UNITED STATES PATENT of FICE TREATMENT of MELAM, MELEM, and MELON Johnstone S
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Patented July 12, 1949 2,475,709. UNITED STATES PATENT of FICE TREATMENT OF MELAM, MELEM, AND MELON Johnstone S. Mackay, Greenwich, and Joseph E. Paden, Stamford, Conn., assignors to American Cyanamid Company, New York, N.Y., a corpo ration of Maine No Drawing. Application April 13, 1945, Serial No. 588,248 6 Claims. (Cl. 260-249.5) 2 This invention relates to a process of prepar Eacample 1 ing melamine from melam, melem and melon. In certain chemical processes involving the A quantity of melam was prepared by heating high temperature treatment of cyanamide, di dicyandiamide to 205° C. and thereafter remov cyandiamide, ammonium thiocyanate, thiourea, is ing melamine, unconverted dicyandiamide, and and other related substances, for example, when other water-soluble substances by leaching with preparing melamine by fusing dicyandiamide or hot water. The insoluble product was free from ammonium thiocyanate, there is usually ob yellow colored material and was therefore pre tained a considerable proportion of an insoluble Sumed to contain no melon. It probably con residue consisting principally of melam, melem O tained, however, a small proportion of melem. and melon. These latter substances are practi 42 g of the melam, prepared as just described, cally worthless as such and interfere with the and 25 g. of anhydrous ammonia were placed in use of the product in many industrial applica an autoclave and heated at 300° C. for two hours. tions. It is usually necessary to separate the The pressure developed in the autoclave was melam, melem or melon from the desired product 15 found to be 2,340 pounds per square inch. When after which these separated substances are the autoclave was opened and the contents ex thrown away. amined, it was found that approximately 96% Although it has been proposed to reconvert of the melam was unchanged, being present as melam to melamine, as for example by hydrolysis an insoluble residue. This experiment indicates to melamine and ammeline, the conversions ob 20 that 300° C. is too low to effect any substantial tained thus far have been very poor, making the Yersion of melam to melamine in two hours' e. conversion commercially unattractive. Insofar Eacample 2 as we are aware, no one has been able to re convert melem or melon to melamine under any 42 g. of melam and 25 g. of anhydrous ammo conditions and these substances, when formed, 25 nia were placed in an autoclave and heated at represent a complete loss. We have discovered, 350 C. for two hours at a pressure of 2,340 however, that melam and also melem and melon pounds per Square inch. When the autoclave may be converted into melamine in substantially Was opened and the contents examined, it was quantitative yields by a relatively simple process found that approximately 90% of the melam which makes it possible for the first time to 30 had been converted to melamine. recover these insoluble by-products and convert Eacample 3 them into a useful article of commerce. It is known that melamine rapidly decomposes 42 g. of melam and 25 g. of anhydrous ammo at temperatures above 350° C. at atmospheric nia Were placed in an autoclave and heated at pressure. In an experimental test at 400° C., 8400° C. for two hours at a pressure of 3600 pounds 80% of the melamine decomposed during a per Square inch. The conversion of the melam thirty minute period to melam, melem and melon. to melamine was found to be practically 100%, Despite the known instability of melamine at the insoluble residue remaining in the autoclave high temperatures, we have discovered that we after extraction with hot water being negligible. can convert melam, melen and melon to mel 40 amine by heating these substances at tempera Eacample 4 tures above 350° C. with anhydrous ammonia, 42 g. of melam and 25 g. of anhydrous ammo under a pressure of at least about 1000 pounds nia Were placed in an autoclave and heated at per square inch. Surprisingly, there is no de 450° C. for two hours under a pressure of 2,890 Composition of the melamine under these condi pounds per square inch. The conversion of tions. melam to melamine in this experiment was found Our discovery enables us to convert melam, to be approximately 98.3%. melem and melon into melamine in a short pe Eacample 5 riod of time with excellent yields. It also makes it possible for us to convert melam, melem and 50 42 g. of melam and 25 g. of anhydrous ammo melon to melamine when these substances are nia were placed in an autoclave and heated at present as impurities in melamine produced by 500 C. for fifteen minutes at a pressure of 2900 conventional processes. pounds per square inch. Upon Opening the In order to illustrate the invention in greater autoclave it was found that the melam was com detail the following examples are given. 55 pletely converted to melamine. cample 6 There is no actual top limit on the pressure but 42 g. of melam and 15 g. of anhydrous ammo Practical limit dictated by apparatus consider nia were heated in an autoclave at 400° C. for ations appears to be about 5000 pounds per square two hours under pressure of 1510 pounds per inch. These pressures are Supplied by the am Square inch. The melam was converted into 5 on in the system and it is necessary to slip melamine to the extent of about 92%. ply enough ammonia to the reaction to react with At 600 pounds per square inch the conversion the melam, melon or melemand result in a pres was about 35%. s Sure of at least 1000 pounds per square inch in the Eacample 7 reaction vessel. Otherwise the amount of an Melon was prepared by heating 200 g. of melam O monia is not critica. to 650 C. and holding the material at this tem We claim: perature for one hour. 112 g. of a yellow prod 1. A method of preparing melamine which con luct was obtained which, upon chemical analysis, Rises heating at least one of the substance was found to be principally melon. This prod the group consisting of melam, melem and melon uct was used in the following experiments. with anhydrous ammonia at temperatures within 42 g. of melon and 25 g. of anhydrous ammonia the range of 400° C. to 500 C. under a pressure were heated in an autoclave to 350° C. for two of at least 1000 pounds per Square inch for a hours at a pressure of 1750 pounds per square period of time not in excess of about two hours, inch. On examining the contents of the auto 2. A method of preparing melamine which clave it was found that 73.8% of the melon was 20 comprises heating melam, with anhydrous am converted to melamine, monia at temperatures of at least 400 C. under pressure of at least 1000 pounds per Sclare ch Eacample 8 for a period of time not in excess of two hours. 42 g. of melon and 25 g. of anhydrous ammonia 3. A method of preparing melamine which Were heated in an autoclave at 400° C. for two 25 comprises heating melem with anhydrous am nours under a pressure of 1950 pounds per square monia at temperatures of at least 400 C. under inch. In this run 94.5% of the melon was con pressure of at least 1000 pounds per Scare Verted to melamine. inch for a period of time not in excess of two hours. Eacample 9 30 4. A method of preparing melanine which The preceding example was repeated at a tem comprises heating melon with anhydrous am perature of 450° C. In this experiment 99.4% of monia at temperatures of at least 400 C. under a the melon was converted to melamine. pressure of at least 1000 pounds per Square inch Eacample 10 for a period of time not in excess of two hours. 5. A method which comprises heating mela. 42 g of melon and 25 g. of anhydrous ammonia nine containing at least one of the Substances of Were heated at 400° C. for fifteen minutes under the group consisting of melam, melem and melon pressure of 1950 pounds per square inch. On With anhydrous ammonia at temperatures of at opening the autoclave and examining the con least 400° C. under a preSSure of at least 100C tents, it was found that 84.5% of the melon had 4. ponds per square inch whereby the said melam, been converted to melamine. melem and melon is converted to melanine for a As will be seen from the foregoing experiments, period of time not in excess of about fifteen melam, melen and melon may be converted to minutes. melamine by heating these substances in an at 6. A method of converting melam, melem and mosphere of ammonia at temperatures above 3500 45 melon to melamine which comprises heating a C. The temperature range that we may employ mixture of Said substances at temperatures of at may vary from about 350° C. to 600° C., preferably least 400° C. under a pressure of anhydrous am between 400° C. and 500° C. At higher tempera monia of at least 1000 pounds per Square inch for tures the conversion takes place more rapidly a period of time not in excess of about two hours, and, as shown, very good results are obtained in 50 periods of time as low as fifteen minutes. In fact, JOHNSTONE S. MACKAY. it appears that an excellent conversion can be ob.