Optimized processing of reactor effluent in the synthesis of methacrolein from propionaldehyde and formaldehyde

Abstract

The invention relates to a process for the preparation of methylpropenal from formaldehyde and propylaldehyde in the presence of a homogeneous catalyst mixture. The resulting reaction mixture is partially transferred into a first distillation column comprising at least one column internal. The reaction mixture is partially introduced into the first distillation column above the at least one column internal and partially below the at least one column internal.

Description

Technical Field

[0001] This invention relates to a method for preparing methacrolein from formaldehyde and propionaldehyde in the presence of a homogeneous catalyst mixture. The resulting reaction mixture is partially transferred to a first distillation column comprising at least one internal component. The reaction mixture is introduced into the first distillation column partially above and partially below the at least one internal component. Background Technology

[0002] WO 2016 / 042000 A1 discloses a method for producing methacrolein from formaldehyde and propionaldehyde in the presence of a catalyst mixture comprising dimethylamine and acetic acid. The reaction is carried out in a tubular or plate reactor with a feed temperature in the range of 100°C to 150°C and an outlet temperature not exceeding 180°C. The water content in the reactor feed is in the range of 45% to 85% by weight. Based on propionaldehyde, the amount of organic base in the reactor feed is greater than 5 mol%. The pressure in the reactor is higher than the boiling pressure of the reaction mixture, and the residence time of the reaction mixture in the reactor is between 1 second and 30 seconds. The resulting reaction mixture is discharged into a column and stripped with steam. The product is obtained at the top of the column, condensed, and separated into an upper phase and a lower phase in a phase separator. The upper phase contains methacrolein, and the lower phase contains substantially water. The lower phase can be recycled back into the column. Further treatment of the recycled lower phase is not disclosed in WO 2016 / 042000 A1.

[0003] EP 3 786 146 A1 discloses a method for processing reactor outputs from the synthesis of methacrolein. The reactor outputs are expanded in an expansion vessel to obtain a gas phase and a liquid phase. The gas phase is condensed and introduced into a phase separator, where a methacrolein-containing phase and an aqueous phase are obtained. The liquid phase from the expansion vessel is transferred to a column for methacrolein extraction. The overhead stream from this column is also condensed and introduced into the phase separator. The bottom stream from this column is partially recycled back to the reactor and partially discharged as waste.

[0004] A method for preparing methacrolein (MAL) is described in DE 3 213 681, characterized in that the reaction is carried out in the presence of a secondary amine and optionally an acid, at a temperature greater than 150 °C for a reaction time of up to 25 minutes. In the best case, propionaldehyde is reacted with formalin at a temperature of 162 °C to 205 °C and a residence time of 6 seconds. The yield under this best case is 97.2%, with a low DIMAL content, but almost 1% by weight. The water content in the feed is 40% by weight, and the amine concentration is 2.5% by weight based on the water content. The significantly low yield and high DIMAL content indicate that this method is not very advantageous. After distilling off the water and methacrolein, the catalyst solution is recycled.

[0005] US 4,408,079 describes a method for preparing MAL, wherein the reaction of propionaldehyde with formalin is carried out in the presence of a secondary amine at a concentration of 0.025 to 0.75 or 0.05 to 1.5 mol and an organic acid at a concentration of 0.05 to 1.5 mol (based on 1 mol of propionaldehyde in each case) at a molar ratio of 0.9 to 1.5:1, a pH of 2.5 to 7, and a temperature of 0°C to 150°C. Therefore, the selected temperature range is significantly lower than that taught in DE 3 213 681. According to US 4,408,079, the reaction is carried out continuously in a stirred tank cascade of 2 to 3 reactors with very long reactant residence times of 10 to 90 minutes. After distillation of water and methacrolein, the catalyst solution is recycled. Because only water and methacrolein are distilled off, any higher-boiling byproducts remain in the catalyst solution, which may interfere with the reaction of propionaldehyde with formalin.

[0006] WO 2015 / 065610 A1, WO 2018 / 217961 A1, WO 2018 / 217962 A1, WO 2018 / 217963 A1 and WO 2018 / 217964 A1 disclose methods for producing anhydrous and methanol-free methacrolein, and their use in the manufacture of methacrylic acid and methyl methacrylate. A mixture of dimethylamine and acetic acid is used as a catalyst. The reaction products are transferred to a phase separator at a temperature below 20°C. The aqueous phase is recycled back to a column. The overhead stream of this column mainly contains methanol and methacrolein and can be further processed. The column also includes a side-drain stream, from which the phase mainly containing water is removed. This side-drain stream is gaseous and requires condensation before further processing.

[0007] All of the above methods require a considerable amount of catalyst for the preparation of methacrolein. Furthermore, a large amount of water is used as wastewater, and impurities are introduced into the reaction during catalyst recycling, which adversely affects the yield of methacrolein. Additionally, in some cases, the catalyst concentration increases, which is also costly.

[0008] Therefore, there is a need for a method that reduces wastewater volume while simultaneously producing high-purity methacrolein. Summary of the Invention

[0009] Purpose

[0010] Therefore, one object of the present invention is to provide a method that allows the production of high-purity methacrolein while simultaneously reducing wastewater volume.

[0011] Solution

[0012] The objective is achieved by a method for preparing methacrolein, the method comprising the steps a) to g):

[0013] a) Formaldehyde and propionaldehyde are reacted in a first reactor in the presence of a homogeneous catalyst mixture comprising at least one acid and at least one base to obtain a reaction mixture comprising methacrolein, water, methanol, the homogeneous catalyst mixture, and unconverted formaldehyde.

[0014] b) Expand the reaction mixture obtained in step a) in an expansion vessel to obtain a gas phase containing methacrolein, water, and methanol, and a liquid phase containing water, the homogeneous catalyst mixture, and unconverted formaldehyde.

[0015] c) The gas phase obtained in step b) is introduced into the first condenser and condensed in the first condenser to obtain the first condensed phase.

[0016] d) The first condensed phase obtained in step c) is separated in a first phase separator to obtain an organic phase containing methacrolein and an aqueous phase containing water, methacrolein residue, and methanol.

[0017] e) The aqueous phase obtained in step d) is introduced into a first distillation column, wherein the first distillation column comprises at least one column internal selected from trays and packing material, and wherein the aqueous phase is introduced into the first distillation column at a first feed point located above the at least one column internal.

[0018] f) Introducing the liquid phase obtained in step b) into a first distillation column, wherein the liquid phase is introduced into the first distillation column at a second feed point located below the at least one column internal.

[0019] g) Distill the aqueous phase and the liquid phase in a first distillation column to obtain a first column top stream and a first column bottom stream.

[0020] It has been surprisingly discovered that the method of the present invention allows for a reduction in the amount of homogeneous catalyst mixture throughout the entire lifespan of the method. Therefore, the method of the present invention is more cost-effective and also more sustainable.

[0021] Compared to known methods, this method can also improve the yield of methacrolein obtained in synthesis.

[0022] It can reduce wastewater volume, thereby saving a significant amount of energy.

[0023] The expansion vessel in step b) is advantageous because the reaction mixture does not need to be completely cooled. Furthermore, cooling is a result of expansion, thus requiring no additional energy consumption or equipment complexity for cooling. Therefore, the method of the present invention saves energy. The combination of the expansion vessel and the first distillation column makes the first distillation column smaller than it would be without the expansion vessel. This combination is also advantageous because the first bottom stream of the first distillation column is substantially free of methacrolein. The organic phase obtained in step c) is sufficiently pure for use in subsequent process steps, such as direct oxidative esterification.

[0024] Surprisingly, it was also found that if, in a preferred embodiment, the flow rate ratio of the aqueous phase entering the first distillation column from the phase separator to the liquid phase entering the first distillation column from the expansion vessel is in the range of 0.15 to 0.5, preferably in the range of 0.2 to 0.4, the amount of amine, particularly from the catalyst mixture preferably containing dimethylamine, and the amount of formaldehyde, both contained in the organic phase, can be reduced.

[0025] In step a), formaldehyde and propionaldehyde are reacted in a first reactor in the presence of a homogeneous catalyst mixture. The homogeneous catalyst mixture comprises at least one acid and at least one base. A reaction mixture comprising methacrolein, water, methanol, the homogeneous catalyst mixture, and unconverted formaldehyde is obtained.

[0026] As the first reactor, any reactor that allows formaldehyde and propionaldehyde to react in the presence of a homogeneous catalyst mixture is suitable. Preferably, the first reactor is a tubular reactor or a plate reactor. These reactors are known for the reaction according to step a) and are disclosed, for example, in EP 3 194 355 B1.

[0027] Method step a) can be carried out at any temperature and pressure suitable for the reaction. Preferably, the temperature is in the range of 110°C to 180°C, more preferably in the range of 120°C to 180°C, and particularly preferably in the range of 125°C to 170°C.

[0028] The pressure inside the first reactor is preferably higher than the boiling pressure of the reaction mixture at the temperature at which the reaction takes place. Therefore, the pressure inside the first reactor is preferably in the range of 10 bar to 50 bar, and particularly preferably in the range of 20 bar to 50 bar.

[0029] Therefore, the reaction in step a) is preferably carried out in the liquid phase.

[0030] Formaldehyde is typically reacted either as pure formaldehyde or as a solution. Preferably, formaldehyde is reacted as an aqueous solution. An aqueous solution of formaldehyde is also known as formalin. Preferably, the aqueous formaldehyde solution contains 35% to 60% formaldehyde based on the total weight of the aqueous solution. It will be apparent to those skilled in the art that the concentration of formaldehyde is based on the aqueous solution prior to its entry into the first reactor, particularly before the reaction in step a). This concentration may change during the reaction in step a). Based on the total weight of the aqueous solution, the aqueous solution may also contain 0.5% to 1% methanol. The aqueous solution may also contain trace amounts of formic acid, for example, approximately 100 ppm formic acid based on the total weight of the aqueous solution.

[0031] Propanal can be reacted as pure propanal or as a solution, preferably as pure propanal. In this context, "pure propanal" means, based on the total amount of water and propanal, that the propanal contains at most 5% by weight of water. Those skilled in the art will understand that the water content is based on the propanal before it enters the first reactor, particularly before the reaction in step a). This concentration may change during the reaction in step a). Propanal may also contain impurities in the ppm range, such as propionic acid.

[0032] Before the reaction in step a), the molar ratio of propionaldehyde to formaldehyde is, for example, in the range of 0.75 to 1, preferably in the range of 0.85 to 0.99, and particularly preferably in the range of 0.94 to 0.98.

[0033] The reaction in step a) is carried out in the presence of a homogeneous catalyst mixture. In this context, "homogeneous" means that when added to the first reactor, the catalyst mixture is in the same phase as the reactants formaldehyde and propionaldehyde, preferably in a liquid phase. It is possible that the phases may differ during or after the reaction, for example, a two-phase mixture may be obtained.

[0034] The homogeneous catalyst mixture contains at least one acid and at least one base.

[0035] "At least one acid" means exactly one acid or a mixture of two or more acids. Preferably, it is exactly one acid. Those skilled in the art will understand that "just one acid" means a catalyst mixture prior to the reaction in step a). Additional acids may be formed during the reaction. Those skilled in the art will also understand that additional acids may be contained in the first reactor. These acids may be, for example, acids contained in formaldehyde and / or propionaldehyde, such as formic acid and / or propionic acid.

[0036] "At least one base" means exactly one base or a mixture of two or more bases. Therefore, exactly one base is preferred. It will be apparent to those skilled in the art that "just one base" refers to a catalyst mixture prior to the reaction in step a). Additional bases may be formed during the reaction. For example, if the at least one base is or contains dimethylamine, trimethylamine is typically formed during the reaction in step a). Furthermore, it is known to those skilled in the art that the at least one base may contain trace amounts of other bases. For example, if the at least one base in a preferred embodiment is dimethylamine, the at least one base may contain approximately 40 ppm by weight of monomethylamine.

[0037] The at least one acid is typically any inorganic acid or organic mono, di, or polycarboxylic acid, preferably an organic monocarboxylic acid. Particularly preferred is an aliphatic monocarboxylic acid, particularly at least one acid selected from formic acid, acetic acid, and propionic acid. Acetic acid is particularly preferred.

[0038] The at least one base is typically an organic base. Suitable organic bases are known in themselves. Preferably, the at least one base is an organic amine, and particularly preferably an organic secondary amine. Organic secondary amines are known in themselves and are preferably selected from dimethylamine, diethylamine, methylethylamine, methylpropylamine, dipropylamine, dibutylamine, diisobutylamine, methyl isopropylamine, methyl isobutylamine, methyl sec-butylamine, methyl(2-methylpentyl)amine, methyl(2-ethylhexyl)amine, pyrrolidine, piperidine, morpholine, N-methylpiperazine, N-hydroxyethylpiperazine, piperazine, hexylmethyleneimine, diethanolamine, methylethanolamine, methylcyclohexylamine, methylcyclopentylamine, and dicyclohexylamine. Dimethylamine is particularly preferred as the at least one base.

[0039] Therefore, according to the present invention, it is preferred that the homogeneous catalyst mixture comprises acetic acid and dimethylamine.

[0040] Preferably, the homogeneous catalyst mixture comprises the at least one acid in the range of 1 to 1.5 mol, preferably 1.1 to 1.5 mol, and particularly preferably 1.1 to 1.4 mol, based on 1 mol of the at least one base. The equivalence ratio of the at least one base to the at least one acid is preferably selected such that a pH of 3.0 to 7.0, preferably 3.5 to 6.5, is obtained when measured at standard pressure and 20°C prior to the reaction in the first reactor.

[0041] Before the reaction in step a), the molar ratio of the at least one base to propionaldehyde is, for example, in the range of 0.03 to 0.15, preferably in the range of 0.05 to 0.1, and particularly in the range of 0.06 to 0.09.

[0042] Based on the total weight of all components in the first reactor before the reaction in step a), the water content in the first reactor before the reaction in step a) is, for example, in the range of 20% to 80% by weight, preferably in the range of 30% to 70% by weight, and particularly preferably in the range of 40% to 60% by weight.

[0043] A preferred embodiment of method step a) is disclosed, for example, in EP 3 194 355 B1, the contents of which are incorporated herein by reference.

[0044] During the reaction in step a), methacrolein is formed. Therefore, in step a), a reaction mixture comprising methacrolein, water, methanol, a homogeneous catalyst mixture, and unconverted formaldehyde is obtained.

[0045] The methanol contained in the reaction mixture obtained in step a) may, for example, come from an aqueous solution of formaldehyde reacted in step a).

[0046] For example, based on the total weight of the reaction mixture, the reaction mixture contains 2 to 60% by weight, preferably 5 to 40% by weight, of methacrolein.

[0047] For example, based on the total weight of the reaction mixture, the reaction mixture contains 40 to 95% by weight, preferably 50 to 90% by weight, of water.

[0048] For example, based on the total weight of the reaction mixture, the reaction mixture contains, in the range of 0.5 to 10% by weight, preferably in the range of 0.7 to 6% by weight, the at least one base contained in the homogeneous catalyst mixture.

[0049] For example, based on the total weight of the reaction mixture, the reaction mixture contains, in the range of 1% to 18% by weight, preferably in the range of 2% to 12% by weight, the at least one acid contained in the homogeneous catalyst mixture.

[0050] For example, based on the total weight of the reaction mixture, the reaction mixture contains methanol in the range of 0.01 to 0.3% by weight, preferably in the range of 0.08 to 0.28% by weight.

[0051] For example, based on the total weight of the reaction mixture, the reaction mixture contains 0.05 to 1% by weight, preferably 0.1 to 0.5% by weight, of unconverted formaldehyde.

[0052] The reaction mixture may contain other components such as dimethyl acrolein (DIMAL), trimethylamine, oligomers of methacrolein, stabilizers such as TEMPOL, and other byproducts that may form during the reaction. If the at least one base contains dimethylamine, trimethylamine is typically formed from the dimethylamine. For example, DIMAL, oligomers, and stabilizers are so-called high-boiling-point compounds. The term "high-boiling-point compound" includes compounds with boiling points higher than methacrolein.

[0053] The reaction mixture leaving the first reactor has a temperature of up to 180°C, preferably in the range of 150°C to 180°C, and particularly preferably in the range of 155°C to 170°C.

[0054] Therefore, a method in which the reaction mixture leaving the first reactor has a temperature in the range of 150°C to 180°C is also preferred.

[0055] The reaction mixture preferably has a pressure in the range of 15 bar (absolute) to 100 bar (absolute) when it leaves the first reactor, particularly preferably in the range of 22 bar (absolute) to 50 bar (absolute), provided that it remains liquid at the selected temperature.

[0056] In step b), the reaction mixture obtained in step a) is expanded in an expansion vessel. This yields a gas phase containing methacrolein, water, and methanol, and a liquid phase containing water, a homogeneous catalyst mixture, and unconverted formaldehyde.

[0057] Expansion vessels typically have an internal temperature ranging from 50°C to 150°C, preferably from 70°C to 100°C. Expansion vessels typically have an internal pressure ranging from 900 mbar to 1.1 bar.

[0058] The expansion of the reaction mixture in step b) causes a portion of the reaction mixture to enter the gas phase, which produces the gas phase obtained in step b).

[0059] Based on the total weight of the gas phase, the gas phase contains typically 19% to 95% by weight, preferably 29% to 90% by weight of methacrolein.

[0060] Based on the total weight of the gas phase, which typically contains water in the range of 4% to 80% by weight, preferably in the range of 9% to 70% by weight.

[0061] Based on the total weight of the gas phase, the gas phase contains methanol, typically in the range of 0.05 wt% to 0.5 wt%, preferably in the range of 0.1 wt% to 0.4 wt%.

[0062] The gas phase may contain other components also included in the reaction mixture, such as homogeneous catalyst mixtures, stabilizers, and DIMAL.

[0063] Preferably, the gas phase further comprises amines. Amines that may be included in the gas phase are particularly those contained as at least one base in the homogeneous catalyst mixture or as a byproduct formed therefrom. Therefore, amines that may be included in the gas phase are particularly dimethylamine and / or trimethylamine.

[0064] For example, based on the total weight of the gas phase, the gas phase may contain up to 1500 ppm by weight of amine.

[0065] The gas phase may also additionally contain at least one of the acids contained in the homogeneous catalyst mixture.

[0066] For example, based on the total weight of the gas phase, the gas phase may contain the at least one acid in the range of 0.01 wt ppm to 0.25 wt ppm, preferably in the range of 0.05 wt ppm to 0.15 wt ppm.

[0067] The liquid phase obtained in step b) contains water, a homogeneous catalyst mixture, and unconverted formaldehyde.

[0068] Based on the total weight of the liquid phase, the liquid phase typically contains water in the range of 55% to 97% by weight, preferably in the range of 70% to 95% by weight.

[0069] Based on the total weight of the liquid phase, the liquid phase contains, typically in the range of 2% to 22% by weight, preferably in the range of 4% to 18% by weight, the at least one acid contained in the homogeneous catalyst mixture.

[0070] Based on the total weight of the liquid phase, the liquid phase contains, typically in the range of 1 wt% to 12 wt%, preferably in the range of 2 wt% to 10 wt%, the at least one base or the reaction product of the at least one base contained in the homogeneous catalyst mixture. For example, in the case of dimethylamine as the at least one base, the reaction product of the at least one base is monomethylamine and / or trimethylamine.

[0071] Based on the total weight of the liquid phase, the liquid phase contains unconverted formaldehyde, typically in the range of 0.01 wt% to 2 wt%, preferably in the range of 0.2 wt% to 1 wt%.

[0072] The liquid phase may contain other components also included in the reaction mixture, such as high-boiling-point compounds like stabilizers, and DIMAL. The liquid phase may in particular contain methacrolein residues. In this context, "methacrolein residues" refers to methacrolein in a range of, for example, from 0.5% to 6% by weight, preferably from 1.5% to 4% by weight, based on the total weight of the liquid phase.

[0073] In step c), the gas phase obtained in step b) is introduced into a first condenser and condensed therein to obtain a first condensed phase. Preferably, this gas phase is condensed together with the first overhead feed obtained in step g) of the method of the present invention in the first condenser. Therefore, the first condensed phase preferably comprises the gas phase in condensed form (i.e., liquid phase) and the first overhead feed. Any condenser known to those skilled in the art can be used as the first condenser. More than one first condenser can also be used. For example, a cascade of first condensers can be used. For example, the first condenser in the cascade can use water in the temperature range of 20°C to 40°C, and the second condenser in the cascade can use cooled brine in the temperature range of 3°C to 10°C.

[0074] In step d), the first condensed phase obtained in step c) is introduced into a first phase separator and separated therein. This yields an organic phase containing methacrolein and an aqueous phase containing water, methacrolein residue, and methanol.

[0075] The organic phase may additionally contain water. For example, based on the total weight of the organic phase, the organic phase contains water in the range of 1% to 2% by weight.

[0076] The organic phase may additionally contain methanol. For example, based on the total weight of the organic phase, the organic phase contains methanol in the range of 0.2% to 0.5% by weight.

[0077] Therefore, based on the total weight of the organic phase, the organic phase contains 95% to 98% methacrolein.

[0078] Surprisingly, the resulting organic phase contained only trace amounts of amines. In the context of organic phases, "trace amines" means, for example, at most 0.01% by weight of amine based on the total weight of the organic phase. The organic phase may also contain trace amounts of high-boiling compounds, such as DIMAL.

[0079] The organic phase can be further reacted. For example, the organic phase can be transferred to a direct oxidative esterification (DOE) step. This method is described, for example, in US 11,661,395, the contents of which are incorporated herein by reference.

[0080] Based on the total weight of the aqueous phase, the aqueous phase obtained in step d) contains, for example, water in the range of 85% to 92% by weight.

[0081] Based on the total weight of the aqueous phase, the aqueous phase obtained in step d) contains, for example, methanol in the range of 2% to 4% by weight.

[0082] The aqueous phase obtained in step d) contains methacrolein residue. In this context, "methacrolein residue" refers to methacrolein in the range of 0.5% to 8% by weight based on the total weight of the aqueous phase.

[0083] The aqueous phase obtained in step d) preferably contains trimethylamine. The trimethylamine may be formed from dimethylamine contained in a homogeneous catalyst mixture. For example, the aqueous phase contains trimethylamine in the range of 200 ppm by weight to 3000 ppm by weight based on the total weight of the aqueous phase.

[0084] The aqueous phase obtained in step d) preferably contains acetic acid contained in the homogeneous catalyst mixture. For example, based on the total weight of the aqueous phase, the aqueous phase contains acetic acid in the range of 500 ppm by weight to 3000 ppm by weight.

[0085] The aqueous phase preferably has a pH value of less than 7 at 20°C. Therefore, it is preferable that the aqueous phase is acidic. More preferably, the aqueous phase is acidic because it contains an excess of the at least one acid contained in the homogeneous catalyst mixture relative to the at least one base contained in the homogeneous catalyst mixture and the byproducts formed therefrom.

[0086] Therefore, a method in which the aqueous phase obtained in the phase separator has a pH value of less than 7 at 20°C is also preferred.

[0087] Suitable first-phase separators for performing step d) are known to those skilled in the art, such as decanters, centrifuges, and / or coalescers. A decanter is preferred as the first-phase separator.

[0088] In step e), the aqueous phase obtained in step d) is introduced into a first distillation column. The first distillation column contains at least one column internal selected from trays and packing materials. The aqueous phase is introduced into the first distillation column at a first feed point located above the at least one column internal.

[0089] As a first distillation column, any column containing at least one column internal known to those skilled in the art is suitable.

[0090] "At least one tower internal" means exactly one tower internal as well as two or more tower internals. Preferably, it means two or more tower internals.

[0091] According to the invention, the at least one column internal is selected from trays and packing materials. These column internals are known in themselves. Suitable trays are, for example, bubble cap trays, sieve trays, stepped trays, and valve trays. Suitable packing materials are, for example, Raschig rings or structured metal plates (e.g., Sulzer Mellapak). TM ).

[0092] The first distillation column can be operated at standard pressure, for example, such that the bottom temperature of the column is slightly above 100°C. The top temperature of the distillation column is preferably in the range of 90°C to 99°C, and more preferably in the range of 91°C to 97°C.

[0093] In step f), the liquid phase obtained in step b) is introduced into the first distillation column at a second feed point. The second feed point is located below the at least one column internal.

[0094] Preferably, the first distillation column includes two or more column internals, and the second feed point is located below the first column internals and above the second column internals.

[0095] Therefore, a preferred method is one in which the first distillation column comprises two or more column internals and the second feed point is located below the first column internals and above the second column internals.

[0096] Preferably, the flow rate ratio of the aqueous phase (step e) obtained in the phase separator in step d) entering the first distillation column to the liquid phase (step f) obtained in step b) entering the first distillation column is in the range of 0.15 to 0.5, and more preferably in the range of 0.2 to 0.4.

[0097] Therefore, it is also preferred that the flow ratio of the aqueous phase entering the first distillation column from the phase separator to the liquid phase entering the first distillation column from the expansion vessel is in the range of 0.15 to 0.5, preferably in the range of 0.2 to 0.4.

[0098] In step g), the aqueous phase and the liquid phase are distilled in the first distillation column to obtain the first column top stream and the first column bottom stream.

[0099] The first column top feed stream contains methacrolein, water, and methanol.

[0100] For example, based on the total weight of the first overhead feed stream, the first overhead feed stream contains 15% to 50% methacrolein.

[0101] For example, based on the total weight of the first overhead feed stream, the first overhead feed stream contains water in the range of 45% to 80% by weight.

[0102] For example, based on the total weight of the first overhead feed stream, the first overhead feed stream contains methanol in the range of 4% to 8% by weight.

[0103] Additionally, if the homogeneous catalyst mixture contains acetic acid as one of the at least one acid and dimethylamine as one of the at least one base, the first overhead feed stream may contain acetic acid and / or trace amounts of amine.

[0104] As summarized above, the first column top feed stream is preferably introduced into the first condenser together with the gas phase obtained in step b).

[0105] Therefore, a preferred method is one in which the first overhead feed stream is obtained at the top of the first distillation column and introduced into the first condenser.

[0106] The bottom stream of the first tower contains unreacted formaldehyde, water, a homogeneous catalyst mixture, and trimethylamine.

[0107] A first column bottom stream is obtained at the bottom of the first distillation column. Preferably, the first column bottom stream has a water content of at least 80% by weight based on the total weight of the first column bottom stream.

[0108] Therefore, it is also preferred to have a method in which a first column bottom stream is obtained at the bottom of the first distillation column and wherein the first column bottom stream has a water content of at least 85% by weight based on the total weight of the first column bottom stream.

[0109] A water content of at least 80% by weight in the first column bottom stream is particularly advantageous, as this reduces the risk of MAL polymerization in the phase separator. If the water content is below 80% by weight, the first column top stream may become alkaline and cause polymerization in the first phase separator.

[0110] For example, based on the total weight of the first tower bottom stream, the first tower bottom stream contains unreacted formaldehyde in the range of 0.05% to 2% by weight.

[0111] For example, based on the total weight of the first column bottoms stream, the first column bottoms stream contains 2% to 20% by weight of the at least one acid contained in the homogeneous catalyst mixture.

[0112] For example, based on the total weight of the first column bottom stream, the first column bottom stream contains 1% to 10% by weight of the at least one base contained in the homogeneous catalyst mixture.

[0113] For example, based on the total weight of the first tower bottom stream, the first tower bottom stream contains trimethylamine in the range of 0.1% to 0.6% by weight.

[0114] The bottom stream of the first tower may contain trace amounts of methacrolein.

[0115] The first portion of the bottom feed stream from the first tower can be recycled back to the first reactor. The second portion of the bottom feed stream from the first tower can be introduced into the boil-out stage. In the boil-out stage, a gas phase and an aqueous phase are obtained. The gas phase contains water and methacrolein, and the aqueous phase mainly contains water and a homogeneous catalyst mixture.

[0116] Alternatively, at least a portion of the second part of the bottom feed stream from the first tower can be discarded, for example, by discarding it into a thermal oxidizer.

[0117] Alternatively, a second portion of the bottom stream from the first column can be introduced into the third distillation column. Alternatively, the aqueous phase from the boiling stage can be introduced into the third distillation column. In this third distillation column, a third overhead stream and a third bottom stream are obtained. The third overhead stream contains water, and the third bottom stream contains a homogeneous catalyst mixture. Therefore, the homogeneous catalyst mixture is recovered in the third distillation column. The third distillation column is therefore also referred to as a "catalyst concentration unit".

[0118] Therefore, a preferred method is one in which a first portion of the first column bottom stream is recycled to a first reactor and a second portion of the first column bottom stream is introduced into a third distillation column, in which a third column overhead stream containing water and a third column bottom stream containing a homogeneous catalyst mixture are obtained.

[0119] The bottom feed stream from the third tower can be at least partially recycled back to the first reactor. It is advantageous, and therefore preferred, to discard approximately 10% to 30% of the bottom feed stream from the third tower, for example, in a thermal oxidizer.

[0120] Preferably, the ratio of the first portion of the first bottom feed stream to the second portion of the first bottom feed stream is adjusted so that the total water content in the feed to the first reactor in step a) does not exceed 56% by weight based on the total weight of the feed. Those skilled in the art will understand that this feed includes all components introduced into the first reactor, such as formaldehyde, propionaldehyde, homogeneous catalyst mixtures, etc.

[0121] Based on the total weight of the third column bottom stream, the third column bottom stream contains 10% to 30% by weight of the at least one acid contained in the homogeneous catalyst mixture.

[0122] Based on the total weight of the third tower bottom stream, the third tower bottom stream contains 2% to 19% by weight of the at least one base contained in the homogeneous catalyst mixture.

[0123] Based on the total weight of the third tower bottom stream, the third tower bottom stream typically also contains water in the range of 30% to 80% by weight.

[0124] Therefore, it is also preferred that the third column bottom stream obtained in the third distillation column contains water in the range of 30% to 80% by weight based on the total weight of the third column bottom stream.

[0125] The bottom feed stream of the third tower may also contain high-boiling-point compounds and trimethylamine.

[0126] The bottom feed stream from the third tower can be recycled back to the first reactor. This is advantageous because the homogeneous catalyst mixture can be reused, making the method of the present invention particularly economical.

[0127] Therefore, it is preferable to recycle the bottom feed stream obtained from the third distillation column back to the first reactor.

[0128] The third overhead stream obtained in the third distillation column preferably has a pH value greater than 7 at 20°C after condensation. Most of the trimethylamine contained in the second portion of the first bottom stream is obtained in the third overhead stream. The pH value of the third overhead stream depends essentially on the amount of trimethylamine obtained in the third overhead stream.

[0129] Therefore, a preferred method is one in which the third column overhead stream obtained in the third distillation column has a pH value greater than 7 at 20°C after condensation.

[0130] The third column overhead stream is preferably introduced at least partially into at least one of the biological wastewater treatment and thermal oxidizers. These methods are known in themselves. Preferably, the third column overhead stream is introduced directly into at least one of the biological wastewater treatment and thermal oxidizers. "Directly introduced" in this context means that the third column overhead stream is not condensed, but introduced in gaseous form into at least one of the biological wastewater treatment and thermal oxidizers.

[0131] In a preferred embodiment of the invention, a side feed stream is drawn from the first distillation column. The side feed stream can be in gaseous or liquid form, preferably in liquid form. Therefore, it is preferable to draw a liquid side feed stream from the first distillation column.

[0132] The side-draw stream, preferably a liquid side-draw stream, mainly comprises water, trace amounts of methacrolein, unconverted formaldehyde, trimethylamine, and at least one acid in a homogeneous catalyst mixture.

[0133] In statements relating to side-batch streams, the term “trace amounts of methacrolein” refers to methacrolein in the range of 500 to 1500 ppm by weight based on the total weight of the side-batch stream.

[0134] Based on the total weight of the side-draw stream, the side-draw stream may contain acetic acid in the range of 200 ppm by weight to 3000 ppm by weight.

[0135] Based on the total weight of the side-draw stream, the side-draw stream may contain trimethylamine in the range of 100 ppm by weight to 2000 ppm by weight.

[0136] Based on the total weight of the side-draw stream, the side-draw stream may contain unconverted formaldehyde in the range of 500 ppm by weight to 5000 ppm by weight.

[0137] Typically, based on the total weight of the side-take stream, the side-take stream contains water in the range of 98% to 99.5% by weight.

[0138] Side-flush feed, particularly liquid side-flush feed, is preferably taken out at a first extraction point. The first extraction point may be located, for example, below a first feed point and above a second feed point.

[0139] Therefore, a method for removing a side feed stream from a first distillation column is also preferred, wherein the side feed stream is removed at a first extraction point located below a first feed point and above a second feed point, wherein the side feed stream mainly comprises water, trace amounts of methacrolein, unconverted formaldehyde, and at least one acid in a homogeneous catalyst mixture.

[0140] The resulting side feed stream can be at least partially recycled back to the first distillation column.

[0141] Therefore, a method in which at least a portion of the side feed stream is recycled back to the first distillation column is also preferred.

[0142] If a side feed stream is removed from the first distillation column, the first distillation column preferably contains the following components in a given order (from top to bottom):

[0143] • First tower top material flow outlet,

[0144] • Liquid distributors for aqueous phases

[0145] • First tower internals,

[0146] • Liquid collector and side feed outlet

[0147] Liquid distributor for liquid phase

[0148] • Partial side feed inlet (can be at the same height as the liquid distributor used for the liquid phase)

[0149] One or more tower internals

[0150] • Bottom of the tower (evaporator)

[0151] As a supplement or alternative to at least partial recycling, the side-feed stream can be introduced at least partially into at least one of a biological wastewater treatment plant and a thermal oxidizer. Biological wastewater treatment plants and thermal oxidizers are known in themselves.

[0152] In a further embodiment, the resulting side feed stream can be at least partially introduced into a second distillation column. By distilling the side feed stream, a second overhead stream and a second bottom stream are obtained. The second overhead stream can be at least partially transferred to a first condenser.

[0153] The bottom feed stream from the second tower can be introduced into at least one of a biological wastewater treatment system and a thermal oxidizer. Biological wastewater treatment and thermal oxidizers are known in themselves.

[0154] Therefore, it is preferable to introduce the side feed stream into the second distillation column to obtain a second column top feed stream and a second column bottom feed stream, wherein the second column top feed stream is at least partially transferred to the first condenser.

[0155] The top feed stream of the second tower typically contains water, methacrolein, and trimethylamine.

[0156] The bottom stream of the second tower typically contains water, unreacted formaldehyde, and acetic acid. Figure Labels

[0157] A First Reactor

[0158] B Expansion Container

[0159] C First Condenser

[0160] D. First Phase Separator

[0161] E First Distillation Column

[0162] F Tower Internals

[0163] Fa First Tower Internals

[0164] Fb Second Tower Internals

[0165] G First Feed Point

[0166] H Second Feed Point

[0167] First extraction point

[0168] J Third Distillation Column

[0169] 1 formaldehyde

[0170] 2-propionaldehyde

[0171] 3 Homogeneous catalyst mixture

[0172] 3a At least one acid

[0173] 3b At least one base

[0174] 4. Reaction mixture

[0175] 5 gas phase

[0176] 6 liquid phase

[0177] 7 First condensation phase

[0178] 8 organic phases

[0179] 9 aqueous phases

[0180] 10 First tower top material flow

[0181] 11 First Tower Bottom Material Flow

[0182] The first part of the bottom material flow of the first tower in 11a

[0183] 11b First Tower Bottom Material Flow Second Part

[0184] 12Side material flow

[0185] 13 Third Tower Bottom Material Flow

[0186] The first part of the bottom material flow of the third tower 13a

[0187] The second part of the bottom material flow of the third tower in 13b

[0188] 14 Third Tower Top Material Flow Attached Figure Description

[0190] In the accompanying drawings, the same reference numerals have the same meaning and refer to the same parts of the manufacturing method.

[0191] Figure 1 This diagram illustrates a method for producing methacrolein according to existing technology. According to the diagram, formaldehyde 1 and propionaldehyde 2 are introduced into a first reactor A along with a homogeneous catalyst mixture 3 containing at least one acid 3a and at least one base 3b. Formaldehyde 1 and propionaldehyde 2 are reacted in the first reactor A in the presence of the homogeneous catalyst mixture 3 to obtain a reaction mixture 4. The reaction mixture 4 is introduced to the top of a first distillation column E. The first distillation column E includes column internals F. The reaction mixture 4 is added above the column internals F. In the first distillation column E, the reaction mixture 4 and aqueous phase 9 are distilled to obtain a first overhead stream 10 and a first bottom stream 11. The first overhead stream 10 is condensed in a first condenser C to obtain a first condensed phase 7. The first condensed phase 7 is introduced into a first phase separator D. In the first phase separator D, an organic phase 8 and an aqueous phase 9 are obtained. The aqueous phase 9 is added to the top of the first distillation column E above the column internals F. The first bottom stream 11 is divided into a first portion 11a and a second portion 11b of the first bottom stream. A first portion 11a of the first column bottom stream is recycled to the first reactor A. A second portion 11b of the first column bottom stream is partially returned to the first distillation column E and partially discarded, for example, to a thermal oxidizer.

[0192] Figure 2 This demonstrates another method for manufacturing methacrolein using existing technology. Only the method described below relates to... Figure 1 The difference is as follows: The reaction mixture 4 obtained from the first reactor 4 is introduced into the expansion vessel B. A gas phase 5 and a liquid phase 6 are obtained in the expansion vessel B. The liquid phase 6 is introduced into the first distillation column E at the second feed point H located above the column internals F. The gas phase 5 is added to the first condenser C along with the first column overhead stream 10. The aqueous phase 9 obtained from the first phase separator D is introduced into the first distillation column E at the first feed point G.

[0193] Figure 3 A method for manufacturing methacrolein according to a first embodiment of the present invention is shown. The following description only relates to… Figure 2 The differences. Figure 3 The first distillation column E shown includes a first column internal Fa and a second column internal Fb. The second feed point H of the liquid phase 6 is located below the first column internal Fa and above the second column internal Fb. The first feed point G of the aqueous phase 9 is located above the first column internal Fa.

[0194] Figure 4 A method for producing methacrolein according to a second embodiment of the present invention is shown below. Figure 3 The difference lies in the side feed stream 12 being drawn from the first distillation column E at the first extraction point I. The first extraction point I is located below the first column internals Fa and above the second column internals Fb. The first extraction point I is also located above the second feed point H.

[0195] Figure 5 A method for manufacturing methacrolein according to a third embodiment of the present invention is shown below. Figure 4 The difference is that a second portion 11b of the first column bottom stream is partially introduced into the third distillation column J. It is preferably introduced at the top of the third distillation column J. The second portion 11b of the first column bottom stream is distilled in the third distillation column J to obtain the third column top stream 14 and the third column bottom stream 13. A first portion 13a of the third column bottom stream is recycled to the first reactor A, and a second portion 13b of the third column bottom stream is partially recycled to the third distillation column J and partially discarded, for example, in a thermal oxidizer. The third column top stream 14 is also discarded, for example, in a thermal oxidizer. Detailed Implementation

[0196] Example

[0197] Comparative Example 1:

[0198] 10.9 kg / h of propionaldehyde (Oxea Oberhausen) and 10.4 kg / h of formaldehyde (55% in water) were mixed in a static mixer and preheated to approximately 126°C in an oil-heated coil heater. Approximately 20.6 kg / h of the first column bottoms stream from the first distillation column was mixed with 0.32 kg / h of acetic acid and 0.523 kg / h of dimethylamine (40% water), and the resulting homogeneous catalyst mixture was also preheated to 126°C in an oil-heated coil. Subsequently, an aldehyde solution containing formaldehyde (55% by weight in water) and propionaldehyde was mixed with the homogeneous catalyst mixture in another static mixer, and this mixture was fed into an oil-heated tubular reactor (first reactor) with a diameter of 4 mm and a length of approximately 8 m. The oil flow temperature was 156.7°C. The pressure in the first reactor was set to 30 bar using a valve located immediately downstream of the first reactor. The resulting reaction mixture is processed according to Option 1: the reaction mixture is expanded to the top of the first distillation column (ID = 100 mm) at a temperature of approximately 158°C. Below the addition point, the Sulzer Melapak is installed. TM Filling material (length = 2.5 m) and another SulzerMelapak TM Packing material (length = 3.5 m). The gas phase obtained from the expansion is fed into the condenser.

[0199] The first overhead feed stream from this first distillation column is condensed in the first condenser, and the condensed phase is fed into a decanter (first phase separator). Approximately 13.3 kg / h of methacrolein is obtained as the organic phase. The aqueous phase obtained in the first phase separator is returned to the top of the first distillation column at a mass flow rate of 7.3 kg / h.

[0200] The bottom of the first distillation column is heated with approximately 5.5 kg / h of 11 bar steam via forced circulation (approximately 600 kg / h) and a shell-and-tube heat exchanger. The first distillation column operates at standard pressure. Approximately 8.8 kg / h of the first column bottom stream is discharged as wastewater, and approximately 20.5 kg / h of the same first column bottom stream is returned to the first reactor for recycling.

[0201] Conversion rate greater than 99.9%. Molecular MAL selectivity is approximately 98.3%.

[0202] Comparative Example 2:

[0203] 9.1 kg / h of propionaldehyde (Oxea Oberhausen) and 8.7 kg / h of formaldehyde (55% in water) were mixed in a static mixer and preheated to approximately 123.4 °C in an oil-heated coil heater. Approximately 22.3 kg / h of the first column bottoms from the first distillation column was mixed with 0.27 kg / h of acetic acid and 0.44 kg / h of dimethylamine (40% water), and the resulting homogeneous catalyst mixture was also preheated to 123.4 °C in an oil-heated coil. Subsequently, an aldehyde solution containing formaldehyde (55% in water) and propionaldehyde and the homogeneous catalyst mixture were mixed in another static mixer, and this mixture was fed into an oil-heated tubular reactor (first reactor) with a diameter of 4 mm and a length of approximately 8 m. The oil flow temperature was 157 °C. The pressure in the first reactor was set to 30 bar using a valve located immediately downstream of the first reactor. The reaction mixture was then processed according to Option 2: the reaction mixture was expanded into an expansion vessel at approximately 157.4 °C. The temperature in the expansion vessel is approximately 79.3°C. The liquid phase is fed from the flash vessel (approximately 27.9 kg / h) to the top of the first distillation column. This feed is located in SulzerMelapak. TM Filler material (length = 2.5 m) and Sulzer Melapak TM Add it on top of the filler material (length = 3.5 m).

[0204] The first overhead feed stream from this first distillation column is combined with the gas phase from the expansion vessel, condensed in the first condenser, and the condensate is fed into a decanter (first phase separator). Approximately 11.1 kg / h of methacrolein is obtained as the organic phase. The aqueous phase obtained from the first phase separator is then distilled at a mass flow rate of 5.3 kg / h in the Sulzer Melapak distillation unit. TM Filler material (length = 2.5 m) and Sulzer Melapak TM The packing material (length = 3.5 m) is fed back to the top of the first distillation column. The ratio of the aqueous phase to the liquid phase fed into the first distillation column is therefore 0.19.

[0205] The first distillation column's bottom stream is heated with approximately 5 kg / h of steam (11 bar) via forced circulation (approximately 600 kg / h) and a shell-and-tube heat exchanger. The first distillation column operates at standard pressure. Approximately 7.5 kg / h of the first distillation column bottom stream is discharged as wastewater, and approximately 22.3 kg / h of the first distillation column bottom stream is returned to the first reactor for recirculation.

[0206] The conversion rate is greater than 99.9%. The selectivity for molar methacrolein (MAL) is approximately 98.3%.

[0207] Example 3:

[0208] 10.9 kg / h of propionaldehyde (Oxea Oberhausen) and 10.4 kg / h of formaldehyde (55% in water) were mixed in a static mixer and preheated to approximately 126°C in an oil-heated coil heater. Approximately 20.6 kg / h of the first column bottoms from the first distillation column was mixed with 0.32 kg / h of acetic acid and 0.523 kg / h of dimethylamine (40% water), and the resulting homogeneous catalyst mixture was preheated to 126°C in an oil-heated coil. Subsequently, an aldehyde solution containing formaldehyde (55% in water) and propionaldehyde was mixed with the homogeneous catalyst mixture in another static mixer, and this mixture was fed into an oil-heated tubular reactor (first reactor) with a diameter of 4 mm and a length of approximately 8 m. The oil flow temperature was 156.7°C. The pressure in the first reactor was set to 30 bar using a valve located immediately downstream of the first reactor. The reaction mixture was then processed according to option 3: the reaction mixture was expanded into an expansion vessel at a temperature of approximately 157.8°C. The temperature in the expansion vessel is approximately 79.2°C. Liquid phase from the expansion vessel (approximately 27.4 kg / h) is fed into the middle of a first distillation column (ID = 100 mm), which has a Sulzer Melapak above the point of liquid phase addition. TM Filler material (length = 2.5 m) and Sulzer Melapak filler material (length = 3.5 m) below the added point.

[0209] The first overhead feed stream from this first distillation column is combined with the gas phase from the expansion vessel, condensed in the first condenser, and the condensed phase is fed into a decanter (first phase separator). Approximately 13.3 kg / h of methacrolein is obtained as the organic phase. The aqueous phase obtained from the first phase separator is then distilled at a mass flow rate of 6.6 kg / h in the Sulzer Melapak distillation unit. TM Filler material (length = 2.5 m) and Sulzer Melapak TM The packing material (length = 3.5 m) is fed back to the top of the first distillation column. The ratio of the aqueous phase to the liquid phase fed into the first distillation column is therefore 0.24.

[0210] The first distillation column's bottom stream is heated with approximately 5.4 kg / h of 11 bar steam via forced circulation (approximately 600 kg / h) and a shell-and-tube heat exchanger. The first distillation column operates at standard pressure. Approximately 8.8 kg / h of the first distillation column bottom stream is discharged as wastewater, and approximately 20.6 kg / h of the same first distillation column bottom stream is returned to the first reactor for recirculation.

[0211] Conversion rate greater than 99.9%. Molecular MAL selectivity is approximately 98.3%.

[0212] Example 4:

[0213] 7.3 kg / h of propionaldehyde (Oxea Oberhausen) and 7 kg / h of formaldehyde (55% in water) were mixed in a static mixer and preheated to approximately 127.4 °C in an oil-heated coil heater. Approximately 14 kg / h of the first column bottoms from the first distillation column was mixed with 0.22 kg / h of acetic acid and 0.35 kg / h of dimethylamine (40% water), and the resulting homogeneous catalyst mixture was also preheated to 127.4 °C in an oil-heated coil. Subsequently, an aldehyde solution containing formaldehyde (55% in water) and propionaldehyde and the homogeneous catalyst mixture were mixed in another static mixer, and this mixture was fed into an oil-heated tubular reactor (first reactor) with a diameter of 4 mm and a length of approximately 8 m. The oil flow temperature was 154 °C. The pressure in the first reactor was set to 30 bar using a valve located immediately downstream of the first reactor. The reaction mixture was processed according to Option 3. The reaction mixture was expanded into an expansion vessel at approximately 157 °C. The temperature in the expansion vessel is approximately 79°C. Liquid phase from the expansion vessel (approximately 19.3 kg / h) is added to the middle of a first distillation column (ID = 100 mm), which has a Sulzer Melapak above the addition point (second feed point). TM Filler material (length = 2.5 m) and Sulzer Melapak below the second feed point. TM Filler material (length = 3.5 m).

[0214] The first overhead feed stream from this first distillation column is combined with the gas phase from the expansion vessel, condensed in the first condenser, and the condensate is fed into a decanter (first phase separator). Approximately 8.9 kg / h of methacrolein is obtained as the organic phase. The aqueous phase obtained from the first phase separator is returned to the top of the first distillation column at a mass flow rate of 9 kg / h. The ratio of aqueous phase to liquid phase fed into the first distillation column is therefore 0.46.

[0215] The first distillation column's bottom stream is heated with approximately 8.4 kg / h of 11 bar steam via forced circulation (approximately 600 kg / h) and a shell-and-tube heat exchanger. The first distillation column operates at standard pressure. Approximately 6.1 kg / h of the first distillation column bottom stream is discharged as wastewater, and approximately 14 kg / h of the same first distillation column bottom stream is returned to the first reactor as recirculation.

[0216] The conversion rate is greater than 99.9%. The selectivity for molar methacrolein (MAL) is approximately 98.3%.

[0217] Example 5:

[0218] 7.3 kg / h of propionaldehyde (Oxea Oberhausen) and 7.1 kg / h of formaldehyde (55%) were mixed in a static mixer and preheated to approximately 127.4 °C in an oil-heated coil heater. Approximately 14 kg / h of the first column bottoms from the first distillation column was mixed with 0.22 kg / h of acetic acid and 0.35 kg / h of dimethylamine (40% water), and the resulting homogeneous catalyst mixture was also preheated to 127.4 °C in an oil-heated coil. Subsequently, an aldehyde solution containing formaldehyde (55% in water) and propionaldehyde was mixed with the homogeneous catalyst mixture in another static mixer, and this mixture was fed into an oil-heated tubular reactor (first reactor) with a diameter of 4 mm and a length of approximately 8 m. The oil flow temperature was 154 °C. The pressure in the first reactor was set to 30 bar using a valve located immediately downstream of the first reactor. The reaction mixture was processed according to Option 3. The reaction mixture was expanded into an expansion vessel at approximately 157.5 °C. The temperature in the expansion vessel is approximately 77°C. Liquid phase from the expansion vessel (approximately 19.3 kg / h) is fed into the middle of a first distillation column (ID = 100 mm), which has a Sulzer Melapak above the addition point (second feed point). TM Filler material (length = 2.5 m) and Sulzer Melapak below the added point. TM Filler material (length = 3.5 m).

[0219] The first overhead feed stream from this first distillation column is combined with the gas phase from the expansion vessel, condensed in the first condenser, and the condensate is fed into a decanter (first phase separator). Approximately 8.9 kg / h of methacrolein is obtained as the organic phase. The aqueous phase obtained from the first phase separator is returned to the top of the first distillation column at a mass flow rate of 5.2 kg / h. The ratio of aqueous phase to liquid phase fed into the first distillation column is therefore 0.27.

[0220] The first distillation column's bottom stream is heated with approximately 5.3 kg / h of 11 bar steam via forced circulation (approximately 600 kg / h) and a shell-and-tube heat exchanger. The first distillation column operates at standard pressure. Approximately 6.2 kg / h of the first distillation column bottom stream is discharged as wastewater, and approximately 14 kg / h of the same first distillation column bottom stream is returned to the first reactor as recirculation.

[0221] The conversion rate is greater than 99.9%. The selectivity for molar methacrolein (MAL) is approximately 98.3%.

[0222] Example 6

[0223] 8.8 kg / h of propionaldehyde (Oxea Oberhausen) and 8.4 kg / h of formaldehyde (55% in water) were mixed in a static mixer and preheated to approximately 123°C in an oil-heated coil heater. Approximately 17 kg / h of the first column bottoms from the first distillation column was mixed with 0.26 kg / h of acetic acid and 0.42 kg / h of dimethylamine (40% water), and the resulting homogeneous catalyst mixture was also preheated to 123°C in an oil-heated coil. Subsequently, an aldehyde solution containing formaldehyde (55% in water) and propionaldehyde and the homogeneous catalyst mixture were mixed in another static mixer, and this mixture was fed into an oil-heated tubular reactor (first reactor) with a diameter of 4 mm and a length of approximately 8 m. The oil flow temperature was 153.9°C. The pressure in the first reactor was set to 30 bar using a valve located immediately downstream of the first reactor. The reaction mixture was processed according to option 3. The reaction mixture was expanded into an expansion vessel at approximately 157.4°C. The temperature in the expansion vessel is approximately 79.1°C. Liquid phase from the expansion vessel (approximately 23 kg / h) is added to the middle of the first distillation column (ID = 100 mm), which has a Sulzer Melapak above the addition point (second feed point). TM Filler material (length = 2.5 m) and Sulzer Melapak below the added point. TM Filler material (length = 3.5 m).

[0224] The first overhead feed stream from this first distillation column is combined with the gas phase from the expansion vessel, condensed in the first condenser, and the condensate is fed into a decanter (first phase separator). Approximately 10.7 kg / h of methacrolein is obtained as the organic phase. The aqueous phase obtained from the first phase separator is returned to the top of the first distillation column at a mass flow rate of 5.2 kg / h. The ratio of aqueous phase to liquid phase fed into the first distillation column is therefore 0.23.

[0225] The first distillation column's bottom stream is heated with approximately 4.7 kg / h of 11 bar steam via forced circulation (approximately 600 kg / h) and a shell-and-tube heat exchanger. The first distillation column operates at standard pressure. Approximately 7.3 kg / h of the first distillation column bottom stream is discharged as wastewater, and approximately 17 kg / h of the same first distillation column bottom stream is returned to the first reactor as recirculation.

[0226] The conversion rate is greater than 99.9%. The selectivity for molar methacrolein (MAL) is approximately 98.3%.

[0227] Example 7

[0228] 10.9 kg / h of propionaldehyde (Oxea Oberhausen) and 10.4 kg / h of formaldehyde (55% in water) were mixed in a static mixer and preheated to approximately 126°C in an oil-heated coil heater. Approximately 20.6 kg / h of the first column bottoms from the first distillation column was mixed with 0.27 kg / h of acetic acid and 0.43 kg / h of dimethylamine (40% water), and the resulting homogeneous catalyst mixture was also preheated to 126°C in an oil-heated coil. Subsequently, an aldehyde solution containing formaldehyde (55% in water) and propionaldehyde was mixed with the homogeneous catalyst mixture in another static mixer, and this mixture was fed into an oil-heated tubular reactor (first reactor) with a diameter of 4 mm and a length of approximately 8 m. The oil flow temperature was 155.7°C. The pressure in the first reactor was set to 30 bar using a valve located immediately downstream of the first reactor. The reaction mixture was then processed according to option 4: the reaction mixture was expanded into an expansion vessel at a temperature of approximately 157.3°C. The temperature in the expansion vessel is approximately 79.3°C. Liquid phase from the expansion vessel (approximately 30 kg / h) is fed into the middle of a first distillation column (ID = 100 mm), which has a Sulzer Melapak above the addition point (second feed point). TM Filler material (length = 2.5m) and Sulzer Melapak below the added point (second feed point). TM Filler material (length = 3.5 m).

[0229] Above the second feed point and in Sulzer Melapak TM Below the packing material (length = 2.5 m), a water collector is located in the first distillation column, which collects the liquid effluent from the aforementioned packing material located above the second feed point. A side feed stream of 1.5 kg / h is drawn from this collector.

[0230] The first overhead feed stream from this first distillation column is combined with the gas phase from the expansion vessel, condensed in the first condenser, and the condensed phase is fed into a decanter (first phase separator). Approximately 13.3 kg / h of methacrolein-rich organic phase is obtained. The aqueous phase obtained from the first phase separator is returned to the top of the first distillation column at a mass flow rate of 5.7 kg / h. The ratio of aqueous to liquid phase fed into the first distillation column is therefore 0.19.

[0231] The first distillation column's bottom stream is heated with approximately 5.2 kg / h of 11 bar steam via forced circulation (approximately 600 kg / h) and a shell-and-tube heat exchanger. The first distillation column operates at standard pressure. Approximately 7.5 kg / h of the first distillation column bottom stream is discharged as wastewater, and approximately 20.6 kg / h of the same first distillation column bottom stream is returned to the first reactor for recirculation.

[0232] The conversion rate is greater than 99.9%. The selectivity for molar methacrolein (MAL) is approximately 98.3%.

[0233] The side feed stream contains approximately 1000 ppm methacrolein, 1800 ppm acetic acid, 850 ppm TMA, 140 ppm DMA, and 3100 ppm formaldehyde. Losses via the side feed stream are minimal: 0.01% methacrolein, 1% acetic acid, and 0.1% formaldehyde are lost via the side feed stream. Approximately 5% of the formed TMA is discharged. The side feed stream contains approximately 14,000 ppm COD (Chemical Oxygen Demand). This represents 17% less catalyst used compared to Comparative Example 1 and Example 3 of the present invention.

[0234] The above embodiments demonstrate significant differences in the purity of the organic phase obtained in the first phase separator. Table 1 shows the amount of byproducts obtained in the organic phase.

[0235] Table 1:

[0236] As can be seen from Table 1, the post-treatment according to Option 1 (Comparative Example 1) resulted in a high amount of acetic acid (ACOH) in the obtained organic phase. The amounts of organic nitrogen (DMA and TMA) were also particularly high. Nevertheless, the amount of unreacted formaldehyde (FO) was quite low.

[0237] The post-treatment according to Option 2 (Comparative Example 2) resulted in lower amounts of ACOH and organic nitrogen (org. N), but still higher than in the embodiments of the present invention. Nevertheless, it demonstrates the advantage of using an expansion container. The amount of FO was higher than in Comparative Example 1.

[0238] The post-treatment according to Option 3 (Examples 3 to 6 of the present invention) resulted in a significant reduction in the amounts of ACOH and organic nitrogen. It can also be seen that the amount of FO is correlated with reflux. The higher the reflux, the more FO is contained in the organic phase.

[0239] If the side feed stream is removed separately (Option 4, Example 7 of the present invention), ACOH and organic nitrogen are reduced. FO is also almost as low as Comparative Example 1 (Option 1).

[0240] Example 8

[0241] In a stainless steel pressure vessel equipped with EKATO Phasejet and EKATO Combijet stirrers, 1 kg of catalyst containing 0.91 wt% gold, 1.10 wt% cobalt, 2.7 wt% magnesium, 7.4 wt% Al₂O₃, and 87.8 wt% SiO₂ (produced according to WO 2022 / 017755 A1, Examples 1 and 2a) was dispersed in methanol, thereby achieving a 9% solids concentration in the suspension. The suspension was pressurized to 5 bar absolute pressure under nitrogen at 80°C. Methacrolein and methanol, along with 100 ppm of TEMPOL stabilizer, were continuously metered at the inlet at a molar ratio of 1:4. The reactor was simultaneously purged with oxygen to achieve an oxygen concentration of 4 vol% in the reactor exhaust (explosion limit 7.8 vol% oxygen). The inlet flow rate and thus the residence time were adjusted to achieve a catalyst loading of 10 mol methacrolein / kg catalyst × 10 h. The pH of the reaction was kept constant at 7 by adding a solution of 4% NaOH, 5.5% H2O, and 90.5% methanol. The reactor was sampled periodically and analyzed using GC. Each batch of methacrolein was metered over a 150-hour period, excluding the first 50 hours in performance testing to ensure that the previous batch of methacrolein was exhausted or removed from the reactor system.

[0242] Table 2 shows the reaction results of methacrolein (organic phase) obtained in the above examples.

[0243] Table 2:

[0244] As can be seen from Table 2, the increase in the amount of organic nitrogen and / or FO in the organic phase leads to a lower conversion rate of MAL.

[0245] The table does not include the results for Comparative Example 1. During the reaction of the organic phase from this embodiment, the 15 mm metal sintered filter in the methacrolein feed line became clogged due to the large amount of organic nitrogen in the organic phase. Therefore, the reaction had to be stopped to clean the filter and was not restarted due to the risk of reclogging.

Claims

1. A method for preparing methacrolein, comprising the steps a) to g): a) Formaldehyde and propionaldehyde are reacted in a first reactor in the presence of a homogeneous catalyst mixture comprising at least one acid and at least one base to obtain a reaction mixture comprising methacrolein, water, methanol, the homogeneous catalyst mixture, and unconverted formaldehyde. b) Expand the reaction mixture obtained in step a) in an expansion vessel to obtain a gas phase containing methacrolein, water, and methanol, and a liquid phase containing water, the homogeneous catalyst mixture, and unconverted formaldehyde. c) The gas phase obtained in step b) is introduced into the first condenser and condensed in the first condenser to obtain the first condensed phase. d) The first condensed phase obtained in step c) is separated in a first phase separator to obtain an organic phase containing methacrolein and an aqueous phase containing water, methacrolein residue, and methanol. e) Introducing the aqueous phase obtained in step d) into a first distillation column, wherein the first distillation column includes at least one column internal selected from trays and packing materials, and wherein the aqueous phase is introduced into the first distillation column at a first feed point located above the at least one column internal. f) Introducing the liquid phase obtained in step b) into a first distillation column, wherein the liquid phase is introduced into the first distillation column at a second feed point located below the at least one column internal. g) Distill the aqueous phase and the liquid phase in a first distillation column to obtain a first column top stream and a first column bottom stream.

2. The method of claim 1, wherein a side feed stream is taken from a first distillation column, wherein the side feed stream is taken from a first extraction point located below a first feed point and above a second feed point, wherein the side feed stream primarily comprises water, trace amounts of methacrolein, unconverted formaldehyde, and at least one acid of the homogeneous catalyst mixture.

3. The method of claim 2, wherein at least a portion of the side feed stream is recycled back to the first distillation column.

4. The method according to any one of claims 1 to 3, wherein the first overhead feed stream is obtained at the top of the first distillation column and introduced into the first condenser.

5. The method according to any one of claims 1 to 4, wherein the first column bottom stream is obtained at the bottom of the first distillation column, and wherein the first column bottom stream has a water content of at least 85% by weight based on the total weight of the first column bottom stream.

6. The method according to any one of claims 2 to 5, wherein the side feed stream is introduced into a second distillation column to obtain a second overhead stream and a second bottom stream, wherein at least a portion of the second overhead stream is transferred to a first condenser.

7. The method according to any one of claims 1 to 6, wherein a first portion of the first column bottom stream is recycled to the first reactor and a second portion of the first column bottom stream is introduced into a third distillation column, wherein a third column overhead stream containing water and a third column bottom stream containing the homogeneous catalyst mixture are obtained.

8. The method of claim 7, wherein the third column bottom stream obtained in the third distillation column is recycled to the first reactor.

9. The method according to claim 7 or 8, wherein the third column bottom stream obtained in the third distillation column contains water in the range of 30% to 80% by weight based on the total weight of the third column bottom stream.

10. The method according to any one of claims 7 to 9, wherein the third column overhead stream obtained in the third distillation column has a pH value greater than 7 at 20°C after condensation.

11. The method according to any one of claims 1 to 10, wherein the reaction mixture exiting the first reactor has a temperature in the range of 150°C to 180°C.

12. The method according to any one of claims 1 to 11, wherein the aqueous phase obtained in the phase separator has a pH value of less than 7 at 20°C.

13. The method according to any one of claims 1 to 12, wherein the homogeneous catalyst mixture comprises acetic acid and dimethylamine.

14. The method according to any one of claims 1 to 13, wherein the first distillation column comprises two or more column internals, and wherein the second feed point is located below the first column internals and above the second column internals.

15. The method according to any one of claims 2 to 14, wherein the flow ratio of the aqueous phase entering the first distillation column from the phase separator to the liquid phase entering the first distillation column from the expansion vessel is in the range of 0.15 to 0.5, preferably in the range of 0.2 to 0.4.

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