2,848,496 United States Patent Office Paterited Aug. 19, 1958

1. 2 embodiment the reaction is carried out in a reactor pro 2,848,496 vided with means for stirring the contents and with aheat DMERSATION OF KETENE IN MEOUM OF exchanger for controlling the temperature of the reactor DKETENE AND ACETCANHYDRDE contents. Ketene, generated preferably by the pyrolysis of acetic acid, is passed into the reactor which contains Richard Norman Lacey, Hull, England, assignor to The the medium of diketene and acetic anhydride, and the Distillers Company Limited, Edinburgh, Scotland, a diketene product is withdrawn at a rate equal to that of its British company formation from the ketene. Desirably acetic anhydride No Drawing. Application August 30, 1956 is added continuously to the medium to maintain the di-, Serial No. 606,960 0. ketene to acetic anhydride ratio at a constant level...The diketene product is passed to a vessel where it is main Claims priority, application Great Britain tained at a temperature between 10 and 40 C., in which September 15, 1955 the ketene concentration is allowed to fall substantially 8 Claims. (C. 260-585.5) to zero and then is fractionated to recover the diketene in 15 a pure state; the acetic anhydride so separated may be The present invention relates to an improved process recycled to the reactor. for the production of diketene. In a second preferred embodiment a circulating system The conversion of ketene to diketene in a medium consists of an absorbing vessel connected with one or consisting predominantly of diketent is well known. One more dimerisation vessels arranged in series. The ke such process consists in feeding ketene, derived for in 20 tene is fed into th base of the absorbing vessel through stance from the pyrolysis of acetic acid, into an absorber which the diketene-acetic anhydride medium is flowing at containing diketene. The resulting solution of ketene a temperature of about 0° C. The rate of feeding the in diketene is passed to one or more dimerisation vessels, ketene is adjusted relative to the rate of flow of the di usually provided with heat exchangers to remove the heat ketene-acetic anhydride medium so as to give a concentrar of dimerisation, where the ketene concentration is al 25 tion of ketene in the reaction mixture of about 4% by lowed to fall to zero. The diketene produced is removed weight. The reaction mixture passes through the di and the remaining diketene is recycled to the absorber merisation vessels at a rate adjusted so that the concentra where the procedure is repeated. tion of ketene falls substantially to zero in the last di It is an object of the present invention to provide a merisation vessel of the series. The dimerisation vessels process which gives improved yields of diketene. 30 are provided with heat exchangers and maintained at a According, to the present invention, the process for temperature in the range of about 10 C. to 40°C. Where the production of diketene from ketene. comprises sub a series of dimerisation vessels is employed, these may jecting ketene to dimerising conditions in a medium com be operated at successively higher temperatures so as to prising diketene and acetic anhydride and removing the achieve the highest reaction rates consistent with the heat of dimerisation. 35 solubility-temperature limitation of ketene in diketene. The proportion of acetic anhydride present in the Acetic anhydride is continuously added to the system at medium may vary within wide limits, but it is preferred to some point to maintain the diketene to acetic anhydride use a medium containing at least 50% by weight and pref ratio at the desired level. The reaction mixture is con erably from 60 to 70% by weight of acetic anhydride. In a tinuously removed and fractionated to recover the dike preferred embodiment of the invention a predetermined 40 tene produced and the acetic anhydride, the latter being ratio of dikene to acetic anhydride is maintained in the recycled to the circulating system. medium by the continuous addition of acetic anhydride The following example illustrates the process of the as the ketene is converted to diketene. present invention. The proportion of ketene introduced into the diketene acetic anhydride medium is also not critical. If desired EXAMPLE an excess of ketene can be added so that the medium re A reactor, provided with an efficient stirrer, means for mains saturated with ketene in order to obtain the maxi the introduction of ketene and diketene-acetic anhydride mum conversion velocity. In one preferred embodiment medium, a thermometer, a condenser and an outlet the diketene-acetic anhydride medium is treated with through which the reaction mixture can be withdrawn, was ketene in an absorbing vessel maintained at a compara 50 charged with the diketene-acetic anhydride medium. Ke tively low temperature, at which the Solubility of ketene tene generated by the pyrolysis of acetic acid, was passed is higher, to reach a concentration of 4% by weight of into the reactor, the temperature of the reaction mixture ketene and the mixture is passed through one or more dimerisation vessels maintained at higher temperatures being maintained at 10° C. Acetic anhydride was con in which the ketene concentration is allowed to fall to tinuously added to the vessel to maintain the diketene to ZO. acetic anhydride ratio at a constant level; the reaction The dimerisation reaction will take place within a fairly mixture was withdrawn at frequent intervals and after it wide temperature range and temperatures between 0 had been allowed to stand at a temperature in the range and 70° C. have been found to be suitable. It is pre from 10 to 20° C. for two hours to permit substantially ferred, however, to carry out the reaction at a tempera 60 complete conversion of the dissolved ketene was fraction ture in the range from 10 to 40 C. ated to recover the diketene and the acetic anhydride, the The process of the invention can be carried out in a latter being recycled to the reaction vessel. number of ways, and can be adapted for either batch A number of runs, each of 5 hours' duration, was wise or continuous operation. However, it is preferred carried out using different ratios of ketene to acetic an to operate the process continuously. In one preferred 65 hydride. 2,848,496 4. The results are given in the Table 1. ture containing at least 33.3% by weight of acetic anhy ride, and removing the heat of dimerisation of the ketene. Table I 2. The process claimed in claim 1 wherein diketene and acetic anhydride are reacted with ketene in an ab Average ke- Percent Percent Run No. tene conc. in anhydride yield of 5 sorbing zone maintained at a temperature below 10° C. moles/litre by weight diketene and thereafter the reaction mixture is passed through one of medium or more dimerisation zones in which the ketene concen tration is allowed to fall substantially to zero, each di merisation zone being maintained at a temperature of at IO least 10 C, and the zones being arranged in series with the absorbing zone. 3. The process claimed in claim 1 wherein the reaction mixture contains at least 50% by weight of acetic anhy dride. 5 4. The process claimed in claim 3 wherein the reac tion mixture contains from 60 to 70% by weight of the acetic anhydride. 5. The process claimed in claim 1 wherein the reaction is carried out at a temperature in the range from 0 to 20 70° C. 6. The process claimed in claim 5 wherein the reaction is carried out at a temperature in the range from 10 to 40° C. As a comparison with the runs shown in the above Ex 7. A process for the production of diketene from ke ample 6 runs were carried out in the same apparatus 25 tene comprising passing ketene into a reaction mixture under the same conditions in the absence of acetic an consisting of diketene and acetic anhydride, said reac hydride using only diketene as the medium, the results tion mixture containing at least 33.3% by weight of acetic shown in Table 2 being obtained. anhydride, withdrawing the diketene so produced at a rate Table 2 equal to that of its formation from the ketene, adding 30 acetic anhydride continuously to the reaction mixture to Average ketene Percent maintain the proportion of acetic anhydride present in the Run No. COInc. in yield of reaction mixture, removing the heat of dimerisation of Inoles litre diketene the ketene and thereafter fractionating the diketene to of Inedium recover diketene in a pure state.

35 0.92 87.8 8. The process claimed in claim 7 wherein acetic an 0.96 89.6 hydride separated from the withdrawn diketene during 0.9 87.4 0.92 88.3 the recovery of pure diketene is recycled to the reaction 0.91 86.8 mixture. 0.83 83.7 40 References Cited in the file of this patent I claim: UNITED STATES PATENTS 1. A process for the production of diketene from ketene comprising passing ketene into a reaction mixture con 2,216,450 Mugdan et al. ------Oct. 1, 1940 sisting of diketene and acetic anhydride, said reaction mix 2,688,640 Schnegg ------Sept. 7, 1954