JPS61227553A - Recovery of amide-type solvent - Google Patents

Abstract

PURPOSE:To recover an amide-type solvent economically in high yield and purity, from a composition containing an N-alkyl-substituted amide-type solvent and inorganic salts, by extracting the solvent with nitromethane, nitroethane, nitropropane, etc. CONSTITUTION:A composition containing one or more N-alkyl-substituted amide- type solvents of formula I-formula IV (R1 is H, methyl or ethyl; R2 and R3 are methyl or ethyl; R4 is -CH2CH2-, -CH2-CH2-CH2-, etc.; R5 is -CH2-CH2-CH2- or -CH2-CH2-CH2-CH2-) and inorganic salts is extracted with a compound selected from nitromethane, nitroethane and nitropropane to recover said N- alkyl-substituted amide-type solvent. The extractant is not only excellent in the extraction capability of an amide-type solvent but also resistant to decomposition and effective to suppress the intrusion of heavy metal ions and the generation of solid product in extraction. A highly pure amide-type solvent can be recovered by the use of said extractant.

Description

Detailed Description of the Invention (a) Field of Application of the Invention The present invention is directed to separating an amide type solvent from a composition containing an N-alkyl substituted amide type solvent (hereinafter simply referred to as an amide type solvent) and an inorganic salt. , regarding the method of recovery.

In recent years, there has been a strong demand in the industry for organic materials that have heat resistance, flame retardancy, high strength, chemical resistance, and dimensional stability. The production of organic heat-resistant polymers is actively conducted. 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;
It does not dissolve in common inexpensive organic solvents.

For polymerization and molding, so-called amide-type solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone, inorganic chlorides such as lithium chloride and calcium chloride as solubilizing agents, and polymerization Since hydrochloric acid is often present as a by-product of the reaction, inorganic salts are often included as a result of the neutralization process, and furthermore, it is used as a liquid medium for recovering the polymer from the polymerization system and for molding. It often contains a liquid coagulating medium. Therefore, in industrial production, it is very important to efficiently recover expensive amide type solvents from such systems.

(c) Conventional technology The amide type solvent is extracted and recovered from the aqueous solution of the amide type solvent and inorganic chloride (e.g. lithium chloride, calcium chloride, etc.) used in polymer molding using a halogenated hydrocarbon solvent such as dichloromethane or chloroform. The method is already known (% Publication No. 48-23415, Special Publication No. 49-Sho.
48432 publications).

However, aromatic radical I to obtain aromatic polyamide
These methods can be used to separate and recover amide-type solvents that are used in polymerizations, such as the reaction between acid chloride and aromatic diamines, and that have become an aqueous solution by neutralizing the hydrochloric acid that is produced as a by-product during polymerization using conventional methods. It has been found that there are problems in the quality of the amide-type solvent obtained by recovery and in the process of extraction and recovery.

That is, the problem with the quality of the recovered amide type solvent 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 certain, it is presumed that the recovered amide type solvent contains impurities that inhibit polymerization.

In addition, process problems in extraction and recovery include solid matter (
This is due to the so-called "noro"). According to the investigation by the present inventors, this solid substance is caused by heavy metal ions mixed in the aqueous solution containing the amide type solvent and inorganic salt, and that the amide type solvent or its decomposition products are combined with the heavy metal ions in some way. It was also found that heavy metal ions were metal chloride produced by reaction with hydrochloric acid produced as a by-product in the polymerization reaction, metal hydroxide produced during neutralization treatment, etc. This solid matter adheres to the inside of the extraction device during the extraction operation, reduces the contact area of liquid-liquid extraction, and gradually reduces the extraction rate.
Eventually, the extraction operation becomes impossible. In addition, this solid substance has buoyant properties and is mixed into the extraction wastewater and extractant phase.
Even in the recovery process after the extraction process, it adheres to the heat exchanger etc. and causes problems such as poor heat conduction and bumping during distillation.

The contamination of heavy metal ions that cause this trouble are those originally contained in inorganic chlorides added as solubilizing agents, hydrochloric acid generated during polymerization, and extractants (halogenated hydrocarbons such as dichloromethane and chloroform). This is due to corrosion of equipment materials due to hydrochloric acid generated during thermal decomposition of water.

As is well known, hydrochloric acid corrodes iron and stainless steel materials that are generally used as equipment materials, and in order to completely eliminate corrosion, one must use very expensive materials, or use polytetrachloroethylene and other fluorine-based polymers, glass linings, etc. Treatment such as coating must be applied. but,
It is not economical to make all devices using such materials, and it is often physically difficult due to the mechanical strength required of the device and the workability during device manufacturing.

In the aqueous solution to be recovered containing the amide type solvent used as the polymerization solvent and the inorganic chloride used as the solubilizing agent,
Contamination with heavy metal ions is an inevitable fact.

(The problem that the invention aims to solve) Conventionally, dichloromethane, chloroform, etc. have been used as extractants for amide-type solvents.Although dichloromethane and chloroform have excellent extraction power for amide-type solvents, It is known that it gradually decomposes even at room temperature, and that decomposition is further accelerated and hydrochloric acid is generated under heated conditions such as in the fractional distillation process after the extraction process.As a result, as mentioned above, corrosion of the equipment due to Furthermore, it not only causes decomposition of the amide type solvent and lowers the recovery rate of the amide powder type solvent, but also generates various polymerization-inhibiting impurities and causes troubles in various processes. Tebru.

An object of the present invention is to provide a method for recovering an amide type solvent from a composition containing an amide type solvent and an inorganic salt in a stable process at low cost, in good yield, and with high purity as described above.

B) Means for Solving the Problems The present inventors have been able to arrive at the present invention as a result of repeated meter readings in order to achieve the above-mentioned object.

When separating and recovering the amide type solvent from a composition containing one or more amide type solvents and inorganic salts selected from the group consisting of 7. Nitromethane, nitroethane, nitroethane j? This can be achieved by extraction with l'S or two or more compounds selected from the group. Here, in the general formula of the amide type solvent, RI is -8
% C[3, from the group C2H5, R2 and R
3 are each selected from the group -CH3, C2H5 and may be the same or different; R4 is +c H2+2, -(-c H
z÷s, (-c)h+-4,-fc)12÷S
R5 is +CHz +3, +CHz
+4 Selected from the group.

Among the amide type solvents represented by the above general formula, N,
” N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylpropionamide, N,N-diethylpropionamide, tetramethylurea, tetraethylurea,
The method of the present invention can be preferably applied to N-methyl-2-pyrrolidone and N-methyl-2-piperidone.

By using nitromethane, nitroethane, nitropropane, etc. as an extractant according to the method of the present invention, not only does it have excellent extraction power for amide type solvents, but also heavy metal ions are obtained since the extractant is a stable substance that is difficult to decompose. This suppresses the contamination of solid matter during extraction, and as a result, the extraction operation can be carried out smoothly, and the amide type solvent can be recovered with high purity and good yield. Furthermore, the polymerization-inhibiting impurities in the recovered amide-type solvent are removed from T, which virtually does not participate in polymerization.
It has been found that the quality problems of recovered amide-type solvents can be solved at once.

In the present invention, compositions containing an amide type solvent and an inorganic salt include calcium chloride, lithium chloride, etc. (often added to the amide type solvent as a solubilizing agent), sodium chloride, potassium chloride, etc. (often produced by neutralizing hydrochloric acid produced in a polymerization reaction with sodium hydroxide, potassium hydroxide, etc.). In the present invention, the proportion of the inorganic salt contained in the composition containing the amide type solvent is not limited, and for example, the coexistence of undissolved solid inorganic salts is also allowed. Further, the content ratio of the amide type solvent in the composition is not limited either.

The method of the present invention can be applied even when the extraction agent used in the present invention contains an organic solvent or water that is difficult to dissolve in addition to the inorganic salt and amide type solvent. In particular, since polymerized polymers and molded products are often washed and coagulated with water, the present invention is preferably applicable to aqueous solutions.

For example, when polyparaphenylene terephthalamide is solution polymerized in an amide type solvent and lithium chloride or calcium chloride, the polymerization reaction product becomes a swollen gel-like solid containing the solvent, but this solid can be converted into a powder. The method of the present invention is also applicable to such compositions.

The extraction conditions for the amide type solvent in the present invention, ie, extraction temperature, amount of extraction agent, etc., can be arbitrarily selected depending on the type of amide type solvent, the concentration of the amide type solvent in the composition, the type of extraction agent, etc.

Also, the equipment used for this extraction is not particularly limited; continuous type,
Batch-type towers with built-in rotary vanes, packed towers, plated towers, extractors using centrifugal force, extraction equipment using a mixing tank with a normal stirring function, etc. can be effectively used.

The method for recovering the amide type solvent from the extraction phase extracted according to the present invention is also not limited, and an easy method is conventional separation distillation, which can be used regardless of whether it is a continuous method or a batch method. The purity of the amide type solvent to be recovered is re-examined! It can be arbitrarily selected according to the conditions to be used.

(E) Effects of the Invention According to the method of the present invention, the amount of amide type solvent to be removed as a distillation residue is reduced, and the recovery rate of amide type solvent can be increased. Furthermore, since the extractant used has a medium boiling point and is a stable substance, there is almost no loss due to escape during distillation or thermal decomposition, and it can be recycled and used, making the recovery cost extremely low. Furthermore, since the amount of "slag" produced by heavy metal ions is small, there are virtually no process problems such as clogging of equipment piping, adhesion to heat exchangers, etc. and impairing heat conduction, and stable operation can be achieved for a long period of time.

(f) Examples and Comparative Examples Examples and comparative examples of the present invention are shown below to more specifically illustrate the embodiments and effects of the present invention.

Here, the characters (f) and (f) indicating the content of the substances in the examples are indicated by weights (t) and (t).

Example 1 In a glass container equipped with a stirrer, one part of N,N-dimethylacetamide (hereinafter abbreviated as DMA) was charged with OK9, and 42 g of lithium chloride and 86 g of metaphenylenediamine were charged.
．． 4g was dissolved. After these were dissolved, 162 g of isophthaloyl chloride was added all at once in powder form and stirred. The power load required for stirring became constant and the polymerization was completed. The resulting viscous liquid was mixed with water containing 3a4g of lithium hydroxide in a small mixer to solidify the polymerized polymetaphenylene inphthalamide, and the polymer was collected by passing through a glass filter and washing with water. Should DMA
15 kg of aqueous solution was obtained. DMA was extracted from this by countercurrent extraction using nitromethane 7.5% as an extractant. The nitromethane solution containing DMA was then separated by distillation, and the recovery rate of DMA was 97%. Using the recovered DMA, polymerization and recovery were repeated 10 times, but there was almost no change in the heavy metal content of the resulting polymer, and the process could be carried out smoothly without any troubles. Furthermore, there was almost no loss of nitromethane used as an extractant due to thermal decomposition and escape during distillation, and 96 pieces of nitromethane were recovered after repeated use 10 times.

Comparative Example 1 Dichloromethane 7.5 KF was added as an oil to the DMA aqueous solution Z5Kq to be recovered obtained in the same manner as in Example 1.
DMA was extracted in the same manner as in Example 1 using Then,
The dichloromethane solution containing DMA was separated by distillation, and the recovery rate of the obtained DMA was 95%. A large amount of chlorides and hydroxides of iron, chromium, nickel, etc., which are components of SUS, were produced as a distillation residue. Polymerization and recovery were repeated in the same manner using the recovered DMA, but as the number of repetitions increased, the ``slag'' increased and the DMA extraction rate gradually decreased, and the degree of polymerization of the polymer observed also gradually decreased. After the fifth attempt, it was not possible to create a polymer that could be used for practical purposes. It can also be used as an oil agent.
In one distillation of dichloromethane, there is a loss of 10 g due to thermal decomposition and escape, and in repeated distillations, the lost amount was replaced with fresh distillate.

Example 2 Folymetaphenylene inphthalamide was converted into N-methylpyrrolidone (hereinafter referred to as NMP) containing 50% calcium oxide.
It is abbreviated as ) to prepare a stock solution for molding with a polymer concentration of 20%, and perform actual spinning of poly-metaphenylene isophthalamide using wet spinning equipment made of 5US316, and the coagulation bath composition was 25% calcium chloride. , N
An aqueous solution containing 30 tons of MP was prepared, and a study was conducted to recover NMP from this coagulation bath.

This liquid was extracted using a continuous extraction device (25 w Ill made of glass,
Equipment consisting of a packed tower with a Raschig ring made of 5US316, a metering pump, and a tank on a pipe with a height of 1.5 cm
) from the bottom of the column at a flow rate of 180 g/min, and the extractant nitroethane was continuously flowed from the top of the column at a flow rate of 250 g/min. No problems were observed during continuous driving for 8 hours.

Comparative Example 2 A continuous extraction process was carried out using the nine NMP aqueous solution used in Example 2 using the same apparatus and under the same conditions using chloroform as an extractant. Approximately 30 minutes after the start of operation, brown solids were clearly generated inside the packed column, and after one hour, drifting was observed throughout the column due to adhesion to the packing. After 1 hour of further operation, the precipitation of brown solids became intense, and floating substances were observed in the extraction wastewater and extract liquid, making the extraction operation impossible.

Example 3 50% NMP was placed in a SUS 316 container equipped with a stirrer.
0g of lithium salt, 15.5g of terephthalic acid/hydrazide, and 22g of unilene diamine were dissolved. The system was cooled and, with continuous stirring, 20.3 g of terephthalic acid chloride was added all at once in powder form. There was a sudden increase in viscous fluid, and it became clear after 1 hour. A solution of lyamide hydrazide was obtained. This solution is extracted using nitroethane 100100O as an extractant. A propane solution shall be used.

Furthermore, the second extraction of Honnotsuchi uses the NMP-containing nitropropane bath liquid used in the third extraction of the previous batch. This process was repeated, and in the sixth wash, a multi-stage extraction was performed to recover NMP using 00 g of fresh nitropronone. The first extraction liquid was used as a recovery liquid and was distilled to recover NMP with a high yield of 99.5%.

Claims (1)

[Claims] 1. General formula {▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ {▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ {▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ {▲ Numerical formulas, chemical formulas, tables, etc. ▼ When separating and recovering the N-alkyl-substituted amide-type solvent from a composition containing one or more N-alkyl-substituted amide-type solvents and inorganic salts selected from the group consisting of , nitromethane, nitroethane, and nitropropane. [In the general formula, R_1 is -H, -CH_3, -C_2H_
R_2 and R_3 are each -CH_
3. R_4 is selected from the group -C_2H_5 and may be the same or different, and R_4 is -(CH_2)-_2, -(CH
_2)-_3, -(CH_2)-_4-(CH_2)-
selected from the group _5, R_5 is -(CH_2)-_3
, -(CH_2)-_4. ]2, N
- the alkyl-substituted amide type solvent is N,N-dimethylformamide, N,N-dimethylaceamide, N,N-diethylacetamide, N,N-dimethylpropionamide,
N,N-diethylpropionamide, tetramethylurea, tetraethylurea, N-methyl-2-pyrrolidone,
The method according to claim 1, characterized in that N-methyl-2-piperidone is used.