The hydrolysis of the methionine amide to produce the methionine is a known process. In particular European Patent Application No228938 discloses a process for the production of methionine by the hydrolysis of the methionine amide using a strong base. A problem with this process is that the acidification step uses a strong acid which results in the co-production of mineral salts such as carbonates, chlorides or sulphates. An additional purification step is generally required to remove the salt.

French patent application No. 9814000 attempts to overcome the aforementioned problem through the use of a titanium catalyst in the hydrolysis reaction. The use of a titanium based catalyst is also disclosed in Japanese patent applications 03093753, 03093754, 03093755, 03093756.

We have now found that methionine can be produced generally without the co- production of salt and in a high yield using a specific titanium catalyst.

Accordingly, the present invention provides a process for the production of methionine which comprises (a) hydrolysing methionine amide in the presence of a porous catalyst comprising titanium to produce ammonium methioninate, said catalyst having a porosity of from 5 to 1000nm, a total pore volume of from 0. 2 to 0. 55 cm3/g and a surface area of from 30 to 150m2/g, and (b) a second step of recuperating methionine from the ammonium methioninate salt by removing ammonia.

The process of the present invention provides the advantage over the known prior art processes for the production of methionine in that the methionine amide can be completely converted to methionine without the need for additional treatment such as purification.

The process of the present invention is directed to the hydrolysis of methionine amide. Suitably, the amide is present in an aqueous solution in an amount of from 0. 01 to 2 mol/kg, preferably from 0. 5 to 1 mol/kg.

The process of the present invention is a catalysed process using a titanium- containing catalyst. The catalyst has a porosity of from 5 to 1000 nm.

Preferably, the catalyst has a macroporous distribution of from 5 to 100 and from 20 to 1000.

The catalyst has a pore volume as determined by mercury porosimetry of from 0. 2 to 0. 55 cm3/g, preferably from 0. 25 to 0. 45 cm3/g.

The catalyst must also have a surface area, as determined by B. E. T., of from 30 to 150m'-/g, preferably from 40 to 120m2/g.

The catalyst may be any suitable shape, for example extrudates, spherical particles, tabular. We have also found that the catalyst is effective when used in the form of extrudates having the particular shape of either a three leaf or a four leaf clover. Suitably, the catalyst particles have a diameter of from 0. 05 to 4mm, preferably from 0. 5 to 2 mm.

The catalyst may comprise titanium as the sole metal or may comprise one or more additional metals. Where titanium is the only metal, the catalyst may be titanium oxide (TiO,). Where the catalyst comprises additional metals, suitable catalysts include Ti-W, TiMo, Ti-Si-W, Ti-Nb-Mo, Ti-Zr, Ti-Al, Ti-Cr, Ti-Zn and Ti-V.

The catalyst may be prepared by any suitable method, for example mixing the dry ingredients, calcining at a suitable temperature and forming the desired shape.

Alternatively, the water and/or an acid may be added to the titanium powder to form a paste. The paste may then be calcined and the resulting product extruded.

The catalyst is suitably used in the process of the present invention in an amount of from 0. 1 to 2g, preferably from 0. 5 to 1. 5g of catalyst per gram of amide.

The catalyst may deactivate after a long period of use in the process and can be regenerated by contacting with water or acidified water containing 1 to 5% mineral acid, followed by heating in an oxygen-containing gas such as air or pure oxygen. The regeneration step may be carried out at a temperature of from 200 to 500°C, preferably from 300 to 400°C.

The process of the present invention may suitably be carried out at a temperature of from 50 to 150°C, preferably from 80 to 130°C and under a pressure of from 1 to 10 bar, preferably from 1 to 5 bar.

In the second step of the reaction, methionine is liberated from the ammonium methioninate salt by removing ammonia. This may be accomplished by any suitable method, for example stripping.

The process may be carried out either as a batch process or as a continuous process. Preferably, the process is carried out as continuous plug flow process and using one or two or more reactors connected in series. Thus configuration is particularly preferred since it requires less catalyst, an advantage which is particularly favourable in an industrial process.

The amide may be obtained from the known prior art processes in which there is a first step which comprises reacting hydroxymethyl thiobutyrnotrile with ammonia or an ammonium solution to produce 2-aminothiobutyronitrile. The 2- aminothiobutyronitrile product may then be reacted with a ketone in the presence of an alkali metal hydroxide to produce methionine amide. The process of the present invention may be incorporated into the known processes to provide a novel industrial process for the production of methionine.

Thus according to further aspect of the present invention there is provided an industrial process for the production of methionine which comprises (a) a first step of contacting hydroxymethylthiobutyronitrile with ammonia or a solution containing ammonia to produce 2-amino methylthiobutvronitrile, (b) a second step of reacting the 2-amino methylthiobutyronitrile with a ketone and an alkali metal to produce methionine amide, (c) third step of hydrolysing the methionine amide in the presence of a catalyst comprising titanium to produce ammonium methioninate, said catalyst having a porosity of from 5 to 1000nm, a total pore volume of from 0. 2 to 0. 55 cm3/g and a surface area of from 30 to 150m~/g ! and (d) a fourth step of recuperating methionine by removing the ammonia.

In the first step of the process of the present invention, hydroxymethylthiobutyronitrile is contacted with ammonia or a solution of ammonium and water, to produce a mixture containing 2-amino methylthiobutyronitrile. The molar amount of ammonia relative to hydroxymethylthiobutyronitrile is suitably from 3 to 10, preferably from 4 to 7.

Where it is desired to use an aqueous solution of ammonia, the solution is suitably at a concentration greater that 25% by weight, preferably greater than 60% by weight. Preferably, the hydroxymethylthiobutyronitrile is contacted with pure ammonia.

This first step of this process is suitably carried out at a temperature of from 40 to 80°C, preferably from 70 to 75°C and under a pressure of froml 0 to 30 bar, preferably from 15 to 25 bar. The reaction may be carried out in a stirred or

tubular reactor with, in particular, a piston-type flow with a calorific exchange system.

At the end of the reaction of the first step it is likely that there exists excess unreacted ammonia. The excess ammonia is preferably removed from the reactor.

This may be implemented by flash depressurisation or by entrainment with an inert gas such as nitrogen. The temperature during this separation step is suitably below 60°C, preferably between 10 and 40°C. The pressure can be atmospheric pressure or below atmospheric pressure. Preferably a pressure of from 0. 1 to 0. 5 x105 Pa is used. The ammonia recovered from the reaction may then be condensed or recuperated by any other suitable process and mixed with additional ammonia and recycled into the reactor.

The 2-amino methylthiobutyronitrile produced in the first step of the process is then hydrated in the presence of a ketone and an alkali metal hydroxide to produce methionine amide. The ketone is suitably present in a concentration of from 0. 1 to 1, preferably 0. 2 to 0. 5 equivalent of ketone. The alkali metal hydroxide is suitably present in a concentration of from 0. 05 to 0. 5, preferably from 0. 1 to 0. 25 equivalent of alkali metal hydroxide. Preferably the ketone is acetone. Suitably the alkali metal hydroxide is potassium hydroxide or sodium hydroxide, especially sodium hydroxide.

The hydration step is suitably carried out at a temperature of from 10 to 40°C, preferably from 25 to 35°C. Suitably the reaction is carried out under atmospheric pressure. The reaction may be carried out in a stirred or in a tubular reactor or in a column packed with suitable packing material with a calorific exchange system.

By-products to this reaction include the alkali metal salt of methionine, residue aminomethylthiobutyronitrile, imidazolidinone (2, 2'-dimethyl-5 (methyl thio ethyl)-4-imidazolidinone), aqueous ammonia, unreacted ketone and the alkali metal hydroxide.

The unreacted ketone and the aqueous ammonia in the product stream is then separated from the other components. To facilitate this separation step, the product stream may be distilled or stripped or by any other suitable separation technique. The ketone and the ammonia may then be recycled back to the reactor.

The methionine amide is then hydrolvsed in the presence of the titanium- containing catalyst as hereinbefore discussed to produce the ammonium methioninate salt. The salt is then treated to remove ammonia as hereinbefore discussed.

The present invention will now be illustrated with the reference to the following examples : Example 1 : Preparation of Catalyst (1) Catalyst 1 : 55g of powdered wet titanium oxide was placed in a BrabenderTM mixer. A solution of nitric acid (6. 26g) and water (27. 39g) was slowly added to the powder and the resulting mixture stirred for 30 minutes at a speed of 50 turns per minute. The paste was then extruded at a speed of 4cm per minute using an extrudate having a diameter of 1. 6mm to provide a extrudate having a diameter of 1. 6mm.

The resulting extrudate was placed in an oven and the temperature increased from 120°C to 480°C at a rate of 3°C per minute. The temperature was maintained at this level for four hours before reducing the temperature to ambient temperature at a rate of 5°C per minute.

The weight loss of the paste was 38. 5%.

(2) Catalyst 2 : 59. 2g of powdered wet titanium oxide was placed in a Brabender mixer. A solution of nitric acid (5. 65g) and water (15. 16g) was slowly added to the powder and the resulting mixture stirred for 30 minutes at a speed of 50 turns per minute. The paste was then extruded at a speed of 4cm per minute using an extrudate having a diameter of 1. 6mm to provide a extrudate having a diameter of 1. 6mm.

The resulting extrudate was placed in an oven and the temperature increased from 120°C to 480°C at a rate of 3°C per minute. The temperature was maintained at this level for four hours before being decreased to ambient temperature at a rate of 5°C per minute.

The weight loss of the paste was 40%.

(3) Catalyst 3 : This catalyst is a commercially available catalyst, obtained from Procatalyse, identified as CRS31.

(4) Catalyst 4 : This catalyst is a commercially available catalyst, obtained from Degussa. identified as 7708.

(5) Catalyst 5 : 228g of powdered wet titanium oxide, 9. 12g of methyl cellulose and 4. 5 6,,, of polysaccharide were mixed in a BrabenderT mixer for 30 minutes.

119. 39g of water was then added to form a paste. The paste was kneaded for 120 minutes and then left for 1 hour.. The paste was then extruded at a speed of 4cm per minute to provide a extrudate having a diameter of 1. 00mm. The resulting

extrudates were then placed in an oven and the temperature increased from 20°C to 140°C at a rate of 1°C per minute over a two hours period. The temperature was then increased to 480°C at a rate of 3°C per minute over a period of 4 hours.

The weight loss of the paste was 45% and the percentage of methyl cellulose and polysaccharide in the paste was 2% in each case.

(6) Catalyst 6 : The procedure used in the preparation of catalyst 5 was repeated except that the weight loss of the paste was 45% and the diameter of the extrudate was 1. 6mm.

(7) Catalyst 7 : The procedure used in the preparation of catalyst 6 was repeated except that the weight loss of the paste was 45%, the percentage of methyl cellulose was 4% and the diameter of the extrudate was 1. 6mm.

(8) Catalyst 8 : The procedure carried out for Catalyst 1 was repeated except that the weight loss of the paste was 40%.

Comparative Catalysts 1, not according to the present invention, is a commercially available catalyst obtained from Degussa, identified as 7709.

Comparative Catalysts 2, not according to the present invention, is a commercially available catalyst obtained from Englehard, identified as Ti-0720.

A summary of the properties of the catalysts prepared as described above is given in Table 1

Table 1 : CHARACTERISTICS OF THE CATALYST CATALYST SHAPE EXTERNAL SURFACE PORE MESOPORE MACROPORE DIAMETER AREA VOLUME POROSITY POROSITY (mm) (m2/g) (cm3/g) (nm) (nm) 1 extrudate 1.6 63 0.38 17 200 2 extrudate 1.4 79 0.30 12 100 3 extrudate 4.0 115 0.29 10 100 4 extrudate 3.2 45 0.39 30 - 5 extrudate 0.8 - 0.44 9 150-160 6 extrudate 1.4 - 0.43 8 150-160 7 extrudate 1.3 - 0.44 9 150-160 8 extrudate 1.5 63 0.45 17 200 9 three leaf 0.8 100 0.36 14 50 clover 10 three leaf 1.6 100 0.34 14 50 clover Comparative extrudate 3.2 12 - 35 - catalyst 1 Comparative tablet 3.3 177 03.6 6 to 20 - catalyst 2

Example 2 : Hvdrolysis of Methionine Amide Using Powdered Catalvst Catalysts 1, 2, 3, 4 9 prepared as detailed above and Comparative Catalysts 1 and 2 were used to hydrolyse methionine amide. An aqueous solution of the methionine amide was placed in a reactor with lOg of powdered catalyst suspended in water to give an initial ratio of catalyst to amide of 1 g of catalyst per gram of methionine amide. The initial concentration of amide in the reactor was 0. 5 mole/kg.

The reaction was carried out at a temperature of between 95 and 100°C and under atmospheric pressure.

The product obtained was analysed using HPLC and the yield and conversion determined.

The results are given in Figure 1 Example 3 : Hvdrolvsis of Methionine Amide Using Catalvst in a Fixed Bed Reactor with Recirculation Catalysts 3, 5, 6 and 7 were used to hydrolyse methionine amide in the amounts as given in Table 2. The catalyst was placed in a fixed bed reactor. 216g of water was added to the reactor. The temperature was increased to 95°C. 122. 9g (21. 7% p/p) of methionine amide was then added to provide an initial concentration of amide of 0. 5mol/kg The product obtained was analysed using HPLC and the yield and conversion determined.

The results are given in Figure 2 Table 2 CATALYST WEIGHT OF DEBIT DIAMETER CALCINATION CATALYST ALIM (mm) TEMPERATURE (g) (kg/hour) (°C) 40 10-15 480 5 20 5 1.4 480 20 10-15 0. 8 400 7 22 10-15 1. 4 480

Example 4 : Hvdrolvsis of Methionine Amide Usina Catalvst in a Fixed Bed Reactor with Pius Flow (a) under atmospheric pressure Catalvsts 4. 6 and 8 were used to hydrolyse methionine amide. A solution of methionine amide having an initial concentration of between 0. 37 and 0. 85 mol. kg was placed in the reactor. The reactor temperature was set at 95°C. A weight of catalyst, as given in Table 3, was placed in the reactor and the process operated under the conditions given in Table 3.

Table 3 CATALYST WEIGHT OF CONC. OF FLOW RATE TIME ON CATALYST AMIDE (g/hour) STREAM* (g) (moles) (minutes) 4 30 0. 37 168. 8, 153. 8 4. 8, 5. 3 4 30 0. 37 210. 8 3. 8 6 5 0. 37 223 0. 6 6 5 0. 37 162 0. 8 6 30 0. 37 145, 188. 9, 5. 5, 4. 2, 3. 7 212. 8 6 30 0. 83 178. 218, 250 3. 2, 3. 7, 4. 5 8 84120. 160. 220 4. 8, 6. 7, 8. 9 ! * Time on stream (ts) is calculated as follows : ts= (60xEm x Wgt of catalyst (g))/flow rate (g/h) where Em = (weight of liquid)/weight of dry catalyst +weight of liquid) Em = 0. 45 for the catalysts of the present invention The results are given in Figure 3 (b) under elevated pressure The above procedure was repeated in a fixed bed using catalysts of different diameter and amounts. The conversion of amide is reported in Table 4 below.

Table 4 CATALYST TEMP. WEIGHT OF D CONVERSION (°C) CATALYS MASSIQUE (%) (g) (g/h) 8 100 40 120 97. 5 8 100 40 300 87 8 100 40 300 95. 5 9 100 20 120 97. 5 9 100 20 300 93. 3 9 120 20 300 95. 8 10* 100 20 120 95. 6 10* 100 20 300 82. 6 10* 120 20 300 90. 5 10** 100 40 120 98. 2 10** 100 40 300 97 10** 120 40 300 98 * : diameter of 0. 8 mm, ** : diameter of 1. 6 mm The time on stream was calculated as in the previous example.