Process for recovering acrylic acid and apparatus for recovering acrylic acid with an intermediate storage vessel

Abstract

The invention relates to a method for continuous recovery of acrylic acid, wherein a side component stream comprising oligomeric acrylic acid is fed from a condensation column to a cracking column, the oligomeric acrylic acid in the side component stream is at least partially cracked in the cracking column to obtain monomeric acrylic acid, the monomeric acrylic acid is separated from the side components contained in the side component stream and fed to the condensation column.

Description

[0001] This invention relates to a method for recycling acrylic acid and an apparatus for recycling acrylic acid.

[0002] Acrylic acid is an important basic chemical. Due to its highly reactive double bonds and acidic function, acrylic acid is particularly suitable as a monomer for the preparation of polymers. For example, most of the amount of acrylic acid monomer prepared is esterified prior to polymerization (e.g., to form binders, dispersions, or varnishes). Only a small portion is directly polymerized (e.g., to form "superabsorbents"). While direct polymerization of acrylic acid typically requires high-purity monomers, the purity requirement is less stringent if the acrylic acid is esterified prior to polymerization.

[0003] Acrylic acid is primarily obtained through a heterogeneous catalytic gas-phase partial oxidation reaction of its C3 precursors with molecular oxygen on a catalyst in a solid aggregate state at high temperatures. The term C3 precursors encompasses compounds that can be formally obtained through the reduction reaction of acrylic acid. In preparation, these gaseous C3 precursors, typically diluted with inert gases such as nitrogen, CO2, saturated hydrocarbons, and / or water vapor, are guided at high temperatures and, where appropriate, under high pressure, in a form mixed with molecular oxygen, through a transition metal mixed oxide catalyst. The resulting oxidation produces a product gas mixture containing acrylic acid and byproducts such as furfural, benzaldehyde, and maleic anhydride, from which acrylic acid must be separated.

[0004] The resulting acrylic acid is not a pure product, but a mixture. In addition to acrylic acid (usually accounting for ≥90% or ≥95% of the total weight), the mixture also contains typical gas-phase oxidation byproducts such as water, lower aldehydes (such as furfural, acrolein or methacrolein, benzaldehyde), lower carboxylic acids (such as acetic acid, propionic acid), and acrylic acid oligomers.

[0005] The formation of acrylic acid oligomers occurs because acrylic acid, existing in the condensed phase, undergoes a reversible Michael addition reaction with itself and the dimer formed in this process to form acrylic acid oligomers (Michael adducts), and also through free radical polymerization. The presence of water (an unavoidable byproduct of the gas-phase catalytic oxidation of acrylic acid) and high temperatures promote the formation of acrylic acid oligomers.

[0006] Because the corresponding oligomers have boiling points higher than those of acrylic acid, they are enriched in high-boiling-point regions (e.g., in the bottom liquid) during the distillation and separation of acrylic acid and during the fractionation and condensation of product gas mixtures prepared by gas-phase catalytic oxidation.

[0007] A method for preparing acrylic acid as described above is known from DE 199 24 533 A1, wherein the basic separation of crude acrylic acid is achieved by fractional condensation of a product gas mixture from heterogeneous catalytic gas-phase partial oxidation. Here, the re-cracking of acrylic acid oligomers contained in the quench liquid outlet should be integrated in such a way that the operating time of the method, particularly the operating time for fractional condensation, is not substantially reduced. The purpose of the re-cracking of acrylic acid oligomers is to increase the yield of valuable products. DE 199 24 533 A1 proposes a circulating reactor for this purpose.

[0008] A very similar method for preparing acrylic acid is described in DE 102 47 240 A1, in which a product gas mixture containing acrylic acid is first cooled by direct cooling with a quenching liquid, and then the cooled product gas mixture is introduced into a condenser equipped with internals for separation. Crude acrylic acid is extracted from the condenser and sent to a further crystallization and purification stage. In this case, the mother acid produced in the crystallization and purification stage is completely returned to the condenser. The bottom liquid containing acrylic acid oligomers is extracted from the bottom of the condenser and used as a quenching liquid. The unevaporated portion of the quenching liquid during the cooling of the product gas mixture is circulated through the bottom of the condenser and, where appropriate, through a heat exchanger, and a portion of the quenching liquid is discharged from this circulation loop as an outlet and sent to a pyrolysis vessel for re-pyrolysis. The pyrolysis gas containing acrylic acid, which escapes in gaseous form, is returned to the quenching liquid circulation loop or condenser, or returned to the quenching liquid circulation loop and condenser, wherein the pyrolysis gas is subjected to countercurrent distillation and at least partial condensation before being returned, wherein the amount of condensate formed corresponds at least to the reflux rate required for countercurrent distillation.

[0009] A method for recovering acrylic acid is described in WO 2016 / 050582 A1. In this method, oligomeric acrylic acid from the bottom liquid of a condenser is cracked into monomeric acrylic acid in a cracking tower and then returned to the condenser.

[0010] The purpose of this invention is to provide a method and corresponding equipment for recovering acrylic acid, which further improves the yield of valuable products compared with the prior art, while making it possible to reduce CO2 emissions and production interruptions.

[0011] This objective is achieved by a method for continuously recovering acrylic acid, wherein a by-component stream comprising oligoacrylic acid is fed from a condenser to a cracking tower, the oligoacrylic acid in the by-component stream is at least partially cracked in the cracking tower to obtain monomeric acrylic acid, and the monomeric acrylic acid is separated from the by-component contained in the by-component stream and fed back to the condenser, characterized in that, when the cracking tower is not in operation, at least a portion of the by-component stream from the condenser is fed to an intermediate storage container and temporarily stored therein, rather than being fed back to the cracking tower, and when the cracking tower resumes operation, the intermediately stored by-component stream from the intermediate storage container is fed back to the cracking tower together with the by-component stream from the condenser.

[0012] This invention offers significant advantages, namely, that even in the event of a cracking tower malfunction, byproducts generated during acrylic acid production, particularly oligomeric acrylic acid, can be cracked, thereby improving the yield and purity of the valuable product (i.e., acrylic acid). Furthermore, the acrylic acid plant can continue operating even when the cracking tower fails, thanks to this invention. Moreover, CO2 emissions are reduced because fewer byproducts must be combusted.

[0013] According to a preferred embodiment, the ratio of the by-component stream from the intermediate storage container to the by-component stream from the condenser, fed together into the cracking tower, is between 1:5 and 2:1, preferably 1:4 and 1:1, and more preferably between 1:3 and 1:0.75. By adjusting this ratio, it is ensured that a sufficient amount of by-component stream can be discharged from the condenser while the intermediate storage container is emptied again. Here, the by-component stream from the intermediate storage container can be fed directly into the cracking tower, or indirectly mixed with the by-component stream from the condenser and fed into the cracking tower. In the second case, it is preferable to feed the by-component stream from the intermediate storage container into the feed from the condenser to the cracking tower.

[0014] It is also conceivable that a portion of the sub-component stream from the condenser is sent to an intermediate storage container, while the remainder of the sub-component stream from the condenser is transferred to the combustion stage.

[0015] According to a preferred embodiment, the sub-component stream from the condenser is cooled to 5°C to 50°C, preferably 10°C to 40°C, more preferably 15°C to 30°C, and particularly preferably below 18°C ​​to 22°C before being fed into the intermediate storage container. In this way, the viscosity can be primarily adjusted.

[0016] According to a preferred embodiment, the intermediate storage container has a volume of 10 m³ to 1,000 m³, preferably 150 m³ to 850 m³, more preferably 250 m³ to 700 m³, and particularly preferably 400 m³ to 600 m³. This volume ensures that sufficient by-component flow can be stored intermediately during periods when the cracking tower is not in operation.

[0017] According to a preferred embodiment, at least the inner surface of the intermediate storage container is made of austenitic steel. The austenitic steel is preferably chromium-nickel steel. Particularly preferably, the austenitic steel contains at least 8% by weight of nickel. Particularly preferably, the austenitic steel contains 16.0% to 20.5% by weight of chromium and 7.0% to 13.0% by weight of nickel. Using austenitic steel as the container material prevents corrosion.

[0018] According to a preferred embodiment, the intermediate storage sub-component is diverted and circulated within the intermediate storage container. Preferably, circulation is performed by means of a pump connected to the inlet and outlet of the intermediate storage container via a bypass line during bypass operation, and continuously circulates the container contents. More preferably, during circulation, the container contents are guided through a heat exchanger in the bypass line, thereby enabling temperature regulation of the container contents.

[0019] According to a preferred embodiment, the intermediate-stored byproduct stream is superimposed with rarefied air in an intermediate storage container. This ensures sufficient oxygen content, which is necessary for the stabilizing effect of the inhibitor system (typically containing phenothiazine (PTZ) and / or 4-methoxyphenol (MEHQ)) to prevent polymerization. Furthermore, maximum oxygen content is ensured to avoid an explosive atmosphere within the intermediate storage tank.

[0020] According to a preferred embodiment, the subcomponent stream from the condenser is fed into an intermediate storage container below the level of the subcomponent stream already stored therein. This is preferably achieved via a submerged piping. This ensures better mixing within the tank and prevents sedimentation.

[0021] Alternatively, a portion of the solvent or mother acid stream can be fed into an intermediate storage container, preferably via a separate pipeline. This method can counteract excessively high viscosity.

[0022] According to a preferred embodiment, the temperature of the intermediate stored subcomponent flow is measured in an intermediate storage container. For this purpose, preferably, at least one temperature sensor is arranged in and / or at the intermediate storage container. More preferably, six temperature sensors are arranged at different heights in opposite directions around the circumference of the intermediate storage container; for example, two sensors are arranged at 5% of the height; two at 30%; and two at 65%. In this way, an overview of the temperature distribution within the container is obtained.

[0023] According to a preferred embodiment, the viscosity of the intermediate stored subcomponent stream is measured in an intermediate storage container. The measurement is preferably performed using a viscometer. Advantageously, the viscosity should be low to ensure that the intermediate stored subcomponent stream has sufficient fluidity.

[0024] According to a preferred embodiment, the sub-stream mainly comprises acrylic acid, diacrylic acid, and polyacrylic acid, and a certain proportion of maleic acid, benzoic acid, benzaldehyde, furfural, and water, particularly 50% to 60% by weight of acrylic acid or methacrylic acid, 20% to 30% by weight of diacrylic acid, and 5% to 10% by weight of polyacrylic acid, as well as 6% to 9% by weight of maleic acid, 1% to 2% by weight of benzoic acid, 0.5% to 1% by weight of water, and 0.5% to 1% by weight of 4-methoxyphenol, and also small amounts (each <0.5% by weight) of acetic acid, furfural, benzaldehyde, phthalic anhydride, phenothiazine, and diacrylic acid. The sub-stream preferably has a temperature of 100°C to 130°C, particularly 105°C to 115°C, to achieve sufficient pre-concentration of the liquid at the bottom of the condenser before transferring it to the cracking tower, and to limit dimer formation in the bottom region of the condenser.

[0025] According to a preferred embodiment, 60% to 95%, preferably 85% to 90%, of the oligomeric acrylic acid in the sub-stream is pyrolyzed. Preferably, the pyrolysis mainly targets the dimers and trimers of acrylic acid. A higher pyrolysis rate of 95% is advantageous in terms of the yield of valuable products, but it is technically difficult to control because when the pyrolysis yield is >95%, the remaining product tends to form a large amount of solids, which are difficult to handle.

[0026] A surprising discovery is that the method according to the invention, utilizing the advantageous application of intermediate storage tanks, offers the advantage over existing technologies in that it allows the method to continue operating without adverse effects in the event of a cracking tower failure. Solid matter continuously accumulates in the cracking tower; this solid either enters the cracking tower as an impurity in the by-component stream or is generated during the cracking process. Therefore, the cracking tower must be periodically shut down and cleaned. Cleaning is preferably performed using sodium hydroxide. During purification, either the entire acrylic acid preparation process must be stopped, or the by-component stream from the condenser must be fed directly into the combustion stage without cracking the oligomeric acrylic acid. Direct combustion of the by-component stream, including the oligomeric acrylic acid, produces more CO2 and results in a lower acrylic acid yield.

[0027] The following describes further preferred details of this method:

[0028] Preferably, the temperature-controlled mother acid stream from the crystallization apparatus is split into two streams, one heading towards the condensation tower and the other towards the cracking tower. In the context of this invention, "temperature control" refers to heating the mother acid stream or its branch stream from the crystallization apparatus to a temperature preferably 50°C to 100°C, preferably 60°C to 90°C, and particularly preferably 70°C to 80°C. Preferred embodiments of this method are not limited to a specific crystallization method, wherein acrylic acid is purified by partial crystallization, separation of the solidified acrylic acid from the impurity-containing liquid (mother acid), and the fusion separation of the pure acrylic acid crystals. In this case, falling film crystallization or suspension crystallization, for example, as a combination of a cooling disc crystallizer and a washing tower, can be used, with the latter variant being preferred.

[0029] In this invention, “mother acid” (also referred to as “mother liquor” in similar publications) refers to an acrylic acid solution which, after being purified in a crystallization apparatus, contains impurities separated in the crystallization apparatus, wherein the weight fraction of acrylic acid in the mother acid is ≥80% by weight.

[0030] Preferably, the first temperature-controlled mother acid is diverted onto the top tray of a pyrolysis column having 45 trays. In this invention, the pyrolysis column is preferably equipped with dual-flow trays as an internal structure for separation. Preferably, the second temperature-controlled mother acid is diverted onto tray 18 of a condenser column comprising 75 trays.

[0031] Preferably, at least one stripping gas stream is introduced below the bottom tray of the cracking tower. Here, the stripping gas stream is preferably directed towards the liquid surface at the bottom of the tower. The stripping gas stream is specifically used as a circulating gas. In the present invention, "circulating gas" is understood to be a gas that dilutes the reactants and absorbs the heat of reaction in gas-phase oxidation, and is substantially inert in the gas-phase reaction. The circulating gas mainly contains nitrogen, and contains oxygen, water vapor, carbon oxides and mixtures thereof in concentrations ranging from <5% by volume, and trace amounts (<0.8% by volume) of ethylene, ethane, propylene, propane, acrolein, acrylic acid, and acetic acid.

[0032] Preferably, the by-component stream comprising oligoacrylic acid is fed from the condenser into the intermediate tray of the cracking tower. The intermediate tray is particularly the tray in tray regions 8 and 10.

[0033] In a cracking column, at least a portion of the oligomeric acrylic acid in the by-component stream is cracked to obtain the monomeric acrylic acid. This preferably occurs at a temperature >150°C. Adding a small amount of sodium hydroxide or amine to the bottom of the cracking column can accelerate the cracking process.

[0034] Preferably, the subcomponents contained in the subcomponent stream are separated by countercurrent distillation in a cracking column installed at the top.

[0035] The obtained monomeric acrylic acid is preferably discharged from the top of the cracking tower in the form of a gas mixture together with the incoming stripping loop gas flow, without condensation, and then preferably the gas mixture is sent to the bottom tray of the condenser tower.

[0036] This allows the monomeric acrylic acid to be returned to the process in an advantageous manner. Since the acrylic acid is fed in gaseous form, it does not require prior evaporation, thus allowing more energy in the condenser to be used for separating the acrylic acid from the by-products. In this invention, the condenser is preferably designed as a plate tower. This condenser is preferably equipped with a two-flow tray in the lower region, a Toman tray in the middle region, and a valve tray in the upper region.

[0037] The preferred method offers advantages over existing technologies in that it eliminates the need for partial condensation of the acrylic acid stripped in the cracking tower to maintain reflux in the distillation tower, and utilizes a portion of the mother acid stream generated in the crystallization unit, rather than reflux produced by condensing vapor at the top of the cracking tower. This eliminates the need for a condensation unit at the top of the cracking tower, reducing equipment investment. Furthermore, no additional cooling performance is required for condensation. Moreover, the energy introduced via the heat exchanger at the bottom of the cracking tower is additionally used in the condensation tower, thereby improving the separation of acrylic acid from by-products.

[0038] Another advantage of this preferred method is that, through the method of the present invention, monomeric acrylic acid can be recovered from the corresponding oligomers in an improved yield and reintroduced into the entire process as a low-boiling-point substance. "Oligoacrylic acid" is specifically understood to refer to dimers and trimers of acrylic acid. Compared to the prior art, the purification loss of acrylic acid is reduced by 0.3%. In this application, "purification loss" is understood to refer to the proportion of acrylic acid fed into the synthesis process that cannot be separated from the by-products.

[0039] In an improvement to this preferred method, it has proven advantageous to switch the mother acid stream relative to the acrylic acid stream from the condenser (particularly thermally) for temperature control. Preferably, the acrylic acid stream, as the target product, is extracted via a side outlet of the condenser and primarily fed into the crystallization unit. This acrylic acid stream is at a very high temperature (i.e., 95°C to 100°C) and a very high concentration (i.e., 95% to 98% wt% acrylic acid), and must be cooled before entering the crystallization unit.

[0040] Preferably, the heat present in the acrylic acid stream is thus transferred to the mother acid stream via a heat exchanger, thereby coupling the two mother acid streams. This means that this energy is provided both in the condenser for the separation of acrylic acid and in the cracking tower for the cracking of diacrylic acid, or in other words, less energy must be introduced into the cracking process via the bottom heat exchanger located at the cracking tower.

[0041] According to a preferred embodiment, the gas mixture is indirectly fed below the bottom tray of the condenser tower, specifically by introducing the gas mixture into a quenching device to quench the product gas mixture containing acrylic acid.

[0042] The mother acid stream extracted from the crystallization unit preferably comprises mainly acrylic acid and a certain proportion of water and acetic acid, particularly 90% to 95% by weight of acrylic acid, 3% to 6% by weight of water, and 1% to 2% by weight of acetic acid, as well as small amounts (each <0.5% by weight) of formaldehyde, propionic acid, furfural, maleic acid, and diacrylic acid. The mother acid stream is collected at a temperature slightly higher than the crystallization temperature of acrylic acid (15°C to 20°C) and preferably preheated to the corresponding thermodynamic equilibrium temperature of about 80°C at the feed point of the condenser (201) to ensure the most efficient separation possible.

[0043] In addition, the stripping gas stream may primarily consist of nitrogen, acrylic acid, water, and oxygen, as well as a certain proportion of carbon dioxide and acetic acid, particularly 80% to 85% by weight of nitrogen, 3% to 5% by weight of acrylic acid, 3% to 5% by weight of water, 3% to 4% by weight of oxygen, 2% to 3% by weight of carbon dioxide, and 1% to 2% by weight of acetic acid, and small amounts (each <0.7% by weight) of carbon monoxide, acrolein or methacrolein, formic acid, propylene, and propane. The stripping gas stream preferably has a temperature of 80°C to 90°C, particularly about 85°C.

[0044] Another subject of the invention is an apparatus for recycling acrylic acid, the apparatus comprising:

[0045] - Condensation tower,

[0046] - Cracking tower,

[0047] -Intermediate storage container

[0048] -The first pipeline connecting the condenser and the pyrolysis tower

[0049] - A second pipeline connecting the condenser tower and the intermediate storage container.

[0050] -A third pipeline connecting the intermediate storage container and the pyrolysis tower, and

[0051] - The fourth pipeline connecting the pyrolysis tower and the condensation tower.

[0052] The method according to the invention can be advantageously performed using the apparatus of the invention.

[0053] The meanings of “condensation tower,” “cracking tower,” and “intermediate storage container” in the context of this invention have been described above with reference to the method of this invention.

[0054] The first pipeline connects the condenser and the cracking tower, and feeds the by-components from the condenser into the cracking tower. A fourth pipeline connects the cracking tower and the condenser, and the separated acrylic acid monomer is fed into the condenser via this fourth pipeline.

[0055] The second pipeline connects the condenser and the intermediate storage container. When the pyrolysis tower stops operating, the byproducts from the condenser are diverted to the intermediate storage container via the second pipeline. Therefore, the second pipeline can be controlled to close / open depending on the operating status of the pyrolysis tower.

[0056] The intermediate storage container and the pyrolysis tower are connected via a third pipeline, through which the intermediate storage byproducts are diverted into the pyrolysis tower when the pyrolysis tower resumes operation. The third pipeline can also be turned on / off in a controlled manner.

[0057] The equipment preferably also includes a fifth pipeline connected to the pyrolysis tower, which sends at least one stream of gas as stripping circuit gas into the bottom region of the pyrolysis tower.

[0058] The sixth pipeline is preferably used to divert a portion of the mother acid produced during crystallization into the cracking tower. Preferably, the crystallization unit and the condenser are connected via a seventh pipeline.

[0059] The foregoing has provided corresponding definitions for the various components of the device and the terms used in relation to the method of the present invention, and these definitions also apply to this device.

[0060] The advantages of the device of the present invention are basically the same as those of the method of the present invention described above. This device creates the necessary conditions for its application.

[0061] In a preferred embodiment of the apparatus of the present invention, the apparatus further includes a quenching device for quenching the product gas mixture containing acrylic acid, the quenching device being arranged in a fourth pipeline between the cracking tower and the condensing tower. In this case, means are provided to efficiently utilize the gas mixture from the cracking tower and its temperature to quench the high-temperature product gas mixture.

[0062] The apparatus of the present invention is particularly advantageous when integrated into a complete apparatus for acrylic acid production. As described above, the apparatus of the present invention can improve the overall efficiency of acrylic acid production.

[0063] If the description relating to the apparatus of the present invention also refers to method features, then these method features preferably refer to the method of the present invention. Similarly, object features relating to the method of the present invention preferably relate to the apparatus of the present invention.

[0064] Further objects, features, advantages, and applications will become apparent from the following description of embodiments of the invention in conjunction with the accompanying drawings. All described and / or illustrated features, whether individually or in any combination, constitute the subject matter of the invention and are not limited to their summaries or references in the claims.

[0065] Figure 1 A schematic diagram of the device 1 of the present invention is shown in one embodiment of the present invention.

[0066] Figure 1 A schematic diagram of the apparatus 1 of the present invention is shown in one embodiment. Key components therein include a condenser tower 201, an intermediate storage container 203, and a pyrolysis tower 205.

[0067] A high-temperature product gas stream at approximately 270°C is introduced from a section of the equipment (not shown) where a heterogeneous catalytic gas-phase partial oxidation reaction takes place. This high-temperature product gas stream is then introduced into a quenching unit 207 to prevent any possible reactions of its components and to lower its temperature. A gas mixture from the cracking tower 205, at approximately 95°C, is also introduced into the quenching unit 207 via a fourth conduit 104. This gas mixture will be discussed in more detail later.

[0068] The gas and liquid fed into the quenching unit 207 are then fed into the bottom region of the condenser tower 201 via pipeline 110 after leaving the quenching unit. In the condenser tower 201, the prepared acrylic acid is separated from the product mixture by absorption and extracted from the condenser tower 201 via pipeline 108 through a side outlet. The extracted acrylic acid stream has a high concentration (approximately 97% acrylic acid) and a temperature of approximately 99°C. This acrylic acid stream (also known as "crude acrylic acid") is fed into a crystallization unit via a series of devices (not described in detail here) for the crystallization and purification of the acrylic acid. In addition to the high-purity acrylic acid crystals, the so-called mother acid remains in the crystallization unit and is extracted as a mother acid stream via pipeline 107.

[0069] The mother acid stream is thermally coupled to the acrylic acid stream drawn from condenser 201. The mother acid stream initially has a temperature of approximately 20°C, which is heated to approximately 93°C through thermal coupling. In this way, excess heat energy from the acrylic acid stream can be transferred to the mother acid stream.

[0070] The temperature-controlled mother acid stream is divided into a first mother acid stream and a second mother acid stream. The second mother acid stream is sent to the condenser 201 via pipeline 109, while the first mother acid stream is sent as reflux to the top tray of the cracking tower 205 via pipeline 106, thereby indirectly coupling the heat energy of the acrylic acid stream to the cracking reaction.

[0071] A stripping gas stream from an undetailed equipment section is fed as a recirculating gas into the bottom tray of the cracking tower 205 via line 105. This stripping gas stream has a temperature of approximately 85°C. A by-component stream comprising oligoacrylic acid, at a temperature of approximately 109°C, is fed from the bottom of the condenser 201 into the intermediate tray of the cracking tower 205 via the first line 101.

[0072] The sub-component stream contains high-boiling-point substances such as benzaldehyde, furfural, and maleic acid. However, the largest component of the sub-component stream is acrylic acid and its oligomers and polyacrylic acid.

[0073] In cracking tower 205, these by-products, particularly acrylic acid oligomers, are further cracked and collected as low-boiling fractions along with the circulating gas at the top of the tower. These low-boiling fractions form a gas mixture and are fed into quenching unit 207 via line 104. At the bottom of cracking tower 205, particularly high-boiling fractions remain; these are collected and sent to the waste disposal stage.

[0074] In this embodiment, by re-pyrolyzing the acrylic acid oligomers and returning them to the condenser 201, the yield of acrylic acid as a valuable product is significantly improved. Using the method and apparatus 1 of this invention, it is feasible to produce 20.4 tons of acrylic acid per hour.

[0075] The subcomponent stream from the condenser 201 is fed into the intermediate storage container 203 via the second line 102. This occurs when the cracker 205 stops operating. When the cracker 205 is restarted, the subcomponent stream stored in the intermediate storage container, along with the subcomponent stream from the condenser 201, is introduced into the cracker 205 via the third line 103.

[0076] The following describes a specific implementation method using the preparation of acrylic acid as an example.

[0077] Example (describes steady state)

[0078] The operation is performed as described in the example of the invention according to WO2016 / 50582 A1. If the cracking tower 205 stops operating or malfunctions, the 2,460 kg / h bottom liquid extracted from the condenser tower 201 is introduced into the intermediate storage container 203 and temporarily stored there, instead of the cracking tower 205. When the cracking tower 205 resumes operation, the bottom liquid temporarily stored in the intermediate storage container 203 is introduced into the cracking tower 205 at a rate of approximately 650 kg / h to 1350 kg / h, together with the bottom liquid from the condenser tower 201.

[0079] Comparative example

[0080] Operate as in Example 1. There is no intermediate storage container 203. If the cracking tower 205 stops operating or malfunctions, the 2,460 kg / h bottom liquid extracted from the condenser tower 201 is degassed and fed into the residue combustion stage after being diluted with methanol. The contained acrylic acid is lost, and exhaust gas pollution is exacerbated.

Claims

1. A method for continuous recycling of acrylic acid, wherein, A byproduct stream comprising oligoacrylic acid is fed from a condenser (201) into a cracking tower (205), wherein the oligoacrylic acid in the byproduct stream is at least partially cracked in the cracking tower (205) to obtain monomeric acrylic acid, and the monomeric acrylic acid is separated from the byproduct contained in the byproduct stream and fed into the condenser (201). The characteristic feature is that when the cracking tower (205) is not in operation, the byproduct stream from the condenser (201) is at least partially fed into an intermediate storage container (203) and temporarily stored therein, instead of being fed into the cracking tower (205); when the cracking tower (205) resumes operation, the byproduct stream intermediately stored in the intermediate storage container (203) is fed into the cracking tower (205) together with the byproduct stream from the condenser (201).

2. The method according to claim 1, characterized in that, The ratio of the flow rate of the subcomponent from the intermediate storage container (203) to the flow rate of the subcomponent from the condenser (201) fed into the cracking tower (205) is between 1:5 and 2:

1.

3. The method according to claim 1 or 2, characterized in that, The sub-component stream from the condenser (201) is cooled to 5°C to 50°C before being fed into the intermediate storage container (203).

4. The method according to any one of claims 1 to 3, characterized in that, The intermediate storage container (203) has a volume of 10 m³ to 1,000 m³.

5. The method according to any one of claims 1 to 4, characterized in that, At least the inner surface of the intermediate storage container (203) is made of austenitic steel.

6. The method according to any one of claims 1 to 5, characterized in that, The intermediate storage component is circulated in the intermediate storage container (203).

7. The method according to any one of claims 1 to 6, characterized in that, The intermediately stored sub-components are superimposed with rarefied air in the intermediate storage container (203).

8. The method according to any one of claims 1 to 7, characterized in that, The subcomponent stream from the condenser (201) is fed into the intermediate storage container (203) below the level of the subcomponent stream that has been intermediately stored.

9. The method according to any one of claims 1 to 8, characterized in that, The temperature of the intermediate stored sub-component stream is measured in the intermediate storage container (203).

10. The method according to any one of claims 1 to 9, characterized in that, The viscosity of the intermediate stored subcomponent stream is measured in the intermediate storage container (203).

11. The method according to any one of claims 1 to 10, characterized in that, The sub-components mainly include acrylic acid, diacrylic acid and polyacrylic acid, as well as a certain proportion of maleic acid, benzoic acid, benzaldehyde, furfural and water.

12. The method according to any one of claims 1 to 11, characterized in that, 60% to 95% of the oligomeric acrylic acid in the subcomponent stream is pyrolyzed.

13. An apparatus (1) for recycling acrylic acid, said apparatus comprising: - Condensation tower (201). - Cracking tower (205). -Intermediate storage container (023). - A first pipeline (101) connecting the condenser (201) and the pyrolysis tower (205). - A second pipeline (102) connecting the condenser (201) and the intermediate storage container (203). -The third pipeline (103) connecting the intermediate storage container (203) and the pyrolysis tower (205) and - A fourth pipeline (104) connecting the pyrolysis tower (205) and the condensation tower (201).

14. The device according to claim 13, characterized in that, The device (1) is integrated into a general-purpose device for the preparation of acrylic acid.

Images