EFFECTS OF CITRIC-ACID WASHING ON THE THERMODYNAMIC INTERACTION OF SOME COALS WITH ACIDS

Samples of Wyodak and Illinois No. 6 coals were subjected to citric acid washing treatment and their heats of immersion (DELTAH(imm)) in 13 acids of varying strength were compared to those of the parent coals and of polyvinylpyridine, a prototype solid base. The effect of the treatment on the Wyodak sample is considerable, but quite dependent on the nature of the acid, while citric acid washing produces only minor effects on DELTAH(imm)s of the higher ranked Illinois coal. Interactions of treated and untreated coals with phenol and 3,5-di-t-butylphenol were also studied by flow microcalorimetry, and by adsorption isotherms from solution. Both of these techniques show that the structure of Wyodak is affected significantly by citric acid washing and that sites are apparently exposed which favour adsorption of aromatic systems.