Volatiles release and porosity evolution during high pressure coal pyrolysis

The kinetics of porosity and of porous structure evolution have been examined during enhanced pressure (0.1-3.0 MPa) pyrolysis for two subbituminous coals on the basis of volatiles release. It has been found that both the volatiles mass release and char porosity decrease with pyrolysis pressure. The behaviour of three pore size groups, 5-30, 30-300 and 300-5000 nm, were observed during pyrolysis. An almost total elimination of the first group (5-30 nm) was found so that the porosity build up was entirely within the third size group (300-5000 nm), particularly at 1 MPa pressure. During the stage of most intensive devolatilization the release of volatiles precedes the porosity evolution.