1 hour of operation, the precipitation of brown solids became intense, and floating substances were observed in the extracted water phase and extract liquid, making the extraction operation impossible. Example 4 Poly-paraphenylene terephthalamide was polymerized using a polymerization apparatus made of SUS, and the solvent used in the polymerization was recovered and tested for use in repeated polymerizations. SUS with a stirring mechanism for incoming purified NMP
Pour 10kg into a 304 container, add 800g of calcium chloride and 540g of paraphenylenediamine and dissolve, then 1015g of terephthalic acid chloride.
was added in powder form while stirring. This liquid rapidly increased in viscosity and turned into a gel in about 3 minutes, making further stirring difficult. This gel-like material was quickly transferred to a batch kneader, and crushed and kneaded for 15 minutes to complete polymerization. The obtained powdered polymer was transferred to a Henschel mixer, and an aqueous slurry solution containing 285 g of calcium hydroxide was added and mixed to solidify the polymer. The solid and liquid were separated, and the polymer was washed with water and dried, while the NMP aqueous solution was stored in a storage tank to be recovered. The above polymerization operation was repeated 5 times to obtain ηinh as shown below. 5.62, 5.54, 5.64, 5.68, 5.57 On the other hand, the stocked NMP aqueous solution was completely mixed and contained 35% NMP at pH=7.2, 4.7% calcium chloride, 30 ppm iron ions, 5 ppm chromium ions, and nickel. It contained 2 ppm of ions and 1 ppm of manganese ions. Using half of this aqueous solution, the following recovery operation was performed and the solution was subjected to polymerization again. First, the aqueous solution was adjusted to PH=4.0 with a 0.1N aqueous hydrochloric acid solution, and extracted and collected using a continuous extraction device. In other words, the extraction device is a packed tower made of a glass pipe with a diameter of 25 mm and a height of 1.5 m and a porcelain interlock saddle.
It is a device consisting of a metering pump and a tank,
Continuous treatment was carried out by flowing the NMP aqueous solution from the bottom of the column at a flow rate of 200 g/min and the extractant dichloromethane from the top of the column at a flow rate of 300 g/min. In order to recover NMP from the obtained extraction phase, separate distillation is performed in a distillation column, and after removing dichloromethane, 10
Got Kg. Using this solution, poly-paraphenylene terephthalamide was polymerized again using the same equipment, the same conditions, and the same raw materials (excluding NMP), and the ηinh was 5.71. Comparative Example 4 An example is shown in which half of the recovered liquid obtained from the initial polymerization in Example 4 was extracted and recovered by conventional techniques and used again for polymerization. The polymerization recovery liquid could not be treated in the same packed tower as in Example 3 without adjusting the pH due to the generation of solid matter. Therefore, the pH of the polymerization recovery liquid was adjusted to 9.
Adjust with 0.1N sodium hydroxide aqueous solution, remove the contained heavy metals as hydroxide using a polypropylene cloth, and then neutralize with hydrochloric acid again to obtain PH=
It was set as neutral of 7. It was found that the heavy metal content in the leaked liquid had decreased to 2 ppm for iron ions, and that nickel, chloroform, and manganese ions were below the detection limit. After removing most of the heavy metals in this way, extraction was carried out using the same equipment and under the same conditions as in Example 4, and a slight amount of solid matter was observed to precipitate during extraction. There was no hindrance to the process. The obtained extract was subjected to separate distillation in a distillation column in the same manner as in Example 3, and after removing dichloromethane, 10 kg was collected as the main fraction of NMP. This solution was used to polymerize poly-paraphenylene terephthalamide, and its ηinh was 3.83.
This showed a clear decrease compared to the initial polymerization. Examples 5 to 7 (Comparative Examples 5 to 6) Into a SUS 304 container with a stirring mechanism, 10 kg of incoming purified DMA was charged, and 500 g of lithium chloride,
A viscous polymer solution was obtained by dissolving 1080 g of metaphenylene diamine, adding 2030 g of isophthaloyl chloride in powder form, and stirring for 1 hour. This solution was transferred to a Henschel mixer together with 800 g of water containing sodium hydroxide, and the polymer was coagulated and ground to obtain an aqueous solution of DMA to be recovered. On the other hand, when the obtained polymer was washed and the solution viscosity was measured, it was found to be ηinh=2.28. The aqueous solution of DMA thus obtained has a pH of
6.8, 19ppm iron ions, chromium ions
It contained 3ppm and 1ppm of nickel ions.
This DMA aqueous solution was divided into 5 parts, each adjusted to the specified pH below, extracted with 1,2-dichloroethane, purified by distillation, and recovered DMA.
The obtained product was used to polymerize polymetaphenylene isophthalamide as shown in Example 1. The results of polymerization using the recovered DMA thus obtained are shown in the following table.

【table】

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Claims (1)

[Claims] 1. In recovering N-alkylamide from an aqueous N-alkylamide solution containing 1 to 50% by weight of inorganic chloride and 5 ppm or more of heavy metal ions,
A method for extracting and recovering N-alkylamides, which comprises adjusting the pH of the aqueous solution to 2.5 to 5.5, and then extracting with an extractant. 2. The heavy metal ions contained in the N-alkylamide aqueous solution belong to the group 4 of the periodic table,
2. The method for recovering N-alkylamide according to claim 1, wherein the N-alkyl amide is a group and one or more metal element ions of the elements constituting the group. 3. N- according to claim 1, in which at least one halogenated hydrocarbon selected from the group consisting of dichloromethane, 1,2-dichloroethane, chloroform, and 1,1,2-trichloroethane is used as an extractant. Method for recovering alkylamide.