CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Provisional Patent Application No. 62/559,126, filed September 15, 2017, the entirety of which is incorporated herein by reference.

FIELD

[0002] The present invention relates generally to the production of acrylic acid. More specifically, the present invention relates to the production of crude acrylic acid via the condensation of acetic acid and formaldehyde and the subsequent purification thereof.

BACKGROUND

[0003] α,β-unsaturated acids, particularly acrylic acid and methacrylic acid, and the ester derivatives thereof are useful organic compounds in the chemical industry. These acids and esters are known to readily polymerize or co-polymerize to form homopolymers or copolymers. Often the polymerized acids are useful in applications such as superabsorbents, dispersants, flocculants, and thickeners. The polymerized ester derivatives are used in coatings (including latex paints), textiles, adhesives, plastics, fibers, and synthetic resins.

[0004] Because acrylic acid and its esters have long been valued commercially, many methods of production have been developed. One exemplary acrylic acid ester production process utilizes: (1) the reaction of acetylene with water and carbon monoxide; and/or (2) the reaction of an alcohol and carbon monoxide, in the presence of an acid, e.g., hydrochloric acid, and nickel tetracarbonyl, to yield a crude product comprising the acrylate ester as well as hydrogen and nickel chloride. Another conventional process involves the reaction of ketene (often obtained by the pyrolysis of acetone or acetic acid) with formaldehyde, which yields a crude product comprising acrylic acid and either water (when acetic acid is used as a pyrolysis reactant) or methane (when acetone is used as a pyrolysis reactant). These processes have become obsolete for economic, environmental, or other reasons.

[0005] More recent acrylic acid production processes have relied on the gas phase oxidation of propylene, via acrolein, to form acrylic acid. The reaction can be carried out in single- or two- step processes but the latter is favored because of higher yields. The oxidation of propylene produces acrolein, acrylic acid, acetaldehyde and carbon oxides. Acrylic acid from the primary oxidation can be recovered while the acrolein is fed to a second step to yield the crude acrylic acid product, which comprises acrylic acid, water, small amounts of acetic acid, as well as impurities such as furfural, acrolein, and propionic acid. Purification of the crude product may be carried out by azeotropic distillation. Although this process may show some improvement over earlier processes, this process suffers from production and/or separation inefficiencies. In addition, this oxidation reaction is highly exothermic and, as such, creates an explosion risk. As a result, more expensive reactor design and metallurgy are required. Also, the cost of propylene is often prohibitive.

[0006] The aldol condensation reaction of formaldehyde and acetic acid and/or carboxylic acid esters has been disclosed in literature. This reaction forms acrylic acid and is often conducted over a catalyst. For example, condensation catalysts consisting of mixed oxides of vanadium and phosphorus were investigated and described in M. Ai, J. Catal, 107, 201 (1987); M. Ai, J. Catal., 124, 293 (1990); M. Ai, Appl. Catal., 36, 221 (1988); and M. Ai, Shokubai, 29, 522 (1987). The acetic acid conversions in these reactions, however, may leave room for improvement.

[0007] US Patent No. 8,658,823 discloses a separation scheme comprising separating at least a portion of the crude product stream to form an alkylenating agent stream and an intermediate acrylic product stream. Preferably, the alkylenating stream comprises at least 1 wt%

alkylenating agent and the intermediate acrylic product stream comprises acrylic acid and/or other acrylate products in high concentrations. Although there exists some disclosure relating to separation schemes that may be employed to effectively provide purified acrylic acid from the aldol condensation crude product, treatment of the crude product stream is not considered in much detail.

[0008] Thus, the need exists for processes for producing purified acrylic acid and, in particular, for separation schemes to effectively purify unique aldol condensation crude products to form the purified acrylic acid.

[0009] The references mentioned above are hereby incorporated by reference. BRIEF DESCRIPTION OF DRAWINGS

[0010] The invention is described in detail below with reference to the appended drawings, wherein like numerals designate similar parts.

[0011] FIG. 1 is a process flowsheet showing an acrylic acid reaction/separation system in accordance with an embodiment of the present invention.

[0012] FIG. 2 is a schematic diagram of an acrylic acid reaction/separation system in accordance with one embodiment of the present invention.

SUMMARY

[0013] The description relates to a process for producing an acrylate product comprising the steps of: providing a crude product stream comprising the acrylate product and an alkylenating agent; cooling the crude product stream to form a cooled crude product stream having a temperature less than 100 °C; absorbing at least a portion of the cooled stream to form an absorbent stream and an absorbed product stream; and separating at least a portion of the absorbed product stream to form an alkylenating agent stream comprising at least 1 wt% alkylenating agent and an intermediate product stream comprising acrylate product. In some cases, the cooling comprises cooling the crude product stream to form a first cooled crude product stream having a temperature less than 250 °C and cooling the first cooled crude product stream to form a second cooled crude product stream having a temperature less than 150 °C. The first cooled crude product stream may have a temperature ranging from 25 °C to 150 °C and the second cooled crude product stream may have a temperature ranging from 15 °C to 100 °C. Preferably the cooling reduces the temperature of the crude product stream by at least 100 °C. The absorbing may comprise absorbing at least a portion of the second cooled crude product stream to form the absorbent stream and the absorbed product stream. Optionally the absorbent has a temperature below 100 °C, e.g., a temperature ranging from 0 °C to 100 °C. Preferably the absorbent is water. The process may further comprise the step of recycling a portion of the cooled crude product stream to the cooling step and preferably adding a polymerization inhibitor to the recycled cooled crude product stream. The process may further comprise the step of recycling a portion of the absorbed product stream to the cooling step and preferably adding a polymerization inhibitor to the recycled absorbed product stream. The process may further comprise drawing a slip stream from at least one of the first cooled crude product stream and the second cooled crude product stream and adding a polymerization inhibitor to the slip stream. The cooled crude product stream may comprise at least 0.5 wt% alkylenating agent and/or the intermediate acrylate product stream may comprise at least 5% wt% acrylate product and/or the intermediate acrylate product stream may comprise less than 25 wt% water and less than 95 wt% acetic acid. The process may further comprise the step of separating the intermediate acrylate product stream to form a finished acrylate product stream comprising acrylate products and a first finished acetic acid stream comprising acetic acid. The crude product stream may be formed by contacting an alkanoic acid and the alkylenating agent in a reactor and at least a portion of the first finished acetic acid stream is recycled to the reactor. The process may further comprise the step of separating the alkylenating agent stream to form a purified alkylenating stream comprising at least 1 wt% alkylenating agent and a purified acetic acid stream

comprising acetic acid and water and optionally the step of separating the purified acetic acid stream to form a second finished acetic acid stream and a water stream.

DETAILED DESCRIPTION

Introduction

[0014] Production of unsaturated carboxylic acids such as acrylic acid and methacrylic acid and the ester derivatives thereof via most conventional processes have been limited by economic and environmental constraints. In the interest of finding a new reaction path, the aldol condensation reaction of acetic acid and an alkylenating agent, e.g., formaldehyde, has been investigated. This reaction may yield a unique crude product that comprises, inter alia, a higher amount of (residual) formaldehyde, which is generally known to add unpredictability and problems to separation schemes. Although the aldol condensation reaction of acetic acid and formaldehyde is known, there has been little if any disclosure relating to the treatment, e.g., cooling, of the crude product stream directly exiting the reactor and the potential benefits thereof. Other conventional reactions, e.g., propylene oxidation or ketene/formaldehyde, do not yield crude products that comprises higher amounts of formaldehyde. The primary reactions and the side reactions in propylene oxidation do not create formaldehyde. In the reaction of ketene and formaldehyde, a two-step reaction is employed and the formaldehyde is confined to the first stage. Also, the ketene is highly reactive and converts substantially all of the reactant formaldehyde. As a result of these features, very little, if any, formaldehyde remains in the crude product exiting the reaction zone. Because no formaldehyde is present in crude products formed by these conventional reactions, the separation schemes associated therewith have not addressed the problems and unpredictability that accompany crude products that have higher formaldehyde content.

[0015] The inventors have now discovered that the cooling and absorption of the crude product stream, prior to separation, e.g., prior to formaldehyde removal, improves overall separation operations. In particular, the cooling and absorption of the crude product stream unexpectedly provides for effective removal of "light ends," which in turn improves the subsequent separation of formaldehyde from the resultant product stream before conventional light ends removal. For example, the size of the column required to achieve the formaldehyde separation may be smaller than the size of the column utilized when the aforementioned cooling is not employed. In addition, it has been found that the use of the cooling step prior to the absorption step provides the additional benefit of reducing acrylic acid content in the feed to the absorption unit, which advantageously reduces or eliminates acrylic acid polymerization. It is believed that without the cooling-absorption configuration, the acrylic acid polymerization would result in significant fouling of the absorption column. Also, in a cooling-absorption configuration that employs multiple cooling units, one of the cooling units may utilize plant cooling water, while another may utilize refrigerated water, which provides for cooling efficiencies due to the use of less refrigerated water overall. In some cases, refrigerated water may only be used in the last cooling operation.

[0016] In one embodiment, the disclosure relates to a process for producing acrylic acid, methacrylic acid, and/or the salts and esters thereof. As used herein, acrylic acid, methacrylic acid, and/or the salts and esters thereof, collectively or individually, may be referred to as "acrylate products." The use of the terms acrylic acid, methacrylic acid, or the salts and esters thereof, individually, does not exclude the other acrylate products, and the use of the term acrylate product does not require the presence of acrylic acid, methacrylic acid, and the salts and esters thereof. [0017] The inventive process, in one embodiment, includes the step of providing a crude product stream comprising the acrylic acid and/or other acrylate products. The crude product stream of the present invention, unlike most conventional acrylic acid-containing crude products, further comprises a significant portion of at least one alkylenating agent. Preferably, the at least one alkylenating agent is formaldehyde. For example, the crude product stream may comprise at least 0.5 wt% alkylenating agent(s), e.g., at least 1 wt%, at least 5 wt%, at least 7 wt%, at least 10 wt%, or at least 25 wt%. In terms of ranges, the crude product stream may comprise from 0.5 wt% to 50 wt% alkylenating agent(s), e.g., from 1 wt% to 45 wt%, from 1 wt% to 25 wt%, from 1 wt% to 10 wt%, or from 5 wt% to 10 wt%. In terms of upper limits, the crude product stream may comprise less than 50 wt% alkylenating agent(s), e.g., less than 45 wt%, less than 25 wt%, or less than 10 wt%.

[0018] In one embodiment, the crude product stream of the present invention further comprises water. For example, the crude product stream may comprise less than 60 wt% water, e.g., less than 50 wt%, less than 40 wt%, or less than 30 wt%. In terms of ranges, the crude product stream may comprise from 1 wt% to 60 wt% water, e.g., from 5 wt% to 50 wt%, from 10 wt% to 40 wt%, or from 15 wt% to 40 wt%. In terms of upper limits, the crude product stream may comprise at least 1 wt% water, e.g., at least 5 wt%, at least 10 wt%, or at least 15 wt%.

[0019] In one embodiment, the crude product stream of the present invention comprises very little, if any, of the impurities found in most conventional acrylic acid crude product streams. For example, the crude product stream of the present invention may comprise less than 1000 wppm of such impurities (either as individual components or collectively), e.g., less than 500 wppm, less than 100 wppm, less than 50 wppm, or less than 10 wppm. Exemplary impurities include acetylene, ketene, beta-propiolactone, higher alcohols, e.g., C2+, C3+, or C ₄ +, and combinations thereof. Importantly, the crude product stream of the present invention comprises very little, if any, furfural and/or acrolein. In one embodiment, the crude product stream comprises substantially no furfural and/or acrolein, e.g., no furfural and/or acrolein. In one embodiment, the crude product stream comprises less than less than 500 wppm acrolein, e.g., less than 100 wppm, less than 50 wppm, or less than 10 wppm. In one embodiment, the crude product stream comprises less than less than 500 wppm furfural, e.g., less than 100 wppm, less than 50 wppm, or less than 10 wppm. Furfural and acrolein are known to act as detrimental chain terminators in acrylic acid polymerization reactions. Also, furfural and/or acrolein are known to have adverse effects on the color of purified product and/or to subsequent polymerized products.

[0020] In addition to the acrylic acid and the alkylenating agent, the crude product stream may further comprise acetic acid, water, propionic acid, and light ends such as oxygen, nitrogen, carbon monoxide, carbon dioxide, methanol, methyl acetate, methyl acrylate, acetaldehyde, hydrogen, and acetone. Exemplary compositional data for the crude product stream are shown in Table 1. Components other than those listed in Table 1 may also be present in the crude product stream.

TABLE 1

CRUDE ACRYLATE PRODUCT STREAM COMPOSITIONS

Cone. Cone. Cone. Cone.

Component (wt%) (wt%) (wt%) (wt%)

Acrylic Acid 1 to 75 1 to 50 5 to 50 7 to 40

Alkylenating Agent(s) 0.5 to 50 1 to 45 1 to 25 1 to 10

Acetic Acid 1 to 90 1 to 70 5 to 50 10 to 40

Water 1 to 60 3 to 50 5 to 40 5 to 20

Propionic Acid 0.01 to 10 0.1 to 10 0.1 to 5 0.1 to 1

Oxygen 0.01 to 10 0.1 to 10 0.1 to 5 0.1 to 1

Nitrogen 0.1 to 20 0.1 to 10 0.5 to 5 0.5 to 4

Carbon Monoxide 0.01 to 10 0.1 to 10 0.1 to 5 0.5 to 3

Carbon Dioxide 0.01 to 10 0.1 to 10 0.1 to 5 0.5 to 3

Other Light Ends 0.01 to 10 0.1 to 10 0.1 to 5 0.5 to 3

[0021] In one embodiment, the process comprises the step of cooling the crude product stream to form a cooled crude product stream. The cooled crude product stream may have a temperature less than 100 °C, e.g., less than 90 °C, less than 80 °C, less than 70 °C, or less than 60 °C. In terms of ranges, the cooled crude product stream may have a temperature ranging from 20 °C to 100 °C, e.g., from 25 °C to 80 °C, from 30 °C to 70 °C, from 35 °C to 65 °C, or from 40 °C to 60 °C.

[0022] The inventors have found that the cooling (preferably along with absorption) of the crude product stream, prior to subsequent separation, surprisingly provides for a more efficient separation of formaldehyde from the resultant stream. Without this cooling, undesirable components, e.g., light ends and other gases, would remain in the crude product stream. The presence of these undesirable components in the crude product stream may have adverse effects on separation operations, e.g., column operations and efficiencies. For example, because of the additional undesirable components, a much larger column would detrimentally be required to handle the higher volumetric flow rate, e.g., the column would need a much larger diameter and/or number of trays.

[0023] In some cases, the cooling step reduces the temperature of the crude product stream by at least 50 °C, e.g., at least 100 °C, at least 125 °C, least 150 °C, least 175 °C, least 200 °C, least 225 °C, or least 250 °C. That is to say, the temperature of the crude product stream is at least 100 °C less than the temperature of the cooled crude product stream.

[0024] In preferred embodiments, the cooling step comprises multiple cooling operations, e.g., at least two cooling operations, at least three cooling operations, or at least four cooling operations. For example, the cooling step may comprise cooling the crude product stream to form a first cooled crude product stream (the first cooling step) and cooling the first cooled crude product stream to form a second cooled crude product stream (the second cooling step). The first cooled crude product stream may have a temperature less than 150 °C, e.g., less than 100 °C, less than 90 °C, less than 80 °C, less than 70 °C, or less than 60 °C. The second cooled crude product stream may have a temperature less than 100 °C, e.g., less than 90 °C, less than 800 °C, less than 70 °C, less than 60 °C, or less than 50 °C.

[0025] In some cases, the first cooling operation reduces the temperature of the crude product stream by at least 50 °C, e.g., at least 100 °C, at least 125 °C, at least 150 °C, at least 175 °C, at least 200 °C, at least 225 °C, or at least 250 °C. In some cases, the second cooling operation reduces the temperature of the first cooled crude product stream by at least 25 °C, e.g., at least 50 °C, at least 75 °C, least 100 °C, least 125 °C, least 150 °C, at least 175 °C, at least 200 °C, at least 225 °C, or at least 250 °C.

[0026] In terms of ranges, the first cooled crude product stream may have a temperature ranging from 25 °C to 150 °C, e.g., from 35 °C to 100 °C, from 35 °C to 80 °C, from 35 °C to 70 °C, or from 40 °C to 60 °C. In terms of ranges, the second cooled crude product stream may have a temperature ranging from 15 °C to 100 °C, e.g., from 20 °C to 95 °C, from 30 °C to 100 °C, from 25 °C to 75 °C, or from 40 °C to 60 °C.

[0027] Cooling units are well known, and the cooling units used in the present process may vary widely. For example, various heat exchange units may be employed, alone or in

combination with one another, to achieve the cooling.

[0028] Preferably, the cooling is achieved using one or more quench condensers (herein referred to simply as quenchers). In one cases, two quenchers configured in series are employed. A quench condenser is known as a particular variety of condenser that quenches a vapor stream (or vapor components of a stream) by using a (recycled) process liquid, e.g., process cooling water. In some embodiments, a slip stream of liquid is drawn from the first cooled product stream and/or the second cooled product stream, and directed to the top of the condenser where it serves as the liquid feed. In some cases, one of the quenchers may utilize process cooling water, while another may utilize refrigerated water, which advantageously provides for cooling efficiencies due to the use of less refrigerated water overall. In some cases, refrigerated water may only be used in the last cooling operation.

[0029] The liquid may be used to achieve the cooling in the quencher. In the present case, at least some of the quenchers effectively utilize process cooling water to achieve the quenching, which, in addition to other aforementioned benefits, improves overall process efficiency.

[0030] The process, in some embodiments, employs the absorbing step. The absorbing step may be preferably configured downstream of the cooling step. The absorbing step may comprise absorbing at least a portion of the crude product stream to form an absorbent stream and an absorbed product stream. The absorbing operation itself may vary widely, and in some cases may comprise contacting at least a portion of the crude product stream with an absorbent.

Preferably the absorbent has a temperature below 100 °C, e.g., below 75 °C, below 50 °C, below 30 °C, below 25 °C, or below 20 °C. In terms of ranges, the absorbent may have a temperature ranging from 0 °C to 100 °C, e.g., from 3 °C to 75 °C, from 3 °C to 50 °C, or from 5 °C to 25 °C.

[0031] The absorbent may vary widely. The absorbent may be selected from the group consisting of water, acetic acid, acrylic acid, formalin, methanol, other alcohols, acrylate esters, acetate esters, acetic anhydride, ketones, and combinations thereof. Preferably, the absorbent is water. In one embodiment, the absorbent fed to the absorbent step has a temperature below 100 °C, e.g., below 75 °C, below 50 °C, below 30 °C, below 25 °C, or below 20 °C. In terms of ranges, the absorbent has a temperature ranging from 0 °C to 100 °C, e.g., from 3 °C to 75 °C, from 3 °C to 50 °C, or from 5 °C to 25 °C.

[0032] Preferably, the process utilizes two cooling operations and an absorption operation. Thus, the cooling, e.g., quenching, comprises cooling the crude product stream to form the first cooled crude product stream and cooling the first cooled crude product stream to form the second cooled crude product stream, and the absorbing comprises absorbing the second cooled crude product stream to form the absorbent stream and the absorbed product stream.

[0033] The absorbed product stream may comprise acrylic acid, alkylenating agent, acetic acid, water, and impurities. Advantageously, the absorbed product stream may comprise low amounts of light ends. Exemplary light ends include oxygen, nitrogen, carbon monoxide, carbon dioxide, methanol, methyl acetate, methyl acrylate, acetaldehyde, hydrogen, acetone, and mixtures thereof. In some embodiments, the cooled crude product stream comprises less than 5 wt% light ends, e.g., less than 3 wt%, less than 2 wt%, less than 1 wt%, less than 800 wppm, less than 500 ppm, less than 300 ppm, or less than 100 ppm. In terms of ranges, the cooled crude product stream may comprise from 0 to 5 wt% light ends, e.g., from 0.1 ppm to 3 wt%, from 1 ppm to 2 wt%, from 25 ppm to 2 wt%, from 50 ppm to 1 wt%, from 100 ppm to 800 ppm, or from 200 ppm to 500 ppm. Weight percentages and ppm levels are based on total weight of the cooled crude product stream.

[0034] Exemplary compositional data for the absorbed crude product stream are shown in Table la. Components other than those listed in Table la may also be present in the absorbed product stream. Others light ends include formic acid, methyl acrylate, methyl acetate, and dimethyl ketone. TABLE la

ABSORBED PRODUCT STREAM COMPOSITIONS

Component Cone. Cone. Cone. Cone.

Acrylic Acid 1 to 75 wt% 1 to 50 wt% 2 to 40 wt% 5 to 35 wt%

Alkylenating Agent(s) 0.1 to 75 wt% 0.5 to 65 wt% 1 to 55 wt% 5 to 55 wt%

Acetic Acid 1 to 90 wt% 5 to 70 wt% 10 to 60 wt% 15 to 55 wt%

Water 1 to 65 wt% 5 to 50 wt% 10 to 35 wt% 10 to 30 wt%

Methanol 0 to 500 ppm 10 to 300 ppm 50 to 250 ppm 100 to 200 ppm

Propionic Acid 0 to 500 ppm 5 to 200 ppm 10 to 100 ppm 25 to 75 ppm

Oxygen 0 to 50 ppm 0.1 to 50 ppm 0.1 to 25 ppm 0.5 to 10 ppm

Nitrogen 0 to 500 ppm 5 to 200 ppm 10 to 100 ppm 25 to 75 ppm

Carbon Monoxide 0 to 50 ppm 0.1 to 50 ppm 0.1 to 25 ppm 0.5 to 10 ppm

Carbon Dioxide 0 to 500 ppm 10 to 300 ppm 50 to 250 ppm 100 to 200 ppm

Other Light Ends 0 to 500 ppm 10 to 300 ppm 50 to 250 ppm 100 to 200 ppm

[0035] The unique absorbed crude product stream of the present invention may be separated in a separation zone to form a final product, e.g., a final acrylic acid product.

[0036] The process may further comprise the step of recycling a portion of the absorbed crude product stream to the cooling step. The inventors have found that the addition of a

polymerization inhibitor surprisingly reduces acrylic acid polymerization in the

cooling/absorption operation and in the separation zone as a whole. In some cases, the polymerization inhibitor may be added to the feed liquid. In cases where a slip stream of liquid is drawn from the first and/or second cooled product stream and directed to the top of the condenser, polymerization inhibitor may be added to the recycled slip stream.

[0037] In one embodiment, the process comprises the step of separating at least a portion of the absorbed crude product stream to form an alkylenating agent stream and an intermediate product stream. This separating step may be referred to as an "akylenating agent split." In one embodiment, the alkylenating agent stream comprises significant amounts of alkylenating agent(s). For example, the alkylenating agent stream may comprise at least 1 wt% alkylenating agent(s), e.g., at least 5 wt%, at least 10 wt%, at least 15 wt%, or at least 25 wt%. In terms of ranges, the alkylenating stream may comprise from 1 wt% to 75 wt% alkylenating agent(s), e.g., from 3 to 50 wt%, from 3 wt% to 25 wt%, or from 10 wt% to 20 wt%. In terms of upper limits, the alkylenating stream may comprise less than 75 wt% alkylenating agent(s), e.g. less than 50 wt% or less than 40 wt%. In preferred embodiments, the alkylenating agent is formaldehyde. [0038] As noted above, the presence of alkylenating agent in the absorbed crude product stream adds unpredictability and problems to separation schemes. Without being bound by theory, it is believed that formaldehyde reacts in many side reactions with water to form byproducts. The following side reactions are exemplary:

• HO(CH ₂ 0)i-iH + HOCH2OH→ HO(CH ₂ 0)iH + H2O for i > 1.

[0039] Without being bound by theory, it is believed that, in some embodiments, as a result of these reactions, the alkylenating agent, e.g., formaldehyde, acts as a "light" component at higher temperatures and as a "heavy" component at lower temperatures. The reaction(s) are exothermic. Accordingly, the equilibrium constant increases as temperature decreases and decreases as temperature increases. At lower temperatures, the larger equilibrium constant favors methylene glycol and oligomer production and formaldehyde becomes limited, and, as such, behaves as a heavy component. At higher temperatures, the smaller equilibrium constant favors formaldehyde production and methylene glycol becomes limited. As such, formaldehyde behaves as a light component. In view of these difficulties, as well as others, the separation of streams that comprise water and formaldehyde cannot be expected to behave as a typical two- component system. These features contribute to the unpredictability and difficulty of the separation of the unique crude product stream of the present invention.

[0040] The present invention, surprisingly and unexpectedly, achieves effective separation of alkylenating agent(s) from the inventive absorbed product stream to yield a purified product comprising acrylate product and very low amounts of other impurities. Due to the low amount of light ends in the absorbed product stream, smaller column(s) may be utilized (as compared to the column(s) otherwise required) to achieve the alkylenating agent(s) separation.

[0041] In one embodiment, the alkylenating split is performed such that a lower amount of acetic acid is present in the resulting alkylenating stream. Preferably, the alkylenating agent stream comprises little or no acetic acid. As an example, the alkylenating agent stream, in some embodiments, comprises less than 50 wt% acetic acid, e.g., less than 45 wt%, less than 25 wt%, less than 10 wt%, less than 5 wt%, less than 3 wt%, or less than 1 wt%. Surprisingly and unexpectedly, the present invention provides for the lower amounts of acetic acid in the alkylenating agent stream, which, beneficially reduces or eliminates the need for further treatment of the alkylenating agent stream to remove acetic acid. In some embodiments, the alkylenating agent stream may be treated to remove water therefrom, e.g., to purge water.

[0042] In some embodiments, the alkylenating agent split is performed in at least one column, e.g., at least two columns or at least three columns. Preferably, the alkylenating agent is performed in a two column system. In other embodiments, the alkylenating agent split is performed via contact with an extraction agent. In other embodiments, the alkylenating agent split is performed via precipitation methods, e.g., crystallization, and/or azeotropic distillation. Of course, other suitable separation methods may be employed either alone or in combination with the methods mentioned herein.

[0043] The intermediate product stream comprises acrylate products. In one embodiment, the intermediate product stream comprises a significant portion of acrylate products, e.g., acrylic acid. For example, the intermediate product stream may comprise at least 5 wt% acrylate products, e.g., at least 25 wt%, at least 40 wt%, at least 50 wt%, or at least 60 wt%. In terms of ranges, the intermediate product stream may comprise from 5 wt% to 99 wt% acrylate products, e.g. from 10 wt% to 90 wt%, from 25 wt% to 75 wt%, or from 35 wt% to 65 wt%. The intermediate product stream, in one embodiment, comprises little if any alkylenating agent. For example, the intermediate product stream may comprise less than 1 wt% alkylenating agent, e.g., less than 0.1 wt% alkylenating agent, less than 0.05 wt%, or less than 0.01 wt%. In addition to the acrylate products, the intermediate product stream optionally comprises acetic acid, water, propionic acid and other components.

[0044] In some cases, the intermediate acrylate product stream comprises higher amounts of alkylenating agent. For example, in one embodiment, the intermediate acrylate product stream comprises from 1 wt% to 50 wt% alkylenating agent, e.g., from 1 wt% to 10 wt% or from 5 wt% to 50 wt%. In terms of limits, the intermediate acrylate product stream may comprise at least 1 wt% alkylenating agent, e.g., at least 5 wt% or at least 10 wt%.

[0045] In one embodiment, the inventive process operates at a high process efficiency. For example, the process efficiency may be at least 10%, e.g., at least 20% or at least 35%. In one embodiment, the process efficiency is calculated based on the flows of reactants into the reaction zone. The process efficiency may be calculated by the following formula:

Process Efficiency = 2NHACA/[NHOA _C + NHCHO + Nmo] where:

• NHACA is the molar production rate of acrylate products; and

• NHOAC, NHCHO , and Nmo are the molar feed rates of acetic acid, formaldehyde, and water. Production of Acrylate Products

[0046] Any suitable reaction and/or separation scheme may be employed to form the crude product stream as long as the reaction provides the crude product stream components that are discussed above. For example, in some embodiments, the acrylate product stream is formed by contacting an alkanoic acid, e.g., acetic acid, or an ester thereof with an alkylenating agent, e.g., a methylenating agent, for example formaldehyde, under conditions effective to form the crude acrylate product stream. Preferably, the contacting is performed over a suitable catalyst. The crude product stream may be the reaction product of the alkanoic acid-alkylenating agent reaction. In a preferred embodiment, the crude product stream is the reaction product of the aldol condensation reaction of acetic acid and formaldehyde, which is conducted over a catalyst comprising vanadium and titanium. In one embodiment, the crude product stream is the product of a reaction in wherein methanol with acetic acid are combined to generate formaldehyde in situ. The aldol condensation then follows. In one embodiment, a methanol-formaldehyde solution is reacted with acetic acid to form the crude product stream.

[0047] The alkanoic acid, or an ester of the alkanoic acid, may be of the formula R-CH2- COOR, where R and R are each, independently, hydrogen or a saturated or unsaturated alkyl or aryl group. As an example, R and R' may be a lower alkyl group containing for example 1-4 carbon atoms. In one embodiment, an alkanoic acid anhydride may be used as the source of the alkanoic acid. In one embodiment, the reaction is conducted in the presence of an alcohol, preferably the alcohol that corresponds to the desired ester, e.g., methanol. In addition to reactions used in the production of acrylic acid, the inventive catalyst, in other embodiments, may be employed to catalyze other reactions. [0048] The alkanoic acid, e.g., acetic acid, may be derived from any suitable source including natural gas, petroleum, coal, biomass, and so forth. As examples, acetic acid may be produced via methanol carbonylation, acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, and anaerobic fermentation. As petroleum and natural gas prices fluctuate, becoming either more or less expensive, methods for producing acetic acid and intermediates such as methanol and carbon monoxide from alternate carbon sources have drawn increasing interest. In particular, when petroleum is relatively expensive compared to natural gas, it may become advantageous to produce acetic acid from synthesis gas ("syngas") that is derived from any available carbon source. US Patent No. 6,232,352, which is hereby incorporated by reference, for example, teaches a method of retrofitting a methanol plant for the manufacture of acetic acid. By retrofitting a methanol plant, the large capital costs associated with carbon monoxide generation for a new acetic acid plant are significantly reduced or largely eliminated. All or part of the syn gas is diverted from the methanol synthesis loop and supplied to a separator unit to recover carbon monoxide and hydrogen, which are then used to produce acetic acid.

[0049] In some embodiments, at least some of the raw materials for the above-described aldol condensation process may be derived partially or entirely from syngas. For example, the acetic acid may be formed from methanol and carbon monoxide, both of which may be derived from syngas. For example, the methanol may be formed by steam reforming syngas, and the carbon monoxide may be separated from syngas. In other embodiments, the methanol may be formed in a carbon monoxide unit, e.g., as described in EP2076480; EP1923380; EP2072490;

EP1914219; EP1904426; EP2072487; EO2072492; EP2072486; EP2060553; EP1741692;

EP1907344; EP2060555; EP2186787; EP2072488; and US Patent No. 7842844, which are hereby incorporated by reference. Of course, this listing of methanol sources is merely exemplary and is not meant to be limiting. In addition, the above-identified methanol sources, inter alia, may be used to form the formaldehyde, e.g., in situ, which, in turn may be reacted with the acetic acid to form the acrylic acid. The syngas, in turn, may be derived from variety of carbon sources. The carbon source, for example, may be selected from the group consisting of natural gas, oil, petroleum, coal, biomass, and combinations thereof.

[0050] Methanol carbonylation processes suitable for production of acetic acid are described in US Patent Nos. 7,208,624, 7,115,772, 7,005,541, 6,657,078, 6,627,770, 6,143,930, 5,599,976, 5, 144,068, 5,026,908, 5,001,259, and 4,994,608, all of which are hereby incorporated by reference.

[0051] US Patent No. RE 35,377, which is hereby incorporated by reference, provides a method for the production of methanol by conversion of carbonaceous materials such as oil, coal, natural gas and biomass materials. The process includes hydrogasification of solid and/or liquid carbonaceous materials to obtain a process gas which is steam pyrolized with additional natural gas to form syn gas. The syn gas is converted to methanol which may be carbonylated to acetic acid. US Patent No. 5,821,111, which discloses a process for converting waste biomass through gasification into syn gas, as well as US Patent No. 6,685,754 are hereby incorporated by reference.

[0052] In one optional embodiment, the acetic acid that is utilized in the condensation reaction comprises acetic acid and may also comprise other carboxylic acids, e.g., propionic acid, esters, and anhydrides, as well as acetaldehyde and acetone. In one embodiment, the acetic acid fed to the condensation reaction comprises propionic acid. For example, the acetic acid fed to the reaction may comprise from 0.001 wt% to 15 wt% propionic acid, e.g., from 0.001 wt% to 0.11 wt%, from 0.125 wt% to 12.5 wt%, from 1.25 wt% to 11.25 wt%, or from 3.75 wt% to 8.75 wt%. Thus, the acetic acid feed stream may be a cruder acetic acid feed stream , e.g., a less- refined acetic acid feed stream.

[0053] As used herein, "alkylenating agent" means an aldehyde or precursor to an aldehyde suitable for reacting with the alkanoic acid, e.g., acetic acid, to form an unsaturated acid, e.g., acrylic acid, or an alkyl acrylate. In preferred embodiments, the alkylenating agent comprises a methylenating agent such as formaldehyde, which preferably is capable of adding a methylene group (=CH2) to the organic acid. Other alkylenating agents may include, for example, acetaldehyde, propanal, butanal, aryl aldehydes, benzyl aldehydes, alcohols, and combinations thereof. This listing is not exclusive and is not meant to limit the scope of the invention. In one embodiment, an alcohol may serve as a source of the alkylenating agent. For example, the alcohol may be reacted in situ to form the alkylenating agent, e.g., the aldehyde.

[0054] The alkylenating agent, e.g., formaldehyde, may be derived from any suitable source. Exemplary sources may include, for example, aqueous formaldehyde solutions, anhydrous formaldehyde derived from a formaldehyde drying procedure, trioxane, diether of methylene glycol, and paraformaldehyde. In a preferred embodiment, the formaldehyde is produced via a a methanol oxidation process, which reacts methanol and oxygen to yield the formaldehyde.

[0055] In other embodiments, the alkylenating agent is a compound that is a source of formaldehyde. Where forms of formaldehyde that are not as freely or weakly complexed are used, the formaldehyde will form in situ in the condensation reactor or in a separate reactor prior to the condensation reactor. Thus for example, trioxane may be decomposed over an inert material or in an empty tube at temperatures over 350 °C or over an acid catalyst at over 100 °C to form the formaldehyde.

[0056] In one embodiment, the alkylenating agent corresponds to Formula I.

[0057] In this formula, Rs and R ₆ may be independently selected from C1-C12 hydrocarbons, preferably, C1-C12 alkyl, alkenyl or aryl, or hydrogen. Preferably, R5 and R ₆ are independently Ci-C ₆ alkyl or hydrogen, with methyl and/or hydrogen being most preferred. X may be either oxygen or sulfur, preferably oxygen; and n is an integer from 1 to 10, preferably 1 to 3. In some embodiments, m is 1 or 2, preferably 1.

[0058] In one embodiment, the compound of formula I may be the product of an equilibrium reaction between formaldehyde and methanol in the presence of water. In such a case, the compound of formula I may be a suitable formaldehyde source. In one embodiment, the formaldehyde source includes any equilibrium composition. Examples of formaldehyde sources include but are not restricted to methylal (1, 1 dimethoxymethane); polyoxymethylenes -(CH2- 0)i- wherein i is from 1 to 100; formalin; and other equilibrium compositions such as a mixture of formaldehyde, methanol, and methyl propionate. In one embodiment, the source of formaldehyde is selected from the group consisting of 1, 1 dimethoxymethane; higher formals of formaldehyde and methanol; and CH3-0-(CH2-0)i-CH3 where i is 2. [0059] The alkylenating agent may be used with or without an organic or inorganic solvent.

[0060] The term "formalin," refers to a mixture of formaldehyde, methanol, and water. In one embodiment, formalin comprises from 25 wt% to 65% formaldehyde; from 0.01 wt% to 25 wt% methanol; and from 25 wt% to 70 wt% water. In cases where a mixture of formaldehyde, methanol, and methyl propionate is used, the mixture comprises less than 10 wt% water, e.g., less than 5 wt% or less than 1 wt%.

[0061] In some embodiments, the condensation reaction may achieve favorable conversion of acetic acid and favorable selectivity and productivity to acrylates. For purposes of the present invention, the term "conversion" refers to the amount of acetic acid in the feed that is converted to a compound other than acetic acid. Conversion is expressed as a percentage based on acetic acid in the feed. The conversion of acetic acid may be at least 10%, e.g., at least 20%, at least 40%, or at least 50%.

[0062] Selectivity, as it refers to the formation of acrylate product, is expressed as the ratio of the amount of carbon in the desired product(s) and the amount of carbon in the total products. This ratio may be multiplied by 100 to arrive at the selectivity. Preferably, the catalyst selectivity to acrylate products, e.g., acrylic acid and methyl acrylate, is at least 40 mol%, e.g., at least 50 mol%, at least 60 mol%, or at least 70 mol%. In some embodiments, the selectivity to acrylic acid is at least 30 mol %, e.g., at least 40 mol%, or at least 50 mol%; and/or the selectivity to methyl acrylate is at least 10 mol%, e.g., at least 15 mol%, or at least 20 mol%.

[0063] The terms "productivity" or "space time yield" as used herein, refers to the grams of a specified product, e.g., acrylate products, formed per hour during the condensation based on the liters of catalyst used . A productivity of at least 20 grams of acrylate product per liter catalyst per hour, e.g., at least 40 grams of acrylates per liter catalyst per hour or at least 100 grams of acrylates per liter catalyst per hour, is preferred. In terms of ranges, the productivity preferably is from 20 to 500 grams of acrylates per liter catalyst per hour, e.g., from 20 to 200 grams of acrylates per liter catalyst per hour or from 40 to 140 grams of acrylates per liter catalyst per hour.

[0064] In one embodiment, the inventive process yields at least 1,800 kg/hr of finished acrylic acid, e.g., at least 3,500 kg/hr, at least 18,000 kg/hr, or at least 37,000 kg/hr. [0065] Preferred embodiments of the inventive process demonstrate a low selectivity to undesirable products, such as carbon monoxide and carbon dioxide. The selectivity to these undesirable products preferably is less than 29%, e.g., less than 25% or less than 15%. More preferably, these undesirable products are not detectable. Formation of alkanes, e.g., ethane, may be low, and ideally less than 2%, less than 1%, or less than 0.5% of the acetic acid passed over the catalyst is converted to alkanes, which have little value other than as fuel.

[0066] The alkanoic acid or ester thereof and alkylenating agent may be fed independently or after prior mixing to a reactor containing the catalyst. The reactor may be any suitable reactor or combination of reactors. Preferably, the reactor comprises a fixed bed reactor or a series of fixed bed reactors. In one embodiment, the reactor is a packed bed reactor or a series of packed bed reactors. In one embodiment, the reactor is a fixed bed reactor. Of course, other reactors such as a continuous stirred tank reactor or a fluidized bed reactor, may be employed.

[0067] In some embodiments, the alkanoic acid, e.g., acetic acid, and the alkylenating agent, e.g., formaldehyde, are fed to the reactor at a molar ratio of at least 0.10: 1, e.g., at least 0.75: 1 or at least 1 : 1. In terms of ranges the molar ratio of alkanoic acid to alkylenating agent may range from 0.10: 1 to 10: 1 or from 0.75: 1 to 5: 1. In some embodiments, the reaction of the alkanoic acid and the alkylenating agent is conducted with a stoichiometric excess of alkanoic acid. In these instances, acrylate selectivity may be improved. As an example the acrylate selectivity may be at least 10% higher than a selectivity achieved when the reaction is conducted with an excess of alkylenating agent, e.g., at least 20% higher or at least 30% higher. In other embodiments, the reaction of the alkanoic acid and the alkylenating agent is conducted with a stoichiometric excess of alkylenating agent.

[0068] The condensation reaction may be conducted at a temperature of at least 250 °C, e.g., at least 300 °C, or at least 350 °C. In terms of ranges, the reaction temperature may range from 200 °C to 500 °C, e.g., from 250 °C to 400 °C, or from 250 °C to 350 °C. Residence time in the reactor may range from 1 second to 200 seconds, e.g., from 1 second to 100 seconds. Reaction pressure is not particularly limited, and the reaction is typically performed near atmospheric pressure. In one embodiment, the reaction may be conducted at a pressure ranging from 0 kPa to 4100 kPa, e.g., from 3 kPa to 345 kPa, or from 6 to 103 kPa. The acetic acid conversion, in some embodiments, may vary depending upon the reaction temperature. [0069] In one embodiment, the reaction is conducted at a gas hourly space velocity ("GHSV") greater than 600 hr ^"1 , e.g., greater than 1000 hr ^"1 or greater than 2000 hr ^"1 . In one embodiment, the GHSV ranges from 600 hr ^-1 to 10000 hr ^-1 , e.g., from 1000 hr ^-1 to 8000 hr ¹ or from 1500 hr ¹ to 7500 hr ^"1 . As one particular example, when GHSV is at least 2000 hr ^"1 , the acrylate product STY may be at least 150 g/hr/liter.

[0070] Water may be present in the reactor in amounts up to 60 wt%, by weight of the reaction mixture, e.g., up to 50 wt% or up to 40 wt%. Water, however, is preferably reduced due to its negative effect on process rates and separation costs.

[0071] In one embodiment, an inert or reactive gas is supplied to the reactant stream.

Examples of inert gases include, but are not limited to, nitrogen, helium, argon, and methane. Examples of reactive gases or vapors include, but are not limited to, oxygen, carbon oxides, sulfur oxides, and alkyl halides. When reactive gases such as oxygen are added to the reactor, these gases, in some embodiments, may be added in stages throughout the catalyst bed at desired levels as well as feeding with the other feed components at the beginning of the reactors. The addition of these additional components may improve reaction efficiencies.

[0072] In one embodiment, the unreacted components such as the alkanoic acid and formaldehyde as well as the inert or reactive gases that remain are recycled to the reactor after sufficient separation from the desired product.

[0073] When the desired product is an unsaturated ester made by reacting an ester of an alkanoic acid ester with formaldehyde, the alcohol corresponding to the ester may also be fed to the reactor either with or separately to the other components. For example, when methyl acrylate is desired, methanol may be fed to the reactor. The alcohol, amongst other effects, reduces the quantity of acids leaving the reactor. It is not necessary that the alcohol is added at the beginning of the reactor and it may for instance be added in the middle or near the back, in order to effect the conversion of acids such as propionic acid, methacrylic acid to their respective esters without depressing catalyst activity. In one embodiment, the alcohol may be added downstream of the reactor.

Catalyst Composition [0074] The catalyst may be any suitable catalyst composition. As one example, condensation catalyst consisting of mixed oxides of vanadium and phosphorus have been investigated and described in M. Ai, J. Catal, 107, 201 (1987); M. Ai, J. Catal, 124, 293 (1990); M. Ai, Appl. Catal., 36, 221 (1988); and M. Ai, Shokubai, 29, 522 (1987). Other examples include binary vanadium-titanium phosphates, vanadium-silica-phosphates, and alkali metal-promoted silicas, e.g., cesium- or potassium-promoted silicas.

[0075] In a preferred embodiment, the inventive process employs a catalyst composition comprising vanadium, titanium, and optionally at least one oxide additive. The oxide additive(s), if present, are preferably present in the active phase of the catalyst. In one embodiment, the oxide additive(s) are selected from the group consisting of silica, alumina, zirconia, and mixtures thereof or any other metal oxide other than metal oxides of titanium or vanadium. Preferably, the molar ratio of oxide additive to titanium in the active phase of the catalyst composition is greater than 0.05: 1, e.g., greater than 0.1 : 1, greater than 0.5: 1, or greater than 1 : 1. In terms of ranges, the molar ratio of oxide additive to titanium in the inventive catalyst may range from 0.05: 1 to 20: 1, e.g., from 0.1 : 1 to 10: 1, or from 1 : 1 to 10: 1. In these embodiments, the catalyst comprises titanium, vanadium, and one or more oxide additives and have relatively high molar ratios of oxide additive to titanium.

[0076] In other embodiments, the catalyst may further comprise other compounds or elements (metals and/or non-metals). For example, the catalyst may further comprise phosphorus and/or oxygen. In these cases, the catalyst may comprise from 15 wt% to 45 wt% phosphorus, e.g., from 20 wt% to 35 wt% or from 23 wt% to 27 wt%; and/or from 30 wt% to 75 wt% oxygen, e.g., from 35 wt% to 65 wt% or from 48 wt% to 51 wt%.

[0077] In some embodiments, the catalyst further comprises additional metals and/or oxide additives. These additional metals and/or oxide additives may function as promoters. If present, the additional metals and/or oxide additives may be selected from the group consisting of copper, molybdenum, tungsten, nickel, niobium, and combinations thereof. Other exemplary promoters that may be included in the catalyst of the invention include lithium, sodium, magnesium, aluminum, chromium, manganese, iron, cobalt, calcium, yttrium, ruthenium, silver, tin, barium, lanthanum, the rare earth metals, hafnium, tantalum, rhenium, thorium, bismuth, antimony, germanium, zirconium, uranium, cesium, zinc, and silicon and mixtures thereof. Other modifiers include boron, gallium, arsenic, sulfur, halides, Lewis acids such as BF ₃ , ZnBr ₂ , and SnCU. Exemplary processes for incorporating promoters into catalyst are described in US Patent No. 5,364,824, the entirety of which is incorporated herein by reference.

[0078] If the catalyst comprises additional metal(s) and/or metal oxides(s), the catalyst optionally may comprise additional metals and/or metal oxides in an amount from 0.001 wt% to 30 wt%, e.g., from 0.01 wt% to 5 wt% or from 0.1 wt% to 5 wt%. If present, the promoters may enable the catalyst to have a weight/weight space time yield of at least 25 grams of acrylic acid/gram catalyst-h, e.g., least 50 grams of acrylic acid/gram catalyst-h, or at least 100 grams of acrylic acid/gram catalyst-h.

[0079] In some embodiments, the catalyst is unsupported. In these cases, the catalyst may comprise a homogeneous mixture or a heterogeneous mixture as described above. In one embodiment, the homogeneous mixture is the product of an intimate mixture of vanadium and titanium oxides, hydroxides, and phosphates resulting from preparative methods such as controlled hydrolysis of metal alkoxides or metal complexes. In other embodiments, the heterogeneous mixture is the product of a physical mixture of the vanadium and titanium phosphates. These mixtures may include formulations prepared from phosphorylating a physical mixture of preformed hydrous metal oxides. In other cases, the mixture(s) may include a mixture of preformed vanadium pyrophosphate and titanium pyrophosphate powders.

[0080] In another embodiment, the catalyst is a supported catalyst comprising a catalyst support in addition to the vanadium, titanium, oxide additive, and optionally phosphorous and oxygen, in the amounts indicated above (wherein the molar ranges indicated are without regard to the moles of catalyst support, including any vanadium, titanium, oxide additive, phosphorous or oxygen contained in the catalyst support). The total weight of the support (or modified support), based on the total weight of the catalyst, preferably is from 75 wt.% to 99.9 wt.%, e.g., from 78 wt.% to 97 wt.% or from 80 wt.% to 95 wt.%. The support may vary widely. In one embodiment, the support material is selected from the group consisting of silica, alumina, zirconia, titania, aluminosilicates, zeolitic materials, mixed metal oxides (including but not limited to binary oxides such as Si0 ₂ -Al ₂ 0 ₃ , Si0 ₂ -Ti0 ₂ , Si0 ₂ -ZnO, Si0 ₂ -MgO, Si0 ₂ -Zr0 ₂ , Al ₂ 0 ₃ -MgO, Al ₂ 0 ₃ -Ti0 ₂ , Al ₂ 0 ₃ -ZnO, Ti0 ₂ -MgO, Ti0 ₂ -Zr0 ₂ , Ti0 ₂ -ZnO, Ti0 ₂ -Sn0 ₂ ) and mixtures thereof, with silica being one preferred support. In embodiments where the catalyst comprises a titania support, the titania support may comprise a major or minor amount of rutile and/or anatase titanium dioxide. Other suitable support materials may include, for example, stable metal oxide-based supports or ceramic-based supports. Preferred supports include silicaceous supports, such as silica, silica/alumina, a Group IIA silicate such as calcium metasilicate, pyrogenic silica, high purity silica, silicon carbide, sheet silicates or clay minerals such as montmorillonite, beidellite, saponite, pillared clays, other microporous and mesoporous materials, and mixtures thereof. Other supports may include, but are not limited to, iron oxide, magnesia, steatite, magnesium oxide, carbon, graphite, high surface area graphitized carbon, activated carbons, and mixtures thereof. These listings of supports are merely exemplary and are not meant to limit the scope of the present invention.

[0081] In some embodiments, a zeolitic support is employed. For example, the zeolitic support may be selected from the group consisting of montmorillonite, NH ₄ ferrierite, H- mordenite-PVOx, vermiculite-1, H-ZSM5, NaY, H-SDUSY, Y zeolite with high SAR, activated bentonite, H-USY, MONT-2, HY, mordenite SAR 20, SAPO-34, Aluminosilicate (X), VUSY, Aluminosilicate (CaX), Re-Y, and mixtures thereof. H-SDUSY, VUSY, and H-USY are modified Y zeolites belonging to the faujasite family. In one embodiment, the support is a zeolite that does not contain any metal oxide modifier(s). In some embodiments, the catalyst composition comprises a zeolitic support and the active phase comprises a metal selected from the group consisting of vanadium, aluminum, nickel, molybdenum, cobalt, iron, tungsten, zinc, copper, titanium cesium bismuth, sodium, calcium, chromium, cadmium, zirconium, and mixtures thereof. In some of these embodiments, the active phase may also comprise hydrogen, oxygen, and/or phosphorus.

[0082] In other embodiments, in addition to the active phase and a support, the inventive catalyst may further comprise a support modifier. A modified support, in one embodiment, relates to a support that includes a support material and a support modifier, which, for example, may adjust the chemical or physical properties of the support material such as the acidity or basicity of the support material. In embodiments that use a modified support, the support modifier is present in an amount from 0.1 wt.% to 50 wt.%, e.g., from 0.2 wt.% to 25 wt.%, from 0.5 wt.% to 15 wt.%, or from 1 wt.% to 8 wt.%, based on the total weight of the catalyst composition. [0083] In one embodiment, the support modifier is an acidic support modifier. In some embodiments, the catalyst support is modified with an acidic support modifier. The support modifier similarly may be an acidic modifier that has a low volatility or little volatility. The acidic modifiers may be selected from the group consisting of oxides of Group IVB metals, oxides of Group VB metals, oxides of Group VIB metals, iron oxides, aluminum oxides, and mixtures thereof. In one embodiment, the acidic modifier may be selected from the group consisting of WO3, M0O3, Fe ₂ 0 ₃ , Cr ₂ 0 ₃ , V ₂ Os, Mn0 ₂ , CuO, Co ₂ 0 ₃ , Bi ₂ 0 ₃ , Ti0 ₂ , Zr0 ₂ , Nb ₂ Os, Ta ₂ Os, A1 ₂ 0 ₃ , B ₂ 0 ₃ , P ₂ Os, and Sb ₂ 0 ₃ .

[0084] In another embodiment, the support modifier is a basic support modifier. The presence of chemical species such as alkali and alkaline earth metals, are normally considered basic and may conventionally be considered detrimental to catalyst performance. The presence of these species, however, surprisingly and unexpectedly, may be beneficial to the catalyst performance. In some embodiments, these species may act as catalyst promoters or a necessary part of the acidic catalyst structure such in layered or sheet silicates such as montmorillonite. Without being bound by theory, it is postulated that these cations create a strong dipole with species that create acidity.

[0085] Additional modifiers that may be included in the catalyst include, for example, boron, aluminum, magnesium, zirconium, and hafnium.

[0086] As will be appreciated by those of ordinary skill in the art, the support materials, if included in the catalyst of the present invention, preferably are selected such that the catalyst system is suitably active, selective and robust under the process conditions employed for the formation of the desired product, e.g., acrylic acid or alkyl acrylate. Also, the active metals and/or pyrophosphates that are included in the catalyst of the invention may be dispersed throughout the support, coated on the outer surface of the support (egg shell) or decorated on the surface of the support. In some embodiments, in the case of macro- and meso-porous materials, the active sites may be anchored or applied to the surfaces of the pores that are distributed throughout the particle and hence are surface sites available to the reactants but are distributed throughout the support particle. [0087] The inventive catalyst may further comprise other additives, examples of which may include: molding assistants for enhancing moldability; reinforcements for enhancing the strength of the catalyst; pore-forming or pore modification agents for formation of appropriate pores in the catalyst, and binders. Examples of these other additives include stearic acid, graphite, starch, cellulose, silica, alumina, glass fibers, silicon carbide, and silicon nitride. Preferably, these additives do not have detrimental effects on the catalytic performances, e.g., conversion and/or activity. These various additives may be added in such an amount that the physical strength of the catalyst does not readily deteriorate to such an extent that it becomes impossible to use the catalyst practically as an industrial catalyst.

Separation

[0088] As discussed above, the cooled crude product stream is separated to yield an intermediate acrylate product stream. The may further comprise the step of separating the intermediate acrylate product stream to form a finished acrylate product stream and a first finished acetic acid stream. The finished acrylate product stream comprises acrylate product(s) and the first finished acetic acid stream comprises acetic acid. The separation of the acrylate products from the intermediate product stream to form the finished acrylate product may be referred to as the "acrylate product split." The process may further comprise the step of separating an alkylenating agent stream to form a purified alkylenating stream and a purified acetic acid stream. The purified alkylenating agent stream comprises a significant portion of alkylenating agent, and the purified acetic acid stream comprises acetic acid and water. The separation of the alkylenating agent from the acetic acid may be referred to as the "acetic acid split."

[0089] In one embodiment, polymerization inhibitors and/or anti-foam agents may be employed in the separation zone, e.g., in the units of the separation zone. The inhibitors may be used to reduce the potential for fouling caused by polymerization of acrylates. The anti-foam agents may be used to reduce potential for foaming in the various streams of the separation zone. The polymerization inhibitors and/or the anti-foam agents may be used at one or more locations in the separation zone. In one embodiment (not shown), a portion of the cooled crude product stream, e.g., absorbed product stream, may be recycled to one or more of the quenchers. In some cases, polymerization inhibitor may be added to the recycled cooled crude product stream.

[0090] FIG. 1 is a flow diagram depicting the formation of the crude product stream and the separation thereof to obtain an intermediate acrylate product stream. Acrylate product system 100 comprises reaction zone 102 and alkylenating agent split zone 132. Reaction zone 102 comprises reactor 106, alkanoic acid feed, e.g., acetic acid feed, 108, alkylenating agent feed, e.g., formaldehyde feed 110, and vaporizer 112.

[0091] Acetic acid and formaldehyde are fed to vaporizer 112 via lines 108 and 110, respectively, to create a vapor feed stream, which exits vaporizer 112 via line 114 and is directed to reactor 106. In one embodiment, lines 108 and 110 may be combined and jointly fed to the vaporizer 112. The temperature of the vapor feed stream in line 114 is preferably from 200°C to 600°C, e.g., from 250°C to 500°C or from 340°C to 425°C. Alternatively, a vaporizer may not be employed and the reactants may be fed directly to reactor 106.

[0092] Any feed that is not vaporized may be removed from vaporizer 112 and may be recycled or discarded. In addition, although line 114 is shown as being directed to the upper half of reactor 106, line 114 may be directed to the middle or bottom of first reactor 106.

Further modifications and additional components to reaction zone 102 and alkylenating agent split zone 132 are described below.

[0093] Reactor 106 contains the catalyst that is used in the reaction to form crude product stream, which is withdrawn, preferably continuously, from reactor 106 via line 116. Although FIG. 1 shows the crude product stream being withdrawn from the bottom of reactor 106, the crude product stream may be withdrawn from any portion of reactor 106. Exemplary composition ranges for the crude product stream are shown in Table 1 above.

[0094] In one embodiment, one or more guard beds (not shown) may be used upstream of the reactor to protect the catalyst from poisons or undesirable impurities contained in the feed or return/recycle streams. Such guard beds may be employed in the vapor or liquid streams.

Suitable guard bed materials may include, for example, carbon, silica, alumina, ceramic, or resins. In one aspect, the guard bed media is functionalized, e.g., silver functionalized, to trap particular species such as sulfur or halogens. [0095] The crude product stream in line 116 is fed to first quencher 180 where it is cooled, as discussed herein. First quencher is fed with liquid feed 181. Although not shown, liquid feed 181 may be a recycled stream from elsewhere in the process. A portion of the first cooled product stream exits first quencher 180 and is directed to second quencher 184 via line 182. Second quencher is fed with liquid feed 186. Although not shown, liquid feed 186 may be a recycled stream from elsewhere in the process, e.g. a refrigerated process stream. Another portion of the first cooled product exits first quencher 180 and is directed to alkylenating agent split unit 132 via line 183. A purge stream in line 188, containing various light ends, exits first quencher 180 and is discarded. The portion of first cooled product stream in line 182 is cooled in second quencher 184, as discussed herein. A portion of the second cooled product stream exits second quencher 184 via line 190 and is directed to absorption unit 192. Another portion of the second cooled product exits second quencher 184 and is directed to alkylenating agent split unit 132 via line 185 (optionally being combined with line 183. A purge stream in line 194, containing various light ends, exits second quencher 184 and is discarded.

[0096] In absorption unit 192, the portion of the second cooled product stream in line 190 is absorbed with an absorbent, which is fed to absorption unit 192 via absorbent feed line 196. Absorption unit 192 yields absorbed product stream in line 198 and absorbent stream in line 199. Absorbed product stream in line 198 contains, among others, acrylic acid, acetic acid, and formaldehyde. Exemplary compositional ranges for the absorbed product stream are shown in Table la. The absorbed product stream in line 198 is fed to alkylenating agent split unit 132.

[0097] Alkylenating agent split unit 132 separates the absorbed product stream into at least one intermediate (acrylate) product stream, which exits via line 118 and at least one alkylenating agent stream, which exits via line 120. Exemplary compositional ranges for the intermediate product stream are shown in Table 2. The intermediate product stream advantageously comprises few if any light ends impurities. TABLE 2

INTERMEDIATE ACRYLATE PRODUCT STREAM COMPOSITION

Cone. (wt%) Cone. (wt%) Cone. (wt%)

Acrylic Acid 5 to 90 10 to 80 25 to 50

Acetic Acid 10 to 95 20 to 80 40 to 60

Water 0.1 to 25 0.5 to 15 1 to 10

Alkylenating Agent 0.1 to 25 0.5 to 15 1 to 10

[0098] In other embodiments, the intermediate acrylate product stream comprises higher amounts of alkylenating agent. For example, the intermediate acrylate product stream may comprise from 1 wt% to 10 wt% alkylenating agent, e.g., from 1 wt% to 8 wt% or from 2 wt% to 5 wt%. In one embodiment, the intermediate acrylate product stream comprises greater than 1 wt% alkylenating agent, e.g., greater than 5 wt% or greater than 10 wt%.

[0099] Exemplary compositional ranges for the alkylenating agent stream are shown in Table 3. The alkylenating agent stream advantageously comprises few if any light ends impurities.

TABLE 3

ALKYLENATING AGENT STREAM COMPOSITION

Cone. (wt%) Cone. (wt%) Cone. (wt%)

Acrylic Acid 0.01 to 25 0.01 to 10 0.05 to 5

Acetic Acid 0.01 to 25 0.01 to 10 0.05 to 5

Water 50 to 95 65 to 90 70 to 85

Alkylenating Agent 1 to 50 5 to 35 10 to 30

[0100] In other embodiments, the alkylenating stream comprises lower amounts of acetic acid.

For example, the alkylenating agent stream may comprise less than 10 wt% acetic acid, e.g., less than 5 wt% or less than 1 wt%.

[0101] As mentioned above, the cooled crude product stream, e.g., the absorbed product stream, of the present invention comprises little, if any, furfural and/or acrolein. As such the derivative stream(s) of the crude product streams will comprise little, if any, furfural and/or acrolein. In one embodiment, the derivative stream(s), e.g., the streams of the separation zone, comprises less than less than 500 wppm acrolein, e.g., less than 100 wppm, less than 50 wppm, or less than 10 wppm. In one embodiment, the derivative stream(s) comprises less than less than 500 wppm furfural, e.g., less than 100 wppm, less than 50 wppm, or less than 10 wppm.

[0102] FIG. 2 shows an overview of a reaction/separation scheme in accordance with the present invention. Acrylate product system 200 comprises reaction zone 202 and alkylenating agent split unit 232. Reaction zone 202 comprises reactor 206, alkanoic acid feed, e.g., acetic acid feed, 208, alkylenating agent feed, e.g., formaldehyde feed 210, and vaporizer 212.

Reaction zone 202 and the components thereof function in a manner similar to reaction zone 102 of FIG. 1. Reaction zone 202 yields a crude product stream, which exits reaction zone 202 via line 216 and is directed to alkylenating agent split unit 232. The components of the crude product stream are discussed above.

[0103] The crude product stream in line 216 is fed to first quencher 280 where it is cooled, as discussed herein. First quencher is fed with liquid feed 281. A portion of the first cooled product stream exits first quencher 280 and is directed to second quencher 284 via line 282. Second quencher is fed with liquid feed 286. Another portion of the first cooled product exits first quencher 280 and is directed to alkylenating agent split unit 232 via line 283. A purge stream in line 288, containing various light ends, exits first quencher 280 and is discarded. The portion of first cooled product stream in line 282 is cooled in second quencher 284, as discussed herein. A portion of the second cooled product stream exits second quencher 284 via line 290 and is directed to absorption unit 292. Another portion of the second cooled product exits second quencher 284 and is directed to alkylenating agent split unit 232 via line 285 (optionally being combined with line 283. A purge stream in line 294, containing various light ends, exits second quencher 284 and is discarded.

[0104] In absorption unit 292, the portion of the second cooled product stream in line 290 is absorbed with an absorbent, which is fed to absorption unit 292 via absorbent feed line 296. Absorption unit 292 yields absorbed product stream in line 298 and absorbent stream in line 299. Absorbed product stream in line 298 contains, among others, acrylic acid, acetic acid, and formaldehyde. Exemplary compositional ranges for Exemplary compositional ranges for the absorbed product stream are shown in Table la. the absorbed product stream are shown in Table la. The absorbed product stream in line 298 is fed to alkylenating agent split unit 232.

[0105] In FIG. 2, alkylenating agent split unit 232 comprises first column 244 and second column 246. Alkylenating agent split unit 232 receives absorbed product stream in line 298 and separates same into at least one alkylenating agent stream and at least one intermediate

(acrylate) product stream. [0106] In operation, as shown in FIG. 2, the absorbed product stream in line 298 is directed to first column 244. First column 244 separates the absorbed product stream into a distillate in line 240 and a residue in line 242. The distillate may be refluxed and the residue may be boiled up as shown. Stream 240 comprises at least 1 wt% alkylenating agent. As such, stream 240 may be considered an alkylenating agent stream. The first column residue exits first column 244 in line 242 and comprises a significant portion of acrylate product. As such, stream 242 is an intermediate product stream. The first column residue in line 242 comprises a significant portion of acrylate product. The first column residue in line 242 may be further purified to obtain a finished acrylate product stream and, optionally, a finished acetic acid streams.

[0107] In one embodiment, the first distillate comprises smaller amounts of acetic acid, e.g., less than 25 wt%, less than 10 wt% , e.g., less than 5 wt% or less than 1 wt%. In one embodiment, the intermediate product stream comprises larger amounts of alkylenating agent, e.g., formadehyde. In some embodiments, the intermediate product stream comprises higher amounts of alkylenating agent, e.g., greater than 1 wt% greater than 5 wt% or greater than 10 wt%.

[0108] Returning to FIG. 2, at least a portion of stream 240 is directed to second column 246. Second column 246 separates the at least a portion of stream 240 into a distillate in line 248 and a residue in line 250. The distillate may be refluxed and the residue may be boiled up as shown. The distillate comprises at least 1 wt% alkylenating agent. Stream 248, like stream 240, may be considered an alkylenating agent stream. The second column residue exits second column 246 in line 250 and comprises a significant portion of acetic acid. At least a portion of line 250 may be returned to first column 244 for further separation. In one embodiment, at least a portion of line 250 is returned, either directly or indirectly, to reactor 206 (not shown).

[0109] Generally, the alkylenating agent split unit may comprise one or more separation units, e.g., two or more or three or more. The alkylenating agent split unit may comprise any suitable separation device or combination of separation devices. For example, the alkylenating agent split unit may comprise a column, e.g., a standard distillation column, an extractive distillation column and/or an azeotropic distillation column. In other embodiments, the alkylenating agent split unit comprises a precipitation unit, e.g., a crystallizer and/or a chiller. In one embodiment, the alkylenating agent split unit comprises two standard distillation columns, as shown in FIG. 2.

[0110] In another embodiment, the alkylenating agent split is performed by contacting the crude product stream with a solvent that is immiscible with water. For example, the

alkylenating agent split unit may comprise at least one liquid-liquid extraction columns.

Preferably, the one or more liquid-liquid extraction units employ one or more extraction agents. Multiple liquid-liquid extraction units may be employed to achieve the alkylenating agent split. Any suitable liquid-liquid extraction devices used for multiple equilibrium stage separations may be used. Also, other separation devices, e.g., traditional columns, may be employed in conjunction with the liquid-liquid extraction unit(s).

[0111] In another embodiment, the alkylenating agent split is performed via azeotropic distillation, which employs an azeotropic agent. In these cases, the azeotropic agent may be selected from the group consisting of methyl isobutylketene, o-xylene, toluene, benzene, n- hexane, cyclohexane, p-xylene, and mixtures thereof. This listing is not exclusive and is not meant to limit the scope of the invention. In another embodiment, the alkylenating agent split is performed via a combination of distillation, e.g., standard distillation, and crystallization. Of course, other suitable separation devices may be employed either alone or in combination with the devices mentioned herein.

[0112] In cases where any of the alkylenating agent split unit comprises at least one column, the column(s) may be operated at suitable temperatures and pressures. In one embodiment, the temperature of the residue exiting the column(s) ranges from 90°C to 130°C, e.g., from 95°C to 120°C or from 100°C to 115°C. The temperature of the distillate exiting the column(s) preferably ranges from 60°C to 90°C, e.g., from 65°C to 85°C or from 70°C to 80°C. The pressure at which the column(s) are operated may range from 1 kPa to 300 kPa, e.g., from 10 kPa to 100 kPa or from 40 kPa to 80 kPa. In preferred embodiments, the pressure at which the column(s) are operated is kept at a low level e.g., less than 100 kPa, less than 80 kPa, or less than 60 kPa. In terms of lower limits, the column(s) may be operated at a pressures of at least 1 kPa, e.g., at least 20 kPa or at least 40 kPa. Without being bound by theory, it is believed that alkylenating agents, e.g., formaldehyde, may not be sufficiently volatile at lower pressures. Thus, maintenance of the column pressures at these levels surprisingly and unexpectedly provides for efficient separation operations. In addition, it has surprisingly and unexpectedly been found that be maintaining a low pressure in the columns of alkylenating agent split unit 232 may inhibit and/or eliminate polymerization of the acrylate products, e.g., acrylic acid, which may contribute to fouling of the column(s).

Examples

Example 1

[0113] A simulation of a process in accordance with FIG. 1 (along with an accompanying acrylic acid split) was conducted using ASPEN™ software. The compositions of the various process streams are shown in Table 4.

[0114] As shown by the simulation, a unique cooled product stream having a low light ends content may be formed via cooling of the crude acrylate product stream. Because this cooled product stream has a low concentration of light ends, this stream can be effectively separated in accordance with the present invention to achieve a finished acrylic acid product having 99.8 wt% purity, while maximizing overall process efficiency, e.g., using relatively small columns. Importantly, approximately 99% of the light ends are effectively removed in the absorbent stream.

[0115] While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited above and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention.