The acidity of A1-, Cr(III)- and Fe(III)-
exchanged montmorillonite was characterised utilising
the bases pyridine and n-butylamine which occupy three
different sites in the interlamellar space:
(i) physisorbed base (ii) base bound to Lewis sites and
(iii) protonated base. The Al- and Cr(III)-forms were
found to be very temperature stable whereas the Fe(III)-
form was not. Isothermal gravimetry in the temperature
range 18 - 105 °G was used to measure the rate of
sorption of three alcohols, methanol (MeOH), propan-2-ol
(i-PrOH), and 2-methylpropan-2-ol (t-BuOH), and three
cyclic ethers, 1,4-dioxan (DIOX), tetrahydropyran (THP)
and tetrahydrofuran (THF), from the vapour phase, onto
the three cation exchanged forms. The rate of alcohol
uptake increased as t-BuOH< i-PrOH< MeOH with integral
diffusion coefficients, D, ranging from -17 2 -1 3.0-16.0 x 10 m s . The sorption rate for i-PrOH
and t-BuOH following the sequence Fe ( III) <. Cr ( III) ^ Al
whereas the cyclic ethers follow the sequence
Cr(III)^Fe(III)-c A l . Activation energies for all the
solvents lie between 2.0 kJ mol ^ and 13.0 kJ mol
In the adsorption of cyclic ethers from binary liquid
mixtures with methanol the isotherm type is dominated by
the binary mixture whereas the amplitude, which follows
the sequence DI OX «£ THP THF is further influenced by the
exchanged cation. Altering the level of hydration
shifts the azeotropic point in favour of the cyclic
ethers DI0X and THP, but only affected the amplitude of
the THF/MeOH system.