Synthetise and Performance Study of Porous Polymer Materials for CO2 Capture
Author:Wang Quan Yong
Supervisor:mi jian guo
Currently, capture CO2 using amine-functionalized porous materials is one of the most promising methods,which can reduce the cost of CO2 capture.Mesoporous silicon and activated carbon are most commonly used to prepare amine-functionalized C02 adsorbent.However,no such adsorbent can meet the demands of industrial process due to their insufficient thermal and mechanical stabilities,short cycle life,low moist resistance,poor thermal conductivity,etc.To overcome these defects,this dissertation is aimed to develop high-efficiency CO2 adsorbent based on high internal phase emulsions(HIPE)for actual application,combing with interface control,amine embedding,and organic-inorganic composite.The main contents are as follows:(1)Firstly,emulsion-templated porous polymers were impregnated with polyethyleneimine(PEI)to prepare polymer composite for CO2 capture.Pore structures of the polymers can be controlled by regulating the contents of dispersion phase,crossing linker,and porogenic agent,and a series of polymer with micro-,meso-,(1～5 nm)and microporous(1～5 pm)structures were prepared.Then the effects of polymer structure,PEI content,and temperature on CO2 adsorption performance were tested.The results show that the macroporous plays the leading role for CO2 capacity.Uniform macropore distribution and suitable surface area are conductive to prepare high-efficiency CO2 adsorbent.CO2 capacity increases as the increase of PEI content.When the PEI content increases to 70%,the polymer still keeps highly-interconnected macroporous structure.The adsorbent exhibits optimum performance at 75℃.With 70%PEI,a high CO2 capacity of 5.6 mmol/g can be achieved.The adsorbent also exhibits good adsorption and desorption kinetics.The resulting time consumptions to reach 90%uptake is 6.5 min,and the time to perform completely desorption is 9.5 min.Meantime,after 50 cycles of C02 adsorption/desorption,the C02 adsorption capacity has not been significantly reduced,with a reduction of about 6.5%compared with the first cycle,showing good stability.(2)In order to largely and steadily load PEI into the polymer matrix and simplify the preparation processes,we utilized the PEI embedding and organic-inorganic hybrid methods to synthesise polymer composite adsorbent.Based on styrene water-in-oil HIPE,PEI and hydrophilic nano-TiO2 particles were added to the water phase.Due to the hydrogen bonding between amine groups in PEI and hydroxyl groups on particle surface,particles can be wrapped by PEI chains.We then used these PEI-enveloped nano-TiO2 particles(in water phase)and Span 80(in oil phase)as the co-emulsifier to regulate the oil-water interfacial tension of styrene/divinylbenzene HIPE.After one-step polymerization of the water-in-oil HIPE,some chain terminals of amphiphilic PEI can be embedded into the polystyrene matrix,resulting in solid connections between PEI chains and polymer matrix to prevent amine leaching and volatilization at high temperature.The effects of the content of internal phase,emulsifier,and PEI on CO2 adsorption performance were tested.When the PEI content reaches 70%,the resulted polymer still shows highly-interconnected macroporous structure.The adsorbent has shown high CO2 capacity of 5.25 mmol/g,rapid adsorption/desorption within 10 min,good moist-resistance in the presence of 10%water,less than 10%capacity loss over 50 cycles in the range of 75-150℃,high thermal diffusivity of 2.8 mm2/s,and strong stress-strain capability up to 0.95 MPa,showing a promising prospect for actual CO2 capture from industrial flue gas.(3)Polymer prepared from traditional HIPE polymerization is a kind of bulk material,which is not suitable for fluidized bed reactors.In order to develop adsorbent which can be directly used in fluidized bed,uniform polymer beads with appropriate density and mechanical strength were successfully synthesized by precipitation polymerization based on acrylamide oil-in-water HIPE via density control and organic-inorganic hybrid.The pore structure of the polymer beads was regulated by nano-TiO2 particles and high speed stirring.The addition of 1%nano-TiO2 particles to the water phase dramaticlly improved the mechanical property,and the stress-strain capability reached 2.32 MPa.Then the polymer beads were impregnated with PEI for CO2 adsorption.The 50%PEI-impregnated polymer beads exhibited a high CO2 capacity of 2.51 mmol/g at 75℃,and can be regenated at 145 ℃ under pure CO2.Using the epoxypropane-modified PEI to impregate the polymer beads,the resulted adsorbent exhibited a CO2 capacity of 2.09 mmol/g at 75℃,and can be regenated at 110 ℃ under pure CO2,showing great energy saving potential.(4)Primary amines in the PEI molecules ware modified by alkylene oxide to obtain oleophilic PEI molecules.The oleophilic PEI was added to toluene as the dispersion phase,and stable acrylamide oil-in-water HIPE was achieved using co-emulsifiers.After precipitation polymerization of the HIPE,PEI-embedded polymer beads with uniform size distribution ware successfully synthesized.With the addition of nano-TiO2 particles,the polymer beads exhibited great mechanical property and met requirement of fluidized bed reactors.Adsorption test showed that the resulted adsorbent presented the best CO2 adsorption performance at 40℃,and could be generated at 110 ℃ under pure CO2,showing great energy saving potential.At the same time,the adsorbent material had faster adsorption and desorption kinetics.90%adsorption capacity was achieved within 18 min,and the adsorbent material can be completely regenerated within 15 min.After 20 adsorption/desorption cycles,the CO2 capacity adsorption remained the same,showing good stability.