Measurement of Physical Properties of Different Solutions and Investigation of Their Performance as a Solvent for CO2 Capture
Creators: name: RAMEZANI, ROUZBEH
Publisher: name: Universit� degli studi di Genova
Year: 2020

description: Industrial activities such as natural gas purification and fossil-fueled power plants emit high quantities of carbon dioxide (CO2), which is the most significant greenhouse gas and has a significant impact on climate change. The most industrially practiced technology for CO2 capture is absorption into various types of amines, particularly monoethanolamine (MEA). However, these absorbents have a limited CO2 absorption capacity, suffer from solvent losses due to the high volatility in the stripping column, have a high energy consumption in the regeneration step, and are corrosive. Therefore, there is a motivation in finding new alternative absorbents to improve the absorption performance and make post-combustion technology more economical. In this work, after a prescreening, several chemical absorbents including 2-((2-aminoethyl)amino)ethanol (AEEA), methyldiethanolamine (MDEA), piperazine (PZ), triethylenetetramine (TETA), 2-methylpiperazine (2-MPZ), 2-Amino-2-methyl-1-propanol (AMP), monoethanolamine (MEA), trisodium phosphate (TSP), potassium carbonate (K2CO3), potassium salts of sarcosine (K-Sar), lysine (K-Lys), glycine (K-Gly), proline (K-Pro), alanine (K-Ala) and serine (K-Ser) were selected based on their chemical structure and also their potential for industrial application. The use of blended absorbents to develop a new solvent with various advantages is considered a suitable method to improve the CO2 absorption. In this regards, blend solutions of K2CO3/TSP with amine additives, MDEA + Lys and MEA + Lys were suggested as absorbent and their CO2 absorption performance was investigated. Several equipment including stirred cell reactor, Ubbelohde viscometer, Gay-Lussac pycnometer, Benchtop pH meter, Metrohm Autolab were used in this work to study of CO2 absorption different solutions. Experiment measurements were performed at temperatures between 298 and 323 K, CO2 partial pressures up to 500 kPa and various concentrations of solvent. Density, viscosity, corrosion rate and as well as pH of solvents were measured. The CO2 loading capacity of solvent was also determined and the results were compared with other conventional solvents such MEA and MDEA. In addition, the effect of temperature, concentration, pressure and additive type on CO2 loading capacity of solution was evaluated and explained in details. Reaction mechanism between CO2 and different solvents was studied and equilibrium constants of reactions were obtained. Then, a thermodynamic model based
on the modified Kent-Eisenberg theory was successfully developed using MATLAB software to predict experimental CO2 loading data. CO2 absorption heat was another important parameter of solvent which was reported in this work. Heat of CO2 absorption of all of blend solutions was estimated using the Gibbs-Helmholtz method and compared with other absorbents. The absorption rate of CO2 in solvents was measured experimentally using a fall in pressure method. Furthermore, characterization and kinetics of the reaction of CO2 with solvents was studied and described in detail using zwitterion mechanism. In order to study reaction kinetics, it was necessary to obtain several physical properties of solvents. Therefore, the values of the liquid mass transfer coefficient, overall mass transfer coefficient, Henry?s constant, CO2 and N2O diffusivity were calculated. The kinetics parameters of each solvent such as Hatta number, enhancement factor, the reaction rate constant, reaction order and activation energy were found and a rate model was developed to describe the experimental absorption rate data. Finally, toxicity of different amines and amino acids was studied and discussed. In this work, 18 blended solutions including 2 inorganic solvents, 5 cyclic diamines, 1 primary amine, 1 tertiary amine, 1 sterically hindered amines, 6 amino acid salts as solvent for CO2 capture from flue gas were screened in terms of density, viscosity, kinetics, absorption heat, CO2 loading capacity, toxicity and corrosion rate, and the results were explained in details in next sections. The objectives of this work are, a) to develop of novel solvents for CO2 capture, b) to measure chemical and physical properties of solvents, c) to understand the fundamental thermodynamic behavior associated with the CO2 absorption in solvent, d) to evaluate potential of different solutions as solvent for CO2 capture.