Synthesis Of Molecular Sieve Composite For CO₂ Adsorption And Separation

At present,CO₂ emissions from coal burning flue gas account for 40%of the total industrial emissions,but the concentration is about 12%.High total amount and low concentration lead to difficult carbon capture and separation.As an adsorption material,molecular sieve has stable structure and good adsorption performance for low concentration of CO₂,so it has certain industrial application prospects.Unfortunately,molecular sieves with high CO₂ adsorption capacity are highly hydrophilic,and industrial flue gas contains a lot of water vapor.After water is preferentially adsorbed,it will inevitably leade to a sharp decline in CO₂ adsorption performance and a rapid increase in regeneration energy consumption.In addition,the CO₂/N₂ dynamic selectivity of molecular sieve is low and the desorption is difficult.In view of the above problems,this paper uses Na Y molecular sieve as the adsorption active component to synthesize composite materials with low hydrophilicity,high adsorption capacity,high selectivity and strong stability through the way of in-situ growth to compsite with polyacrylate matrix.The main research contents are as follows:（1）The porous polyacrylate material was prepared by emulsion suspension polymerization method as the matrix.The particle size distribution of the matrix material was 0.8-1.4mm,the pore size of the matrix material was mainly concentrated in 1-2μm with well-developed internal pores,providing space for the in-situ growth of molecular sieve crystals and producing a certain limiting effect.The graft of TEPA on the macroporous surface of the matrix material is beneficial to increase the surface energy and promote the impregnation of precursor.The surface energy provided by TEPA allows enrichment of silicon and aluminum sources on the pore surface,which enhances local supersaturation,reduces nuclear barrier formation,promotes crystal growth and creates a large number of lattice defects,thus allowing Na Y/Poly（acrylates）composites with core-shell structure to be prepared.The results showed that the CO₂ adsorption capacity of the composite reached 51.8m L/g at 25℃and 0.1 bar,which was 17.9%higher than that of the pristine Na Y,indicating that crystals growing in confined space have more lattice defects and CO₂ adsorption sites.At 25℃and 40%RH,the H₂O absorption of pristine Na Y was 379.6 m L/g,while the composite material was reduced to240.4 m L/g which was attributed to the fact that the hydrophobic polyacrylate shell can effectively block partial water vapor inhalation.Therefore,the composite material synthesized by in-situ self-assembly not only increases the amount of CO₂ adsorption,but also reduces the amount of H₂O adsorption.（2）In order to further reduce H₂O absorption,a layer of hydrophobic ZIF-8 crystals is then grown in situ on the shallow surface of Na Y/Poly（acrylates）composite to form ZIF-8/Na Y/Poly（acrylates）composite structure.The results showed that the H₂O absorption capacity of the material was further reduced（171.2 m L/g at 25℃,40%RH）,and it took 15.1 minutes to complete the 90%CO₂ adsorption.After 100 cycle tests,the adsorption capacity only decreased by 0.3%.In order to further verify the hydrothermal stability of the material,the composite was soaked in water in a reaction kettle at 110℃for seven days,and the adsorption capacity was only reduced by1.9%.Therefore,the synthesized molecular sieve composite provides a new idea to solve the effect of water vapor in flue gas on the adsorption performance of CO₂.