Design And Preparation Of Porous Carbon Materials And Their Adsorption Performance

Since the time of the industrial revolution, the atmospheric CO2concentration hasrisen by nearly35%to its current level of390ppm. The increased carbon dioxideconcentration in the atmosphere has been considered to be a leading contributor to globalclimate change. To slow this increase, reductions in anthropogenic CO2emissions arenecessary. Large emission point sources, such as fossil-fuel-based power generationfacilities, are the first target for these reductions. A benchmark, mature technology for theseparation of dilute CO2from gas streams is via absorption with aqueous amines. However,the use of solid adsorbents is now being widely considered as an alternative, potentiallyless-energy-intensive separation technology. Recently, porous carbon materials have beenconsidered as the next generation adsorbents due to their high specific surface area, largepore volume, large adsorption capacity, low price, high chemical stability and ease ofsurface decoration. However, the pristine activated carbon has a low CO2uptake capacityand poor selectivity because the interaction between CO2and pristine activated carbon isweak Vander Waals force, belonging to physisorption. To enhance this interaction, it isessential to produce basic sites and increase surface polarity through modification withelectron-donating elements, such as N. Up to now, two different types of strategies havebeen adopted to generate such N basic sites. One is to treat the porous carbons withammonia at high temperatures and the other is to use chemical compounds containingnitrogen as carbon precursor. It has been well documented that the latter is more attractivebecause of its simple synthesis and high nitrogen content.In this thesis, we have synthesized several N-doped porous carbon materials andapplied them for CO2capture and storage (CCS). The results indicated that they all exhibitoutstanding CO2adsorption capatity and high selectivity1. A series of N-doped porous carbon monoliths were synthesized. For the preparationof the N-doped porous carbon monoliths, low-cost, non-toxic, and commercially availablebiomass materials, alginic acid (AA), was subjected to hydrothermal treating in thepresence of pyrrole, ethylenediamine and glutaraldehyde at180oC to form a precursor monolith, which was then freeze-dried and annealed at different temperatures under amixed gas atmosphere (the volume ratio Ar: CO2=3:1). The as-obtained samples atdifferent pyrolysis temperatures are named as AA-750, AA-850, AA-950and AA-1000,respectively. In this synthesis, pyrrole and glutaraldehyde were used as swelling agents andethylenediamine as nitrogen source. The N-doped carbon monolith AA-950exhibitedsignificantly high CO2capture capacity of16.20mmol g-1(298K and20bar).2. Highly porous N-doped carbon monolith has been successfully prepared by usingbinary H3PO4-HNO3mixed acid as a co-activating agent for the first time and sodiumalginate (SA), a natural biopolymer, as carbon precursor. It has a narrow micropore sizedistribution and high content of pyrrolic N. Particularly, the sample SA-2N-P with highsurface area (1740m2g-1) exhibits a high CO2adsorption capacity of8.99mmol g-1at273K and4.57mmol g-1at298K, along with an initial CO2adsorption energy of43kJ mol-1atlower CO2coverage and32kJ mol-1at higher CO2coverage. Remarkably, this sampleshows the high CO2capacity [66.44mg (CO2)/g (adsorbent) at25°C and0.15atm] underlow CO2pressures, which is of more relevance for flue gas applications. Except forexcellent CO2adsorption capacity, the selectivity of CO2over N2is also calculated forbinary mixture at (v (N2):v (CO2))=85:15according to ideal adsorbed solution theory(IAST). Combined with its simple preparation, high adsorption capacity, and highselectivity for CO2, the sample SA-2N-P is one of the promising solid-state absorbentsreported so far for CO2capture and storage.3. N-doped porous carbons have been successfully fabricated via a facile one-potevaporation induced self-assembly (EISA) method under acid conditions. In this process,HNO3not only promoted polymerization as a catalyst, but also served as a nitrogen source.The as-resulted porous carbons possessed a high specific surface area and a high nitrogencontent (up to6.73wt%) and consequently they exhibited excellent performance for CO2capture. Particularly, the CN-950sample with a high surface area of1979m2g-1shows thehighest CO2adsorption capacity of4.3mmol g-1at298K and1atm. Furthermore, it wasobserved that the CN-950sample exhibited a good selectivity for CO2/N2separation, which ispromising for industrial production. 4. Highly basic MgO modified nanoporous carbon composites have been fabricatedvia a facile evaporation induced self-assembly (EISA) strategy and a subsequent heattreatment. Especially, the as-obtained composites intrinsically possess strong basicitywithout the need of post-functionalization. Highly crystalline cubic-phase MgOnanoparticles uniformly disperse in the porous carbon matrix and the composites have largesurface areas (1138m2g-1at maximum) and pore volumes (0.616cm3g-1at maximum).Methanol vapor adsorption is investigated systematically on the C-MgO composites. Thelargest methanol adsorption capacity is up to11.90mmol g-1and this result is veryoutstanding as compared to those of previously reported porous materials. The methanolisotherms exhibit an overall organophilic nature and Langmuir model is applied to describethe methanol adsorption behavior on the C-MgO composites. Furthermore, theC-MgO-15.4%sample with the highest adsorption capacity exhibits high selectivity formethanol/water separation at298K, indicating that the C-MgO-15.4%sample could be apotential adsorbent material for methanol adsorption and separation.