Characterization of gases and solid residues from closed system pyrolysis of peat and coals at two heating rates

Closed system gold-tube pyrolysis experiments were performed on a peat and two coals (TY: Ro = 0.51%; SX: Ro = 0.94%) at temperatures ranging from 337 to 600 °C and a pressure of 50 MPa with heating rates of 2 and/or 20 °C/h. Solid reaction residues were analyzed microscopically. Yields and chemical and isotopic compositions of the generated gases were also determined. All three samples had similar thermal evolution pathways. With increasing heating temperature, vitrinite reflectances (VRr) of the residues increased linearly from 0.72% to 4.50%. This increase was lesser for the sample with a higher hydrocarbon generation potential and at faster heating rates. Gas compositions are dominated by CO2 and CH4 throughout the experimental process. Total gas and CH4 yields gradually increase with pyrolysis temperature for all samples. The carbon isotopic compositions of CH4 generated from the peat are lighter than those from the coals. The δ13CCH4 values exhibit a generic evolution pattern which the initial CH4 is isotopically heavy, then becomes lighter at moderate temperatures, and finally becomes heavier again. Methane produced from the samples at low heating rate has higher transformation ratio than that at high heating rate under the same temperature, so tends to be isotopically heavy after pyrolysis temperature of more than 408 °C.