The kinetics and mechanism of lignite dehydration

A kinetic study of the dehydrations of the alums KCr(SO4)2. 12H2O and KAl(SO4)2. 12H2O

“…Kinetic behaviour then is independent of the interface area and rate of pressure rise is expressed by dp/dt = Jc'(pe-p) (see Beruto & Searcy 1974). The same pressure dependency of rate was found in lignite dehydration (Brady et al 1990), where, however, geometric control was maintained because no comparable dissociation equilibrium was established within the residual product.…”

“…The vacuum apparatus was identical with that already described by Carr & Galwey (1986) and used for the previous dehydration studies of Li2S04.H 20 (Galwey et al 1990) and of lignite (Brady et al 1990). The pressure of product water vapour in the constant volume was recorded automatically at specified times from the output of a MKS 222B absolute pressure gauge (range 0-1500 N m-2, read with an accuracy of +0.1 N m-2).…”

“…Studies of the dehydrations of alums have contributed significantly towards the establishment of theoretical foundations for the rate expressions that are used in kinetic descriptions of solid state reactions (Brown et al 1980;Galwey et al 1981) and, in particular, the characterization of nucleation (Galwey & Laverty 1990) and growth ) processes. However, rate studies which investigated the reactions of this type that occur during the dehydrations of KCr(S04)2.12H20, KA1(S04)2.…”

“…and the number of dimensions in which nuclei grow (A). Examples of kinetic obediences (Brown et al 1980) to equation (1) with values of 1, 2, 3 or 4 have been reported from studies of various reactions of diverse solids. Such obedience is often accepted as conclusive evidence of the operation of a particular pattern of interface development during the reaction concerned, from which the nucleation and the growth kinetic behaviour can be inferred.…”

A kinetic study of the thermal dehydration of calcium sulphite hemihydrate

“…Previous work has been concerned with the release of water from alums (1,2), lithium potassium tartrate monohydrate (3), lithium sulphate monohydrate (4), magnesium chloride dihydrate ( 3 , and lignite (brown coal) (6). Conclusions based on dehydration studies have contributed significantly to our theoretical understanding of solid state reactions generally (7)(8)(9)(10) and the reaction models developed have been applied to diverse chemical changes proceeding in varied crystalline reactants (7).…”