Preparation And CO₂ Adsorption Perfornmance Of Silica-based Solid Amine Sorbents

Solid amine sorbents prepared by modifying porous materials with amino groups,as new CO2 capture materials,have become one of current research hotspots in the field of CO2 capture.The large specific surface area of porous materials can improve the uniformity of amino groups and increase the contact area between amino groups and gas phase.Solid amine sorbents possess several advantages such as simple operation,weak equipment corrosion,low regeneration energy and so on that overcome the shortcomings of amine solutions.In this paper,based on the review of current researches on CO2 capture technology and solid amine sorbents,new solid amine sorbents possessing outstanding adsorption performance were prepared through wet impregnation method using porous silica-based monoliths as the amines carrier.The synthesis mechanism of silica-based monoliths as well as the adsorption conditions and behaviors of the sorbents were investigated in detail,providing new ideas for the development and application of solid amine sorbents.The results are as follows:(1)Porous methylsilsesquioxane(MSQ)monoliths with pore diameter of 0.5-5?m and specific surface area of 483 m2·g-1 were prepared via sol-gel process accompanied by phase separation,using methyltrimethoxysilane(MTMS)as precursor,0.01 mol·L-1 hydrochloric acid as catalyst,methyl alcohol as solvents,propylene oxide(PO)along with ammonia chloride(NH4Cl)as phase separation inducer.MSQ-PEI solid amine sorbents were prepared by modifying the as-prepared MSQ monoliths with polyethyleneimine(PEI).When loading 40 wt%PEI on the monolith,MSQ-PEI-40 sorbent reaches the highest CO2 adsorption capacity of 1.23 mmol·(g sorbent)-1.(2)Solid amine sorbents were prepared via loading amines on porous silica monoliths with co-continuous macropores,which were synthesized using tetramethoxysilane(TMOS)as precursor and poly(ethylene glycol)(PEG)as phase separation inducer.A series of characterization results show that PEI is successfully loaded in the pore channels and the mass of PEI changes little during the preparation process.The use of PEI has a remarkable improvement on the CO2 adsorption capacity.The highest CO2 adsorption capacity of 1.61 mmol·(g sorbent)-1 is obtained at 75 ? in the CO2 partial pressure of 100 kPa for the porous silica monoliths loaded with 50 wt%PEI,and the MP-PEI-50 sorbent shows good regeneration performance after six adsorption/desorption cycles.(3)PT-PEI solid amine sorbents were prepared by loading PEI on hierarchically porous silica monoliths with macropores-uniform spherical mesopores structure,which were synthesized adding poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)(P123)as phase separation inducer and templates,1,3,5-trimethylbenzene(TMB)as swelling agent.During the modifying process,PEI is distributed in the pore channels in the skeletons first.When the pore channels are all filled,PEI mainly coats the outer surface of frameworks and scatters in macropores until almost all the surface is completely covered by PEI.When loading 60 wt%PEI on the monolith,the highest CO2 adsorption capacity of 2.44 mmol·(g sorbent)-1 is obtained at 75 ? in the CO2 partial pressure of 100 kPa,and the adsorption capacity of PT-PEI-60 only decreases 4%of initial capacity after eight adsorption/desorption cycles,showing good regeneration performance.Generally speaking,PT-PEI solid amine sorbents possess better CO2 adsorption performance and are more suitable for practical applications.