Design And Synthesis Of Porous Carbon-based Adsorbents For CO₂ Adsorption And Their Regeneration Performance

Porous carbons have attracted considerable attention due to their wide availability,designable structure and surface chemistry,making them be good candidates for CO2 capture.Although great progresses have been achieved in the preparation of porous carbons,lots of issues including the scalable preparation,design of the morphology,optimization of the adsorption process as well as the regeneration methods of porous carbon-based adsorbents should be further illustrated.This thesis mainly focused on the controllable synthesis of porous carbon-based CO2 adsorbents both in nanoscale porosity and macroscopic architecture.The systematic study of the CO2 adsorption process and the regeneration performance of porous carbons were conducted.The main results of this thesis are summarized as follows:?1?Scalable preparation of nitrogen-enriched carbon microspheres for CO2 adsorptionMonodispersed nitrogen-enriched carbon microspheres with uniform particle size were prepared by simple carbonization of melamine-resorcinol-formaldehyde microspheres.The synthesis is simple,scalable and very flexible,allowing the easy tailoring of the microsphere size and the nitrogen content in the carbon framework.The carbon microspheres possess fine micropores with largest BET specific surface area and pore volume of 796 m²/g and 0.36 cm³/g,respectively.CO2 capture performances were evaluated between 273 K and 348 K,and high adsorption capacity of 4.50 mmol/g at 273 K,1 bar is achieved.Moreover,the carbon microspheres show fast CO2 adsorption kinetics and good regeneration performance.?2?Cellulose-derived nitrogen-doped carbon aerogels for CO2 adsorptionNitrogen-doped high-surface-area carbon aerogels were prepared through polymerization,freeze drying,and carbonization/activation by using cellulose,NaOH and urea as precursor.NaOH could break the intra-/intermolecular hydrogen bonding of cellulose to form uniform dispersion in the solution.Urea could provide nitrogen source and act as crosslink agent during the polymerization process,which makes the carbon aerogels possess robust honeycomb-like 3D network structure.High surface area of 2298 m²/g and pore volume of 2.2 cm³/g are achieved by the good activation effect of NaOH.The well developed micropores and the suitable nitrogen content make the carbon aerogels be good candidates for CO2 capture with the high adsorption capacities of 5.01 mmol/g and 3.32 mmol/g at 273 K and 298 K,respectively.?3?Shape-customizable macro-/microporous carbon monoliths for structure-to-functionality CO2 adsorption and novel electrical regenerationHierarchical carbon monoliths with good mechanical strength were prepared through a fiber felt-reinforcement sol-gel approach,which offers an opportunity to tune and optimize carbon structure both in nanoscale and macroscopic dimension.The hierarchical structure is beneficial for CO2 diffusion and adsorption,and the resulting carbon monolith exhibits high CO2 adsorption capacities of 5.0 mmol/g at 273 K,lbar and 15.9 mmol/g at 298 K,25 bar.In particular,a novel scroll-type carbon monolith is constructed,which can avoid the packing problems arising from the granules or powders of conventional activated carbons.Moreover,owing to the integrated structure and good electrical conductivity,the carbon scroll can be easily regenerated by the low-energy electrical desorption technique.?4?Adsorption and regeneration study of polyethylenimine-impregnated millimeter-sized mesoporous carbon spheres for post-combustion CO2 captureMesoporous carbon spheres were prepared via a suspension assisted sol-gel method using resorcinol-formaldehyde resin as carbon precursor and colloidal silica sol as hard template.The developed mesoporous structure could accommodate high amount of polyethylenimine?PEI?,providing large gas/solid interface.High-molecular-weight PEI is screened to be the optimal amine due to its thermal stability.The addition of diffusion addictive polyethylene glycol?PEG?could facilitate CO2 diffusing into the deeper PEI films,leading to high amine efficiency.The adsorbent exhibits high adsorption capacity of 3.73 mmol/g mg/g for 15%CO2 at 75?.Moisture plays a promoting effect on CO2 adsorption capacity and could suppress the detrimental effect of O2.The presence of O2,SO₂,NO and NO₂ would lead to the decreased adsorption capacity after consecutive adsorption-desorption cycles,due to the irreversible chemical reaction.Thermal swing adsorption,vacuum swing adsorptionand novel electric swing adsorption processes can be employed to regenerate the adsorbents.