Effect of condensation-assisted solid media on the production of bio-oil by fast pyrolysis of cassava residues in a free-fall reactor

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This research elucidates the effect of condensation-assisted media on the production of bio-oil from a mixture of cassava stalk and rhizome in a free-fall fast pyrolysis reactor. The media were non-porous solid substances including steel balls and glass beads, and porous solid substances including silica gel and 3A molecular sieve. For experiments with solid media, the biomass feed rate was fixed at 100 g/h and the total run duration was varied to 60, 90 and 120 min to vary the total amounts of biomass feed to 100, 175 and 250 g, respectively. The use of solid media did not significantly influence the total bio-oil yields and hardly affected the yields of heavy bio-oil. The highest increase of the heavy bio-oil was achieved when applying 3A molecular sieve and 250 g of biomass in which the yield was increased from 40.2 to 53.8 wt%. It was found that the bio-oils from low-temperature condensers were separated into two phases, namely light bio-oil and aqueous liquid. The yield of the light bio-oil increased from ∼1 to 8.8 wt% when the 3A molecular sieve was applied. According to the bio-oil analysis, all solid media could ameliorate the bio-oil water and oxygen contents as well as their heating values. It is for the first time discovered that the use of 3A molecular sieve as a condensation-assisted medium while producing bio-oil could effectively and significantly improve the bio-oil quality. Comparing the non-condensation-assisted media with the 3A molecular sieve, the water content of heavy bio-oil was reduced from 29 wt% to 10 wt% and the HHV was increased from ∼22 MJ/kg to 26 MJ/kg. Importantly, the heating value of the light bio-oil produced with the aid of 3A molecular sieve was as high as 31 MJ/kg.