The Preparation And Modification Of Porous Carbon For CO₂ Capture

The selective capture of CO₂,as current hot topic in environmental and energy field,have been attracting extensive research recently due to the significant role of CO₂ as a greenhouse gas and a renewable CI source.Selective capturing and recovering CO₂ by economical and energy-efficient pressure swing adsorption technology have spurred much research on custom-designed porous materials as adsorbents.Thus,porous materials,with excellent CO₂ capture performance,have attracted more and more attention from researchers.Among the various adsorbents,the porous carbon shows a high specific surface area,high CO₂ adsorption capacity,low regeneration energy,superior cycling capability and moisture tolerance,which results in its congenital advantage in CO₂ capture field.Therefore,the development of porous carbons with specific structure is of significant importance in CO₂ adsorption.The present study focuses on the chemical synthesis of the porous carbon.We control their pore structure and surface chemical properties by changing the synthesis condition,and then apply to the CO₂ capture field.On the basis of the above study,we preliminarily discuss the relationship between pore structure and surface chemical properties of porous carbon and CO₂ adsorption performance.Specific research contents and results are as follows:?1?On the basis of discarding the effects of surface chemical properties on CO₂ capture performance,the strictly microporous carbon was synthesized by chemical activation using corncob residue as carbon precursor and K₂CO₃ as activating agent.Microporosity of sample is up to 81.6%.Studies have shown that in the case of near surface area,micropore volume plays a more important role in the process of CO₂ adsorption at low pressure?? 1 bar?.CR-700-1.5 shows the highest microporosity and CO₂ adsorption capacity.At 1 bar,the material has extremely high CO₂ capacities of 4.48 mmol g-1?298 K?and 6.92 mmol g-1?273 K?.?2?Based on the study of the effects of activation conditions on pore structure of corncob residue-derived porous carbon,it is found that two possible mechanisms of K₂CO₃ activation:?a?carbothermic reaction leading to surface etching;?b?the formation and widening of pores relating to the CO₂ released from decomposition of K₂CO₃ at the certain temperature in the course of activation,and these pores are suitable to capture CO₂ molecule.All samples have very similar pore size distribution centered about 0.58 nm.The similarity in PSD can be interpreted by “Molecular Imprinting”.?3?Considering that the effects of pore structure and surface chemical properties on CO₂ capture performance,Nitrogen-rich porous carbon was synthesized using Zn?NO3?2×6H2O as metal ion source and C4H6N2 as ligand on the basis of the chemical idea of the coordination between metal ions imidazole.Studies have shown that ZIF-8,with the best dispersion,was prepared by room temperature ventilation drying.For the porous carbon,the change of temperature will not largely affect pore structure of materials when the carbonization temperature reaches a certain value,and nitrogen content of samples decreases with the increase of carbonization temperature.Thus,the increase of carbonization temperature will result in the reducing of CO₂ adsorption capacity;water vapor activation can result in the decreasing of surface area and pore volume of materials,K₂CO₃ activation can result in the broader pore size distribution of materials,carbonization-K₂CO₃ activation can result in the larger aperture of materials,and nitrogen content of the porous carbon dramatically decreases after activation.Thus,three activation methods will result in the reducing of CO₂ adsorption capacity.At 298 K and 1 bar,ZIF-8-700 DC has the highest CO₂ capacity of 4.04 mmol g-1.