Study on the effect of condensing temperature of walnut shells pyrolysis vapors on the composition and properties of bio-oil

•Biomass pyrolysis experiments were conducted at 290–370 K condensing temperatures.•The variations in condensing efficiency and composition were analyzed.•The most significant temperature range is 320–360 K in fractional condensation.•The optimum condensing temperatures for bio-oil modification were given. The effect of condensing temperature on composition of bio-oil obtained via fractional condensation was investigated by pyrolysis-condensation experiments of walnut shells at condensing temperatures from 290 K to 370 K. The condensing efficiency of the first stage condenser decreased from 0.59 to 0.12 with increasing temperature. Moisture of bio-oil decreased from 40% to 5%, but the C/O ratio increased from 0.50 to 1.50. Compared with contents observed at the lowest condensation temperature, the maximum content of each component increased by 50%–500%. Combined with variations in condensing efficiency and composition content, the optimum condensing temperature range for declining water in bio-oil was 340–350 K. The condensing temperature associated with the enrichment of acetic acid and furfural was 345 K. The 355 K optimum condensing temperature could be selected to achieve the maximum enrichment of guaiacol and its derivatives.