Sustainable NOX scrubbing with lignin-based materials: Lignin sulfonate and vanillin as model compound

Pretreatment of flue gas prior to CO 2 capture via amine scrubbing is important for maintaining CO 2 capture efficiency and avoiding formation of toxic byproducts due to the presence of NO X . One flue gas cleaning method for that has increasingly gained attention is NO X scrubbing, in which NO is pre-oxidized to NO 2 which can be absorbed using aqueous solutions containing suitable additives. While commonly used sulfur-based additives achieve high absorption efficiencies, they suffer from high consumption rates due to oxidative consumption. A recent study on phenolic additives demonstrated that e.g. 4-methylaminophenol could be used as efficient additive which has much lower consumption rates. This compound however is limited for industrial application due to environmental concerns. The present study aims to demonstrate the usage of bio-based phenolic polymers for NO 2 absorption which should be more suitable for industrial usage on the example of lignin sulfonate. Additionally, vanillin was studied as a model compound to better understand NO 2 absorption chemistry with such additives. Tests were conducted using lignin sulfonate at different pH values and additive concentrations with 50 ppm inlet NO 2 at a total gas flow rate of 2.3 NL/min. Lignin sulfonate at 500 mg/100 mL and pH 9 maintained high NO 2 absorption efficiency of approximately 90 %. Vanillin at 5 mM showed efficiencies of 91 % and 94 % at 50 and 100 ppm inlet NO 2 , respectively, at the same gas flow rate. With vanillin, absorption efficiency remained at a high level even after more than 1 mol NO 2 per mole additive was absorbed, while sulfur-based additives showed a much lower ratio than 1 when fully consumed. NO 2 absorption by the sulfur-based additives was successfully modeled, highlighting the lower chemical consumption of vanillin. Overall, these results demonstrate the high potential of lignin-based additives for NO 2 scrubbing.