DE102004008574A1 - Process and plant for purification of (meth)acrylic acid, used for making fiber, molding, film, foam, superabsorbent polymer or hygiene article, uses dimer cracker and separation system to remove protoanemonin and maleic acid and anhydride - Google Patents

Abstract

Purification of (meth)acrylic acid (I) involves working up a composition (A) containing (I), water, (I) dimer, protoanemonin, maleic acid and maleic anhydride by (a) passing (A) into a dimer cracker and cracking (I) dimer at 50-300[deg]C; (b) removing the top product (B) and sump product (C) from this cracker; and (c) separating (I) from (B), preferably giving a separated product (D) based on (I). Independent claims are also included for the following: (1) plant for operating this process; (2) (I) obtained by this process, in the form of fibers, moldings, films, foams, superabsorbent polymers or hygiene articles.

Description

The The present invention relates to a process for the purification of (Meth) acrylic acid, (meth) acrylic acid obtainable according to This method, its use and substances based on this (meth) acrylic acid, a Apparatus for the production of very pure (meth) acrylic acid as well the use of this device.

"(Meth) acrylic acid" is in this text for the Compounds with the nomenclature names "methacrylic acid" and "acrylic acid" are used. From both Compounds is acrylic acid preferred according to the invention.

Acrylic acid is usually by catalytic vapor-phase oxidation of propylene with an oxygen-containing Get gas. In this process, the propylene is produced in a two-stage process first oxidized catalytically to acrolein, which subsequently in a second process stage also using catalysts converted to acrylic acid becomes. The acrylic acid thus obtained is removed from the gaseous reaction mixture by absorption with water in the form of an aqueous solution. Subsequently the purification of the acrylic acid is carried out by azeotropic distillation the acrylic acid solution. In Comparable manner, the synthesis of methacrylic acid by catalytic oxidation of isobutylene, tert-butanol, methacrolein or isobutylaldehyde in the gas phase.

at the production of (meth) acrylic acid arise however, besides (meth) acrylic acid a significant amount of high-boiling by-products, such as (Meth) acrylic acid oligomers, in particular (meth) acrylic acid dimers and (meth) acrylic acid trimers, as well as in the case of acrylic acid synthesis maleic acid, maleic anhydride and protoanemonin.

The However, obtained in the azeotropic distillation crude (meth) acrylic acid contains in addition to the above-mentioned high boilers also a considerable Proportion of monomeric (meth) acrylic acid, which it is due to the (meth) acrylic acid loss to minimize and increase the yield of (meth) acrylic acid. For work-up Various methods have been proposed for this stream (JP Sho 45-19281B2, JP Sho 51-9120A, JP Sho 61-35977B2, JP Sho 61-36501 B2).

So For example, in JP Sho 61-36501 B2, thermal cleavage becomes the dimeric acrylic acid simultaneous distillation of the eliminated, monomeric acrylic acid described. this leads to to a separation of a large part the high-boiling components, leaves but the concentration of maleic acid, maleic anhydride and protoanemonin almost untouched. The thus reclaimed stream is returned to the process and causes an accumulation of protoanemonin, maleic acid and maleic anhydride in the finely purified acrylic acid, what their quality decreases.

EP 0 887 334 A1 describes a process for the recovery of acrylic acid from a composition comprising acrylic acid dimers, acrylic acid and maleic acid, wherein initially in a distillation apparatus, the acrylic acid is separated and the bottom product obtained in the distillation, which is enriched with the acrylic acid dimers and with maleic acid, in a Dimerenspaltreaktor is transferred. Finally, the bottom product obtained in the dimer gap reactor is returned to the distillation apparatus. A reduction in the concentration of protoanemonin is not mentioned, although protoanemonin hinders the further processing of acrylic acid and also has a health-endangering potential. In addition, the leads in the EP 0 887 334 A1 described arrangement with a downstream dimer gap reactor and the partial recycling of the overhead stream of the dimer gap reactor in the upstream distillation apparatus to an unnecessary increase in the feed stream into the distillation apparatus and thus to a larger-sized distillation column.

Of the Present invention was based on the object resulting from the Overcome prior art disadvantages.

Farther the present invention was based on the object, a method to provide, with which it is possible is, in the workup of crude (meth) acrylic acid impurities such as maleic acid, maleic anhydride and protoanemonin purposefully separate. The procedure should be on an industrial scale well applicable and therefore economical like ecological Position to be superior to the method of the prior art. In particular, an excellent purification capacity is in this context Compliance with high ecological and more economical To call requirements.

In addition, another object of the present invention was to provide an apparatus for producing high purity (meth) acrylic acid, which can purify contaminated (meth) acrylic acid to the highest purity with low energy consumption, trouble-free and environmentally friendly operation, and the lowest possible loss of (meth) acrylic acid in the form of (meth) acrylic acid dimers and / or (meth) acrylic acid trimers.

Finally lay The invention is based on the object, a method and an apparatus to be provided, wherein in the production and in particular in the purification of (meth) acrylic acid increases the risk of it uncontrolled polymerization of (meth) acrylic acid is reduced.

These Tasks are solved by a method, apparatus, (meth) acrylic acid Fibers, shaped bodies, Films, foams, superabsorbent polymers or hygiene articles and by a Use in each case with the features of the corresponding claims and the following comments solved. Further advantageous embodiments and further developments are the subject of the respective dependent claims and the following remarks, each applied individually or combined with each other can be.

• a) Zuführen der Zusammensetzung Z₁ in einen Dimerenspaltreaktor und Spaltung der (Meth)Acrylsäure-Dimere bei einer Temperatur in einem Bereich von 50 bis 500°C, vorzugsweise in einem Bereich von 150 bis 400°C und besonders bevorzugt in einem Bereich von 250 bis 300°;
• b) Entnahme eines Kopfproduktes des Dimerenspaltreaktors als eine Zusammensetzung Z₂ und eines Sumpfproduktes des Dimerenspaltreaktors als eine Zusammensetzung Z₃;
• c) Abtrennen von (Meth)Acrylsäure aus der Zusammensetzung Z₂, wobei vorzugsweise eine auf (Meth)Acrylsäure basierende Zusammensetzung Z₄ als abgetrenntes Produkt erhalten wird.

The process according to the invention for the preparation of (meth) acrylic acid comprises a process step for working up a composition Z ₁ comprising (meth) acrylic acid, water, (meth) acrylic acid dimers, protoanemonin, maleic acid and maleic anhydride, the process step comprising the following process steps:

• a) feeding the composition Z ₁ into a dimeric gap reactor and cleaving the (meth) acrylic acid dimers at a temperature in a range of 50 to 500 ° C, preferably in a range of 150 to 400 ° C and more preferably in a range of 250 up to 300 °;
• b) withdrawing a top product of the dimer gap reactor as a composition Z ₂ and a bottoms product of the dimer gap reactor as a composition Z ₃ ;
• c) separating (meth) acrylic acid from the composition Z ₂ , wherein preferably a (meth) acrylic acid-based composition Z _{4 is obtained} as a separated product.

With This process is more surprising Way, for that but no less advantageous to high-purity products that are also for the use in polymers, eg. B. for the hygiene sector, are suitable.

When Top product in the context of the present invention is preferably a product understood, which a device unit of addition the energy present in the product still more energy - preferably thermal energy - is supplied for example, a rectification column or a dimer gap reactor, anywhere in the upper half, more preferably in the upper third and above also preferred in the upper fifth, in this device unit, can be removed. Vice versa is preferred as the bottom product in the context of the present invention understood a product which a device unit on a anywhere in the lower half, more preferably in the lower third and beyond preferably in the lower fifth, can be removed.

The method preferably operates continuously. For this purpose, the (meth) acrylic acid is generated in a reactor, then it is brought into aqueous solution in a quench absorber-also sometimes referred to as quench tower-then this aqueous acrylic acid solution is distilled in a distillation apparatus. The resulting in the distillation, the high-boiling compounds containing bottom product (= composition Z ₁ ) is fed to the purification device. The process allows the production of very pure (meth) acrylic acid from comparatively contaminated crude (meth) acrylic acid. As a result, the distillation step can be carried out more gently, whereby a premature polymerization of (meth) acrylic acid is reduced and the quality of the (meth) acrylic acid is increased.

In the case of producing acrylic acid, the composition used in the inventive process in process stage for working up the composition Z ₁ Z contains ₁ acrylic acid dimers and acrylic acid trimers in a total amount in a range of 1 to 90 wt .-%, more preferably in a total amount in a range of 10 to 60% by weight, and more preferably in a total amount in a range of 20 to 50% by weight, each based on the weight of the composition Z ₁ . Maleic acid and maleic anhydride in the composition Z _{1 are} preferably in a total amount in a range of 1 to 30% by weight, more preferably in a total amount in a range of 2 to 20% by weight, and more preferably in a total amount in one Range of 5 to 10 wt .-%, each based on the weight of the composition Z ₁ , in the composition Z ₁ included. Protoanemonin is preferably contained in an amount of up to 3,000 ppm, more preferably of up to 500 ppm and more preferably of up to 300 ppm, based on the composition Z ₁ . The content of acrylic acid in the composition Z ₁ is preferably in a range of 0.1 to 70% by weight, more preferably in a range of 5 to 60% by weight, and further preferably in a range of 10 to 50% by weight .-%, in each case based on the weight of the composition Z ₁ . Furthermore, the composition Z ₁ to 0 to 40 wt .-% further impurities or suitable additives and 0.01 to 10 wt .-%, preferably 0.1 to 5 wt .-% water. As further impurity In the case of the production of acrylic acid, phenotiazine is included, for example hydroquinone, which is added as a polymerization inhibitor, belongs to the additives. The sum of the wt .-% - information of the individual components are to be selected so that these together give 100.

This composition Z ₁ is first transferred to the dimer gap reactor and under the above-mentioned temperature conditions, preferably at a pressure in a range of 0.1 to 1000 bar, more preferably at a pressure in a range of 10 to 800 bar, moreover at a pressure in a range of 80 to 600 bar, split. The residence time of the individual components of the composition Z ₁ in the dimer gap reactor is preferably in a range of 0.1 second to 1 hour, particularly preferably in a range of 1 second to 15 minutes and moreover preferably in a range of 1 minute to 10 minutes.

After cleavage of the (meth) acrylic acid dimers or trimers in the cleavage reactor, the dimer-gap reactor is deprived of the composition Z ₂ as top product and the composition Z ₃ as bottom product.

In the case of the production of acrylic acid, the composition Z ₂ withdrawn as a top product from the dimer-gap reactor preferably contains acrylic acid dimers and acrylic acid trimers in a total amount in a range from 0 to 10% by weight, more preferably in a total amount within a range of 0 , 1 to 5 wt .-% and more preferably in a total amount in a range of 0.5 to 1 wt .-%, each based on the weight of the composition Z ₂ . Maleic acid and maleic anhydride are in the composition Z ₂ preferably in a total amount in a range of 1 to 20 wt .-%, more preferably in a total amount in a range of 2 to 3 wt .-% and more preferably in a total amount in one Range of 2.2 to 2.8 wt .-%, each based on the weight of the composition Z ₂ , in the composition Z ₂ included. Protoanemonin is preferably contained in an amount of up to 3,000 ppm, more preferably of up to 400 ppm and more preferably of up to 300 ppm, based on the composition Z ₂ . The content of acrylic acid in the composition Z ₂ is preferably in a range of 70 to 99 wt .-%, more preferably in a range of 85 to 95 wt .-% and more preferably in a range of 90 to 93 wt. %, in each case based on the weight of the composition Z ₂ .

The composition Z ₃ withdrawn as the bottom product from the dimer-gap reactor contains acrylic acid dimers and acrylic acid trimers preferably in a total amount in a range from 30 to 90% by weight, more preferably in a total amount in a range from 50 to 80% by weight and moreover, preferably in a total amount in a range of 60 to 70% by weight, based in each case on the weight of the composition Z ₃ . Maleic acid and maleic anhydride in the composition Z _{3 are} preferably in a total amount in a range of 5 to 40% by weight, more preferably in a total amount in a range of 10 to 30% by weight, and more preferably in a total amount in one Range of 20 to 25 wt .-%, each based on the weight of the composition Z ₃ included. Protoanemonin is preferably contained in an amount of up to 10,000 ppm, more preferably of up to 2,000 ppm and more preferably of up to 5,000 ppm, based on the composition Z ₃ . The content of acrylic acid in the composition Z ₃ is preferably in a range of 0 to 50% by weight, more preferably in a range of 0.1 to 25% by weight, and further preferably in a range of 1 to 10% by weight .-%, in each case based on the weight of the composition Z ₃ .

The bottom product of the composition Z ₃ is preferably fed to thermal utilization, while the (Z) acrylic acid is separated from the top product of the composition Z ₂ in step c) of the process according to the invention, wherein a composition Z ₄ based on (meth) acrylic acid is preferably obtained , This is preferably recycled to the distillation apparatus in which the aqueous acrylic acid solution obtained from the quench absorber is purified. However, it can also be fed directly to a crystallization apparatus in which the (meth) acrylic acid crystallizes and the resulting (meth) acrylic acid crystals are separated by means of suitable separation devices.

The separation of the (meth) acrylic acid from the composition Z ₂ is preferably carried out by converting the (meth) acrylic acid into the gas phase. Particularly preferably, the separation of the (meth) acrylic acid by fractional distillation in a rectification column. A preferred distillation column consists of a column tray having an evaporation device, a column head having a condenser and an underlying reflux divider and a discharge for removing the distillate, as well as from a separating device located between the column bottom and the column top. It is further preferred that the rectification column has 1 to 40, more preferably 2 to 30 theoretical plates. The feed of the composition Z ₂ takes place in the rectification column preferably in the lower half of the column, more preferably in the lower third. Soil internals and commercially available structured packings, such as Montz B1 or Sulzer Mellapak, and / or fillers, such as Raschig rings or Berlsättel, can be used as column internals. The column can be equipped for the bottom circulation with a forced circulation overheater or natural run evaporator. The rectification process is preferably carried out at reduced pressure, particularly preferably at a pressure in a range from 20 to 200 mbar, moreover preferably at a pressure in a range from 40 to 150 mbar. The bottom temperature in the rectification is preferably in a range between 40 and 200 ° C, more preferably in a range between 60 and 130 ° C. To reduce the formation of (meth) acrylic acid polymers, the composition in the rectification column is preferably added with an inhibitor such as hydroquinone. The addition of the inhibitor is preferably carried out continuously at the top of the column. The reflux ratio, which is defined as the ratio of the amount of liquid dripping from the top of the column to the amount of liquid withdrawn at the top of the column, is preferably in a range of 0.1 to 2, more preferably in a range of 0.5 to 1.5 , The product of composition Z ₄ taken at the top of the column is preferably fed to the distillation apparatus in which the aqueous acrylic acid solution obtained from the quench absorber is purified. However, the separation of the (meth) acrylic acid from the composition Z ₂ is not limited to the above-described distillation. It is also possible to have the separation carried out by any other methods that appear to be suitable for a person skilled in the art, such as crystallization, freezing and separation via a semipermeable membrane.

In the case of the production of acrylic acid, the composition Z ₄ withdrawn as top product from the rectification column preferably contains acrylic acid dimers and acrylic acid trimers in a total amount in a range from 0 to 20% by weight, particularly preferably in a total amount within a range of 0.001 to 2 wt .-% and moreover preferably in a total amount in a range of 0.005 to 0.35 wt .-%, each based on the weight of the composition Z ₄ . Maleic acid and maleic anhydride in the composition Z _{2 are} preferably in a total amount in a range of 0 to 20% by weight, more preferably in a total amount in a range of 1 to 10% by weight, and more preferably in a total amount in one Range of 3 to 5 wt .-%, each based on the weight of the composition Z ₄ included. Protoanemonin is preferably contained in an amount of up to 3,000 ppm, more preferably of up to 500 ppm and more preferably of up to 300 ppm, based on the composition Z ₄ . The content of acrylic acid in the composition Z ₂ is preferably in a range of 60 to 98 wt .-%, more preferably in a range of 85 to 95 wt .-% and more preferably in a range of 90 to 93 wt. %, in each case based on the weight of the composition Z ₄ .

It is further preferred that the rectification column is withdrawn from a bottom product (SPRK), the amount taken off in a specific time interval preferably being 1 to 40% by weight, more preferably 6 to 12% by weight and moreover preferably 8 to 9% by weight .-%, in each case based on the rectification column in the same time interval supplied amount of the composition Z ₂ , is. The bottom product taken from the rectification column is preferably discarded.

In a preferred embodiment of the method according to the invention, the by-products contained in the composition Z ₁ are dispensed in an additional process step. In the case of the production of acrylic acid, maleic acid, maleic anhydride and protoanemonin are preferably depleted of the composition Z ₁ in this additional process stage.

In this case, the depletion of the by-products from the composition Z ₁ before carrying out step a) or between the process steps b) and c).

If, in the case of acrylic acid synthesis, the depletion of by-products from composition Z ₁ occurs prior to step a), the dimer splitter is fed a composition Z ₁ in which maleic acid, maleic anhydride and protoanemonin are added in a total amount within a range of 0-10 wt %, preferably in a range of 0.1 to 5 wt .-% and more preferably in a range of 0.2 to 2 wt .-%, based on the total weight of the composition Z ₁ , are included. From the dimer splitter, the composition Z ₂ 'is taken as the top product, in which maleic acid, maleic anhydride and protoanemonin are present in a total amount ranging from 0 to 10% by weight, preferably in a range of 0.01 to 5% by weight more preferably in a range of 0.1 to 1 wt .-%, based on the total weight of the composition Z ₂ , are included. From this composition Z ₂ ', the acrylic acid is separated in process step c), wherein preferably an acrylic acid-based composition Z ₄ ' is obtained as a separated product. This is preferably in the distillation apparatus in which the Quen chabsorber aqueous acrylic acid solution is purified, recycled. In this composition, Z ₄ 'in the maleic acid, maleic anhydride and protoanemonin are in a total amount in a range of 0 to 1% by weight, preferably in a range of 0.001 to 0.5% by weight, and more preferably in one range from 0.01 to 0.1% by weight, based on the total weight of the composition Z ₁ .

If, in the case of acrylic acid synthesis, the depletion of the by-products from composition Z _{1 takes place} between process steps b) and c), maleic acid, maleic anhydride and protoanemonin are depleted of the composition Z ₂ extracted as the top product from the dimeric cleavage apparatus, a composition Z ₂ " is obtained. In this composition Z ₂ "are maleic acid, maleic anhydride and protoanemonin in a total amount in a range of 0 to 10 wt .-%, preferably in a range of 0.01 to 5 wt .-% and more preferably in a range of 0.1 to 1 wt .-%, based on the total weight of the composition Z ₂ '', included. From this composition Z ₂ ", the acrylic acid is subsequently separated off in process step c), preferably giving an acrylic acid-based composition Z ₄ " as a separated product. This is preferably recycled to the distillation apparatus in which the aqueous acrylic acid solution obtained from the quench absorber is purified, or fed to a crystallizer in which the acrylic acid is crystallized. In this composition Z ₄ "are maleic acid, maleic anhydride and protoanemonin in a total amount in a range of 0 to 1 wt .-%, preferably in a range of 0.001 to 0.1 wt .-% and more preferably in a range of 0.01 to 0.05 wt .-%, based on the total weight of the composition Z ₄ '' included.

The Depletion of by-products, especially the depletion of maleic acid, maleic anhydride and protonanemonin is preferably carried out at a temperature is lower than the temperature at separation of (meth) acrylic acid in the step c) the method according to the invention. Particularly preferably, the enrichment of these by-products takes place by crystallization.

Of the Advantage of the enrichment of the by-products consists inter alia in that the separation of the (meth) acrylic acid in process step c) at a lower temperature can be done compared to the separation of (meth) acrylic acid a composition from which the by - products are not in one additional Step was granted. So is the previous separation of the By-products, especially in the case of prior separation of maleic acid, maleic anhydride and protoanemonin, a separation of the (meth) acrylic acid in the process step c), for example, even at a temperature of less than 60 ° C possible. so low temperatures lead to reduce the formation of (meth) acrylic acid polymers or (Meth) acrylic acid oligomers in step c) of the method according to the invention.

• (β1) der Dimerenspaltreaktor einen Zulauf, der eine Zusammensetzung beinhaltend (Meth)Acrylsäure und (Meth)Acrylsäure-Dimere führt, einen ersten Ablauf DS₁ zur Entnahme des Kopfproduktes der Zusammensetzung Z₂ aus dem Dimerenspaltreaktor, sowie einen zweiten Ablauf DS₂ zur Entnahme des Sumpfproduktes, vorzugsweise der Zusammensetzung Z₃, aus dem Dimerenspaltreaktor, aufweist;
• (β2) die (Meth)Acrylsäure-Abtrennungsvorrichtung einen Zulauf, der mit dem ersten Ablauf DS₁ des Dimerenspaltreaktors verbunden ist, einen ersten Ablauf AV₁, der Destillationsvorrichtung verbunden ist, zur Entnahme des Kopfproduktes, vorzugsweise der Zusammensetzung Z₄, der (Meth)Acrylsäure-Abtrennungsvorrichtung und einen zweiten Ablauf AV₂ zur Entnahme des Sumpfproduktes der (Meth)Acrylsäure-Abtrennungsvorrichtung, aufweist.

The invention also relates to an apparatus for the production of (meth) acrylic acid comprising, as components connected in fluid communication, a (meth) acrylic acid synthesis unit, a quench absorber, a distillation apparatus and a working-up device for the bottom product obtained in the distillation in the distillation apparatus, the processing apparatus having a Dimeric gap reactor and a (meth) acrylic acid removal device, wherein

• (β1) the dimer gap reactor a feed containing a composition containing (meth) acrylic acid and (meth) acrylic acid dimers, a first sequence DS ₁ for removing the overhead of the composition Z ₂ from the dimer gap reactor, and a second sequence DS ₂ for removal the bottom product, preferably the composition Z ₃ , from the dimer gap reactor;
• (β2) the (meth) acrylic acid separation device has a feed, which is connected to the first outlet DS _{1 of} the dimer gap reactor, a first outlet AV ₁ , the distillation device is connected, for the removal of the overhead product, preferably the composition Z ₄ , the (meth ) Acrylic acid separation device and a second sequence AV ₂ for withdrawing the bottom product of the (meth) acrylic acid separation device comprises.

"Fluit-conducting" is understood according to the invention as that gases or liquids or mixtures thereof are passed through appropriate lines. For this purpose, in particular piping, pumps and the like deploy.

An apparatus for the production of (meth) acrylic acid in the range comprising a (meth) acrylic acid synthesis unit and a quench absorber preferably has the following structure in the synthesis of acrylic acid: propylene and optionally further inert gases such as nitrogen or combustion gases such as CO ₂ or nitrogen oxides are fed in a first reactor to a first catalytic oxidation via a educt feed, which opens into a first reactor. The first reactor is connected via a further line to a second reactor into which the product of the first catalytic oxidation from the first reactor for a second catalytic oxidation is introduced. The acrylic acid-containing product of the second cataly Table oxidation is fed via a located between the second reactor and the Quenchabsorber line of the lower half of Quenchabsorbers. In the quench absorber, the product of the second catalytic oxidation is contacted with water, the water being fed into the quench absorber above the feed of the product of the second catalytic oxidation. On the one hand, a first phase comprising acrylic acid and water (= aqueous acrylic acid solution) is removed from the quench absorber below the feed of the product of the second catalytic oxidation. The first phase can be at least partially recycled back into the quench absorber. The first phase not returned to the quench absorber is supplied to a distillation apparatus to undergo, for example, an azeotropic separation in which the acrylic acid is concentrated and purified. The bottom product of this distillation apparatus has the composition Z ₁ , which is then further processed according to the inventive method.

An apparatus for producing methacrylic acid comprises the (meth) acrylic acid synthesis unit and a quench absorber in the synthesis of methacrylic acid by catalytic gas phase oxidation of C ₄ starting compounds with oxygen. Methacrylic acid is particularly preferably obtainable by catalytic gas-phase oxidation of isobutene, isobutane, tert-butanol, isobutyraldehyde, methacrolein or meth-tert-butyl ether. Further details are in EP 0 092 097 B1 . EP 0 058 927 and EP 0 608 838 , the contents of which are hereby incorporated by reference as part of this disclosure.

In a preferred embodiment the device according to the invention includes the workup device next to the dimer gap reactor and the (meth) acrylic acid separation device a Separation device for By-products, in the case of acrylic acid synthesis, a separation device for maleic acid, maleic anhydride and protoanemonin, on.

In one embodiment of this preferred embodiment, this by-product separation device has an inlet, which preferably carries the composition Z ₁ , and an outlet, which is connected to the inlet of the dimer-gap reactor and preferably has the composition Z ₁ '.

In another embodiment of this preferred embodiment, this by-product separation device has an inlet which is connected to the first outlet DS _{1 of} the dimer gap reactor and which preferably has the composition Z ₂ , and an effluent which is in contact with the inlet of the (meth) acrylic acid Separation device is connected and preferably the composition Z ₂ '' leads.

Farther the present invention relates to (meth) acrylic acid, which according to the available method described is. This (meth) acrylic acid preferably has a purity such that maleic acid and maleic anhydride in a total amount of not more than 1% by weight, more preferably of not more than 0.1% by weight, and more preferably not more than 0.01 wt .-%, each based on the total weight of the inventive method available (meth) acrylic acid are. It is further preferred that the inventive (meth) acrylic acid a has such purity that protoanemonin in an amount of not more than 100 ppm, more preferably not more than 20 ppm and above in addition, preferably not more than 10 ppm, in each case based on those by the method according to the invention available (Meth) acrylic acid, is included.

In Another embodiment, the invention is concerned with the use of the inventively prepared (Meth) acrylic acid in a process for the preparation of polymers, preferably superabsorbents, detergents or special polymers for the area: sewage treatment, emulsion paints, cosmetics, textiles, Leather finishing, papermaking.

moreover The invention relates to fibers, moldings, films, foams, superabsorbent Polymers or toiletries, at least based on or including the above-described (meth) acrylic acid according to the invention.

Farther The invention relates to the use of those described above (meth) acrylic acid according to the invention in or for the production of fibers, moldings, films, foams, superabsorbent Polymers or hygiene articles.

advantageously, is the inventive (meth) acrylic acid to Production of polymers, preferably superabsorbents, detergents or special polymers for sewage treatment, emulsion paints, cosmetics, textiles, Leather finishing or papermaking used.

Superabsorbent polymers are understood to mean polymers which can absorb a multiple of their own weight of water or aqueous liquids. Preferably, more than half of superabsorbent polymers are based on acrylic acid as a monomer. Further details of superabsorbent polymers, their preparation and use in sanitary articles are available from "Modern Superabsorbent Polymer Technology", Fredric L. Buchholz, Andrew T. Graham, Wiley-VCH 1998 whose contents are incorporated by reference as part of this disclosure.

Further Details and advantageous developments are based on the following drawings which illustrate the invention by way of example should, closer explained.

It show schematically:

1 a process scheme according to the invention;

2 a process scheme according to the invention, wherein a separation of by-products takes place before carrying out step a);

3 a process scheme according to the invention, wherein a separation of by-products takes place between the process steps b) and c);

The 1 shows a process scheme in which the inventive method is described in summary.

It shows the 1 :

1

the Distillation apparatus with which in the production of (meth) acrylic acid the in the quench absorber obtained aqueous (Meth) acrylic acid solution becomes;

2

a feed with which in the distillation apparatus 1 obtained bottom product in the dimer gap reactor 3 is transferred;

3

one Dimerenspaltreaktor;

4

a sequence with which in the dimer gap reactor 3 obtained bottom product can be removed;

5

a sequence with which in the dimer gap reactor 3 obtained overhead and in the (meth) acrylic acid separation device 6 can be transferred;

6

a (Meth) acrylic acid removal device;

7

a process with which in the (meth) acrylic acid separation device 6 obtained bottom product can be removed;

8th

a process with which in the (meth) acrylic acid separation device 6 obtained overhead product and into the distillation apparatus 1 can be returned.

The 2 shows a process scheme in which the inventive method is described in summary and in which a depletion of by-products before performing the process step a).

It shows the 2 in addition to the in 1 represented elements:

9

the device for the depletion of by-products, which comprises the bottom product 1 about the feeder 2 is supplied;

10

a process by which the 9 depleted product in the dimer gap reactor 3 to be led.

The 3 shows a process scheme in which the inventive method is described in summary and in which a depletion of by-products takes place between the process steps b) and c).

It shows the 3 in addition to the in 1 represented elements:

9

the device for the depletion of by-products, which is the top product from the dimer gap reactor 3 about the feeder 5 is supplied;

10

a process by which the 9 depleted product in the (meth) acrylic acid separation device 6 to be led.

Claims (17)

A process for purifying (meth) acrylic acid with a process step for working up a composition Z ₁ comprising (meth) acrylic acid, water, (meth) acrylic acid dimers, protoanemonin, maleic acid and maleic anhydride, comprising the following steps: a) feeding the composition Z ₁ into a dimer gap reactor and cleavage of the (meth) acrylic acid dimers at a temperature in a range of 50 to 300 ° C; b) withdrawing the overhead product of the dimer gap reactor as a composition Z ₂ and a bottoms product of the dimer gap reactor as a composition Z ₃ ; c) separating (meth) acrylic acid from the composition Z ₂ , wherein preferably a (meth) acrylic acid-based composition Z _{4 is obtained} as a separated product. The method of claim 1, wherein prior to step a) by-products are depleted of the composition Z ₁ . The method of claim 1, wherein between the steps b) and c) by-products of the composition Z _{2 are} depleted. The method of claim 2 or 3, wherein the depleting the by-products are made by crystallization. A process according to any one of the preceding claims, wherein the composition Z _{3 is} taken from the dimer-gap reactor in an amount ranging from 1 to 40% based on the amount of the dimer-gap reactor fed composition. Method according to one of the preceding claims, wherein the residence time of (meth) acrylic acid dimers in the dimer gap reactor in a range of 0.1 seconds to 1 hour lies. Method according to one of the preceding claims, wherein the bottom temperature in the dimer gap reactor in a range between 50 and 500 ° C is located. Method according to one of the preceding claims, wherein separating the (meth) acrylic acid in step c) by means of a rectification column. The method of claim 8, wherein the rectification column a bottoms product (SPRK) in an amount ranging from 1 to 40%, based on the amount of the rectification column fed composition, is removed. Method according to one of the preceding claims, wherein separating the (meth) acrylic acid in step c) at a pressure in a range of 20 to 200 mbar he follows. An apparatus for producing (meth) acrylic acid comprising, as components conductively connected to each other, a (meth) acrylic acid synthesis unit, a quench absorber, a distillation apparatus, and a work-up apparatus for the bottom product obtained in the distillation in the distillation apparatus, the processing apparatus comprising a dimer gap reactor and a (meth ) And wherein (β1) the dimer-gap reactor has a feed containing a composition comprising (meth) acrylic acid and (meth) acrylic acid dimers, a first feed DS ₁ for removing the top product from the dimer gap reactor, and a second feed DS ₂ for removing the bottoms product SPDS from the dimer gap reactor, comprising; (β2) the (meth) acrylic acid separation device comprises a feed connected to the first effluent DS _{1 of} the dimer gap reactor, a first effluent AV ₁ , the distillation device connected to remove the top product of the (meth) acrylic acid separation device and a second Sequence AV ₂ for removal of the bottom product of the (meth) acrylic acid separation apparatus having. Apparatus according to claim 11, wherein the work-up device comprises a by-product separation device, said separation device having an inlet which has the composition Z ₁ defined in claim 1 and a discharge connected to the inlet of the dimer-gap reactor. An apparatus according to claim 11, wherein the work-up device comprises by-product separation means, said separation means having a feed connected to the first effluent DS _{1 of} the dimer gap reactor and a effluent connected to the feed of the (meth) acrylic acid separation device , (Meth) acrylic acid, available according to a method according to the claims 1 to 10 in fibers, moldings, Filming, foaming, superabsorbent polymers or hygiene articles. Use of (meth) acrylic acid according to claim 14 in or for the production of fibers, shaped articles, films, foams, superabsorbent polymers or hygiene items. Fibers, shaped bodies, Films, foams, superabsorbent polymers or toiletries, at least based on or containing (meth) acrylic acid according to claim 14. Use of a device as in any of claims 11 to 13, or a refurbishment device, as in one the claims 11 to 13, for the preparation of (meth) acrylic acid, the a purity of more than 90 wt .-% based on the (meth) acrylic acid with Impurities.