CO₂ Adsorption Performance Of Nitrogen-doped Porous Crbons

The concentration of CO₂ in the atmosphere has increased to 403 ppmv at January 2016,123 ppmv higher than the preindustrial period. This has caused serious concerns for climate change, since CO₂ is the main greenhouse gas and therefore a major contributor to global warming. To mitigate CO₂ emissions, carbon capture and sequestration （CCS） is considered to be one of the most promising method. Adsorption via solid sorbent has been proposed as an promising CO₂ capture and storage technique. Generally speaking, adsorption has the advantages of low cost and simple operation, less energy intensive, easy in sorbent regeneration, and no equipment corrosion problems. However, the key of this new technology is to find solid sorbents with superior CO₂ adsorption properties. In this thesis, nitrogen-doped porous carbons have been prepared and their CO₂ adsorption properties have been investigated. The summaries of the results are as follows:1. Using carbonized coconut shell as the precursor, a series of N-doped highly porous carbons were synthesized by ammoxidation process followed by KOH activation under different prepation conditions The resulting carbons were characterized by SEM, TEM, XRD. elemental analysis, XPS, FT-IR and N₂ adsorption and desorption etc. The CO₂ adsorption performance of these N-doped porous sorbents were also tested at 25(C and 0(C under 1 bar. It has been found that this series of porous carbons exhibits high CO₂ adsorption capacities ranging from 3.44-4.26 mmol/g and 4.77-6.52 mmol/g at 25(C and 0(C under 1 bar, respectively. Specifically, the sample NC-650-1 prepared at 650(C with KOH/precursor ratio of 1 shows the highest CO₂ uptake of 4.26 mmol/g at 25(C, which is among the best of the known N-doped porous carbons. This high CO₂ capture capacity is due to the synergy of the sorbent’s high narrow microporosity and nitrogen content. In addition, this sorbent shows rather high CO₂/N₂ selectivity, stable circulation ability and superior dynamic CO₂ capture capacity under simulated flue gas conditions and high initial CO₂ heat of adsorption. Combining other advantages of the sorbent such as easy synthesis and low cost, these coconut shell based N-doped nanoporous carbons is very promising in terms of CO₂ capture.2. To further increase the narrow microporosity and nitrogen content and thus increase the CO₂ uptake capacities of porous carbon, coconut shell was firstly treated with H2O₂ to increase the surface oxygen groups. The introduction of extra oxygen groups is expected to increase the amount of nitrogen incorporated into the carbon matrix in the subsequent ammoxidation process. The nitrogen-enriched carbons obtained after ammoxidation treatment were further activated by KOH to develop their micropore structures. The resulting sorbents were characterized by different techniques. The CO₂ adsorption performance of these sorbents were also tested at 25(C and 0(C under 1 bar. It was found that under the same preparation condition, the sorbents obtained with H2O₂ pretreatment showed higher CO₂ uptake than the one without pretreatment. The highest CO₂ uptake for this series of samples is 4.47 mmol/g at 25(C and 1 bar. This suggests that the H2O₂ pretreatment has a positive effect on the CO₂ uptake of these N-doped porous carbons. Again, the results further confirm that the CO₂ adsorption capacity in the carbon sorbents is determined by narrow microporosity and nitrogen content.3. Using industrial by-product-petroleum coke as the precursor, a series of N-doped highly porous carbons were synthesized by ammoxidation process followed by KOH activation under different prepation conditions. The resulting sorbents were characterized by different techniques. The CO₂ adsorption performance of these sorbents were also tested at 25(C and 0(C under 1 bar. These N-doped carbons show high CO₂ uptake at 1 bar with maximum values of 4.57 mmol/g at 25 ℃, which is higher than those of coconut shell-based N-doped porous carbons. Moreover, this N-doped sorbent shows reasonable selectivity for CO₂/N₂ separation, stable circulation ability, high initial heat of CO₂ adsorption, fast CO₂ adsorption kinetics, and high dynamic CO₂ capture capacity under simulated flue gas conditions. Obviously, these N-doped carbon sorbents are some of the most promising sorbents for CO₂ capture due to their low cost and high efficiency.