JPS61238735A - Method of recovering solvent of amide type - Google Patents

Abstract

PURPOSE:To recover in high yield in high purity the titled solvent from a composition containing inorganic salts by a stable process, by using a F atom- containing aliphatic hydrocarbon compound as an extractant. CONSTITUTION:A composition containing one or more solvents of N-alkyl- substituted amide shown by the formulas I-IV [R1 is H, CH3, or C2H5; R2 and R3 are CH3 or C2H5; R4 is -(CH2)n- (n is 2-5); R5 is -(CH2)3- or -(CH2)4-] (e.g., N,N-dimethylformamide, tetraethylurea, or N-methyl-2-pyrrolidone) and inorganic solvents is treated with a compound shown by the formula CkHlXmFn (X is halogen except F; l+m+n=2k+2; k=1-4; l>=1; m>=0, n>=1) having preferably 0-150 deg.C, especially 30-120 deg.C boiling point at normal pressure to recover the solvent. The compound is relatively stable, has low loss by thermal decomposition, a small amount of slat formed by heavy metallic ions and hardly no process troubles.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a method for extracting 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 separation and recovery methods.

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. Organic heat-resistant polymers 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;
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, and inorganic chlorides such as lithium chloride and calcium chloride as solubilizers are required. Hydrochloric acid is often present as a by-product of the polymerization reaction, and as a result of neutralization, it often contains inorganic salts. It often contains a liquid medium for coagulation and molding. Therefore, in industrial production, it is very important to efficiently recover expensive amide type solvents from such systems.

(Prior art) An amide type solvent is extracted from an aqueous solution of an amide type solvent and an inorganic chloride (e.g. lithium chloride, calcium chloride, etc.) used for polymer molding with a halogenated hydrocarbon solvent such as dichloromethane or chloroform. A method for recovering is already known (Japanese Patent Publication No. 48-2341.5 and Japanese Patent Publication No. 49-48432).

However, amide-type solvents used in polymerization, such as the reaction of aromatic dicarboxylic acid chloride and aromatic diamine to obtain aromatic polyamide, are made into an aqueous solution by neutralizing the hydrochloric acid by-produced during polymerization according to a conventional method. It has been found that when separating and recovering amide using these methods, there are problems both in terms of the quality of the amide-type solvent obtained by recovery and in the process of extraction and recovery.

In other words, the quality problems of the recovered amide type solvent are as follows.
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 into an aqueous solution containing an amide type solvent and an inorganic salt, and the amide type solvent or its decomposition product is somehow mixed with heavy metal ions. Also, metal chloride produced by the reaction of heavy metal ions with hydrochloric acid produced as a by-product in the polymerization reaction,
It turned out to be metal hydroxide etc. produced during the neutralization process. This solid matter adheres to the interior of the extraction device during the extraction operation, reduces the contact area for liquid-liquid extraction, and gradually reduces the extraction rate, eventually making the extraction operation impossible. Also,
This solid matter also floats and mixes into the extraction waste water and extractant phase, and even in the recovery process after the extraction process, it adheres to heat exchangers etc. and impairs heat conduction. This causes problems such as bumping during distillation.

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

As is well known, hydrochloric acid generally corrodes iron and stainless steel materials used as equipment materials, and to completely eliminate corrosion, it is necessary to use extremely expensive materials or to use fluorine-based polymers such as polytetrafluoroethylene. Treatments such as glass lining and coating must be applied. However, 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.

It is an unavoidable fact that heavy metal ions are mixed into the aqueous solution to be recovered, which contains an amide type solvent used as a polymerization solvent and an inorganic chloride used as a solubilizing agent.

(Problem to be solved by the invention) Although dichloromethane, chloroform, etc., which have been conventionally used as extractants for amide-type solvents, have excellent extraction power for amide-type solvents, they cannot be used at room temperature in the presence of water and iron. However, it is known that it gradually decomposes, and that decomposition is further accelerated under heating conditions such as in the distillation process after the extraction process, and hydrochloric acid is generated.

As a result, as mentioned above, the hydrochloric acid causes corrosion of the equipment and further decomposition of the amide type solvent, which not only lowers the recovery rate of the amide type solvent, but also generates various polymerization-inhibiting impurities. This has problems such as causing process troubles.

(Objective of the Invention) As described above, the object of the present invention is to provide a method for recovering an amide-type solvent in a stable process, in good yield, and with high purity from a composition containing an amide-type solvent and an inorganic salt. It is in.

(Structure of the Invention) The present inventors have been able to arrive at the present invention as a result of intensive studies to achieve the above-mentioned object.

That is, the present invention provides one or more N-
When separating and recovering an amide type solvent from a composition containing an alkyl-substituted amide type solvent and an inorganic salt, the formula
C3cH7XmFn (wherein, X represents a halogen substituent other than the F atom, +2 at t+m+n=2, k=1 to 4,
t≧1, m≧0, n≧1, where ks tSm
, n is an integer. ) This is achieved by extraction with one or more compounds selected from the group of aliphatic hydrocarbon compounds having at least one F atom as shown in the following. here,
In the general formula of the amide type solvent, RI is -H1CH:l, C
2H5, and R2 and R,l are each -C
H3, CzHs, which may be the same or different, R4 is 1,000CH, +CH2+-:+,
+CH soup 4, →CH soup.

R9 is selected from the group consisting of +CH3. -(-CHma.

selected from the group.

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

The aliphatic hydrocarbon compound having at least one F atom used as an extractant in the present invention is, for example,
When the parent aliphatic hydrocarbon is ethane, CHF2CC
1zF CHF zCH2Cl, CHF t CHCI
F, CHF2CHZF.

CHF2CC1zF, CHFzCC/3, CH3P C
H2Cl, CH3P CH3P.

CHtFCHCIF, CH2FCH2Cl.

CHzFCHCIF, CH2FCCIfFz, CHz
F CCl z F −, CHCI F CCl s,
CHCI F CCI F z , CHCI F CC
I2 F z, etc. Furthermore, even when the parent substance is methane, propane, or butane, the above-mentioned -CHF2, CH
zF.

Compounds having bonding groups such as -CHCj2F and -CHF- are applied in the present invention. Furthermore, even if the C1 atom of the compound is substituted with a Br atom or a -atom, the invention is applicable.

The compound represented by the formula used as an extraction agent in the present invention must have ≧1, that is, at least one H atom, and must also have at least one F atom. Aliphatic hydrocarbon compounds are excellent extractants for amide-type solvents.

By using an aliphatic hydrocarbon compound having at least one F atom as an extractant according to the method of the present invention, not only does the extractant have extremely excellent extraction power for amide type solvents, but also the extractant has an F atom. Although the reason for this is not clear, it becomes a relatively stable substance that is difficult to decompose compared to chloroform etc., which suppresses the contamination of heavy metal ions and suppresses the generation of solids during extraction. The extraction operation can be performed smoothly, and the amide type solvent can be recovered with high purity and good yield.

Furthermore, we have discovered that it is now possible to reduce the polymerization-inhibiting impurities in the recovered amide-type solvent to an amount that does not actually participate in polymerization, and that the quality problems of the recovered amide-type solvent can be solved at once.

The aliphatic hydrocarbon compounds having at least one F atom used in the present invention are those whose boiling point ('rb) at normal pressure is within the range of 0°C≦Tb≦150°C. The effect is noticeable.

For compounds with a Tb of less than 0°C, the extraction power of the amide type solvent is poor and the boiling point of the compound is too low, resulting in large losses due to escape in the recovery process of the compound after the extraction process, resulting in economical and It is also unfavorable in terms of pollution and the environment. On the other hand, although the compound with Tb exceeding 150°C is a relatively stable substance, as mentioned above, during the fractional distillation process with an amide type solvent after the extraction process, it causes corrosion of the equipment due to generated hydrochloric acid, boiling acid, etc. Furthermore, it causes decomposition of the amide type solvent, which not only lowers the recovery rate of the amide type solvent but also produces various polymerization-inhibiting impurities, which is not preferable. Furthermore, it is particularly preferable that the boiling point (Tb) of the compound at normal pressure is within the range of 30°C≦Tb≦120°C, which exhibits the effects of the present invention more markedly. Tb is 5
When using the compound at 0° C. or lower, it is possible to prevent loss due to escape of the compound by applying pressure during the extraction and distillation steps.

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 with water, the present invention can be preferably applied 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. The method of the present invention is also applicable to compositions made of

The extraction conditions for the amide type solvent in the present invention, that is, 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.

Furthermore, the equipment used for this extraction is not particularly limited, and may be a continuous type, a batch type, a rotary vane type tower, a packed type tower, a tray type tower, an extraction device using centrifugal force, or a normal stirring function. An extraction device using a mixing tank, etc., can be effectively used.

The method for recovering the amide-type solvent from the extraction phase extracted according to the present invention is not limited, and a simple 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 solvent to be recovered can be arbitrarily selected depending on the conditions under which it will be reused.

(Operations and 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 can be reduced, and the recovery rate of amide type solvent can be increased. In addition, since the extractant used is a relatively stable substance, there is little loss due to thermal decomposition and it can be used repeatedly, making the recovery cost extremely low. moreover,
Since the amount of "slag" generated by heavy metal ions is small, there are almost no process problems such as clogging of equipment piping or adhesion to heat exchangers, which impairs heat conduction, and can operate stably for a long period of time.

(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 percentages indicating the content of substances in Examples and Comparative Examples are expressed in weight percent.

Example 1 Poly-metaphenylene isophthalamide was converted into N-methylpyrrolidone (hereinafter referred to as NMP) containing 5% calcium chloride.
An experiment was conducted in which a stock solution for molding with a polymer concentration of 20% was prepared by dissolving poly-metaphenylene isophthalamide in 5US316 wet spinning equipment, and the coagulation bath composition was calcium chloride. 25%, N.M.
An aqueous solution containing 30% P was prepared, and a study was conducted to recover NMP from this coagulation bath.

This liquid was extracted using a continuous extraction device (glass diameter 25 mm, height 1.5
The extractant CHCIZF was injected from the top of the column at 180 g/min from the bottom of a device consisting of a packed column with a Raschig ring made of 5 US 316, a metering pump, and a tank in a pipe of 180 g/min.
It was run continuously at a flow rate of 50 g/min.

It was possible to operate continuously for 8 hours, and no events were observed that would impede operation after that. Furthermore, the degree of NMPs in the extracted waste water was found to be 50 ppm or less by gas chromatography, and a completely complete extraction operation was possible.

Comparative Example 1 The NMP aqueous solution used in Example 1 was mixed with CHCl as an extractant.
Continuous extraction treatment was performed using the same apparatus and the same conditions using 3 (chloroform). From about 30 minutes after the start of operation,
Obvious generation of brown solids was observed inside the packed column, and after 1 hour, uneven flow was observed throughout the column due to adhesion to the packings. After 1 hour of further operation, the precipitation of brown solids became intense, and suspended matter was observed in the extraction waste water and extract liquid, making the extraction operation impossible.

Example 2 1.0 kg of N,N-dimethylacetamide (hereinafter abbreviated as DMA) was placed in a glass container equipped with a stirrer, 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. 38.4 g of lithium hydroxide was added to the resulting viscous liquid.
The polymerized polymetaphenylene isophthalamide is coagulated by mixing with water containing water in a small mixer, and the polymer is filtered through a glass filter and washed with water to recover D.
2.5 kg of MA aqueous solution was obtained. Chz as an extractant to this
Using 4.0 kg of F CHz F (1,2-difluoroethane, hereinafter abbreviated as DFE), DMA was extracted using the same packed column type countercurrent extraction apparatus as in Example 1.

Next, the DFE solution containing DMA was separated by distillation, and the recovery rate of the obtained DMA was 9971%. The recovered DMA was further polymerized and recovered for 10 minutes.
Although the process was repeated several times, there was almost no change in the degree of polymerization of the obtained polymer, and there were almost no process troubles.
I was able to do it smoothly. In addition, the DFE used as an extraction agent does not migrate into the extraction waste water, has almost no loss due to thermal decomposition, and has a 98% yield after repeated use 10 times.
I was able to recover it.

Comparative Example 2 To 2.5 kg of the DMA aqueous solution to be recovered obtained in the same manner as in Example 2, te CHt C12CHz C1 was added as an extraction agent.
2 (1,,2-dicolethane, hereinafter abbreviated as DCE)> Using 4.0 kg, DM was carried out in the same manner as in Example 2.
A was extracted. Next, the DCE solution containing DMA was separated by distillation, and the recovery rate of the obtained DMA was 92%.
Met. 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, "slag" increased, the DMA extraction rate gradually decreased, and the degree of polymerization of the resulting polymer gradually decreased. After the 5th attempt, it was not possible to produce a polymer that could be used for practical purposes.

In addition, the DCE used as an extraction agent had a loss of 12% due to migration into the extraction waste water and thermal decomposition, and in repeated experiments, the loss was replaced with new one.

Example 3 500 ml of NMP was added to a 5US316 container equipped with a stirrer.
25 g of lithium chloride, 15.5 g of terephthalic acid dihydrazide, and 2.2 g of para-phenylenediamine were dissolved. The system was cooled and while stirring was continued, 20.3 g of terephthalic acid chloride was added in powder form all at once. A rapid increase in viscosity was observed and a clear polyamide hydrazide solution was obtained within 1 hour. CH2FCHFCH2F (1,2,3
-) Refluoropropane (hereinafter abbreviated as TFE)
Extraction is carried out using 1000 g, and the extracting agent used at this time is the NMP-containing TFE solution used in the second extraction of the previous batch obtained by polymerization in the same manner as described above. Furthermore, the second extraction of this batch was performed using the NMP-containing TFE used in the third extraction of the previous batch. Assume that there is no liquid in the container. These steps were repeated, and in the sixth wash, a new T F ElooOg was used to perform multi-stage extraction to recover NMP.

The first extraction liquid was used as a recovery liquid and was distilled to recover NMP with a high yield of 99.8%.

Claims (3)

[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. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ In the group consisting of One or more types of N− selected from
When separating and recovering the N-alkyl-substituted amide-type solvent from a composition containing the alkyl-substituted amide-type solvent and an inorganic salt, the formula C_kH_lX_mF_n (wherein, X represents a halogen atom other than the F atom, l+m+n=2k
+2, k=1 to 4, l≧1, m≧0, n≧1, where k, l, m, and n are integers. ) An N-alkyl-substituted amide type solvent characterized by extraction with one or more compounds selected from the group of aliphatic hydrocarbon compounds having at least one F atom shown in Collection method. (In the general formula of the N-alkyl substituted amide type solvent, R_1 is selected from the group consisting of -H, -CH_3, -C_2H_5,
R_2 and R_3 are -CH_3 and -C_2H_5 respectively
R_
4 is -(CH_2)-_2, -(CH_2)-_3, -
(CH_2)-_4, -(CH_2)-_5, and R_5 is -(CH_2)-_3, -(CH_2
)-_4. ) (2) The N-alkyl substituted amide type solvent is N,N-dimethylformamide, N,N-dimethylacetamide, N,
N-diethylacetamide, N,N-dimethylpropionamide, N,N-diethylpropionamide, tetramethylurea, tetraethylurea, N-methyl-2-
The method according to claim 1, wherein pyrrolidone and N-methyl-2-piperidone are used. (3) As an aliphatic hydrocarbon compound having at least one F atom, its boiling point (T_b) at normal pressure
The method according to claim 1, wherein T_b is in the range of 0°C≦T_b≦150°C.