Preparation,Modification And Performance Evaluation Of CO₂ Adsorbent Derived From Coke Powder

The CO₂ emission from burning of fossil fuels has been proved to be the main contributor to global warming.CO₂ capture is an effective way to solve the global warming problems and control carbon emission.Traditional aqueous amine-based process is widely used for capturing CO₂,but it possessed the disadvantages involving high energy cost,apparatus erosion and solvent degradation.Compared to the traditional aqueous amine-based process,adsorption is an effective separation technology because of its easy regeneration,less damage to equipment and superior cycling capability.However,the adsorbents used in adsorption process encountered the disadvantages of complex preparation process and high cost,which limited their large-scale utilization.Therefore,it is urgent to develop new materials with cost effective and good adsorption performance so as to accelerate its industrial application.Semi-coke is the solid by-product produced in the low rank coal pyrolysis.There are about 10%semi-coke with small size?<3 mm?.Coke powder has low chemical activity,high fixed carbon content,low volatile content and low sulfur content.There is a large amount of coke powder,which is difficult to be used efficiently.If coke powder could be as carbon precursors to develop adsorbents for capturing CO₂ from flue gas,this would be an effective way to realize high-value and resource utilization of coke powder.In order to realize the effective capture of low concentration CO₂ in flue gas,the key point is to realize the targeted control of the pore structure and surface chemical properties of the coke powder.In this paper,the microporous coke powder based CO₂ adsorbents were prepared using water vapor activation method.First,we investigated the effect of preparation parameters on the pore structure of coke powder based CO₂adsorbents and corelated its pore structure with CO₂ sorption performance.Second,the amine-functionalized coke powder based CO₂ adsorbents were developed by wet impregnation method with tetraethylenepentamine?TEPA?and diethanolamine?DEA?to improve the interaction between sorbent and CO₂molecule.The effects of different amines modifiers on amine efficiency and CO₂adsorption performance were analyzed.The main obtained results are described as follows:?1?Deashing before activation is effective approach to achieve coke powder based CO₂ adsorbent with microporous structure.The activation conditions played important roles in the developing of pore structure of sorbents.The optimal activation conditions were found to be 700°C,70 min,and a water vapor flow of 150 mL/min.The sorbent obtained under these conditions had a CO₂ adsorption capacity of 0.85 mmol/g at 40°C and 15%CO₂/N₂ atmosphere,exhibiting high selectivity with CO₂.Compared with commercial activated carbon?0.5 mmol/g?,the coke powder based CO₂ adsorbent has the better adsorption performance because its pore structure is beneficial to adsorb CO₂.?2?The CO₂ adsorption capacity was greatly improved after TEPA modification.Among the modified coke powder based sorbents,the sorbent loading 30 wt%TEPA had the highest CO₂ sorption capacity?1.63 mmol/g?at60°C and 15%CO₂/N₂ atmosphere.It can be seen that sorbents has good thermal stability from the TG curves of modified coke powder based CO₂ adsorbent.After10 adsorption-desorption cycles,the CO₂ sorption capacity dropped from 1.63mmol/g to 1.52 mmol/g,which showed good regeneration performance.?3?DEA with hydroxyl was further selected to modify the coke powder based adsorbent,and the CO₂ adsorption performance was investigated.When the weight loading for DEA was 50%,it had the highest CO₂ sorption capacity at60°C and 15%CO₂/N₂ atmosphere,and after 10 adsorption-desorption cycles,the CO₂ sorption capacity decreased to 1.95 mmol/g,which indicated that it had good regeneration performance.Moreover,the DEA modified coke powder based adsorbent has a fast adsorption-desorption rate and can realize the efficient capture of CO₂.?4?Compared with TEPA,DEA has a small molecular diameter,so DEA had higher load capacity,which can increase the CO₂ adsorption capacity.When DEA loading was 50%,the N content was 7.31 wt%and the amine efficiency was 0.39;when TEPA loading was 30%,the N content was 10.04 wt%and the amine efficiency was 0.23,which indicated that the amine efficiency was higher after modification with DEA.The possible reason is that the-OH in DEA changes the reaction mole ratio of amine active site with CO₂ molecular from 2:1to 1:1,which increased the effective utilization rate of N and made the CO₂adsorption performance better.