Enhancing the Strength of Formed Coke from Woody Biomass with the Addition of Biomass Extracts

The replacement of coal with lignocellulosic biomass as feedstock for blast furnace coke is a crucial approach to decarbonizing the steel industry, which is a sector that is difficult to abate. Unlike the addition of a small amount of biomass or its charcoal to blended coal for conventional coke, the use of 100% biomass as a raw material is possible with formed coke, while its practical application requires an improvement in strength. Here, we report that the addition of a low-molecular-weight fraction obtained from degradative solvent extraction of biomass, called Soluble, is highly effective in enhancing the strength of the formed coke from softwood biomass. When used alone as a raw material, Soluble foams during carbonization, preventing coke formation. However, when mixed with woody biomass, it disperses within and between biomass particles during pelletization (hot press at 130 °C) or carbonization (cold press). Soluble has a minimal impact on the pyrolysis of biomass and dimensional changes of the biomass-derived carbonaceous substrate during carbonization, but it acts as a binder to sustain the strength of the resulting coke. As a result, the tensile strength of formed coke from biomass alone, which was 1.2 MPa with a cold press and 7.5 MPa with a hot press, improved with the increasing addition of Soluble, reaching around 25 MPa at 30 wt % addition. The effect of addition varied significantly depending on the preparation method and properties of Soluble, particularly highlighting the importance of the resolidification temperature during the carbonization process. This method was also effective for formed coke derived from lower-quality raw materials such as rice husk and lignite compared to softwood, but the optimal addition amount varied due to differences in the Soluble retention capacity.