Synthesis Of Porous Polymers And Microporous Carbons For CO₂ Capture

Due to the economic growth,the world energy consumption by energy source increases every year.Even though the nonfossil fuels(solar power,hydrogen energy,biomass,etc.)are expected to grow faster than that of fossil fuels,it is predicted that fossil fuels still account for more than three-quarters of world energy consumption up until 2040.And the CO2 emission derived from such energy sources into the atmosphere is becoming a huge threat to our global climate and environment.Therefore,efficient and reversible carbon capture and storage(CCS)technology is one of the potential solutions,which is highly desired.The physical adsorption of CO2 in porous solid materials provides a promising method for selective removal of CO2 from post-combustion capture.In the past few decades,a series of porous solid adsorbents have been developed by scientists,mainly including porous carbon materials,porous organic polymers,molecular sieves and newly-developing adsorbent materials with unique functionality.Among these materials,nanoporous carbons have received increasing interest for CO2 capture owing to their high specific surface area,robust chemical and thermal stability,low regeneration energy,as well as their low cost.However,traditional porous carbon materials have abundant disadvantages,such as poor structural diversity,uncontrolled pore structure and chemical composition.One of the key solution is to use designed POPs(porous organic polymers)as precursors to prepare microporous carbon with tunable pore structure and chemical composition.The main task of this Ph.D.thesis is to synthesize a series of porous polymers with specific structures or heteroatom functional groups via the polymerization of Si,O,N and S-contained monomers.The obtained porous polymers are used as carbon sources to obtain a series of microporous carbon materials with high specific surface area and unique structure by carbonization.The mechanism for the pore structure regulation and the relationship between the N,S heteroatom content of these microporous carbon materials and their CO2 adsorption performance are studied.The main contents and conclusions of the thesis are listed as follows:1.Novel organic-inorganic hybrid microporous polymers with excellent thermal stability,high surface areas(1041 m2 g-1)and controlled pore structure have been prepared by Scholl coupling and Friedel-Crafts reactions by using Octaphenylcyclotetrrasiloxane(OPCTS)as the structural unit.The pore structure of these OPCTS-based microporous polymers can be tuned by the choice of crosslinking agents with different lengths of rigid linking structure.In addition,the prepared microporous polymers can be used as ideal carbon precursor to prepare microporous carbons with uniform micromorphology,narrow pore size distribution,high microporosity(94%)and carbonization yield(58.8%).The hybrid microporous polymers and microporous carbons both exhibit high CO2 adsorption capacities of 8.94 wt%(2.03 mmol g-1)and 14.78 wt%(3.36 mmol g-1)(273 K and 1 bar),respectively.2.High adsorption capacity and selectivity of microprous carbon are critical for the post-combustion CO2 capture.We propose a novel strategy to prepare N-doped microprous carbon with high surface area(2363 m2 g-1 for CPTHB-7),narrow pore size distribution and high ultramicropore ratio(<0.7 nm,68%for CPTHB-6)via a simple chemical activation of a rigid polymer porous framework(PTHB)synthesized via polycondensation reaction of 1,3,5-THB in the presence of nitrobenzene.The as-prepared microprous carbon exhibit high CO2 adsorption capacities of 5.6-6.3 mmol g-1(273K and lbar)and sufficient CO2/N2 selectivity of 12-22 for a 0.15/0.85 CO2/N2 mixture at 298K and 1 bar(conditions of CO2 capture application).The effect of microporosity and N content of our materials on the CO2 adsorption performance had also been investigated.Microporous volume below critical size contributed to the adsorption capacity for CO2,while the N content and nitrogen species play a role in the CO2/N2 selectivity.3.N,S-containing porous polymer was prepared by using cyanuric chloride and thiophene as building blocks.After carbonization,the N,S co-doped microporous carbon materials were obtained by using this polymer as carbon precursor with KOH activation.The prepared microporous carbon material has a large specific surface area of 1631 m2 g-1 and a high microporosity of 96.3%.The CO2 adsorption test shows that the CO2 adsorption capacity of CCTP-6 reached 5.5 mmol g-1(273 K/1.0 bar).In addition,the mechanism of electric double layer capacitor is the charge-adsorption/desorption process.This process is similar to the gas adsorption/desorption process.These N,S co-doped microporous carbon materials also show high supercapacitor properties based on their high specific surface areas.At a current density of 0.5 A g-1,CCTP-7 has the highest specific capacitance of 210 Fg-1.