GRANULAR CATALYST FOR THE HYDROLYSIS OF AMINO NITRILES AND AMINO AMIDES TO AMINO ACIDS OR DERIVATIVES THEREOF

Abstract

A granular catalyst may be used for hydrolyzing amino nitriles and/or amino amides to amino acids or derivatives thereof. A process for preparing such a catalyst and a method for preparing an amino acid or derivative thereof may include contacting a solution or suspension including an amino nitrile and/or an amino amide with water in the presence of such a catalyst or in the presence of a catalyst obtained by such a process.

Claims

1. A process for preparing a granular CeO.sub.2 comprising catalyst suitable for hydrolyzing an amino nitrile and/or amino amide to an amino acid or derivative thereof, the process comprising: (a) subjecting a ceria-comprising powder comprising CeO.sub.2 and a liquid binder to a high shear wet granulation to provide granulates; (b) drying and/or calcinating the granulates obtained from the subjecting (a), to obtain dried and/or calcinated granulates; and (c) sieving the dried and/or calcinated granulates obtained from the drying and/or calcinating (b) to a particle size in a range of from 100 to 5000 m, to give the granular CeO.sub.2 comprising catalyst.

2. The process of claim 1, wherein the ceria-comprising powder comprises the CeO.sub.2 in a range of from 50 to 100 wt. %, has a BET surface area in a range of from 35+/10% to 300+/10% m.sup.2/g, measured according to DIN ISO 9277-5 from 2003, and a mean maximum Feret diameter xF.sub.max, mean in a range of from 3+/10% to 40+/10% nm, and mean minimum Feret diameter x.sub.Fmin, mean in a range of from 2+/10% to 30+/10% nm, both measured according to DIN ISO 9276-6 from 2012.

3. The process of claim 2, wherein the ceria-comprising powder has a BET surface area in a range of from 35+/10% to 65+/10% m.sup.2/g, measured according to DIN ISO 9277-5 from 2003, and a mean maximum Feret diameter x.sub.Fmax, mean in a range of from 10+/10% to 40+/10% nm and mean minimum Feret diameter x.sub.Fmin, mean in a range of from 5+/10% to 30+/10% nm, both measured according to DIN ISO 9276-6 from 2012(21-2).

4. The process of claim 2, wherein the CeO.sub.2 comprising material has a BET surface area in a range of from 175+/10%+/10% to 300+/10% m.sup.2/g or from 225+/10% to 265+/10%, measured according to DIN ISO 9277-5 from 2003, and a mean maximum Feret diameter x.sub.Fmax, mean in a range of from 3+/10% to 40+/10% nm and mean minimum Feret diameter x.sub.Fmin, mean in a range of from 2+/10% to 30+/10% nm, both measured according to DIN ISO 9276-6 from 2012.

5. The process of claim 1, wherein the ceria-comprising catalyst comprises the CeO.sub.2 in a range of from 50 to 100 wt. %.

6. The process of claim 1, wherein, in the sieving (c) the dried and/or calcinated granulates obtained from the subjecting (a) are sieved to a particle size in a range of from 125 to 500 m, from 500 to 1000 m, from 1000 to 2500 m, and/or from 2500 to 5000 m.

7. The process of claim 1, wherein the liquid binder comprises an organic binder.

8. The process of claim 1, wherein the liquid binder comprises water as granulating liquid.

9. A granular catalyst, comprising CeO.sub.2, wherein the granular catalyst is suitable for hydrolyzing an amino nitrile and/or amino amide to an amino acid or derivative thereof, wherein the granular catalyst is obtained by a process of claim 1.

10. The catalyst of claim 9, having a particle size in a range of from 125 to 500 m, from 500 to 1000 m, from 1000 to 2500 m, and/or from 2500 to 5000 m.

11. The catalyst of claim 9, having a d50 value in a range of from 400+/10% to 2000+/10% m, measured according to ISO 13322-1:2004 and determined according to ISO 9276.

12. The catalyst of claim 9, wherein having a pore volume 4 nm<d<400 m in a range of from 0.3+/10% to 1.2+/10% mL/g and/or a pore volume 4 nm<d<1 m in a range of from 0.1+/10% to 0.7+/10% mL/g

13. The catalyst of claim 9, comprising the CeO.sub.2 in a range of from 50 to 100 wt. %.

14. A process for preparing an amino acid or a derivative thereof, the process comprising: contacting a solution or suspension comprising an amino nitrile and/or an amino amide with water in the presence of a catalyst obtained by the process of claim 1.

15. The process of claim 14, wherein the amino acid prepared is an alpha-amino acid, or a derivative thereof.

16. The process of claim 1, wherein, in the sieving (c) the dried and/or calcinated granulates obtained from the subjecting (a) are sieved to a particle size in a range of from 125 to 500 m.

17. The process of claim 1, wherein, in the sieving (c) the dried and/or calcinated granulates obtained from the subjecting (a) are sieved to a particle size in a range of from 500 to 1000 m.

18. The process of claim 1, wherein, in the sieving (c) the dried and/or calcinated granulates obtained from the subjecting (a) are sieved to a particle size in a range of from 1000 to 2500 m.

19. The process of claim 1, wherein, in the sieving (c) the dried and/or calcinated granulates obtained from the subjecting (a) are sieved to a particle size in a range of from 2500 to 5000 m.

Description

DESCRIPTION OF THE FIGURES

[0095] FIG. 1 shows the progress of the conversion and the yields in the example 3.4 being continuously operated at T=80 C. and WHSH=0.6 h.sup.1 for 96 h. The solid black line (-) at the top represents the conversion of 2-amino-4-(methylthio)butane nitrile (methionine nitrile, MMP-AN), the broken black line (- -) in the middle represents the yield for 2-amino-4-(methylthio)butane amide (Met-amide), and the dotted line ( ) at the bottom represents the yield for methionine (Met).

[0096] FIG. 2 shows the particle size distribution of the catalyst #3 before and after its use in example 3.4 at T=80 C., WHSH=0.6 h.sup.1 for 100 h. The broken black line (- -) represents the particle size distribution of catalyst #3 prior to its use in the testing and the solid black line (-) represents the particle size distribution of catalyst #3 after its use in the testing for a total time of 100 hours.

EXAMPLES

1. Analytical Methods

1.1 HPLC-Chromatography:

[0097] Chromatographic analyses of 2-hydroxy-4-(methylthio)butane nitrile (MMP-CN), 2-amino-4-(methylthio)butane nitrile (methionine nitrile, MMP-AN), 2-amino-4-(methylthio)butane amide (methionine amide, Met-amide), 3-(methylthio)propionaldehyde (MMP), and methionine (Met) were performed using HPLC systems from JASCO or Agilent with an RP-18 column (2504.6 mm; 5 m) and a subsequent UV detection at 210 nm. A mixture consisting of 3.3 g H.sub.3PO.sub.4, 6.8 g CH.sub.3CN, and 89.9 g H.sub.2O was used as eluent with a flow of 1 mL/min. 10 L of the respective sample solution (50 mg sample in 25 mL H.sub.2O) were injected into the eluent for analysis. Calibration was done in advance by injection of suitable standard stock solutions of the analyst and a subsequent comparison of peak areas with external standards as commonly done in organic chemical syntheses.

1.2 BET Surface Area:

[0098] The BET surface areas ABET were determined by physical adsorption of nitrogen on the surface of the solid and by calculating the amount of adsorbate gas corresponding to a monomolecular layer on the surface according to the Brunauer, Emmett, and Teller (BET) method. The samples used (0.2-0.9 g) were degassed at 150 C. for 20 min under vacuum prior to the measurement. The determination was then carried out at the temperature of liquid nitrogen (77 K). The amount of gas adsorbed was measured by a static-volumetric, 3-point measurement using a TriStar 3000 Micrometrics instrument. The method is described in general in DIN ISO 9277-5 (2003) and was applied accordingly.

1.3 Determination of Pore Volume and Mean Pore Diameter

[0099] The pore volume and the mean pore diameter were determined according to DIN 66134 (N2 sorption according to Barret, Joyner, Halenda) with respect to pore sizes between either 4 nm<d<400 m or between 4 nm<d<1 m.

1.4 Thermogravimetric Analyses (TGA)

[0100] Thermogravimetric analyses (TGA) were performed under air at a heating rate of 5 K/min in the range from 25 to 500 C.

1.5 Particle Size of Granular Catalysts

[0101] The particle size of the granular catalysts was determined by means of optical analysis of 200 mL of each granular catalyst using a CCD camera in a Camsizer (Retsch Technology GmbH) according to ISO 13322-1:2014 and the median d50 was determined according to ISO 9276.

1.6 Particle Size Distribution of Powders

[0102] The particle size distribution of powders was determined by means of laser diffraction according to ISO 13320:2009 and the median d50 was determined according to ISO 9276. For this purpose, a spate point of the material was mixed with 10 mL water and 0.5 g/L tetrasodium pyrophosphate and the thus obtained mixture was subjected to laser diffraction using an LS 13320 laser diffraction spectrometer (Beckmann-Coulter) with Universal Liquid Module (ULM).

1.7 Sieving of the Granulates to Target Particle Size Range

[0103] Sieving of the granulates to a target particle size range was performed using a sieving machine AS200DIGIT (Retsch GmbH). Two sieve bottoms were used to get granulates in the target particle size range: a sieve bottom having a mesh size representing the upper limit and a sieve bottom having a mesh size representing the lower limit. First, the sieve bottom having a mesh size representing the upper limit, e.g., a mesh size of 1000 m, was applied to the machine and the portion was sieved, that had a larger particle size than desired, here >1000 m. Next, the granulates that went through that sieve was subjected to a second sieving, now with the sieve bottom representing the lower limit, e.g., a mesh size of 500 m. The sieving material retained in this sieve bottom represents the target sieving fraction, here a fraction with a particle size from 500 to 1000 m. The fractions outside the target particle size range, i.e., <500 m and >1000 m, were ground once more and then used for further granulation.

1.8 Determination of Abrasion and Bulk Density of the Granular Catalysts

[0104] The abrasion of the granular catalysts was determined using a sieving machine AS200 (Retsch GmbH) with a sieve bottom having a mesh size of 500 m. 10.00 g of the already pre-sieved granulates was placed on the sieve bottom and subjected to sieving in continuous operation at a frequency of 70 Hz for 6 minutes. After sieving has been completed, the sieve bottoms were removed from the sieving machine and the final weight was determined for the coarse material of the granulates, that was retained by the sieve bottom having a mesh size of 500 m. Abrasion on a percentual basis was calculated using the formula:

[00003]$\mathrm{Abrasion}\left[\%\right]=\frac{10.g-m\left(\mathrm{final}\mathrm{weight}\right)\left[g\right]}{10.g}$

[0105] The bulk density of the granular catalysts was determined using a measuring cylinder with a volume of 50 mL. That cylinder was placed on an analytical balance, filled with the granulates obtained from sieving to target particle size range until a volume of 50 mL was reached and then the final weight was read from the analytical balance. The bulk density of the material in question was obtained by means of the formula:

[00004]$\mathrm{bulk}\mathrm{density}\left[\frac{g}{\mathrm{mL}}\right]=\frac{m\left(\mathrm{granulates}\right)\left[g\right]}{50\mathrm{mL}}$

2. Preparation of the Catalytically Active Material

[0106] The CeO.sub.2 powders used for the preparation of the granular catalysts according to the present invention have the characteristics disclosed in EP 3199519 A1, WO 2020/161067 A1 or WO 2020/249495 A1 regarding their composition, degree of crystallinity, lattice plane distance, BET surface area ABET, mean maximum Feret diameter x.sub.Fmax, mean, minimum Feret diameter x.sub.Fmin, mean, mean aspect ratio x.sub.Fmin, mean/x.sub.Fmax, mean, and mean equivalent circular diameter x.sub.A, mean.

[0107] The other chemicals used in the catalyst preparation such as tylose MH 1000 (methylhydroxy ethylcellulose), zusoplast PS1 (polysaccharide), mowiol 8-88 (polyvinyl alcohol) or PVP K30 (polyvinyl pyrrolidone) were purchased from various distributors such as Sigma Aldrich and were used without additional pre-treatment.

2.1 Extrusion of a CeO.SUB.2 .Nano-Powder (not According to the Invention)

[0108] 416.1 g CeO.sub.2 nano-powder, 5 g zusoplast PS1 (Zschimmer & Schwarz) and 15 g tylose H 30000 P2 (Shin Etsu) were provided in a universal kneader with a trough volume of 2.5 L (LUK 2.5) and pre-mixed with a kneader rotation speed of 40 rounds per minute and a reverse operating discharge screw conveyor having a rotation speed of 11 rounds per minute for 10 minutes. The trough was cooled over a cryostat to a temperature of 10 C. Subsequently, desalinated water was added in portions of each 50 g directly after the pre-mixing, after a further minute, and after a further minute kneading time and the rotation speed of the reverse operating discharge screw conveyor was increased to 25 rounds per minute. After a further two minutes 8.8 g desalinated water was added and after further three minutes once more a further 6.7 g desalinated water was added to adjust the plasticity of the kneading mass. The kneading mass showed a good plastic deformability. Finally, 5 g zusoplast WE 8 (Zschimmer & Schwarz) were added after eight minutes to adjust the wall slippage of the mass.

[0109] Extrusion was started after 37 minutes of kneading time at the conditions described above. A nozzle with a 42.7 mm drillings was used for this. The kneader rotation speed was set to 40 rounds per minute and the mass was pressed through the nozzle by means of the now forward running screw conveyor at a rotation speed of 68 rounds per minute. Here, a pressure of 6.8 bar set in at the screw outlet. The extrudates coming out of the nizzle were cut with a wire granulator to wire lengths of 4 mm+/0.5 mm (rotation speed 400-600 rounds per minute, 2 wires).

[0110] The wet wires thus obtained were then pre-dried on a conveyor belt at 60 C. for 30 minutes and subsequently in air at room temperature overnight. The thus pre-dried extrudates were calcinated in a muffle furnace (Nabertherm LT15/11/P320). The following temperature program was used: heat-up rate 5 C./min, final temperature 500 C. was maintained for 5 hours, and subsequently cooling to 25 C. within 1 hour.

[0111] The obtained extrudates had a length of 4 mm and a diameter of 2.7 mm (catalyst #1). They were analyzed as described in chapter 1, which gave the following results: ABET=27 m.sup.2/g; pore volume 4 nm<d<400 m [mL/g]=2.26; pore volume 4 nm<d<1 m=0.21; abrasion=7.23%; bulk density=1.5 g/mL.

2.2 Granulation of a CeO.SUB.2 .Nano-Powder According to the Invention

[0112] 100 g CeO.sub.2 nano-powder according to table 1 was provided in an Eirich laboratory mixer EL 1 (Eirich Mischbehalter 1 L). The laboratory mixer was equipped with a pin-type rotator. The mixing tank ran with on step 1 (85 rounds per minute) opposite to the rotation direction of the pin-type rotator. Prior to the addition of the binder solution, a CeO.sub.2 nano-powder was mixed at 5 m/s circulation speed of the pin-type rotator for 80 seconds. Then 85% of the amount of the aqueous binder solution mentioned in table 1 were added at 10 m/s circulation speed of the pin-type rotator within 140 seconds. The tank wall was cleaned with a rubber wiper. Subsequently, the remaining 15% of the amount of aqueous binder solution mentioned in table 1 were added at 10 m/s circulation speed of the pin-type rotator within 50 seconds. Then the tank wall was cleaned again with a rubber wiper. The thus obtained mass was granulated at 30 m/s circulation speed of the pin-type rotator for the time mentioned in table 1.

[0113] The obtained wet granulate was calcinated in muffle furnace (Nabertherm LT15/11/P320). The following temperature program was used: heat-up rate 5 C./min, final temperature 500 C. was maintained for 5 hours, and subsequently cooling to 25 C. within 1 hour.

[0114] The final weight was 96.1 g and thus 96.1% the theory. The obtained granulate was separated to the following sieving fractions by means of analysis sieve (Retsch) on a sieving machine AS 200 digit (Retsch):

[00005]$\begin{array}{cc}>2500m=12.14g=12.63\%& \mathrm{Fraction}1\end{array}$$\begin{array}{cc}1000-2500m=43.08g=43\%& \mathrm{Fraction}2\end{array}$$\begin{array}{cc}500-1000m=24.25g=25.29\%& \mathrm{Fraction}3\end{array}$$\begin{array}{cc}250-500m=11.5g=11.93\%& \mathrm{Fraction}4\end{array}$$\begin{array}{cc}125-250m=4.52g=4.7\%& \mathrm{Fraction}5\end{array}$$\begin{array}{cc}<125m=3.34g=2.41\%& \mathrm{Fraction}6\end{array}$

TABLE-US-00001 TABLE 1 Preparation details of the used catalyst. Composition Density Amount of Catalyst of the used of the used CeO.sub.2 Used aqueous binder Additional Granulation d50 prior to # CeO.sub.2 nano-powder nano-powder binder solution solution [g] additive time [s] sieving [m] #2 CeO.sub.2 0.07 Tylose MH 1000 100 120 1594 (1.5 wt.-%) #3 70% CeO.sub.2 1.06 Tylose MH 1000 36 30 7669 30% CeO.sub.2- 0.32 (1.5 wt.-%) ZrO.sub.2 #4 80% CeO.sub.2 0.07 Tylose MH 1000 110 90 1295 20% CeO.sub.2- 0.32 (1.5 wt.-%) ZrO2 #5 CeO.sub.2 0.07 Tylose MH 1000 76 640 (1.5 wt.-%) #6 CeO.sub.2 0.07 Tylose MH 1000 190 TiO.sub.2 10 (1.5 wt.-%) (Hombikat, d = 3.9 g/mL) #7 CeO.sub.2 0.07 Mowiol 8-88 130 20 1671 1.0 wt.-% #7 CeO.sub.2 0.07 PVP K30 130 40 1380 3.0 wt.-%

[0115] target sieving fractions, 500-1000 m and 1000-2500 m, were analyzed for their physical characteristics as described in chapter 1, which gave the results summarized in table 2.

TABLE-US-00002 TABLE 2 Physical characteristics of the prepared catalysts Pore Pore Composition Sieving Bulk volume volume Ignition Catalyst of catalyst fraction Abrasion density 4 nm < d < 400 4 nm < d < 1 A.sub.BET d50 loss # granulates [m] [%] [g/mL] m [mL/g] m [mL/g] [m.sup.2/g] [m] [%] #2 CeO.sub.2 500- 11.0 0.14 1.18 0.65 71 756 3.1 1000 #2 CeO.sub.2 1000- 7.8 0.19 0.92 0.68 73 1970 2.0 2500 #3 (CeO.sub.2).sub.0.85 500- 9.0 1.37 0.34 0.19 126 456 3.8 (ZrO.sub.2).sub.0.15 1000 #4 (CeO.sub.2).sub.0.9 500- 10.1 0.49 (ZrO.sub.2).sub.0.1 1000 #5 (CeO.sub.2).sub.0.7 500- 6.1 0.69 (TiO.sub.2).sub.0.3 1000 #6 CeO.sub.2 500- 7.4 0.34 1000 # CeO.sub.2 500- 8.5 0.31 1000 #8 CeO.sub.2 500- 11.6 0.38 1000

3. Synthesis Examples

3.1 Synthesis of 2-amino-4-(methylthio)butane nitrile starting from 2-hydroxy-4-(methyl-thio)butane nitrile

[0116] 10.1 g 2-hydroxy-4-(methylthio)butane nitrile (MMP-CN; 90 wt.-% in water, 69.3 mmol, 1 mol. eq.) were mixed with 26.0 g NH.sub.3 (32 wt.-% in water, 7 mol. eq., 48.8 mmol) in a glass reactor and sealed subsequently. The slightly beige colored and turbid emulsion containing 25 wt.-% MMP-CN was stirred and heated to 50 C. for 30 minutes by means of a pre-heated water bath. The obtained light yellow solution was analyzed by HPLC chromatography confirming a 100% conversion of MMP-CN with a selectivity of 98.8% towards 2-amino-4-(methylthio)butane nitrile (MMP-AN; 67.2 mmol) and 2-amino-4-(methylthio)butane amide (Met-amide; 1.2 mmol). The MMP-AN solution thus obtained consisted of 8.75 g MMP-AN (67.2 mmol), 0.18 g Met-amide (1.2 mmol), 7.14 NH.sub.3 (419 mmol, 6 mol.eq.) and 19.9 g water.

3.2 Direct Conversion of the Obtained 2-amino-4-(methylthio)butane nitrile Towards a Mixture Comprising 2-amino-4-(methylthio)butane amide and methionine

[0117] The MMP-AN solution obtained in example 3.1 consisted of 8.75 g MMP-AN (67.2 mmol), 0.18 g Met-amide (1.2 mmol), 7.14 NH.sub.3 (419 mmol, 6 mol. eq.) and 19.9 g water. A further 36.2 g water was added to this solution to set an MMP-AN concentration of 12 wt.-%, that was used in this example.

[0118] The conversion was performed in a vertically installed fixed bed reactor containing 3.0 g of the various catalyst granulates of the sieving fraction 500-1000 m obtained according to example 2.2 and identified in table 3 below as used catalysts #2 to #8. For this purpose, the reaction solution obtained according to example 3.1 and having an MMP-AN concentration of 12 wt.-% was pumped with a customary double piston lifting pump, as typically used for HPLC devices, at a flow rate of 1.0 mL from above or below into said fixed bed reactor, which corresponds to a weight hourly space velocity of 2.4 hW. The fixed bed reactor was either heated with an electric jacket heating or a double wall oil heating using a thermostat. The internal temperature was monitored with a PT100 thermocouple and the heating was set up in such a way that a temperature of 70 C. was kept constant over the whole reaction. The reactor was operated at ambient pressure. The inner diameter was 10 mm. The reactor was started up with pure water and brought to the operating temperature before the feed was switched to the solution comprising 12 wt.-% of MMP-AN. After 2 h operating time the reaction solution was collected for analytics using HPLC-chromatography. The results are summarized in table 3 below.

TABLE-US-00003 TABLE 3 Results of the experiments 3.2 at a WHSV of 2.4 h.sup.1 and 70 C. Con- Ratio version Yield of Selectivity of Met + yields Met + MMP- Met- Yield Met: Met- Selectivity Used AN amide Met Met- amide Met catalyst [%] [%] [%] amide [%] [%] #2 94.3 92.7 48.1 1.1 98.4 50.9 #3 86.9 84.2 49.2 1.4 96.9 56.2 #4 94.1 94.1 56.3 1.4 100.0 59.7 #5 85.3 81.1 35.0 0.8 96.3 40.5 #6 85.3 81.7 36.2 0.8 95.8 42.0 #7 97.4 97.4 58.8 1.5 100.0 60.3 #8 96.5 95.8 55.3 1.4 99.3 57.2
3.3 Direct Conversion of the 2-amino-4-(methylthio)butane nitrile Towards a Mixture Comprising 2-amino-4-(methylthio)butane amide and methionine at Various Particle Sizes of the Used Granulates and at Different Weight Hourly Space Velocities

[0119] The granulated catalyst #2 was sieved to various particle size fractions as described in chapter 2.2 and used as mentioned in table 4 below. The extruded catalyst #1 prepared according to chapter 2.1 was used as comparison catalyst, see table 4 below.

[0120] As described in example 3.2 the catalysts were used in a fixed bed reactor and the reaction solution obtained from example 3.1 was set to the desired MMP-AN concentration as indicated in table 4 below by addition of the appropriate amount of water. The fixed bed reactor filled with the catalysts of different sieving fractions or even extruded catalysts was operated at a pressure of 10 bar that was set with a pressure retention valve. The, weight hourly space velocities and the internal temperature were adjusted as mentioned in table 4 below.

TABLE-US-00004 TABLE 4 results of the example 3.3 with different concentrations of 2-amino-4-(methylthio)butane nitrile (MMP-AN), catalysts of different sieving fractions or even extruded catalysts subjected to different weight hourly space velocities and different temperatures (* identifies comparison examples). Yield Met Ratio Selectivity Concentration Sieving Internal Conversion + Yield of yields Met + Selectivity Used MMP-AN fraction WHSV temperature MMP-AN Met-amide Met Met: Met-amide Met catalyst [wt.-%] [m] [h.sup.1] [ C.] [%] [%] [%] Met-amide [%] [%] #1* 5.9 extrudate 0.22 70 87.0 72.8 20.5 0.4 83.7 23.5 #1* 5.2 extrudate 1.0 70 30.9 28.1 16.4 1.1 90.8 44.6 #2 5.8 500-1000 0.25 60 100 97.8 96.4 26.7 97.8 96.4 #2 5.8 500-1000 0.9 60 100 93.0 81.6 4.4 93.0 81.6 #2 5.8 500-1000 5.2 60 94.7 89.5 50.4 1.1 94.5 53.1 #2 5.5 125-500 4.9 60 93.8 93.8 52.9 1.3 100 56.3 #2 12.0 2500-5000 3.6 70 98.0 94.9 55.0 1.3 97.3 56.1 #2 12.0 1000-2500 3.6 70 98.8 98.8 57.4 1.4 100 58.0 #2 18.0 1000-2500 2.7 70 90.8 86.9 32.8 0.6 95.7 36.0 #2 16.0 1000-2500 1.2 85 100 100 88.3 7.5 100 88.3
3.4 Direct Conversion of the 2-amino-4-(methylthio)butane nitrile Towards a Mixture Comprising 2-amino-4-(methylthio)butane amide and methionine

[0121] These experiments were performed in a fixed bed reactor as described in example 3.2 with a solution comprising 12 wt.-% of MMP-AN, with the exception that the experiments were performed at an internal temperature of 80 C. and a WHSV of 0.6 h.sup.1 for 96 hours in total. The catalyst #3 with a sieving fraction of 500 to 1000 m according to table 1 was used as the CeO.sub.2 catalyst granulate catalyst. The fixed bed reactor was operated at a pressure of 10 bar that was set with a pressure retention valve. After the experiment durations mentioned in table 5 below the product solution was collected separately and its composition, and resulting from this, the conversion of MMP-AN, the yield for Met-amide, the yield for Met and the selectivity for Met+Met-Amide were determined, which are summarized in table 5 below. The progress of the conversion and the yields are shown in FIG. 1.

TABLE-US-00005 TABLE 5 Results of the continuously performed experiment (96 h, 80 C., WHSV = 0.6 h.sup.1). Conversion Yield Yield Selectivity Experiment MMP-AN Met-amide Met Met + Met- duration [h] [%] [%] [%] amide [%] 6 100 5 95 100 12 99 6 93 100 18 98 5 92 99 24 99 19 80 100 30 97 14 83 100 36 97 15 82 100 42 98 18 79 99 48 99 16 82 99 54 98 20 78 100 60 98 16 81 99 66 97 14 82 99 72 96 14 82 100 78 96 20 75 99 84 96 28 68 100 90 95 30 65 100 96 96 27 69 100

[0122] After 100 hours testing the catalyst was analyzed for any potential changes in the particle size distribution of the catalyst #3. The FIG. 2 shows the particle size distribution of catalyst #3 prior to its use in the testing and after its use in the testing for a total time of 100 hours. Compared to its particle size distribution before the testing, there are no significant changes in the particle size distribution of catalyst #3 after its use in the testing for a total time of 100 hours. This shows that the catalyst particles are stable under the synthesis condition applied in this testing.

3.5 Reacting the Obtained Solution Comprising 2-amino-4-(methylthio)butane nitrile and 2-amino-4-(methylthio)butane amide

[0123] This experiment used the reaction solution obtained with catalyst #2 as described in example 3.2 consisting of 0.7 wt.-% 2-amino-4-(methylthio)butane nitrile (MMP-AN), 6.8 wt.-% 2-amino-4-(methylthio)butane amide (Met-amide), 6.9 wt.-% methionine (Met), 10 wt.-% NH.sub.3, and 76.3 wt.-% water.

[0124] This solution was subjected according to example 3.2 in a fixed bed reactor equipped with the catalyst #3 (see table 1), with the exception that an internal temperature of 100 C. and a WHSV of 0.25 h.sup.1 was set for a testing time of 78 hours in total (see table 6 below). The reactor operated at a pressure of 10 bar that was set with a pressure retention valve. After the experiment durations mentioned in table 6, the product solution was collected separately and its composition, and resulting from this, the conversion of MMP-AN, the yield for Met-amide, the yield for Met and the selectivity for Met+Met-Amide were determined, which are summarized in table 6 below.

TABLE-US-00006 TABLE 6 Results of the continuously performed experiment (78 h, 100 C., WHSV = 0.25 h.sup.1). Duration of Conversion Yield Yield Selectivity experiment MMP- Met-amide Met Met + Met- [h] AN [%] [%] [%] Amide [%] 2 100 10 90 100 4 100 10 90 100 24 100 12 88 100 33 100 10 90 100 50 100 12 88 100 78 100 10 90 100