WO2014102311A1

WO2014102311A1 - Method for purifying an untreated solvent stream containing an n-alkyl pyrrolidone

Info

Publication number: WO2014102311A1
Application number: PCT/EP2013/078030
Authority: WO
Inventors: Christoph Sigwart; Jörg Erbes; Martin Weber; Gerhard Lange; Jutta VONEND; Cornelis Hendricus DE RUITER
Original assignee: Basf Se
Priority date: 2012-12-28
Filing date: 2013-12-27
Publication date: 2014-07-03

Abstract

Proposed is a method for purifying an untreated solvent stream containing an N-alkyl pyrrolidone and, in addition, as an impurity, the corresponding N–alkyl succinimide to obtain a purified solvent stream that meets the requirements for use in a method for producing polymers, wherein high boilers and low boilers relative to N-alkyl pyrrolidone are separated by distillation, said method being characterized in that, prior to, during or following purification by distillation, an alkali metal- or alkaline earth metal hydroxide, in a substance volume corresponding to a substance volume ratio of at least 0.1 : 1 of the corresponding hydroxide to the N–alkyl succinimide, is added to the respective solvent streams present prior to, during or following the purification by distillation.

Description

A process for purifying a crude solvent stream containing an N-alkyl pyrrolidone

description

The invention relates to a process for purifying a crude solvent stream containing an N-alkyl-pyrrolidone and besides as impurity the corresponding N-alkyl-succinimide to obtain a pure solvent stream, which meets the requirements for use in a process for the preparation of polymers , Polymers are often prepared by polymerizations or polycondensations in the presence of a polar aprotic solvent, such as N-alkyl-2-pyrrolidones, hereinafter referred to as NAP, are used. Suitable NAPs are, in particular, N-methyl- or N-ethyl-pyrrolidone, in particular N-methyl-pyrrolidone, hereinafter referred to as NMP for short.

The above process produces contaminated solvent which must be worked up for economic and environmental reasons and recycled in the process.

The solvent used in the above process must therefore meet the criteria for a so-called pure NAP, that is, a content of at least 99.0 wt .-% NAP or at least 99.5 wt .-% NAP, or at least 99.8% by weight NAP, in each case based on the total weight of the pure NAP stream, and having as specification-damaging components not more than 0.1% by weight water and not more than 0.02% by weight N-alkyl succinimide, or also a maximum of 0.01 wt .-% N-alkyl succinimide hereinafter abbreviated as NAS, in each case based on the total weight of the pure NAP stream.

Higher levels of NAS in the solvent NAP are detrimental to the color of the polymers. This is surprising since both NAP itself and NAS, which can be formed by oxidation of NAP with atmospheric oxygen, for example, are colorless substances. On the market, however, polymers with the lowest possible intrinsic color are in demand. According to previous findings, there is a causal relationship between the NAP formed by oxidation of the NAP, for example the N-methyl succinimide (NMS) formed by oxidation of the N-methyl-pyrrolidone (NMP):

and the undesirable inherent color of the final polymer product.

It is believed that NAS is a precursor to higher molecular weight coloring components that degrade the intrinsic color of the polymers. NAP-containing recycle streams are therefore purified prior to recycling in the preparation of the polymers by pure distillation in a classical distillation column so far that a pure NMP is obtained, which corresponds to the criteria defined above. The separation of the N-alkyl succinimides from the corresponding N-alkyl pyrrolidones, however, in the required purity, due to the close boiling points, a difficult distillation separation task. For example, the boiling point of NMP under atmospheric pressure is about 204 ° C, and the boiling point of NMS under atmospheric pressure at about 238 ° C. A conventional distillative separation would require a lot of energy for this purpose.

It was therefore an object of the invention to provide a method for purifying a crude solvent stream containing an N-alkyl pyrrolidone and besides as impurity the corresponding N-alkyl succinimide, after which obtain a pure solvent stream, which meets the requirements for corresponds to the use in a process for the preparation of polymers, which can be carried out in a simple manner and without high expenditure on equipment and which leads in a reliable manner to the required purity of the pure solvent stream. The object is achieved by a process for purifying a crude solvent stream containing an N-alkyl-pyrrolidone and in addition as impurity the corresponding N-alkyl-succinimide to obtain a pure solvent stream, which meets the requirements for use in a process for the preparation of Polymers, wherein high boilers and low boilers are separated by distillation over the N-alkyl pyrrolidone, which is characterized in that before, during or after the distillative purification of an alkali metal or alkaline earth metal hydroxide, in a molar amount corresponding to a molar ratio of at least 0, 1: 1 of the corresponding hydroxide to the respective N-alkyl-succinimide in the corresponding before, during or after the purification by distillation present solvent stream is added.

It has been found that the abovementioned technical problem can be solved in a simple and reliable manner by the above specific selection of the molar ratio in which the hydroxide, based on the proportion of the corresponding N-methyl succinimide, is added to the solvent stream.

The NMS concentration in the solvent stream is preferably determined by gas chromatography.

Under substance amount or molar ratio is, according to Wikipedia, usually understood as follows:

Substance amount is the quantitative amount of substances, in particular in the stoichiometry called. This quantity of substance is defined in the International System of Units (SI) by arbitrary agreement as a basic variable of its own kind. The unit of substance quantity is the mole, a basic SI size.

When using the mole, the underlying number of particles (especially atoms and molecules) must be specified; One mole of a substance contains about 6.02214129 (27) 10 ^{23 of} such particles (Avogadro number NA) according to current measurement accuracy. These particles may also be imaginary fragments of real particles (e.g., 1/4 of a molecule or ion) - so-called equivalent particles or short equivalents - such that the obsolete equivalent weight unit Val can be replaced by the mole without changes to known numerical values , Lots Details were in the German standard DIN 32625. However, this was withdrawn in April 2006, because there was no need for it.

For the substance amount n _x and the mass m _{x of} a substance portion of a pure substance X and its molar mass Mx, the following relationship holds: n _x = m _x / Mx

With molar ratio is accordingly called the ratio of two amounts of substance.

The process for producing polymers is preferably a process for producing one or more polyarylene ether sulfones. Polyarylene ether sulfones are known for example under the trade name Ultrason ^® of BASF SE, and in particular include polyethersulfones (Ultrason ^® E), polysulfones (Ultrason ^® S) and polyphenylsulfones (Ultrason ^® P).

Ultrason ^® E, Ultrason ^® S and Ultrason ^® P are transparent, high temperature resistant plastics. They are used in many applications in apparatus construction and in the electrical / electronics sector. There are also numerous reasons for use in the food and household sector as glass, metal, ceramic and porcelain substitute: temperature resistance up to 180 ° C or briefly at 220 ° C, good mechanical properties and high resistance to breakage, resistance to superheated steam and a excellent resistance to chemicals.

Ultrason ^® E, S and P are amorphous thermoplastic polymers with the following basic structure: Ultrason ^® E

Ultrason ^® S

Ultrason ^® P

Ultrason ^® molded parts are strong, stiff and tough, with high dimensional stability, close to the glass transition temperature.

The most important features of Ultrason ^® are:

temperature-independent properties

very high continuous service temperatures

- good dimensional accuracy

high rigidity

high mechanical strength

good electrical insulation

favorable dielectric properties

- very favorable fire behavior

extraordinary hydrolysis resistance

As amorphous thermoplastics, the three Ultrason ^® base polymers are transparent. However, due to the high temperatures required in their manufacture and processing, they have a certain inherent color (light golden yellow to ocher), which prevents the theoretically possible transmission values for visible light being achieved. Nevertheless, the qualities available today are suitable for a large number of transparent applications. Ultrason ^® also has high refractive indexes in the visible wavelength range, making it useful in functional optical applications such as lenses for electronic cameras. Polyarylene ether sulfones are often prepared by polycondensation in the presence of an N-alkyl-2-pyrrolidone, hereinafter referred to as NAP, as a polar aprotic solvent. As N-alkyl-2-pyrrolidones in particular N-methyl or N-ethyl-pyrrolidone, in particular N-methyl-pyrrolidone, are used. Such methods are known, for example, from US 4 870 153, EP-A 1 13 1 12, EP-A 297 363 and EP-A 135 130.

The process for preparing the polyarylene ether sulfones is in particular a polycondensation of aromatic bishalogen compounds and aromatic bisphenols or their salts in the presence of at least one alkali metal or ammonium carbonate.

The alkali metal or alkaline earth metal hydroxide is preferably added in an amount of substance corresponding to a molar ratio of 0.1: 1 to 10: 1 to the respective N-alkyl succinimide in the corresponding present before, during or after the purification by distillation solvent stream.

It is further preferred that the alkali metal or alkaline earth metal hydroxide in a molar amount corresponding to a molar ratio of 0.2: 1 to 2: 1 to the respective N-alkyl succinimide in the corresponding present before, during or after the purification by distillation solvent stream added ,

The N-alkyl-pyrrolidone is preferably N-ethyl- or N-methyl-pyrrolidone, in particular N-methyl-pyrrolidone.

The crude solvent stream is in particular a recycle stream from a plant for producing polyarylene ether sulfones by polycondensation of aromatic bishalogen compounds and aromatic bisphenols or their salts in the presence of at least one alkali metal or ammonium carbonate or bicarbonate in N-methyl-pyrrolidone as solvent, containing 60 up to 90% by weight of water, 10 to 40% by weight of N-methylpyrrolidone and, as a specification-hazardous impurity, up to 5000 ppm by weight of N-methyl-succinimide and, in addition, up to 1000 ppm by weight of further high-boiling components compared to N-methylpyrrolidone. Methylpyrrolidone, in particular inorganic salts, in each case based on the total weight of the recycle stream, the sum of the components resulting in 100% by weight, to obtain a pure N-methyl pyrrolidone stream which is traceable to the plant for the production of polyarylene ether sulfones. Preferably, the purification is carried out by pure distillation in a pure column, which is preceded by a pre-cleaning by evaporation in one or more evaporator stages to reduce the content of other high boilers to N-methyl pyrrolidone, ins-particular inorganic salts, wherein one or more feed streams for Pure column can be obtained and wherein the bottom stream discharged from the last evaporator stage and the bottom stream from the pure column is completely recycled to the last stage of the evaporator.

The pre-cleaning by evaporation is preferably carried out in two or three evaporator stages.

The addition of the alkali metal or alkaline earth metal hydroxide is advantageously carried out in the first evaporator stage, wherein the alkali metal or alkaline earth metal hydroxide is fed together with the recycle stream or separately from the first evaporator stage.

Additionally or alternatively, the addition of the alkali metal or alkaline earth metal hydroxide can be carried out in the second evaporator stage.

In a further embodiment, the addition of the alkali metal or alkaline earth metal hydroxide can be carried out in the third evaporator stage.

In a further embodiment, the addition of the alkali metal or alkaline earth metal hydroxide may be carried out after the distillation. The addition of the alkali metal or alkaline earth metal hydroxide can be carried out in the solid state or preferably as a solution in water, wherein the concentration of the alkali metal or alkaline earth metal hydroxide is preferably 1 to 50 wt .-%, more preferably 2 to 25 wt .-%, in particular 5 to 10 wt .-%, each based on the total weight of the solution. The alkali metal or alkaline earth metal hydroxide is preferably sodium hydroxide.

More preferably, the alkali metal or alkaline earth metal hydroxide is potassium hydroxide. The distillative purification can be carried out continuously or batchwise, preferably continuously.

The invention is explained in more detail below on the basis of exemplary embodiments: Syntheses of polyaryl ether sulfones in NaOH-free NMP (comparative example) and in NMP, to which NaOH had been added (examples according to the invention), were carried out.

Analytical determinations

1) Viscosity number (VZ) of the polyarylethersulfones:

The viscosity number (VZ) of the polyarylethersulfones was determined in 1% solution of N-methylpyrrolidone at 25 ° C. (DIN EN ISO 1628-1).

2) N-methylsuccinimide content of the N-methylpyrrolidone used:

The N-methylsuccinimide content of the N-methylpyrrolidone used was determined by gas chromatography.

3) Color determination on polyarylethersulfone:

The optical properties of the polyarylethersulfone granules were determined by color measurements on plastic platelets which were produced by injection molding from the polyarylethersulfone granules. The color determination is carried out on the polyarylethersulfone platelets compared to a measurement on a reference sample. The reference sample is characterized by its particularly bright and colorless appearance. The color of the product is described in the L ^* a ^* b ^* color space (a three-dimensional coordinate system), in which system the b ^* and L ^* values are relevant for the samples considered. The b ^* axis describes the blue or yellow part of a color, with negative values for blue and positive values for yellow. The L ^* axis describes the brightness (luminance) of the color. The b ^* and L ^* values of the samples are compared with the b ^* and L ^* values of the reference sample and expressed as the deviation from the reference sample:

The larger the dl_ ^* value with dl_ ^* = L * p _r0 be - L * R _e ference, the brighter the product. The smaller the db ^* value with db ^* = b * p _r0 be * b * R _e ference), the "blueer" the product appears and the lower the yellowness of the color.

Color measurements were taken on the Datacolor DC 3890 instrument. Comparative example

For the polyarylethersulfone synthesis, freshly distilled NMP was used, to which no NaOH was added. The NMP contained 62 ppm of N-methylsuccinimide. The monomers, dichlorodiphenylsulfone (574 g) and dihydroxydiphenylsulfone (500 g) were dissolved in NMP (1050 ml). K 2 CO 3 (290 g) was added and the reaction medium was heated at 190 ° C for 4 h while feeding 30 l / h nitrogen and stirring. Thereafter, additional NMP (1,950 ml) was added and gassed at temperatures of 120 ° C to 150 ° C for 1 h with 15 l of methyl chloride. Then the suspension was cooled to below 80 ° C and then filtered. The polymer was precipitated in water and the precipitated polymer particles were washed with boiling water and dried at 150 ° C for 20 h in vacuo.

The resulting polymer had a VZ of 56.5 ml / g.

The polymer was then processed on a twin-screw extruder (PTW16) at 360 ° C into granules and injection-molded as platelets. The optical properties were measured on the platelets. Color result: dl_ ^* = -8.40; db ^* = 6.37

Example 1 (according to the invention):

For the synthesis, the same, freshly distilled NMP from the comparative experiment was used, to which, however, an additional 0.2 g of a 2 molar aqueous NaOH solution per liter of NMP had been added. The NaOH / NMS molar ratio was 0.7. The same polymer synthesis and work-up as described in the comparative experiment was carried out. The resulting polymer had a VN of 58.3 ml / g.

The polymer was then processed into granules as described in the comparative experiment and injection-molded into platelets on which the optical properties were measured.

Color result: dl_ ^* = 3.58, db ^* = -5.56 Example 2 (according to the invention):

For the synthesis, the same, freshly distilled NMP from the comparative experiment was used, to which, however, an additional 0.15 g of a 2 molar aqueous NaOH solution per liter of NMP had been added. The NaOH / NMS molar ratio was 0.5.

The same polymer synthesis and work-up as described in the comparative experiment was carried out. The resulting polymer had a VN of 58.3 ml / g.

The polymer was then processed into granules as in Comparative Example and Example 1 and injection molded into platelets on which the optical properties were measured. Color result: dL ^* = 2.21, db ^* = -3.32

The examples thus show that significantly better color results are achieved by the process according to the invention.

Claims

claims

A process for purifying a crude solvent stream containing an N-alkyl pyrrolidone and further impurity the corresponding N-alkyl succinimide to obtain a pure solvent stream which meets the requirements for use in a process for the preparation of polymers, high boilers and Low boilers over the N-alkyl pyrrolidone are separated by distillation, characterized in that, before, during or after the distillative purification of an alkali metal or alkaline earth metal hydroxide, in a molar amount corresponding to a molar ratio of at least 0.1: 1 of the corresponding hydroxide to the respective N-alkyl-succinimide in the appropriate, before, during or after the purification by distillation present solvent stream is added.

Process according to Claim 1, characterized in that the process for the preparation of polymers is a process for the preparation of one or more polyarylene ether sulfones.

A method according to claim 1, characterized in that the process for the preparation of polymers is a polycondensation of aromatic bishalogen compounds and aromatic bisphenols or their salts in the presence of at least one alkali metal or ammonium carbonate.

Method according to one of claims 1 to 3, characterized in that the alkali metal or alkaline earth metal hydroxide in a molar amount corresponding to a molar ratio of 0.1: 1 to 10: 1 to the respective N-alkyl succinimide in the corresponding before, during or after the distillative purification present solvent stream is added.

A method according to claim 4, characterized in that the alkali metal or alkaline earth metal hydroxide in a molar amount corresponding to a molar ratio of 0.2: 1 to 2: 1 to the respective N-alkyl-succinimide present in before, during or after the purification by distillation Solvent flow is added. Method according to one of claims 1 to 5, characterized in that the N-alkyl-pyrrolidone N-ethyl-pyrrolidone or N-methyl-pyrrolidone, preferably N-methyl-pyrrolidone is.

Method according to one of claims 3 to 6, characterized in that the crude solvent stream is a recycle stream from a plant for the production of polyarylene ether by polycondensation of aromatic bishalogen compounds and aromatic bisphenols or their salts in the presence of at least one alkali metal or ammonium carbonate or - hydrogen carbonate in N-alkylpyrrolidone as solvent containing

60 to 90% by weight of water,

10 to 40 wt .-% N-alkylpyrrolidone and

up to 5000 ppm by weight of N-methyl-succinimide and up to 1000 ppm by weight of further high boilers towards N-alkyl-pyrrolidone, in particular inorganic salts, in each case based on the total weight of the recycle stream, the sum 100 wt .-% of the components, to obtain a pure N-alkyl pyrrolidone stream, which in the Appendix to

Preparation of polyarylene ether sulfones is traceable.

A method according to claim 7, characterized in that the purification is carried out by pure distillation in a pure column, preceded by a pre-cleaning by evaporation in one or more evaporator stages to reduce the content of other high boilers to N-methyl pyrrolidone, especially inorganic salts, wherein one or more feed streams are obtained to the pure column, and wherein the bottom stream discharged from the last evaporator stage and the bottom stream from the

Pure column is completely recycled to the last stage of the evaporator.

9. The method according to claim 8, characterized in that the pre-cleaning by evaporation in two or three, preferably in three evaporator stages, is performed.

10. The method according to claim 9, characterized in that the addition of the alkali metal or alkaline earth metal hydroxide is carried out in the first evaporator stage, wherein the alkali metal or alkaline earth metal hydroxide is fed together with the recycle stream or separately from the first evaporator stage.

1 1. A method according to claim 9, characterized in that the addition of the alkali metal or alkaline earth metal hydroxide takes place in the second evaporator stage.

12. The method according to claim 9, characterized in that the addition of the alkali metal or alkaline earth metal hydroxide takes place in the third evaporator stage.

13. The method according to any one of claims 1 to 12, characterized in that the alkali metal or alkaline earth metal hydroxide is sodium hydroxide.

14. The method according to any one of claims 1 to 12, characterized in that the alkali metal or alkaline earth metal hydroxide is potassium hydroxide.