Degradation of Amine Solvents in a CO₂ Capture Plant at Lab-Scale: Experiments and Modeling

Abstract

Carbon dioxide (CO2) concentrations in the atmosphere have increased significantly over the past century. Many methods have been devised to reduce CO2 industrial emissions, e.g., CO2 postcombustion absorption by amine-based solvents. Solvent degradation losses are very critical in this process, due to economic and environmental issues. The two main degradation pathways of amine-based aqueous solutions in the presence of CO2 are oxidative and thermal degradation. In this work, a lab-scale pilot plant has been set up to carry out degradation experiments during continuous and dynamic cycles of absorption and stripping with three different amine solvents: MEA (monoethanolamine) used as benchmark solvent for CO2 capture, a blend of 1MPZ (1-methylpiperazine) and PZ (piperazine), and a blend of MDEA (methyldiethanolamine) and MEA. The experimental data have been used to assess the performance of CO2 absorption over time and experimental conditions. The variation of CO2 fraction at the gas outlet of the reactor has been used as an indicator of solvent degradation. To simulate the behavior of the plant at different experimental conditions and with each solvent, a dynamic model has been developed, on the basis of the validation of a fast reaction regime. It reproduces accurately the pilot plant’s behavior during the absorption and stripping phases. Among the solvents’ physical properties, the effect of viscosity appears to be the most critical for the CO2 absorption efficiency. Kinetics of solvent degradation has finally been optimized to match experimental observations. Of the three solvents studied, 1MPZ/PZ is the most stable, whereas MEA and MDEA/MEA have quite similar degradation rates.

Development of a Predictive Model to Correlate the Chemical Structure of Amines with Their Oxidative Degradation Rate in a Post-Combustion Amine-Based CO2 Capture Process Using Multiple Linear Regression and Machine Learning Regression Approaches

“…Generally, the degradation of any amine solution used in the CO 2 capture process occurs via thermal and oxidative degradation pathways. The first one usually occurs at high temperatures in the stripper (100–150 °C) and in the presence of CO 2 . − The second one mainly takes place in the presence of oxygen (O 2 ), NO x , SO x , and free metal ions under absorber conditions . It can also occur in the rich solvent at the cross-exchanger outlet at 100–145 °C .…”

“…20−24 The second one mainly takes place in the presence of oxygen (O 2 ), NO x , SO x , and free metal ions under absorber conditions. 11 It can also occur in the rich solvent at the crossexchanger outlet at 100−145 °C. 25 In the case of the oxidative degradation pathway, two main mechanisms, namely, electron abstraction and hydrogen abstraction, have been proposed in the literature.…”

“…They typically occurr during the plant start-up and operation. Amine degradation is one of the serious operational problems that occur through side reactions with CO 2 and other flue gas components. − It causes the reduction of process efficiency due to solvent loss that requires a fresh solvent to be made up in order to maintain the CO 2 capture performance efficiency. , In addition, the generated degradation products also cause other severe operational problems such as foaming, fouling, , increased viscosity, corrosion, and environmental issues due to waste disposal and generated volatile compounds. − The additional cost from these problems is estimated to be about 10% of the total CO 2 capture cost …”

Process Intensification of CO2 Desorption

“…Additionally, the solvent regeneration temperature is high (373–413 K), resulting in solvent degradation. Thus, compensating for the solvent loss and corrosion caused by the formation of harmful degradation byproducts increases the OPEX. − Although chemical absorption methods can achieve a high capture efficiency, the considerable amount of energy required for solvent regeneration is the main drawback of this technology …”

Highly efficient capture of CO2 through the synergy of intramolecular amines within piperazine‐derived alcoholamines

“…Ring-structured molecules are known for their relatively robust physicochemical stabilities, 22,23 as evidenced by the negligible degradation of piperazine (PZ) during the chemical absorption of acid gases. 24 Moreover, the low steric hindrance of PZ can help to enhance the absorption rate for acid gases. 25,26 Unfortunately, the limited solubility and low desorption ability of PZ have hindered its further application.…”