Claims:1. A process for recovering methacrolein from a reactor effluent stream (str1) containing methacrolein and methacrylic acid, said process comprising the steps of:
cooling the effluent stream (str1) in a quench column (4) to a temperature ranging from 20°C to 100°C affording a first top stream (str2) and a first bottoms stream (str3);
compressing the first top stream (str2) to a pressure ranging from 3 bars to 7 bars affording a compressed stream (str5);
cooling the compressed stream (str5) to a temperature ranging from 10°C to 70°C affording a two phase mixture;
subjecting the two phase mixture to a gas liquid separator (7) affording a first gaseous stream (str7) and a first liquid stream (str6);
subjecting the first gaseous stream (str7) to an absorption column (8) affording a liquid stream having methacrolein (str9) and a second gaseous stream (str8), said absorption column (8) being operated at a pressure ranging from 3 bars to 5 bars and using an aqueous solution of acetic acid as an absorbent;
subjecting the liquid stream having methacrolein (str9) to a first stripper column (9) affording a first methacrolein rich gaseous stream (str11) and a second bottoms stream (str10); and
subjecting the first liquid stream (str6) and at least a part of the first bottoms stream (str3) to a second stripper column (11) affording a third bottoms stream (str15) and a second methacrolein rich gaseous stream (str4).

2. The process as claimed in claim 1, wherein the step of cooling the effluent stream (str1) in the quench column (4) comprises cooling the effluent stream (str1) to a temperature ranging from 20°C to 70°C.
3. The process as claimed in claim 1, wherein the step of subjecting the liquid stream having methacrolein (str9) to the first stripper column (9) comprises stripping the liquid stream having methacrolein (str9) with a stripping gas, and wherein the stripping gas flows in a direction counter-current to direction of the stream having methacrolein (str9).

4. The process as claimed in claim 1, wherein the step of subjecting the first liquid stream (str6) and at least the part of the first bottoms stream (str3) to the second stripper column (11) comprises: (a) combining the first liquid stream (str6) and at least the part of the first bottoms stream (str3) to form a combined stream; and (b) stripping the combined stream with a stripping gas, wherein the stripping gas flows in a direction counter-current to direction of the combined stream.

5. The process as claimed in claim 1, wherein the second bottoms stream (str10) is subjected to cooling, and wherein the cooled stream is fed to the absorption column (8) as the absorbent.

6. The process as claimed in claim 1, wherein the second bottoms stream (str10) is split into a recycle stream (str12) and a rejected stream.

7. The process as claimed in claim 6, wherein the third bottoms stream (str15) is subjected to an extractor and a raffinate stripper, and wherein raffinate bottoms stream is combined with the recycle stream (str12).

8. The process as claimed in claim 7, wherein the combined stream is subjected to cooling, and wherein the cooled combined stream (str13) is fed to the absorption column (8) as the absorbent.

9. The process as claimed in claim 1, wherein the second gaseous stream (str8) is subjected to incineration in an incinerator (12) affording recovery of the stripping gas.

10. The process as claimed in claim 1, wherein the first methacrolein rich gaseous stream (str11) and the second methacrolein rich gaseous stream (str4) are fed to reactor (2).

, Description:TECHNICAL FIELD
[0001] The present disclosure relates generally to the field of production of methacrylic acid. More particularly, the present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Methacrylic acid is an important material that finds wide spread usage across gamut of industries. Methacrylic acid is typically produced by catalytic partial oxidation of isobutene, wherein firstly, isobutene undergoes partial oxidation to form methacrolein, which is then subjected to further oxidation to form methacrylic acid. The presently known and industrially implemented processes of production of methacrylic acid does not allow complete conversion of methacrolein to methacrylic acid, necessitating separation of methacrolein and methacrylic acid from the reactor effluent streams and feeding the recovered methacrolein back in the reactor for effecting its conversion to methacrylic acid. Consequently, the process of separating methacrolein from methacrylic acid and recovering methacrolein from the reactor effluent stream has been an active area of research for several decades, if not more.
[0004] US5248819A discloses a method of production of methacrylic acid by the vapor phase catalytic oxidation of isobutylene, t-butanol, methacrolein isobutyl aldehyde or isobutyric acid, or mixture thereof, the reaction product gas is condensed by contact with an aqueous phase containing methacrylic acid and acetic acid thereby forming an aqueous solution of methacrylic acid and a gas phase containing methacrolein and methacrylic acid. The aqueous solution of methacrylic acid is extracted with a saturated hydrocarbon solvent containing from 6-9 carbon atoms. The methacrylic acid is extracted into the solvent phase and an aqueous phase containing acetic acid is also formed. Methacrolein is recovered from the gas containing methacrolein and methacrylic acid by contacting the gas with an aqueous phase containing methacrylic acid and acetic acid. An aqueous phase containing methacrylic acid, acetic acid and methacrolein is formed in the methacrolein recovery step. This aqueous phase is contacted with a molecular oxygen containing gas to desorb methacrolein into a gas containing methacrylic acid and methacrolein and also forming an aqueous phase containing methacrylic acid and acetic acid. This aqueous phase is recycled to either or both of the methacrylic acid condensation step and the methacrolein recovery step. Methacrylic acid is recovered from the gas containing methacrylic acid and methacrolein produced in the methacrolein desorption step by mixing this gas with an aqueous phase containing acetic acid recovered from the methacrylic acid extraction step (C). This results in a gas-containing methacrolein which is recycled to the vapor phase reaction. Content of US5248819A is incorporated herein, in its entirety, by way of reference. The method disclosed in US5248819A suffers from several shortcomings. For example, the process of US5248819A only affords suboptimal recovery of methacrolein leading not only to significant loss in yield of the methacrylic acid, but the methacrolein also tend to appear in a significant amount in the methacrylic acid product stream increasing the downstream processing/purification costs. In the process of US5248819A, relatively high conc. of MAA (about 4%) in the methacrolein recovery section necessitates utilization of a methacrylic acid recovery column to scrub out the methacrylic acid in the methacrolein rich vapor recycle stream. Importantly, methacrolein recovery is reduced owing to absorption of some amounts of methacrolein in the methacrylic acid recovery column by the acetic acid rich stream. Further, in the process of US5248819A, the acetic acid rich stream, after absorption and separation of methacrolein, is mixed with the main product stream via the methacrylic acid condensation column, significantly increasing the material cost (and consequently, the capital cost) and energy load on the downstream equipments viz. extractor, raffinate stripper, solvent recovery column etc. making the overall process non-viable or at least less preferable for industrial implementation.
[0005] Accordingly, there remained a long-felt need in the art for an improved process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that obviates one or more shortcomings of the conventional processes.

OBJECTS OF THE INVENTION
[0006] An object of the present disclosure is to provide a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that is economical.
[0007] Another object of the present disclosure is to provide a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that aids in reduction of wastage of methacrolein, conserves energy and improves overall yield of methacrylic acid.
[0008] Another object of the present disclosure is to provide a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that reduces wastage of water.
[0009] Further object of the present disclosure is to provide a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that obviates the need of expensive and energy intensive purification means such as distillation.
[0010] Other objects of the present invention will be apparent from the description of the invention herein below.

SUMMARY
[0011] The present disclosure relates generally to the field of production of methacrylic acid. More particularly, the present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid.
[0012] An aspect of the present disclosure relates to a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid, said process comprising the steps of: (a) cooling the effluent stream (str1) in a quench column (4) to a temperature ranging from 20°C to 100°C affording a first top stream (str2) and a first bottoms stream (str3); (b) compressing the first top stream (str2) to a pressure ranging from 3 bars to 7 bars affording a compressed stream (str5); (c) cooling the compressed stream (str5) to a temperature ranging from 10°C to 70°C affording a two phase mixture; (d) subjecting the two phase mixture to a gas liquid separator (7) affording a first gaseous stream (str7) and a first liquid stream (str6); (e) subjecting the first gaseous stream (str7) to an absorption column (8) affording a liquid stream having methacrolein (str9) and a second gaseous stream (str8), said absorption column (8) being operated at a pressure ranging from 3 bars to 5 bars and using an aqueous solution of acetic acid as an absorbent; (f) subjecting the liquid stream having methacrolein (str9) to a first stripper column (9) affording a first methacrolein rich gaseous stream (str11) and a second bottoms stream (str10); and (g) subjecting first liquid stream (str6) and a part of the first bottoms stream (str3) to a second stripper column (11) affording a third bottoms stream (str15) and a second methacrolein rich gaseous stream (str4).
[0013] In an embodiment, the step of cooling the effluent stream (str1) in the quench column (4) comprises cooling the effluent stream (str1) to a temperature ranging from 20°C to 70°C. In an embodiment, the step of subjecting the liquid stream having methacrolein (str9) to the first stripper column (9) comprises stripping the liquid stream having methacrolein (str9) with a stripping gas. In an embodiment, the stripping gas flows in a direction counter-current to that of the stream having methacrolein (str9). In an embodiment, wherein the step of subjecting first liquid stream (str6) and the part of the first bottoms stream (str3) to the second stripper column (11) comprises: (i) combining the first liquid stream (str6) and the part of the first bottoms stream (str3) to form a combined stream; and (ii) stripping the combined stream with a stripping gas. In an embodiment, the stripping gas flows in a direction counter-current to that of the combined stream. In an embodiment, the second bottoms stream (str10) is subjected to cooling, and the cooled stream is fed to the absorption column (8) as the absorbent. In an embodiment, the second bottoms stream (str10) is split into a recycle stream (str12) and a rejected stream. In an embodiment, the third bottoms stream (str15) is subjected to an extractor and a raffinate stripper, and the raffinate bottoms stream is combined with the recycle stream (str12). In an embodiment, the combined stream is subjected to cooling and the cooled combined stream (str13) is fed to the absorption column (8) as the absorbent. In an embodiment, the second gaseous stream (str8) is subjected to incineration in an incinerator (12) affording recovery of the stripping gas. In an embodiment, the first methacrolein rich gaseous stream (str11) and the second methacrolein rich gaseous stream (str4) are fed to reactor (2).

BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 illustrates an exemplary schematic showing a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0015] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0016] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0017] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0018] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0019] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0020] The present disclosure relates generally to the field of production of methacrylic acid. More particularly, the present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid.
[0021] An aspect of the present disclosure relates to a process for recovering methacrolein from a reactor effluent stream (str1) containing methacrolein and methacrylic acid, said process comprising the steps of: (a) cooling the effluent stream (str1) in a quench column (4) to a temperature ranging from 20°C to 100°C affording a first top stream (str2) and a first bottoms stream (str3); (b) compressing the first top stream (str2) to a pressure ranging from 3 bars to 7 bars affording a compressed stream (str5); (c) cooling the compressed stream (str5) to a temperature ranging from 10°C to 70°C affording a two phase mixture; (d) subjecting the two phase mixture to a gas liquid separator (7) affording a first gaseous stream (str7) and a first liquid stream (str6); (e) subjecting the first gaseous stream (str7) to an absorption column (8) affording a liquid stream having methacrolein (str9) and a second gaseous stream (str8), said absorption column (8) being operated at a pressure ranging from 3 bars to 5 bars and using an aqueous solution of acetic acid as an absorbent; (f) subjecting the liquid stream having methacrolein (str9) to a first stripper column (9) affording a first methacrolein rich gaseous stream (str11) and a second bottoms stream (str10); and (g) subjecting first liquid stream (str6) and at least a part of the first bottoms stream (str3) to a second stripper column (11) affording a third bottoms stream (str15) and a second methacrolein rich gaseous stream (str4).
[0022] In an embodiment, the step of cooling the effluent stream (str1) in the quench column (4) comprises cooling the effluent stream (str1) to a temperature ranging from 20°C to 70°C. In an embodiment, the step of subjecting the liquid stream having methacrolein (str9) to the first stripper column (9) comprises stripping the liquid stream having methacrolein (str9) with a stripping gas. In an embodiment, the stripping gas flows in a direction counter-current to that of the stream having methacrolein (str9). In an embodiment, the step of subjecting the first liquid stream (str6) and at least the part of the first bottoms stream (str3) to the second stripper column (11) comprises: (i) combining the first liquid stream (str6) and at least the part of the first bottoms stream (str3) to form a combined stream; and (ii) stripping the combined stream with a stripping gas. In an embodiment, the stripping gas flows in a direction counter-current to that of the combined stream. In an embodiment, the second bottoms stream (str10) is subjected to cooling, and the cooled stream is fed to the absorption column (8) as the absorbent. In an embodiment, the second bottoms stream (str10) is split into a recycle stream (str12) and a rejected stream. In an embodiment, the third bottoms stream (str15) is subjected to an extractor and a raffinate stripper, and the raffinate bottoms stream is combined with the recycle stream (str12). In an embodiment, the combined stream is subjected to cooling and the cooled combined stream (str13) is fed to the absorption column (8) as the absorbent. In an embodiment, the second gaseous stream (str8) is subjected to incineration in an incinerator (12) affording recovery of the stripping gas. In an embodiment, the first methacrolein rich gaseous stream (str11) and the second methacrolein rich gaseous stream (str4) are fed to reactor (2).
[0023] FIG. 1 illustrates an exemplary schematic showing the advantageous process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid in accordance with an embodiment of the present disclosure. As can be seen from FIG. 1, isobutylene (IBEN) can be subjected to a catalytic oxidation with an oxygen containing gas (e.g. air) in one or more reactors (1, 2). In an embodiment, isobutylene and oxygen containing gas are introduced in a first reactor (1), wherein isobutylene undergoes catalytic oxidation producing methacrolein (MAL), as known conventionally. The reaction may be carried out on any one of a fixed bed, a fluidized bed and a moving bed as known to persons skilled in the art, and the same is not detailed herein. The methacrolein so produced in the first reactor (1) can then be fed to a second reactor (2), wherein methacrolein further reacts with oxygen and gets converted to Methacrylic Acid (MAA). The effluent stream (str1) from the second reactor (2) typically includes methacrylic acid along with some amounts of unreacted methacrolein in gaseous form (for example, in the range of 1-5% by weight of the effluent stream). The effluent stream from the second reactor (2) can be subjected to the advantageous process of the present disclosure for recovering methacrolein, as detailed below.
[0024] As can also be seen from FIG. 1, the effluent stream (str1) is subjected to cooling in a quench column (4) to a temperature ranging from 20°C to 100°C affording a first top stream (str2) and a first bottoms stream (str3). In an embodiment, the effluent stream (str1) is firstly cooled to a temperature ranging from 150°C to 250°C in a cooler (3) recovering the heat, and then subjected to further cooling in the quench column (4) to a temperature ranging from 20°C to 100°C. In an embodiment, the effluent stream (str1) is cooled to a temperature of about 50°C in the quench column (4) affording a first top stream (str2) and a first bottoms stream (str3). In an embodiment, recirculate from the first bottoms stream (str3) can be contacted with the effluent stream (str1) for cooling. Methacrylic Acid (MAA) has a greater tendency to undergo polymerization at elevated temperatures, and hence, cooling of the effluent stream (str1) aids in precluding formation of polymer in the column.
[0025] The first top stream (str2) from the quench column (4) is subjected to compression, using a compressor (5) at a pressure ranging from 3 bars to 7 bars affording a compressed stream (str5). In an embodiment, the first top stream (str2) is compressed at a pressure ranging from 4 bars to 6 bars, preferably, at about 4 bars pressure. Compression of the first top stream (str2) may aid in absorption in the absorption column (8).
[0026] The compressed stream (str5) is then subjected to cooling, in a cooler (6), to a temperature ranging from 10°C to 70°C affording a two phase mixture. In an embodiment, the compressed stream (str5) is subjected to cooling to a temperature ranging from 10°C to 60°C, preferably, to a temperature ranging from 10°C to 50°C, and most preferably, at a temperature of about 20°C. The two phase mixture is then subjected to a gas liquid separator (7) affording a first gaseous stream (str7) and a first liquid stream (str6).
[0027] The first gaseous stream (str7) is subjected to an absorption column (8) to separate methacrolein from the non-condensables viz. N2, O2,, CO and CO2 by absorption in an absorbent. The absorbent may be sprayed from the direction opposite to the direction of flow of the first gaseous stream (str7). In an embodiment, the first gaseous stream (str7) is introduced near bottom of the absorption column (8) and the absorbent is sprayed from the top such that direction of flow of the absorbent and the direction of flow of the first gaseous stream (str7) are counter-current to each other maximizing the contact therebetween. In an embodiment, the absorbent is an aqueous solution of acetic acid. It could be noted during the experimentation that methacrolein (MAL) and Methacrylic Acid (MAA) have affinity towards acetic acid and accordingly, usage of aqueous solution of acetic acid as an absorbent affords higher absorption of methacrolein (MAL) and Methacrylic Acid (MAA) in the aqueous phase. The absorbent may also include minor amount of Methacrylic Acid (MAA). In an embodiment, the absorbent is an aqueous solution of acetic acid having concentration of acetic acid ranging from 5% to 15%, preferably, 7% to 12% and most preferably, about 10%. Subjecting the first gaseous stream (str7) to the absorption column (8) affords a liquid stream having methacrolein (str9) and a second gaseous stream (str8). The second gaseous stream (str8) has negligible amounts of methacrolein (MAL) and Methacrylic Acid (MAA). In an embodiment, the second gaseous stream (str8) has about 10 ppm to 100 ppm of methacrolein (MAL). The second gaseous stream (str8) can be subjected to incineration in an incinerator (12) for removal of any residual organic components and carbon monoxide therefrom. A part of the treated/incinerated second gaseous stream (str14) containing N2 can be recycled for its usage as a stripping gas in first stripper column (9) and/or as a sweep gas in second stripper column (11).
[0028] The liquid stream having methacrolein (str9) is subjected to a first stripper column (9) affording a first methacrolein rich gaseous stream (str11) and a second bottoms stream (str10). In the first stripper column (9), methacrolein is removed from the liquid stream having methacrolein (str9) using a stripping gas. The stripping gas may be a nitrogen or nitrogen containing gas. However, any other gas may also be used. As explained above, preferably, a part of the treated/incinerated second gaseous stream (str8) containing N2 is used as a stripping gas. In an embodiment, the stripping gas is at a temperature ranging from 100°C to 300°C, preferably, at a temperature ranging from 150°C to 250°C, and most preferably, at a temperature of about 200°C.
[0029] The first methacrolein rich gaseous stream (str11) may be sent to the second reactor (2) for its conversion to Methacrylic Acid (MAA). The second bottoms stream (str10) can be recycled and reused as the absorbent in the absorbent column (8). In an embodiment, the second bottoms stream (str10) is subjected to cooling and reused as absorbent in the absorbent column (8). In an embodiment, the second bottoms stream (str10) is split into a recycle stream (str12) (rich in acetic acid) and a rejected stream. In an embodiment, the recycle stream (str12) is combined with the raffinate bottoms stream such that the same may be used as absorbent in the absorption column as detailed below.
[0030] The first liquid stream (str6) and at least a part of the first bottoms stream (str3) are subjected to a second stripper column (11) to recover methacrolein therefrom. In an embodiment, the first liquid stream (str6) and at least the part of the first bottoms stream (str3) are combined and the combined stream is subjected to the second stripper column (11). In the second stripper column (11), methacrolein is removed from the combined stream using a sweeping gas. The sweeping gas may be a nitrogen or nitrogen containing gas. However, any other gas may also be used. As explained above, preferably, a part of the treated/incinerated second gaseous stream (str8) containing N2 is used as a sweeping gas. In an embodiment, the sweeping gas is at a temperature ranging from 100°C to 300°C, preferably, at a temperature ranging from 150°C to 250°C, and most preferably, at a temperature of about 200°C. Subjecting the first liquid stream (str6) and at least the part of the first bottoms stream (str3) to the second stripper column (11) affords a third bottoms stream (str15) and a second methacrolein rich gaseous stream (str4). The second methacrolein rich gaseous stream (str4) may be sent to the second reactor (2) for its conversion to Methacrylic Acid (MAA). In an embodiment, the first methacrolein rich gaseous stream (str11) and the second methacrolein rich gaseous stream (str4) are combined before being fed to the second reactor (2).
[0031] The third bottoms stream (str15) may be sent to an extractor (not shown) to recover Methacrylic Acid (MAA) therefrom. The extractor affords extraction of MAA in the organic phase (e.g. an organic solvent phase), while the aqueous phase obtained from the extractor, having some amount of the organic solvent, is sent to a raffinate stripper for distillation and separation of the organic solvent from the aqueous phase. The aqueous phase so obtained from the raffinate stripper as raffinate bottoms stream, which typically is rich in acetic acid, may be cooled and directly used as an absorbent in the absorbent column (8). Alternatively, the raffinate bottoms stream can be combined with the recycle stream (str12) (obtained from the second bottoms stream (str10)) and subjected to cooling. The cooled combined stream (str13) can then be fed to the absorption column (8) as the absorbent.
[0032] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
[0033] The process as illustrated in FIG. 1 was carried out using the equipments, details whereof are provided in Table 1A and 1B below. The composition and parameters of various streams are provided in Table 2A and 2B below.
Table 1A: Details of the reactors and incinerator
Reactor (1) Reactor (2) Incinerator (12)
Type Fixed Bed Single Tube Reactor Fixed Bed Single Tube Reactor Fixed Bed
Tube. ID 25 mm 30 mm 50 mm
Tube Length 5 m 5 m 0.5 m
Catalyst Chamber Length 3.5 m 3.5 m 0.4 m
Operation Temp. 420 oC 320 oC 350 oC
Operation Press. 1.5 bar 1.4 bar 2 bar
MOC SS 316L SS 316L SS316L
Catalyst Molybdenum type composite Oxide Heteropoly acid compound based on Molybdenum-Phosphorus acid series Supported Pt.

Table 1B: Details of the columns
Quench Col. (4) Absorption Col. (8) Stripper Col. (11) Stripper Col. (9)
Type Staged Spray
45 Spray Stages Packed Packed Packed
Packing - Porcelain Raschig Rings Porcelain Raschig Rings Porcelain Raschig Rings
Flow Pattern Countercurrent Countercurrent Countercurrent Countercurrent
Length 2 m 2.5 m 1.2 m 2.5 m
Dia. 80 mm 50 mm 20 mm 40 mm
Top Temp. 44 10.5 63 60
Bot. Temp. 44.5 12.5 97 88
Operating Pressure (abs) 1.2 bar 3.7 bar 1 bar 1 bar

Table 2A: Composition and parameters of various streams
Str 1 Str 2 Str3 Str 5 Str 6 Str 8 Str 13
Temp. C 304 43.7 50 206 20 10 10
Pressure bar 1.5 1.3 1.25 4.2 4.1 3.7 7
Phase Vap. Vap. Liq. Vap. Liq Vap Liq.
Flow (kg/hr) 12 10.3 2.17 10.3 0.53 9.6 19.4
Composition: wt %
MAL 1.9 2 1.85 2 4.3 30ppm 0.01
MAA 6.4 0.75 35.2 0.75 14 0 0.5
Water 10 4.1 54.3 4.1 74 0.2 90.3
Acetic Acid 1.1 0.35 5.92 0.35 6.2 0.03 9.2
Trace * Balance
N2+ ** 80 92.5 0 92.5 0 99.5 0

Table 2B: Composition and parameters of various streams
Str 7 Str 9 Str 10 Str 12 Str4 Str11 Str15 Str14
Temp. C 20 12.5 88 88 63 60 97.5 200
Pressure bar 4.1 4.0 1.2 1.2 1 1 1.2 1.8
Phase Vap. Liq. Liq. Liq. Vap. Vap. Liq. Vap.
Flow (kg/hr) 9.82 19.6 19.1 18.21 0.14 2.12 2.1 1.63
Composition: wt %
MAL 1.9 1 0.008 0.008 30 8.7 0.1 -
MAA 0.02 0.5 0.5 0.5 2 0.16 36.2 -
Water 0.33 89.5 90.3 90.3 9.52 13.8 55.43 0.2
Acetic Acid 0.03 9 9.1 9.1 0.7 1.87 6 -
Trace * Balance
N2+ ** 97.5 0 0 0 56.5 73.5 0 99.8
* Miscellaneous organic compounds viz. Acrylic Acid, Acrolein, Maleic Anhydride, Formic Acid, Heavies.
** Non-condensable gases viz. N2, O2, CO2, CO.
[0034] As can be seen from Tables 2A and 2B above, the advantageous process of the present disclosure affords more than about 99% recovery of methacrolein from the reactor effluent stream, affording increased yield of the methacrylic acid. As can also be seen from Table 2A and 2B above, loss of methacrylic acid in the recycle stream is less than about 0.5%, which in the conventional processes tend to be significantly higher resulting in formation of polymer when fed to the second reactor (2) owing to exposure to higher temperature. Further, usage of aqueous solution of acetic acid as absorbent in absorption column (8) allows operation at lower compression ratios and lower stripper column (9) reboiler duty contributing significantly towards conservation of energy. Enhanced separation of methacrolein from non-condensables also allows usage of lower stages in the absorption column (8) contributing to significant capital cost reduction. Implementation of the process of the present disclosure also affords significantly reduced (about 25% less) emission of waste water, particularly owing to recycle/reuse of the bottoms stream (str10) as absorbent. Further, precluding entry/injection of bottoms stream (str10) in the extractor precludes extra load on the extractor column. It is also noteworthy that the process of the present disclosure does not involve routing of the methacrylic acid product stream to the absorption column ensuring that methacrylic acid throughput is not reduced, further, it aids in precluding methacrylic acid polymerization and subsequent choking of the absorption column. Further, usage of dual stripper column affords greater flexibility and robustness of the system. Accordingly, the advantageous process of the present disclosure affords uninterrupted operation of the overall system with minimal downtime. Needless to mention, the advantageous process of the present disclosure allows substantial or near complete recovery/removal of the methacrolein from the extractor feed streams (str3, str6) obviating any need for methacrolein removal in later stages of methacrylic acid purification, which otherwise would have to be done via expensive means viz. distillation. Accordingly, the advantageous process of the present disclosure affords several fold technical advancement over the conventionally known processes.
[0035] Although the subject matter has been described herein with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein. Furthermore, precise and systematic details on all above aspects are currently being made. Work is still underway on this invention. It will be obvious to those skilled in the art to make various changes, modifications and alterations to the invention described herein. To the extent that these various changes, modifications and alterations do not depart from the scope of the present invention, they are intended to be encompassed therein.

ADVANTAGES
[0036] The present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that is economical.
[0037] The present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that aids in reduction of wastage of methacrolein, conserves energy and improves overall yield of methacrylic acid.
[0038] The present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that reduces wastage of water.
[0039] The present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that obviates the need of expensive and energy intensive purification means such as distillation.
[0040] The present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that minimizes polymer formation in the system and affords long duration operation with minimum downtime.
[0041] The present disclosure provides a process for recovering methacrolein from a reactor effluent stream containing methacrolein and methacrylic acid that affords high degree of operational flexibility and robustness.