Patented Oct. 10, 1939 2,175,811 UNITED STATES PATENT OFFICE 2,175,811 . MANUFACTURE OF KETENES Donald J. Loder, Wilmington, Del, assignor to E. I. du Pont de Nemours & Company, Will mington, Del, a corporation of Delaware No Drawing. Application October 28, 1936, Serial No. 108,005 19 Claims. (C. 260-550) This invention relates to a process for the manufacture of ketenes and more particularly Spectively. These terms are used since the mech to a process for the manufacture of ketenes by anism of the reaction appears to be, in most the thermal decomposition of aliphatic car instances, that as the ester decomposes an alco 5 boxylic acid esters. hol is split of leaving the ketene or substituted The industrial pyrolysis of acetone to acetic ketene. anhydride and ketene is well known, as well as The esters which may be used in the process the similar treatment of acetaldehyde and alkyl of the present invention are primarily the ali ketones generally to produce ketene or substi phatic monocarboxylic acid esters of the aliphatic 10 tuted ketenes. These processes, however, have monohydric alcohols, such, for example, as methyl acetate, ethyl acetate, propyl acetate, isobutyl 0 not been attractive from the commercial stand acetate, and the higher esters of acetic acid with point for the primary reason that the raw ma straight or branched chain aliphatic Saturated terials have been obtainable only at high cost or unsaturated alcohols, of these esters methyl 15 economicaland the ketenes yield. produced therefrom only in un acetate decomposes to ketene and methanol much An object of the present invention is to pro more readily and efficiently than do the higher 5 vide a process for the preparation of ketenes by ester to their corresponding products. Not Only the thermal decomposition of organic esters. can esters of acetic acid be thermally decomposed Another object of the invention is to provide a in accord with the process of this invention to 20 process wherein ketenes generally, such, for ex give ketene, but likewise the higher aliphatic ample, as ketene, methyl ketene, diethyl ketene, acid esters may be treated to give substituted 20 and the like, may be prepared by dehydroal ketenes. For example, when methyl propionate koxylating appropriate esters of the carboxylic is dehydromethoxylated, a methyl ketene and acids. A more specific object is to provide a methanol will be the major products; when ethyl 25 process for the preparation of ketene by ther isobutyrate is dehydroethoxylated, dimethyl ke mally decomposing methyl acetate. A still more tene and ethanol will be the major reaction prod 25 Specific object is to provide a process wherein ucts. Accordingly, in a Substantially analogous methyl acetate is passed at elevated tempera manner, other substituted ketenes may be pro tures and subatmospheric pressures over a cata duced from the higher monocarboxylic acid es 30 lyst which accelerates the thermal decomposi ters of the straight or branched chain type alco tion of the ester into ketene and methanol. Other hols. Generally speaking the methyl esters of 30 objects of the invention will hereinafter appear. the higher acid ester acylates give the substituted The above objects are realized by subjecting in ketenes and alcohols more readily than do the the vapor phase an aliphatic carboxylic acid ester . higher alkyl esters of the corresponding acids. to comparatively high temperatures and pref While usually the monocarboxylic acid esters may erably pressures somewhat lower than atmos be thermally decomposed to ketenes much more 35 pheric. With these conditions, under which the readily than polycarboxylic acid esters, never reaction is preferably accelerated in the presence theless, the latter type esters, and more particu of a suitable catalyst, the ester is decomposed to larly the di and tricarboxylic acid esters, can be 40 give ketene and an alcohol. In many instances, treated in accord with the process herein de owing to the high reactivity of the ketene, it scribed to produce valuable compounds. 40 may react with the products formed, such as, The process is preferably conducted in the water and the alcohol produced, to give, in ad -vapor phase, the ester is vaporized either prior dition to the ketene and alcohol, acids and an to or during the reaction, and is thermally de 45 hydrides. In order, however, to control the di composed at a temperature of from approximately 500 to 1000° C. and preferably from 650-800° C. 45 rection of the reaction and obtain the desired in the presence of a suitable type catalyst, such, product, namely, ketene, various expedients are for example, as sodium meta phosphate, silica. hereinafter.resorted to which will be more fully described gel or silica gel supporting a suitable promoter 50 When reference is made to dehydroalkoxylat such as phosphoric acid or hydrated or anhydrous ing, dehydromethoxylating, and the like, in the boron oxide and like dehydrating catalysts. 50 specification and claims appended hereto, it will It has been found that the reaction proceeds, be understood that these terms will connote the particularly when methyl acetate is being ther removal from the ester of an aikosy group and mally decomposed to ketene, at subatmospheric hydrogen or a methoxy group and is 'droger, re pressures preferably ranging between 10 and 700 mm, with space velocities ranging between 500 55 2 2,175,811 and 10,000 under these pressures. (The space Eacample IW velocity is the number of unit volumes of gas, Methyl ketene was obtained by charging a cop at standard conditions, passing per hour through per lined catalyst converter with a silica gel cata a unit volume of the catalyst.) lyst, and approximately, 1.03 mols of methyl 5 In order to inhibit the decomposition of the propionate were passed through the converter at ester of valueless by-products the presence of a Space velocity of approximately 1,500. The water vapor has proved to be remarkably effec converter was maintained at a temperature rang tive. For example, if announts of up to 8% are ing between 500 and 650 C. and the pressure introduced with the ester, it has been found that Within the converter at approximately 90 mm. 10 while the yields of ketene continue to be high, Eacanape V O a much larger part of the ester decomposed in the absence of water vapor is converted to a Into a copper converter containing no catalyst uSable product, namely, the acid corresponding to approximately 0.315 mol of liquid methyl acetate was injected. The converter was held at a ten the ester used. Higher amounts are not usually perature of approximately 763 C. and its con- 15 5 advisable because of greater dilution of the prod tents at approximately 28 mm. pressure. A luct.Catalyst, temperatures, and space velocity are 21.5% yield of ketene was obtained. more or less interdependent, that is, to avoid un Various methods may be employed for recov due decomposition, an increase of temperature ery of the ketene, e. g., compressing the gaseous requires, for optimum results, a like increase in products and scrubbing the thus compressed 20 20 Space velocity. AS is usual in chemical reac products with acetone or nethyl acetate or if tions the higher the temperature the more favor desired the ketene may be absorbed, without the able the reaction rate, and accordingly in this necessity of the compression step, directly in reaction also when high temperatures are en aceticFrom acid. a consideration of the above specifica-2r 25 ployed, in which reaction rates are high, com tion it will be appreciated that many changes paratively high space velocities should be en may be made in the details therein given with ployed. It has been found that to limit side out departing from the invention or Sacrificing reactions it is advisable to operate at diminished any of the advantages that may be derived there pressures, and pressures around 100 mm. of mer from. O 30 cury or lower have generally produced optimum operating conditions, although at higher pres 1.I claim:A process for the preparation of a ketene Sures decreased yield of ketene is partially con which comprises thermally decomposing, in the pensated for by increased conversion to the acid vapor phase, a lower alkyl ester of a lower ali corresponding to the ester treated. phatic monocarboxylic acid at a temperature 35 I shall now describe by way of examples meth ranging between approximately 500 and approxi ods for carrying into practice my invention but mately 1000 C. it will be understood that the details therein given 2. The process according to claim 1 conducted will not limit in any way the scope of the in under pressures lower than atmospheric. vention. 3. The process according to claim 1 conducted 40 cample I - by contacting the ester of the aliphatic carboxylic Into a copper lined catalyst tube maintained at acid with a silica gel catalyst. a temperature between 506 and 631 C., 1.15 4. The process according to claim i in which mols of methyl acetate was injected at a space the ester of the aliphatic carboxylic acid is con tacted with boric oxide supported on silica gel. 45 velocity of approximately 1400. The catalyst 5. A process for the preparation of ketene tube was filled with a silica gel catalyst support which comprises thermally decomposing, in the ing boric acid. This catalyst was prepared by vapor phase, a methyl ester of a mono-basic adding 100 parts of silica gel to 200 parts of lower aliphatic acid at a temperature between boiling water containing 40 parts of boric acid, approximately 500 and approximately 1000° C.