Valorization of CO2 in flue gas through alkalinity production: Parametric optimization for application in anaerobic digesters

Abstract The main aim of this work was to investigate the production of alkalinity by CO2 absorption in sodium hydroxide (NaOH) solution and optimizing the CO2 absorption efficiency (E) using statistically designed experiments. Based on the Box–Behnken's experimental design, fifteen experiments were conducted in a lab-scale batch reactor (80 mm × 1000 mm). The effect of three process parameters, i.e. NaOH solution concentration, X 1 (0.5 ∼ 1.5% w/w), influent gas (10% CO2 and 90% N 2 ) flow rate, X 2 (300 ∼ 700 ml/min) and initial solution temperature, X 3 (20 ∼ 60 °C) on the CO2 absorption efficiency were investigated and statistically analyzed. A maximum CO2 absorption efficiency of 74.3% was obtained at the following optimal conditions: X 1 - 1.5% (w/w), X 2 - 300 ml/min and X 3 −60°C. It was also observed that the hydroxide alkalinity shifts to carbonate and bicarbonate alkalinity at the end of reaction, which implied that the CO2 can be recovered and the alkaline solution could then be utilized as a valuable carbonate and bicarbonate alkalinity resource. The results obtained from this research is intended to be utilized for economic bicarbonate neutralization in biological anaerobic digestion systems.