Flow Calorimetric Comparison of the Acid-Base Bonding in the Outer Surface and Subsurface Regions of Coal

Abstract

A flow calorimetric method was developed for comparing the strength and/or extent of acid-base bonding in the outer surface and subsurface regions of fine coal particles. This method was applied to an ultrafine sample of a low-sulfur, low-ash bituminous coal. Information about the acid-base bonding in the outer surface region of the fine particles was deduced from heats of interaction of 4-tert.-butylpyridine dissolved in 2.2,4-trimethylpentane (“"isooctane”). The penetration of this basic probe molecule into the particles is limited by its tert.-butyl group. The acid-base character of the subsurface region was deduced from heals of interaction with acetone and pyridine. good coal penetrants/swelling agents. The results suggest that the outer surface of the low-sulfur, low-ash coal studied is H-bonded to a considerably greater extent than the subsurface region. Such results are rationalized on the basis of mild oxidative weathering conditions, which may render the outer surface of coals richer in ether oxygens than the subsurface region. Once formed, such oxygens are expected to H-bond to acidic protons from contiguous portions of the coal.

Keywords:

• Flow calorimetry
• Coal
• Surface chemistry
• Penetration/swelling
• Acid-base characterization
• Surface area