Abstract

Constant pressure (12.07 MPa) pyrolysis of woody spruce biomass was tested using a 2K factorial design to evaluate the effects of independent variables, including reactor temperature, reaction time, biomass feedstock, biomass moisture content, and acetic acid content, on transient plastic phase (TPP) formation, fixed carbon yields, and ultimate tensile strengths of biochars. Two-factor interactions were also observed. Temperature had the greatest effect on fixed carbon yields and ultimate tensile strengths. Minimal differences in fixed carbon yields and ultimate tensile strengths occurred between TPP and non-TPP (NTPP) biochars produced under similar reaction conditions. Reaction conditions that led to improved ultimate tensile strength sacrificed fixed carbon yield. The spruce biochar sample with the highest measured pellet tensile strength, 4.36 ± 0.50 MPa, was formed at a temperature of 230 °C and a nominal moisture content of 113.85%.