Performance assessment of dilute-acid leaching to improve corn stover quality for thermochemical conversion

Abstract Lignocellulosic biomass is a sustainable energy source that can help meet the demand for biofuels in the United States. However, the quality and availability of such feedstocks greatly affect their suitability for downstream conversion. This work reports the effects of dilute-acid leaching at various aqueous loadings, temperatures and catalyst loadings (sulfuric acid) on the quality of a traditional biochemical feedstock, corn stover, as a potential feedstock for thermochemical conversions. At 95 wt% aqueous, dilute-acid leaching was observed to effectively remove 97.3% of the alkali metals and alkaline earth metals that can negatively affect degradation pathways during pyrolysis and result in greater yield of non-condensable gases. In addition, up to 98.4% of the chlorine and 88.8% of the phosphorus, which can cause equipment corrosion and foul upgrading catalysts, respectively, were removed. At 25 °C in the absence of the acid catalyst, only 6.8% of the alkali metals and alkaline earth metals were removed; however, 88.0% of chloride was still removed. The ratio of alkaline/acidic ash species has been suggested to proportionately relate to slagging in combustion applications. The initial alkali/acid ratio of the ash species present in the untreated corn stover was 0.38 (significant slagging risk). At 95 wt% aqueous, this ratio was decreased to 0.18 (moderate slagging risk). At 0 wt% catalyst and 90 °C, the ratio was decreased to 0.07, 0.08 and 0.06 at 0.5 wt% catalyst at 25 °C, 50 °C and 90 °C, respectively (low slagging risk). Increasing the catalyst loading to 1.0% slightly decreased the measured alkali/acid ratio of remaining ash. The results presented here show that a water wash or a dilute-acid preprocessing step can improve corn stover quality for pyrolysis, hydrothermal liquefaction and combustion.