Experimental Investigation of Amine Regeneration for Carbon Capture through CO2 Mineralization

Abstract

Summary The most common method for point-source carbon capture involves the absorption of CO2 from flue gas by amine solutions. The CO2 is then stripped from the amine solution by desorption with steam or heat. While amine solvents exhibit high CO2 absorption efficiency, their desorption process consumes a substantial amount of energy. A more energy-efficient alternative for the regeneration of the amine can be done through a mineralization process. Past studies have shown the feasibility of mineralizing captured CO2 from amine solution using calcium oxide (CaO) or other CaO-containing industrial waste. This study aims to show experimentally the extent of mineralization over time in near-ambient conditions and develop a mechanistic model. Lab-scale experiments are conducted to determine the absorption characteristics of CO2 in monoethanolamine (MEA) solutions and the extent of mineralization. We observe that pH serves as an indicator for CO2 loading in amine solutions. At high concentrations of MEA, CO2 absorption efficiency is about 0.5 mol CO2/mol MEA. Under ambient pressure and a temperature of 40°C, CaO effectively mineralizes CO2 and regenerates MEA. The CaO initially reacts with water to produce calcium hydroxide (Ca(OH)2) and subsequently reacts with dissolved CO2, forming calcium carbonate (CaCO3). Both 13C nuclear magnetic resonance (NMR) and FTIR indicate that MEA can be regenerated with an efficiency close to 69 to 98%, by comparing the carbamate and bicarbonate peaks in the 13C NMR response. A model to describe the absorption and mineralization reaction is proposed using the PHREEQC software; the pH is matched within less than 3% error. This study demonstrates that CO2 desorption from MEA solutions can occur through mineralization, converting CO2 into carbonates at low pressure and temperature with CaO. This method has lower energy consumption and results in the most stable form of CO2, making it a safer sequestration strategy than supercritical CO2 storage in reservoirs.