Structural changes in coal chars after pressurized pyrolysis

The aim of this work was to evaluate the effect of pressure on the structural properties and subsequent reactivity of coal chars. Pyrolysis reactions were carried out in a fixed bed reactor by varying the pressure up to 2.0 MPa. Two coal samples with a substantial difference in the swelling index were used for the analysis. Pyrolysis experiments were carried out at 800 °C for 30 min after heating the sample at a constant rate of 20 °C/min and some samples were pyrolyzed at 900 °C and 0.1 MPa for comparison. Structural analysis of the coal chars was performed using Raman microscopy; this characterization was complemented by scanning electron microscopy analysis, gas adsorption and reactivity towards molecular oxygen in a thermogravimetric equipment. Characteristic Raman bands of coal chars exhibited significant changes from 0.1 to 0.5 MPa, after this pressure no significant changes were observed with pressure increments. The pyrolysis pressure showed to have an influence in the ordering of the carbonaceous structures through the deconvoluted Raman spectra.

► Raman spectroscopy of the coal chars showed slight variations in the carbonaceous structures after the pressurized pyrolysis.
► Observed differences in morphology after pressurized pyrolysis do not appear to have a meaningful impact in the reactivity in air of the coal chars.
► The invariant reactivity with pyrolysis pressure could find a better explanation through the BET surface areas of the coal chars.