含胺類之中孔洞矽材用於捕獲二氧化碳

Carbon Dioxide Capture by Mesoporous Silica Containing Amines

詹木泉(Worasaung Klinthong)

指導教授 ： 談駿嵩

國立清華大學/工學院/化學工程學系/博士(2014年)

摘要

Carbon dioxide (CO2) is a key global warming gas and its capture and sequestration is an important issue that has drawn global attention. Although the use of alkanolamines as chemical absorbents is currently one of the most viable means of capturing CO2, this technology has several drawbacks, including corrosion problem, foaming problem, large solvent makeup and amine loss in cycles due to degradation and evaporation. The application of silica materials is proposed to overcome these drawbacks, because their adsorption capacities toward CO2 can be enhanced by loading amines onto their internal surfaces. Accordingly, this research focuses on the synthesis and development of amine-containing silica adsorbents for CO2 capture. There are five parts as follows: (1) the application of supercritical propane (SC-propane) as the solvent for grafting 3-aminopropyltriethoxysilane (APS) onto mesoporous silica SBA-15, (2) the use of non-porous fumed silica as the amine support, (3) the preparation of as-synthesized APS-functionalized MCM-41 through direct synthesis method for CO2 capture, (4) the use of polyallylamine (PAA) and NaOH as a novel binder to pelletize amine-functionalized mesoporous silicas for CO2 capture, and (5) the preparation of PEI-containing mesoporous silica particles through one-pot synthesis for CO2 capture.
Firstly, SC-propane was found to be a promising solvent for grafting APS onto SBA-15 for CO2 capture. The influences of operating conditions in SC-propane for CO2 capture at different pressures (8.3 to 13.8 MPa), temperatures (85 to 120 °C), and periods of time (4 to 16 h) were evaluated. The results showed a reduction in pore characteristics and an increased amount of grafted APS with increased pressure and temperature after grafting. After grafting in SC-propane at 11.0 MPa and various temperatures for 16 h, 3 to 20% increase in the amount of grafted APS and 6 to 49% increase in the CO2 adsorption capacity over the toluene refluxing were observed. In addition, the time required for grafting in SC-propane could be reduced while maintaining higher nitrogen content and CO2 adsorption capacity compared with grafting in toluene refluxing.
Secondly, the non-porous fumed silica and SBA-15 were used as the support for tetraethylenepentamine (TEPA) impregnating and APS grafting. The TEPA-loaded silica adsorbents exhibited higher CO2 adsorption capacities but lower thermal stability than the APS-grafted silica adsorbents. The low cost and commercially available nonporous fumed silica was found to be an appropriate support for amine loading. The TEPA-loaded fumed silica possessed a CO2 adsorption capacity of 3.97 mmole/g (175 mg/g) and a CO2/N mole ratio of 0.37 under a 15% CO2/N2 mixed gas flow at 75 oC, which were higher than those of the TEPA-loaded SBA-15 due to the less CO2 diffusion hindrance. Besides, a high stability of TEPA on fumed silica in cyclic adsorption-desorption of CO2 over the TEPA loaded on SBA-15 was observed as well.
Thirdly, the as-synthesized amine-functionalized MCM-41 (as-APS/MCM) material was prepared through the direct synthesis by co-condensation of tetraethyl orthosilicate with APS at different molar ratios and a pH of approximately 13 for CO2 capture under various CO2 concentrations, temperatures and moistures. The CO2 adsorption capacity of as-APS/MCM was 73% higher than the APS-grafted calcined MCM-41 prepared by post-modification. Because the CO2 adsorption capacity of the as-APS/MCM was found to come mainly from the coated APS rather than the incorporated APS, the prehydrolysis of TEOS and post-treatment including template removal and APS neutralization were not required. Dynamic adsorption-desorption cycles revealed that the as-APS/MCM possessed high thermal stability for CO2 capture.
Forthly, a binder solution containing PAA and NaOH is proposed to construct pellets from amine-containing mesoporous silica powders, thereby providing active sites for CO2 capture in addition to reduction of pressure drop in a packed bed. Various powdered amine-containing adsorbents were prepared and pelletized, including APS-functionalized MCM-41 obtained through post-modification and direct synthesis, and polyethylenimine (PEI)-loaded MCM-41 obtained through impregnation. The pellets prepared after mixing the powdered adsorbents with an aqueous solution of 3 wt% PAA and 2 wt% NaOH exhibited the CO2 adsorption capacity slightly lower than the powdered adsorbent, a recovery of greater than 90% of the powdered adsorbents was observed, while their mechanical strength was over 0.4 MPa and durability could be over 90%. Moreover, the pelletized adsorbents possessed the high thermal stability in cyclic adsorption-desorption. As a result, the proposed binder formula can be used to provide pelletized amine-containing adsorbents for CO2 capture from power plants.
Finally, the PEI-containing mesoporous silica particles (PEI-MSP) were prepared through a simple one-pot synthesis for CO2 capture. The prepared PEI-MSP possessed the CO2 adsorption capacity under 15% CO2 in N2 mixed gases at 95 oC up to 3.34 mmol/g (147 mg/g). The CO2 adsorption capacity of PEI-MSP was 10% greater than that of PEI-loaded SBA-15 (PEI/SBA) prepared through impregnation. For practical use, the binder solution featuring 3% PAA and 2% NaOH was applied to pelletize both PEI-MSP and PEI/SBA. Both pelletized adsorbents possessed adequate mechanical properties - mechanical strength of greater than 0.5 MPa and durability of 100% - that fit the criteria for practical use. The pelletized PEI-MSP demonstrated the greater CO2 adsorption capacity and recovery than the pelletized PEI/SBA since external PEI of PEI-MSP facilitated the access of CO2 to amine active sites after pelletized. Dynamic adsorption-desorption cycles of both powdered and pelletized PEI-MSP revealed that they possessed high thermal stability. Therefore, this alternative one-pot synthesis is promising for the preparation of PEI-containing mesoporous silica materials regarding as appropriate adsorbents for CO2 capture when a temperature swing adsorption technology is applied.

關鍵字

二氧化碳 ； 吸附 ； 胺類 ； 錠 ； 改質 ； 一鍋式

並列摘要

無資料

並列關鍵字

Carbon dioxide ； Adsorption ； Amine ； Pellet ； Grafting ； One-pot

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