Demineralization of common ivy-derived biomass and biochar and its effect on the resulting activated carbon properties

Abstract

Conventional activated carbon (AC) production relies heavily on unsustainable feedstocks (coal or wood from deforestation), which incites the need for alternative biomass-based resources to create sustainable biobased products. However, biomass residue streams generally contain large amounts of impurities (heavy metals, alkali minerals) which limit their industrial applicability. Conventionally occurring problems entail fouling and corrosion of industrial equipment or reductions in the efficiency of the manufactured products, e.g., decreased adsorption capacities of the resulting AC’s. Therefore, novel green demineralization techniques should be studied. Natural deep eutectic solvents (NADES) are promising green demineralization solvents. Currently, most NADES research focuses on applying these solvents to fractionate (lignocellulosic) biomass, extract valuable bioactive compounds, or replace non-natural deep eutectic solvents in chemical synthesis. A novel lignocellulosic biomass feedstock is common ivy (CI), Hedera helix L. However, its high mineral content, derived from the adsorption of atmospheric fine particulate matter during its growth, limits its applicability in future bio-refinery processes. Therefore, this biomass stream is a prime subject to be examined in a comparative evaluation of the promising green NADES demineralization treatment in lieu of conventional environmentally unfriendly acid treatments. The investigated NADES was choline chloride-malic acid (CCl:MA). Its demineralization efficiency was compared with conventional demineralization agents: H2O and dilute hydrochloric acid (HCl). Moreover, the preferred washing sequence (before or after pyrolysis) for AC-production was investigated. Demineralization before pyrolysis removed a large fraction of the biomass’s minerals for each of the washing agents: HCl (97.1% removal), CCl:MA (84.7%), and H2O (75.2%). The main difference was attributed to the removal of different Ca-containing species. Demineralization after pyrolysis created highly microporous AC’s. In this case, the solvent performance was ranked: HCl = CCl:MA > H2O. Lastly, the AC’s phosphate removal efficiency showed that biomass washing with either H2O or CCl:MA yields functional AC’s (phosphate adsorption capacities 19.3 and 16.5 mg/g). Ultimately, this investigation demonstrated CCl:MA’s potential as demineralization agent to treat metal-contaminated lignocellulosic biomass in future bio-refinery processes.