The influence of long-term storage on thermal behaviour of lower rank coal on the example of Polish coals. Part 2. The influence of expired ibuprofen (IB) and aspirin (AS) on changes in volume of long-term stored coal and on the composition of condensed material (CM) on the surface of grains

Abstract The influence of ibuprofen (IB) and aspirin (AS) additives on the changes in volume of the carbonized charge of long-term stored coal (LTSC) was investigated in a laboratory coking oven using X-raying. An almost 1.4-fold decrease of the growth in volume of the carbonized charge under the influence of AS and a twofold increase of the growth in volume of the charge under the influence of IB at the stage of coal grain swelling were observed. The carbonized swollen grains from the charge were rinsed in an ultrasonic washer to separate the condensed material (CM) on the surface of grains. The obtained CM was analyzed by the UV and FT-IR spectroscopies. The LTSC samples with and without additives were pyrolyzed in a TG/FT-IR measuring set. An increase in yield of the volatile products of pyrolysis of LTSC with additives and the changes in their composition under the influence of additives were stated. The swollen grains and carbonizates at the stage of maximum plasticity were investigated by the SEM method. The presence of the rods of 50–120 nm in diameter was ascertained on the surface of the swollen grains from LTSC charge with additives. It is suggested that the presence of nanorods and the modification of CM composition by IB and AS additives cause an increase in thermal diffusivity of the charge with additives. The bands, which originate from compounds containing chromophore groups, are visible on the UV spectra for CM from the charge with additives. The ATR spectra show a decrease in contribution of carbonyl groups in the composition of CM that was obtained under the influence of the additives. The changes in composition of volatile products of pyrolysis, mainly an increase in contribution of the compounds containing carbonyl groups, were registered on the FT-IR spectra. It is suggested that the carbonyl compounds, which are present in the composition of volatile products of pyrolysis, can contribute to the formation of nanorods on inorganic elements of the material of coal grains under the influence of the additives.