(583ax) Depolymerization of Alginate Via Hydrothermal Treatment

Alginate from sea algae is polymer material composed of two types of uronic acids as monomer, mannuronic acid and guluronic acid. Depolymerization of sodium alginate under subcritical water conditions is one of the methods to produce biofuels and valuable chemicals from the marine biomass. Hydrothermal decomposition leads to the formation of unsaturated uronic acid derivatives and various organic acids.

In present work, hydrothermal treatment of sodium alginate (2 wt%) in subcritical water conditions (120–240 °C) was. The various operating conditions of hydrothermal treatment such as temperature, time, pH, and concentration of alginate were changed. The product solution was analyzed with various analysis techniques, such as gel permeation chromatography (GPC), matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and high performance liquid chromatography (HPLC).

Increasing retention time of peaks in GPC indicated that the depolymerization proceeded as the reaction temperature increased. However, after 200 °C, the retention time of peaks was almost identical with small differences in intensity. This means that the uronic acid monomers were significantly generated after 200 °C.

MALDI-TOF-MS spectrum of the product obtained by the hydrothermal process at 180 °C for 10 min indicated that differences between each peak were consistently observed as 176, which is the molecular weight of the unit monosaccharides of alginate. This implies that the monomers and oligomers were generated, by the selective hydrolysis of 1,4-glycosidic bonds, from monosaccharides rather than from alginate directly.

It can be summarized that hydrothermal treatment using subcritical water can provide the condition to depolymerize alginate via selective hydrolysis at the glycosidic bonds, especially increasing the reaction temperature up to 200 °C.