INDUSTRIAL A N D ENGINEERING (;HEMISTRY
November, 1924
1133
Distillation of Acetate of Lime' By E. G. R. Ardagh, A. D. Barbour, G. E. McClellan, and E. W. McBride SCHOOL OF ENGINEFRING RESEARCH, UNIVERSITY OF
N Y O N E who has had occasion to consult the literature dealing with the manufacture of acetone by the dry distillation of acetate of lime must have been struck, not only by the vagueness of the descriptions and the paucity of the figures, but also by statements that are actually incorrect. A few of such statements which the w r i t e r s h a v e c o m e across in articles written by some of the best known authorities are given here :
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The rate at which acetone is formed on heating calcium acetate is quite low until the temperature rises well abooe 400" C. The statements appearing in the literature-that "a temperature of 300 O to 400" C. is required," or that ' . a temperature in the neighborhood of 400" C. is suficient"-are clearly wide of the mark. The rate of formation of acetone from calcium acetate between 430" and 490" C. is satisfactory. In order to obtain a high yield of acetone, it is necessary to iemooe the acetone vapor as soon as it is formed. The higher the temperature the greater the loss if the acetone vapor is allowed to remain in the retort. This loss is probably due to polymerization. The presence of metallic copper or metallic iron does not appear to aflect the yield of acetone. Either nitrogen or carbon dioxide can be used to sweep out the acetone vapors. but air is unsatisfactory since with it the yield of acetone is greatly reduced. Pure anhydrous calcium acetate cannot be made by drying the slightly acid product obtained by adding pure calcium carbonate pure acid-
Acetone is made by the dry distillation of gray acetate of lime a t 290" t o 400" C.2 Large quantities (of acetone) are made from gray acetate of lime by dry distillation a t high temperature. ** The distillation takes place in three stages. At first water containing a small percentage of acetone comes over, in the second stage when the temperature of the mass has risen to 400" C. acetone oils are obtained.3 To secure a maximum yield of acetone, the points to be attained are uniformity of temperature throughout the whole mass and slow heating t o not over 300' C.4 The conversion into acetone is effected by simply heating the acetate a t about 300" C. **The decomposition of the acetate does not become active until the temperature reaches about 380' C., the bulk of the distillate comes over between 380' and 400' C . 5 Barium acetate decomposes a t 400" to 405' C., calcium acetate a t a higher temperature, while the most suitable temperature for decomposition of acetic acid t o yield acetone is 500" C.6 Acetone is usually prepared by the dry distillation of barium acetate a t a moderate heat. Calcium acetate can also be employed, but the temperature required is greater, and the product is contaminated with impurities, such as dumasin, an isomeride of mesil yl oxide.
I n view of the indefiniteness of certain of these statements and the conflict of several others, it seemed that an investigation of this important industrial process would be well worth while. Owing to the complex character of commercial gray acetate of lime, it was thought advisable to begin -the investigation using pure calcium acetate. The gray acetate of lime of commerce "generally contains 80 to 82 per cent of calcium acetate as determined by analysis, and 4 to 7 per cent of water, the remainder being made up of various impurities. Of the 80 to 82 per cent, however, several per cent consist of formate, propionate, and salts of other organic acids."5 When formates are present dry distillation gives aldehydes. If propionates are present we get methylethyl ketone and diethyl ketone. Higher homologs yield the corresponding Received August 16, 1924. Rogers, "Manual of Industrial Chemistry," 1915, p. 643. 8 Veitch, "Chemical Methods for the Utilization of Wood," Dcpt. Agv., Circ. 36, 38 (1907). Sadtler, J. SOC.Chem. Ind., 8, 1008 (1889). Marshall, "Explosives," Vol. I, p. 341. 8 Squibb, J. SOC. Chem. I n d . , 15, 612 (1896). 7 Thorpe, "Dictionary Applied Chemistry," Vol. I, 1012, p. 21. 1
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higher ketones. This, however, is not the whole story. I
