Preparation And CO₂ Adsorption Of Biomass-derived Nitrogen-Doped Porous Carbon

CO2 emission has caused the global warming and serious environmental problems,since CO2 is a major greenhouse gas.It has been reported that the CO2 concentration of atmosphere has arrived 408 ppm.It is an urgent issue to mitigate the CO2 emission and thus reduce the global warming effect CO2 capture and storage have been proposed as an effective method to reduce the CO2 emission.Among various CO2 capture techniques,adsorption by sorbents has many advantages such as low capital investment costs,ease of operation,low energy expenditure,ease of adsorbent regeneration and no corrosion problem,to name a few.The key of this technology is finding solid materials with superior CO2 capture properties.Among various solid porous materials,porous carbonaceous sorbents have manifested many merits including facile synthesis,low synthesis cost,large accessible surface area,easy control of porosity and surface functionality,inertness to both bases and acids,and high resistance to moisture.Thus,porous carbonaceous sorbents have been proposed as the most promising sorbents in the CO2 capture application.In this thesis,nitrogen-doped porous carbons were synthesized through carbonization,nitrogen doping and chemical activation reactions using biomass materials coconut shell and glucose as the precursors.The CO2 adsorption properties of these carbonaceous adsorbents were carefully investigated.The summaries of the results are as follows:1?A series of porous carbons were developed by carbonization and KOH activation of coconut shell.Different techniques such as nitrogen sorption,X-ray diffraction,scanning emission microscope,transmission electron microscopy were used to characterize these sorbents.These coconut shell-based carbons show high CO2 capture capacities in a range of 3.56-4.23 mmol/g and 4.63-6.20 mmol/g at 25?and 0? under 1 bar,respectively.Owing to the high amount of narrow micropores within the carbon framework,the porous carbon prepared at KOH/precursor ratio of 3 and 600?(C-600-3)exhibits the highest CO2 adsorption capacity among all the samples.In addition to the high CO2 uptake,these samples also show fast adsorption kinetics,moderate heat of adsorption,high CO2 over N2 selectivity,excellent recyclability and stability,and superior dynamic CO2 capture capacity.The application of coconut shell as precursors for porous carbons provides a cost-effective way for the development of better adsorbents for CO2 capture.2.Nitrogen-doped hydrochar precursors were obtained by one-step hydrothermal reaction of the aquesou solution of glucose and urea.A series of nitrogen-doped porous carbons were subsequently synthesized by KOH activation under different conditions.These glucosesbased carbons show high CO2 capture capacities in a range of 3.42-4.26 mmol/g and 5.24-6.70 mmol/g at 25? and 0?under 1 bar,respectively.The porous carbon prepared at KOH/precursor ratio of 1 and 650?(GN-650-1)exhibits the highest CO2 adsorption capacity among all the samples at 25? and 1 bar,which is attributed the synergetic effect of narrow microporosity and nitrogen content.These glucose-based carbons also have many merits such as good CO2/N2 selectivity,high reusability and stability,fast CO2 adsorption kinetics and excellent dynamic CO2 capture capacity.When combined with the low cost of the glucose precursor,these properties make them exceptionally attractive sorbent candidates for CO2 capture.3.A series of nitrogen-doped porous carbons were synthesized by hydrothermal reaction of biomass D-glucose followed by urea modification and K2CO3 activation.This series of carbons display high CO2 uptake at 1 bar,up to 3.92 mmol/g at 25?and 6.23 mmol/g at 0?.It is found that the synthetic effect of nitrogen content and narrow microporosity determine the CO2 capture capacity under ambient condition for these N-doped porous carbons.Additionally,these sorbents possess quick CO2 adsorption kinetics,high reusability,modest heat of CO2 adsorption,high CO2/N2 selectivity,and excellent dynamic CO2 capture capacity under simulated flue gas conditions.