Study On The Effect Of High Performance Porous Carbon Materials On The Adsorption Performance Of Low-concentration CO₂

The large amount of CO₂ emissions caused by industrial production has caused increasingly serious environmental impacts.Therefore,CO₂ emission reduction has become one of the urgent problems at home and abroad.Carbon capture utilization and storage?CCUS?technology is an important type of CO₂ emission reduction technologies.Among them,CO₂ capture technology is an indispensable part of CCUS technology,but it faces a major bottleneck of excessive cost in the development of technology,and the adsorption method is expected to significantly reduce costs.Carbon materials in solid adsorbents have become research hotspots due to their unique pore structure,high specific surface area,good thermal stability and chemical stability,and low production costs.This thesis focuses on the capture of CO₂ in the flue gas,and adjusts the surface chemical properties and pore structure of the carbon material to obtain a series of high-performance materials.Based on systematic characterization and evaluation,the structure-activity relationship is summarized.The main research results include:1.In view of the heterogeneous doped carbon materials,the existence of pore development and the heterogeneous functional group concentration require different carbonization temperatures,which reduce the doping level,ultimately leading to an unsatisfactory CO₂ adsorption.By using potassium with better thermal stability as the carbon's dopant of the material has developed a method for anchoring potassium species on the carbon surface,and a series of"rivet-modified"carbon materials named as PTCs?potassium tethered carbons?have been prepared.After calcining PTC at high temperature,a series of new carbon materials named as PICs?potassium intercalated carbons?,were synthesized.Characterizing the series of samples by FT-IR,XPS,TG-MS,and N₂ physical adsorption,we found that carbon reacts with K species during high-temperature calcination.This reaction not only causes new pores in the carbon material,but the K ions were successfully embedded in the carbon matrix,which changed the surface electric field distribution of the obtained material.In addition,the micro-meso-porous multi-stage channel structure in the formed PICs sample also has significance for the improvement of CO₂ adsorption performance:micropores make CO₂ molecules can interact with the pore walls on both sides,and provide an advantageous site for CO₂adsorption;mesoporous channels can greatly reduce the mass transfer resistance of CO₂ and improve the utilization efficiency of micropores;meanwhile,high-temperature calcination causes the material to be introduced into the surface in the early stage.The problem of decreased specific surface area due to the blockage of some pores caused by functional groups and potassium species was also fixed,and finally the PICs samples had better characteristics such as specific surface area and pore size distribution.The interaction between the potassium-supported species and the carbon matrix during this reaction can be regarded as an"in situ activation"process.Through the activation process in this reaction,the material finally has a prominent pore structure,surface chemistry,and CO₂ adsorption performance.The above characteristics have an important influence on the CO₂adsorption performance of the material.At the optimal calcination temperature?700 ^oC?,the sample PIC-700 not only shows a CO₂adsorption up to an amount of 5.23 wt.%under flue gas conditions,but also has a good cycle stability and regeneration performance.2.For the surface chemical modification of carbon materials,the steps of"concentrated acid oxidation?K ion exchange?high temperature calcination"are more complicated,which is not conducive to the subsequent preparation and scale-up of materials,and the high degree of dispersion of potassium species in PICs still has negative effects on the rapid adsorption and desorption kinetics of original carbon materials.By removing the template agent F127 and adding nitrogen source melamine,a carbon material precursor was synthesized by a solventless method,and then a high-temperature carbonization and KOH activation method were used to synthesize a microporous carbon material rich in N atoms.It was found that due to the loss of the guiding effect of F127,the obtained material did not have mesoporous characteristics,but had a large number of micropores.After KOH activation,the carbon can further increase the micropore content.The micropores and ultramicropores in the structure can simultaneously interact with CO₂ molecules through the pore walls on both sides,thereby forming efficient adsorption sites.In addition,by adding melamine to the preparation,nitrogen-containing functional groups can be introduced into the final carbon material.This species effectively modifies the surface electric field distribution of the carbon material,thereby strengthening the interaction between the material and the CO₂molecules,thus improving the CO₂ adsorption performance of the sample especially under the condition of low concentration of CO₂.By optimizing the carbonization temperature,the amount of KOH introduced,and the activation temperature,we found that the NPR-K600 sample obtained at 700 ^oC carbonization,a KOH/C ratio of 1:1,and an activation temperature of 600 ^oC has the best flue gas CO₂capture performance.Under flue gas conditions,the CO₂ adsorption capacity of the material reaches 5.41 wt.%,and the material absorption-desorption rate is extremely fast.At the same time,the material has a higher CO₂/N₂ adsorption selectivity and reversible cycle performance.