Process for producing alkyl methacrylates with improved water and acid management

Abstract

A process for producing alkyl methacrylates, in particular methyl methacrylate (MMA), includes production of methacrolein (MAL) in a first reaction stage; direct oxidative esterification (DOE) of the methacrolein with an alcohol, preferably methanol, to afford an alkyl methacrylate in a second reaction stage: and workup of the alkyl methacrylate crude product from the second reaction stage. An optimized workup of the reactor output from the oxidative esterification of methacrolein involves minimizing the amount of employed water, the amount of employed acid, and/or the amount of aqueous waste streams, through an optimized recycling of the generated process water streams.

Claims

1-16. (canceled)

17: A process for producing alkyl methacrylates, the process comprising: producing methacrolein in a first reaction stage in a reactor I, and oxidatively esterifying the methacrolein with an alcohol in a second reaction stage in a reactor II in the presence of an oxygen-containing gas, to form reaction water in a liquid phase and to afford an alkyl methacrylate, wherein a workup of a reaction mixture from the reactor II to afford the alkyl methacrylate comprises at least one distillation and at least one extraction; wherein an aqueous phase containing the alcohol and an alkali metal and/or alkaline earth metal salt of a Brønsted acid from the at least one extraction is treated in at least one second distillation in a column II to form, in a bottom of the column II, a process water stream containing the reaction water and the alkali metal and/or the alkaline earth metal salt of a Brønsted acid, wherein in the process water stream a content of the alcohol and the alkyl methacrylate is less than 5% by weight based on a total process water stream, and wherein the process water stream from the bottom of the column II is partially discharged from the process and sent for disposal and partially recycled into the workup of the reaction mixture from the reactor II.

18: The process according to claim 17, wherein the process water stream from the bottom of the column II is partially recycled into the at least one extraction, and is contacted with an alkyl methacrylate- and alcohol-containing organic phase in the at least one extraction.

19: The process according to claim 17, wherein the process water stream from the bottom of the column II is partially recycled into a reactor III, and is contacted in the reactor III with an alkyl methacrylate- and alcohol-containing organic phase which has a content of methacrolein acetal of less than 3% by weight based on the alkyl methacrylate- and alcohol-containing organic phase.

20: The process according to claim 17, wherein the at least one extraction is performed in an extraction column and/or in a serially arranged series of at least two mixer-settler apparatuses, and wherein the process water stream from the bottom of the column II is added below a top of the extraction column or in a mixer region of a mixer-settler apparatus of the at least two mixer-settler apparatuses, and water is optionally added in the top of the extraction column.

21: The process according to claim 20, wherein the addition of water and optionally, of a Brønsted acid, to the at least one extraction is carried out above the addition of the process water stream from the bottom of the column II.

22: The process according to claim 19, wherein an addition of a Brønsted acid is carried out in the reactor III and the addition is chosen such that in continuous operation a pH in the range from 1.5 to 2.5 is established in the process water stream from the bottom of the column II.

23: The process according to claim 22, wherein the addition of the Brønsted acid is carried out exclusively via the addition in reactor III.

24: The process according to claim 17, wherein the at least one extraction affords an organic phase containing alkyl methacrylate and methacrylic acid and the organic phase from the at least one extraction is separated in a distillation stage IV into a bottoms fraction containing alkyl methacrylate and a lower-boiling tops fraction.

25: The process according to claim 24, wherein the tops fraction from the distillation stage IV is admixed with water and subsequently separated in a phase separator I into a further organic phase and into a further aqueous phase.

26: The process according to claim 25, wherein the further aqueous phase from the phase separator I is mixed with at least one Brønsted acid in a reactor IV, wherein ester byproducts present in the further aqueous phase from the phase separator I are cleaved and alcohol is recovered, and the process water stream from the bottom of the column II is optionally partially passed into the reactor IV.

27: The process according to claim 26, wherein a product from the reactor IV is completely or partially passed into the column II.

28: The process according to claim 25, wherein the further aqueous phase from the phase separator I is completely or partially passed into the column II.

29: The process according to claim 17, wherein the reaction mixture from the reactor II is separated in a distillation stage I, wherein methacrolein and in part alcohol are removed via a tops fraction and recycled to the reactor II.

30: The process according to claim 29, wherein the methacrolein is completely or partially added to the distillation stage I and passed to the reactor II via the tops fraction from the distillation stage I.

31: The process according to claim 17, wherein the alcohol is methanol and the alkyl methacrylate is methyl methacrylate.

32: The process according to claim 22, wherein the Brønsted acid is sulfuric acid.

33: The process according to claim 20, wherein the water optionally added in the top of the extraction column is demineralized water.

34: The process according to claim 17, wherein the Brønsted acid is used.

35: The process according to claim 17, wherein the Brønsted acid is not used.

36: The process according to claim 17, wherein the workup of the reaction mixture further comprise a reactor III, and where the process water stream from the bottom of the column II is partially recycled into the reactor III.

Description

DESCRIPTION OF THE FIGURE AND LIST OF REFERENCE NUMERALS

[0134] FIG. 1 shows by way of example a possible schematic flow diagram of the second process step (oxidative esterification of MAL and workup of the product stream) of the process according to the invention for producing alkyl methacrylate. Reactor I of the process according to the invention for MAL synthesis is not shown.

[0135] (1) MAL feed into reactor II [0136] (2) Reactor II for oxidative esterification of MAL [0137] (3) Alcohol (in particular methanol) feed into reactor II [0138] (4) Oxygen and/or air feed into reactor II [0139] (5) Base feed into reactor II [0140] (6) Distillation column I for removal of MAL [0141] (7) Low-boiling fraction containing MAL and alcohol for recycling into reactor II (recycling stream) [0142] (8) Reactor III (acetal cleaver) for cleavage of acetal byproducts (for example dimethoxyisobutene (DMIB) to afford MAL and MeOH) (optional) [0143] (9) Extraction [0144] (10) Optional acid feed I to (8) [0145] (11) Optional water feed II to (9) [0146] (12) Distillation column II for recovery of alcohol [0147] (13) Low-boiling fraction from distillation column II containing alcohol for recycling into reactor II [0148] (14) Bottoms fraction from distillation column II containing water, acid and alkylmethacrylic acid and/or salts thereof [0149] (15) Distillation column III for removal of high boilers [0150] (16) Distillation column IV for removal of low boilers [0151] (17) Distillation column V for final purification of MMA [0152] (18) Distillation column VI for reducing the amount of alkyl methacrylate in the bottoms stream from (15) (optional) [0153] (19) Phase separator I for workup of the low-boiling fraction from column IV (16) [0154] (20) Distillation column VII for recovery of MAL from organic phase from phase separator I (19) (optional) [0155] (21) Reactor IV (ester cleaver) for recovery of alcohol from ester byproducts (for example saturated esters such as alkyl isobutyrate, alkyl propionate) (optional) [0156] (22) Apparatus for mixing the reactants mixer I (optional) [0157] (23) Water treatment (optional) [0158] (24) Water feed III to (19) (optional) [0159] (25) Acid feed IV to (21) (optional) [0160] (26) Alkyl methacrylate product stream [0161] (27) Recycling stream containing MAL [0162] (A1)/(A2) Aqueous waste stream [0163] (B1)/(B2) Organic waste stream

EXPERIMENTAL SECTION

Example 1—with Recycling of W4 into the Extraction (9)

[0164] The reaction of methacrolein with methanol in the presence of an oxygen-containing gas in the liquid phase to afford methyl methacrylate (MMA) was carried out in reactor II. The reactor output from reactor II had the following composition: MEOH 43.1% by wt, MAL 8.8% by wt, MMA 37.0% by wt, H2O 6.6% by wt, MAL acetal 360 ppm, remainder 4.4% by wt.

[0165] The output from reactor II (2) was directly supplied to the extraction (9). The extraction was performed in an extraction column. A partial water feed II (11) to the extraction was carried out. The aqueous phase P2 from the extraction was passed into column II (12). An aqueous wastewater stream A1 was discharged from the bottoms stream from the column II. A partial recycling of the bottoms stream from the column II (W4) to the extraction (9) was carried out.

[0166] In the case of experiment 3 the addition of W4 and water was carried out at the top of the extraction column (9). In the case of experiment 4 the addition of W4 was carried out below the top of the extraction column and the addition of water was carried out at the top of the extraction column (9).

[0167] The workup of the organic phase from the extraction was carried out using the columns III (15), IV (16) and V (17). In the column V the MMA product stream (26) was withdrawn as the tops fraction.

[0168] The feeds into the extraction (9) and the amount of aqueous waste streams are summarized in table 1 below.

TABLE-US-00001 TABLE 1 Summary of experiments 1-4 Extraction feeds Content of Water Wastewater Product methanol and feed II W4 stream A1 stream MMA MMA in W4 V no. kg/h kg/h kg/h kg/h % by wt pH W4 1 24.1 water / 29.2 15.65 MEOH 2 (Ref) 0.50 acid W4 complete 500 ppm MMA 0 2 0 water 24.1 6.5 15.65 MEOH 2 0.19 acid (75% of W4) (25% of W4) 500 ppm MMA 0 3 8.8 water 15.3 15.3 15.65 MEOH 2 0.30 acid (50% of W4) (50% of W4) 500 ppm MMA 0 4 8.8 water 15.3 15.3 15.65 MEOH 2 0.30 acid (50% of W4) (50% of W4) 500 ppm (top) (below top) MMA 0

Example 2—with Recycling of W4 into Reactor III/Acetal Cleaver

[0169] The reaction of methacrolein with methanol in the presence of an oxygen-containing gas in the liquid phase to afford methyl methacrylate (MMA) was carried out in reactor II. The reactor output from reactor II had the following composition: MEOH 43.1% by wt, MAL 8.8% by wt, MMA 37.0% by wt, H2O 6.6% by wt, MAL acetal 360 ppm, remainder 4.4% by wt.

[0170] The output from reactor II (2) was passed into the reactor III (8) for workup. Reactor III was in the form of a continuously operated stirred tank with a downstream decanter. A partial feed of 96% sulfuric acid (acid S) to reactor III was carried out via acid feed I (10). The output from reactor III was supplied to the extraction (9).

[0171] The extraction was performed in an extraction column. A partial water feed II (11) to the extraction was carried out. The aqueous phase P2 from the extraction was passed into column II (12). An aqueous wastewater stream A1 was discharged from the bottoms stream from the column II. A partial recycling of the bottoms stream from the column II (W4) to the reactor III and/or the extraction (9) was carried out.

[0172] The workup of the organic phase from the extraction was carried out using the columns III (15), IV (16) and V (17). In the column V the MMA product stream (26) was withdrawn as the tops fraction.

[0173] The feeds into reactor III and the extraction are summarized in table 2 below.

TABLE-US-00002 TABLE 2 Summary of experiments 5-7 Feeds Feeds Reactor III Extraction Content of Feed I Feed II Wastewater MAL acetal Product methanol and water & acid W4 water W4 A1 content in W2 stream MMA MMA in W4 V no. kg/h kg/h kg/h kg/h kg/h ppm kg/h % by wt pH W4 5 21.0 water / 3.1 / 29.2 14 15.65 MEOH 2 (Ref) 0.50 acid (W4 complete) 500 ppm MMA 0 6 0 Water 21.0 Water 3.1 / 9.6 14 15.65 MEOH 2 0.23 acid (69% of W4) (31% of W4) 500 ppm MMA 0 7 0 Water 21.0 0 3.1 6.5 14 15.65 MEOH 2 0.19 acid (69% of W4) (10% of W4) (21% of W4) 500 ppm MMA 0

Example 3—with Recycling of W4 into Phase Separator I

[0174] The experiment was performed as described in example 1. The tops fraction from the column IV was admixed with water via the water feed III (24) and subsequently separated in phase separator I(19) into an organic phase P3 and into an aqueous phase P4. The aqueous phase P4 was recycled into the column II (12).

[0175] A partial recycling of the bottoms stream from the column II (W4) to the phase separator I and/or to the extraction was carried out. The feeds into phase separator I and the extraction are summarized in table 3 below.

TABLE-US-00003 TABLE 3 Summary of experiments 8-10 Feeds Feeds Phase separator I Extraction Content of Feed III Feed II Wastewater Product methanol and water W4 water and acid W4 A1 stream MMA MMA in W4 V no. kg/h kg/h kg/h kg/h kg/h kg/h % by wt pH W4 8 2.5 / 24.1 water / 29.2 15.65 MEOH 2 (Ref) 0.5 acid (W4 complete) 500 ppm MMA 0 9 0 2.5 24.1 water / 26.7 15.65 MEOH 2 (9% of W4) 0.5 acid (91% of W4) 500 ppm MMA 0 10  0 2.5 0 water 24.1 4.0 15.65 MEOH 2 (8% of W4) 0.19 acid (78% of W4) (14% of W4) 500 ppm MMA 0

Example 4—with Recycling of W4 into Reactor IV/Ester Cleaver

[0176] The experiment was performed as described in example 3. The phase separator I was provided with water via water feed III (24). The aqueous phase P4 from phase separator I (19) was passed into the reactor IV (ester cleaver) (21) and via acid feed IV mixed with a 96% sulfuric acid (acid S). The aqueous phase P5 from reactor IV was recycled into column II (12).

[0177] A partial recycling of the bottoms stream from the column II (W4) to the reactor IV and/or to the extraction was carried out. The feeds into the reactor IV and the extraction are summarized in table 4 below.

TABLE-US-00004 TABLE 4 Summary of experiments 11-13 Feeds Feeds Reactor IV Extraction Content of Feed IV Feed II Wastewater Product methanol and acid W4 water and acid W4 A1 stream MMA MMA in W4 V no. kg/h kg/h kg/h kg/h kg/h kg/h % by wt pH W4 11 0.016 / 24.1 water / 29.2 15.65 MEOH 2 (Ref) 0.5 acid (W4 complete) 500 ppm MMA 0 12 0 1.4 24.1 water / 29.2 15.65 MEOH 2 (5% of W4) 0.5 acid (95% of W4) 500 ppm MMA 0 13 0 1.4 0 water 24.1 6.5 15.65 MEOH 2 (4% of W4) 0.19 acid (75% of W4) (21% of W4) 500 ppm MMA 0

[0178] It has been found that the process mode according to the invention allows savings in water and/or acid feeds and minimization of the aqueous wastewater stream A1 at identical product quality and yield.