Flue gas pretreatment method for removal of SO2 for solvent-based post-combustion carbon dioxide capture

Abstract

There is no doubt that our current best bet to significantly reduce the carbon footprint in the atmosphere while buying us the time to shift from our over-dependence on fossil fuels to greener/cleaner energies is the amine-based post-combustion carbon capture process (PCC). Nevertheless, amidst advances in amine-based PCC technology and its well-known reputation in CO2 capture, flue gas impurities (SO2 and NO2) cause much harm to the capturing efficiency and render the absorbing solvent unable to stand the test of time (degradation). Conventional pretreatment technologies such as Selective Catalytic Reduction (SCR), Selective Non-catalytic Reduction (SNCR), and Flue Gas Desulfurization (FGD) are employed in industries to control SO2 and NO2 emissions. However, with the deployment of these pollutant removal technologies, residual quantities of SO2 and NO2 remain in the flue gas entering the carbon capture system. As a result, to optimize the performance of aminebased CO2 capture systems, it is essential to develop effective pretreatment methods that enable the removal of SO2 and NO2 from flue gas before carbon capture with amine solvents. For this reason, the present study was set forth to provide a novel solution to the detrimental effect of SO2 on the amine-based post-combustion carbon capture process. To selectively remove SO2 from a flue gas stream, an inexpensive deep eutectic solvent (Im:EG) of mild pH (8.42) composed of Imidazole (Im) and Ethylene Glycol (EG) was developed. The physicochemical properties such as density and viscosity were determined at 50 ℃ were 1.09090 𝑔𝑐𝑚−3 and 6.258 mPa.s respectively. The absorption-desorption behavior of Im:EG DES was studied at the bench-scale level using a simulated flue gas composed of 10.2 ppm SO2 (10.1% O2, N2 balance) The results showed that Im:EG DES maintained a good absorption-desorption behavior for three continuous cycles. For example, the absorption capacities of Im:EG DES (μg/l), stood at 2.88, 2.85, 2.85, which indicates an excellent regeneration ability and a good cyclic capacity. Additionally, the effect of desorption temperature on the initial rate of SO2 desorption, cyclic capacity, and the amount of desorbed SO2 was investigated from 70 ℃ to 100 ℃, at increments of 10 ℃. The outcome showed a positive correlation between temperature, the initial rate of SO2 desorption, cyclic capacity, and the total amount of SO2 desorbed, such that the desorption process was thermally activated and conforms well with thermodynamic principles. Also, the results from the kinetic analysis showed that the desorption reaction order was 4.0, and the minimum energy required to trigger SO2 desorption from Im:EG DES was 60.65 kJ/mol. Finally, based on experimental results and the chemical properties of Im:EG DES, it was inferred that Im:EG DES effectively removed SO2 from the gas stream through H-bonding and electrophile–nucleophile interactions.