Research On Preparation And Performance Of Porous Composite Adsorbents For Air Capture Of CO₂

Global CO₂emissions rebound to the highest level ever in 2021,neutralizing the substantial decline in carbon emissions due to COVID-19 in 2020.There is a global extensive consensus and general trend to actively address the greenhouse effect caused by a dramatic rise in carbon emissions.Carbon dioxide capture,utilization and storage（CCUS）is widely considered to be an important technology for achieving large-scale CO₂reductions in the short term,as well as global sustainable energy development.Direct Air CO₂Capture（DAC）is a flexible and efficient technology for negative emission technologies,and has broad commercial and industrial application prospects,as it can break through the constraints of time,space and industrial emission sources of traditional capture methods,which achieves the capture and utilization of distributed CO₂sources.The high energy consumption restriction of variable temperature/pressure is broken by moisture swing technology,it is judged to have been the most promising low energy consumption air capture techniques,as it can achieve ultra-low partial pressure CO₂adsorption and separation under normal temperature and pressure conditions,which using the evaporation free energy of water molecules.Since the adsorbent materials can be used to provide the driving force for the adsorption and separation process by regulating the partial pressure of ambient water vapor,low grade heat could be used from the viewpoint of cascade utilization of energy,which can effectively improve the economics of recycling in the field of DAC capture and has the industrial potential to significantly reduce the energy and cost.However,the economic cost is still an important factor restricting the industrial application of DAC technology.The moisture swing adsorption continues to be the laboratory period of mechanistic research and experimental testing,the kinds of adsorbent materials available are restricted and thermodynamic and kinetic properties of adsorption/desorption are still short of systematic research systematic research.In this paper,the preparation of adsorbent was developed and systematical analysis of adsorption and separation properties was established from the perspective of moisture swing adsorption materials.For the preparation of adsorbents,strong base anion exchange resins with quaternary ammonium functional groups was selected as active adsorption component,and a low-temperature hot pressing method and an improved phase inversion method was used to develop mature and viable methods for the preparation of variable moisture adsorbents by optimizing the parameters of forming temperature,raw material ratio,feeding sequence and stirring time.Compared with six porous carriers:polystyrene（PS）,polyvinyl chloride（PVC）,polyethylene（PE）,polyethersulfone（PES）,vinyl acetate（VA）and cellulose acetate fiber（CAF）,two carrier materials with excellent performance,wide source and low price,vinyl acetate（VA）and cellulose acetate fiber（CAF）,were selected for the synthesis of porous composite adsorbents.The physical and chemical properties of adsorbents were investigated by means of analytical instruments:Benchtop Scanning Electron Microscope,Mercury Injection Apparatus,Universal Material Testing Machine,FTIR Spectrometer,Thermal Gravimetric Analyzer and so on.The findings indicate that the hot-pressing process is convenient,with a short cycle time and low cost,and is appropriate for industrial production processes on a large scale,while the phase inversion method has flexible and adjustable process parameters,allowing precise regulation of the adsorbent’s structure.D290/CAF adsorbent has rich pore structures,higher specific surface area and porosity,good hydrophobic performance;HPR/VA adsorbent has high exchange capacity,high tensile strength,better toughness and good thermal stability.The adsorption/desorption experimental system was used to investigate the mechanisms of temperature,humidity,thickness and CO₂partial pressure.The results showed that the saturation adsorption capacities of the HPR/VA and D290/CAF adsorbents were 0.83 mmol/g and 0.70 mmol/g respectively,and both achieved high quaternary ammonium functional group utilization.The Langmuir single-molecule layer adsorption model can accurately describe the adsorption and desorption thermodynamic processes,and temperature positively correlating with the increase in chemical rate of the adsorption and desorption processes.The modified proposed first order kinetic adsorption rate equation（MPFO）can fit the adsorption kinetic process well.Increasing the temperature significantly reduces the time to reach adsorption equilibrium.The increase of ambient water vapor partial pressure has a significant negative effect on the kinetic performance of the adsorbent,and the adsorption rate decreases with increasing thickness at low CO₂saturation.The adsorption rate of D290/CAF adsorbent was much higher than that of HPR/VA adsorbent in an ultra-low CO₂partial pressure adsorption environment at 400 ppm.MPFO model was established to describe the desorption process,which showed that the higher the temperature,the more thoroughly the desorption of adsorbents.At the same pressure,improvement in the partial pressure of CO₂increases the concentration of the product,which further inhibits the production of CO₂.A reasonable reduction in the thickness of the adsorption materials can increase desorption rate to some extent.