OPTIMIZED PROCESS FOR SYNTHESIZING METHACRYLIC ACID (MAA) AND/OR ALKYL METHACRYLATE BY REDUCING UNWANTED BYPRODUCTS
20240010604 · 2024-01-11
Assignee
Inventors
- Steffen Krill (Muehltal, DE)
- Florian Klasovsky (Haltern am See, DE)
- Daniel Helmut König (Stuttgart, DE)
- Patrick Wings (Koeln, DE)
Cpc classification
International classification
Abstract
An improved process for synthesizing methacrylic acid and/or alkyl methacrylates, in particular methyl methacrylate (MMA), involves reacting acetone and hydrogen cyanide in the presence of an alkaline catalyst in a first reaction stage such that a first reaction mixture containing acetone cyanohydrin (ACH) is obtained. The process then involves working up the first reaction mixture containing acetone cyanohydrin (ACH), reacting acetone cyanohydrin (ACH) and sulfuric acid in a second reaction stage (amidation), and heating the second reaction mixture in a third reaction stage (conversion), such that methacrylamide (MAA) is obtained. The process further involves hydrolyzing or esterifying methacrylamide (MAA) with water and, optionally, alcohol, preferably water and optionally methanol, in a fourth reaction stage such that methacrylic acid or alkyl methacrylate is formed. The sulfuric acid used has a concentration of 98.0 wt % to 100.0 wt %.
Claims
1. A process for preparing methacrylic acid and/or alkyl methacrylate, the process comprising: a. reacting acetone and hydrogen cyanide in the presence of a basic catalyst in a first reaction stage for synthesis of acetone cyanohydrin (ACH), to obtain a first reaction mixture comprising the acetone cyanohydrin (ACH); b. working up the first reaction mixture comprising the acetone cyanohydrin (ACH); c. reacting the acetone cyanohydrin (ACH) and sulfuric acid in one or more reactors I in a second reaction stage for amidation, at an amidation temperature in the range from 85 C. to 130 C., to obtain a second reaction mixture comprising sulfoxyisobutyramide and methacrylamide; d. converting the second reaction mixture by heating to a conversion temperature in the range from 130 C. to 200 C., in one or more reactors II in a third reaction stage for conversion to obtain a third reaction mixture comprising predominantly methacrylamide (MAA) and sulfuric acid; e. reacting the third reaction mixture with water and optionally alcohol, in one or more reactors III in a fourth reaction stage for hydrolysis or esterification, to obtain a fourth reaction mixture comprising the methacrylic acid and/or the alkyl methacrylate; and f. optionally, separating the alkyl methacrylate from the fourth reaction mixture obtained from the fourth reaction stage; wherein the sulfuric acid used in the second reaction stage has a concentration in the range from 98.0% by weight to 100.0% by weight; wherein a pure ACH mixture which is fed to the second reaction stage has a water content within a range from 0.1 mol % to 10 mol %, based on the ACH present in the pure ACH mixture, and wherein a total amount of water used in the second reaction stage is within a range from 0.1 mol % to 20 mol %, based on the ACH present in the pure ACH mixture.
2. The process according to claim 1, wherein the workup of the first reaction mixture in b. comprises a distillation step, wherein the acetone cyanohydrin (ACH) is separated at least partly from impurities and/or by-products that are lower-boiling than & acetone cyanohydrin (ACH).
3. The process according to either claim 1, wherein an acetone reactant which is used in the first reaction stage contains 0.1% by weight to 1% by weight of water, based on the overall amount of the acetone reactant.
4. The process according to claim 1, wherein a hydrogen cyanide reactant which is used in the first reaction stage contains 0.01% by weight to 0.1% by weight of water, based on the overall amount of the hydrogen cyanide reactant.
5. The process according to claim 1, wherein the total amount of the ACH fed to the second reaction stage is fed in with the pure ACH mixture.
6. The process according to claim 1, wherein the sulfuric acid and the acetone cyanohydrin (ACH) are used in the second reaction stage in a molar ratio of the sulfuric acid to the ACH in the range from 1.3 to 1.8, based on the total amount of ACH fed to the second reaction stage.
7. The process according to claim 1, wherein the third reaction mixture comprising the methacrylamide (MAA) contains not more than 3% by weight of g methacrylic acid (MA), not more than 2% by weight of alpha-hydroxyisobutyramide (HIBAm), and not more than 0.3% by weight of methacrylonitrile (MAN), based in each case on the overall amount of the third reaction mixture.
8. The process according to claim 1, wherein the third reaction mixture contains 30% by weight to 40% by weight of the methacrylamide (MAA), based on the overall amount of the third reaction mixture.
9. The process according to claim 1, wherein the second reaction stage comprises conversion of the acetone cyanohydrin (ACH) and the sulfuric acid in at least two separate reaction zones.
10. The process according to claim 1, wherein the second reaction stage comprises conversion of the acetone cyanohydrin (ACH) and the sulfuric acid in the one or more reactors I, wherein the one or more reactors I comprises at least two separate reactors I, wherein the sulfuric acid and the acetone cyanohydrin (ACH) are used in a first reactor I in a molar ratio of the sulfuric acid the ACH in the range from 1.6 to 3.0, based on an amount of the ACH used in the first reactor I, and wherein the sulfuric acid and the acetone cyanohydrin (ACH) are used in a second reactor I in a molar ratio of the sulfuric acid to the ACH in the range from 1.2 to 2.0, based on the total amount of ACH fed into the second reaction stage.
11. The process according to claim 1, wherein the fourth reaction mixture comprising the alkyl methacrylate, which is obtained in the fourth reaction stage, is worked up in further steps comprising at least one distillation step and/or at least one extraction step.
12. The process according to claim 1, wherein the fourth reaction mixture comprising the alkyl methacrylate, which is obtained in the fourth reaction stage, is guided in gaseous form into a distillation step, wherein a tops fraction comprising the alkyl methacrylate, water, and alcohol, and a bottoms fraction comprising higher-boiling components are obtained, and wherein the bottoms fraction is recycled fully or partly into the fourth reaction stage.
13. The process according to claim 12, wherein the tops fraction comprising the alkyl methacrylate, water, and alcohol is separated in a phase separation step into an organic phase comprising a predominant portion of the alkyl methacrylate and into an aqueous phase comprising the alcohol and further water-soluble compounds, and wherein the aqueous phase is recycled fully or partly into the third reaction stage, and the organic phase comprising the predominant portion of the alkyl methacrylate is subjected to an extraction using water as extractant, wherein a further aqueous phase from this extraction is recycled into the third reaction stage.
14. The process according to claim 1, wherein the alkyl methacrylate is methyl methacrylate.
15. The process according to claim 1, wherein the alcohol in the third reaction mixture is methanol.
16. The process according to claim 1, wherein the pure ACH mixture has a water content within a range from 0.4 mol % to 5 mol %.
17. The process according to claim 1, wherein the total amount of water used in the second reaction stage is within a range from 0.4 mol % to 10 mol %.
18. The process according to claim 3, wherein the acetone reactant contains 0.1% by weight to 0.5% by weight of water.
19. The process according to claim 6, wherein in the second reaction stage, the molar ratio of the sulfuric acid to the ACH is in a range from 1.4 to 1.6.
Description
DESCRIPTION OF THE FIGURES
[0206]
[0207] The abbreviations in
[0220]
[0221] In
[0222] Apparatuses [0223] (A) ACH synthesis reactor 1 [0224] (B) ACH synthesis reactor 2 [0225] (C) ACH distillation, workup [0226] (D) amidation reactor (first reactor 1) [0227] (E) first converter [0228] (F) amidation reactor (second reactor 1) [0229] (G) second converter [0230] (H) hydrolysis or esterification
[0231] Streams of Matter [0232] (1) acetone feed (acetone reactant) [0233] (2) hydrogen cyanide feed [0234] (3) diethylamine feed [0235] (4) sulfuric acid feed [0236] (5) synthesis mixture [0237] (6) first reaction mixture, crude ACH to distillation [0238] (7) low boiler recycle stream [0239] (8a) pure ACH mixture [0240] (8b) ACH feed to 1st stage (first substream of pure ACH mixture) [0241] (8c) ACH feed to 2nd stage (second substream of pure ACH mixture) [0242] (8) degassed amide mixture [0243] (9) offgas from ACH distillation [0244] (10) sulfuric acid feed [0245] (11) stirred-up mixture, 1st stage [0246] (12) intermediately converted reaction mixture [0247] (13) stirred-up mixture, 2nd stage [0248] (14) converted reaction mixture (third reaction mixture) [0249] (15a) offgas from stage 1 amidation reactors [0250] (15b) offgas from stage 2 amidation reactors [0251] (16) optional methanol feed [0252] (17) water feed [0253] (18) cleavage acid [0254] (19) esterification offgas [0255] (20) overall offgas [0256] (21) pure MA or MMA
EXAMPLES
[0257] The preparation of methacrylamide in sulfuric acid solution, comprising the preparation of acetone cyanohydrin in a first reaction stage, the reaction thereof with sulfuric acid in the amidation of the second reaction stage, the thermal reaction of the second reaction mixture in the conversion of the third reaction stage, and the subsequent esterification with methanol and water in the third reaction stage was effected by the embodiment according to
[0258] There follows a comparison of five inventive examples (Examples 1 to 5) using varying water contents in the ACH (8a, 8b, 8c) that was obtained in the first reaction stage (A, B) and the workup (C) and was fed to the second reaction stage (D, F), and in the sulfuric acid (10) in the feed to the amidation (D), with four comparative examples (Examples 6 to 9).
[0259] To ascertain the respective amidation yield, samples were taken downstream of the second conversion reactor (G). The concentrations of MAA, MA and HIBAm ascertained after quantification by means of HPLC were used for the mass balance of the process steps of the amidation (second reaction stage, D, F) and the conversion (third reaction stage, E, G). Results based on the individual process steps are shown in Tables 1 to 8 for the comparative examples and the inventive examples. In the listing of the measurement results, a measurement error in the HPLC analysis of 0.2% is disclosed in each case.
[0260] The third reaction mixture (14) comprising MAA, MA and HIBAm obtained from the conversion (G) was subsequently admixed and esterified with methanol and water in a cascade of multiple esterification reactors III (H); in a separation column on top. MMA-containing crude mixture was withdrawn as vapours, condensed (21) and separated into an organic phase and an aqueous phase. MMA was obtained by workup of the organic phase.
[0261] The water content in the sulfuric acid feeds (4, 10) was determined by mass balance based on the sulfuric acid content in the streams, and the sulfuric acid content was ascertained by measuring the density and the speed of sound. The water content of the acetone feed (1) was determined by gas chromatography using a thermal conductivity detector. The water content of the hydrogen cyanide feed (2) was ascertained by Karl Fischer titration, and the water content of the pure ACH mixture (8a) was determined by mass balance based on the ACH content, with the ACH content ascertained by means of HPLC.
Inventive Example 1
[0262] Methacrylamide was prepared from acetone cyanohydrin and sulfuric acid having a total water content of 18.48 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0263] 9500 kg/h of an acetone reactant (1) having a water content according to Table 10 was reacted with 4439 kg/h (2) of hydrogen cyanide (HCN) that had a water content of about 0.03% by weight, based on the overall stream (2), and 8 kg/h of diethylamine (3) as catalyst in reactor (A) in the liquid phase. In addition, a circulation distillate stream (7) from the ACH distillation (C) that contained ACH, acetone and HCN was recycled into reactor (A).
[0264] Reactor (A) is executed as a loop reactor with downstream delay vessel (B), with removal of the heat of reaction released in reactor (A) by means of cooling water via a shell-and-tube heat exchanger. The reactor was operated at 35 to 40 C. and standard pressure.
[0265] The synthesis gas mixture (5) at about 40 C. which was obtained in reactor (A), containing more than 85% by weight of ACH, based on the overall stream (5), was fed continuously to the downstream delay vessel (B) in which the synthesis mixture (5) matured. The delay vessel (B) is executed in the form of a cooled reservoir vessel with a pumped circulation system and was operated at about 10 C. and standard pressure.
[0266] The crude ACH obtained downstream of the delay vessel (B) (first reaction mixture, 6) with an elevated ACH content of 92.7% by weight, based on the overall stream (6), was subsequently fed continuously to a distillation step (C). For stabilization of the ACH obtained and for neutralization of the diethylamine catalyst still present, 32 kg/h of 98% sulfuric acid (4) was fed into the crude ACH (first reaction mixture, 6) via a mixing zone. The result was a stabilized crude ACH stream (6a).
[0267] The stabilized crude ACH stream (6a) was fed in continuously at the top of a distillation column (C). The distillation column (C) was operated as a stripping column at about 120 mbar, heated indirectly with hot steam (10 bar) and separated acetone, HCN and further low-boiling by-products from a pure ACH mixture (8a) as bottom product that contained 98.5% by weight of ACH, based on the overall stream (8a), and water and acetone as by-products. The correspondingly obtained composition can be found in Table 10.
[0268] The low-boiling distillate from distillation (C) was returned continuously to the first reaction stage (A) together with a vacuum pump condensate obtained as low-boiling recycle stream (7).
[0269] The output air (9) that was obtained in the vacuum station of the distillation (C) was removed continuously from the process and sent to controlled incineration.
[0270] The pure ACH mixture (8a) obtained, at a mass flow rate of 13 850 kg/h, was cooled down to 10 C. downstream of the distillation (C). Subsequently, the overall stream of the pure ACH mixture (8a) was divided into two substreams (8b, 8c) which, in the second reaction stage, were fed into the first reactor I (D) or into the second reactor I (F) for the amidation.
[0271] Substream 8b, at a mass flow rate of 9000 kg/h, was applied to the first amidation reactor I (D) together with the sulfuric acid stream (10) that had a total mass flow rate of 22 440 kg/h, and the composition of which is shown in Table 10. Sulfuric acid stream 10 was admixed with 50 ppm of phenothiazine as stabilizer before entering the first amidation reactor I.
[0272] The first amidation reactor I (D) is designed as a loop reactor and was operated at 98 C. Substream (8b) was fed to the first amidation reactor I (D) continuously and at a temperature of 20 C.
[0273] The amount of sulfuric acid (in stream 10) needed for the optimal conversion of the ACH in the first reactor I (D) and the second reactor I (F) was fed into the first reactor I (D) in a mass ratio to the total amount of ACH in the feed (8b+8c) of 1.62 kg.sub.H2SO4/kg.sub.ACH or 1.41 mol.sub.H2SO4/mol.sub.ACH.
[0274] A hot stirred-up mixture (11) at 98 C. was obtained from the first reactor I (D), which contained sulfoxyisobutyramide (SIBA), methacrylamide (MAA) and hydroxyisobutyramide (HIBAm), each dissolved in sulfuric acid. The stirred-up mixture (11), after gas separation, was fed continuously to an intermediate conversion in the first converter (E). The pressure differential required for conveying was implemented by means of the reactor circulation pump of the amidation reactor (D). The resultant offgas (15a) was removed from the process in the direction of the amidation output air (20).
[0275] The first converter (E) is executed as a flow tube reactor comprising a preheater segment and a delay segment. The stirred-up mixture (11) entering the first converter (E) was heated to 130 C. in the preheater segment. This was followed by further conversion in the delay segment.
[0276] The reaction mixture (12) exiting from the first converter (E) was then fed into the second amidation reactor I (F). The second amidation reactor (F) is constructed as a loop reactor analogously to the first amidation reactor I (D) and was likewise operated at about 98 C. The ACH-containing substream 8c at 4850 kg/h which is required in the second amidation reactor I (F) was introduced directly into the reaction mixture (12) in the second amidation reactor I (F) as well. Resultant offgas (15b) was removed from the process in the direction of the overall offgas (20).
[0277] For final conversion of the active constituents of the reaction mixture (13) that was obtained from the second amidation reactor I (F), a second conversion step was subsequently conducted in the second converter (G).
[0278] The second converter (G) is likewise executed as a flow tube reactor and comprises a preheater segment and a delay segment.
[0279] The reaction mixture (13) that entered the second converter (G) was first heated in the preheater segment to an optimal temperature shown in Table 10. The temperature to be established in the second converter (G) was ascertained by preliminary experiments and led to a maximum conversion of SIBA and HIBAm to MAA.
[0280] Subsequently, the reaction mixture (13) was converted further in the delay segment of the second converter (D), while maintaining the temperature established beforehand.
[0281] The reaction mixture obtained from the second converter (D) was then separated from gaseous secondary components that were removed in the form of an offgas stream (15c). The resulting third reaction mixture (14) was withdrawn continuously in liquid form from the second converter (G). The third reaction mixture (14) contained the components methacrylamide (MAA), methacrylic acid (MA) and hydroxyisobutyramide (HIBAm) according to Table 10. The respective HPLC analysis for determination of the respective components was conducted in triplicate; the respective arithmetic averages are entered in Table 1. Sampling and analysis were effected twice per day, with sampling on five successive days in total in steady-state operation of the plant.
[0282] The resultant overall yield of components (methacrylamide, methacrylic acid) which are convertible to the target product (methyl methacrylate) and were subsequently sent to an esterification (H) for preparation of methyl methacrylate is likewise shown in Table 1. The concentrations reported are based on the overall flow rate of the third reaction mixture (14). The average yield of 10 representative samples measured in steady-state operation of a process with the conditions specified was 93.0%. In stream (14), by means of HPLC, a MAN content of 120 ppm was measured.
TABLE-US-00001 TABLE 1 Results of Inventive Example 1 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide methacrylic acid 1 Day 1; 10:10 33.81 1.20 1.60 93.04 2 Day 1; 13:40 33.90 1.15 1.63 93.29 3 Day 2; 07:30 33.72 1.15 1.55 92.79 4 Day 2; 10:26 33.78 1.12 1.58 92.96 5 Day 3; 09:05 33.80 1.17 1.56 93.01 6 Day 3; 11:08 33.98 1.17 1.54 93.51 7 Day 4; 10:34 34.00 1.12 1.53 93.56 8 Day 4; 14:11 33.71 1.12 1.51 92.76 9 Day 5; 07:46 33.76 1.18 1.62 92.90 10 Day 5; 09:19 33.40 1.19 1.81 91.91 Average 93.0 Range of variation of the yield 1.7%
Inventive Example 2
[0283] Methacrylamide was prepared from acetone cyanohydrin and sulfuric acid having a total water content of 3.66 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0284] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D, F) are shown in Tables 2 and 10 respectively. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0285] The variation in the water content in the feed (8a,10) to the amidation (D, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 2. The resulting yield is likewise shown in Tables 2 and 10.
[0286] The average yield of 10 representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 94.5%.
TABLE-US-00002 TABLE 2 Results of Inventive Example 2 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide methacrylic acid 1 Day 1; 16:10 34.66 1.03 1.03 94.49 2 Day 1; 19:50 34.51 1.05 1.08 94.08 3 Day 2; 07:20 34.72 1.05 0.98 94.65 4 Day 2; 11:26 34.78 1.02 1.03 94.82 5 Day 3; 07:05 34.80 1.04 1.04 94.87 6 Day 3; 10:09 34.68 1.07 1.04 94.54 7 Day 4; 08:30 34.50 1.01 1.01 94.05 8 Day 4; 14:11 34.71 1.02 1.06 94.63 9 Day 5; 07:30 34.76 1.03 0.96 94.76 10 Day 5; 10:29 34.40 0.90 1.00 93.78 Average 94.5% Range of variation of the yield 1.1%
Inventive Example 3
[0287] Methacrylamide was prepared from acetone cyanohydrin and sulfuric acid having a total water content of 0.47 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0288] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D, F) are shown in Tables 3 and 10 respectively. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0289] The variation in the water content in the feed (8a,10) to the amidation (D, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 3. The resulting yield is likewise shown in Tables 3 and 10.
[0290] The average yield of 10 representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 92.2%.
TABLE-US-00003 TABLE 3 Results of Inventive Example 3 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide methacrylic acid 1 Day 1; 09:05 35.01 1.21 0.06 92.18 2 Day 1; 10:50 34.80 0.93 0.08 91.63 3 Day 2; 07:30 35.31 0.86 0.05 92.97 4 Day 2; 10:15 34.70 0.89 0.03 91.36 5 Day 3; 07:20 35.26 0.98 0.08 92.84 6 Day 3; 10:19 34.93 0.96 0.03 91.97 7 Day 4; 08:22 35.05 0.99 0.03 92.29 8 Day 4; 11:04 35.08 0.95 0.06 92.36 9 Day 5; 07:35 34.78 1.01 0.08 91.57 10 Day 5; 10:29 35.29 0.97 0.07 92.92 Average 92.2% Range of variation of the yield 1.6%
Inventive Example 4
[0291] Methacrylamide was prepared from acetone cyanohydrin and sulfuric acid having a total water content of 15.67 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0292] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D, F) are shown in Tables 4 and 10 respectively. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0293] The variation in the water content in the feed (8a,10) to the amidation (D, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 4. The resulting yield is likewise shown in Tables 4 and 10.
[0294] The average yield of 10 representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 94.1%.
TABLE-US-00004 TABLE 4 Results of Inventive Example 4 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide methacrylic acid 1 Day 1; 10:05 34.49 1.13 1.12 94.49 2 Day 1; 12:50 34.30 1.15 1.11 93.97 3 Day 2; 08:30 34.32 1.05 1.06 94.02 4 Day 2; 11:30 34.33 1.13 1.08 94.05 5 Day 3; 07:10 34.31 1.10 1.12 94.00 6 Day 3; 10:20 34.38 1.07 1.11 94.19 7 Day 4; 08:20 34.28 1.11 1.06 93.91 8 Day 4; 11:22 34.28 1.12 1.11 93.91 9 Day 5; 07:30 34.29 1.17 1.12 93.94 10 Day 5; 10:20 34.30 1.06 1.09 93.97 Average 94.1% Range of variation of the yield 0.6%
Inventive Example 5
[0295] Methacrylamide was prepared from acetone cyanohydrnn and sulfuric acid having a total water content of 5.62 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0296] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D. F) are shown in Tables 5 and 10 respectively. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0297] The variation in the water content in the feed (8a,10) to the amidation (D, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 5. The resulting yield is likewise shown in Tables 5 and 10.
[0298] The average yield of 10 representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 96.7%.
TABLE-US-00005 TABLE 5 Results of Inventive Example 5 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide methacrylic acid 1 Day 1; 10:00 36.21 0.93 0.22 96.24 2 Day 1; 13:50 36.30 0.94 0.26 96.69 3 Day 2; 07:40 36.32 0.96 0.26 96.81 4 Day 2; 11:23 36.34 0.92 0.30 96.84 5 Day 3; 08:05 36.36 0.92 0.31 96.91 6 Day 3; 11:05 36.40 0.92 0.29 96.90 7 Day 4; 09:34 36.27 0.94 0.28 96.65 8 Day 4; 13:10 36.35 0.95 0.26 96.71 9 Day 5; 08:40 36.30 0.95 0.25 96.63 10 Day 5; 11:18 36.37 0.93 0.22 96.81 Average 96.7 Range of variation of the yield 0.7%
Comparative Example 6
[0299] Methacrylamide was prepared from acetone cyanohyddn and sulfuric acid having a total water content of 5.62 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0300] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D. F) are shown in Table 10. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0301] In a departure from the above examples, the amidation reactors I (D) and (F) were operated at 80 C. rather than at 98 C. This much lower amidation temperature in the second reaction stage led to a significant increase in viscosity of the reaction mixture (11, 13), which immediately significantly reduced the circulation of the reaction medium in the first reactor I (D) and in the second reactor I (F) that was needed for heat exchange. This mode of operation then led to partial subcooling of the reaction medium in subregions of the cooling water-operated heat exchangers of the first reactor I (D) or of the second reactor I (F), and ultimately led to precipitation reactions. This blocked the plant, which had to be shut down.
[0302] For that reason, it was not possible to record any analysis data with regard to the concentrations in steady-state operation.
Comparative Example 7
[0303] Methacrylamide was prepared from acetone cyanohydrin and sulfuric acid having a total water content of 20.66 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0304] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D, F) are shown in Tables 6 and 10 respectively. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0305] The variation in the water content in the feed (8a,10) to the amidation (D, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 6. The resulting yield is likewise shown in Tables 6 and 10.
[0306] The average yield of 10 representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 89.1%.
[0307] Very watery conditions existed in the feed (8a, 10) to the amidation, and even adjustment of the conversion conditions (cf. Table 10) achieved only a very low yield. The high water content in the amidation reactors (D, F) made it impossible to convert the HIBAm inevitably formed in the amidation (D, F) to MAA without breakdown of MAA already present.
TABLE-US-00006 TABLE 6 Results of Comparative Example 7 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide Methacrylic acid 1 Day 1; 08:05 32.57 1.71 2.30 89.92 2 Day 1; 10:05 32.23 1.62 2.37 88.98 3 Day 2; 07:45 32.39 1.63 2.39 89.42 4 Day 2; 11:45 32.28 0.89 2.21 89.12 5 Day 3; 08:15 31.92 1.77 2.80 88.13 6 Day 3; 11:05 32.19 1.58 2.12 88.87 7 Day 4; 08:32 31.90 1.62 2.74 88.07 8 Day 4; 11:19 32.61 1.59 2.40 90.03 9 Day 5; 08:21 32.54 1.62 2.30 89.84 10 Day 5; 11:19 32.10 1.80 2.22 88.62 Average 89.1 Range of variation of the yield 2%
Comparative Example 8
[0308] Methacrylamide was prepared from acetone cyanohydrnn and sulfuric acid having a total water content of 3.66 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0309] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D, F) are shown in Tables 7 and 10 respectively. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0310] The variation in the water content in the feed (8a,10) to the amidation (D, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 7. The resulting yield is likewise shown in Tables 7 and 10.
[0311] The average yield of 10 representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 89.9%.
[0312] Oleum (100.5% H.sub.2SO.sub.4, 0.5% free SO.sub.3) was fed into the amidation in the sulfuric acid feed (10), and even by adjusting the conversion conditions (cf. Table 10) it was possible to achieve only a low yield. Surprisingly, it was not possible to achieve high yields in combination with oleum in the sulfuric acid feed (10), i.e. with a feed of water into the amidation (D, F) solely via the ACH feed (8a). A high water content in the ACH feed (8a) that led to a good yield in Inventive Examples 1 to 4, for example, was found to be disadvantageous in combination with oleum in the sulfuric acid feed (10).
TABLE-US-00007 TABLE 7 Results of Comparative Example 8 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide Methacrylic acid 1 Day 1; 07:00 34.10 0.29 0.23 90.49 2 Day 1; 10:08 33.91 0.14 0.15 89.99 3 Day 2; 08:40 33.73 0.15 0.15 89.51 4 Day 2; 11:25 33.52 0.22 0.20 88.95 5 Day 3; 07:23 33.49 0.26 0.21 88.87 6 Day 3; 11:02 33.22 0.25 0.22 88.15 7 Day 4; 07:49 34.06 0.26 0.25 90.38 8 Day 4; 11:10 34.08 0.28 0.29 90.44 9 Day 5; 08:13 34.29 0.24 0.22 90.99 10 Day 5; 11:17 34.26 0.24 0.23 90.91 Average 89.9 Range of variation of the yield 2.4%
Comparative Example 9
[0313] Methacrylamide was prepared from acetone cyanohydrin and sulfuric acid having a total water content of 0.47 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0314] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D, F) are shown in Tables 8 and 10 respectively. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0315] The variation in the water content in the feed (8a,10) to the amidation (0, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 8. The resulting yield is likewise shown in Tables 8 and 10.
[0316] The average yield of 10 representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 90.9%.
[0317] Low-water conditions existed in the ACH feed (8a, 10) to the amidation, and even adjustment of the conversion conditions (cf. Table 10) achieved only a low yield. It was not possible to compensate for the lack of water in the sulfuric acid feed (10) via the water content in the ACH feed (8a).
TABLE-US-00008 TABLE 8 Results of Comparative Example 9 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide methacrylic acid 1 Day 1; 07:22 34.85 0.04 0.02 91.60 2 Day 1; 10:56 34.60 0.05 0.02 90.94 3 Day 2; 08:07 34.73 0.04 0.02 91.28 4 Day 2; 10:05 34.64 0.03 0.06 91.05 5 Day 3; 07:03 34.32 0.00 0.04 90.21 6 Day 3; 11:16 34.78 0.00 0.01 91.42 7 Day 4; 09:49 34.77 0.03 0.00 91.39 8 Day 4; 12:10 34.68 0.05 0.02 91.15 9 Day 5; 08:41 34.29 0.04 0.03 90.13 10 Day 5; 11:53 34.14 0.04 0.03 89.73 Average 90.9 Range of variation of the yield 1.9%
Comparative Example 10
[0318] Methacrylamide was prepared from acetone cyanohydrin and sulfuric acid having a total water content of 0.05 mol % in the feed (8a, 10) from the amidation in the second reaction stage (D, F), based on the total amount of ACH fed into the second reaction stage (8a). The individual water contents of the ACH (8a/8b/8c) and sulfuric acid (10) feedstocks are shown in Table 10.
[0319] The process conditions with varied water content with regard to the ACH (8a) and sulfuric acid (10) feedstocks in the second reaction stage (D, F) are shown in Tables 9 and 10. Unless stated otherwise, the process was conducted under identical process conditions to those in Inventive Example 1.
[0320] The variation in the water content in the feed (8a,10) to the amidation (D, F) resulted in reaction conditions, the effect of which on the concentration in the third reaction mixture (14) downstream of the second converter (G) is summarized in Table 9. The resulting yield is likewise shown in Tables 9 and 10.
[0321] The average yield of three representative samples measured in steady-state operation of the process by means of HPLC, under the conditions specified, was 89.5%.
[0322] Low-water conditions existed in the ACH feed (8a, 10) to the amidation, and even adjustment of the conversion conditions (cf. Table 10) achieved only a low yield. It was not possible to compensate for the lack of water in the sulfuric acid feed (10) via the water content in the ACH feed (8a). The further decrease in water content in the ACH feed (8a) compared to Comparative Example 9 resulted in another significant lowering of the yield.
TABLE-US-00009 TABLE 9 Results of Comparative Example 10 Concentration in the product stream [% by wt.] Yield [%] Methacrylic Methacrylamide + Sample Time Methacrylamide acid Hydroxyisobutyramide methacrylic acid 2 Day 1; 10:32 34.60 0.03 0.02 90.94 3 Day 2; 08:11 34.53 0.04 0.02 91.28 4 Day 2; 10:24 34.64 0.03 0.04 91.05 Average 89.5
[0323] Summary of the examples:
TABLE-US-00010 TABLE 10 Selected process parameters Example 1 Example 2 Example 3 Example 4 Example 5 Unit Water content of acetone, based on stream 1 0.9 0.9 0.1 0.1 0.5 % by wt. H.sub.2SO.sub.4 concentration, based on stream 10 98.0 100.0 100.0 98.0 99.5 % by wt. Water content of sulfuric acid, based on stream 10 2.0 (10.0) 0.0 (0) 0.0 (0) 2.0 (10.0) 0.5 (2.7) % by wt./(mol %) ACH concentration, based on stream 8a 98.5 98.5 99.2 99.2 98.9 % by wt. Water content in the ACH, based on stream 8a 0.8 (3.66) 0.8 (3.66) 0.1 (0.47) 0.1 (0.47) 0.4 (1.7) % by wt./(mol %) H.sub.2O from ACH (8a) and H.sub.2SO.sub.4 18.48 3.66 0.47 15.67 5.62 mol % (10) based on total amount of ACH (8a) Amidation temperature in first reactor I (D) 98 98 98 98 98 C. Amidation temperature in second reactor I (F) 98 98 98 98 98 C. Optim. converter temperature (G) 165 160 155 164 159 C. Molar H.sub.2SO.sub.4(10)/ACH(8a) ratio 1.41 1.41 1.41 1.41 1.41 mol/mol ACH division (8b/8c) 65/35 65/35 65/35 65/35 65/35 kg/kg Total mass flow rate of third reaction mixture (14) 36243 36196 36058 36253 36266 kg/h MAA concentration, based on stream 14 33.8 34.6 35.0 34.6 35.4 % by wt. MA concentration, based on stream 14 1.2 1.0 0.2 1.1 1.1 % by wt. HIBAm concentration, based on stream 14 1.6 0.5 0.1 1.1 0.2 % by wt. Average yield (methacrylamide + methacrylic 93.0 94.5 92.2 94.1 96.7 % acid in 14) based on ACH in 8a Range of variation of the yield 1.7 1.1 1.6 0.6 0.7 % Comp. Comp. Comp. Comp. Comp. Example 6 Example 7 Example 8 Example 9 Example 10 Unit Water content of acetone, based on stream 1 0.5 0.5 0.9 0.1 0.01 % by wt. H.sub.2SO.sub.4 concentration, based on stream 10 99.5 97.5 100.5 100.5 100.3 % by wt. Water content of sulfuric acid, based on stream 10 0.5 (2.7) 2.5 (12.3) 0.0 (0) 0.0 (0) 0.0 (0) % by wt./(mol %) ACH concentration, based on stream 8a 98.9 98.9 98.5 99.2 99.2 % by wt. Water content in the ACH, based on stream 8a 0.4 (1.7) 0.4 (1.7) 0.8 (3.66) 0.1 (0.47) 0.01 (0.05) % by wt./(mol %) H.sub.2O from ACH (8a) and H.sub.2SO.sub.4 (10) 5.62 20.66 3.66 0.47 0.05 mol % based on total amount of ACH (8a) Amidation temperature in first reactor I (D) 80 98 98 98 98 C. Amidation temperature in second reactor I (F) 80 98 98 98 98 C. Optim. converter temperature (G) 159 166 154 152 152 C. Molar H.sub.2SO.sub.4(10)/ACH(8a) ratio 1.41 1.41 1.41 1.41 1.41 mol/mol ACH division (8b/8c) 65/35 65/35 65/35 65/35 65/35 kg/kg Total mass flow rate of third reaction mixture (14) 36166 35976 36021 35948 kg/h MAA concentration, based on stream 14 32.4 34.1 34.8 34.6 % by wt. MA concentration, based on stream 14 1.7 0.2 0.04 0.03 % by wt. HIBAm concentration, based on stream 14 2.3 0.2 0.02 0.02 % by wt. Average yield (methacrylamide + methacrylic acid 89.1 89.9 90.9 89.5 % in 14) based on ACH in 8a Range of variation of the yield 2.0 2.4 1.9 2.6 %
[0324] A comparison of Inventive Examples 1 to 5 emphasizes that a water content according to the invention in the amidation (D, F, 8a, 10), determined both by the water content of the acetone reactant (1) fed into the first reaction stage (A, B) and by the water content of the sulfuric acid (10) used in the amidation (0), is essential for high and stable yields. According to Table 10, a total amount of water between 0.5 and 18.5 mol %, based on the total amount of ACH fed into the second reaction stage, achieves the highest yields, provided that no oleum has been used in place of sulfuric acid (see Comparative Examples 8, 9 and 10), which worsened the yields further. Furthermore, the scatter of the yield measured was at its lowest, and hence the overall process was at its most stable, within a range from 6 to 16 mol % of the total amount of water, based on the total amount of ACH that was fed to the second reaction stage.
[0325] It was likewise found that, as well as the total amount of water that leads to achievement of the maximum yield, the concentration of sulfuric acid (10) fed in is of particular relevance (cf. Examples 2 and 5, and 2 and 8).
[0326] In addition, it was found that, in the case of exceedance of a total amount of water in the amidation of 16 mol %, based on a total amount of ACH fed into the second reaction stage, a distinct increase in the MA and HIBAm components is apparent in the third reaction mixture (14), which caused a loss of yield among other effects. Although it is possible to reduce the proportion of HIBAm by establishing a higher conversion temperature (E, G), with conversion to MAA, there are limits to this process. On comparison of Examples 4, 1 and 7, which represent a rising total water content from 5.6 to 18.5 and 20.6 mol %, higher conversion temperatures were used in order to convert the proportion of HIBAm that rose to an increasingly significant extent. This was no longer fully possible over and above a total water content of 16 mol % (cf. Examples 1 and 4), and ultimately led to loss of yield.
[0327] A comparison of Examples 2 and 8 follows on from this effect. Operation with 3.66 mol % of total water that was fed in exclusively with the ACH (8a) in both cases led to different yields here. In the case of 100% sulfuric acid (Example 2), the yield achieved is already at a good level, whereas the use of oleum (10) in Example 8 led to distinct yield losses. If the proportion of HIBAm and MA in the third reaction mixture (14) is considered in this connection, it is apparent that, in the case of 100% sulfuric acid (Example 2) at conversion temperature 160 C., a moderate proportion of HIBAm and MA has been produced with good yield. Even though these components occurred to a distinctly reduced degree in the case of the oleum method (100.5% in Example 8) and a conversion temperature of 152 C., a poorer overall yield was nevertheless found. If the product mass flow rates (14) of Examples 2 and 8 are compared, it becomes clear that the loss of yield arose from offgas losses (reduced product flow rate) and hence the formation of HIBAm was not solely responsible for the loss of yield. The use of oleum (10) in the case of a high water content in the ACH feed (8a) led to greater yield losses than was the case for 100% sulfuric acid (10).