Effect of synergism between biomass and coal during co-pyrolysis in a free fall reactor on tar components

The liquid products from co-pyrolysis of Dayan lignite (DY) and legume straw (LS) and from pyrolysis of the single fuel were classified into asphalts, phenols, aliphatic, aromatics and polar fractions by solvent extraction-column chromatography. Compared with the calculated yield of asphalts, i.e. the mass weighted mean value 19.0% from pyrolysis of the single coal and biomass, the experimental yield from co-pyrolysis decreased to 11.4%, and the aromaticity of the co-pyrolysis asphalts increased. At the same time, the yield of light molecular weight phenols, methylphenol, dimethylphenol and their derivatives increased at about 5% during the co-pyrolysis; while the content of aliphatic hydrocarbons with long chains decreased. The content of decalins was 43.37% in aromatic fraction of the co-pyrolysis tar, whereas it was almost not found in the tars from pyrolysis of the individual fuel. These results verified that the synergy existed during co-pyrolysis of coal and biomass under the experimental conditions. It was contributed to the reactions such as hydropyrolysis and hydrogenation during co-pyrolysis of coal and biomass under the hydrogen atmosphere mainly supplied by biomass pyrolysis. Co-pyrolysis of coal and biomass favors producing low molecular weight compounds and improving the quality of the liquid product.