Process for manufacturing a complexing agent

Abstract

The present invention is directed towards a process for manufacturing a complexing agent, said process comprising the steps of (a) Providing a nitrile according to general formula (I a) or (I b) ##STR00001## With M being selected from alkali metal and hydrogen and combinations thereof, (b) Saponification with a total alkali amount of 2.5 to 2.9 mol of alkali metal hydroxide per mole of nitrile according to general formula (I a) or (I b), respectively, and a pH value in the range of from 9.5 to 11.5 at the end of step (b), (c) Adding an amount of alkali metal hydroxide so that the total alkali content is 2.9 to 3.15 moles per mole nitrile according to general formula (I a) or (I b), respectively, and (d) Allowing further conversion.

Claims

1. A process for manufacturing a complexing agent, the process comprising: (a) providing a nitrile according to general formula (I a) or (I b): ##STR00004## with M being selected from alkali metal and hydrogen and combinations thereof, (b) saponifying with a total alkali metal hydroxide amount of 2.5 to 2.9 mol of alkali metal hydroxide per mole of nitrile according to general formula (I a) or (I b), respectively, and a pH value in the range of from 9.5 to 11.5 at the end of step (b), (c) adding an amount of alkali metal hydroxide so that the total alkali metal hydroxide content is 2.9 to 3.15 moles per mole of nitrile according to general formula (I a) or (I b), respectively, wherein, if a total of 2.9 moles alkali metal hydroxide per mole of nitrile according to general formula (I a) or (I b) are employed by the end of step (c), the amount of alkali metal hydroxide in the respective step (b) is in the range of from 2.5 to less than 2.9 moles, and (d) further saponifying, neutralizing, or removing ammonia.

2. The process according to claim 1, wherein step (d) is neutralizing or saponifying.

3. The process according to claim 1, wherein the nitrile according to formula (I b) is selected from the racemic mixture, enantiomerically pure L-(I b) and mixtures of enantiomers of (I b) in which the L-isomer prevails.

4. The process according to claim 1, wherein the saponification in step (b) is carried out at a temperature in the range of from 25 to 200° C.

5. The process according to claim 1, wherein the alkali metal hydroxide in step (b) or step (c) is potassium hydroxide or sodium hydroxide.

6. The process according to claim 1, wherein the addition of alkali metal hydroxide according to step (c) is performed at a temperature in the range of from 25 to 100° C.

7. The process according to claim 1, wherein in step (c) an amount of alkali metal hydroxide is added so that the total alkali metal hydroxide content is 2.9 to 3.0 moles per mole nitrile according to general formula (I a) or (I b), respectively.

8. The process according to claim 1, further comprising an ammonia removal step between steps (b) and (d).

9. The process according to claim 1, wherein said process comprises the additional step (e) of spray-drying or spray granulating the resultant complexing agent.

Description

(1) The invention is further illustrated by working examples.

(2) With exception of ee values, percentages in the context of the examples refer to percent by weight unless expressly indicated otherwise.

(3) I.1. Providing an Aqueous Solution of L-Alanine N,N-Bis Acetonitrile, Step (a.1)

(4) A 5-litre stirred flask was charged with 1,170 g of de-ionized water and heated to 40° C. 668.5 g of L-alanine (99.2 wt-% representing 7.44 mol with >98% ee) were added. To the resultant slurry 390.0 g of 50% by weight aqueous sodium hydroxide solution (4.88 mol) were added over a period of 30 minutes. During the addition the temperature raised to 60° C. After complete addition of the sodium hydroxide the slurry was stirred at 60° C. for 30 minutes. A clear solution was obtained.

(5) At 38 to 42° C. the above solution, formaldehyde as 30% aqueous solution, and HCN (80% of total amount) were added to the first stirred tank reactor in a cascade comprising three stirred tank reactors. In the second stirred reactor additional HCN (20% of total amount) was added at 38-42° C. In the third stirred reactor at 38-42° C., the reaction was completed. An aqueous solution of partially neutralized L-alanine N,N-bis acetonitrile was obtained. It was used as feed for the cold saponification.

(6) I.2 Syntheses of Aqueous Solutions of MGDA-Na.sub.x with Sub-Stoichiometric Amounts or Equimolar Amounts of NaOH: Saponification (b.1)

(7) (b.1-1) Cold Saponification:

(8) The cold saponification was conducted in a cascade of two stirred tank reactors and a tubular reactor. The temperature was approximately 55° C. in all three reactors.

(9) In a first stirred reactor, the feed solution as provided in step (a.1) and NaOH as 50% aqueous solution were added. For completion of the reaction, the mixture was further reacted in a second stirred tank reactor and in a tubular reactor. The solution obtained under steady state conditions was used as feed in the hot saponification.

(10) (b.1-2) Hot Saponification:

(11) The hot saponification was performed at 180° C. and 24 bar in a tubular plug flow reactor at 30 to 45 min retention time. No steps (c) or (d) were performed.

(12) The solution obtained under steady state conditions was expanded to ambient pressure and stirred in a tank reactor at 970 mbar at 94 to 98° C. in order to remove ammonia. Then it was stripped in a wiped film evaporator at 900 mbar at 100° C. to further remove ammonia. Then, the concentration of total complexing agent (A) was adjusted to approximately 40% by weight (based on iron binding capacity).

(13) The molar ratios of the feed materials are summarized in Table 1.

(14) TABLE-US-00001 TABLE 1 Summary of comparison examples Eq Eq Eq MGDA-Na.sub.3 NTA-Na.sub.3 Example NaOH* HCN H.sub.2C═O [wt. %]** [wt. %]*** C-1 2.86 2.03 1.98 40.27 0.05 C-2 2.91 2.02 1.98 39.00 0.05 C-3 2.96 2.03 1.98 40.39 0.04 C-4 3.00 2.03 1.98 39.11 0.07 *The equivalents of NaOH refer to the sum of NaOH from the feed solution and NaOH addition during the cold saponification. **based on iron binding capacity. Expressed as trisodium salt ***based on HPLC

(15) Examples according to the present invention:

(16) Steps I.1 and I.2 were performed as above.

(17) I.3 Addition of NaOH

(18) The solution obtained under steady state conditions was submitted in continuous mode to a stirred tank reactor at 970 mbar at 94 to 98° C. An additional amount of NaOH in accordance with Table 2 was added to the stirred tank reactor. Then the combined flows were stripped in a wiped film evaporator at 900 mbar at 100° C. to further evaporate ammonia. Then, the concentration of total complexing agent (A) was adjusted to approximately 40 wt % (based on iron binding capacity).

(19) TABLE-US-00002 TABLE 2 Experimental Details Eq Add. EQ MGDA-Na.sub.3 NTA-Na.sub.3 Example NaOH* pH value .sup.(x) of NaOH Eq HCN Eq H.sub.2C═O [wt. %]** [wt. %]*** 5 2.87 9.9 +0.04 2.03 1.98 39.90 0.06 6 2.61 9.6 +0.30 2.03 1.98 40.04 0.05 *The equivalents of NaOH refer to the sum of NaOH from the feed solution and NaOH addition during the cold saponification. .sup.(x) at the end of respective step (b) **based on iron binding capacity ***based on HPLC
I.4 Addition of NaOH at Ambient Temperature

(20) The following examples were prepared corresponding to the aforementioned steps I.1 and I.2, but additional amounts of NaOH were dosed to the product after step I.2 (b.1-2).

(21) A 1-litre stirred flask was charged with 500 g of the corresponding product (after step I.2). Then an additional amount of aqueous sodium hydroxide solution (50 wt.-%) were added at ambient temperature. This solution was heated to 80° C. and stirred for 60 minutes at 80° C. Then the reaction solution was cooled to 20° C. and the concentration of total complexing agent (A) was adjusted to approximately 40 wt % (based on iron binding capacity).

(22) TABLE-US-00003 TABLE 3 Experimental Details Eq Add. EQ MGDA-Na.sub.3 NTA-Na.sub.3 Example NaOH* pH value .sup.(x) of NaOH Eq HCN Eq H.sub.2C═O [wt. %]** [wt. %]*** 7 2.86 10.0 +0.04 2.03 1.99 40.25 0.05 8 2.86 10.0 +0.09 2.03 1.99 39.89 0.06 9 2.86 10.0 +0.13 2.03 1.99 39.50 0.04 *The equivalents of NaOH refer to the sum of NaOH from the feed solution and NaOH addition during the cold saponification. .sup.(x) at the end of respective step (b.1-2) **based on iron binding capacity ***based on HPLC
II. Spray Granulation, General Remarks

(23) A commercially available laboratory spray granulator with a two-component nozzle and a zigzag air classifier was used, Glatt Lab Systems. The spray granulator was charged with about 1.5 kg of commercially available (Trilon® M) MGDA-Na.sub.3. The spray granulator was run according to Table 4. Percentages of overs were determined when the laboratory spray granulator was operated in the steady state.

(24) Then, the solution of MGDA sodium salt was pumped from a stirrer tank to the two-fluid nozzle and then introduced into the laboratory spray granulator. Formation of a granule was observed.

(25) The particles that were large (heavy) enough fell through the zigzag air classifier into a sample bottle, together with value fraction. The sample bottle would contain value fraction and overs. The smaller (lighter) granules were blown through the recycle back into the fluidized bed by the air classifier. Fines were withheld in the granulator with help of the internal filters.

(26) TABLE-US-00004 TABLE 4 Parameters of spray granulating C-2.1 Commercially C-2.2 2.3 available Example C-1 Example 9 Equivalents of NaOH 3.05 2.86 2.99 Inlet air temperature [° C.] 163 to 166 163 165 Drying air amount [m.sup.3/h] 200 200 200 Bed temperature [° C.]  98 to 102 97 to 101 99 to 100 Nozzle gas pressure [bar] 4 4 4 Throughput feed [kg/h] 6.8 7.2 7.1 Temperature feed 25° C. 70° C. 70° C. Overs, % by weight 13% 18% 5% referring to contents of sample bottle

(27) The particles in the sample bottle were classified by a 1000 μm screen. The particles with a diameter of 1000 μm and below constituted the value fraction. The granules over 1000 μm were defined as overs. The overs were milled down with a hammer mill to a diameter of 700 μm maximum and re-introduced into the fluidized bed together with a small share of milled value fraction through the milled product recycle.

(28) In the experiment C-2.1, commercially available MGDA-Na.sub.3 solution was used.