Production of Bio-coal and Activated Carbon from Biomass

The slow pyrolysis of different biomasses (maple wood, birch bark, switch grass, coffee pulp and corn stalk) was studied with the aim to produce a solid pyrolysis product (bio-coal) with promising properties and potential for use in traditional fossil-coal applications. Batch pyrolysis experiments were conducted in a Mechanically Fluidized Reactor (MFR) at temperatures ranging from 143 to 665 oC, which includes the torrefaction temperature range (200-300 oC). The effects of temperature and holding time on bio-coal mass yields were determined. The bio-coals were characterized in detail and a highly-controlled study on bio-coal hygroscopicity is presented. Optimal conditions for bio-coal production ranged from a top temperature of 238 °C for maple wood to 286 °C for birch bark. Converting these two feedstocks to bio-coal reduces hygroscopy by about 60 % and increases the heating value by 20 to 36 %, respectively. In both cases, 84 to 89 % of the energy of the original biomass is recovered in the bio-coal. Surface area enhancement of the different biomasses was studied through pyrolysis (MFR) and CO2 activation in a fixed bed reactor. Only birch bark and maple wood provided activated carbon with a high surface area of about 400 m2/g. Interestingly, carbon dioxide activation greatly increases the surface areas of birch bark char but does not have a significant effect on maple wood char. For birch bark, activation was performed either consecutively on the MFR, or as a second stage on a fixed bed reactor. Technologies provided activated carbons with similar surface areas and were compared according to their mass yield. The MFR provides a higher activated carbon yield, a more homogenous product and a more controllable process than the fixed bed reactor