Method for continuously upgrading heavy by-products from acrylic acid production

Abstract

The present invention relates to a method for regenerating acrylic acid (AA) by thermal cracking from heavy by-products (residues called AAHP) from an acrylic acid (AA) production unit, and it is intended to recycle the heavy by-products in an acrylic acid production plant. This process consists of two continuously operating steps, and the current performance of the cracking plant is improved.

Description

Technical Field

[0001] The present invention relates to a method for regenerating acrylic acid from heavy by-products (residues called AAHP) from an acrylic acid (AA) production unit by thermal cracking, and it is intended to recycle the heavy by-products in an acrylic acid production plant. This process consists of two continuously operating steps, and the current performance of the cracking plant is improved.

Background Art

[0002] Under the temperature action during the distillation process, the production of acrylic acid involves the formation of heavy compounds (derivatives by the addition of compounds having nucleophilic properties to the double bond of unsaturated carbonyl-containing monomers by Michael reaction). Compounds having a boiling point higher than that of the produced acrylic monomer are called "heavy" compounds.

[0003] In the case of the AA production unit, basically, the following exist: · Derivatives in which acrylic acid is added to the double bond of another acrylic acid molecule: 3-acryloyloxypropionic acid, also called "acrylic acid dimer" or "AA dimer"; · Derivatives in which acrylic acid is added to the double bond on the AA dimer molecule to form "AA trimer", and other oligomers formed by the continuous addition of acrylic acid to the double bond of the above AA oligomers; and · Derivatives of carboxylic acid adducts formed as by-products of acrylic acid, or derivatives in which water is added to the double bond of AA, or the double bond of the above oligomers.

[0004] Recovering upgradable monomers from heavy Michael derivative compounds is difficult in the case of heavy products derived from the AA production unit. Specifically, residues remain during the thermal cracking process that regenerates distilled and upgraded acrylic acid, and the viscosity of these residues increases significantly when high cracking efficiency is required, making it impossible to extract them from the cracking reactor.

[0005] The main factor limiting the regeneration efficiency of compounds derived from the Michael reaction contained in the heavy stream from the AA plant is the increase in the viscosity of the heavy residue obtained at the bottom of the cracker (decomposer) when the acrylic monomer-rich fraction is evaporated.

[0006] When light compounds evaporate during cracking, heavy products are concentrated in the residue stream, increasing the viscosity of this stream. However, the residue must remain sufficiently fluid for transport after cooling and then be processed to destroy it.

[0007] If light esters (methyl acrylate (MA) or ethyl acrylate (EA)) are produced near the AA production unit, the situation can be improved by co-cracking the respective heavy products together, which makes the cracking residue more fluid. The proposed solution enables the recovery of the maximum amount of AA for each cracking operation while managing the viscosity of the residues formed without relying on another production unit.

[0008] Therefore, in European Patent No. 717,031 (EP 717 031), it has been shown that if cracking is carried out with a mixture of heavy products derived from an AA production unit and an acrylic ester (EA) production unit, the recovery efficiency of these upgradable valuable products can be improved compared to cracking the heavy product streams from these units individually. Adding the heavy product derived from the ester unit (EAHP) to the heavy product derived from the AA unit (AAHP) has the effect of reducing the viscosity of the final residue. The cracking reaction is carried out with a mixture having an AA heavy product / ester heavy product ratio of 9 / 1 to 1 / 9 at a temperature of 180°C to 220°C under atmospheric pressure with a residence time of 0.5 to 3 hours. In this process, the cracking and evaporation of the resulting light compounds are carried out in the reactor, and then the resulting gas stream is sent to a distillation column. Finally, the bottom stream from the distillation column is recycled to the reactor. On the other hand, since the light fraction obtained by cracking mainly consists of AA and ester acrylic monomers that are sensitive to polymerization, the distillation step must be carried out under reduced pressure and the temperature needs to be lowered to prevent polymer formation in the column. Furthermore, the polymerization inhibitor entrained in the gas mixture is efficiently separated by the rectifying plates of the distillation column, and the gas mixture flows countercurrently to the bottom of the column. Therefore, it is necessary to introduce a new polymerization inhibitor at the top of the column to prevent polymer formation at the top of the column.

[0009] For this reason, it is necessary to separate the reaction stage (carried out under high pressure) from the distillation stage (carried out under reduced pressure). Therefore, the equipment for carrying out the process needs to be equipped with a reactor and an upper condenser (which operate at the same pressure), and a distillation column operating under reduced pressure (to which the condensed product is supplied), and it is necessary to have a boiler at the bottom, a condenser at the top, a reflux device member, and a supply section for the inhibitor. Such an arrangement configuration is complex and expensive.

[0010] Furthermore, cracking AA heavy products and EA heavy products together in a mixed state leads to operational constraints. Specifically, when the ester unit is shut down, it is necessary to shut down the cracking operation. This leads to economic losses.

[0011] In other scenarios, AA heavy products are thermally cracked batch by batch without adding ester heavy products, resulting in extremely viscous residues. These residues limit the performance of this cracking and cause problems in terms of storage and transfer of the residues.

[0012] To overcome problems related to viscosity, it is also known to add a solvent to the cracking residue of AA heavy products.

[0013] European Patent Application Publication No. 3255030 (EP 3255030) teaches adding a higher alcohol while the residue is cracking to convert maleic anhydride present in the residue into a maleic acid ester with low polymerization sensitivity.

[0014] U.S. Patent No. 6414183 (US 6414183) teaches a method of diluting the discharged residue with a solvent (such as acetic acid, water, methanol).

[0015] International Publication No. 2021 / 224044 (WO 2021 / 224044) describes a process for decomposing a Michael adduct of acrylic acid by diluting with Solvent 1 (having a boiling point of at least 170 °C at 1013 hPa and a solubility in water of at least 20 g per 100 g of water at 25 °C), and the solvent is selected from alcohols (such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and 2-ethoxyethanol), carboxamides (such as N,N-dimethylacetamide, N-methylacetamide, and N,N-dimethylformamide), sulfoxides (such as dimethyl sulfoxide), and sulfones (such as sulfolane).

[0016] However, this solution has several drawbacks, such as the generation of waste to be burned or the provision of additional equipment for mixing, in cases where it is not an internal flow. Furthermore, most of these solvents, when burned, produce derivatives containing nitrogen or sulfur.

[0017] Therefore, it is necessary to improve the efficiency of regenerating heavy compounds derived only from the AA unit by thermal cracking.

[0018] Summary of the Invention The present invention relates to a method for regenerating a mixture of heavy by-products (AAHP) from an acrylic acid production unit, the method comprising the following steps: i. introducing the heavy by-products into a hydrolyzer together with water and subjecting them to continuous hydrolysis for 1 to 10 hours, preferably 1 to 5 hours, at a water:AAHP ratio in the range of 0.1 to 1.3 (including the end values), to obtain a mixture of hydrolyzed products; ii. continuously injecting the mixture of hydrolyzed products into a reactor and subjecting it to thermal cracking to produce a gaseous overhead stream containing acrylic acid and water and a bottom stream (residue) in which heavy products are concentrated; iii. recovering a light fraction rich in AA and water that can be recycled at various points in the method; iv. recovering the residue for the purpose of removal treatment and including.

[0019] According to various embodiments, the method, when appropriately combined, includes the following characteristics.

[0020] According to one embodiment, the pressure in the hydrolyzer varies between 0.1 and 2 MPa, preferably between 0.5 and 1.5 MPa.

[0021] According to one embodiment, the temperature in the hydrolyzer varies between 80°C and 200°C, preferably between 150°C and 200°C.

[0022] According to one embodiment, the cracking temperature is between 140 °C and 260 °C, preferably between 160 °C and 210 °C.

[0023] According to one embodiment, the residence time of the reaction mixture in the cracking reactor is between 0.5 hours and 10 hours, preferably between 4 hours and 10 hours.

[0024] According to one embodiment, the thermal cracking reaction is carried out at atmospheric pressure or a slight pressure (up to 0.2 MPa).

[0025] According to one embodiment, the bottom stream (residue) from the reactor obtained at the end of the thermal cracking operation has a dynamic viscosity of less than 1 Pa·s when measured at a temperature of 100 °C using, for example, a cone / plate type Brookfield viscometer "CAP 1000+".

[0026] According to one embodiment, a gaseous overhead stream containing acrylic acid and water is injected into the condenser.

[0027] According to one embodiment, the thermal cracking reaction is carried out in the absence of a catalyst.

[0028] The present invention makes it possible to overcome the drawbacks of the prior art. The present invention makes it possible to recover the maximum amount of AA for each cracking operation while managing the viscosity of the formed residue without depending on another production unit. This is achieved by combining the step of hydrolyzing the heavy by-products from the acrylic acid production unit and the thermal cracking step of the hydrolyzed product.

[0029] The main advantages of the method according to the present invention are as follows: · Practically, an inexpensive and simple process in terms of investment: only one additional piece of equipment (hydrolyzer) is required compared to the cracking process alone; · A process that enables the reduction of emissions by reducing the amount of cracking residue; · Since the cracking temperature is lower than that of cracking without a hydrolysis step, energy can be saved; · Compared with cracking without a hydrolysis step, the viscosity of the residue is lower; · The cracking step does not depend on other units (ester units); · To ensure the discharge of the residue, it is also possible by hydrolysis to avoid special treatment of the residue (for example, addition of a solvent, for example, to fluidize the residue); · By further promoting the cracking reaction, the efficiency of recovering valuable products from Michael derivative products present in the heavy product stream from the AA plant increases, and reaching the viscosity limit of the residue is slower compared to solutions without hydrolysis.

Brief Description of the Drawings

[0030]

Figure 1

Modes for Carrying Out the Invention

[0031] The present invention will be described in more detail and non - limitatively in the following description.

[0032] The term "heavy by - products derived from units for acrylic acid production" means · Derivatives in which acrylic acid is added to the double bond of another acrylic acid molecule: 3 - acryloyloxypropionic acid, also called "acrylic acid dimer" or "AA dimer"; · Derivatives in which acrylic acid is added to the double bond on the AA dimer molecule to form "AA trimer", and other oligomers formed by the continuous addition of acrylic acid to the double bonds of the above AA oligomers; · Derivatives in which a carboxylic acid formed as a by - product of acrylic acid (for example, acetic acid) or water is added to the double bond of AA or the above oligomers are included.

[0033] The term "hydrolyzer" refers to a reactor capable of performing a hydrolysis reaction on a mixture of water and AA heavy products. This reactor can be heated and can maintain pressure. The latter can be a conventional stirred reactor, can be a plug flow reactor (with or without an internal premixer), or can be in a heat exchanger.

[0034] The present invention is based on a thermal cracking process involving a prior hydrolysis operation on the heavy by-products from the AA production unit.

[0035] The acrylic monomers involved in the Michael addition derivatives can be regenerated by hydrolyzing the oligomers before the heat treatment step. This hydrolysis reaction forms hydroxypropionic acid (HPA), which is thermally cracked to obtain acrylic acid. Hydrolysis makes it possible to reduce the oligomer chain and decreases the viscosity of the residue.

[0036] Hydrolysis in continuous mode is carried out under a pressure in the range of 0.1 - 2 MPa.

[0037] The regeneration efficiency (expressed as cracking efficiency) basically depends on the following: · a. Hydrolysis parameters: temperature and pressure, hydrolysis residence time, and the ratio of water / AA heavy products, and · b. Cracking parameters: temperature and residence time of the heat treatment.

[0038] Increasing the last two of these parameters (b.) tends to improve the regeneration efficiency, but this occurs in exchange for an increase in the viscosity of the cracking residue.

[0039] The cracking performance is characterized by the following two values: · URR or useful recovery rate: This is the ratio of the amount of acrylic acid recovered after cracking to the amount of AA heavy products fed to the cracker. URR = Mass of AA recovered / Mass of AA heavy products in cracker feed · Cracking rate or efficiency: The ratio of the amount of acrylic acid recovered after cracking to the total of the upgradable compounds in the cracker feed (acrylic acid (AA), acrylic acid dimer (AA2), and hydroxypropionic acid (HPA)).

[0040] According to an embodiment of the process shown in FIG. 1, a stream containing the heavy by - product from the acrylic acid production plant (AAHP), and water, are introduced into reactor R1 in continuous mode, either together or separately. The AAHP stream is rich in heavy Michael addition derivative compounds that occur during the synthesis and purification steps of acrylic acid, and this AAHP stream also contains other heavy compounds accumulated during the synthesis and purification processes, especially polymerization inhibitors.

[0041] A mixture (1) containing heavy acrylic acid compounds and water is heated to a temperature necessary to hydrolyze the Michael addition derivatives to obtain relatively light compounds. The stream (2) exiting the hydrolyzer R1 is then continuously introduced into a second reactor R2, where this stream is heated to a temperature necessary to crack the Michael addition derivatives to obtain lighter compounds, and the light compounds are extracted in the form of a gas mixture (3) at the top of the reactor.

[0042] This vapor stream, rich in acrylic acid and containing some heavy compounds with low concentrations of inhibitors, is advantageously recycled directly in vapor form or, after being entirely condensed as stream (4) in condenser E1, to the acrylic acid production process.

[0043] According to one embodiment, at least one polymerization inhibitor is introduced into the condenser E1. These inhibitors are selected from polymerization inhibitors known to those skilled in the art: phenol derivatives such as hydroquinone and its derivatives such as hydroquinone methyl ether, 2,6 - di(tert - butyl)-4 - methylphenol (BHT) and 2,4 - dimethyl - 6-(tert - butyl)phenol (topanol A), phenothiazine and its derivatives, manganese salts such as manganese acetate, salts of thiocarbamic acid or dithiocarbamic acid such as metal thiocarbamates and metal dithiocarbamates such as copper di(n - butyl)dithiocarbamate, N - oxyl compounds such as 4 - hydroxy - 2,2,6,6 - tetramethylpiperidine oxyl (4 - OH - TEMPO), compounds having a nitroso group such as N - nitrosophenylhydroxylamine and its ammonium salts, amine compounds such as paraphenylenediamine derivatives, or mixtures of these inhibitors.

[0044] The residual stream recovered at the reactor bottom (5) is cooled and then removed in the form of a liquid of appropriate viscosity, so that it can be easily transported by a pump, for example, to a storage tank or an incineration unit.

[0045] Examples The following examples illustrate the present invention and do not limit the present invention.

[0046] Example 1: Continuous hydrolysis and cracking (according to the present invention) This assembly consists of a plug - flow reactor with a total volume of 16.3 cm 3 placed in an oil bath heated to 150°C. The hydrolysis is carried out at a pressure of 0.4 MPa with a residence time of 1 hour. The hydrolyzed stream is continuously introduced into a glass reactor with a total volume of 500 cm 3 and heated by recirculating oil through a double - wall, and by providing a lateral outlet for the residue outlet, the usable volume of the liquid contained in the reactor is kept constant (156.6 cm 3 ).

[0047] The reactor is equipped with a stirrer, a temperature probe immersed in the liquid phase, a vertical tube at the top (for extracting steam), and a condenser. The liquid (distillate) is collected in a receiving flask and analyzed.

[0048] Test time: 55 hours Hydrolysis: T = 150 °C, residence time: 1 hour, P = 0.4 MPa, ratio of water / AA heavy product = 0.5 Cracking: T = 173 °C, atmospheric pressure, residence time: 10 hours, ratio of water / AA heavy product = 0.5 · URR = 68.95% · Overall cracking rate = 94.85% · Viscosity = 0.785 Pa.s

[0049] Example 2 (comparison): Cracking without prior hydrolysis In this case, the flow of the AA heavy product is continuously introduced directly into a glass reactor with a total volume of 500 cm 3 and heated by recirculating oil through a double wall. By having a side outlet for the residue, the usable volume of the liquid contained in the reactor is kept constant (156.6 cm 3 ).

[0050] The reactor is equipped with a stirrer, a temperature probe immersed in the liquid phase, a vertical tube at the top (for extracting steam), and a condenser. The liquid (distillate) is collected in a receiving flask and analyzed.

[0051] Cracking: T = 183 °C, atmospheric pressure, residence time: 10 hours URR = 29.2% Overall cracking rate = 45.1% The viscosity after 24 hours is 1.034 Pa.s

[0052] The test was aborted because the residue outlet became blocked after 32 hours.

[0053] The results obtained are shown in Table 1 below.

[0054] Table 1 TIFF2025519426000002.tif74170

[0055] These contrasting examples demonstrate that the hydrolysis step significantly improves performance at low temperatures and reduces the viscosity of the resulting residue. By adding water, cracking can be operated without facing clogging problems.

[0056] The hydrolysis step enables the generation of a stream in which cracking is efficient (high URR and low viscosity) despite a relatively long residence time.

Claims

1. A method for regenerating heavy by-products (AAHP) from an acrylic acid production unit, comprising the following steps: i. The heavy by-products are introduced into a hydrolyzer together with water, and subjected to continuous hydrolysis for 1 to 10 hours, preferably 1 to 5 hours, at a water:AAHP ratio in the range of 0.1 to 1.3, to obtain a mixture of hydrolyzed products. ii. A step of continuously injecting the mixture of hydrolyzed products into a reactor and subjecting it to thermal cracking to produce a gaseous top stream containing acrylic acid and water, and a bottom stream (residue) in which heavy products are concentrated. iii. A process for recovering AA-rich light fractions and water that can be recycled at various points in the method. iv. A step of recovering the residue for the purpose of removal treatment. Methods that include...

2. The method according to claim 1, wherein step i) is performed at a pressure between 0.1 and 2 MPa, preferably between 0.5 and 1.5 MPa.

3. The method according to claim 1, wherein the hydrolysis temperature is between 80 and 200°C, preferably between 150 and 200°C.

4. The method according to claim 1, wherein the cracking temperature is between 140 and 260°C, preferably between 160 and 210°C.

5. The method according to claim 1, wherein the residence time of the reaction mixture in the cracking reactor is between 0.5 and 10 hours, preferably between 4 and 10 hours.

6. The method according to claim 1, wherein the bottom flow (residue) from the reactor obtained at the end of the thermal cracking operation has a dynamic viscosity of less than 1 Pa.s when measured at 100°C.

7. The method according to claim 1, comprising the step of injecting the gaseous top flow containing acrylic acid and water into a condenser.

8. The method according to claim 7, wherein at least one polymerization inhibitor is introduced in the condenser.

9. The method according to claim 1, wherein the thermal cracking reaction occurs in the absence of a catalyst.

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