Organic acid-assisted organosolv fractionation of sawdust and using the fractionated lignin to prepare activated carbon pellets for high-temperature applications

Abstract

In present, activated carbon (AC) pellets that are commonly prepared by petroleum-based binders have been used to control NOx, SOx, and volatile organic compounds (VOCs) emissions in the iron/steel industry. However, the use of petroleum-based binders leads to great challenges toward sustainability and environment. Alternatively, lignin as a natural bio-binder derived from biomass and organic waste can act as a potential additive for preparing AC pellets. Therefore, in this study, pinewood sawdust was initially fractionated into crude cellulose and lignin by organosolv fractionation method at 90–120 °C for 180 min in an acetic acid/formic acid/water mixed solvent of 3/5/2, 3/6/1, and 5/4/1, vol%/vol%/vol%. Afterward, the fractionated crude lignin was used as bio-additive to substitute 50 wt% of petroleum-derived phenol to synthesize phenol-formaldehyde resole resins (PLPF) and compared with those prepared using 100% petroleum-derived phenol resole resins (PF). PLPF and PF resins were further fabricated to AC pellets by thermal treatment/curing at 150 °C and different loadings of resins (i.e., 10–50 wt%), followed by carbonization at 400 and 700 °C. In the fractionation, it was found that temperature played a role in determining the yield and purity of crude cellulose and lignin, while the effect of solvent composition was insignificant. PLPF resins (loading of 50 wt%)-based AC pellets obtained from thermal treatment at 150 °C followed by carbonization at 400 °C showed a relatively higher compressive strength, which meets the national standard and could ensure their uses as an emission control method in the iron/steel industry. Overall, it can be concluded that lignin-derived from woody biomass by organosolv fractionation in acetic acid/formic acid/water mixture is an alternative bio-binder to prepare AC pellets for emission control at high temperatures.