An investigation of the molecular change in coal maceral concentrates prepared under dimensional heating condition

Three maceral samples with vitrinite content of 88, 77 and 66 vol% (mmf) obtained from an Australian coking coal were investigated to understand the difference in their thermoplastic development. Each sample was packed in a quartz tube and heated from the bottom by a heating plate of which temperature was set to slowly ramp from room temperature to 900 degrees C. A thermocouple was inserted at 55 mm from the base to monitor the temperature change at this position as heat transferred through via thermal conduction. At the end of the experiment, the thermocouple measured temperatures at 469, 485 and 495 degrees C for the three respective maceral samples, suggesting a greater thermal gradient existed in samples with higher vitrinite concentration. The heated samples were then analysed by laser desorption/ionization time of flight imaging mass spectrometry (LDI-TOF-IMS) to track the change in molecular weight distribution across the sample length. Significant intensity of ionisable species was recorded in regions close to the thermocouple position for all maceral samples. Samples with higher vitrinite content displayed a greater molecular weight discrepancy (Delta m/z) in the plastic region compared to that in samples with lower vitrinite content, indicating a larger molecular variation occurred in these samples.