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Feb. 22, 1938. ' I J. -slxT ET AL PROCESS OF PRODUCING KETENE Filed Sept. 6, 1934 y ¿iff/c @wel 2002600@ 74'. MMM.“ ' 2,108,829 nasal resa-,1938 ` 2,108,829 UNlTED STATES PATENT OFFICE 2,108,829 PltooEss or rnonnomo KETENE Johann Sixt and lMartin Mugdan, Munich, (llor-` many, assignors to Consortium für Elektro chemischc Industrie. G. m. b. H., Munich, Ger many, a corporation oi' Germany Appllooaop september s, 1934, serial No. 'Masas ~ In Germany September 16. 1933 9 claims. (ci. zoo-12s) ,This invention relates to a process of producing ketene from acetic acid. _ ~ the ketene to recombine with the excess acetic ' acid and thereby disappear. It was never thought In the processes disclosed in Meingast 8i” Mugdan Patents No. 1,570,514 of Jan. 19, 1926, 5 No. 1,636,701 of July 26, 1927, and No. 1,946,707 of Feb. 13,- 1934 and other patents, acetic anhydride is obtained by heating acetic acid vapor to possible to obtain ketene as a ilnal product, hence no measures have ever been taken with a view to its isolation or further elaboration. The applica- 5 tion of such measures, herein described, is essen -‘ tial for the present process. We have also found temperatures of 40G-800° C., in the presence of catalysts. The reaction takes place “according to lo the equation: ' that the partial recombination of the ketene with water to form acetic acid in the spaces behind the . ’ _ ddl H g a t ng o th _ u e vapors sma m quant f es o nitrogen ~ ZCHÑOOH‘@ o) 2O+H2O _ containing bases such as ammonia, pyridine, di y It has been ~assumed that the primary product methylamine or trimethylamine. ' 0f this' Splitting up is not anhydride.,but ketene. 15 which is generated according to equation: The invention is illustrated by the following ex amples taken in connection with the accompany- 15 cnooooH=CHico+Hio and only then forms `anhydride with -acetic acid beyond the heating zone, according to the follow20 ing formula: apparatus for carrying4` out the process. Example I , ' __ CH2CO+¢H3COOH(CHQCO) 20 We have found that the ,ketene primarily formed according to-this assumption can be pre'25 vented to a great, in fact to a predominant degree, from combining with acetic acid and water to form anhydride 0r acetic vafßldiëmd can be iSOlated. by Acarrying out the process of splitting up the acetic acid under leSS than atmospheric pressure, 30 at between 400-900° C. and by subjectinge the vaporous product of the splitting, which is under vacuum, to condensation by cooling under `such conditions as to allow the ketene insufficient time to combine with the acetic acid or the water. thi bo In ' sem diment of the invention, which is illustrated in Fig. 1, we employed an electrically 20 _heated copper tube 1 measuring 25 mm. in diam eter and 1000 mm. in length, iìlled with pea size “Carborundum” pieces coated with sodium meta- 25 phosphate. One end of the tube was connected to an acetic acid evaporator 2 while the other end was connected to a narrow tube 3 >adapted to carry oil’ the dissociation products. The tube emptied into a Liebig cooler 4 to which a cooled receiver 30 or condenser 5 was joined. 'I'his was followed by a second condenser 6 cooled by means of cooling brine of minus 50° C. From condenser 6 the gases were'passed into two vessels 1 and 8 filled with . 35 'I‘his can be done, for example. by preventing the ' acetic acid, the vessel 8 being cooled to minus 60° 35 \ condensation from taking place in spaces which C. and containing an addition of acetone in order ‘ l are too large, or by passing the split vapors to prevent freezing up. These two latter vessels through a cooled liquid such as water _which dissolves the ketene not at all or only to a small ex- 40 tent. or by using from the very beginning dilute acetic acid for the ketene formation. 'I'he ketene into» anhydride. A vacuum pump 9 located at the end ofthe apparatus-maintained the system 40 under an absolute pressure of about 15_ mm. In gas .thus separated under low pressure from the one hour 1055 grams of acetic acid vapor were sup- ‘ acetic anhydride, acetic acid and water is then isolated by cooling to aflow temperature or by plied to the tube I at a contact temperature of 650° C. (measured at the end the contact layer). 45 absorption, or it is obtained on the pressure side of the vacuum pump. 'I'he ketene gas can also be transformed into anhydride or other com-A pounds by permitting it to react' upon water-free ' `acetic acid. 50 served to `determine the ketene by transformation It has already been proposed to eil'ect the splitting up of acetic acid under reduced pressure but ketene has never been obtained by-that method. It would seem that the split vapors have always been condensed in apparatus of very large sur55 face or under such other conditions as to allow 0f the total anhydride formed, namely 18.5 45 ' grams, 75% was found in receivers 5 and 6 and 25% was found inthe two acetic acid receivers 1 and 8, as anhydride. This latter portion corre decomposition were negligible. Í’ E ` l H _ _ ramp e 105 grams oi' acetic acid vapor, containing 0.2% pyridine vapor, were passed-through the appara tus described. in Example I, at 650° C. OI the 55 2,108,829 2 total anhydride produced (47.85 grams), 83% was up. Of the anhydride a quantity of 21% was found in the condensates of the two coolers I3 found in receivers 5 and 6 and 17% was found in and I4, and 79%l had formed from ketene in the 8 as transformation product of the free ketene. Losses by decomposition were dripping tower I5. The loss in acetyl amounted to 5.5% of the acetic acid used for the splitting practically nil. processes. extent that, instead of the Liebig cooler I and re ceiver 5, we used a vessel containing 100 grams of 1,946,707, particularly the use of phosphorus, ` receivers 1 and Example III' The apparatus of Example I was modified to the 10 water cooled to 0° C., through which the hot split vapor products were passed. 105 grams of con cent1-ated acetic acid produced, in one hour at / We furthermore found that in carryingÀ out this process the utilization of the gaseous cata lysts described in the above mentioned Patent 10 phosphoric acid and volatile esters of phosphoric acid, offers considerable advantages as thereby - 650° C. contact temperature, a total of 19.0 grams of anhydride, of which 11% was found in receiv 15 ers 5 and 6, and 89% (as transformation product of the free ketene) was found in receivers land 3. disturbances through scattering or spraying " which may otherwise occur at high gas velocities, are avoided. 15 Example VII The apparatus of ExampleVI was employed but the carbon tube I0 was empty. At an in terior temperature of 700 to 740° ., 400 grams 20 The operation was the same as in Example III of acetic acid vapor were passed through the 20 except that 1% pyridine was added to the water ‘ reaction tube in one hour. Four parts per mil. as a preliminary measure. An aggregate quantity triethylester of phosphoric acid were added to the of 55.5 grams anhydride was produced of which acetic acid vapor, as catalyst. At the end of the 31.6% were obtained in receivers 5 and 6, and appara?is an absolute pressure of 35 mm. mer cury was maintained. 0f the total quantity of f 68.4% in receivers 1 and 8. Erllmple 1V Example V The operation was performed according to Ex ample III except that the ketene discharged from receivers 5 and 6.„was not allowed to react upon 30 acetic acid, but was separated out by means of two low-cooled receivers arranged one behind the other like vessels 1 and 8 of Fig. l and each filled with 100 cubic centimeters of acetone to dissolve anhydride formed, which was 200 grams, 41% was found in the absorption tower as transfor mation product of ketene` gas, and 59% was found in the cooler condensates. 30 Example VIII The operation was carried out according to Example VII except that 3 parts pyridine per mil. were added to the acetic acid-triethylphosphate out the ketene. With an average of 105 grams of concentrated acetic acid per -hour there were formed 20 molecules of anhydride plus _ketene to every 100 moleculesof acetic acid vapor, of which mixture and 300 grams of the mixture were sup plied to the heaterin lan hour. 0f the aggregate quantity of 220 grams of anhydride formed, 75% 4.4 molecules were found in receivers 5 and 6 as anhydride and 15.6 molecules in receivers 1 and 3 40 as pure ketene. ` There were no acetyl losses. It is also possible to condense the ketene with 46 out solvents if thetemperature is maintained suf iiciently low, as, for example, less than -100°. Example VI In this embodiment of the invention, which is illustrated in Fig. 2, we employed a vertical tube I0 composed of carbon, measuring 50 mm. in di ameter and 800 mm. in height, stopped at the 50 lower end by a carbon stopper. This vessel was mounted in an iron container II closely sur rounding the carbon tube and heated electrically. From the flanged cover of container II a copper tube is led nearly to the bottom of .the carbon tube. The carbon tube I0 was ñlled to a height of 100 mm. with an equimolecular mixture of sodium metaphosphate and lithium metaphos phate. Two cooled receivers I3 and Il were at tached to the iron container II, receiver I3 be 60 ing cooled with water and receiver Il being cooled with brine at minus 20° C. The gases were then carried up through a dripping tower I5 which was filled with _Raschig rings, and sprayed with concentrated acetic acid. The gases passed thenthrough a water filled bottle I6 which re-v tained traces of acetic acid; a vacuum pump I1 was attached to this bottle, whereby an absolute pressure of 30 to 60 mm. of mercury was main was obtained by absorption of the ketene gas in the dripping tower, and only 25% condensed out ` of the split vapor products by the cooler. The\ 40 loss amounted to only 4% of the acetic acid em ployed for the splitting process. Example' IX The operation was performed according to 45 Example VII except that, instead of triethyïphos phate, 0.5 part per mil. of phosphorus vapor Vwas added to the acetic acid vapor. Of the total anhydride obtained, 27% was found in the ketene absorption. ' ' Example X The operation was performed according to Ex ample VIII except that, instead of ethyl phos phate and pyridine, 1 part per mil. phosphoric acid and 1 part per mil. ammonia were added to the acetic acid vapor. Of the total anhydride obtained, 40% was the result of absorption of ketene. It was further found that in this process the 00 operation can be carried on with very good re sults substantially above 800° C. The ketene yield increases without increasing _the decom-' position to any substantial extent. The explana tion of this may possibly be found in the short 65 sojourn of the diluted vapors in the hot space and at the hot wall of the reaction chamber. Example XI An empty heated carbon tube, as in Example VI, without a catalyst charge, was used as the 70 tained. The glacial acetic acid was passed reaction vessel. Also the other disposition was 70 through the melted catalyst heated to 730° C. - the same as in Example VI. The interior of with 0.3% pyridine vapor with a speed of about the tube was maintained at a maximum tem 600 grams per hour. Altogether 296 grams of perature of 830° C., 600 grams of acetic acid anhydride were obtained from 330 grams of vapor containing 3 parts triethylphosphate per 75 acetic acid which were exposed >to the splitting 2,108,829 mil. were supplied to the carbon tube in an hour, «while an absolute pressure of 35 mm.V mercury was maintained at the end of the apparatus. An aggregate quantity of 475» grams of anhydride was formed. Of this, 17% was in the cooled condensates and 83% in the liquid iiowing from taining catalyst and under at least a partial vacuum, to form ketene as a primary dissociation product, and subjecting at least a part of the ketene to treatment for preventing its recombina tion into acetic acid and acetic anhydride.- 4 the ketene absorption tower sprayed with acetic"l 3. A catalytic process for the production of acid. 'I'he decomposition loss amounted to only ketene, which comprises heating acetic acid va about 3% of the acetic acid used for the splitting 10 process. at a temperature between 400° C. and 900° C. to 10 form ketene as a primary dissociation product, and separating water, acetic acid and acetic an hydride from the ketene before it has had time to Example XII The operation was performed according to Ex ample XI except that instead of the triethyl 15 phosphate 0.5 part phosphorus per mil. was sup recombine into acetic` acid and acetic anhydride. plied to the acetic acid vapor. At a maximum temperature of 870° C. in the interior of the re action space, from 800 grams of acetic acid vapor which were supplied in one hour, 375 grams of 20 anhydride were obtained, 74% of which was pro duced through absorption ofthe ketene and 26% of which was found in the condensates. 'I'he de composition was small. ' pors containing a non-metallic, acetic anhydride ' forming catalyst under at least a partial vacuum '4. A process for producing ketene, which com prises heating acetic acid vapors under at least a partial vacuum at a temperature greater than 500° C. but less than 900° C. in the presence of an‘acetic anhydride-forming catalyst, to form ketene as the primary dissociation product, and 20 separating water, acetic acid and acetic anhy dride from the ketene. 5. A catalytic process for the production of ' Example XIII 'I‘he operation was performed'according to Example XI except that, in addition to the `triethylphosphate, 3 parts pyridine vapor per ketene, which comprises subjecting aceticl acid vapors containing an acetic anhydride-forming catalyst which is gaseous at the reaction tempera ture, to heating at a temperature between mil. were added -to the acetic acid vapor. At a 400° C.-900° C.; conducting the heating at least 30 maximum temperature of 890° C. in the interior ' under a partial vacuum whereby a mixture con of the carbon tube, and with 1160 grams of acetic ' taining ketene, water, acetic acid and acetic an acid introduced in one hour, there was formed altogether _1120 grams of anhydride. 'I'he pro hydride is formed, separating at least a part of the ketene, and reducing the recombination of portion of anhydride from absorbed ketene » ,the ketene during separation by carrying out the amounted to 89.5% of the total...0nly 5% of separation in the presence of a nitrogen-con`-` taining'base. the acetic acid employed was lost by decomposi tion. ' 6. A catalytic process for the production _of Example XIV ketene by the thermal dissociatiön of acetic acid,- 'I‘he operation was carried out according to 40 Example XIII except that ammonia was em ployed‘as the baise addition instead of pyridine. The aggregate output in anhydride amounted to 88% of the weight of acetic acid used. The por tion of K the anhydride obtained from ketene 45 amounted to 83%.y The `decomposition loss was - Small. In carrying out our invention we may also em _ ploy various other steps or expedients which have proven advantageous for the production of 50 anhydride, as, for example, ‘preheating the acetic which comprises subjecting acetic acid to heat ing at a temperature between about 400° C. and 900° C. in the presence of_ a phosphorus-contain 40 ing catalyst iand under at least a partial vacuum, to formI ketene as a` primary dissociation product, and subjecting at least a part of the ketene to treatmentv in the presence of a nitrogen-_contain ing base for preventing its recombination into 45 acetic acid and acetic anhydride. 7. A catalytic processv for producing ketene, which comprises subjecting acetic acid vapors to heating under a partial vacuum at a temperature between400° C. and 900° C. in the presence of a acid vapor, utilization of other or special cata-_ non-metallic, acetic anhydride-forming catalyst 50 lysts, construction materials and apparatus. to form a mixture containing ketene, water, acetic rli'he term “vacuum” as used ln the claims is acid and acetic anhydride, and separating the intended to indicate a_ pressure substantially be 55 low atmospheric pressure, and such asis obtained _ water, acetic acid and acetic anhydride com ponents from the ketene by condensation of said 55 through the use of a vacuum pump or other suit components in the presence of nitrogen-contain ing compounds. l . 'I'he invention claimed is: 8. A process for producing ketene, which com-` 1. A catalytic process for~ the production of 60 ketene, which comprises subjecting acetic acid l prisesheating acetic acid vapors under at least vapors containing an acetic anhydride-forming a. partial vacuum at a temperature greater than 400° C. but less than 900° C. in the presence of an catalyst which is gaseous at the reaction temper ature, to heating at a temperature between acetic anhydride-forming catalyst, to form_-- a 500° C..-900° C., conducting the heating at least mixture containing ketene. and subjecting the mixture to a separation treatment which includes 65 under a partial vacuum whereby a mixture con able pressure reducing arrangement. ' taining ketene, water, acetic acid and acetic an hydride is formed and immediately separating at least a part oi' the ketene from the other com ponents. 70 . cooling to substantially below 0° C. ' - 9. A catalytic process for the production of ketene, which comprises heating~acetic acid va pors containing a volatile ester of phosphoric, 2. A catalytic process for the production of - acid, under at least a partial vacuum a a tem perature between 400° C. and 900° C., _ o form ketene by the thermal dissociation of acetic acid in the presence of a phosphorus-containing cat ketene as a primary dissociation product and im 70 mediately water, acetic acid and acetic alyst, which'comprises subjecting acetic acid to `anhydride separating from the ketene. heating at a temperature between about 400° C. JOHANN SIXT. and 900° C. in the presence of a phosphorus-con MARTIN MUGDAN.