Abstract: Co-liquefaction of biomass(sawdust and rice straw) with plastic(high density polyethylene,HDPE) in sub-and supercritical water(SCW)was investigated using a 500mL stainless-steel autoclave. A series of liquefaction experiments were carried out with biomass and plastic individually and in combination. To obtain basic knowledge about degradation of biomass and plastic into oil, the effects of reaction temperature, reaction time, ratio of water to biomass and polyethylene(PE) and degradation pressure were investigated. At 653K the maximum yield of oil was achieved. At this temperature, the most important parameter for oil yield was biomass/plastic ratio in the feedstock. Yield of oil up to 60% was obtained using 1:4 weight ratio of biomass/PE mixture. Co-liquefaction of biomass with plastic increased the yield of oils. Results showed that addition of biomass to plastic could decrease the degradation temperature of plastic to supply hydrogen, and the synergistic effects of biomass and plastic,could enhance oil yield and ease the requirement of reaction condition.

Key words: supercritical water, sub-critical water, co-liquefaction, biomass, plastic