Introduction of piperazine (PZ) as activator

https://doi.org/10.3389/fenrg.2021.785039

“Monoethanolamine (MEA) and piperazine (PZ) are the most commonly used activators, and related mixed amine systems have been extensively studied (Aronu et al., 2011; Choi et al., 2009; Dash et al., 2011; Mandal et al., 2001; Puxty and Rowland, 2011; Sakwattanapong et al., 2009).

The disadvantage of PZ as an activator is its low boiling point and high melting point. It is easy to crystallize at low temperatures and cannot be configured with higher-concentration solutions, which reduces the absorption. Its boiling point of 146°C is within the range of 120–160°C, the maximum working temperature of the device, so it is easy to volatilize at high temperatures, increasing the amount of amine loss and emission in large-scale carbon capture deployment. PZ derivatives have a similar molecular structure with PZ and in recent years have also been used to study their activation properties in mixed-amine solvents (Choi et al., 2016; Li et al., 2014a; Li et al., 2014b; Li et al., 2013; Yuan et al., 2017). Rochelle’s group from the University of Texas had studied about the absorption kinetics of PZ derivatives for CO₂ capture (Chen and Rochelle, 2011). Our group’s previous study (Li et al., 2014b) measured the cyclic capacity of these PZ derivatives and calculated the heat of CO₂ absorption by using the simplified Gibbs–Helmholtz equation. According to Chen and Rochelle’s research, the screening results indicate that there is a lower heat-of-CO₂ absorption and an equal absorption rate as well as a higher cyclic capacity in 1-methylpiperazine (1MPZ) than in PZ. However, 1MPZ has greater volatility than MEA and PZ (Mandal et al., 2001). The high volatility is usually a problem for commercial use. Among all derivatives of PZ, N-(2-Hydroxyethyl) piperazine (HEPZ) has the highest boiling point of 246°C, a melting point of −38.5°C, and better water solubility and thermal stability than PZ. The chemical structure of HEPZ is shown in Figure 1. HEPZ can withstand higher temperatures and configure higher-concentration solutions in industrial applications, which show the potential of HEPZ to replace PZ as an activator. Since no literature studied the absorption performance of the HEPZ aqueous solution and mixed-amine system with HEPZ, there is a need to measure the relevant experimental data.”