Phase Separation Behavior Of Amine-based CO₂ Phase Change Absorbents

Chemical absorption is currently the most mature carbon capture technology,but the high energy consumption of traditional absorbents is an urgent problem.CO₂ Phase chang absorbents（CPCAs）have garnered widespread attention due to the potential of saving energy consumption CO₂ capture.Currently,the research on phase change absorbents mainly focuses on the composition screening of novel absorbents and their absorption-desorption performance,while the phase separation mechanism is not clear yet.In this dissertation,combined with experimental determinaton of phase separation behavior,the phase change mechanism was investigated from three sections,which were:interpreting the causes of phase separation from the microscopic intermolecular interactions,constructing a thermodynamic model to correlate the microscopic intermolecular interactions with the phase separation behavior,and proposing a components selection guided by the physical parameters such as the relative E_T（30）and the relative dielectric constant.This work improves the basic theory of CPCAs and provides support for the design of CPCAsEthanolamine（MEA）and diethylenetriamine（DETA）,whose absorption products are carbamates,were used as the reactants with CO₂.Comparative analysis was carried out between the above amines and 14 kinds of phase change agents（physical solvents organic solvents）miscible with water constituting the absorbents.The phase separation state and the properties of two phases was investigated to explore the regularity of phase separation behavior of different systems.The experimental results showed that the hydrophilicity of the phase change agent and the electrostatic effect caused by the salt ions of the absorption products are the main factors affecting the phase separation behavior.A three-component simulation system consisting of salt,phase change agent,and water was constructed.The study dissected the types of interactions in different solution systems and the relationships between component interactions.Energy calculations further clarified that ion-dipole interaction is the predominant interaction in solution.Through the analysis of interactions between salt,phase change agent,and water,it was proposed that the degree of enhancement of self-aggregation of phase change agent due to ion-dipole interaction is the primary factor influencing the differences in phase separation behavior among different systems.This interpretation sheds light on the phase separation mechanism of CPCAs at the microscale.The relative dielectric constant and relative E_T（30）and concentration parameters were introduced into the Fowler-Guggenheim equation,and thermodynamic equations for determining the phase separation state of CPCAs composed of different phase change agents were established.For the most commonly used MEA,the predictability of the phase separation state of the equation was verified to be good by using multiple phase-separating agents.The liquid-liquid phase equilibrium data of MEA+1,4-dioxane/n-propanol/tert-butanol+water phase change absorbent systems were correlated with the E-NRTL model for the CPCA systems,and the binary interaction parameter in the model was obtained.The calculated values of E-NRTL for CPCA systems were in good agreement with the experimental values,which provided the basis for the application and process simulation of the CO₂ absorption by CPCAs.A rapid selection method for phase change agent in CPCAs was proposed using relative E_T（30）and relative dielectric constant.The charges and sizes of the amine absorption products were used as a basis for comparison to predict the phasing of the other amine absorbents,using the MEA carbamate as a benchmark.On this basis,four DETA phase change absorbents for industrial applications were designed,among which the 20wt.%DETA+40 wt.%Diethylene Glycol Dimethyl Ether（DGDME）+40wt.%CPCA has a cyclic CO₂ loading of 3.16 mol·kg^-1,which is 89.8%higher than that of the 20 wt.%DETA aqueous solution.