Hydrothermal conversion of alginic acid to furfural catalyzed by Cu(II) ion

•Furfural was produced from alginic acid over metal cations under hydrothermal conditions.•Cu(II) ions exhibited the highest furfural yield, 13.19% at 200 °C for 30 min.•The production of furfural was depending on the electronegativity of metal ions.

Alginic acid, a major carbohydrate material of macroalgae, was hydrothermally treated to produce furfural over various metal cations as catalysts. Among the metal cations, Cu(II) ions showed the highest furfural yield (13.19 mol%) at 200 °C for 30 min. In the hydrothermal reaction of alginic acid catalyzed by Cu(II) ion at reaction temperatures from 160 to 220 °C, the yields of furfural were proportional to reaction time, however, the maximum furfural yields decreased after certain reaction times due to the conversion of furfural to humins or organic acids. The catalyst concentration was significantly influential on the yield of furfural, the optimal concentration of Cu(II) ions was 0.01 M for the most effective production of furfural. In addition to furfural, lactic acid, glycolic acid and formic acid were produced in different amounts depending on the metal cations. The effect of Cu(II) ion on the depolymerization of alginate was studied with gel permeation chromatography (GPC) analysis in various reaction conditions. A plausible reaction pathway of furfural production catalyzed by Cu(II) ions was suggested.

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