Reexamination of the Kinetics of the Thermal Desorption of Dimethylsulfoxide and N-Methyl Formamide From a Greensplatt Kaolin

Christopher Breen1 and Sean Lynch
School of Chemical Sciences, National Institute for Higher Education Glasnevin, Dublin 9, Ireland
1 Current address: Chemistry Department, Sheffield City Polytechnic, Pond Street, Sheffield SI IWB, United Kingdom.

Abstract: The kinetics of the thermal decomposition of the kaolin: dimethylsulfoxide (kaolin: DMSO) and the kaolin: N-methylformamide (kaolin: NMF) intercalates have been reexamined. Two different sample sizes (2 mg and 8 mg) and grain-size distributions (<45 µm and 45–63 µm) were investigated using isothermal and dynamic gravimetry in the temperature range 100°–200°C. All sample configurations for the kaolin: DMSO intercalate (2 mg, <45 µm; 2 mg, 45–63 µm; 8 rag, <45 µm; 8 mg, 45–63 µm) followed the rate law -ln(1 - α) = kt to a value for α, the reaction fraction complete, of .6, yielding activation energies and standard deviations at the 99% confidence level of 85.5 ± 3.79 and 71.75 ± 8.75 kJ/mole for the isothermal and dynamic runs, respectively. The kaolin: NMF intercalate (2 mg, <45 µm) also followed the same rate law for α < .8, with activation energies and standard deviations at the 99% confidence level of 89 ± 5.05 and 79.25 ± 6.47 kJ/mole for the isothermal and dynamic studies, respectively. In solution the rate law -ln(1 - α) = kt is known as first-order kinetics, but here it appears to represent the non-instantaneous nucleation of uniformly sized particles, followed by the inward movement of a reaction interface.

Key Words: Activation energy • Desorption • Dimethylsulfoxide • Kaolinite • N-methyl formamide • Thermal treatment

Clays and Clay Minerals; February 1988 v. 36; no. 1; p. 19-24; DOI: 10.1346/CCMN.1988.0360103
© 1988, The Clay Minerals Society
Clay Minerals Society (www.clays.org)