Preparationand CO₂ Adsorption Performance Of The New Amine-modified Solidsorbents

With the rapid progress of global industrialization and further increase in energy demand, the greenhouse gas effect, which is caused by the excessive emission of CO₂, has led to serious climate and environmental deterioration. In China, more than70% of primary energy is supplied by the coal-fired power plants, in which the CO₂ emission accounts for approximate 30% of the total CO₂ emissions, and realizing effective CO₂ capture from coal-fired power plants plays great role in bettering the environment and improving China’s international competition. The amine-modified solidsorbents have the merits of simple preparation, low energy loss during regeneration and good adsorption performance, having the potential of realizing industrialization application. However, the active components, such as tetraethylenepentamine（TEPA） and polyethyleneimine（PEI） are characterized by weak thermal stability, high viscosity and easy agglomeration, which largely reduce the efficiency for CO₂ capture. Moreover, the complex process and high cost for preparing porous supports raised the cost for CO₂ capture. In view of the above-mentioned demerits, this thesis centered at reducing the agglomeration and improving the diffusion of TEPA, and reducing the preparation cost for the amine-midofied solid sorbents, prepared a series of amine-modified solid sorbents and studied their CO₂ adsorption performance.1. Preparationand CO₂ adsorption performance of the amine-modified MCM-41 sorbentsprepared using a two-step method.MCM-41 was chosen as the support and 3-aminopropyltrimethoxysilane（APTS） was grafted onto the inner surface of MCM-41,and thenTEPA was impregnated in the pores of the APTS-grafted MCM-41 to prepare a series of solid sorbents.The effects of the weight loading ratios of APTS to TEPA, adsorption temperature and influent velocity on CO₂ adsorption were investigated in a fixed bed reactor, and the cyclic regenerability, adsorption mechanism and kinetics were studied. When the weight loadingsfor APTS and TEPA were 30% and 40%, and the influent velocity was 40 m L/min, the adsorption capacity forthe prapred sorbent was 3.50 mmol/g at 70°C,and after ten adsorption-desorption cycles, the adsorption capacity dropped only 3.43%.The CO₂ adsorption on APTS and TEPA co-modified MCM-41 was a combination process of both physisorption and chemisorption, in which chemisorption was dominated.2. Preparation and CO₂ adsorption performance of the mixed amine-modified MCM-41 sorbents.The TEPA and 2-amino-2-methyl-l-propanol（AMP） were physically mixed andimpregnated in MCM-41 to prepare a series of mixed amine-modified MCM-41 particles.The effects of the weight ratios of TEPA toAMP, adsorption temperature and influent velocity on CO₂ adsorption were investigated, and the cyclic regenerability and adsorption kinetics of the composite sorbents were studied.In addition, the effective amine efficiency was calculated. When the weight loadings for both TEPA and AMP were 30% andthe influent velocity was 30 mL/min, the adsorption capacity for the prepared sorbent was 3.01 mmol/g at 70°C,and afterfifteen adsorption-desorption cycles, the adsorption capacity reduced by 4.32%.The amine efficiency was 0.33, which increased by 94% compared withthe TEPA-modified MCM-41.3. Preparation and CO₂ adsorption performance of the TEPA-modified composite supports with hierarchical mesoporous structures.Mesoporous silica gel（Gel）andMCM-41 were physically mixed to obtain the supporting materials, in which TEPA was impregnated to prepare the composite sorbents with hierarchical mesoporous structures.The effects of the weight ratios of Gel toMCM-41, TEPA loadings, adsorption temperature and CO₂ concentration on CO₂ adsorption were investigated, and the selectivity of the pore size distribution to TEPA was discussed.In addition, the cyclic regenerability, adsorption thermodynamics and kinetics were studied. When the weight ratio of Gel toMCM-41 was 1:1 and TEPA loading was 50%, the adsorption capacity for the prepared sotbent was 4.27 mmol/g, which was significantly better than that of the TEPA-modified MCM-41 and TEPA-modified Gel.During the impregnation of TEPA into the composite supports, TEPA preferred to enter the relatively small pores, which showed higher selectivity to TEPA, and TEPA was well-dispersed in the composite supports.4. Preparation and CO₂ adsorption performance of the TEPA-modified activated coal char.The coal powder which is cheap and easily available was used as the raw material andthe activated char was obtained by passing water vapor through a reactor while pyrolyzing coal at 650 °C, which was further pore-expanded using HCl.Then,the pore-expanded activated char was impregnatedwith TEPA for the preparationof theamine-modified solid sorbents for CO₂ capture. The effects of the coal type, HCl concentration, activation time and adsorption temperature were investigated, and the cyclic regenerability and adsorption kinetics for the prepared sorbents were studied. When the HCl concentration was 6 M and activation time was 120 min, the adsorption capacity for 10 wt.% TEPA-modified Ordos coal char was 3.38 mmol/g at 60 °C, and after ten cycles, the adsorption capacity decreased by 5.6%. The deactivation rate for the TEPA-modified activated coal char was significantly slower than that of the TEPA-modified MCM-41 and TEPA-modified Gel, and the breakthrough adsorption capacity was about 80% of the saturated adsorption capacity, suggesting that the TEPA-modified activated char sorbents could realize effective CO₂ capture from the coal-fired power plants.