Use of Plasticized Biochar Intermediate for Producing Biocarbons with Improved Mechanical Properties

Abstract

Slow pyrolysis of woody materials under elevated pressure was previously shown to result in macroscopic morphology changes, appearing as a solid that had experienced a molten phase, described as "transient plastic phase biochar" (TPPB). Experiments have been conducted to study the influence of process variables on the formation of TPPB. Results suggest TPPB formation is mediated through hydrolysis that allow for a molten phase to occur. Elevated pressure plays a key role by keeping water in the condensed phase. Despite drastic changes in material morphology, notable differences between TPPB and standard biochar (not TPPB or "NTPPB") were not detected using proximate analysis, solid state 13C NMR, and helium pycnometry, indicating the material chemistry was minimally affected. Clear differences between the mechanical properties of the TPPB and NTPPB powders and pellets were shown using tabletability experiments. The utility of TPPB was then demonstrated by comparison of tensile and compression strengths of materials calcined (N2) at (900 degrees C) to form transient plastic phase biocarbon (TPPC). The TPPB precursor resulted in a TPPC pellet with 10 times greater tensile (4.4 MPa) and compressive strength (17.6 MPa) and nearly two times greater density than carbon pellets produced from NTPPB.