Effects of CO2 enriched atmosphere on chars from walnut shells pyrolysis in a drop tube reactor

A laminar drop tube reactor (DTR) was used to perform fast pyrolysis of walnut shells, a ligno-cellulosic biomass sample, in nitrogen and carbon dioxide atmospheres. The DTR reached the temperature of 1300 degrees C and the heating rate of 10(4)-10(5) degrees C/s. Char samples collected at different residence times along the reactor were characterized by ultimate and proximate analysis and by SEM. Char combustion reactivity was then measured by non-isothermal thermogravimetric analysis (TGA) in air. The analyses show that at residence times of 66 ms pyrolysis in N-2 is not complete, whereas it is complete in CO2. For residence times of 115 ms the differences between samples produced in N-2 and CO2 atmospheres level off.