Analysis of tars formed during co-pyrolysis of coal and biomass at high temperature in carbon dioxide atmosphere

The analysis of tars from the high temperature (1573 K–1773 K) co-pyrolysis of coal (Pittsburgh #8) and biomass (Switchgrass and White Pine) in CO₂ has been carried out. The analysis shows that naphthalene content is the maximum in all the tar samples irrespective of biomass and coal blend proportion. Samples with high percentages of coal as well as experiments conducted at 1773 K showed the highest concentration of aromatic compounds. The largest aromatic compound found had five benzene rings (benzo(e)pyrene). Aliphatic hydrocarbons as well as oxygenated hydrocarbons were mostly found in samples containing high percentages of biomass or in experiments conducted at 1573 K. About 100 compounds have been identified in the tars of which 25% account for 90% of the mass of tar. The study indicates that the atomic N/C and S/C ratio increases whereas H/C ratio decreases with pyrolysis temperature. The rate of variation of H/C ratio reduces as the temperature increases. The biomass content in the fuel feed seems to have an impact on the H/C ratio of the tars only at lower temperatures. That is, at lower temperatures, the higher the biomass content of the fuel, the higher the H/C ratio of the resulting tars. These observations also apply to the O/C ratio of the tar. For both switchgrass and pine sawdust, the biomass content of the fuel seems to have no influence on the nitrogen content of the tars. The distribution of sulfur in the tar is inversely proportional to the biomass percentage in the fuel. The higher the biomass content of the fuel, the lower the atomic S/C of the tars.