Acid-catalyzed synthesis of methyl acrylate from acrylic acid and methanol
The described method addresses inefficiencies in conventional methyl acrylate synthesis by optimizing reaction conditions and distillation processes, resulting in high-purity methyl acrylate production with reduced energy and washing liquid requirements.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ROHM & HAAS CO
- Filing Date
- 2025-06-05
- Publication Date
- 2026-06-02
AI Technical Summary
Conventional processes for synthesizing methyl acrylate using an acid catalyst are inefficient and require large amounts of washing liquid and energy.
A method involving a reaction zone where a mixture of acrylic acid, methanol, and an acid catalyst is heated with a methanol-to-acrylic acid molar ratio greater than 1 and less than 2, followed by distillation and phase separation, with organic reflux and extraction to produce methyl acrylate.
The process achieves high purity methyl acrylate production with reduced energy consumption and washing liquid usage, enhancing efficiency.
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Abstract
Description
Technical Field
[0001] The present invention relates to a process for synthesizing methyl acrylate from acrylic acid and methanol using an acid catalyst.
Background Art
[0002] Various processes have been proposed for preparing (meth)acrylates from (meth)acrylic acid and alcohol using an acid catalyst.
[0003] U.S. Patent Application Publication No. 2004 / 0236143 discloses a process for preparing (meth)acrylate by reacting (meth)acrylic acid, which may be crude (meth)acrylic acid, with an alcohol in the presence of at least one acid catalyst. In this process, acrylic acid reacts with an alcohol in a reaction zone connected to a distillation unit in the presence of at least one acid catalyst. The (meth)acrylic acid is condensed together with a low-boiling solvent, a Michael adduct, and reaction water, and sent to a scrubbing unit where it is treated with a washing liquid. The effluent from the washing step is separated into an organic phase and an aqueous phase, a part of the organic phase passes through the distillation unit as reflux, and the remainder is subjected to low-boiling solvent removal, where the organic phase from the distillate is fed to a further distillation unit. The bottom product of the low-boiling solvent removal operation is subjected to purification distillation to obtain the desired ester.
Summary of the Invention
Problems to be Solved by the Invention
[0004] Conventional processes for the synthesis of methyl acrylate using an acid catalyst are inefficient and require large amounts of washing liquid and energy.
[0005] There is a need for a more efficient process to address one or more of these problems.
[0006] The present invention relates to a method for preparing methyl acrylate.
[0007] According to one aspect of the present invention, a method for preparing methyl acrylate is: a) A mixture containing acrylic acid, methanol, and an acid catalyst is heated and reacted in a reaction zone to form a product containing methyl acrylate, which is vaporized together with other light components and then supplied to a distillation zone, wherein the feed stream entering the reaction zone contains methanol to acrylic acid in a molar ratio greater than 1 and less than 2, and the residence time in the reaction zone is in the range of 0.25 to 2 hours. b) Condensing and phase-separating the distillate from the distillation zone to form an organic phase containing methyl acrylate and an aqueous phase, c) Returning a portion of the organic phase to the distillation zone as organic reflux product, d) supplying the remaining organic phase and the aqueous phase of the distillation zone to an extraction column to form a methanol-enriched aqueous effluent and an organic effluent containing methyl acrylate. [Brief explanation of the drawing]
[0008] [Figure 1] Figure 1 shows a schematic diagram of one embodiment according to the present invention. [Modes for carrying out the invention]
[0009] In the present invention, the terms “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably. The terms “comprise,” “include,” “contain,” and their variations are not limited in meaning when they appear in this specification and in the claims. That is, for example, a mixture containing a polymerization inhibitor can be interpreted as meaning that the mixture contains at least one polymerization inhibitor.
[0010] As used herein, an enumeration of numerical ranges by endpoints includes all numbers within that range (for example, 1-5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). For the purposes of the present invention, it should be understood, in accordance with what those skilled in the art would understand, that numerical ranges are intended to include and support all possible subranges that fall within that range. For example, the range 1-100 is intended to convey 1.1-100, 1-99.99, 1.01-99.99, 40-6, 1-55, etc.
[0011] Where used herein, any enumeration of numerical ranges and / or numbers, including such enumeration in the claims, can be read as including the term “about,” where the term “about” refers to numerical ranges and / or numbers that are substantially the same as those enumerated herein.
[0012] Unless otherwise stated or implied by context, all parts and percentages are based on weight, and all test methods are as of the filing date of this application. For the purposes of U.S. patent practice, the contents of any referenced patent, patent application, or published specification are incorporated by reference in whole or in equivalent U.S. editions, particularly with respect to the disclosure of definitions (to the extent that it does not conflict with any definitions specifically provided in this disclosure) and general knowledge of the art.
[0013] One aspect of the present invention relates to a method for preparing methyl acrylate, the method comprising heating a mixture containing methyl acrylate, acrylic acid, methanol, and an acid catalyst in a reaction zone to form a product containing methyl acrylate. The reaction in the reaction zone occurs in the liquid phase.
[0014] In the process of the present invention, the feed stream to the reaction zone contains methanol in a molar excess relative to acrylic acid, i.e., the molar ratio of methanol to acrylic acid supplied to the reaction zone is greater than 1. The methanol-to-acrylic acid molar ratio is the molar ratio of methanol to acrylic acid in the mixed feed stream supplied to the reaction zone, which may include both new feed entering the system and recycled stream from other unit operations in the system. As used herein, the terms “mixed feed stream” and “feed stream” mean all reactants entering the reaction zone, including reactants entering the system (i.e., new feed) and reactants recycled from other unit operations in the system.
[0015] For example, the molar ratio of methanol to acrylic acid supplied to the reaction zone may be 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8 or higher. Preferably, the molar ratio of methanol to acrylic acid is 1.1 or higher. More preferably, the molar ratio of methanol to acrylic acid is 1.2 or higher. Even more preferably, the molar ratio of methanol to acrylic acid is 1.3 or higher.
[0016] The molar ratio of methanol to acrylic acid may be 2 or less. For example, the molar ratio of methanol to acrylic acid may be 1.9, 1.8, 1.7, 1.6, or 1.5 or less. Preferably, the molar ratio of methanol to acrylic acid is 1.8 or less. More preferably, the molar ratio of methanol to acrylic acid is 1.7 or less. Even more preferably, the molar ratio of methanol to acrylic acid is 1.6 or less.
[0017] The molar ratio may be in the range of any of the endpoints disclosed above. For example, the molar ratio may be in the range of 1.1 to 1.8, 1.2 to 1.9, or 1.3 to 1.6. Preferably, the molar ratio of methanol to acrylic acid supplied to the reaction zone is in the range of 1.1 to 1.8. More preferably, the molar ratio of methanol to acrylic acid is in the range of 1.2 to 1.7. Even more preferably, the molar ratio of methanol to acrylic acid is in the range of 1.3 to 1.6.
[0018] The acrylic acid introduced into the process is preferably overhead-grade acrylic acid that has been distilled to remove dimers (e.g., Michael adducts) and heavy fraction components such as maleic acid. The acrylic acid supplied to the system may contain at least 98% by weight of acrylic acid, for example, at least 98.5% by weight of acrylic acid or at least 99% by weight of acrylic acid. Preferably, the acrylic acid is substantially free of impurities such as Michael adducts and acetic acid. As used herein, the term “substantially free of impurities” means that the acrylic acid contains less than 2% by weight of impurities, preferably less than 1.5% by weight of impurities, and more preferably less than 1% by weight of impurities.
[0019] The mixture introduced into the system (i.e., the new feed stream) contains, essentially consists of, or may consist of, acrylic acid, methanol, an acid catalyst, and optionally a polymerization inhibitor. As used herein, "essentially consisting of acrylic acid, methanol, and an acid catalyst" means that the new feed stream does not contain impurities that would contaminate the system or adversely affect the yield of methyl acrylate. As used herein, the term "new feed stream" means the material entering the system and excludes any material that is recycled within the system. Preferably, the new feed stream is supplied continuously into the system so that the process is a continuous process.
[0020] If a lower grade of acrylic acid is used, it may be purified by any known process before being supplied to the reaction zone.
[0021] Polymerization inhibitors include alkylphenols, such as o-, m- or p-cresol (methylphenol), 2-tert-butyl-4-methylphenol, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, 2-methyl-4-tert-butylphenol, 4-tert-butyl-2,6-dimethylphenol, or 2,2'-methylenebis(6-tert-butyl-4- Methylphenol; hydroxyphenols, e.g., hydroquinone, 2-methylhydroquinone, 2,5-di-tert-butylhydroquinone, pyrocatechol (1,2-dihydroxybenzene) or benzoquinone; aminophenols, e.g., para-aminophenol; nitrosophenols, e.g., para-nitrosophenol; alkoxyphenols, e.g., 2-methoxyphenol (guaiacol, pyrocatechol monomethyl ether), 2-ethoxyphenol, 2-isopropylphenol, 4-methoxyphenol (hydroquinone mono Methyl ether), mono- or di-tert-butyl-4-methoxyphenol; tocopherol, e.g., α-tocopherol and 2,3-dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2-dimethyl-7-hydroxycoumaran); N-oxyl, e.g., 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 2,2,6,6-tetramethylpiperidine- N-oxyl, 4,4',4''-tris(2,2,6,6-tetramethylpiperidine-N-oxyl) phosphite or 3-oxo-2,2,5,5-tetramethylpyrrolidine-N-oxyl; aromatic amines or phenylenediamines, e.g., N,N-diphenylamine, N-nitrosodiphenylamine, N,N'-dialkyl-para-phenylenediamine; hydroxylamines, e.g., N,N-diethylhydroxylamine; phosphorus-containing compounds, e.g., triphenylphosphine, triphenylphosphite, hypophosphorous acid or triethylphosphite;Sulfur-containing compounds, such as diphenyl sulfide or phenothiazine, may be mentioned. When contained in the feed stream, the polymerization inhibitor may be present in an amount in the range of 0.01 to 0.1% by weight. If necessary, additional polymerization inhibitors can be added at other locations in the system.;
[0022] The acid catalyst may include sulfuric acid or sulfonic acid, such as p-toluenesulfonic acid (PTSA), benzenesulfonic acid, dodecylbenzenesulfonic acid, methanesulfonic acid (MSA), and mixtures thereof. Preferably, the acid catalyst is sulfuric acid.
[0023] The acid catalyst may be present in an amount in the range of 1 to 10% by weight based on the total weight of the liquid bleed, i.e., the bottoms stream exiting the reaction zone. Preferably, the acid catalyst is present in an amount in the range of 2 to 8% by weight based on the total weight of the bottoms stream exiting the reaction zone. More preferably, the acid catalyst is present in an amount in the range of 3 to 7% by weight based on the total weight of the bottoms stream exiting the reaction zone.
[0024] The reaction zone has a volume that provides a residence time of at least 0.25 hours for the feed stream. For example, the volume of the reaction zone provides a residence time of at least 0.35 hours or at least 0.5 hours for the feed stream. Preferably, the residence time of the reaction zone is at most 2.5 hours, such as at most 2 hours, at most 1.5 hours, or at most 1 hour.
[0025] The product can exit the reaction zone as vapor entering the distillation zone or as a liquid bleed. The liquid bleed can be disposed of as organic waste. The liquid bleed can constitute less than 5% by weight based on the total amount of reactants entering the system, i.e., the mixed feed stream.
[0026] The temperature within the reaction zone can be in the range of 60 to 160 °C, preferably 70 to 150 °C, more preferably 90 to 140 °C, and even more preferably 100 to 130 °C. The column can be operated at atmospheric pressure. Thus, the reaction zone can be operated at a pressure slightly higher than atmospheric pressure, such as 0.1 to 5 psig.
[0027] As used herein, the term "reaction zone" refers to the location where the reaction of acrylic acid and methanol occurs in the presence of an acid catalyst. The reaction zone comprises a reactor such as a glass-lined vessel having, for example, a reboiler for heating to the reaction temperature and for removing or separating product / lights by distillation from the bottommost stage of the catalyst or distillation column. Preferably, the reaction zone comprises a reactor that functions as a feed to the distillation column.
[0028] As used herein, the term "distillation zone" refers to the region within a distillation column where component separation takes place. The distillation zone may comprise a distillation column connected to a reactor (i.e., the reaction zone). If the reaction zone comprises the bottommost stage of the distillation column, the distillation zone may comprise other stages of the distillation column. Preferably, the distillation zone comprises a distillation column that is connected to a separate reactor that comprises the reaction zone and functions as the bottommost stage of the column.
[0029] The distillate from the distillation zone can be condensed by any conventional means such as, for example, shell and tube condensers to form a condensate comprising a two-phase distillate product. The condensate can be phase separated to form an organic phase and an aqueous phase. The phase separation can be carried out with any liquid-liquid separator known in the art such as, for example, a decanter. The organic phase mainly comprises organic components containing methyl acrylate. The aqueous phase comprises water formed in the reaction zone and a soluble fraction of the organic materials containing methanol and methyl acrylate.
[0030] A portion of the organic phase can be returned to the distillation zone as organic reflux. The portion of the organic phase returned to the distillation zone may constitute up to 67% by weight of the total amount of organic phase from the phase separator. Preferably, the portion of the organic phase returned to the distillation zone as reflux includes at least 5% by weight of the total amount of organic phase from the phase separator, for example, at least 10% by weight, at least 15% by weight, at least 20% by weight, at least 25% by weight, at least 30% by weight, or at least 40% by weight of the total amount of organic phase from the phase separator. Preferably, the portion of the organic phase returned to the distillation zone constitutes less than 67% by weight, less than 60% by weight, less than 55% by weight, or less than 50% by weight of the total amount of organic phase from the phase separator. Increasing the amount of organic phase returned to the distillation zone as reflux may increase the purity of the methyl acrylate product exiting the distillation zone, but it may also increase the size of the apparatus and the energy required.
[0031] The remaining organic phase, i.e., the organic phase that is not returned to the distillation zone as reflux, can be supplied to the extraction column. The aqueous phase can be combined with the remaining organic phase and supplied to the extraction column.
[0032] In the extraction column, water is used to bulk separate excess methanol from the organic phase. The extraction column provides a methanol-enriched aqueous effluent and an organic effluent mainly containing methyl acrylate. The methanol-enriched aqueous effluent also contains soluble methyl acrylate.
[0033] The methanol-enriched aqueous effluent can then be fed to an alcohol recovery column. The alcohol recovery column may include a distillation column where the methanol-enriched aqueous effluent is distilled, separating water from methanol and other organic components more volatile than water. The bottom flow contains water and is substantially free of organic substances more volatile than water.
[0034] As used herein, the term “substantially free of organic matter more volatile than water” means that the bottom flow contains less than 2% by weight of organic matter more volatile than water, preferably less than 1% by weight, and more preferably less than 0.5% by weight, of organic matter more volatile than water, based on the total weight of the bottom flow. Preferably, the bottom flow consists substantially of water. As used herein, the term “substantially composed of water” means that the bottom flow contains at least 97% by weight of water, preferably at least 98% by weight, more preferably at least 99% by weight, and even more preferably at least 99.5% by weight, based on the total volume of the bottom flow.
[0035] The distillate from the alcohol recovery column contains methanol and organic components that are more volatile than water, such as methyl acrylate. The distillate from the alcohol recovery column may be condensed whole or partially, and a portion of the condensed distillate may be returned to the alcohol recovery column as reflux. This reflux may constitute, for example, at least 65% by weight of the total weight of the condensed distillate. Preferably, the portion of the condensed distillate supplied to the alcohol recovery column as reflux may constitute at least 75% by weight, more preferably at least 85% by weight, of the total weight of the condensed distillate. The remainder of the distillate from the alcohol recovery column can be recycled to the reaction zone.
[0036] The bottom flow from the alcohol recovery column can be disposed of as waste. Alternatively, a portion of the bottom flow from the alcohol recovery column can be recycled and supplied to the extraction column along with water used for bulk separation of excess alcohol from the organic phase. Preferably, a portion of the bottom flow is recycled.
[0037] The organic effluent from the extraction column is fed to a light material removal column, and the organic effluent can be separated into a distillate containing organic matter more volatile than methyl acrylate and a bottom flow.
[0038] The distillate from the light-removal column may contain methanol, water, and methyl acetate. The distillate from the light-removal column may be partially condensed, and the distillate may be separated into an organic phase and an aqueous phase. Some light impurities may not condense and may be discharged from the process as vapor through the condenser's vent system. A portion of the organic phase may be returned to the light-removal column as organic reflux. For example, the portion of the organic phase returned to the light-removal column as reflux constitutes at least 50% by weight, e.g., at least 60% by weight, at least 70% by weight, at least 80% by weight, or at least 90% by weight of the total amount of organic phase from the phase separator. The remainder of the organic phase may be recycled into the feed for the extraction column. The aqueous phase may also be recycled to the extraction column and mixed with the feed for the extraction column together with the remainder of the organic phase.
[0039] Preferably, less than 15% by weight of the total feed entering the light material removal column is removed as a light fraction in the distillate. More preferably, less than 13% by weight of the total feed entering the light material removal column is removed as a light fraction in the distillate. Even more preferably, less than 11% by weight of the total feed entering the light material removal column is removed as a light fraction in the distillate.
[0040] Occasionally, a small portion of the organic phase from the light fraction removal column is discharged from the system to facilitate the removal of light fractions accumulated during the process.
[0041] The bottom flow from the light material removal column can be supplied to the finish column.
[0042] In the finishing column, the bottom flow from the light material removal column is separated, forming a distillate containing methyl acrylate and a bottom flow containing heavier components less volatile than methyl acrylate. Preferably, the distillate from the finishing column constitutes at least 85% by weight of the total feed to the finishing column. More preferably, the distillate from the finishing column constitutes at least 90% by weight of the total feed to the finishing column, and even more preferably, at least 95% by weight of the total feed to the finishing column.
[0043] The distillate from the finishing column may be condensed, and a portion of the condensed distillate may be supplied to the finishing column as reflux. The remainder of the condensed distillate forms a methyl acrylate product stream. The portion of the condensed distillate supplied to the finishing column as reflux may constitute, for example, at least 10% by weight of the total weight of the condensed distillate. Preferably, the portion of the condensed distillate supplied to the finishing column as reflux may constitute at least 20% by weight, more preferably at least 45% by weight, of the total weight of the condensed distillate.
[0044] The product stream may contain at least 98% by weight of methyl acrylate relative to the total weight of the product stream. Preferably, the product stream contains at least 99% by weight of methyl acrylate, more preferably at least 99.5% by weight of methyl acrylate.
[0045] By recycling the bottom flow from the finishing column into the reaction zone, any additional methyl acrylate that may have exited the finishing column in the bottom flow can be recovered.
[0046] One embodiment of the process according to the present invention is schematically shown in the drawings. System 100 has a reactor column 10 supplied by a fresh feed of acrylic acid 1, methanol 2, and acid catalyst 3. The fresh feed enters the bottom section of the reactor column 10, which is heated and functions as a reaction zone. Liquid bleed 12 exits the bottom section of the reactor column 10. The upper section of the reactor column 10 functions as a distillation zone for rectifying the reaction product, and the distillate 11 exits the top of the reactor column 10.
[0047] The distillate 11 from the reactor column 10 is condensed and then separated into an organic phase 21 and an aqueous phase 22 in the decanter 20. A portion 21' of the organic phase 21 is returned to the reactor column 10 as reflux, and the remaining 21'' of the organic phase 21 is mixed with the aqueous phase 22 and fed to the extraction column 30.
[0048] A new water feed 4 enters the top of the extraction column 30 and is used for bulk separation of excess methanol. The methanol-enriched aqueous effluent 32 exits the bottom of the extraction column 30, and the organic effluent 31 exits the top of the extraction column 30.
[0049] The methanol-enriched aqueous effluent 32 is fed to the alcohol recovery column 40, where the distillate 41 exits the top of the alcohol recovery column 40 and the bottom flow 42 exits the bottom of the alcohol recovery column. A portion 41' of the distillate 41 is returned to the column as reflux, and the remaining 41'' of the distillate 41 is recycled to the reactor column 10 and joins with the feed flow. A portion 42' of the bottom flow 42 of the alcohol recovery column 40 is recycled to the top of the extraction column 30 and joins with a new water feed 4, and the remaining 42'' of the bottom flow 42 is sent to the waste.
[0050] The organic effluent 31 from the extraction column 30 is fed to the light material removal column 50. The distillate 51 from the light material removal column 50 is condensed and then separated into an organic phase 61 and an aqueous phase 62 in the decanter 60. A portion 61' of the organic phase 61 exiting the decanter 60 is returned to the light material removal column 50 as reflux, another portion 61'' of the organic phase 61 is discharged from the system, and the remaining 61''' of the organic phase 61 is mixed with the aqueous phase 62 and recycled back to the extractor along with the reactor column distillate 21'' and 22 feeds heading towards the extraction column 30.
[0051] The bottom flow 52 of the light material removal column 50 is supplied to the finish column 70. The distillate 71 exits the top of the finish column 70, a portion 71' of the distillate 71 is returned to the column as reflux, and the remaining 71'' of the distillate 71 contains the methyl acrylate product. The bottom flow 72 is recycled to the reactor column 10.
[0052] In the diagram, the mixed feed to the reactor column 10 consists of a fresh feed (i.e., acrylic acid 1, methanol 2, and acid catalyst 3), as well as distillate 41 from the alcohol recovery column 40 and bottom flow 72 from the finish column 70. [Examples]
[0053] The following examples illustrate the present invention, but are not intended to limit its scope.
[0054] In the embodiments of the present invention, the feed mixture was fed at a rate of 938 g / hour into the bottom of a 2-inch diameter glass Oldershaw reactor column equipped with a 550 ml working sump volume and 14 trays for rectification. The feed mixture was prepared to acrylic acid grade by distillation to remove heavy fraction components including dimers (e.g., Michael adducts) and maleic acid, and also containing 0.05 wt% phenothiazine as an inhibitor. The bulk composition of the feed mixture was 50.9 wt% acrylic acid, 34 wt% methanol, 14.4 wt% methyl acrylate, and 0.7 wt% water, resulting in a methanol-to-acrylic acid molar ratio of 1.5. If necessary, a small amount of 98 wt% sulfuric acid was added to the bottom of the column, and the composition of the bottom was maintained at 5 wt% sulfuric acid by acid titration. Furthermore, the inhibitor solution was added to the condenser at approximately 14 g / hour, and it consisted of 1.2 wt% phenothiazine and 1.2 wt% hydroquinone in methyl acrylate. In addition, the inhibitor solution was added to the reflux return line to the column at 5 g / hour, and it consisted of 1.2 wt% phenothiazine in methyl acrylate.
[0055] The bottom of the reactor column was heated and maintained at a temperature of 120°C, and the vapor product was supplied to a distillation column operating at atmospheric pressure above the upper tray, while the bottom of the column was operated at a pressure slightly above atmospheric pressure (0.2 psig) by a pressure drop through an Oldershaw column. A liquid bleed of 8 g / hour, consisting of 23 wt% acrylic acid, 55 wt% acrylic acid dimer, 6 wt% methyl acrylate, 2 wt% methanol, 5 wt% sulfuric acid, and 6 wt% water, and the remaining heavy by-products, which constituted less than 1 wt% of the total amount supplied to the reactor, were withdrawn from the bottom for level control.
[0056] The reaction product was rectified as it passed through a distillation column, and the overhead vapor was condensed to produce a two-phase distillate product, which was separated into an organic phase and an aqueous phase. The organic phase was mainly methyl acrylate, containing 10.4 wt% water, 9.4 wt% methanol, 0.6 wt% acrylic acid, 0.4 wt% methyl acetate, and small amounts of other trace impurities. The aqueous phase was water, containing 24.1 wt% methanol, 13.8 wt% methyl acrylate, 0.3 wt% acrylic acid, and small amounts of other trace impurities. Approximately 33 wt% of the condensed organic phase was returned to the distillation column as reflux, and the remaining organic and aqueous phases were sent to an extraction column.
[0057] The extraction step was performed under atmospheric conditions using a KARR® Column Bench Top Unit, Model BTU-48, with an active area of 5 / 8 inch inner diameter and 48 inches in length. Water containing 0.005 wt% hydroquinone was supplied to the top of the column at a rate of 390 g / hour to perform bulk separation of excess methanol from the organic phase and supplied to the bottom of the extraction column. A stream containing 95 wt% methyl acrylate and 5 wt% methyl acetate was also supplied to the bottom of the extraction column at a flow rate of 60 g / hour to simulate distillate recycling from the light material removal column. A methanol-enriched aqueous effluent, consisting of water containing 14 wt% methanol, 7 wt% methyl acrylate, 0.2 wt% acrylic acid, and small amounts of other trace impurities, was recovered from the bottom of the column at a rate of 630 g / hour and supplied to an alcohol recovery column to recover methyl acrylate and excess methanol. The organic effluent from the extractor consisted of methyl acrylate containing 3.2% by weight water, 1% by weight methyl acetate, 0.5% by weight acrylic acid, 0.4% by weight methanol, and small amounts of trace impurities. This effluent was collected from the top of the extraction column at a rate of 730 g / hour and fed to the light fraction removal column.
[0058] The aqueous effluent from the extractor was fed into an alcohol recovery column, a 2-inch Oldershaw column with 31 trays, and used as feed for tray 22, with methanol and methyl acrylate recovery carried out under atmospheric conditions. The aqueous effluent from the extractor consisted of water containing 9.5 wt% methanol, 5.5 wt% methyl acrylate, 0.1 wt% acrylic acid, and small amounts of trace impurities, and was fed into the alcohol recovery column at an average rate of 950 g / hour. An inhibitor solution containing 5 wt% hydroquinone in methyl acrylate was fed into the condenser at 11 g / hour. The alcohol recovery column was operated with a distillate-to-feed ratio of 0.19, and approximately 89% of the distillate was returned to the column as reflux. The average bulk composition of the distillate was 54 wt% methanol, 44 wt% methyl acrylate, 1.3 wt% water, and trace amounts of heavy matter, and was recycled back to the reactor as feed. The bottom of the alcohol recovery column consisted of water containing 0.1% by weight methyl acrylate, 0.1% by weight acrylic acid, and small amounts of other trace components.
[0059] The organic effluent from the extractor was fed into a light fraction removal column, i.e., a 2-inch Oldershaw column with 31 trays, and fed to tray 14. The column was operated at a maximum absolute pressure of 600 mmHg to remove the light fraction containing methanol and methyl acetate. The organic effluent from the extractor consisted of methyl acrylate, 3.2 wt% water, 2.3 wt% methyl acetate, 0.5 wt% acrylic acid, 0.4 wt% methanol, and 1 wt% other impurities, and was fed into the light fraction removal column at an average rate of 660 g / hour. In addition, an inhibitor solution was added to the condenser at approximately 15 g / hour, which consisted of 1.2 wt% phenothiazine and 1.2 wt% hydroquinone in methyl acrylate. Furthermore, an inhibitor solution was added to the reflux line to the column at 5 g / hour, which consisted of 1.2 wt% phenothiazine in methyl acrylate. During operation of the light material removal column, the distillate was condensed to obtain a two-phase distillate product, which was separated into an organic phase and an aqueous phase, and a portion of the organic phase was recycled back into the column. During operation of the light material removal column, approximately 92% of the organic distillate was returned to the column as reflux, and the remaining organic distillate (41 g / hour) was mixed with the aqueous distillate (20 g / hour) to make it 10% by weight of the feed flow of the light material removal column, so that it could be recycled back into the extractor feed.
[0060] The bottom of the light material removal column was fed to the purification column, a 1.25-inch Oldershaw column with 16 trays, and used as the feed for tray 6, operated at a maximum absolute pressure of 300 mmHg. In addition, during the column feed, the inhibitor solution was added to the condenser at approximately 8 g / hour and to the reflux line to the column at 15 g / hour. Both inhibitor solutions consisted of 0.1 wt% hydroquinone monomethyl ether in methyl acrylate. The finish column was operated so that 44% of the distillate was returned to the column as reflux, resulting in a distillate product to feed ratio of 90%. The composition of the 555 g / hour distillate product was 99.78 wt% methyl acrylate, containing 0.1 wt% methanol, 0.1 wt% methyl propionate, and 0.02 wt% water. The composition of the 54 g / hour subsoil was 84 wt% methyl acrylate, 6 wt% acrylic acid, and 10 wt% other heavy substances.
[0061] The bottom flow from the finishing column was recycled back into the reactor to recover methyl acrylate, leaving the heavier components in the bleed of the liquid reactor.
Claims
1. A method for preparing methyl acrylate, a) In a reaction zone, a mixture containing acrylic acid, methanol, and an acid catalyst is heated and reacted to form a product containing methyl acrylate, which is vaporized together with other light components and then fed into a distillation zone, where the feed stream entering the reaction zone contains methanol to acrylic acid in a molar ratio greater than 1 and less than 2, the residence time in the reaction zone is in the range of 0.25 to 2 hours, and the acrylic acid introduced into the process is overhead grade acrylic acid that has been distilled to remove heavy fraction components. b) Condensing and phase-separating the distillate from the distillation zone to form an organic phase containing methyl acrylate and an aqueous phase, c) Returning a portion of the organic phase to the distillation zone as organic reflux, where the portion of the organic phase returned to the distillation zone as organic reflux constitutes 20% to less than 50% by weight of the total amount of the organic phase from the phase separator. d) The remainder of the organic phase and the aqueous phase of the distillation zone are supplied to the extraction column to form a methanol-enriched aqueous effluent and an organic effluent containing methyl acrylate. e) The organic effluent is supplied from the extraction column to a light material removal column to separate the organic effluent into a distillate containing organic matter more volatile than methyl acrylate and the bottom flow, and f) A method comprising the following: the bottom flow is supplied from the light material removal column to the finish column to form a distillate containing methyl acrylate and a bottom flow containing a heavier component less volatile than methyl acrylate, the distillate from the finish column constitutes at least 90% by weight of the total amount of feed to the finish column, the distillate from the finish column is condensed, a portion of the condensed distillate is supplied to the finish column as reflux, the remainder of the condensed distillate forms a methyl acrylate product stream, the product stream contains at least 99.5% by weight of methyl acrylate relative to the total weight of the product stream, and at least a portion of the bottom flow of the finish column is recycled to the reaction zone.
2. The method according to claim 1, wherein the acid catalyst is sulfuric acid or sulfonic acid.
3. The method according to claim 1 or 2, wherein the acrylic acid entering the reaction zone as a new feed contains less than 2% by weight of impurities.
4. The method according to any one of claims 1 to 3, further comprising supplying the methanol-enriched aqueous effluent from the extraction column to an alcohol recovery column to form a methanol-containing distillate and a bottom flow, wherein the bottom flow contains less than 2% by weight of organic matter more volatile than water based on the total weight of the bottom flow.
5. The method according to claim 4, wherein at least a portion of the distillate from the alcohol recovery column is recycled to the reaction zone.
6. The method according to claim 4 or 5, wherein a portion of the bottom flow of the alcohol recovery column is recycled to the extraction column.
7. The method according to claim 1, wherein the distillate containing an organic substance more volatile than methyl acrylate is at least partially condensed and phase-separated into an organic phase and an aqueous phase, at least a portion of the organic phase is returned to the light substance removal column as organic reflux, and the remainder of the organic phase and at least a portion of the aqueous phase are recycled to the extraction column.
8. The method according to any one of claims 1 to 7, wherein the reaction zone is operated at a temperature in the range of 60 to 150°C, and the acid catalyst contains sulfuric acid in an amount in the range of 2 to 8% by weight relative to the total weight of the bottom flow leaving the reaction zone.