Production of Char from Woody Biomass via Pyrolysis: Effect of Temperature and Pressure

This work evaluates the influence of pyrolysis temperature (350 ºC and 450 ºC) and pressure (0.1, 1.0 and 2.0 MPa) on product yields and char properties produced from spruce biomass in a fixed bed reactor. The results showed that char yield increased with increasing pyrolysis pressure for both studied temperatures while the yields of liquids and gases decreased, in a higher extent in the range from 0.1 to 1.0 MPa. Pyrolysis temperature also affected the product distribution; char yield suffered a decline with pyrolysis temperature. Higher gas yields and larger amount of liquid fraction, were obtained as temperature rose, although this effect was less important as pyrolysis pressure increased. The porosity study revealed that pressure presented a more relevant influence for chars obtained at 450 ºC than those at 350 ºC. Additionally, surface area results suggested a possible deposition of secondary char and occlusion of the smaller pores for the chars produced at the highest temperature. A clear influence of pyrolysis conditions on char reactivity was presented; chars prepared at 450 ºC showed lower reactivity and a decreasing reactivity with pyrolysis pressure.