Effects of surface and porosity changes on adsorption heat in acidified coking coal

ZHANG Xiaodong; LI Binghui; ZHANG Shuo; SUN Zeyuan; LIU Xiao

doi:10.16186/j.cnki.1673-9787.2022050093

Abstract：Objective In order to explore the impact of changes in the surface and porosity of coking coal after acidification on the adsorption heat.Methods The coking coal from the Gujiao mining area of Shanxi Province was selected as the research sample.Through hydrochloric acid(HCl)and hydrofluoric acid(HF)treatments,the changes of the coal-water contact angle,surface tension,pore structure before and after acidification were analyzed and the impact mechanism of these changes on adsorption heat was discussed by using the contact angle method,low-temperature liquid nitrogen adsorption method and microcalorimetry method.Results After acidification,the coal-water average contact angle increases from 75.1° to 80.11°,and the average surface tension decreases from 44.44 mJ/m2 to 39.48 mJ/m2,suggesting that the coal hydrophilicity weakens.Mean-while,the total pore volume,mesopore volume,specific surface area and average pore diameter of coal in-crease after acidification,but the pore volume and specific surface area of micropores and macropores de-crease.This phenomenon indicates that the removal of minerals is conducive to the transformation of micro-pores to mesopores.Further,with the increase of temperature,the molecular thermal motion strengthens,and then the molecular energy breaks through the solid surface potential barrier to promote gas molecules to be-come free states,resulting in a decrease in the integral adsorption heat and differential adsorption heat of raw coal and deashed coal,while the adsorption heat of deashed coal is higher than that of raw coal.Con-clusion The existence of minerals can weaken the adsorption capacity of coal to gases and occupy the ad-sorption sites on the coal surface.Therefore,the increase of the adsorption sites on the surface of coking coal,caused by the removal of minerals after acidification,is the main reason for the increase in adsorption heat.