Acid catalyzed synthesis of methyl acrylate from acrylic acid and methanol

Abstract

SOLUTION: A method for preparing methyl acrylate comprises 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. A feed stream entering the reaction zone comprises methanol and 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. A distillate from the distillation zone is condensed and phase-separated to form an organic phase comprising methyl acrylate and an aqueous phase. A portion of the organic phase is returned to the distillation zone as organic reflux. The remainder of the organic phase and the aqueous phase of the distillation zone is fed to an extraction column to form a methanol rich aqueous effluent and an organic effluent comprising methyl acrylate. The organic effluent from the extraction column is purified in a single finishing column, wherein a light fraction stream is removed from the top of the finishing column, a bottoms stream is removed from the bottom of the finishing column, and methyl acrylate is removed from a side draw stream.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

[0003] US 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 boilers, Michael adducts and reaction water and sent to a scrubbing unit and 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 as reflux in a distillation unit and the rest is subjected to low boiler removal, where the organic phase from the distillate is subjected to a further distillation unit. The bottom product in the low boiler removal operation is subjected to a 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 washes and energy, and require multiple columns for product purification, resulting in additional capital and operational costs.

[0005] A need exists for more efficient processes that address 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 a feed stream entering the reaction zone comprises methanol and acrylic acid in a molar ratio 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; e) purifying the organic effluent from the extraction column in a single polishing column; and Including, A light ends stream is removed from the top of the finishing column; A bottom stream is removed from the bottom of the finishing column; Methyl acrylate is removed from a side draw stream. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 shows a schematic diagram of one embodiment according to the invention using a distillation column with a side draw as the finishing column. [Diagram 2] FIG. 2 shows a schematic according to one embodiment of the present invention using a dividing wall column as the finishing column. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 containing a polymerization inhibitor can be interpreted to mean that the mixture contains at least one polymerization inhibitor.

[0010] As used herein, the recitation of numerical ranges by endpoints includes all numbers contained 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 is to be understood that numerical ranges are intended to include and support all possible subranges contained within the range, consistent with what one of skill in the art would understand. For example, the range 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, may be read as including the term "about." In such cases, the term "about" refers to numerical ranges and / or values ​​that are substantially the same as those recited herein.

[0012] Unless stated to the contrary or implied 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 U.S. patent practice, the contents of any referenced patent, patent application, or published specification are incorporated herein by reference in their entirety or their U.S. equivalent, particularly with respect to the disclosure of definitions to the extent not inconsistent with definitions specifically set forth in this disclosure, and with respect to the general knowledge in the art.

[0013] One aspect of the 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 to form a product comprising methyl acrylate, the reaction in the reaction zone occurring in the liquid phase.

[0014] In the process of the present invention, the feed stream to the reaction zone contains 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 mixed feed stream fed to the reaction zone, which may include both fresh feeds entering the system and recycle streams from other unit operations in the system. As used herein, the terms "mixed feed stream" and "feed stream" refer to all reactants entering the reaction zone, including reactants entering the system (i.e., fresh feeds) and reactants recycled from other unit operations in 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 more. Preferably, the molar ratio of methanol to acrylic acid is 1.1 or more. More preferably, the molar ratio of methanol to acrylic acid is 1.2 or more. Even more preferably, the molar ratio of methanol to acrylic acid is 1.3 or more.

[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 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 ranges from 1.1 to 1.8. More preferably, the molar ratio of methanol to acrylic acid ranges from 1.2 to 1.7. Even more preferably, the molar ratio of methanol to acrylic acid ranges from 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 into 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, 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, acid catalyst, and any polymerization inhibitors. As used herein, "consists essentially of acrylic acid, methanol, and 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, making the process 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, the polymerization inhibitors may be present in amounts ranging from 0.01 to 0.1 weight percent. 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 products may exit the reaction zone as vapors entering the distillation zone or as a liquid bleed. The liquid bleed may be disposed of as organic waste. The liquid bleed may comprise less than 5 wt. % based on the total amount of reactants entering the system, i.e., the combined feed streams.

[0026] The temperature in the reaction zone may 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 may be operated at atmospheric pressure. Thus, the reaction zone may 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 reaction temperature and having a reboiler for distilling off products / lights for removal or separation from the catalyst or 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 the distillation column where separation of components takes place. The distillation zone may comprise a distillation column connected to a reactor (i.e., reaction zone). When the reaction zone comprises the bottom stage of a distillation column, the distillation zone may comprise other stages of a distillation column. Preferably, the distillation zone comprises a distillation column, which is connected to a separate reactor that comprises the reaction zone and serves as the bottom 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% 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 comprises at least 5% by weight of the total amount of organic phase from the phase separator, such as at least 10% by weight, at least 15% by weight of the total amount of organic phase from the phase separator. It comprises at least 20% by weight, at least 25% by weight, at least 30% by weight, or at least 40% by weight. Preferably, the portion of the organic phase returned to the distillation zone comprises 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 the portion of the organic phase returned to the distillation zone as reflux can increase the purity of the methyl acrylate product leaving 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 aqueous effluent enriched in methanol 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 that are more volatile than water. The understream comprises water and is substantially free of organics that are more volatile than water.

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

[0035] The distillate from the alcohol recovery column comprises methanol and organic components that are 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, constitute at least 65% by weight of the total weight of the condensed distillate. Preferably, the portion of the condensed distillate fed 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 may be recycled to the reaction zone.

[0036] The bottoms stream from the alcohol recovery column may be disposed of as waste. Alternatively, a portion of the bottoms stream from the alcohol recovery column may 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 single finishing column for purification of methyl acrylate. Preferably, no further purification steps are necessary. From the finishing column, a distillate consisting of a light ends stream containing organics more volatile than methyl acrylate is removed from the top of the finishing column, a bottoms stream containing components less volatile than methyl acrylate is removed from the bottom of the finishing column, and methyl acrylate in a side draw stream is withdrawn from the middle section of the finishing column. As used herein, the term "middle section of the finishing column" means any location between the bottom and the top of the finishing column.

[0038] Preferably, less than 15 wt.% of the total amount of feed entering the finishing column is removed in the light ends stream. More preferably, less than 13 wt.% of the total amount of feed entering the finishing column is removed as a light end in the distillate. Even more preferably, less than 11 wt.% of the total amount of feed entering the finishing column is removed as a light end in the distillate.

[0039] The light ends stream from the finishing column may be partially condensed and the condensed liquid 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 via the condenser vent system. A portion of the organic phase may be returned to the finishing column as organic reflux. For example, the portion of the organic phase returned to the finishing column as reflux comprises at least 50 wt.%, such as at least 60 wt.%, preferably at least 70 wt.%, of the total amount of organic phase from the phase separator. %, more preferably at least 80 wt.%, and even more preferably at least 90 wt.% of the total amount of organic phase from the phase separator.

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

[0041] The remainder of the organic phase from the light ends stream from the finishing column may be recycled to the extraction column. Similarly, the aqueous phase from the light ends stream may be recycled to the extraction column and combined with the remaining organic phase from the light ends stream into the feed to the extraction column.

[0042] The bottoms stream from the finishing column may be recycled to the reaction zone to recover additional methyl acrylate that may have exited the bottoms finishing column. Preferably, the bottoms stream from the finishing column comprises less than 40 wt.% of the total feed to the finishing column. More preferably, the bottoms stream from the finishing column comprises less than 30 wt.% of the total feed to the finishing column, and even more preferably, comprises less than 20 wt.% of the total feed to the finishing column.

[0043] The methyl acrylate is removed from the finishing column in a sidedraw stream. The sidedraw stream may comprise at least 98 wt.% methyl acrylate, based on the total weight of the sidedraw stream. Preferably, the sidedraw stream comprises at least 99 wt.% methyl acrylate, more preferably at least 99.5 wt.% methyl acrylate.

[0044] The finishing column may comprise a distillation column with a side draw, or the finishing column may comprise a distillation column with a dividing wall that vertically divides a portion of the interior of the distillation column into two sections, i.e., a dividing wall distillation column. Dividing wall columns are known in the art and their designs are discussed, for example, by Pendergast et al., "Consider Dividing Wall Columns," Chemical Processing (Dec. 19, 2008), which is incorporated herein by reference.

[0045] In a dividing wall distillation column, the dividing wall does not extend into the top or bottom sections of the column, allowing the column to reflux and reboil in the same way as a conventional column. The dividing wall divides the column into two sides, providing a fluid-impermeable baffle that divides the interior of the column. The feed inlet to the column is located on one side of the dividing wall, and the side draw is located on the other side. The dividing wall allows the non-inlet side of the column to function more stably, minimizing the effects of fluctuations in flow rate, condition, or composition at the inlet. This increased stability allows the column to be designed and operated in such a way that a side draw stream having a different composition from either the overhead or bottom stream can be removed from the column.

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

[0047] The distillate 11 from the reactor column 10 is condensed and then separated in a decanter 20 into an organic phase 21 and an aqueous phase 22. 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 an extraction column 30.

[0048] Fresh water feed 4 enters the top of the extraction column 30 and is used for bulk separation of excess methanol. A methanol-enriched aqueous effluent 32 exits the bottom of the extraction column 30 and an organic effluent 31 exits the top of the 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. 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 where it combines 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 where it combines 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 a finishing column 50. In the embodiment shown in FIG. 1, the finishing column 50 is a distillation column with a side draw. The light ends 51 of the finishing column 50 are condensed and then separated into an organic phase 61 and an aqueous phase 62 in a decanter 60. A portion 61′ of the organic phase 61 leaving the decanter 60 is returned to the finishing 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 extraction column 30 along with the reactor column distillates 21″ and 22 feed to the extraction column 30.

[0051] The bottoms stream 52 of finishing column 50 is recycled to reactor column 10 .

[0052] Methyl acrylate is removed from the finishing column in a side draw stream 53.

[0053] In FIG. 1, 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 bottom stream 52 from finishing column 50.

[0054] Another embodiment of a process according to the invention is shown diagrammatically in Figure 2, where like parts are numbered as in Figure 1. In Figure 2, finishing column 250 of system 200 is a dividing wall finishing column. Finishing column 250 has a vertical wall 255 that divides the interior of the column into two sides. Organic effluent 31 from extraction column 30 enters finishing column 250 on one side of dividing wall 255. On the other side of finishing column 250, opposite the inlet, a side draw is located for removing side draw stream 53.

[0055] Partition wall 255 does not extend to the top or bottom of finishing column 250. Preferably, partition wall 255 is sized such that substantially no heavy components desired to exit underflow 52 are present at the top of partition wall 255, and no light components desired to exit light ends 51 are present at the bottom of partition wall 255. EXAMPLES

[0056] The following examples illustrate the present invention but are not intended to limit the scope of the invention.

[0057] In a modeled example of the present invention, the feed mixture is fed at a rate of 1044 g / h to the bottom stage of a distillation column with a working sump volume of 550 ml and 14 trays for rectification. The bottom stage has an efficiency of 100%, while the 14 rectification trays have an efficiency of 50%. The feed mixture is distilled to remove heavy end components including dimers (e.g. Michael adducts) and maleic acid, and is produced to an acrylic acid grade containing 0.05 wt% phenothiazine as an inhibitor. The feed mixture is modeled with a bulk composition of 46 wt% acrylic acid, 31 wt% methanol, 21 wt% methyl acrylate, 0.7 wt% water, and 1 wt% acrylic acid dimer, resulting in a molar ratio of methanol to acrylic acid of 1.5. Optionally, 98 wt% sulfuric acid is added to the bottom stage of the column to maintain the composition of the bottom stage at 5 wt% sulfuric acid. Also, about 3 g / h of an inhibitor solution is added to the condenser, which is composed of 6.2 wt. % phenothiazine and 6.2 wt. % hydroquinone in methyl acrylate. In addition, 1 g / h of an inhibitor solution is added to the reflux return line to the column, which is composed of 6 wt. % phenothiazine in methyl acrylate.

[0058] The bottom stage of the reactor column is maintained at a temperature of 115°C by heating and the vapor product is fed above the top tray to a distillation column operating at atmospheric pressure, while the bottom stage of the column is operated at slightly above atmospheric pressure (0.2 psig) by a pressure drop through the distillation column. A liquid bleed consisting mainly of heavies is withdrawn from the bottom stage at 48 g / h.

[0059] As the reaction product passes through the distillation column it is rectified and the overhead vapor is condensed to produce a two-phase distillation product which separates into organic and aqueous phases. The organic phase is composed mostly of methyl acrylate with 5.1 wt% water, 8.4 wt% methanol and 0.3 wt% methyl acetate. The aqueous phase is water with 27.8 wt% methanol and 19.1 wt% methyl acrylate. Approximately 44 wt% of the condensed organic phase is returned to the distillation column as reflux and the remaining organic and aqueous phases are sent to the extraction column.

[0060] The extraction step is carried out at atmospheric conditions in a 6-stage column. Water is fed to the top of the column at a rate of 811 g / h and bulk separation of excess methanol from the organic phase is carried out and fed to the bottom of the extraction column. 5% by weight water / HQ is added to the column at a rate of 0.8 g / h. A methanol-enriched aqueous effluent, containing water, 8.5% by weight methyl acrylate and 9.7% by weight methanol, is withdrawn from the bottom of the column at a rate of 1153 g / h and fed to an alcohol recovery column to recover methyl acrylate and excess methanol. The organic effluent from the extractor, consisting mainly of methyl acrylate, 2.7% by weight water and 0.5% by weight methyl acetate, is withdrawn from the top of the extractor column at a rate of 717 g / h and fed to a light ends removal column.

[0061] The aqueous effluent from the extractor is fed to an alcohol recovery column with 36 trays for rectification. The condenser is fed with 5 wt.% hydroquinone / methyl acrylate at 8 g / h. The alcohol recovery column is operated with a distillate to feed ratio of 0.19, with approximately 89% of the distillate being returned to the column as reflux. The average bulk composition of the distillate is 49 wt.% methanol, 46 wt.% methyl acrylate, 3.3 wt.% water, which is recycled to the reactor as feed. The bottom stream of the alcohol recovery column consists of water with small amounts of other trace components.

[0062] The organic effluent stream of the extractor is sent to a finishing distillation column with 32 trays, feed on tray 12, operated at a maximum pressure of 600 mmHg absolute, to remove light ends including methanol and methyl acetate. Also, about 3 g / h of inhibitor solution is added to the condenser, which consists of 6.2 wt. % phenothiazine and 6.2 wt. % hydroquinone in methyl acrylate. Additionally, 1 g / h of inhibitor solution is added to the reflux line to the column, which consists of 6.2 wt. % phenothiazine in methyl acrylate. When operating the finishing column, the distillate is condensed to obtain a two-phase distillate product, which is separated into an organic phase and an aqueous phase, and a portion of the organic phase is recycled to the column. When operating the finishing column, about 96% of the organic distillate is returned to the column as reflux, and the remaining organic distillate (39 g / h) is mixed with the aqueous distillate (20 g / h), both of which are recycled to the extract feed. A side draw stream containing 99.8 wt.% methyl acrylate is removed from tray 20 at 535 g / h and condensed, and 0.1 wt.% MeHQ / MA is added to the condensed fluid at 5 g / h. The bottom stream is recycled to the reactor, where the methyl acrylate is recovered, and the heavies remain in the liquid reactor bleed.

Claims

1. 1. A process for preparing methyl acrylate comprising the steps of: 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 methanol and acrylic acid in a molar ratio of greater than 1 and less than 2, and wherein the residence time in said 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 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; and e) purifying the organic effluent from the extraction column in a single finishing column. Including, a light ends stream is removed from an upper portion of the finishing column; a bottoms stream is removed from a bottom of the finishing column; Methyl acrylate is removed from a side draw stream; the side draw stream comprises at least 99.5 wt.% methyl acrylate, based on the total weight of the side draw stream; the finishing column is a distillation column equipped with a side draw; The process of claim 1, wherein the finishing column does not include a dividing wall vertically bisecting a portion of the interior of the distillation column to form a divided section.

2. 2. 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 said reaction zone as fresh feed contains less than 2% by weight of impurities.

4. 4. The method of any one of claims 1 to 3, 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 process of claim 4, wherein at least a portion of said distillate of said alcohol recovery column is recycled to said reaction zone.

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

7. The process of any one of claims 1 to 6, wherein the bottoms stream from the finishing column is recycled to the reaction zone.

8. The process of any one of claims 1 to 7, wherein a portion of the light ends stream from the finishing column is recycled to the extraction column.

9. 9. The process of any one of claims 1 to 8, 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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