GB1561144A - Process for preparing iminoiacetonitrile - Google Patents

Description

(54) PROCESS FOR PREPARING IMINODIACETONITRILE (71) We, W. R. GRACE & CO., a corporation organized and existing under the laws of the State of Connecticut, United States of America, of 1114 Avenue of the Americas, New York, New York 10036, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is in the field of iminodiacetonitrile (IDAN) preparation. More particularly it is directed to a process for preparing IDAN by reacting hexamethylenetetramine (HMTA), formaldehyde, (HCHO) and HCN in an aqueous reaction medium. Even more specifically, this invention is directed to a continuous process in which said aqueous reaction mixture is passed through a continuous reaction zone (e.g., a tubular reactor or a continuous overflow autoclave, to form IDAN.

It was reported over eighty years ago that IDAN is obtained in an unspecified yield by reacting hydrogen cyanide with HMTA, (Eschweiler, Ann., 278, 229-239, (1894). Later, in 1921, Dubsky et al, Ber., 54, 2659, confirmed that IDAN can be formed by reacting HMTA with aqueous hydrogen cyanide. In 1957, in U. S. Patent 2,794,044, Miller disclosed the preparation of IDAN in a yield of about 65% by reacting ammonia, formaldehyde and hydrogen cyanide in an aqueous acid solution having a pH of 5.5 to 6.5. More recently, in U. S. Patent 3,167,580, Saunders showed in examples that IDAN is obtained rapidly in a continuous process comprising bringing into reactive contact acid stabilized formaldehyde and hydrogen cyanide mixture and ammonia under carefully controlled reactant ratios and temperatures and at a pH of greater than 7 using a continuous reaction zone (a tubular reactor).

Stutts, U. S. Patent 3,412, 137, teaches a process for preparing IDAN by reacting an aqueous solution of HMTA (hexamethylenetetramine) and HCN (hydrogen cyanide) in an aqueous medium buffered at a pH of about 5-6.5.

Philbrook et al, U. S. Patent 3,886,198, teach a process for preparing IDAN which comprises forming an aqueous mixture of HMTA, HCN, and a strong acid and continuously passing said mixture (which has an acidic pH - e.g., a pH of 3-5) through a tubular reactor at about 50-120"C. to form the desired IDAN.

Philbrook et al, U. S. Patent 3,866,198, teach a process for preparing IDAN which comprises forming an aqueous mixture of HMTA, HCN, and a strong acid and continuously passing said mixture (which has an acidic pH - e.g., a pH of 3-5) through a tubular reactor at about 50-120"C. to form the desired IDAN.

Sexton, U. S. Patent 2,895, 989, teaches the conversion of IDAN to an alkali metal salt of iminodiacetic acid (i.e., to IDAM) by hydrolyzing the IDAN with an alkali metal hydroxide. Sexton also teaches the conversion of such salt to iminodiacetic acid (IDA).

In our co-pending Application No. 49339/74, now published as Specification No.

1,484,628 we claim a method of making IDAN which comprises reacting hexamethylene tetramine, hydrogen cyanide and glycolonitrile having a molar ratio 1:5.2-6.8:1.2-2.2.

According to Specification 1,484,628, the precursors of glycolonitrile may be used, and these are described as equimolar amounts of HCN and HCHO. The claims of that specification are concerned with the case where glycolonitrile, pre-formed or formed in situ, is a reactant in forming IDAN.

The present invention is concerned with formation of IDAN from HMTA, HCN and HCHO in defined molar ratios; the mechanism by which IDAN is formed from these reactants is not established - it is for example possible that N-methylene-aminoacetonitrile is formed as an intermediate which reacts with HCN to form IDAN, and that glycolonitrile is not formed at all.

The process of the present invention for preparing IDAN comprises by continuously feeding into a reaction zone an aqueous hexamethylenetetramine solution having a temperature of 0-80"C, an aqueous formaldehyde solution having a temperature of 0-80 C. and HCN having a temperature of 0-25"C. in amounts sufficient to form a reaction mixture having a molar ratio hexamethylenetetramine: formaldehyde: HCN in the range 1:12.2:6.9-8.6 and having a pH in the range 5 to 10; continuously passing said mixture through the reaction zone at a speed to establish a residence time in the reaction zone of 0.05 to 20 minutes while maintaining the temperature in the reaction zone at 50-2500C., thereby forming a product mixture containing iminodiacetonitrile; and withdrawing the product mixture from the reaction zone and recovering iminodiacetonitrile therefrom.

In a preferred embodiment of this process: 1. The temperature within the continuous reaction zone is 120-170"C.

2. The residence time within the continuous reaction zone is 0.1-5 minutes.

3. The pH of the aqueous reaction mixture is 6.5-9.5.

4. The aqueous system i.e. the product mixture, withdrawn from the continuous reaction zone is cooled to 0-400C. to cause crystals of iminodiacetonitrile to separate therefrom.

5. The mole ratio of HMTA to formaldehyde to HCN is 1:1.6-2.2:7.2-8.0, and more preferably is 1:1.8:7.6.

The GIMTA and formaldehyde can be fed to the reaction zone as a combined solution formed by admixing an aqueous formaldehyde solution with an aqueous HMTA solution in a mixing and storage zone. If desired two mixing and storage zones can be used. In an operation using two mixing and storage zones the aqueous solution of HMTA and formaldehyde can be prepared in a first mixing and storage zone while feeding a previously prepared aqueous solution from a second mixing and storage zone. When the second mixing and storage zone become empty (or nearly empty), it can be replaced with the filled first mixing and storage zone from which the aqueous solution of HMTA and formaldehyde contained therein can be fed to the continuous reaction zone while preparing a new lot of said aqueous solution in the now empty (or nearly empty) first mixing and storage zone. By feeding from one mixing and storage zone while charging (preparing) a new lot of said aqueous solution in the other, continuous runs of long duration can be made without interrupting feed of the aqueous solution of HMTA and formaldehyde to the continuous reaction zone.

The concentration of HMTA and formaldehyde in the aqueous solution of HMTA and formaldehyde is not critical. However said solution generally contains 5-30% HMTA. The mole ratio of HMTA to formaldehyde in said solution - which is generally prepared from an aqueous formaldehyde solution containing 30-50% formaldehyde - should be 1:1-2.2 In a preferred embodiment of this invention there is fed to the reaction zone (i) an aqueous hexamethylenetetramine solution and (ii) an acid-stabilized aqueous mixture of formaldehyde and HCN.

The acid stabilized aqueous mixture of formaldehyde and HCN can be prepared by admixing a stabilizing acid and an aqueous formaldehyde solution with HCN in a mixing and storage zone. If desired, two mixing and storage zones can be used. In an operation using two mixing and storage zones the acid stabilized aqueous mixture can be prepared in a first mixing and storage zone while feeding a previously prepared acid stabilized mixture from a second mixing and storage zone. When the second mixing and storage zone become empty (or nearly empty), it can be replaced with the filled first mixing and storage zone from which the acid stabilized aqueous mixture of formaldehyde and HCN contained therein can be fed to the continuous reaction zone while preparing a new lot of said acid stabilized mixture in the now empty (or nearly empty) first mixing and storage zone. By feeding from one mixing and storage zone while charging (preparing) a new lot of acid stabilized mixture in the other, continuous runs of long duration can be made without interrupting feed of the acid stabilized aqueous mixture of formaldehyde and HCN to the continuous reaction zone.

When preparing the acid stabilized aqueous mixture of formaldehyde and HCN sufficient acid (e.g., H2S04, HC1 or H3P04 is included in the mixture to cause it preferably to have a pH of 1 to 2. The pH is not critical so long as the amount of acid causes the acid stabilized aqueous admixture of formaldehyde and HCN to establish a pH within the abovementioned range of 5-10 in the reaction mixture, when mixed with the HMTA.

The concentration of the formaldehyde solution used is not critical and is generally 30-50%. Neither is the concentration of HCN and formaldehyde in the acid stabilized mixture of formaldehyde critical, however the mole ratio of formaldehyde to HCN should be 1-2.2:6.9-8.6. In general, the formaldehyde concentration in said acid stabilized mixture is 5-30%.

As noted above, Miller's U. S. Patent 2,794,044 teaches a process for preparing IDA.

The Miller reference states correctly that: The obvious equation for the reaction producing iminodiacetonitrile is: NH3 + 2CH20 + 2HCNeHN(CH2CN)2 + 2H20 When, however, the reactants are mixed in the stiochiometric ratio demanded by this equation, no product can be isolated regardless of the pH adjustment. The following different equation expresses the stoichiometric ratios necessary to obtain the best yield, ca.

65%.

[H+] 4NH3 + 2CH20 + 6HCNe3HN(CH2CN)2 + NH3 + 6H20.

Since NH3 and CH20 in this ratio yields HMTA, and if H2S04 is used to neutralize the NH3 as it is formed, an equivalent equation would be: (CH2)6N4 + 6HCN + 1/2 H2S04 < 3HN(CH2CN)2 + 1/2 (NH4)2S04 This equation illustrates several disadvantages of said method of IDAN manufacture; only 3/4 of the N in the HMTA is converted to IDAN, the remaining 1/4 being released as NH3 (i.e. as (NH4)2S04). Consequently, the HMTA is not used efficiently. The release of NH3 requires constant pH control by the addition of H2S04. The product is thus a slurry of IDAN crystals in a liquor containing dissolved IDAN, HCN, other organic by-products, and large amounts of (NH4)2S04. In practice, this liquor cannot be recycled; it must, therefore, receive costly effluent treatment before it can be discharged.

We have found that IDAN can be prepared from HMTA, formaldehyde, and HCN according to the following equation: (CH2)6N4 + 8HCN + 2HCHO4HN(CH2CN)2 + 2H20 (HMTA) (IDAN) Such a procedure avoids the above problems. Since no NH3 is released, all the HMTA is potentially available for conversion to IDAN and no H2S04 is required. Thus, higher yields can be obtained, close pH control is not needed, and the formation of intermediate glycolonitrile is avoided. The process can therefore readily be made continuous.

Furthermore, since the product is essentially IDAN with no inorganic contamination, the reaction mixture in its entirety can be hydrolyzed with alkali metal hydroxide to give IDAM2. When this is done, the effluent problem is totally eliminated. If IDAN is the desired product, it can be crystallized from the reaction product. The resulting liquor would be free of (NH4)2S04 and, therefore could be hydrolyzed with NaOH to give useful IDANa2 without the production of sodium sulphate - an undesirable side product.

When hydrolyzing IDAN to IDANa2 (or IDAK2) the ammonia which is produced is recovered and can be used in fertilizer (e.g., as ammonium sulphate or ammonium phosphate); alternatively, the recovered ammonia can be converted to HMTA and/or HCN and recycled into the process. Other uses for the recovered ammonia will be readily apparent to those skilled in the art.

Conveniently, the continuous reaction zone used in the process of this invention can be surrounded by heat exchange medium (e.g. oil, that sold under the Registered Trade Mark, Downtherm, chlorinated hydrocarbons or steam) maintained at a predetermined temperature to provide heating or cooling, if required. Alternatively, electrical heating can be used to maintain a predetermined temperature within the reaction zone if heating is required.

Still other temperature control methods will be readily apparent to those skilled in the art.

The aqueous system (reacted mixture containing product IDAN) withdrawn from the continuous reaction zone can be cooled by passing it through a heat exchanger or by placing it in a tank or vessel provided with cooling coils or a cooling jacket. Other methods for cooling said aqueous system will be readily apparent to those skilled in the art.

The IDAN product, which is a solid, can be separated from the cooled aqueous mixture from the tubular reactor by centrifugation, decantation, or filtration.

Alternatively the aqueous mixture from the tubular reaction zone can be fed into an alkali metal hydroxide solution and hydrolyzed directly to alkali metal iminodiacetate (IDAM2).

When operating at temperatures in the continuous reactor above 100"C. a pressure in excess of atmospheric pressure (760 Torr) is maintained on the aqueous system in the reaction zone to prevent excessive vaporization in the reactor.

The weight ratio of water to reactants (HMTA, formaldehyde, and HCN) can be varied over wide limits. Weight ratios of water to reactants as high as 10:1 or higher produce excellent results, and excellent results can also be obtained when using just enough water to maintain a solution (a one phase system) in the mixing zone (e.g., Tee or cross) and in the continuous reaction zone.

In the process of our invention the continuous reaction zone can be a tubular reactor or a continuous outflow (e.g., continuous overflow) autoclave.

When using a tubular reactor, a mixing cross and/or one or more mixing Tees (depending on the number of feed streams being fed into the reactor) can comprise an inlet and mixing zone which is a part of the reactor, and the feed streams can be mixed in such mixing cross and/or mixing Tee(s) which comprise a part of the reactor.

When using a continuous outflow autoclave, reactant feed streams can be fed into the autoclave and admixed therein by mixing means provided within the autoclave.

Alernatively, a mixing cross and/or one or more mixing Tees can be attached to the autoclave to comprise an inlet to the autoclave, and the feed streams can be mixed in such mixing cross and/or mixing Tee(s) which comprise a part of the reactor.

When using a mixing cross and at least one mixing Tee or where using more than one mixing Tee, the cross and Tee(s) or the Tees are connected in series so that discharge from the discharge arm of one constitutes feed into a feed receiving arm of the other.

The concentrations of the solutions used in forming the aqueous reaction mixture in the process of our invention are not critical. However, we generally prefer to use an aqueous formaldehyde solution containing 30-50% HCH0 and an aqueous HMTA solution containing 10-30% HMTA. HCN can be supplied as an aqueous HCN solution containing 20-99% HCN, as HCN vapor, or peferably as anhydrous liquid HCN.

The instant invention will be better understood by referring to the following examples and procedures. The examples were actually run. The procedures, while not actually run, further illustrate the preparation of IDAN by certain embodiments of the process of our invention.

EXAMPLE 1 An aqueous solution of HMTA and formaldehyde containing 14.2% HMTA and having a mole ratio of HMTA to formaldehyde of 1:1.95 was prepared. This solution and HCN were pumped simultaneously with separate metering pumps into a mixing Tee at the head (inlet) of a continuous tubular reactor. The mole ratio of HMTA to HCN was maintained at 1:7.78.

The continuous reactor was constructed of ten sections of 1/8" x 10' jacketed steel pipe, followed by three sections of 1/8" x 20' unjacketed steel pipe, the sections being connected in series. At the end of each section was mounted a thermocouple and a sample valve.

Temperature of the mixture within the reactor was controlled at 140"C. by passing steam at 40 pounds per square inch gauge pressure (psig) through the jacket. Pressure within the continuous reactor was controlled at 200-250 psig with an adjustable pressure relief valve.

Weighed samples of the nitrile product were collected at various sample valves and saponified with sodium hydroxide solution. The saponified samples were analyzed by silylation-gas chromotography for glycine, IDA, and nitrilotriacetic acid (NTA). The saponified samples were also titrated with standard copper (II) chloride solution. The results obtained are reported in Table I, below: EXAMPLE 2 The general method of Example 1 was repeated but at other temperatures, residence times, and mole ratios. In this instance samples were taken only from the first sample point at which the reaction was complete (i.e., at the minimum residence time at which reaction was complete). The results obtained are presented in Table II, below.

EXAMPLE 3 The general method of Example 2 was repeated, but in this instance the aqueous solution of HMTA and formaldehyde was heated prior to being fed into the continuous reactor (continuous reaction zone) in which it (the aqueous solution of HMTA and formaldehyde) was admixed with the HCN. In this example the first two sections of the continuous reactor were unheated, but steam was applied to the next eight sections as in Example 1. The results obtained are shown in Table III, below.

Saunders et al (U. S. Patent No. 3,167,580) reported that product mixtures of IDAN and glycinonitrile are obtained when preparing IDAN by the reaction of formaldehyde, HCN, and ammonia. Their product sometimes contains small amounts of N-methylglycinonitrile.

We have found that glycinonitrile and a small amount of NTAN* are formed as side products when preparing IDAN by the process of our invention.

We have also found (see Table II) that the ratio of glycinonitrile to IDAN in the product from our continuous reaction zone can be increased by adjusting the mole ratio of the reactants (HMTA, formaldehyde, and HCN). This technique is especially useful when both IDA and glycine are desired as final products because IDAN rach in glycinonitrile can be prepared, converted to the H2NCH2C00Na and IDANa2 which can, in turn, be converted to glycine and IDA. The glycine and IDA can be separated by crystallization from an aqueous solution, and recovered separately.

Thus (see Run No. 8 in Table II) a product yielding (as an upper limit) 14% glycine and (as a lower limit) 84% IDA was obtained by feeding the reactants in a mole ratio of HMTA to HCH0 to HCN of 1:1:6.95, in contrast a product from the continuous reaction zone which was considerably richer in glycinonitrile and considerably poorer in IDAN was obtained by adjusting the mole ratio of said reactants to 1:1:6.82 and 1:0:5.93, respectively.

(See comparative Runs Nos. 9 and 10 in Table II).

*Nitrilotriacetonitrile A mole ratio of HMTA:HCH0:HCN of about 1:0:5.4 will produce a still higher ratio of glycinonitrile to IDAN in the product from the continuous reaction zone.

TABLE I IDAN PREPARATION AT 140"C. (1) (Mole Ratio In Aqueous Reaction Mixture, HMTA:HCHO:HCN Is 1:1.95:7. 78 Residence Time, Minutes 0.2 0.4 0.6 1.3 1.6 2.1 4.0 % Reaction (2) 94 96 96 96 97 97 99 Product Composition (3) IDA (5) (5) 63% 78% 83% 83% 90% Glycine (5) (5) 33% 19% 15% 14% 7% NTA (5) (5) 3% 3% 3% 4% 3% Yield of IDA (4) (6) (6) 49% 66% 74% 77% 91% (1) The pH of the aqueous reaction mixture was 6.9.

(2) % of total HCN consumed.

(3) % of contained acids (the nitrile product was hydrolyzed with sodium hydroxide solution and analyzed; the results were reported as % IDA, Wo Glycine, and % NTA).

(4) Based on HCN charged.

(5) Not analyzed.

(6) Not calculated.

TABLE II IDAN PRODUCTION Composition of Product (1) Run Mole Ratio Average Reaction Res. Time, % IDA %Glycine %NTA IDA NO. HMTA:HCH0:HCN Temperature, C. Minutes Yield (2) 1 1.00:1.95:7.72 140 1.5 89 8 5 85 2 1.00:1.95:7.38 140 1.5 89 8 3 93 3 1.00:1.93:7.73 140 1.5 89 7 4 91 4 1.00:1.93:7.58 140 1.5 89 6 4 91 5 1.00:1.60:7.45 140 1.5 85 10 5 85 6 1.00:1.60:7.35 140 1.5 89 9 2 90 7 1.00:1.60:7.27 140 1.5 88 10 2 85 8 1.00:1.00:6.95 140 1.5 84 14 2 81 9 1.00:1.00:6.82 (3) 140 1.5 73 24 4 60 10 1.00:0:5.93 (3) 125 1.5 65 33 2 60 (1) The nitrile product was hydrolysed with sodium hydroxide and analyzed; the results were reported as % IDA, % Glycine, and % NTA.

(2) Based on HCN charge.

(3) Runs 9 and 10 illustrate for the sake of comparison a process in which the product from the continuous reaction zone is rich in both IDAN and glycinonitrile.

TABLE III IDAN PRODUCTION Composition of Product (1) Run Mole Ratio, Temperature Average Res. Time, % IDA %Glycine %NTA IDA No. HMTA:HCH0:HCN of Aqueous Reaction Minutes Yield Solution of Temperature, (2) HMTA and C HCH0, C.

1 1.00:1.84:7.58 40 130 2.5 90 7 3 90 2 1.00:1.84:7.58 67 130 2.5 88 8 4 89 3 1.00:1.84:7.20 40 130 2.5 84 13 3 84 4 1.00:1.84:7.71 44 150 1.2 88 8 4 89 (1) The nitrile product was hydrolyzed with sodium hydroxide and analyzed; the results were reported as % IDA, % Glycine, and % NTA.

(2) Based on HCN charged.

Procedure 1 The method of Example 1 can be carried out by separately metering the aqueous HMTA solution, the aqueous formaldehyde solution, and the HCN into the continuous reaction zone (continuous reactor) using mole ratos of HMTA to formaldehyde to HCN of 1:1-2.2:6.9-8.6 or 1:1.6-2.2:7.2-8.0. Such procedures will produce IDAN in a conversion of 85-90% based on the HCN charged.

Procedure 2 The method of Example 1 can be carried out by first preparing an acid stabilized aqueous mixture (solution) of formaldehyde and HCN by admixing an aqueous solution of formaldehyde, HCN, and an amount of an acid (e.g., HCl, H2SO4 or H3PO4) to produce acid stabilized aqueous solution of formaldehyde and HCN. Said solution will generally have a pH of 1-4, or 1-2. The mole ratio of formaldehyde to HCN in such solution should be 1-2.2:6.9-8.6 or 1.6-2.2:7.2-8.0. This solution and an aqueous HMTA solution can be separately metered into the continuous reactor to provide a mole ratio of HMTA to formaldehyde to HCN of 1:1-2.2:6.9-8.6 or 1:1.6-2.2:7.2-8.0. IDAN will be produced in a yield of 85-90% of theory based on the HCN charged.

IDAN is an intermediate on a route to IDA which can be prepared from IDAN by a method taught by Eschweiler (Ann. 1894, 278, 229-239). IDA is used in metal plating baths. German Patent No. 1,034,946 (Chem. Abstracts 1960, 54, 16237e) teaches the use of IDA in cyanide-containing copper (and copper alloy) plating baths. The presence of IDA in such baths causes copper (or the copper alloy) to plate (precipitate) as a bright coating.

The use of IDA in the preservation of rubber latex is taught by British Patent 800,089 (Chem. Abstracts 1959, 53, 2672i).

When heated in an aqueous medium with about a stoichiometric quantity of sodium hydroxide solution IDAN yields disodium iminodiacetate (IDANa2) according to the following equation: HN(CH2CN)2 + 2H2O + 2NaOH = NH)CH2COONa)2 + 2NH3 (IDAN) (Sodium Salt of IDA (i.e., IDANa2)) French Patent 1,190,714 (Chem. Abstracts 1960, 54, 25993g) teaches the use of IDANa2 as an agent for removing residual catalyst (e.g., Ti, Cr, Fe, V, or Al salts) from polyolefins.

Claims (12)

WHAT WE CLAIM IS:

1. A continuous process for preparing iminodiacetonitrile which comprises: continuously feeding into a reaction zone an aqueous hexamethylene-tetramine solution having a temperature of 0-80"C., an aqueous formaldehyde solution having a temperature of 0-80oC. and HCN having a temperature of 0-25"C. in amounts sufficient to form a reaction mixture having a molar ratio hexamethylenetetramine:formaldehyde:HCN in the range 1:1-2.2:6.98.6 and having a pH in the range 5 to 10; continuously passing said mixture through the reaction zone at a speed to establish a residence time in the reaction zone of 0.05 to 20 minutes while maintaining the temperature in the reaction zone at 50-250"C., thereby forming a product mixture containing iminodiacetonitrile; and withdrawing the product mixture from the reaction zone and recovering iminodiacetonitrile therefrom.

2. A process according to Claim 1 wherein the formaldehyde and HCN are fed into the reaction zone as components of an aqueous solution which contains also a stabilizing acid to ensure that the reaction mixture has a pH in the range 5-10.

3. A process according to Claim 1 or 2 wherein the iminodiacetonitrile is recovered from the reaction mixture by removal of crystals of iminodiacetonitrile or by hydrolysis to alkali metal iminodiacetate.

4. A process according to Claim 1 or 2, in which the product mixture withdrawn from the reaction zone is cooled to 0-40"C. to cause crystals of iminodiacetonitrile to form, which precipitate from the product mixture and are recovered.

5. A process according to any preceding Claim in which the temperature within the continuous reaction zone is maintained at 120-170"C.

6. A process according to any preceding Claim in which the residence time in the continuous reaction zone is 0.1-5 minutes.

7. A process according to any preceding Claim in which the pH of the aqueous reaction mixture is 6.5-9.5.

8. A process according to any preceding Claim in which the mole ratio of hexamethylenetetramine to formaldehyde to HCN is 1:1.6-2.2:7.2-8.0.

9. A process according to Claim 8 in which the mole ratio of hexamethylenetetramine to formaldehyde to HCN is 1:1.8:7.6

10. A process according to Claim 1 substantially as herein described.

11. Iminodiacetonitrile when made by a process according to any preceding Claim, and the alkali metal salts formed therefrom.

12. Process for preparing an alkali metal iminodiacetate, which comprises preparing iminodiacetonitrile according to any preceding Claim and reacting the product with an alkali metal hydroxide.