The effect of hot water pretreatment on the heavy metal adsorption capacity of acid insoluble lignin from Paulownia elongata

BACKGROUND Biorefinery processes utilize carbohydrates from biomass in order to produce biochemical and biomaterials. Lignin as the byproduct after biorefinery needs to be studied for applications. This study evaluated how hot water pretreatment, a typical biorefinery process, will impact on the heavy metal adsorption capacity of lignin. RESULTS Paulownia elongata acid insoluble lignin was tested for its heavy metal adsorption capacities for Pb(II), Cu(II) and Cd(II). Hot water pretreatment was conducted on the lignin with both water and dilute acetic acid solution. Samples with both increased and decreased adsorption capacity were observed after the pretreatment, while samples with long duration of pretreatment encountered a substantial loss in the adsorption ability. Depolymerization and condensation lignin reaction schemes under acidic environment were summarized and applied to explain the capacity changes. NMR analysis was performed to quantify the functional groups in the lignin samples. Changes in the amount of functional groups were found in the samples after pretreatment. CONCLUSION Hot water pretreatment can either increase or decrease the adsorption capacity of lignin depending on the treatment duration. Lignin byproducts after treatment under acidic and high temperature environments with long duration is no longer suggested for use as a heavy metal adsorbent. © 2017 Society of Chemical Industry