IL30623A - Process of manufacturing nitrilotri-acetonitrile - Google Patents

Description

Process of manufacturing nitrllotriacetonitrlle STAtJFFER CHEMICAL COMPANY PROCESS OF MANUFACTURING NITRILOTRIACETO ITRILE Abstract of the Invention A process for manufacturing nitrilotriacetonitrile consisting of reacting stoichiometric aqueous portions of ammonia, formaldehyde and hydrogen cyanide in the presence of an acid. The reaction is carried out continuously at critical temperatures of above 120°C. and at autogeneous pressure to maintain homogeneous reaction conditions. The reaction product in the liquid phase is quenched to below 90°C. to minimize hydrolysis of the nitrile and to precipitate the reaction product.

Background of the Invention Nitrilotriacetonitrile (hereinafter referred to as NTN) is an old and well known composition and may be described as a white crystalline solid having a melting point of between 126-128°C., that is insoluble in water. This material finds uses as highly reactive intermediates and as a chelating agent.

Prior processes for manufacturing the NTN involve the reaction of ammonia, formaldehyde, and hydrogen cyanide in the presence of a mineral acid. The ingredients were usually introduced into a reaction vessel and agitated with a stirring mechanism to bring about intimate contact of the various components. The reaction of these components is carried out at atmospheric pressure at a temperature ranging from room temperature up to 8o°C. Under these prevailing reaction is formed within 3 to 6 days. However, at the upper level of T5°C, this time can be reduced to h to 5 hours. When the reaction is complete, the NTN, in a crystalline form, can be recovered and washed in good yields. .

Various alternatives have been proposed, one of which involves the reaction of ammonia and formaldehyde to form hexamethylenetetraamine. The hexamethylenetetraamine is then introduced into a reaction vessel and agitated with hydrogen cyanide and additional formaldehyde in the presence of a mineral acid to form NTN as the end product. Again, these reactions take place at either room temperature or up to 8o°C, i resulting in a heterogeneous medium. Also, at these temperatures the formation of NTN from the reaction products takes from 3 to 5 hours, also in relatively good yields.

Another method of forming the NTN product is o react ammonium sulfate, formaldehyde and hydrogen cyanide in an aqueous acidic medium to form NTN. However, this reaction is even more sluggish than the previous method. Moreover, because of the long reaction time requirements, and because of the heterogeneous nature of the reaction, all the known methods of forming NTN are. limited to batch process operations at temperatures of up to 8o°C and at atmospheric pressure. At these temperatures and pressures, the large in-process inventories of hydrogen cyanide necessitates the use of especially designed safety equipment to maintain control of the high exothermic reaction and volatility of the unreacted hydrogen cyanide. These precautions must be maintained This, of course, requires a large capital investment. Moreover, the time involved of up to four to five hours to produce a commercial yield of the NTN product materially increases the cost thereof. Thus, there is a need in the industry for forming the NTN composition at materially reduced rates or times, yet retaining the high yield of over 8o# necessary for commercialization.

Brief Description of the Invention It has been discovered that above 120°C, and under superatmospheric pressure, preferably autogeneous pressure, an aqueous mixture of ammonia, formaldehyde and hydrogen cyanide can be reacted without the formation of solid reaction products and with a significant reduction in reaction time. In its preferred form, hexamethylenetetraamine is formed from formaldehyde and ammonia and is then reacted with hydrogen cyanide in the presence of additional formaldehyde and an aqueous medium, preferably sulfuric acid, to form the NTN product. The total time for the reaction of the hexamethylenetetraamine with the hydrogen cyanide and formaldehyde to form the NTN product has shown to be less than thirty minutes- Moreover, this reaction is adapted to a continuous process wherein the materials are maintained in a liquid state. Thus, a homogeneous reaction or process is maintained so as to prevent difficulties in handling the heterogeneous or liquid solids reaction.

Brief Description of the Drawings Figure 2 is a graph illustrating the yield vs. the temperature when practicing the present invention.

Detailed Description of the Invention In the practice of the present invention, ammonia, formaldehyde, and hydrogen cyanide are reacted together under aqueous acid conditions and at critical temperatures and at autogeneous pressure to produce NTN. In its preferred form, ammonia is first reacted with formaldehyde to form hexamethylene-tetraamine (hereinafter referred to as HMTA) in a conventional manner. This reaction is carried out in a reactor with the components being in the aqueous phase, The HMTA can then be reacted with hydrogen cyanide in the presence of additional formaldehyde under acid conditions to form the NTN product.

Thus, HMTA, formaldehyde, and hydrogen cyanide are contacted within a reactor to form the NTN product. In its preferred form, the mineral acid employed is sulfuric acid, although other acids such as hydrochloric acid and phosphoric acid can be used.

It is essential to the practice of the present invention that the temperature within the reactor be maintained at least above 120° C. The reactor vessel should also be under pressure, preferably autogeneous pressure of about 5 to 100 psig. By maintaining the reactor vessel under pressure in this manner, the hydrogen cyanide at the temperatures involved will be essentially in a liquid state, In its preferred form, the reactor is of longitudinal or tubular plug-flow design to minimize backmixing and to minimize vaporization of the reactants minimize the space needed for the process. The spiral configuration will also prevent backmixing and will minimize the vaporization of the reactants and solvents. Under operating conditions, the reactor will provide turbulence so that there will be intimate contact between the hydrogen cyanide and the HMTA and formaldehyde to give fast reaction. It has been found in practice that a pH of 5 or below must be maintained, ' although it is preferred to be at least below 3« By maintaining these conditions within the reactor, it has been found that high yields of the NTN product can be formed within a period of from 1 to 30 minutes. This is clearly contrasted to what has been known in the prior art i the batch system which takes from 3 to 5 hours.

After the NTN product has been formed, it is immediately conveyed to a quenching station where it is rapidly cooled to at least below 90°C, preferably below 50°C, to avoid hydrolysis of the product and to precipitate the NTN product and thus convert it from a liquid to a solid state. If there is a large time lapse between the reaction and the quenching, the NTN product will hydrolyze in the acid medium, resulting in a reduced yield. The NTN solid product is then conveyed to a cyclone, centrifuge or other suitable solids-liquid separation device where it is separated from the acid medium, washed and purified. The acid medium is then recycled back into the reaction and quenching systems along with a small amount of ammonium salt formed from the ammonia liberated during hydrolysis.

Referring now to Figure 1 of the drawings, the numeral l The numeral 2 designates a source of a mixture of hydrogen cyanide, formaldehyde, sulfuric acid with traces of ammonium salt that is pumped into the reactor tube 3· These materials are conveyed to the longitudinal or tubular reactor 3 that is maintained at a temperature of above 120°C, with a suitable heat transfer medium k. Throttle valves 5 and 5' are provided at the ends of the reactor 3 to maintain autogeneous pressure. The pressure within the tubular reactor can range up to about 100 psig- The valves 5 and 5' are connected to a conventional flow controller as indicated at 10. By maintaining the temperature within the reactor 3 of at least 120°C, the NTN product formed will be maintained in a liquid state. After the NTN product is formed, it is conveyed to a quenching station 6, where it is cooled by an aqueous medium conveyed through pipe 8. The NTN product and acid medium are conveyed through pipe 9 to a solids-liquid separator 7 where the acid is separated from the NTN product. If desired, part of the acid can be conveyed into the pipe 8 and used for quenching. Thus, by maintaining these pressures and temperature conditions within the reactor 3, the residence time of the reactants, HMTA and hydrogen cyanide and formaldehyde to form the NTN product, will be approximately 5 minutes. The NTN product can then be used in forming sodium nitrilotriacetate that is well known in the art as a detergent builder.

It should be noted that the reactants of the present invention, that is ammonia, formaldehyde and hydrogen cyanide, herein. This reaction is substantially identical with reacting HMTA with hydrogen cyanide and formaldehyde and takes place under identical conditions. Furthermore, since the reactants of the present invention are maintained within the reaction tube 3 for only a short length of time, the problem with other competing reactions at high temperatures is substantially eliminated.

These competing reactions may be defined as the formation of intermediate nitriles along with the NTN product and a second reaction of the hydrolysis of the nitrile formed under the prevailing acid reaction conditions. Thus, high yields of the NTN product can be achieved according to the process of the present invention.

The following examples illustrate the invention: EXAMPLE- 1 The reactants of the present invention were blended together by adding 2^3 grams of a 37$ solution of formaldehyde, 3 moles, to a mixture of 25 grams of water and 25 grams of concentrated sulfuric acid, 0.25 moles, dropwise at ice temperature followed by 58.6 grams of a 29$ solution of ammonia,, l mole, and 86 grams of hydrogen cyanide, 3 moles, into a mixing vessel. The pH of the reagents was determined to be 2. The temperature of the mixed reagents were cooled by dry ice and maintained at a temperature of below 10°C EXAMPLE 2 A 5 gallon vessel equipped with a mechanical stirrer and heater was filled with five gallons of silicone oil. The approximately half full, about 5 milliliters, with the mixture of reagents of Example 1. The test tubes were sealed and maintained at below 10°C. Seven runs were then conducted with the seven test tubes filled with the reactants of Example 1 at five minutes duration and at temperatures of 91°C, 115°C., 117° 120°C, 122°C, 130°C, and llt2°C Yields are tabulated below: TABLE 1 Reaction Temperature °C. Yield j> 91 73 115 75 117 75 120 76 122 8i 130 86 142 79 The results of Example 2 tabulated above have been plotted and illustrated in Figure 2: Figure 2 clearly illustrate that at temperatures below 120° the yields are substantially the same. However, at temperatures above 120°C. the yields sharply increase to commercial proportions. Thus, a critical temperature of above 120° for the reaction temperature of the process of the present invention is established.

EXAMPLE 3 Hexamethylenetetraamine was reacted with formaldehyde, hydrogen cyanide and sulfuric acid at 130°C The amount of reactions were stoichiometric portions. The yields obtained usin five different samples are tabulated below: TABLE 2 Reaction Time (minutes) Yields $ 86 7 75 ' ■ . . 10 . 73 EXAMPLE The procedure as outlined in Example 3 was repeated in its entirety except the temperature was 1 2°C. The results obtained using three different samples are tabulated below: TABLE 3 Reaction Time (Minutes) Yield 79 7 76 70 EXAMPLE 5 Using a one inch diameter, ten foot long tubular reaction, equipped for a continuous operation similar to that described in Figure 1, wherein the reactor was maintained at a controlled temperature of 130°C, with a heat transfer medium, a 40 weight percent HMTA solution was continuously contacted with an aqueous solution consisting of 13· 9 weight percent formaldehyde, 26.3 weight percent hydrogen cyanide and 7.7 weight percent concentrated sulfuric acid. Flow rates to the reactor were controlled so as to maintain a weight ratio between the to about 50°C, using a liquid cyclone with an acidic quench medium consisting essentially of dilute sulfuric acid. NTN crystallized immediately on contact of the reactor discharged with the quench medium. The resultant slurry was filtered using a rubber lined centrifuge and the NTN product was washed several times with water. After drying the product to remove residual moisture, a total of 120 pounds of high purity NTN product was obtained, corresponding to a yield of 91$.

Referring now to Figure 2, the yield of the above example has been plotted thereon and indicated at x. It should be noted that this yield has not been plotted on the curve since the curve represents different conditions to produce the yields obtained. However, it should be noted that this example is a pilot plant operation which simulates commercial production. The 1$ yield at a residence time of J to 5 minutes at the temperatures involved was unexpected.

A comparison of Examples 3 and k shows that at a residence time of over 10 minutes, the yields begin to be sharply reduced. This is apparently due to hydrolysis of the NTN product.

Claims (2)

1. What is claimed is: 1. A process of manufacturing nitrilotriacetonitrile comprising the steps of: a) continuously contacting in a liquid state at least stoichiometric aqueous portions of ammonia, formaldehyde and at a pH maintained "below 5 and preferably below 3 hydrogen cyanide in the presence of a mineral acid' in a reaction means to form nitrilotriacetonitrile; b) maintaining the reaction means at a temperature of at least above 120°C., and under pressure to maintain the ammonia, formaldehyde, hydrogen cyanide and nitrilotriacetonitrile product formed in substantially the liquid state; c) continuously conveying the substantially liquid nitrilotriacetonitrile product formed to a quenching means to reduce the temperature of said nitrilotriacetonitrile product to 'at least below 90°C, which precipitates the nitrilotriacetonitrile product.

2. The process as set forth in Claim ,l, wherein the ammonia is prereacted with additional formaldehyde to form hexamethylenetetraamine which is then contacted with said formaldehyde and hydrogen cyanide. 3· The process as set forth in Claim 1, wherein the pressure is autogeneous and maintained between 5 and 100 psig. h. The process as set forth in Claim 1, wherein the reaction means is of a tubular plug-flow design. 6 . The process as set forth in Claim l , wherein the residence time of the ammonia, formaldehyde and hydrogen cyanide within the reaction means is from l to 30 minutes. 7 . The process as set forth in Claim l , wherein the nitrilotriacetonitrile product is quenched to a temperature of below 5 0°C. 8 . The process as set forth in Claim 1 , wherein the temperature of the reaction means is maintained at between 125°C. and 135°C. 9 . The process as set forth in Claim l , wherein the mineral acid is sulfuric acid. 10. The process as set forth in Claim l , wherein said mineral acid is continuously conveyed to the quenching means after it has been separated from said precipitated nitrilotriacetonitrile product. I I