Applied Fundamental Research On CO₂ Capture Using Aqueous Potassium Lysinate Solutions From Power Plant Flue Gas

Carbon dioxide capture,utilization and storage（CCUS）is one of the key technologies for global climate change and reducing large-scale carbon emissions from coal-fired power stations.Chemical absorption is the most common used and feasible method.But high energy consumption and costs is still the major obstacle for industrial applications.Compared with the conventional aqueous alkanolamines,amino acid salts（AAS）have been paying more attentions recently,due to their advantages such as low volatility,low toxicity and good resistance to degradation.Among these absorbents,basic amino acid salts,especially for aqueous potassium lysinate（LysK）,have shown excellent features on kinetics of CO₂ absorption.However,limited information is available on their absorption performance,thermodynamic equilibrium and desorption features under the flue gas conditions for post-combustion capture,which is highly valuable for further design and applications with reliable experimental data.In this thesis,we have investigated the capture performances such as the absorption and desorption rate of CO₂,cyclic capacity and heat of absorption for aqueous LysK and aqueous monoethanolamine（MEA）at the simulated flue gas conditions in a screening absorption-desorption setup.Their stability at extreme conditions was analyzed qualitatively.CO₂ solubility in aqueous LysK at various conditions was determined and the experimental data were interpreted by thermodynamic empirical modellings.Meanwhile,the effect of solid acids on thermal regeneration was discussed in order to reduce the heat duty for solvent regeneration.It was found from the a comparative study on CO₂ capture performance that,the comparable absorption rate(about 5.0 x 10^-4mole/（L·s）)and absorption capacity（2.5mol/kg）for aqueous 2.5M LysK and aqueous 5.0 M were observed at 313K.However,the effect of temperature on desorption rate of CO₂-rich LysK solution was emphasized.Results show that there is no significant change in solvent behavior after eight cycle runs of absorption（313K）-desorption（379K）and from qualitative analysis of ¹³C NMR spectra when compared with the fresh absorbent,and the average cyclic capacity is about 1.36mol CO₂/kg solution,which is a litter higher than conventional MEA（about 1.10 mol CO₂/kg）.The heat of absorption of CO₂ in aqueous 2.5M LysK decreases when CO₂loading is greater than 0.8 mol/mol.A rapid decrease in the enthalpy value was observed with increasing CO₂ loading.Thermal degradation of aqueous LysK was not found at423K and nitrogen gas exposure for 15 days.But the decrease about 12%in total alkalinity under O₂ exposure at 423K reveals that oxidative degradation happened.It was also observed that CO₂ loading had a little effect of on degradation rate.The vapor-liquid equilibrium（VLE）data for the system of CO₂-LysK-H₂O at temperatures from 298 to 393 K was measured in a stirred reactor.It was observed that CO₂ solubility,i.e.CO₂ loading,decreases with the increase in temperature and the concentration of LysK,and increases with the increasing CO₂ partial pressures over the solutions for any given concentration and temperature.Data were interpreted using a semi-empirical model and a Kent-Eisenberg model.The predictions from the semi-empirical model,i.e.CO₂ partial pressure as a function of CO₂ loading and temperature,match well with the experimental data within 20%average absolute deviation（AAD）.In the modified Kent-Eisenberg model,the non-idealities of the systems are lumped into the apparent equilibrium constants of carbamate hydrolysis and amino acid deprotonation expressed as a function of temperature,CO₂ loading（expressed as mole CO₂ per mole LysK）and LysK concentration.The parameters were correlated by Matlab software to fit the experimental solubility data.The proposed model satisfactorily predicted the VLE data for the H₂O-LysK-CO₂ system with an AAD within 10%.The addition of solid acids into the aqueous CO₂-loaded LysK solutions can improve the desorption performance by reducing the regeneration temperature or increasing the CO₂ amount released.For the screening study using the six solid acids,under the same operational conditions,the more the addition amount of solid acids,the more the CO₂amount released.It was found that Br?nsted acids can enhance desorption efficiency greatly.Among them,the solid acid resin（MAC-3）can increase the desorption efficiency from 28%to 60%when its addition amount is about one third of solution mass,compared with the same conditions without solid acid.In summary,the comparable absorption rate and absorption capacity,higher cyclic capacity and better resistance to thermal degradation compared with MEA,reveal that the aqueous LysK can be considered as a promising alternative for the conventional MEA.However,more work needs to be done for further validation before taking action for the practical use in future.