Synthesis Of Porous Carbon Monoliths For CO₂ Adsorption

In recently years, the greenhouse effect is becoming more and more serious with the incresing CO2 emission worldwide. As known, carbon dioxide (CO2) is a two-sided gas. It is a main kind of greenhouse gas, on the other hand, it is also an important chemical resource, so CO2 capture and conversion had attracted wide attention from scientific researchers. Among all of the techniques for CO2 capture, adsorption method had been investigated deeply because of its no corrosion, low power consumption, easy operation, and depth removal, the core in this method is the design and synthesis of the adsorbents. Porous carbons are a kind of efficient adsorbents due to their hydrophobicity, developed porousity, recycling stability, low cost and low renewable energy consumption. Polymer-based porous carbons are synthesized chemically, their pore structure and surface functional group can be controlled precisely. In addition, the doping method can be used to meet the needs of adsorption under different conditions.In this study, a series of carbon nanosheets monoliths were designed and prepared. The macropore structures of the samples were tuned in order to enhance the volumetric capacity. In addition, oxides doped carbon monoliths were synthesized and their adsorptive properties at varied temperatures(50-150℃) were studied. The specific content is as follows:(1) To enhance the CO2 capacity on a volumetric basis of carbonaceous adsorbents, a series of porous carbon monoliths were prepared by using resorcinol and formaldehyde as the carbon precursors and graphene oxides with varied sizes as the sheet-directing agents. We can realize the variation of the macropore volumes but retaining the micropore structure, surface groups identical of the obtained monoliths. The SBET was about 500 m2 g-1, micropore volume was about 0.23 cm3 g-1, and the pore size concentrated at ca.0.5 nm. The results indicated that the macropore diameter varied from 0.6μm to 1.8μm, and fitted linear correlation with the graphene oxides mixing proportion. The adsorption capacities at 273 K and 800 mmHg for all of the adsorbents were about 3.8 mmol g-1, and the CO2 capacity on a volumetric basis of the sample consist of small size carbon nanosheets was ～2.5 times higher than the sample consist of large size carbon nanosheets. The separation ratios of CO2/N2 and CO2/CH4 gas mixture were 15.9 and 3.3, respectively. In addition, all of the monoliths had excellent recycling stability, and can be regenerated easily through argon blow at ambient temperature.(2) In order to improve the adsorption property of porous carbons at elevated temperature other than room temperature, Laponite was doped into the carbon framework. A series of samples were prepared through changing the dosage of Laponite. SBET of the typical sample was 797 m2 g-1, micropore area was 353 m2 g-1, the adsorption capacities at 298 K and 343 K,800 mmHg were 2.64 mmol g-1 and 1.24 mmol g-1 respectively, and the separation ratio of CO2/CH4 gas mixture was 4.0. The isosteric heat of adsorption of the sample was 42 kJ mol-1, which indicated the strong interaction between CO2 and the adsorbent.