PROCESS FOR PRODUCING NITRILOTRIACETONITRILE

Abstract: A process for producing nitrilotriacetonitrile from an ammonia derivative, formaldehyde, and hydrogen cyanide, in which hydrogen cyanide is scrubbed from a gas stream containing hydrogen cyanide with a dilute solution of a mineral acid, which is used directly in the nitrilotriacetonitrile production without the purification process normally used to produce hydrogen cyanide.

Description: PROCESS FOR PRODUCING NITRILOTRIACETONITRILE Background of the Invention Fieldof the Invention This invention relates to the production of nitrilotriacetonitrile, and more particularly to the source and manner of addition of hydrogen cyanide to the reaction mixture to produce nitrilo triacetonitri le. Background It is well known that ammonia, an ammonium salt, or an ammonia-formaldehyde condensation product will react with formaldehyde and hydrogen cyanide to produce nitrilotriacetonitrile. A common ammonia-formaldehyde condensation product is hexamethylenetetramine (HMTA) These reactions have been generally defined in the following U.S. Patents to J. J. Singer, et al: 2,855,428, and 3,061,628 and to Morgan, et al: 3,463,805. Nitrilotriacetonitrile can be produced from hexamethylenetetramine by the following reaction: EMI2.1 If the hexamethylenetetramine is replaced by equivalent amounts of ammonia or ammonium and formaldehyde, nitrilotriacetonitrile can be produced from ammonia or an ammonium salt by the following reaction: EMI2.2 <tb> <SEP> pH < <SEP> I <tb> NH3(or <SEP> NN4+) <SEP> + <SEP> 3CH20 <SEP> + <SEP> 3HCN <tb> <SEP> N(CHzCN)3(1H <SEP> if <SEP> NH4 <SEP> is <SEP> used <SEP> (2) <tb> The effect of many factors on these reactions has been studied, including dilution ratios, temperature rangei order of addition of reactants, order of reaction steps, and others. But, current processes use hydrogen cyanide as commercially available, which is anhydrous or substantially anhydrous form. Hydrogen cyanide is most commonly produced cómmercially by reaction of ammonia with methane, methanol or other suitable volatile hydrocarbon, at elevated temperatures to produce hydrogen cyanide, hydrogen, and other inert gases. Hydrogen cyanide is normally purified to greater than 98X purity and liquified prior to use. This -purification process typically comprises cooling the product gas stream; removing ammonia with a sulfuric acid solution or a monoammonium phosphate solution; absorbing hydrogen cyanide from the resulting gas stream in an acidic aqueous solution; stripping the hydrogen cyanide from the resulting solution; condensing the stripped hydrogen cyanide and water mixture; fractionating to produce hydrogen cyanide; liquifying the hydrogen cyanide, and stabilizing the liquified hydrogen cyanide to prevent polymerization. Purification of hydrogen cyanide to the commercial grade anhydrous hydrogen cyanide as outlined above, is a complex process requiring large expenditures for equipment, energy, and material handling. Additionally, cyanide-containing waste streams are produced that must be treated and disposed of. It would be an advancement in the art to be able to use hydrogen cyanide to produce nitrilotriacetonitrile without the costly and waste producing purification steps. It is an advantage of this invention that nitrilotriacetonttrike can be produced using hydrogen cyanide without undergoing the usual purfi cat ion. It is a further advantage of this in vention that the amount of waste in the hydrogen cyanide product process is reduced. Further advantages can be seen from the following description and examples. Summary of the Invention This invention provides a process for producing nitrilotriacetonitrile consisting essentially of: a. producing a gas stream containing hydrogen cyanide; b. cooling said gas to a temperature suitable for scrubbing; c. scrubbing said cooled gas stream with a dilute aqueous solution of an inorganic acid to produce a hydrogen cyanide-containing solution; d. adding formaldehyde and an ammonia derivative selected from the group consisting of ammonia, an ammonium derivative, and hexamethylenetetramine to said hydrogen cyanide-containing solution, to produce a reaction mixture; and e. reacting said reaction mixture to produce nitrilotriacetonitrile. Description of the Preferred Embodiment Hydrogen cyanide can be produced by the reaction of methane, methanol, or other volatile hydrocarbon with ammonia in the presence of a catalyst or in a fluidized bed at a temperature in excess of 1000or. The gas stream produced contains nitrogen, methane-, ammonia, hydrogen, hydrogen cyanide, and other gas components. Unless otherwise specified, all parts and percents are by weight. Hydrogen cyanide is produced commer cially primarily by the Andrussow Process, the Degussa Process, also called the BMA Process, and the Fluohmic Process, and ammoxidation of methanol or other hydrocarbons. All of these processes use ammonia as the source of nitrogen, and the product gas stream will contain some unreacted ammonia. Since ammonia will react with hydrogen cyanide, removal of this unreacted ammonia is an important step in the purification process. The Andrussow Process produces hydrogen cyanide by the following theoretical reaction: EMI5.1 at about 11000C, with heat being supplied by combustion of methane. Metal catalysts from Group VIII of the Periodic Table are normally used, preferably a Platinum-Rhodium gauze. The oxygen is normally supplied by mixing an appropriate amount of air with the other reactants. A typical product gas stream produced by the Andrussow Process has the following composition: nitrogen 64X, water 13Z, hydrogen cyanide 11X, carbon monoxide 7X, hydrogen 2X, ammonia 2X, carbon dioxide methane 0.4X. The Degussa Process produces hydrogen cyanide by the following theoretical reaction: EMI5.2 in a tubular reactor impregnated with a platinum catalyst at 12000C, with heat being supplied by indirectly heating the tubes with gas or electricity. A typical product gas stream contains: hydrogen cyanide 71X, hydrogen 17%, nitrogen 7X, methane 4X, ammonia 2X. Other processes for production of hydrogen cyanide include the Fluohmic Process; by reacting ammonia and propane in an electrically heated fluidized carbon bed; ammoxidation of methanol or other hydrocarbons; and a decomposition of formamide, which is produced from ammonia and carbon monoxide. Any process that produces hydrogen cyanide in sufficient quantities can be used with this invention. Under the process of this invention, an unpurified hydrogen cyanide-containing gas stream is scrubbed with an aqueous solution of an inorganic acid suitable for use in nitrilotriacetonitrile synthesis. Preferred is an aqueous solution containing sulfuric acid, and preferably about 10% to about 25Z apparent sulfuric acid concentration. Apparent sulfuric acid concentration is determined by titration against a standard sodium hydroxide solution. The unpurified gas stream may be cooled prior to scrubbing, preferably to about 800C to about 1000C, or may be both cooled and treated to remove the unreacted ammonia. The resulting solution preferably contains about 10% to about 60Z, more preferably about 20% to about 40%, hydrogen cyanide. This hydrogen cyanidecontaining solution can be used without further purification to produce nitrilotriacetonitrile, using any suitable process for synthesizing nitrilotriacetonitrile. Example 1 The scrubbing efficiency of hydrogen cyanide by a dilute sulfuric acid solution and by a dilute sulfuric acid solution containing nitrilotriacetonitrile mother liquor were determined at about 440C and at about 320C. Five percent hydrogen cyanide in an inert gas was bubbled at a rate of about 10 milliliters per minute into 100 milliliters of solution, through 5.5 centimeters of the solution, in a constant temperature water bath, until the scrubbed gas contained abut 1X hydrogen cyanide. By these tests, the dilute sulfuric acid solution and the nitrilotriacetonitrile mother liquor showed similar scrubbing efficiencies, even though theoretically the hydrogen cyanide should be somewhat more soluble in the dilute sulfuric acid solution than in the mother liquor. At about 440c, the hydrogen cyanide concentration of the scrubbing solution reached about 25%, and at about 320C, the hydrogen cyanide concentration of the solution reached about 57X. Example 2 Nitrilotriacetonitrile was produced in a batch reaction in a sealed, rocking autoclave. The reaction mixture consisted of the following: 35 9 H20 50 g HCN 13 g 03.5% H2S04 53 g 51.3X CH2O 62 g 33X HMTA The water, hydrogen cyanide, and sulfuric acid represent a solution with S1X hydrogen cyanide, which 5s equivalent to a solution produced by scrubbing a hydrogen cyanide-containing gas stream at about 330C with the water-sulfuric acid solution. The entire reaction mixture was placed in an autoclave that had been cooled in a methanol ice bath and sealed. The sealed autoclave was placed on a beater/rocker, was rocked to provide agitation, and was heated to about 950C. This temperature was maintained for about 40 minutes. The autoclave was cooled in an air stream to about 50-550C, and was cooled in an ice bath to below 300C. Nitrilotriacetonitrile was produced with a yield of 93.4% based upon the hexamethylenetetramine, which was the limiting reactant. Example 3 This example describes the process of thiS invention with the Degussa Process for production of hydrogen cyanide. Ammonia and methane are fed into an indirectly heated tubular reactor. The product gas stream is then cooled to 800C to 1000C. This cooled gas stream contains about 71% hydrogen cyanide, with the remainder being methane, ammonia, hydrogen, and nitrogen. This cooled gas stream is then scrubbed with a solution of sulfuric acid with an apparent sulfuric acid concentration of about 18.5X. The hydrogen cyanide-free gas stream is removed, and the hydrogen cyanide-containing solution, with about 33X hydrogen cyanide is then used in the reaction with hexamethylenetetramine and formaldehyde or with ammonia and formaldehyde to produce nitrilotriacetonitrile. Example 4 This example describes the process of this invention with the Andrussow Process, with ammonia scrubbing prior to the hydrogen cyanide scrubbing. Methane, ammonia, and air are fed into a reactor containing platinum-rhodium catalyst. The product gas stream is then cooled to 800C to 100 C. This cooled gas stream is then scrubbed with a solution containing about 30% monoammonium phosphate. The ammonium-containing solution could be treated to recover the ammonia, or could be used directly as diammonium phosphate. The ammonia-free gas stream is then scrubbed with a solution of sulfuric acid with an apparent sulfuric acid - concentration of about 18.5X. The hydrogen cyanide-containing gas stream is removed, and the hydrogen cyanide-containing solution, with about 33% hydrogen cyanide is then used in the reaction with hexamethylenetetramine and formaldehyde or with ammonia and formaldehyde to produce nitrilotriacetonitrile. Those skilled in the art will recognize many possible variations on the examples. Any process producing a gas stream containing hydrogen cyanide can be used as the source of hydrogen cyanide. Ammonia may be scrubbed out of the gas stream or this step may be omitted as desired, Many variations of the reactions to produce nitrilotriacetonitrile from the hydrogen cyanidecontaining solution are also known. In addition, other¯variations will be recognized by one skilled in the art. It is intended that this invention include all of these variations. These examples are intended to illustrate and explain the process of this invention and are not intended to in any way limit the process of this invention.

Claims: What is claimed is: 1. A process for producing nitrilot triacetonitrile consisting essentially of: a. producing a gas stream containing hydrogen cyanide; b. cooling said gas to a temperature suitable for scrubbing; c. scrubbing said cooled gas stream with a dilute aqueous solution of an inorganic acid to produce a hydrogen cyanide-containing solution; d. adding formaldehyde and an ammonia derivative selected from the group consisting of ammonia, an ammonium derivative, and hexamethylene tetramine to said hydrogen cyanide containing solution, to produce a reaction mixture; and e. reacting said reaction mixture to produce nitrilotriacetonitrile. 2. The process of Claim 1 wherein the ammonia derivative is hexamethylenetetramine. 3. The process of Claim 1 wherein the ammonia derivative is ammonia or an ammonium salt. 4. The process of Claim 1 wherein the gas stream containing hydrogen cyanide is produced by reacting methane, ammonia, and oxygen in the presence of a metal catalyst from Group VIII of the Periodic Table. 5. The process of Claim 1 wherein the gas stream containing hydrogen cyanide is produced by reacting methane and ammonia in an indirectly heated reactor. 6. The process of Claim 1 wherein the gas stream containing hydrogen cyanide is produced by reacting ammonia and propane in an electrically heated fluidized carbon bed. 7. The process of Claim 1 wherein the aqueous scrubbing solution contains sulfuric acid. 8. The process of Claim 7 wherein the apparent concentration of sulfuric acid is about 10X to about 25X. 9. The process of Claim 1 wherein the hydrogen cyanide-containing solution contains abput 10X to about 60X hydrogen cyanide. 10. The process of Claim 1 wherein the hydrogen cyanide-containing solution contains about .20% to about 40X hydrogen cyanide. 11. The process of Claim 1, further consisting of treating the gas stream containing hydrogen cyanide to remove ammonia, prior to scrubbing of Cc).

Inventors: SHEN, CHUNG YU
Applicants: MONSANTO COMPANY
Application year: 1983
Main classification: C07C121
IPC codes: C07C255, C01C3, B01J23, C07C67, C07C253