Absorption of SO2 from flue gas by aqueous fulvic acid solution

Abstract

A new regenerable flue gas desulfurization process was proposed, in which fulvic acid derived from biomass residues was used as an absorbent to absorb SO₂ from flue gas, based on acid–base buffering capacity. Experiments have been carried out to examine the absorption, desorption and reabsorption performance of fulvic acid solution in a lab-scale reactor. The results show fulvic acid solution (0.04 g mL⁻¹, pH 5.5) could excellently absorb SO₂ with a maximum absorption efficiency of 97.5% (298 K, 2200 ppm SO₂, 5% O₂, 0.14 m³ h⁻¹). In the process of SO₂ absorption, chemical absorption is the predominant mechanism. The SO₂-loaded solution is readily desorbed and regenerated under ambient pressure by heating at 343 K, and the regenerated fulvic acid solution still exhibits good absorption performance after seven absorption/desorption cycles. Trace metal ions binding to fulvic acid play a decisive role in the absorption process. Fulvic acid samples before and after absorbing SO₂ were well characterized by Fourier transform infrared spectroscopy, near-edge X-ray absorption fine structure and X-ray photoelectron spectroscopy. These results demonstrate that no chemical change is found, except that carboxylate groups are protonated to carboxylic groups, indicating that fulvic acid is stable as a regenerable absorbent.