Hot water extraction as a pretreatment for reducing syngas inorganics impurities – A parametric investigation on switchgrass and loblolly pine bark

The effects of hot water extraction on the removal of inorganic impurities (N, S, Na, K, Mg and Ca) in biomass that are detrimental to gasification were investigated on switchgrass and loblolly pine bark. As hot water extraction severity increased from 13 to 141 h °C, the extraction liquor pH decreased from 6.0 to 4.5 for switchgrass and 3.6 to 3.1 for pine bark, thus resulting in 20.7–69.6% of ash reduction for switchgrass and 57.0–73.3% for pine bark, respectively. In addition, the nitrogen content which results in ammonia (NH3) formation was reduced by 9.3–22.9% for switchgrass and 1.0–6.8% for pine bark following increment of severity. Furthermore, sulfur which leads to hydrogen sulfide (H2S) formation was reduced from 48.3 to 62.5% and 5.6 to 17.3% for switchgrass and pine bark, respectively. The range of potassium, sodium, magnesium and calcium reductions were 94.9–98.8, 47.9–72.4, 58.7–83.5 and 8.5–13.0 for switchgrass and 50.8–67.5, 29.2–60.1, 9.7–50.8 and 3.3–33.0% for pine bark. Finally, statistical analysis was carried out on the statistical significance of the extraction temperature and time as well as their interaction on the removal of inorganic impurities. The extraction temperature, time, and the interaction differed in their effect on liquor pH, ash reduction, mass loss, and reduction of individual inorganics.