FLOW MICROCALORIMETRIC STUDY OF METHANOL ADSORPTION FROM N-HEXANE ON COALS

The heat evolved by mixing of methanol and a coal was measured by flow microcalorimetry (FMC) to investigate interactions between coal and m ethanol. Such interactions were classified into weak and strong adsorp tion. Two adsorption methods were used: continuous flow for measuring combined weak and strong adsorption, and pulse injection to distinguis h strong adsorption. Akabira bituminous coal and Yallourn brown coal, having different oxygen contents, were used as adsorbents. Experimenta l results achieved by the continuous flow method show that both amount and heat of methanol adsorption (2 g of methanol/L in n-hexane) depen ds on the structure of coal. Methanol uptakes were also measured, off- line, by immersing the coals in methanol-hexane solutions of different concentrations and comparing methanol concentrations in n-hexane befo re and after adsorption. Methanol adsorption isotherms so obtained hav e the same shape and the total uptakes of methanol adsorption are almo st the same in spite of different coal rank. Strong adsorption of meth anol gives a molar heat distribution between 30 and 60 kJ/mol, slightl y higher than the hydrogen bond energies in donor-acceptor systems. St rong methanol adsorption may be attributed to formation of new hydroge n bonds between methanol and oxygen-containing functional groups on th e coal. The molar heat of adsorption for methanol adsorbed by weak int eractions with coal is about 23 kJ/mol. The site for strong methanol a dsorption on Yallourn brown coal is more energetically heterogeneous t han that on Akabira bituminous coal.