Characteristics Of CO₂ Adsorption In AlFu MOFs Pellet Packed Bed

Massive emissions of greenhouse gases contribute to global warming,which have led to a series of problems such as climate change,glacier melting,sea level rise and ecological damage.Carbon dioxide accounts for more than 60%of greenhouse gases,while 41.42%of CO₂ emissions from electricity production among many CO₂ emission sources.Therefore,carbon dioxide capture in power plants is an effective measure to reduce carbon dioxide emissions and mitigate global warming.Over the past 20 years,metal organic framework materials（MOFs）have been extensively studied for carbon dioxide capture and separation due to their characteristics of high specific surface area,good thermal stability,adjustable pore size and surface modification.Among many MOFs,aluminum fumarate（AlFu）,a fumarate based metal organic framework material synthesized with water as a solvent,is safe and harmless in synthesis method;In addition,AlFu has a high specific surface area and good water stability and high CO₂ adsorption capacity,which make it have a good application prospect in the adsorption and separation of CO₂ from power plant flue gas.When CO₂ adsorption and separation are carried out on the adsorbent powder packed bed,the gas flow resistance is large,the adsorbent powder is easy to lose stability and dissipation,and it is easy to bond and block pipelines under the wet condition.In order to overcome the above-mentioned shortcomings,the granulation and molding of aluminum fumarate metal-organic framework materials（AlFu MOFs）were studied in this paper firstly,and AlFu MOFs pellets are prepared.Then,the effects of different operating conditions such as gas flow rate,gas concentration,adsorption temperature and humidity on CO₂ adsorption characteristics in AlFu MOFs pellet packed bed were studied.Finally,in view of the actual industrial application process,the pressure swing adsorption（PSA）process of AlFu MOFs pellet packed bed was modeled and simulated,and the CO₂separation performance of AlFu pellets in pressure swing adsorption cycle was investigated.The main research contents and conclusions are as follows:（1）AlFu MOFs was quickly synthesized by solvent method at room temperature,and then AlFu MOFs pellets were prepared using aluminum sol（AS）and sodium carboxymethyl cellulose（CMC）as binders.The results show that AlFu MOFs pellets prepared with CMC as binder have better mechanical strength,and the optimal binder content is 2.5 wt%,AlFu@CMC-2.5 wt%pellet with a mechanical strength of 1.486 Mpa;the CO₂ adsorption capacity of AlFu is 1.31 mmol/g at 35°C and 1 bar,and the CO₂adsorption capacity of AlFu@CMC-2.5 wt%pellets is 96.18%of AlFu powder.In addition,BET,SEM,TGA characterizations on AlFu and AlFu@CMC-2.5 wt%pellet shows that they both have typical microporous structures and same micro-morphology and thermal stability.Part of the pores were blocked due to the addition of the binder,the specific surface area and pore volume of the AlFu MOFs pellet decreased.The specific surface areas of AlFu and AlFu@CMC-2.5 wt%pellet are 837.57 m²/g and 726.06 m²/g respectively,the pore volume are 0.35 cm³/g and 0.33 cm³/g respectively.（2）The CO₂ dynamic adsorption experimental platform was built,and the CO₂dynamic adsorption characteristics of the AlFu MOFs pellets packed bed under dry and wet conditions were studied respectively.The results show that the presence of water vapor inhibits the CO₂ adsorption in AlFu MOFs pellet,and the CO₂ saturated adsorption capacity decreases by 13.7%at 30%relative humidity;In addition,cyclic adsorption experiments under dry and wet conditions show that AlFu MOFs pellet have excellent cyclic stability.After ten cycles,the CO₂ adsorption amount under dry and wet conditions is 94.76%and 96.99%of the initial value,respectively,which also indicates that the presence of water vapor will reduce the CO₂adsorption amount of AlFu MOFs pellets,but will not affect its cyclic stability.（3）The AlFu MOFs pellet packed bed model was established,and the single-bed and double-bed pressure swing adsorption（PSA）process simulation research was carried out.The single-bed four-step PSA process study shows that a longer purge time or a shorter adsorption time is helpful to obtain a high CO₂ recovery rate（99.54%）,but the CO₂ purity will be decreased.Compared with the four-step PSA process,the five-step PSA process can improve the CO₂ purity and the CO₂ capture performance of the PSA process,meanwhile a higher CO₂ recovery rate and productivity can be ensured.In addition,the variation trend and size of CO₂ recovery rate in the double-bed PSA process are consistent with that in the single bed,but in terms of CO₂ purity and productivity,the double-bed PSA process is superior to the single-bed PSA process.Under different adsorption times,the CO₂ purity and productivity in the double-bed PSA cycle are 3.4%and 0.66 mol/kg/h higher than that in the single-bed PSA cycle on average.