Solid Amine Sorbents For CO₂Capture

Solid amine sorbents have attracted considerable attention due to their high efficiency and selectivity for CO2capture from gas mixtures. Although great progress has been achieved in advancing the support, the systematic study of the CO2adsorption on the solid amine sorbents including facilitating the CO2kinetic diffusion to improve the CO2capture capacity, the relation of porous structure and application performance, capturing of low-concentration CO2on solid amine sorbents at ambient temperature and optimizing morphology of the support is still limited. Moreover, the current solid amine sorbents only have a small capture capacity and low utilization ratio of the amine compound. This thesis mainly focused on the impregnation of amine on the mesoporous supports to obtain the solid amine sorbents for CO2adsorption. The CO2adsorption capacity over the solid amine sorbents with control structures were detailed studied and the CO2capture materials with a large adsorption capacity, high selectivity and sorption/desorption rates were developed. The main results of this thesis are summarized as follows:(1) Process conditions of CO2capture using polyethylenimine-loaded mesoporous carbons:Mesoporous carbon was synthesized via a combined sol-gel process and hard templating and a supercritical drying process. Solid amine sorbents was obtained by impregnated with different amines. Mesoporous carbons impregnated with low molecule amines (MEA, DEA and DETA) had low CO2adsorption capacities owing to the decomposition at high temperature while mesoporous carbons impregnated with PEI and TEPA showed an excellent CO2adsorption performance at75℃. The addition of ECH could improve the performance of MC-TEPA in the cyclic process. The optimal PEI loading was fixed to be65wt.%with a CO2adsorption capacity of4.82mmol/g in15%CO2/N2at75℃, owing to low mass-transfer resistance and high utilization ratio of the amine compound (63%). Moreover, the sorbents have very good water tolerance, which is significant in eliminating the need for strict humidity control prior to CO2capture.(2) Improvement of CO2adsorption capacity based on the balance of kinetic diffusion and thermodynamic adsorption. A new strategy to improve the CO2capture performance of solid amine sorbents was developed. The CO2-neutral surfactant was introduced into polyethylenimine (PEI) to create extra CO2transfer pathways, facilitating CO2diffusion into the deeper PEI films. The addition of surfactants could break the bulk PEI film or its CO2 adsorption product from a compact entity into a dual interpenetrated composite, allowing the diffusion of more CO2into the deeper PEI films. Consequently, the surfactant-promoted sorbents offered increased amount of reactive sites and high utilization efficiency of amine groups for CO2capture, leading to an enhanced CO2capture capacity, especially for the sorbents working at low temperature. This method of introducing CO2natural surfactant into solid amine sorbents to improve adsorption performance is universal for different supports and different amines. For the hierarchical porous silica support, Span80was screened to be an optimal candidate and a maximum adsorption capacity of4.96mmol/g was achieved at7wt.%of Span80, which was26%greater than the surfactant-free sorbent. The surfactant-promoted sorbents also exhibited much better adsorption kinetics and regeneration performance.(3) Solid amine sorbents for low temperature CO2capture. A novel high efficiency solid amine sorbents were developed for regenerative removing CO2at low temperature. The adequate pore volume, proper pore size and interconnected3D framework of as-prepared MC allow the easy dispersion and immobilization of PEI within their channels. The structure generates considerable gas/amine interfacial area and provides access to fast CO2diffusion for reactivity with the amine groups. In addition, the kinetic inhibition to CO2diffusion within the PEI films could be alleviated by the introduction of polymer surfactant, offering increased amount of reactive sites and higher utilization efficiency of amine groups. The highest adsorption capacities of4.67mmol/g at30℃and2.80mmol/g at0℃are attained. They also show fast kinetic, a good selectivity for CO2/N2separation, and very reversible and durable CO2capturing performance at low temperature.(4) Adsorption of low-concentration CO2on mesoporous carbon-based solid amine sorbents. Surfactant promoted mesoporous carbon-based solid amine sorbents were employed for low-concentration CO2capture at ambient temperature. The adsorption behavior toward CO2(0.5vol.%) was investigated in a fixed-bed column. After the addition of span80, the adsorption capacity reached3.3mmol/g and the amine utilization ratio of50.8%at25℃. In comparison to many other types of modified carbon or silica sorbents in the literature, the solid amine sorbent had a higher adsorption capacity at the same temperature. The CO2single component adsorption isotherm at25℃was obtained and fitted well by the Langmuir-Freundlich isotherm models. The deactivation model, capable of describing the uptake of CO2, was applied under various conditions. In all cases, the experimental data agreed with the predicted breakthrough model. The adsorption capacity was also improved by moisture and reached as high as4.04mmol/g (20%RH). The adsorption capacity for CO2remained almost the same after10cyclic regeneration experiments. (5) Solid amine sorbents with controlled morphology for dynamic CO2adsorption. Mesoporous carbon spheres (MCSs) with controlled particle size and pore structure were synthesized via a combined hard templating and sol-gel processing within water-in-oil emulsions, using resorcinol-formaldehyde polymer as carbon precursor and colloidal silica nanoparticles as hard templates. The sphere size of MCSs can be controlled in the range from10to500μm by changing the emulsification conditions. The pore structure of MCSs can be tuned by adjusting the mass ratio of resorcinol-formaldehyde polymer to silica nanoparticles and the diameter of silica nanoparticles. The mesoporous carbon spheres were employed as support for solid amine sorbents and showed a CO2adsorption capacity of2.7mmol/g at25℃, The experimental data of sorbents with different particle sizes were fitted well by the deactivation model models.