Co-pyrolysis of LDPE and cellulose: Synergies during devolatilization and condensation

•Synergistic effects were observed for co-pyrolysis of cellulose and LDPE.•The liquid yield and total energy recovery were increased by 14% and 15% respectively.•The synergies were evinced to happen both during devolatilization and condensation.•The sum of these synergisms was similar to the overall synergistic effect of co-pyrolysis.

The nature and mechanisms of synergistic effects observed during the co-pyrolysis of cellulose and low density polyethylene (LDPE), two major components in municipal solid wastes, were investigated at milligram and gram-scales. Pyrolysis of a mixture of LDPE and cellulose increased the yield of the liquid product, with an 83% increase in the energy recovery, compared to a mixture of the liquid products from pyrolysis of the individual components. Further experiments distinguished the synergistic effects during devolatilization and condensation, respectively. Synergism during devolatilization was investigated by mixing cellulose char (prepared at 400 °C) with LDPE, and resulted in an increase in liquid yield, indicating an interaction between char and LDPE to promote liquid production. Solid-gas and/or gas-gas interactions occurred, where in the former the char acted as a catalyst rather than a reactant. For synergistic effects during the condensation process, LDPE was pyrolysed and the hot volatiles were condensed while the liquid products of cellulose pyrolysis were present in the condensation system, which also increased the liquid yield. Gas-gas and/or gas-liquid interactions occurred during condensation which enhanced the formation of the liquid phase. Moreover, the sum of the synergisms during devolatilization and condensation was similar to the overall synergistic effects observed during co-pyrolysis of the mixture, confirming the contribution of both to the overall positive synergistic effect on the liquid yield.