Improved acrylic acid production process with increased product purity

Abstract

A process for producing acrylic acid comprises feeding a stream comprising acrylic acid to a dehydration tower to produce an overhead stream comprising noncondensibles and lights and a bottoms stream comprising acrylic acid and Michael addition products of acrylic acid. At least a portion of the bottoms stream from the dehydration tower is fed to a finishing tower to distill the bottoms stream of the dehydration tower to produce an acrylic acid-rich stream comprising acrylic acid and organic carbonyl compounds, and a bottoms stream comprising acrylic acid and Michael addition products of acrylic acid. At least a portion of the acrylic acid-rich stream is fed to a crystallizer to form a glacial acrylic acid stream and a mother liquor stream. The glacial acrylic acid stream comprises less than 20 ppm combined of furfural, benzaldehyde, formaldehyde, and acrolein.

Description

[0001] IMPROVED ACRYLIC ACID PRODUCTION PROCESS WITH INCREASED

[0002] PRODUCT PURITY

[0003] FIELD OF THE INVENTION

[0004] The invention relates to a method for preparing acrylic acid having increased product purity.

[0005] BACKGROUND OF THE INVENTION

[0006] Acrylic acid and its ester derivatives are used in the manufacture of a broad spectrum of polymer products found across multiple market segments. For example, polyacrylic acid (PAA) formulations are commonly found in detergent applications, sodium salts of PAA are used as super absorbent polymers (SAP) found in baby diapers and other adult hygiene products. Copolymers of acrylic monomers with methacrylic monomers, styrene, butadiene and other functionalized vinyl monomers are used to manufacture dispersions and resins that are ubiquitous in consumer and industrial products such as architectural, industrial, paper and automotive coatings, performance additives for concrete admixtures and asphalts, textiles, adhesives, sealants and caulks to name just a few applications.

[0007] Commercially, acrylic monomer production is dominated by acrylic acid which serves as a platform chemical for a broad range of acrylate derivatives. Acrylic acid may be produced using a variety of different methods. For example, acrylic acid can be made via propylene oxidation, bio-based processes (e.g., using any one of glycerol, 3- hydroxypropionic acid, lactate, lactic acid, etc., as a starting material), the ethylene cyanohydrin process, the acetylene process (i.e., the Reppe process), the 0-propiolactone process, acrylonitrile hydrolysis, or coupling carbon dioxide with ethylene or ethane. Industrially, most of the global capacity of acrylic acid is manufactured via the two-stage heterogeneously catalyzed oxidation of propylene over mixed metal oxide catalysts. There are various commercial technologies practiced to either condense or quench the acrylic acid-containing exit gas from the oxidation reactor(s). One common process uses water to condense the acrylic acid oxidation reactor exit gas to generate an aqueous grade of acrylic acid, which requires the use of an absorber tower with structured packing materials, inhibitor and steam addition. The aqueous acrylic acid can then be concentrated and purified by a variety of methods. Acrylic acid can be subjected to an extraction stage using a suitable organic solvent immiscible in water to separate the acrylic acid from the water phase. After the organic phase is separated from the aqueous phase, the solvent can be removed by distillation to afford crude acrylic acid suitable for further purification. In another approach, the aqueous acrylic acid can be then be combined with an azeotroping agent inside a dehydration distillation tower to separate the lower boiling azeotrope from the heavier boiling acrylic acid, which exits the tower as a crude grade of acrylic acid (CAA), which is typically 95-96 wt% acrylic acid. CAA is further refined to remove unwanted acetic acid and the overhead stream is also processed to recover and recycle the azeotroping agent.

[0008] Newer technologies have been developed which rely on the use of process streams that already contain acrylic acid to quench and condense the acrylic acid exiting the oxidation reactor, which eliminates the need for a solvent. These processes are known as solvent-less processes.

[0009] U.S. Patent No. 8,242,308 is an example of a solvent-less process. The process uses a coupled two distillation tower system to effect acrylic acid condensation, acetic acid and light component removal, and generates two grades of acrylic acid. The first tower is a dehydration tower, which removes water naturally formed from the oxidation of propylene to acrylic acid and other light components. The second tower is known as a finishing tower, which removes acetic acid and other light components and generates two product grades of acrylic acid. An overhead or technical grade of acrylic acid (TGAA) is obtained as a side draw from the finishing tower, and a bottoms or ester grade of acrylic acid (EGAA) is removed in the bottoms stream of the finishing tower.

[0010] A drawback of this process is the presence of residual organic carbonyl content in TGAA in the form of aldehydes, maleic anhydride, and other species. The presence of these organic carbonyls makes the TGAA less useful in demanding applications, such as the formation of SAPs where low aldehyde concentrations are required to reduce costs and provide a product of acceptable molecular weight range and color.

[0011] There is a need for an improved process for producing acrylic acid having improved product purity.

[0012] SUMMARY OF THE INVENTION

[0013] The invention is directed to a process for producing acrylic acid comprising: a) feeding a crude acrylic acid stream to a dehydration tower to produce an overhead stream comprising noncondensibles and lights and a bottoms stream comprising acrylic acid and Michael addition products of acrylic acid; b) feeding at least a portion of the bottoms stream from the dehydration tower to a finishing tower to distill the bottoms stream of the dehydration tower to produce an acrylic acid-rich stream comprising acrylic acid and organic carbonyl compounds, and a bottoms stream comprising acrylic acid and Michael addition products of acrylic acid; and c) feeding at least a portion of the acrylic acid-rich stream to a crystallizer to form a glacial acrylic acid stream and a mother liquor stream, wherein the glacial acrylic acid stream comprises less than 20 ppm combined of furfural, benzaldehyde, formaldehyde, and acrolein.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a schematic diagram showing the process according to an embodiment of the present invention.

[0016] FIG. 2 is a schematic diagram showing the process according to another embodiment of the present invention.

[0017] DETAILED DESCRIPTION OF THE INVENTION

[0018] All percentage compositions are weight percentages (wt%), and all temperatures are in °C, unless otherwise indicated. Averages are arithmetic averages unless otherwise indicated. An “average concentration” is the arithmetic average of the concentration entering a region and the concentration exiting the region, where the region is an individual reactor, a reactor system, or a zone within a reactor or reactor system. An “average ratio” is the ratio of the average concentration of one component relative to the average concentration of another component.

[0019] As used herein, the terms “light” and “light compound” refer to a compound or compounds having a boiling point or boiling points below the boiling point of the desired product. For example, water is an example of a light compound when the desired product is acrylic acid. A lights stream contains at least one light compound. Similarly, the term "heavies" means compounds having a boiling point above the boiling point of the desired product. Oligomers of acrylic acid and well known Michael addition products are examples of heavies when the desired product is acrylic acid.

[0020] As used herein, the term “oligomers of acrylic acid” refers to “dimers, trimers, and higher oligomers of acrylic acid.” The oligomers of acrylic acid can reversibly react to form acrylic acid and higher or lower oligomers of acrylic acid. The process described herein refers to different grades of acrylic acid, each of which is defined by their purity level. “Ester grade acrylic acid” (EGAA) refers to the bottoms stream of the finishing tower which can be sent to an ester plant for ester manufacture. This grade of acrylic acid is variable in composition and AA strength depends on the operation of the finishing tower. EGAA broadly covers any composition of acrylic acid up to 90%. Crude acrylic acid (CAA) as used herein, refers to an acrylic acid composition comprising 90 to 96 % acrylic acid by weight. The terms “technical grade acrylic acid” and “TGAA” refer to an acrylic acid comprising at least 98.5% acrylic acid by weight. The terms “glacial acrylic acid” and “GAA” refer to an acrylic acid comprising at least 99.6 % acrylic acid by weight.

[0021] The present invention relates to a process for producing acrylic acid having improved purity.

[0022] In the present invention, acrylic acid is produced by any known acrylic acid production process. For example, acrylic acid can be made via propylene oxidation, a biobased process (e.g., using any one of glycerol, 3-hydroxypropionic acid, lactate, lactic acid, etc., as a starting material), an ethylene cyanohydrin process, an acetylene process (i.e., the Reppe process), a P-propiolactone process, an acrylonitrile hydrolysis process, or a process performed by coupling carbon dioxide with ethylene or ethane. The reaction mixture produced during the acrylic acid production process may be processed in one or more unit operations. These operations may include, for example, cooling processes, quenching processes, separations, purifications, etc.

[0023] Preferably, the acrylic acid is produced by an exothermic, vapor stage, two-step propylene oxidation process. In a first step, propylene is oxidized in the presence of air and a first mixed metal oxide catalyst to produce acrolein. In a second step, the acrolein is oxidized in the presence of air and a second mixed metal oxide catalyst to produce a gaseous reaction mixture comprising acrylic acid.

[0024] The gaseous reaction mixture is cooled or quenched and partially condensed to form a liquid crude acrylic acid stream. The gaseous reaction mixture typically is superheated as it comes from the two-step oxidation process, wherein it contains more heat (energy) than the amount of heat required to vaporize the condensable components of the mixture. Preferably, the cooling step removes essentially all of the amount of superheat from the condensable portion of the gaseous reaction mixture . The cooling step can be conducted directly or indirectly in one or more pieces of equipment. For example, the cooling of the gaseous reaction mixture stream can be initiated in a quench or flash vessel, or can be integrated into the bottom of the dehydration column, with or without column internals. Preferably, the cooling step is initiated or primarily conducted in the dehydration column. The cooling step advantageously is initiated by bringing the gaseous reaction mixture stream into direct contact with a liquid, which preferably has a lower temperature. In one embodiment of the invention, the gaseous reaction mixture is introduced directly into the dehydration column where it is contacted with a liquid having a temperature lower than the temperature of the gaseous reaction mixture in order to at least partially cool the gaseous reaction mixture. In a preferred embodiment of the invention, the gaseous reaction mixture is introduced into the dehydration column and contacted with a spray of a cooler liquid.

[0025] Advantageously, the gaseous reaction mixture stream is cooled to a temperature of from about 50 to about 300°C, preferably from about 70 to about 200°C, below the boiling point of the majority of the highest-boiling components of the mixture. Preferably, the reaction gas mixture is cooled to a temperature of from about 50 to about 200°C, more preferably from about 60 to about 180°C.

[0026] The at least partially cooled gaseous reaction mixture stream is dehydrated. The dehydration preferably is conducted in the dehydration column, also referred to as the dehydration tower. The dehydration tower functions to remove the majority of water from the crude acrylic acid stream exiting as the dehydration tower bottoms stream. Advantageously, the dehydration tower is operated such that there is at least a bottoms stream and an overhead stream, and in some cases a side stream. Preferably, at least a portion of the overhead stream is condensed and is returned as a reflux liquid to the dehydration tower. Preferably a portion of the bottoms stream is cooled and used to cool the gaseous reaction mixture.

[0027] Preferably, essentially all noncondensibles and lights exit the dehydration tower in the overhead stream. Examples of noncondensibles present during the production of acrylic acid include, for example, nitrogen, oxygen, CO, carbon dioxide, and unreacted hydrocarbons such as propane and propylene. Advantageously, the overhead stream is introduced into a condenser, and at least a portion of the lights and acrylic acid are condensed and returned to the dehydration tower as a reflux stream.

[0028] The dehydration tower functions, at least partially, as a distillation column.

[0029] However, as noted above, the dehydration column can also serve as a contacting zone for cooling of the gaseous reaction mixture. Preferably, the temperature of the bottoms stream from the dehydration tower is less than about 120°C. The temperature of the overhead stream from the dehydration tower is at least about 40°C.

[0030] The vent stream from the overhead condenser on the dehydration tower may be partially recycled to the reactor system. The remaining portion of the vent stream is removed from the separation system as a purge stream.

[0031] The bottoms stream, or liquid crude acrylic acid stream, from the dehydration tower advantageously is sent to a second column, except that a portion of this stream can be employed to cool the gaseous reaction mixture. In one embodiment of the invention, a portion of the bottoms stream from the dehydration tower is sent to a heat exchanger, which can be a reboiler. However, it is noted that the process can also be operated under conditions such that the heat exchanger is a cooler, depending on whether the process design requires heating or cooling. Preferably, a portion of the bottoms stream from the dehydration tower is fed to a second column. Advantageously, the feed point is near the top of the second column. The second column preferably is a distillation column and is used in conjunction with a reboiler and a condenser.

[0032] Preferably, the overhead stream from the second column is sent to a condenser. Preferably, the condenser is operated as a "total condenser" in that essentially all of the overhead stream is condensed. However, it is possible to remove a purge stream of noncondensible compounds from this condenser. A portion of the condensate of the second column is used to provide reflux and the remaining portion of the condensate is returned to the dehydration tower for lights removal. Advantageously, the condensate from the second column condenser is used to cool the gaseous reaction mixture, either as is or after additional heat exchange.

[0033] The bottoms stream from the second column advantageously is at least partially sent to the second column reboiler. The remainder of the bottoms stream can be incinerated or can be further treated to recover acrylic values. Preferably, the majority of acrylic acid is recovered from an acrylic acid-rich stream, such as, for example, a side draw stream, from the second column. A portion of the acrylic acid will be present in the bottoms stream of the second column. For example, the acrylic acid-rich stream may comprise technical grade acrylic acid (TGAA) and the bottoms stream may comprise primarily heavies, including Michael addition products of acrylic acid, soluble polymer and polymerization inhibitor residues. Alternatively, the acrylic acid-rich stream may comprise TGAA and the bottoms stream may comprise a lower grade stream of acrylic acid, such as ester grade acrylic acid (EGAA). Preferably, the acrylic acid-rich stream comprises at least 95 wt%, more preferably at least 96 wt%, even more preferably at least 97 wt%, and still more preferably at least 98 wt% acrylic acid based on the total weight of the acrylic acid-rich stream.

[0034] The process of the invention can remove the acrylic acid-rich stream at a point above or below the point where the liquid crude acrylic acid stream is fed to the second column, depending on the purity desired, i.e. the acrylic acid-rich stream can be removed above or below the feed in the second column. The acrylic acid-rich stream may be removed as a liquid or vapor.

[0035] The temperature and pressure in the second column can be determined according to design considerations well-known to those skilled in the art. Preferably, the second column is operated pressures so that the bottoms temperature is less than 120°C . More preferably, the second column is operated at pressures so that the bottoms temperature is less than 100°C. The advantage of allowing the second column to operate at lower temperatures is to minimize undesired dimer, oligomer and / or polymer formation. Advantageously, the temperature of the overhead stream as it leaves the second column is from about 40 to about 90°C when producing acrylic acid and operating the second column at a head pressure of from about 40 to about 500 mm Hg. The temperature of the bottoms stream from the second column advantageously is from about 60 to about 100°C when producing acrylic acid.

[0036] The design details of the dehydration column and of the second column, including their operating conditions such as temperatures, pressures, flow rates, equipment sizing including column height and diameters, choice of materials of construction, arrangement and choice of type of auxiliary equipment such as heat exchangers and pumps, choice and arrangement of column internals, and location of piping including take-off streams, can readily be determined by those skilled in the art according to well-known design considerations. Examples of distillation column configurations that can be used in the process of the invention include, for example, packed columns, trayed columns, divided wall columns, multi-stage devolatilizers, and the like. Any type of tray can be employed, including bubble trays, valve trays, cross flow trays, dual flow trays, and combinations thereof for those skilled in the art. Similarly, if packing is employed, any type of packing can be used, including randomly- or regularly-spaced packing. In a preferred embodiment of the invention, the dehydration column comprises packing in its upper section, and in its lower section provides for direct cooling of the incoming gaseous reaction mixture. Surge tanks optionally can be employed within the separation system such as, for example, at one or more locations between the dehydration column and the second column.

[0037] Steel alloys such as 316 SS and other higher alloys may be used as the material(s) of construction for the process equipment by using criteria well known to those skilled in the art for process equipment to be used in the distillation of corrosive streams. Alternatively, the process equipment can be partially constructed using copper or copper-containing alloys, such as various alloys sold under the name Monel. While not wishing to be bound by any theory, it is the believed that the presence of copper inhibits the undesired polymerization of acrylic acid.

[0038] The use of inhibitors is preferred in the process of the invention, regardless of the choice of materials of construction. Various compounds are well known to inhibit the reaction of acrylic acid, and are commercially available. Examples of preferred inhibitors include complexes and salts of manganese compounds, copper complexes and salts thereof, hydroquinone (HQ), monomethyl ether hydroquinone (MEHQ), phenothiazine (PTZ), 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO), its derivatives, and related compounds such as 4-hydroxy TEMPO. Combinations of inhibitors can be employed that offer synergistic interactions and provide more effective polymerization inhibition than the additive performance of the individual inhibitors. In a preferred embodiment of the invention, a mixture of a source of soluble manganese ions, such as manganese acetate, and 4-hydroxy TEMPO are employed in the dehydration column as an inhibitor. Hydroquinone can also be added to this inhibitor mixture. It is also preferred, as is well-known in the art, to employ a molecular oxygen or air to the second column, as oxygen is known to be a polymerization retarder. The inhibitor is employed in an amount sufficient to prevent or reduce the polymerization of acrylic acid, as is well known to those skilled in the art.

[0039] Preferably, the dehydration tower and second column form a coupled distillation tower system. The coupled distillation tower system comprises the dehydration tower and a finishing tower (i.e., the second column). Other suitable process configurations are possible and are known to those skilled in the art which use intermediate tanks to contain certain process streams prior to being fed to each tower.

[0040] The inventor has discovered that the acrylic acid in the acrylic acid-rich stream produced in the second column comprises residual organic carbonyl compounds that are byproducts of the heterogeneously -catalyzed oxidation of propylene, such as maleic acid, maleic anhydride, propionic acid, acetic acid, formaldehyde, furfuraldehyde, benzaldehyde, acrolein, protoanemonin, acrylic acid dimer among others. High levels of maleic anhydride, aldehydes and other similar species, that can render the acrylic acid unsuitable for use in certain products, such as the formation of super absorbent polymers (SAP), which require low aldehyde concentrations. Examples of the residual organic carbonyl compounds include furfural, benzaldehyde, acrolein, maleic acid, and formaldehyde. The amount of these compounds varies according to reactor catalyst performance and may be present individually in the acrylic acid-rich stream in amounts ranging from 10 ppm to 2000 ppm depending on the individual component.

[0041] To further purify the acrylic acid-rich stream and reduce the amount of residual organic carbonyl compounds, and preferably to reduce the amount of residual aldehydes, at least a portion of the acrylic acid-rich stream is fed to a crystallizer to form a glacial acrylic acid (GAA) stream. The crystallizer may use any known crystallization methods, such as, for example, static, falling film, suspension, or others, as well as combinations thereof. Preferably, the crystallizer comprises a suspension crystallizer.

[0042] Preferably, the acrylic acid-rich is fed to a surge tank before proceeding to the crystallizer. The surge tank may help manage fluctuations in flow rates or pressure, and may also be used as to divert the acrylic acid-rich stream into one or more streams. For example, a first portion of the acrylic acid-rich stream may be fed to the crystallizer, and a second portion of the acrylic acid-rich stream may be fed to a downstream unit, such as an ester unit for manufacturing acrylic acid esters from the side draw stream. Preferably, at least a portion of the acrylic acid-rich stream is fed to the crystallizer and a remainder of the acrylic acid-rich stream is fed to an ester unit for manufacturing acrylic acid esters.

[0043] The GAA produced in the crystallizer preferably comprises less than 20 ppm of furfural, benzaldehyde, formaldehyde, and acrolein combined, i.e., the total content of furfural, benzaldehyde, formaldehyde, and acrolein in the GAA is less than 20 ppm. More preferably, the GAA comprises less than 10 ppm of furfural, benzaldehyde, formaldehyde, and acrolein combined, and still more preferably, less than 5 ppm of furfural, benzaldehyde, formaldehyde, and acrolein combined.

[0044] In at least one preferred embodiment, the GAA produced in the crystallizer comprises less than 5 ppm of each of furfural, benzaldehyde, formaldehyde, and acrolein. More preferably, the GAA comprises less than 3 ppm of each of furfural, benzaldehyde, formaldehyde, and acrolein, and even more preferably less than 2 ppm of each of furfural, benzaldehyde, fonnaldehyde, and acrolein. The crystallizer also forms a mother liquor. The mother liquor may comprise acrylic acid, dimers, trimers, and higher oligomers, as well as a relatively high level of polymerization inhibitors. Depending on the crystallization technology, the mother liquor may be subjected to additional crystallization cycles to increase the yield of GAA and / or reduce the amount of residual carbonyl or aldehydes, or it may be recycled back to the finishing tower as supplementary recycle inhibitor or may be disposed of by incineration. After removal of the desired GAA , at least a portion of the mother liquor is preferably recycled back to the finishing tower.

[0045] Preferably, a bottoms stream from the second column, such as an ester grade acrylic acid (EGAA) or a heavies stream, is further processed by feeding the bottoms stream to a dimer cracker. In the dimer cracker, dimers, trimers, and higher -oligomers are converted back to acrylic acid. The distillate from the dimer cracker may be recycled to the second column. Alternatively, the distillate from the dimer cracker may be fed to an ester unit for conversion to an acrylic acid ester. The bottoms of the dimer cracker forms a waste oil stream containing high levels of soluble polymer, solids, and inhibitor residues. The bottoms waste oil stream may be incinerated.

[0046] One embodiment of the present invention is shown in FIG. 1. A crude acrylic acid stream CAA is fed to a dehydration tower 10, where the gaseous crude acrylic acid stream is quenched and condensed. The lights 11 from dehydration tower 10 are sent to condenser 15. Condensible materials 17 are returned to dehydration tower 10 as reflux. Lights and noncondensible materials 16 may be vented or incinerated. A portion of the bottoms stream 12 is sent to a heat exchanger 20 and liquid stream 21 exiting the heat exchanger 20 is returned to dehydration tower 10 as a cooling liquid.

[0047] The remainder of bottoms stream 12 is fed to second column 30, which functions as a distillation column. An overhead stream 31 from second column 30 is condensed in condenser 35 and the condensed overhead stream 36 is returned to dehydration tower 10. A side draw 32 comprising primarily acrylic acid is removed from second column 30. A bottoms stream 33 comprising acrylic acid and heavies exits the bottom of finishing column 30.

[0048] Side draw 32 is fed to surge tank 40, which is then split into two streams 41, 42 exiting surge tank 40. First stream 41 is fed to an ester unit (not shown) where a corresponding acrylic acid ester is produced. Second stream 42 is fed to a crystallizer 50. A product stream 51 exiting crystallizer 50 comprises GAA. Bottoms stream 52 from crystallizer 50 contains acrylic acid, oligomers of acrylic acid and residual polymerization inhibitors . Bottoms stream 52 may be returned to reboiler 60 to be recycled to second column 30 as stream 61. Alternately, the bottoms stream of crystallizer 50 may be sent to a tank (not shown) from which stream 53 can be recycled to the crystallizer or sent to incineration as waste oil.

[0049] Another embodiment is shown in FIG. 2. In FIG. 2, dimer cracker 70 is added to the system shown in FIG. 1. In dimer cracker 70, dimers, trimers, and higher -oligomers are cracked to recover additional acrylic acid from bottoms stream 33. Product stream 71 exiting dimer cracker 70 may be fed to a downstream ester unit (not shown) to convert the recovered acrylic values to corresponding acrylic acid esters. Waste stream 72 exits the bottom of dimer cracker 70, and contains a waste oil that may be incinerated. Crystallizer bottoms stream 53 normally recycled to the crystallizer or fed to the finishing tower reboiler 60 can alternatively be fed to dimer cracker 70 for GAA acrylic value recovery.

Claims

CLAIMS:

1. A process for producing acrylic acid comprising: a) feeding a stream comprising acrylic acid to a dehydration tower to produce an overhead stream comprising noncondensibles and lights and a bottoms stream comprising acrylic acid and Michael addition products of acrylic acid; b) feeding at least a portion of the bottoms stream from the dehydration tower to a finishing tower to distill the bottoms stream of the dehydration tower to produce an acrylic acid-rich stream comprising acrylic acid and organic carbonyl compounds, and a bottoms stream comprising acrylic acid and Michael addition products of acrylic acid; and c) feeding at least a portion of the acrylic acid-rich stream to a crystallizer to form a glacial acrylic acid stream and a mother liquor stream, wherein the glacial acrylic acid stream comprises less than 20 ppm combined of furfural, benzaldehyde, formaldehyde, and acrolein.

2. The process of claim 1, wherein the glacial acrylic acid stream comprises less than 5 ppm of each of furfural, benzaldehyde, formaldehyde, and acrolein.

3. The process of claim 1 or 2, wherein the crystallizer is selected from the group consisting of a static crystallizer, a falling film crystallizer, a suspension crystallizer or a combination thereof.

4. The process of any one of the preceding claims, wherein the acrylic acid-rich stream is fed to a surge tank before feeding at least a portion of the side draw stream to the crystallizer.

5. The process of claim 4, wherein the acrylic acid-rich stream is split into two streams exiting the surge tank, where a first stream comprises the portion of the acrylic acid-rich stream fed to the crystallizer, and a second stream is fed to an ester unit to produce at least one acrylic acid ester.

6. The process of any one of the preceding claims, wherein at least a portion of the mother liquor is recycled to the finishing tower to recover polymerization inhibitor present in the mother liquor.

7. The process of any one of the preceding claims, wherein at least a portion of the mother liquor incinerated.

8. The process of any one of the preceding claims, further comprising feeding at least a portion of the bottoms stream of the finishing tower to a dimer cracker to recover acrylic acid monomer from dimer, trimer and higher -oligomers of acrylic acid.

9. The process of claim 8, wherein a distillate from the dimer cracker is recycled to the finishing tower.

10. The process of claim 8, wherein a distillate from the dimer cracker is fed to an ester unit for conversion to an acrylic acid ester.

11. The process of any one of claims 8 to 10, wherein a bottoms stream from the dimer cracker is incinerated.

12. The process of any one of the preceding claims, wherein the acrylic acid-rich stream is removed from the finishing tower as a vapor or a liquid.

13. The process of any one of the preceding claims, wherein the acrylic acid in the stream fed to the dehydration tower is produced by a method selected from the group consisting of propylene oxidation-based process, a bio-based process, an ethylene cyanohydrin-based process, an acetylene -based process, a P-propiolactone -based process, an acrylonitrile hydrolysis-based process, or a process performed by coupling carbon dioxide with ethylene or ethane.

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