| The excessive consumption of fossil fuels has caused a significant growth of anthropogenic CO2 emission, especially in the power plant using coal. The fossil fuels are difficult to be replaced by new and renewable energy within a short period, but reducing CO2 emissions is becoming an increasingly urgent issue. Therefore, the development of efficient technologies for CO2 capture and sequestration (CCS) is urgently required.CO2 capture by solid amine sorbents has attracted much attention due to their higher adsorption-desorption rates, lower energy consumption, and reduced corrosion. However, the support materials used in the preparation of the solid amine sorbents are primarily mesoporous silica. The preparation of these materials is quite complicated, and the cost is high. To reduce the sorbent preparation cost, the commercially available and inexpensive mesoporous silica gel (MSG) was selected as a support in this paper. A series of amine-functionalized MSG were developed for the removal of CO2 from flue gas. The main results are as follows:1 A novel tetraethylenepentamine (TEPA) modified MSG was prepared by wet impregnation method, and the CO2 adsorption performance was investigated in a fixed bed reactor. The results showed that, when the MSG particle size varied from 48 to 75 μm, TEPA loading of 40 wt.%, adsorption temperature of 70℃, and influent flow rate of 30 mL·min-1, the CO2 adsorption capacity reached the maximum value of 2.21 mmol·g-1. Moreover, the adsorption capacity was increased to 2.70 mmol·g-1 by adding a desirable amount of PEG which promoted the reaction of CO2 with amines. After ten-cycle adsorption-desorption test, the adsorption capacity of TEPA40-MSG and TEPA30/PEG10-MSG dropped 8% and 1.5%, respectively.2 A certain amount of TEPA was loaded on MSG which was treated by acid activation and oxalate, ammonium carbonate, urea calcinations. The effects of pretreatment methods on CO2 adsorption capacity were investigated. The results indicated that 1:1 (NH4)2CO3·MSG calcination is favored for pretreatment of MSG, which increased the optimal TEPA loading and adsorption capacity to 50 wt.% and 4.26 mmol·g-1.3 3-Aminopropyltrimethoxysilane (APTS) and TEPA co-functionalized MSG were prepared by a two-step method. The higher thermal stability and amino group density were obtained, and the TEPA dispersion was facilitated by a new formed Si-O-Si networks. When the APTS loading of 30 wt.%, TEPA loading of 30 wt.%, adsorption temperature of 70℃, and influent flow rate of 30 mL·min-1, the CO2 adsorption capacity reached 3.04 mmol·g-1. In addition, the cyclical data reveal that the performance of TEPA30/APTS30-MSG is relatively stable, with only a 3% decrease in the adsorption capacity after ten adsorption-desorption cycle.4 The adsorption equilibrium, adsorption thermodynamics and adsorption kinetics of CO2 on amine functionalized MSG were analyzed. The isosteric heat of CO2 adsorption on TEPA30/PEG10-MSG ranged from 30 to 40 kJ·mol-1, and the adsorption mechanism was dominated by physical and chemical adsorption. In an initial period of adsorption, there is a rapid CO2 adsorption rate which is determined by the chemical reaction. As the adsorption increased time, most of the active sites were gradually occupied, the adsorption rate dropped greatly due to the effect of gas diffusion. After amine modification, CO2 adsorption rate decreased because of the increased CO2 diffusion resistance. With increasing temperature, CO2 adsorption rate was significantly increased. |
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