Method and system comprising residue container and comminuting system for recovering acrylic acid

Abstract

The invention relates to a method for continuously recovering acrylic acid, wherein an auxiliary component stream, which comprises oligomeric acrylic acid, is supplied from a condensation column to a splitting column, at least one part of the oligomeric acrylic acid is split from the auxiliary component stream in the splitting column, thereby obtaining monomeric acrylic acid, and the monomeric acrylic acid is separated from the auxiliary components contained in the auxiliary component stream and is supplied to the condensation column, wherein a split residue is supplied from the sump of the splitting column to a residue container before being further processed, and the split residue, optionally in a diluted state, is continuously circulated in the residue container and comminuted via a comminuting device.

Description

[0001] Process and plant with residue tank and crushing plant for the recovery of acrylic acid

[0002] The present invention relates to a process and a plant for the recovery of acrylic acid.

[0003] Acrylic acid is an important commodity chemical. Due to its highly reactive double bond and its acid function, it is particularly suitable as a monomer for the production of polymers. Of the acrylic acid monomers produced, for example, the majority is esterified prior to polymerization (e.g., to form adhesives, dispersions, or coatings). Only a small portion is polymerized directly (e.g., to form "superabsorbents"). While high-purity monomers are generally required for the direct polymerization of acrylic acid, the purity requirements for acrylic acid are not as high when it is esterified prior to polymerization.

[0004] Acrylic acid is obtainable, among other things, by heterogeneously catalyzed gas-phase partial oxidation of Ca precursors of acrylic acid with molecular oxygen over catalysts in the solid state at elevated temperatures. The term Ca precursor refers to chemical compounds that are formally obtainable by the reduction of acrylic acid. During production, these Ca precursors are diluted in the gaseous state, usually with inert gases such as nitrogen, CO2, saturated hydrocarbons and / or steam, mixed with molecular oxygen at elevated temperatures and, if appropriate, elevated pressure, over transition-metal mixed oxide catalysts and oxidatively converted into a product gas mixture containing acrylic acid and secondary components such as furfurals, benzaldehyde and maleic anhydride, from which the acrylic acid must be separated.

[0005] The acrylic acid obtained is not a pure product, but a mixture which, in addition to acrylic acid (usually > 90%, or > 95% of the total weight), also contains typical by-products of gas phase oxidation such as water, lower aldehydes (e.g. furfurals, acrolein or methacrolein, benzaldehyde), lower carboxylic acids (e.g. acetic acid, propionic acid) etc. as well as oligomers of acrylic acid.

[0006] The formation of acrylic acid oligomers is caused by acrylic acid in the condensed phase forming acrylic acid oligomers (Michael adducts) through reversible Michael addition to itself and to the resulting dimer, as well as oligomers formed by radical polymerization. The presence of water, the unavoidable byproduct of gas-phase catalytic oxidative production of acrylic acid, as well as elevated temperatures, promote the formation of acrylic acid oligomers.

[0007] Since the respective oligomers have a higher boiling point than acrylic acid, they accumulate in the high-boiling range (e.g. in the bottom liquid) both during distillative separation of acrylic acid and during fractional condensation of the product gas mixture of a gas-phase catalytic oxidative production.

[0008] DE 199 24 533 A1 discloses a process for producing acrylic acid as described above, in which a basic separation of crude acrylic acid is carried out by fractional condensation of the product gas mixture of the heterogeneously catalyzed gas-phase partial oxidation. A recleavage of the acrylic acid oligomers present in the outlet of a quench liquid is to be integrated in such a way that the runtime of the process, in particular the fractional condensation, is not substantially reduced. The aim of the recleavage of the acrylic acid oligomers is to increase the yield of the desired product. DE 199 24 533 A1 provides a circulation reactor for the recleavage.

[0009] DE 10 2014 114 193 A1 describes a process for producing acrylic acid, in which a temperature-controlled mother acid stream is withdrawn from a crystallization apparatus for obtaining purified acrylic acid and is passed toward a condensation column and a cracking column. In addition, a secondary component stream containing oligomeric acrylic acid is fed to the cracking column to obtain monomeric acrylic acid. With the aid of a stripping gas stream, monomeric acrylic acid is introduced into a quench apparatus as a constituent of a recycle gas stream, where it is mixed with a product gas stream, and the resulting mixture is then introduced into the bottom of the condensation column.

[0010] WO 2016 / 050582 A1 describes a process for recovering acrylic acid. Oligomeric acrylic acid from the bottom liquid of the condensation column is split into monomeric acrylic acid in a splitting column and recycled to the condensation column.

[0011] It was the object of the present invention to provide an improved process for the recovery of acrylic acid and a corresponding plant, in particular a more efficient residue processing.

[0012] The object is achieved by a process for the continuous recovery of acrylic acid, wherein a secondary component stream comprising oligomeric acrylic acid is fed from a condensation column to a cracking column, the oligomeric acrylic acid from the secondary component stream is at least partially cracked in the cracking column to obtain monomeric acrylic acid, the monomeric acrylic acid is separated from secondary components contained in the secondary component stream and is fed to the condensation column, characterized in that a cracking residue from the bottom of the cracking column is fed to a residue container before further processing, the cracking residue in the residue container, optionally diluted, and continuously circulated and crushed via a crushing device.

[0013] The present invention has the significant advantage that the method according to the invention enables significantly better and more reliable processing of split residues.

[0014] According to the invention, the comminution device is designed to reduce larger (polymer) particles in the gap residue in order to avoid blockages or accumulations of particles in the residue container or the lines connected thereto, which can lead to a complete blockage of the line-Zpump systems.

[0015] According to a preferred embodiment, the splitting residue is fed to the comminution device via the bottom of the residue container, and the crushed splitting residue is returned laterally into the residue container. The comminution device is connected such that the feed to the comminution device, i.e., the outlet from the residue container to the comminution device, is connected to the lowest part of the container or the container bottom, thus preventing permanent sedimentation or clogging of polymer particles in the bottom. The comminution device is arranged in a circulation line for the splitting residue of the residue container.

[0016] According to a preferred embodiment, the residue container has a curved bottom, in particular a dished bottom or a basket-arch bottom, and the feed to the comminution device is located centrally at the bottom. This prevents permanent sedimentation of particles, since the outlet to the comminution device is located at the lowest point of the bottom, and the entire gap residue can be fed to the comminution device.

[0017] According to a preferred embodiment, the residue container has a volume of 1 to 100 m 3 , preferably 5 to 75 m 3 , more preferably 8 to 50 m 3 , particularly preferably 10 to 25 m 3 . Due to this dimensioning, the residue container can hold sufficient gap residue and can still almost completely circulate and shred the gap residue by means of the shredding device.

[0018] According to a preferred embodiment, the comminution device is a comminution pump, in particular a mill pump. Thus, the comminution device can simultaneously transport and comminute the splitting residue. The operating principle of a comminution pump or mill pump is well known in the art and will not be explained in detail here. Examples of suitable comminution devices include the TrigonalO machines from Siefer and the CAVITRONO machines from CAVITRON.

[0019] According to a preferred embodiment, cracking residue from the residue container is fed for further processing by means of a pump that removes the cracking residue from the side of the residue container. This means that the suction line of the pump is not connected in / on the bottom, but rather to the preferably cylindrical part of the residue container. The pump serves to discharge the cracking residue from the residue container. This prevents polymer particles from entering the suction line of the pump. In the case of a curved bottom, the suction line of the pump is preferably connected above the bottom on the cylindrical part of the container. Further processing can involve, for example, combustion, fermentation, or catalytic oxidation.

[0020] According to a preferred embodiment, the cleavage residue in the residue container is diluted by adding a solvent, in particular an alcohol, and / or an aqueous mixture to the residue container. This prevents the viscosity of the cleavage residue from becoming too high, which would make efficient transport for further processing impossible. Blockages are also prevented. The alcohol is preferably methanol. The aqueous mixture preferably originates from the condensation column and is formed during the synthesis of acrylic acid. In particular, the aqueous mixture from the condensation column is acidic, so-called sour water. The topic of sour water is explained, inter alia, in EP 2 114 852 B1.

[0021] According to a preferred embodiment, the cleavage residue from the cleavage column is fed to the residue tank below the liquid level of the cleavage residue already contained. This is preferably done via a submerged line. This ensures better mixing in the tank and prevents further deposits.

[0022] According to a preferred embodiment, the temperature of the cracking residue is measured in the residue container. For this purpose, at least one temperature sensor is preferably arranged in and / or on the residue container. More preferably, six temperature sensors are arranged at different heights of the residue container, e.g., 2x at 5%; 2x at 30%; 2x at 65% of the height, in opposite directions around the circumference of the residue container. This provides an overview of the temperature distribution in the container.

[0023] According to a preferred embodiment, the viscosity of the splitting residue is measured in the residue container. The measurement is preferably carried out using a viscometer. The viscosity should advantageously be low to ensure sufficient flowability of the splitting residue.

[0024] According to a preferred embodiment, the secondary component stream essentially comprises acrylic acid, diacrylic acid and polyacrylic acid and proportions of maleic acid, benzoic acid, benzaldehyde, furfurals and water, in particular 50 wt.% to 60 wt.% acrylic acid or methacrylic acid, 20 wt.% to 30 wt.% diacrylic acid and 5 wt.% to 10 wt.% polyacrylic acid and 6 wt.% to 9 wt.% maleic acid, 1 wt.% to 2 wt.% benzoic acid, 0.5 wt.% to 1 wt.% water and 0.5 wt.% to 1 wt.% 4-methoxyphenol, in addition small proportions (each < 0.5 wt.%) of acetic acid, furfural, benzaldehyde, phthalic anhydride, phenothiazine and diacrylic acid. The secondary component stream preferably has a temperature of 100 °C to 130 °C, in particular 105 °C to 115 °C, in order to achieve, on the one hand, sufficient pre-thickening of the bottom liquid of the condensation column before transfer to the cracking column and, on the other hand, to limit the formation of dimers in the bottom region of the condensation column.

[0025] According to a preferred embodiment, 60% to 95%, preferably 85% to 90%, of the oligomeric acrylic acid from the secondary component stream is cleaved. Preferably, the dimers and trimers of acrylic acid are cleaved. Regarding the yield of the desired product, higher cleavage rates of 95% are advantageous, but are difficult to control industrially, since at cleavage yields > 95%, the remaining product tends to form massive solids and is therefore very difficult to handle.

[0026] According to a preferred embodiment, in the crushing device between 1 and 100 m 3 / h, preferably 3 and 70 m 3 / h, more preferably 5 and 40 m 3 / h, particularly preferably 8 and 25 m 3 / h of gap residue is circulated and comminuted. The comminution device preferably operates at an operating pressure of 1 to 40 bar, preferably 3 to 30 bar, more preferably 5 to 20, particularly preferably 8 to 15 bar. The operating temperature of the comminution device is preferably between 50 and 150 °C, preferably 70 and 130 °C, more preferably 90 and 110 °C. The pumping capacity of the comminution device is preferably between 0.1 and 20 bar, preferably 0.3 and 15 bar, more preferably 0.5 and 12 bar, particularly preferably 0.8 and 8 bar. The comminution device preferably commins the gap residue to a particle size of < 2 mm, preferably < 1.5 mm, more preferably < 1.0 mm and particularly preferably < 0.75 mm. The comminution device can preferably process gap residues with a particle size orcontaining particles with a particle size of up to 25 mm, preferably 22, more preferably 19, particularly preferably 17 mm.

[0027] It was surprisingly found that the process according to the invention, with the advantageous use of the residue container with comminution device, has the advantage over the prior art that (polymer) particles in the cracking residue are reliably comminuted and the occurrence of blockages and thus plant failures can be efficiently prevented. This is all the more surprising since comminution devices according to the invention, in particular mill pumps, are generally not suitable for processing such types of residues. Mill pumps are used for the wet comminution of solids. However, the polymer particles in the cracking residue are viscoelastic and are sheared rather than crushed. The liquid prevents re-clumping. Alternative measures such as filtration of the cracking residue or simply not removing the particles led to blockages and associated operational failures over time.

[0028] Further preferred details of the method are described below:

[0029] Preferably, a temperature-controlled mother acid stream from a crystallization device is divided into two substreams in the direction of the condensation column and in the direction of the splitting column. "Temperature-controlled" in the context of the present invention means that the mother acid stream or the mother acid substreams, after being discharged from the crystallization device, have been heated to a temperature of preferably 50°C to 100°C, preferably 60°C to 90°C, in particular 70°C to 80°C. The preferred embodiment of the process is not limited to a specific crystallization process, whereby acrylic acid is purified by partial crystallization, separation of the frozen acrylic acid from the impurity-containing liquid (mother acid), and melting of the separated pure acrylic acid crystals. For example,A falling film crystallization or a suspension crystallization as a combination of cooling disc crystallizers and washing columns can be used, the latter process variant being preferred.

[0030] In the present invention, "mother acid" (in comparable documents possibly also called "mother liquor") refers to a solution of acrylic acid which, after separation of the pure product in a crystallization device, contains the impurities separated in the crystallization device, wherein the acrylic acid in the mother acid accounts for a weight proportion of > 80 wt.%.

[0031] Preferably, a first temperature-controlled mother acid substream is fed to the topmost tray of the 45-tray cracking column. In the present invention, the cracking column is preferably equipped with dual-flow trays as separating internals. A second temperature-controlled mother acid substream is preferably fed to tray 18 of the 75-tray condensation column.

[0032] Preferably, at least one stripping gas stream is fed below the lowest tray of the cracking column. The stripping gas stream is preferably directed toward the liquid surface of the bottom liquid. The stripping gas stream is used in particular as recycle gas. For the purposes of the present invention, "recycle gas" is understood to mean a gas which serves to dilute the reactants and absorb reaction heat in the gas-phase oxidation and which is essentially inert in the gas-phase reaction. The recycle gas essentially contains nitrogen and, in the concentration range <5 vol.%, oxygen, water vapor, carbon oxides and mixtures thereof, and very small amounts (<0.8 vol.%) of ethylene, ethane, propene, propane, acrolein, acrylic acid, and acetic acid.

[0033] Preferably, the secondary component stream comprising oligomeric acrylic acid from the condensation column is fed to a middle tray of the cracking column. This middle tray is, in particular, a tray in tray regions 8 and 10.

[0034] In the cleavage column, at least a portion of the oligomeric acrylic acid from the secondary component stream is cleaved to yield monomeric acrylic acid. This preferably occurs thermally at temperatures > 150 °C. The cleavage can be accelerated by adding small amounts of sodium hydroxide solution or amines to the bottom of the cleavage column.

[0035] Preferably, the secondary components contained in the secondary component stream are separated by countercurrent rectification in the attached cleavage column.

[0036] The monomeric acrylic acid obtained is preferably removed from the cleavage column as a gas mixture together with the supplied stripping cycle gas stream at the top of the cleavage column without condensation, and the gas mixture is then preferably fed below the lowest tray of the condensation column.

[0037] This advantageously recycles the monomeric acrylic acid back into the process. Since the acrylic acid is supplied in gaseous form and does not have to be evaporated there first, more energy is available in the condensation column to separate the acrylic acid from secondary components. The condensation column in the present invention is preferably designed as a tray column. It is preferably equipped with dual-flow trays in the lower section, Thormann trays in the middle section, and valve trays in the upper section.

[0038] The preferred process has the advantage over the prior art that partial condensation of the acrylic acid stripped in the cracking column to serve the reflux of the rectification column is dispensed with, and instead of the reflux generated by condensing the vapors at the top of the cracking column, a portion of the mother acid stream generated in the crystallization device is used. This eliminates the need for a condensation unit at the top of the cracking column, which reduces the equipment required. Furthermore, no cooling capacity is required for condensation. Furthermore, the energy introduced into the cracking column via a bottom heat exchanger is also available in the condensation column, which improves the separation of acrylic acid from secondary components.

[0039] A further advantage of the preferred process may be that, by conducting the process according to the invention, monomeric acrylic acid can be recovered from the respective oligomers in an improved yield and recycled to the overall process as low boilers. "Oligomeric acrylic acid" refers in particular to dimers and trimers of acrylic acid. Compared to the prior art, the processing loss of acrylic acid is reduced by 0.3%. In this application, "processing loss" is understood to mean the proportion of acrylic acid that, based on the acrylic acid supplied from the synthesis, cannot be separated from the secondary components and recovered as product.

[0040] In a further development of the preferred process, it has proven advantageous if the mother acid stream is switched against an acrylic acid stream from a condensation column for temperature control, in particular thermally. The acrylic acid stream is preferably withdrawn as the target product via a side draw of the condensation column and essentially fed to a crystallization device. This acrylic acid stream is hot (i.e., 95°C to 100°C) and highly concentrated (i.e., 95% to 98% by weight acrylic acid) and must be cooled before entering the crystallization device.

[0041] Therefore, the thermal energy present in the acrylic acid stream is preferably transferred to the mother acid stream by means of a heat exchanger and thus coupled into the two mother acid substreams. This energy is thus available both in the condensation column for separating the acrylic acid and in the splitting column for splitting the dimeric acrylic acid, or less energy needs to be introduced into the splitting process via a bottom heat exchanger provided in the splitting column.

[0042] According to a preferred embodiment, the gas mixture is fed below the lowest tray of the condensation column indirectly by passing the gas mixture into a quenching device for quenching a product gas mixture containing acrylic acid.

[0043] The mother acid stream withdrawn from the crystallization device preferably comprises essentially acrylic acid and proportions of water and acetic acid, in particular 90% by weight to 95% by weight of acrylic acid, 3% by weight to 6% by weight of water and 1% by weight to 2% by weight of acetic acid and small proportions (each < 0.5% by weight) of formaldehyde, propionic acid, furfural, maleic acid and diacrylic acid. The mother acid stream is withdrawn at a temperature just above the crystallization temperature of acrylic acid (15°C to 20°C) and preferably preheated to the corresponding thermodynamic equilibrium temperature of approximately 80°C at the feed point of the condensation column (201) in order to ensure the most effective separation possible. In addition, the stripping gas stream can essentially comprise nitrogen, acrylic acid, water and oxygen and proportions of carbon dioxide and acetic acid, in particular 80% by weight to 85% by weight of nitrogen, 3% by weight to 5% by weight of acrylic acid, 3% by weight to 5% by weight of-% water, 3 wt.% to 4 wt.% oxygen, 2 wt.% to 3 wt.% carbon dioxide, and 1 wt.% to 2 wt.% acetic acid, as well as small amounts (each < 0.7 wt.%) of carbon monoxide, acrolein or methacrolein, formic acid, propene, and propane. The stripping gas stream preferably has a temperature of 80 °C to 90 °C, in particular approximately 85 °C.

[0044] Another object of the present invention is a plant for the recovery of acrylic acid, comprising

[0045] - a condensation column,

[0046] - a splitting column,

[0047] - a residue container with shredding device,

[0048] - a first line connecting the condensation column and the splitting column,

[0049] - a second line connecting the cracking column and the residue container,

[0050] - a circulation line connecting the residue container and the shredding device,

[0051] - a third line connecting the cracking column and the condensation column, and

[0052] - a fourth line connected to the residue container.

[0053] The method according to the invention can advantageously be carried out by means of the system according to the invention.

[0054] What is meant by the condensation column, the splitting column, the residue container and the comminution device in the sense of the present invention has already been described above with reference to the process according to the invention.

[0055] A first line connects the condensation column and the splitting column and feeds a secondary component stream from the condensation column to the splitting column. The splitting column and the condensation column are connected by a third line, through which the separated monomeric acrylic acid is fed to the condensation column.

[0056] A second line connects the cracking column and a residue tank. The cracking residue from the bottom of the cracking column is fed to the residue tank via the second line. A fourth line is connected to the residue tank and carries the cracking residue from the residue tank to a further processing facility not shown here. The fourth line is preferably a circulation line. The residue tank and the comminution device are connected via a circulation line, with the cracking residue in the residue tank being circulated and comminuted by the comminution device. The cracking residue is removed via the circulation line through the bottom of the residue tank and, after passing through the comminution device, is returned laterally to the comminution tank.

[0057] The plant preferably further comprises a fifth line connected to the cracking column, which feeds at least one gas stream as stripping cycle gas to the bottom region of the cracking column.

[0058] A sixth line preferably serves to feed a partial stream of the mother acid produced during crystallization to the cleavage column. A crystallization device and the condensation column are preferably connected by a seventh line.

[0059] Corresponding definitions of the elements of the system and the terms used have already been given above with regard to the method according to the invention and also apply to this system.

[0060] The advantages of the system according to the invention are essentially the same as those of the above-described process according to the invention. The present system provides the necessary equipment.

[0061] In a preferred embodiment of the plant according to the invention, it further comprises a quenching device for quenching a product gas mixture containing acrylic acid, which is arranged in the third line between the cracking column and the condensation column. This provides an apparatus for efficiently utilizing the gas mixture from the cracking column and its temperature for quenching the hot product gas mixture.

[0062] The plant according to the invention is particularly advantageous when integrated into an overall plant for acrylic acid production. As described above, the plant according to the invention can increase the overall efficiency of acrylic acid production.

[0063] If process features are mentioned in the description in connection with the system according to the invention, these preferably refer to the process according to the invention. Likewise, physical features listed in connection with the process according to the invention preferably refer to the system according to the invention. Further objectives, features, advantages, and possible applications emerge from the following description of exemplary embodiments of the invention with reference to the figure. All described and / or illustrated features, individually or in any combination, form the subject matter of the invention, regardless of their summary in the claims or their reference back to them. It shows:

[0064] Fig. 1 is a schematic representation of the system 1 according to the invention in one embodiment of the invention.

[0065] Figure 1 shows a schematic representation of the plant 1 according to the invention in one embodiment of the invention. Central elements are the condensation column 201, the residue tank 203, the comminution device 207, and the cracking column 205.

[0066] A hot product gas stream at a temperature of approximately 270 °C is fed from a plant section (not shown), in which the heterogeneously catalyzed gas-phase partial oxidation is carried out. This gas stream is fed into a quench device 209 to prevent possible reactions between its components and to reduce its temperature. A gas mixture from the cracking column 205 at a temperature of approximately 95 °C is also fed to the quench device 209 via a third line 103. This gas mixture will be discussed in more detail later.

[0067] The gases and liquids fed to the quench device 209 are fed via line 110 into the bottom region of the condensation column 201 after exiting the quench device. In this condensation column 201, the acrylic acid produced is separated from the product mixture and removed from the condensation column 201 via a side draw via line 108. The removed acrylic acid stream is highly concentrated (approx. 97% acrylic acid) and has a temperature of approximately 99 °C. This acrylic acid stream (also referred to as "crude acrylic acid") is fed via a series of devices not described further here to a crystallization device, in which the acrylic acid is purified by crystallization. In addition to crystalline, high-purity acrylic acid, so-called mother acid remains in the crystallization device and is removed via line 107 as a mother acid stream.

[0068] The mother acid stream is thermally coupled with the acrylic acid stream withdrawn from condensation column 201. The mother acid stream initially has a temperature of approximately 20 °C and is heated to approximately 93 °C by thermal coupling. In this way, the excess thermal energy of the acrylic acid stream can be transferred to the mother acid stream.

[0069] The temperature-controlled mother acid stream is divided into a first and a second mother acid substream. While the second mother acid substream is fed to the condensation column 201 via a line 109, the first mother acid substream is fed as reflux to the top tray of the cracking column 205 via a line 106, thus indirectly coupling the thermal energy of the acrylic acid stream into the cracking reaction.

[0070] A stripping gas stream is fed to the cracking column 205 via a line 105 as recycle gas from a plant section below the lowest tray (not to be described in detail). This stripping gas stream has a temperature of approximately 85 °C. A secondary component stream comprising oligomeric acrylic acid at a temperature of approximately 109 °C is fed to a middle tray of the cracking column 205 from the bottom of the condensation column 201 via a first line 101. The secondary component stream contains high boilers such as benzaldehyde, furfural, and maleic acid. However, the largest constituent of the secondary component stream is acrylic acid, its oligomers, and polyacrylic acid.

[0071] In the splitting column 205, these secondary components, particularly the acrylic acid oligomers, are split back and removed via the top as the low-boiling fraction together with the recycle gas. This low-boiling fraction forms the gas mixture and is fed via line 104 to the quench device 209. The bottom of the splitting column 205 contains, in particular, the high-boiling fractions, which are removed and disposed of.

[0072] In the present embodiment, the yield of acrylic acid as a valuable product is significantly increased by splitting the acrylic acid oligomers and recycling them to the condensation column 201. Using the process according to the invention and the plant 1 according to the invention, it is possible to produce 20.4 t / h of acrylic acid.

[0073] The cracking residue from the bottom of the cracking column 205 is fed to a residue tank 203 via a second line 102. A comminution device 207 is connected to the residue tank 203 via a circulation line 111, which discharges the cracking residue via the bottom of the residue tank 203, feeds it to the comminution device 207, and returns it laterally into the residue tank 203.

[0074] The splitting residue from the residue container 203 is fed via a fourth line 104 to a further processing step (not shown).

[0075] A concrete embodiment is described below using the example of the production of acrylic acid.

[0076] Example 1 (according to the invention; the steady state is described)

[0077] The procedure is as in the example of WO2016 / 50582 A1.

[0078] The cracking residue (high-boiling fractions) from the bottom of the cracking column 205 is fed to a residue container 203. The cracking residue in the residue container 203 is crushed by a comminution device 207 (CAVITRON® machine CD 1018; throughput 12 m 3 / h, operating pressure 10 bar, operating temperature 100 °C, pump output 1-6 bar) is continuously circulated and crushed. The gap residue or the particles in the gap residue are crushed to a particle size of approximately < 1 mm. The gap residue is fed from the residue container 203 for further processing.

[0079] No deposits are observed in the residue tank 203 and the connected pumps and lines.

[0080] Example 2 (Comparative Example) The procedure is as in Example 1. No comminution device 207 is used.

[0081] The splitting residue, which is discharged from the residue container 203, is filtered through a filter (filter fabric with a mesh size of < 4 mm) before being fed for further processing.

[0082] Deposits have been observed in the residue tank 203 and the filter, which clog the filter over time. The system must be shut down, and the residue tank and filter must be cleaned. Cleaning such a full filter is only possible by boiling it with a hot (>70°C) 10% NaOH solution or mechanically using high-pressure water, which can lead to damage to the filter fabric.

[0083] Example 3 (comparison example)

[0084] The procedure is as in Example 1. No comminution device 207 is used.

[0085] The splitting residue is fed directly for further processing.

[0086] Deposits are observed in the residue tank and the connected pumps and lines, leading to blockages. The system must be shut down, and the residue tank, pumps, and lines must be cleaned.

Claims

Patent claims 1. A process for the continuous recovery of acrylic acid, wherein a secondary component stream comprising oligomeric acrylic acid from a condensation column (201) is fed to a cracking column (205), the oligomeric acrylic acid from the secondary component stream is at least partially cracked in the cracking column (205) to obtain monomeric acrylic acid, the monomeric acrylic acid is separated from secondary components contained in the secondary component stream and fed to the condensation column (201), characterized in that a cracking residue from the bottom of the cracking column (205) is fed to a residue container (203) before further processing, the cracking residue in the residue container (203), optionally diluted, and continuously circulated and crushed via a crushing device (207).

2. Method according to claim 1, characterized in that the splitting residue is fed to the comminution device (207) via the bottom of the residue container (203) and the crushed splitting residue is returned laterally into the residue container (203).

3. Method according to claim 2, characterized in that the residue container (203) has a curved bottom and the feed to the comminution device (207) is arranged centrally on the bottom.

4. Method according to one of claims 1 to 3, characterized in that the residue container (203) has a volume of 1 to 100 m 3 has.

5. Method according to one of claims 1 to 4, characterized in that the comminution device (207) is a comminution pump, in particular a mill pump.

6. Method according to one of claims 1 to 5, characterized in that splitting residue from the residue container (203) is fed to further processing by means of a pump which removes the splitting residue from the side of the residue container (203).

7. Method according to one of claims 1 to 6, characterized in that the splitting residue is diluted in the residue container (203) by supplying a solvent, in particular an alcohol, and / or an aqueous mixture to the residue container.

8. Method according to one of claims 1 to 7, characterized in that the temperature of the gap residue in the residue container (203) is measured.

9. Method according to one of claims 1 to 8, characterized in that the viscosity of the gap residue in the residue container (203) is measured.

10. Method according to one of claims 1 to 9, characterized in that in the comminution device (207) between 1 and 100 m 3 / h of splitting residue is circulated and crushed.

11. Process according to one of claims 1 to 10, characterized in that the secondary component stream essentially comprises acrylic acid, diacrylic acid and polyacrylic acid as well as proportions of maleic acid, benzoic acid, benzaldehyde, furfurals and water.

12. Process according to one of claims 1 to 11, characterized in that 60% to 95% of the oligomeric acrylic acid is split from the secondary component stream.

13. Plant (1) for the recovery of acrylic acid, comprising - a condensation column (201), - a splitting column (205), - a residue container (203) with a crushing device (207), - a first line (101) connecting the condensation column (201) and the splitting column (205), - a second line (102) connecting the splitting column (205) and the residue container (203), - a circulation line (103) connecting the residue container (203) and the comminution device (207), - a third line (103) connecting the splitting column (205) and the condensation column (201), and - a fourth line (104) connected to the residue container (203).

14. Plant according to claim 13, characterized in that the plant (1) is integrated into an overall plant for the production of acrylic acid.

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