Preparation And CO₂ Adsorption Performances Of Sepiolite-based Solid Amine Adsorbents

With the extensive exploitation and consumption of fossil fuels,excessive CO₂are being pumped into the atmosphere,which have resulted in some serious problems,such as global warming and ocean acidification.The reduction of CO ₂ emissions has became the common recognition of the world.CO₂ capture and utilization of flue gas from coal-fired power plants is the most direct and effective way to successfully realize CO₂ emission reduction.Meanwhile,the demand of efficiently and economically CO₂capture and separation in coal chemical industry is an driving force for the development of CO₂ capture technologies.Recently,CO₂ adsorption by solid amine adsorbents has been drawing increasing interest all around the world because of its low energy consumption,environmental friendliness and high efficiency,which is considered to be a promising CO₂ capture technology.However,the current solid amine adsorbents generally face the problems of high material cost and poor stability,which can't achieve good CO₂ capture performance and low price at the same time.In this work,a series of low-cost solid amine adsorbents were prepared by acid pre-treatment and amine-functionalization based on the industrial sepiolite abundant in xiangtan area of Hunan Province.The adsorption properties were investigated,the adsorbent with high CO₂ adsorption capacity as well as the optimized adsorption process were selected.The main research contents are as follows:1.Industrial sepiolite was pre-treated with HCI to prepare SEP with improved surface area and pore structure.TEPA was then loaded into SEP usin g impregnation method to create TEPA functionalized SEP adsorbent.The effects of amine loading,adsorption temperature,cycle number on CO₂ adsorption capacity were investigated in a thermogravimetric device,the adsorption kinetics and thermal stability of the adsorbent were also studied.Experiment results showed that the optimal TEPA loading was 20%,the corresponded adsorbent of SEP-TEPA-20%obtained the highest CO₂adsorption capacity of 1.76 mmol/g at 50°C,and exhibited good thermal stability.The dynamic adsorption process of SEP corresponded to the Pseudo-first-order model,Pseudo-second-order model and Avrami model can well describe the CO₂ adsorption kinetics of the adsorbent.The CO₂ adsorption capacity decreased by 8.5%after ten adsorption-desorption cycles.2.Industrial grade sepiolite?IG-SEP?was premodified with hydrochloric acid to prepare SEP,the effects acid modificaion was studied.we found that acid pre-modification can increase the purity,specific surface area,pore volume and mesoporous distribution of the sepiolite.A novel TETA functionalized SEP adsorbent was successfully developed by impregnating TETA noto SEP.The adsorbents were characterized by various methods.It was found that TETA functionalized SEP maintained the morphological structure of sepiolite itself,and its surface area and pore volume decreased gradually with the increase of TETA loading.The effects of TETA loading,adsorption temperature,CO₂ pressure and water vapor on CO₂ adsorption capacity were investigated,the thermal stability,cyclic regenerability,adsorption kinetics as well as thermodynamics were also studied.Results show that,when SEP was optimized at 30 wt.%TETA,SEP-TETA-30%attained a CO₂ adsorption capacity as high as 1.93 mmol/g at 50°C with fast adsorption kinetics,and it can work stably under 150°C.The Freundlich model was best able to fit the experimental adsorption isotherm of SEP-TETA-30%,and its isosteric heat of adsorption was 28⁶0 kJ/mol.The dynamic adsorption behavior of TETA functionalized SEP adsorbents were fitted well with the pseudo-second-order model,and the activation energy of CO₂ adsorption on SEP-TETA-30%was calculated to be 8.07 kJ/mol.The presence of moisture in simulated gas has a positive effect on the adsorption capacity without affect the stablity of the adsorbent.After ten cycles of adsorption-desorption,the CO₂ adsorption capacity of the adsorbent dropped by 7%,with good regenerability.3.The optimal amine loading,adsorption capacity,temperature effect,t hermal stability,cycle regeneration performance and adsorption k inetic constants of the selected TEPA and TETA functionalized SEP were compared with other solid amine adsorbents.It was found that the adsorption capacity,cyclic adsorption stability and adsorption rate of TETA functionalized SEP were better than that of TEPA system,and its cyclic adsorption performance and thermostability were also better than the mainstream solid amine adsorbents.4.An cost-efficiency index was proposed to evaluate the practicability and competitiveness of solid amine adsorbents.SEP-TETA-30%exhibited the optimum cost-efficiency,which was higher than SEP-TEPA-20%and other reported adsorbents.SEP-TETA-30%achieved good CO₂ adsorption performance at dramatically lower costs,suggesting it is a promising adsorbent for cyclic postcombustion CO ₂ capture.