Adsorptive purification of crude glycerol by sewage sludge-derived activated carbon prepared by chemical activation with H3PO4, K2CO3 and KOH

摘要

Adsorptive purification of crude glycerol (CG) from a used-oil/methanol utilizing biodiesel production plant was performed using sewage sludge-derived activated carbons (ACs) at a laboratory scale and ambient conditions. The effect of different chemical activating agents (H3PO4, K2CO3 and KOH) and carbonization temperatures (500-900 °C) on the surface properties of the obtained sludge-derived ACs, as well as the adsorption efficiency of impurities from pre-treated crude glycerol (PTCG), was explored. The results showed that both the activating agent type and the carbonization temperature affected the textural properties and the surface chemistry of the sludge-derived AC. The oxygen-containing surface functional groups, particularly the carbonyl groups, as well as the textural properties played a more important role in the adsorptive purification of CG. Among the as-prepared sludge-derived AC, the activated carbon impregnated by KOH (KOH-AC) carbonized at 800 °C (KOH-800AC) exhibited suitable surface properties to enhance the purity of the PTCG up to 93.0 wt.% when using an AC dose of 67 g/L, 2 h adsorption time and a shaking rate of 250 rpm. The adsorption of either ash or other contaminants via the sludge-derived AC followed the Langmuir isotherm.