Effect of the presence of trace sulfur dioxide on piperazine-based amine absorbents for carbon dioxide capture

Abstract

The effect of the presence of trace SO2 in industrial flue gas on the amine-scrubbing-based absorption process for CO2 capture has been a matter of concern. This study aimed to investigate the effect of trace SO2 on the CO2 capture process using piperazine-based amine absorbents, focusing on SO2-resistance capability, SO2/CO2 absorption selectivity, and cyclic stability. The presence of trace SO2 not only restrains CO2 absorption, but also promotes the formation of carbamate within the piperazine-based amine absorbents. Remarkably, the incorporation of aminoethyl group in piperazine-based amine absorbents can enhance the SO2-resistance capability by promoting the formation of carbamate, while piperazine-based amine absorbents with hydroxyethyl group can promote the formation of bicarbonate to reduce the SO2-resistance capability. The work offers valuable insights into the efficient application of novel amine absorbents for CO2 capture from practical industrial flue gas.

1. Introduction

Since the Industrial Revolution, the endless release of CO2 has contributed significantly to environmental degradation [1e3]. Particularly, industrial flue gas resulting from the combustion of fossil fuels stands out as the primary source of CO2 emissions [4,5]. Developing efficient carbon capture, utilization, and storage (CCUS) technologies to effectively reduce the flue gas CO2 emissions is a challenging task [6e8]. Of the various CCUS technologies, the amine scrubbing-based absorption technology stands out prominently due to its rapid absorption kinetics, high absorption capacity, and ease of operation [9e14]. In reality, the composition of flue gas is extremely complicated, especially in the case of coal-fired power plants, where it contains various components such as dust, NOx, SO2, H2O, and CO2 [15e17]. These components can significantly affect the capability of the amine absorbents during CO2 capture process. Despite the initial desulfurization and dust removal, there is still a trace amount of SO2 in the flue gas entering the CO2 capture stage [18e21]. Due to its higher acidity, the remaining trace SO2 can form stronger bonds with the amine absorbents [22,23]. For typical amine absorbents, the process of CO2 absorption usually takes place at pH value greater than 8, while the SO2 absorption can occur at pH value greater than 3 [24]. As a result, the effect of the presence of trace SO2 in the flue gas needs to be further investigated when utilizing amine absorbents for CO2 capture.

The effect of trace SO2 in the flue gas on the process of CO2 capture by solid-based absorption separation has been studied by various researches [18,25,26]. For instance, Fan et al. [27] conducted multi-cycle experiments to simulate the flue gas conditions (0.05% SO2/10% CO2/N2), it can be observed a rapid decrease in the absorption capacity of the amine-modified absorption for CO2 in the presence of trace SO2. Subsequently, the adsorption capacity stabilized at its lowest level as the system reached equilibrium for CO2 absorption. Unlike the absorption process, CO2 capture by amine absorbents relies primarily on chemical reactions that generate more stable carbamates and bicarbonates. Li et al. [28] conducted an experiment to determine the mass transfer coefficient of CO2 in ammonium hydroxide with various amounts of SO2. The results indicated a decreasing trend in the mass transfer coefficient of CO2 in ammonium hydroxide as the concentration of SO2 in the gas phase increased. Gao et al. [29] revealed that the introduction of SO2 can result in a reduction in the pH value and an increase in the viscosity of the monoethanolamine (MEA) solution. Moreover, it also leads to a reduction in both the overall reaction rate and mass transfer coefficient for CO2. These investigations provide some explanations for the reduced CO2 capture efficiency of amines caused by SO2. However, there is currently remains scarce with regard to the effect of the presence of SO2 on CO2 capture by amines, as well as the structure-activity relationships between the SO2-resistance capability of different amines [30].