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Pyrolytic decomposition of volatile fatty acid salts
was studied using three different methods. The acetate,propionate and butyrate salts of sodium and calcium were examined with thermogravimetric analysis (TGA). In an inert environment, five out of the six salts decomposed according to the theoretical mass ratio between the salt and its corresponding ketone (i.e. acetate -> acetone, propionate -+ diethyl ketone (DEK), butyrate -+ dipropyl ketone (DPK)). The sodium salts decomposed at temperatures above 4250C, and the calcium salts did so above 3600C. In a closer study of the calcium salts, two types of experiments were used to determine the kinetics and yields with respect to temperature. A reactor was designed and built to bring the salts to their decomposition temperatures under vacuum and allow a quantification and subsequent analysis of the condensed products. A series of small-scale runs for each salt were performed while the reactor was held at specific temperatures to determine the variation in the product composition with temperature. Three large-scale runs, analogous to the TGA runs, gave rate-of-decomposition data over a large range of temperatures. These data were analyzed to determine the Arrhenius constants for each salt, which are presented in Table 1, along with the liquid product yield from each run. Two sets of kinetic parameters are provided for calcium propionate, since this salt displays different behavior in different temperature regions. These yields reflect the results of 1-2 hours of reaction; the literature indicates that 7 hours of reaction may improve these figures by a few percent. Table 1. Large-scale decomposition results Salt:Ca(AC)2 Ca(Pr)2 Ca(BU)2 Yield (% of theoretical):(93.1 ︢0.9)% (87.5 ︢0.7)% (94.4 ︢0.9)% E (activation energy, kJ/mol):+642.6 ︢28.0 +2327. ︢162. (1)+386.5 ︢15.8 +691.7 73.3(2) A (frequency factor, min-1): 109.4 ︢0.4414.7 ︢0.4(1) 66.12 ︢0.22 121.1 ︢0.2(2) (1)3980C and below; (2) 3990C and above
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Includes bibliographical references: pages 50-51.