Hofmann degradation kinetics of n-octylamine adsorbed on layered aluminosilicates prepared from apophyllite

Kinetic analyses of the Hofmann degradation of n-octylamine adsorbed on layered aluminosilicates prepared from apophyllite are reported. The data were collected by simultaneous thermogravimetry and evolved gas analysis (TG-DTG-EGA). Based on Kissinger plots using the DTG data, it is indicated that the activation energy of the Hofmann degradation increases with increasing Al/Si ratio of the layered aluminosilicates. Using the EGA data for l-octene, a similar tendency is observed. However, there is no such tendency for the results using the EGA data for ammonia. This indicates that ammonia remain on the surface after the Hofmann degradation. Hence, the activation energy obtained for ammonia is not that of the noctylamine decomposition, but from the analyses, using Ozawa's method, no tendency is observed in the relationship between the activation energy and the Al/Si ratio of the samples. This indicates that the Hofmann degradation is not a single elementary reaction in the strict meaning. However, the reaction mechanism could be estimated; e.g. two-dimensional dispersion (D2) for the sample with an Al/Si ratio in the range of 0.13-0.18 and three-dimensional dispersion (D4) for the Al/Si ratio of 0.05-0.09.