| dc.description.abstract | Global warming has become one of the world’s most important challenges over the last decades and carbon dioxide (CO2) emissions are determined to be a major contributor. Various carbon dioxide capture and storage (CCS) technologies are available worldwide but post combustion CO2 capture with chemical absorbents is considered today to be the most advanced and mature technology for mitigating CO2 emissions from burning fossil fuels. Implementing CCS has the potential of reducing and reversing the effects of CO2 on global warming and climate change.
In reactive absorption, carbon dioxide chemically reacts to form chemical bond and is thereby moved from a gas to a liquid phase. The chemical reaction is reversible and CO2 is released from the solvent during regeneration by raising the temperature. Thereby almost pure CO2 is collected, compressed and sent to storage and the regenerated solvent is sent for re-use. Amines are usually employed as absorbents for CO2 capture and monoethanolamine (MEA), diisopropanolamine (DIPA), N-methyldiethanolamine (MDEA) and 2-amino-2- methyl-1-propanol (AMP) are commonly used. However, due to problems associated with alkanolamines, such as their degradation in oxygen rich atmospheres, considerable energy need for solvent regeneration, environmental issues and recycling efficiency, the quest to find alternative candidates is very important.
In this work spectroscopic methods, Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR), are used, to both qualitatively and quantitatively characterize a range of absorbents for CO2 capture including primary, secondary, tertiary or blended amine systems in addition to amine-amino acid absorbents.
Liquid phase speciation is one of the most important experimental data for thermodynamic and kinetic modeling of absorption systems. First a comprehensive standard method for liquid phase speciation in amine and amino acid-CO2-H2O systems by Nuclear Magnetic Resonance Spectroscopy is presented and validated against measurements on monoamine, diamine and amine-amino acid systems. This method was then used for all our measurements presented in the current work. These measurements provide valuable information about the parameters that should be considered when studying different amine, amine-amino acid-CO2-H2O system by NMR spectroscopy.
Carbamate stability is a very important parameter for determining the absorption capacity and regeneration energy requirement. Therefore, 13C-NMR was employed to study the carbamate formation and to estimate the apparent carbamate stability constant in aqueous solutions of CO2 and sterically hindered amine, 2-amion-2-methyl-propan-ol, (AMP) at different temperatures. In order to determine the apparent carbamate stability constant of AMP, a method for separating amine/protonated amine and bicarbonate/carbonate was developed and presented in our work. The apparent carbamate stability constant was reported to be loading and temperature dependency.
Phase change solvents for CO2 capture was another important topic where our research was also focused. Liquid phase speciation of blended aqueous solutions of DEEA/MAPA/CO2/H2O as well as unblended MAPA/CO2/H2O and DEEA/CO2/H2O system is presented here. One of the most important information we can gain from 13CNMR spectroscopy is the ability to distinguish between primary, secondary, di-carbamate and carbonate/bicarbonate species. Blended system of DEEA/MAPA can form two liquid phases after being loaded with CO2 and both phases were analyzed quantitatively by NMR spectroscopy.
Qualitative and quantitative NMR experiments to investigate the liquid phase speciation in amino acids (Glycine, L-Alanine, Taurine, L-Serine and L-Proline) neutralized by equimolar quantities of monoethanolamine amine (MEA) and 2-amino-2-methyl-1- propanol (AMP) were performed at 25°C for different CO2 loadings. AMP was found to have better performance in neutralizing the amino acids and enhancing the bicarbonate/carbonate formation.
Further, studies were performed to develop calibration models for prediction of various systems using Fourier Transform Infrared (FTIR) spectroscopy. Multivariate data analyses were performed to develop the models. Online analysis of monoethanolamine solvent in a pilot plant was demonstrated by application of the developed model using a mobile setup for extractive sampling to an FTIR analyzer. These results showed the possibility of developing a comprehensive multivariate calibrated model such as Partial Least Square (PLS) for on-line prediction and is well suited for analysis of amine solvents, both in the lab and for online process monitoring. | nb_NO |
