Acid catalyzed synthesis of methyl acrylate from acrylic acid and methanol

Abstract

To provide a method for preparing methyl acrylate from acrylic acid and methanol using acid catalysts.SOLUTION: A method for preparing methyl acrylate comprises: a) heating in a reaction zone a mixture comprising acrylic acid, methanol, and an acid catalyst to react and form a reaction product comprising methyl acrylate which is vaporized with other light components and then fed to a distillation zone, wherein a feed stream entering the reaction zone comprises methanol to acrylic acid in a molar ratio of greater than 1 and less than 2, and a residence time in the reaction zone ranges from 0.25 to 2 hours; b) condensing and phase-separating a distillate from the distillation zone to form an organic phase comprising methyl acrylate and an aqueous phase; c) returning a portion of the organic phase to the distillation zone as organic reflux; and d) feeding the remainder of the organic phase and the aqueous phase of the distillation zone to an extraction column to form a methanol rich aqueous effluent and an organic effluent comprising methyl acrylate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a process for the acid-catalyzed synthesis of methyl acrylate from acrylic acid and methanol. [Background technology]

[0002] Various processes have been proposed for the preparation of (meth)acrylates from (meth)acrylic acid and alcohols using acid catalysts.

[0003] U.S. Patent Application Publication No. 2004 / 0236143 discloses a process for preparing (meth)acrylates 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 is reacted with an alcohol in the presence of at least one acid catalyst in a reaction zone connected to a distillation unit. The (meth)acrylic acid is condensed together with low-boiling solvents, Michael adducts, and reaction water and sent to a scrubbing unit where it is treated with a wash solution. The effluent from the wash step is separated into an organic phase and an aqueous phase. A portion of the organic phase is passed as reflux in a distillation unit, while the remainder is subjected to low-boiling solvent removal, where the organic phase from the distillate is subjected 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 [Problem to be solved by the invention]

[0004] Conventional acid-catalyzed processes for the synthesis of methyl acrylate are inefficient, requiring large amounts of wash solutions and energy.

[0005] There is a need for a more efficient process that addresses one or more of these challenges.

[0006] The present invention relates to a process for preparing methyl acrylate.

[0007] According to one aspect of the present invention, a process for preparing methyl acrylate comprises the steps of: a) heating and reacting in a reaction zone a mixture comprising acrylic acid, methanol, and an acid catalyst to form a product comprising methyl acrylate, which is vaporized along with other light components, and then fed to a distillation zone, wherein the feed stream entering the reaction zone comprises a molar ratio of methanol to acrylic acid of 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 comprising methyl acrylate and an aqueous phase; c) returning a portion of the organic phase to the distillation zone as organic reflux; d) feeding the remainder of the organic phase and the aqueous phase of the distillation zone to an extraction column to form an aqueous effluent enriched in methanol and an organic effluent comprising methyl acrylate. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows a schematic diagram according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] As used herein, the terms "a," "an," "the," "at least one," and "one or more" are used interchangeably. The terms "comprise," "include," "contain," and variations thereof, do not have a limiting meaning when these terms appear in the specification and claims. That is, for example, a mixture comprising a polymerization inhibitor can be interpreted to mean that the mixture comprises at least one polymerization inhibitor.

[0010] As used herein, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). For purposes of the present invention, it should be understood that numerical ranges are intended to include and support all possible subranges subsumed within that range, consistent with what one of ordinary skill in the art would understand. For example, a range of 1 to 100 is intended to convey 1.1 to 100, 1 to 99.99, 1.01 to 99.99, 40 to 6, 1 to 55, etc.

[0011] As used herein, numerical ranges and / or recitations of values, including such recitations in the claims, can be read as including the term "about." In such cases, the term "about" refers to a numerical range and / or value that is substantially the same as that recited herein.

[0012] Unless stated to the contrary or implicit from the context, all parts and percentages are by weight and all test methods are as of the filing date of this application. For purposes of United States patent practice, the contents of any referenced patent, patent application, or published specification are incorporated by reference in their entirety, or the equivalent United States version thereof, particularly with respect to the disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure), and general knowledge in the art.

[0013] One aspect of the present invention relates to a process for preparing methyl acrylate, the process comprising heating a mixture comprising methyl acrylate, acrylic acid, methanol, and an acid catalyst in a reaction zone to react and form a product comprising methyl acrylate, the reaction occurring in the liquid phase within the reaction zone.

[0014] In the process of the present invention, the feed stream to the reaction zone comprises a molar excess of methanol relative to acrylic acid, i.e., the molar ratio of methanol to acrylic acid fed to the reaction zone is greater than 1. The molar ratio of methanol to acrylic acid is the molar ratio of methanol to acrylic acid in the combined feed stream fed to the reaction zone, which may include both fresh feeds entering the system and recycled streams from other unit operations within the system. As used herein, the terms "combined feed stream" and "feed stream" refer to all reactants entering the reaction zone, including reactants entering the system (i.e., fresh feed) and reactants recycled from other unit operations within the system.

[0015] For example, the molar ratio of methanol to acrylic acid fed to the reaction zone can be 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8 or greater. Preferably, the molar ratio of methanol to acrylic acid is 1.1 or greater. More preferably, the molar ratio of methanol to acrylic acid is 1.2 or greater. Even more preferably, the molar ratio of methanol to acrylic acid is 1.3 or greater.

[0016] The molar ratio of methanol to acrylic acid can be 2 or less. For example, the molar ratio of methanol to acrylic acid can 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 can range between any of the endpoints disclosed above. For example, the molar ratio can range from 1.1 to 1.8, 1.2 to 1.9, 1.3 to 1.6, etc. Preferably, the molar ratio of methanol to acrylic acid fed 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 heavy end components such as dimers (e.g., Michael adducts) and maleic acid. The acrylic acid fed 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 fresh feed stream) can comprise, consist essentially of, or consist of acrylic acid, methanol, an acid catalyst, and optionally, a polymerization inhibitor. As used herein, "consisting essentially of acrylic acid, methanol, and an acid catalyst" means that the fresh feed stream does not contain impurities that would foul the system or adversely affect the yield of methyl acrylate. As used herein, the term "fresh feed stream" refers to the material entering the system and excludes any material recycled within the system. Preferably, the fresh feed stream is continuously fed into the system so that the process is a continuous process.

[0020] If lower grade acrylic acid is used, the acrylic acid may be purified by any known process before being fed 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- Methylphenols; hydroxyphenols such as hydroquinone, 2-methylhydroquinone, 2,5-di-tert-butylhydroquinone, pyrocatechol (1,2-dihydroxybenzene) or benzoquinone; aminophenols such as para-aminophenol; nitrosophenols such as para-nitrosophenol; alkoxyphenols such as 2-methoxyphenol (guaiacol, pyrocatechol monomethyl ether), 2-ethoxyphenol, 2-isopropylphenol, 4-methoxyphenol (hydroquinone monomethyl ether), methyl ether), mono- or di-tert-butyl-4-methoxyphenol; tocopherols, such as α-tocopherol and 2,3-dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2-dimethyl-7-hydroxycoumaran); N-oxyls, such as 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, such as N,N-diphenylamine, N-nitrosodiphenylamine, N,N'-dialkyl-para-phenylenediamine; hydroxylamines, such as N,N-diethylhydroxylamine; phosphorus-containing compounds, such as triphenylphosphine, triphenylphosphite, hypophosphorous acid or triethylphosphite;Sulfur-containing compounds, such as diphenyl sulfide or phenothiazine, may be included. If included in the feed stream, polymerization inhibitors may be present in amounts ranging from 0.01 to 0.1% by weight. Additional polymerization inhibitors may be added elsewhere in the system, if desired.

[0022] The acid catalyst may include sulfuric acid or a 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 ranging from 1 to 10 wt. % based on the total weight of the liquid bleed, i.e., underflow, exiting the reaction zone. Preferably, the acid catalyst is present in an amount ranging from 2 to 8 wt. % based on the total weight of the underflow, exiting the reaction zone. More preferably, the acid catalyst is present in an amount ranging from 3 to 7 wt. % based on the total weight of the underflow, exiting the reaction zone.

[0024] The reaction zone has a volume that provides a residence time for the feed stream of at least 0.25 hours. For example, the volume of the reaction zone provides a residence time for the feed stream of at least 0.35 hours or at least 0.5 hours. Preferably, the residence time in the reaction zone is at most 2.5 hours, e.g., at most 2 hours, at most 1.5 hours, or at most 1 hour.

[0025] The product can exit the reaction zone as a vapor entering the distillation zone or as a liquid bleed. The liquid bleed can be disposed of as organic waste. The liquid bleed can comprise less than 5 wt. % based on the total amount of reactants entering the system, i.e., the combined feed stream.

[0026] The temperature in the reaction zone can range from 60 to 160°C, preferably from 70 to 150°C, more preferably from 90 to 140°C, and even more preferably from 100 to 130°C. The column can be operated at atmospheric pressure. Thus, the reaction zone can be operated at a pressure slightly above atmospheric pressure, for example, from 0.1 to 5 psig.

[0027] As used herein, the term "reaction zone" refers to the location where the reaction of acrylic acid with methanol occurs in the presence of an acid catalyst. The reaction zone comprises a reactor, such as, for example, a glass-lined vessel, heated to the reaction temperature and having a reboiler for distilling off products / lights for removal or separation from the catalyst or the bottom stage of the distillation column. Preferably, the reaction zone comprises a reactor that serves as a sump to the distillation column.

[0028] As used herein, the term "distillation zone" refers to the region within a distillation column where separation of components occurs. The distillation zone may comprise a distillation column connected to a reactor (i.e., reaction zone). When the reaction zone comprises the lowest stage of a distillation column, the distillation zone may comprise other stages of a distillation column. Preferably, the distillation zone comprises a distillation column that is connected to a separate reactor that comprises the reaction zone and serves as the lowest stage of the column.

[0029] The distillate from the distillation zone can be condensed by any conventional means, such as, for example, a shell and tube condenser, 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. Phase separation can be carried out in any liquid-liquid separator known in the art, such as, for example, a decanter. The organic phase primarily comprises organic components, including methyl acrylate. The aqueous phase comprises water formed in the reaction zone and soluble fractions of the organic material, including 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 can comprise up to 67 wt.% 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 comprises at least 5 wt.% of the total amount of organic phase from the phase separator, e.g., at least 10 wt.%, at least 15 wt.%, at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, or at least 40 wt.% of the total amount of organic phase from the phase separator. Preferably, the portion of the organic phase returned to the distillation zone comprises less than 67 wt.%, less than 60 wt.%, less than 55 wt.%, or less than 50 wt.% of the total amount of organic phase from the phase separator. Increasing the amount of the portion of the organic phase returned to the distillation zone as reflux can increase the purity of the methyl acrylate product exiting the distillation zone, but can also increase the size of the equipment and the energy required.

[0031] The remainder of the organic phase, i.e., the organic phase not returned to the distillation zone as reflux, may be fed to an extraction column. The aqueous phase may be combined with the remaining organic phase and fed 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 an aqueous effluent enriched in methanol and an organic effluent containing primarily methyl acrylate. The methanol-enriched aqueous effluent also contains soluble methyl acrylate.

[0033] The methanol-enriched aqueous effluent may then be fed to an alcohol recovery column, which may comprise a distillation column, in which the methanol-enriched aqueous effluent is distilled to separate the water from the methanol and other organic components more volatile than water. The understream comprises water and is substantially free of organics more volatile than water.

[0034] As used herein, the term "substantially free of organics more volatile than water" refers to an understream containing less than 2% by weight of organics more volatile than water, preferably less than 1% by weight of organics more volatile than water, and more preferably less than 0.5% by weight of organics more volatile than water, based on the total weight of the understream. Preferably, the understream is composed essentially of water. As used herein, the term "substantially composed of water" means that the understream contains at least 97% by weight of water, preferably at least 98% by weight of water, more preferably at least 99% by weight of water, and even more preferably at least 99.5% by weight of water, based on the total weight of the understream.

[0035] The distillate from the alcohol recovery column comprises methanol and organic components more volatile than water, such as methyl acrylate. The distillate from the alcohol recovery column may be wholly or partially condensed, and a portion of the condensed distillate may be returned to the alcohol recovery column as reflux. This reflux may, for example, comprise at least 65 wt.% of the total weight of the condensed distillate. Preferably, the portion of the condensed distillate fed to the alcohol recovery column as reflux may comprise at least 75 wt.%, more preferably at least 85 wt.%, of the total weight of the condensed distillate. The remainder of the distillate from the alcohol recovery column may be recycled to the reaction zone.

[0036] The bottoms stream from the alcohol recovery column can be disposed of as waste. Alternatively, a portion of the bottoms stream from the alcohol recovery column can be recycled to feed the extraction column along with water used in the bulk separation of excess alcohol from the organic phase. Preferably, a portion of the bottoms stream is recycled.

[0037] The organic effluent from the extraction column may be fed to a lights removal column where the organic effluent may be separated into a distillate containing organics more volatile than methyl acrylate and a bottoms stream.

[0038] The distillate from the lights removal column may include methanol, water, and methyl acetate. The distillate from the lights 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 be condensed and may be discharged from the process as vapor through the condenser vent system. A portion of the organic phase may be returned to the lights removal column as organic reflux. For example, the portion of the organic phase returned to the lights 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 to the extraction column feed. The aqueous phase may also be recycled to the extraction column and combined with the remainder of the organic phase into the feed to the extraction column.

[0039] Preferably, less than 15 wt.% of the total amount of feed entering the lights removal column is removed as a light fraction in the distillate. More preferably, less than 13 wt.% of the total amount of feed entering the lights removal column is removed as a light fraction in the distillate. Even more preferably, less than 11 wt.% of the total amount of feed entering the lights removal column is removed as a light fraction in the distillate.

[0040] Occasionally, a small portion of the organic phase from the lights removal column is bled from the system to facilitate removal of light ends that have accumulated during the process.

[0041] The bottom stream from the lights removal column may be fed to a finishing column.

[0042] In the finishing column, the bottoms stream from the lights removal column is separated to form a distillate comprising methyl acrylate and a bottoms stream comprising heavier components less volatile than methyl acrylate. Preferably, the distillate from the finishing column comprises at least 85 wt.% of the total feed to the finishing column. More preferably, the distillate from the finishing column comprises at least 90 wt.% of the total feed to the finishing column, and even more preferably, comprises at least 95 wt.% of the total feed to the finishing column.

[0043] The distillate from the finishing column can be condensed, and a portion of the condensed distillate can be fed to the finishing column as reflux. The remainder of the condensed distillate forms the methyl acrylate product stream. The portion of the condensed distillate fed to the finishing column as reflux can, for example, comprise at least 10 wt.% of the total weight of the condensed distillate. Preferably, the portion of the condensed distillate fed to the finishing column as reflux can comprise at least 20 wt.%, more preferably at least 45 wt.%, of the total weight of the condensed distillate.

[0044] The product stream may comprise at least 98 wt% methyl acrylate, based on the total weight of the product stream. Preferably, the product stream comprises at least 99 wt% methyl acrylate, more preferably at least 99.5 wt% methyl acrylate.

[0045] The bottoms stream from the finishing column can be recycled to the reaction zone to recover additional methyl acrylate that may have exited the bottoms finishing column.

[0046] One embodiment of a process according to the present invention is shown schematically in the drawing. System 100 has a reactor column 10 fed by a fresh feed of acrylic acid 1, methanol 2, and acid catalyst 3. The fresh feed enters the bottom stage of reactor column 10, which is heated and functions as a reaction zone. A liquid bleed 12 exits the bottom stage of reactor column 10. The top stage of reactor column 10 functions as a distillation zone for rectifying the reaction product, and distillate 11 exits the top of reactor column 10.

[0047] The distillate 11 from reactor column 10 is condensed and then separated in decanter 20 into an organic phase 21 and an aqueous phase 22. A portion 21′ of organic phase 21 is returned to reactor column 10 as reflux, and the remaining 21″ of organic phase 21 is mixed with aqueous phase 22 and fed to extraction column 30.

[0048] Fresh water feed 4 enters the top of extraction column 30 and is used for bulk separation of excess methanol. A methanol-enriched aqueous effluent 32 exits the bottom of extraction column 30, and an organic effluent 31 exits the top of extraction column 30.

[0049] The methanol-enriched aqueous effluent 32 is fed to an alcohol recovery column 40, where a distillate 41 exits the top of the alcohol recovery column 40 and a bottoms stream 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 to combine with the feed stream. A portion 42' of the bottoms stream 42 from the alcohol recovery column 40 is recycled to the top of the extraction column 30 to combine with the fresh water feed 4, and the remaining 42'' of the bottoms stream 42 is sent to waste.

[0050] The organic effluent 31 from the extraction column 30 is fed to the lights removal column 50. The distillate 51 from the lights removal column 50 is condensed and then separated in a decanter 60 into an organic phase 61 and an aqueous phase 62. A portion 61' of the organic phase 61 exiting the decanter 60 is returned to the lights removal column 50 as reflux, another portion 61'' of the organic phase 61 is discharged from the system, and the remaining portion 61''' of the organic phase 61 is mixed with the aqueous phase 62 and recycled back to the extractor along with the reactor column distillates 21'' and 22 feed to the extraction column 30.

[0051] The bottoms stream 52 from lights removal column 50 is fed to finishing column 70. Distillate 71 exits the top of finishing column 70, with a portion 71' of distillate 71 being returned to the column as reflux and the remaining portion 71'' of distillate 71 comprising methyl acrylate product. Bottoms stream 72 is recycled to reactor column 10.

[0052] In the diagram, the mixed feed to reactor column 10 is composed of fresh feed (i.e., acrylic acid 1, methanol 2, and acid catalyst 3), as well as distillate 41 from alcohol recovery column 40 and bottoms 72 from finishing column 70. [Example]

[0053] The following examples illustrate the present invention but are not intended to limit the scope of the invention.

[0054] In the present example, the feed mixture was fed at a rate of 938 g / hr to the bottom tray of a 2-inch diameter glass Oldershaw reactor column with a 550 ml working sump volume and 14 trays for rectification. The feed mixture was distilled to remove heavy end components, including dimers (e.g., Michael adducts) and maleic acid, and was prepared to an acrylic acid grade 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. Small amounts of 98 wt. % sulfuric acid were added to the bottom tray of the column as needed to maintain the bottom tray composition at 5 wt. % sulfuric acid by acid titration. Approximately 14 g / hr of inhibitor solution was added to the condenser, which consisted of 1.2 wt. % phenothiazine and 1.2 wt. % hydroquinone in methyl acrylate. Additionally, 5 g / hr of inhibitor solution was added to the reflux return line to the column, which consisted of 1.2 wt. % phenothiazine in methyl acrylate.

[0055] The bottom tray of the reactor column was heated and maintained at a temperature of 120°C, and the vapor product was fed above the top tray to a distillation column operating at atmospheric pressure, while the bottom tray of the column was operated at slightly above atmospheric pressure (0.2 psig) by pressure drop through an Oldershaw column. A liquid bleed of 8 g / hr consisting of 23 wt% acrylic acid, 55 wt% acrylic acid dimer, 6 wt% methyl acrylate, 2 wt% methanol, 5 wt% sulfuric acid, 6 wt% water, and the remaining heavy by-products, which constituted less than 1 wt% of the total amount fed to the reactor, was withdrawn from the bottom tray 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 organic and aqueous phases. The organic phase consisted primarily of methyl acrylate with 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 consisted of 24.1 wt.% methanol, 13.8 wt.% methyl acrylate, 0.3 wt.% acrylic acid, and water with 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 carried out at atmospheric conditions using a KARR® Column Bench Top Unit, Model BTU-48, with an internal diameter of 5 / 8 inch and an active area length of 48 inches. Water containing 0.005 wt.% hydroquinone was fed to the top of the column at a rate of 390 g / hr to achieve bulk separation of excess methanol from the organic phase and fed to the bottom of the extraction column. A stream containing 95 wt.% methyl acrylate and 5 wt.% methyl acetate was also fed to the bottom of the extraction column at a rate of 60 g / hr to simulate a distillate recycle from the lights 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 / hr and fed to an alcohol recovery column to recover methyl acrylate and excess methanol. The organic effluent from the extractor, which was methyl acrylate containing 3.2 wt. % water, 1 wt. % methyl acetate, 0.5 wt. % acrylic acid, 0.4 wt. % methanol and small amounts of trace impurities, was collected from the top of the extraction column at a rate of 730 g / hr and fed to the light ends removal column.

[0058] The aqueous extractor effluent was fed to an alcohol recovery column, a 2-inch Oldershaw column with 31 trays, with tray 22 serving as the feed for methanol and methyl acrylate recovery, conducted at ambient conditions. The aqueous extractor effluent, consisting of 9.5 wt.% methanol, 5.5 wt.% methyl acrylate, 0.1 wt.% acrylic acid, and water containing small amounts of trace impurities, was fed to the alcohol recovery column at an average rate of 950 g / h. The condenser was fed with an inhibitor solution containing 5 wt.% hydroquinone in methyl acrylate at 11 g / h. The alcohol recovery column was operated at a distillate-to-feed ratio of 0.19, with approximately 89% of the distillate returning 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 traces of heavies, which were recycled to the reactor as feed. The bottoms of the alcohol recovery column consisted of water containing 0.1 wt % methyl acrylate, 0.1 wt % acrylic acid, and small amounts of other trace components.

[0059] The organic extractor effluent was fed to a lights removal column, a 2-inch Oldershaw column with 31 trays, operated at a maximum pressure of 600 mmHg absolute, with tray 14 serving as the feed, to remove light ends, including methanol and methyl acetate. The extractor organic effluent 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 to the lights removal column at an average rate of 660 g / hr. Approximately 15 g / hr of inhibitor solution was added to the condenser, consisting of 1.2 wt.% phenothiazine and 1.2 wt.% hydroquinone in methyl acrylate. Additionally, 5 g / hr of inhibitor solution was added to the reflux line to the column, consisting of 1.2 wt.% phenothiazine in methyl acrylate. In operating the lights removal column, the distillate was condensed to provide a two-phase distillate product that separated into organic and aqueous phases, with a portion of the organic phase recycled to the column. In operating the lights removal column, approximately 92% of the organic distillate was returned to the column as reflux, and the remaining organic distillate (41 g / hr) was mixed with the aqueous distillate (20 g / hr) to provide 10 wt.% of the lights removal column feed stream, which could be recycled to the extractor feed.

[0060] The bottoms of the lights removal column were fed to a purification column, a 16-tray, 1.25-inch Oldershaw column, feeding tray 6 and operating at a maximum pressure of 300 mmHg absolute. The column feed also contained an inhibitor solution added to the condenser at approximately 8 g / hr and to the reflux line to the column at 15 g / hr, both inhibitor solutions consisting of 0.1 wt.% hydroquinone monomethyl ether in methyl acrylate. The finishing column was operated so that 44% of the distillate was returned to the column as reflux, giving a distillate product-to-feed ratio of 90%. The composition of the 555 g / hr distillate product was 99.78 wt.% methyl acrylate with 0.1 wt.% methanol, 0.1 wt.% methyl propionate, and 0.02 wt.% water. The composition of the 54 g / hr understream was 84 wt. % methyl acrylate, 6 wt. % acrylic acid and 10 wt. % other heavies.

[0061] The bottoms stream from the finishing column was recycled to the reactor to recover methyl acrylate, with the heavier components remaining in the liquid reactor bleed.

Claims

1. 1. A process for preparing methyl acrylate, comprising: a) heating and reacting a mixture comprising acrylic acid, methanol, and an acid catalyst in a reaction zone to form a product comprising methyl acrylate, which is vaporized along with other light components and then fed to a distillation zone, wherein a feed stream entering said reaction zone comprises a molar ratio of methanol to acrylic acid of greater than 1 and less than 2, the residence time in said reaction zone is in the range of 0.25 to 2 hours, and said acrylic acid introduced into the process is overhead grade acrylic acid that has been distilled to remove heavy end components; b) condensing and phase separating the distillate from said distillation zone to form an organic phase comprising methyl acrylate and an aqueous phase; c) returning a portion of said organic phase to said distillation zone as organic reflux; d) feeding the remainder of the organic phase and the aqueous phase of the distillation zone to an extraction column to form an aqueous effluent enriched in methanol and an organic effluent comprising methyl acrylate; e) feeding the organic effluent from the extraction column to a lights removal column to separate the organic effluent into a distillate containing organics more volatile than methyl acrylate and a bottom stream; and f) feeding the bottoms stream from the lights removal column to a finishing column to form a distillate comprising methyl acrylate and a bottoms stream comprising heavier components less volatile than methyl acrylate, the distillate from the finishing column comprising at least 90 wt.% of the total feed to the finishing column, the distillate from the finishing column being condensed, a portion of the condensed distillate being fed to the finishing column as reflux, and the remainder of the condensed distillate forming a methyl acrylate product stream, the product stream comprising at least 99.5 wt.% methyl acrylate, based on the total weight of the product stream, and at least a portion of the bottoms stream from the finishing column being recycled to the reaction zone.

2. 10. The method of claim 1, wherein the acid catalyst is sulfuric acid or a sulfonic acid.

3. 3. The process of claim 1 or 2, wherein the acrylic acid entering the reaction zone as fresh feed contains less than 2 wt. % impurities.

4. 4. The method of claim 1, further comprising feeding the methanol-enriched aqueous effluent from the extraction column to an alcohol recovery column to form a distillate comprising methanol and a bottoms stream, the bottoms stream comprising less than 2 wt. % organics more volatile than water, based on the total weight of the bottoms stream.

5. 5. The method of claim 4, wherein at least a portion of the distillate of the alcohol recovery column is recycled to the reaction zone.

6. 6. The method of claim 4 or 5, wherein a portion of the bottom stream of the alcohol recovery column is recycled to the extraction column.

7. 2. The method of claim 1, wherein the distillate containing organics 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 lights 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. 8. The process of any one of claims 1 to 7, wherein the reaction zone is operated at a temperature in the range of from 60 to 150°C and the acid catalyst comprises sulfuric acid in an amount in the range of from 2 to 8 wt%, based on the total weight of the underflow exiting the reaction zone.

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