Browsing by Author "Yu, Ching-Tsung"

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Ca-Rich Ca-Al-Oxide, High-Temperature-Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO2 Capture Capacity
(2011)
Chang, Po-Hsueh
;
Chang, Yen-Po
;
Chen, San-Yuan
;
Yu, Ching-Tsung
;
Chyou, Yau-Pin
We present the design and synthesis of Ca-rich Ca-Al-O oxides, with Ca(2+)/Al(3+) ratios of 1:1, 3:1, 5:1, and 7:1, which were prepared by hydrothermal decomposition of coprecipitated hydrotalcite-like Ca-Al-CO(3) precursors, for high-temperature CO(2) adsorption at 500-700 degrees C. In situ X-ray diffraction measurements indicate that the coprecipitated, Ca-rich, hydrotalcite-like powders with Ca(2+)/Al(3+) ratios of 5:1 and 7:1 contained Ca(OH)(2) and layered double hydroxide (LDH) phases. Upon annealing, LDH was first destroyed at approximately 200 degrees C to form an amorphous matrix, and then at 450-550 degrees C, the Ca(OH)(2) phase was converted into a CaO matrix with incorporated Al(3+) to form a homogeneous solid solution without a disrupted lattice structure. CaO nanocrystals were grown by thermal treatment of the weakly crystalline Ca-Al-O oxide matrix. Thermogravimetric analysis indicates that a CO(2) adsorption capacity of approximately 51 wt.% can be obtained from Ca-rich Ca-Al-O oxides prepared by calcination of 7:1 Ca-Al-CO(3) LDH phases at 600-700 degrees C. Furthermore, a relatively high CO(2) capture capability can be achieved, even with gas flows containing very low CO(2) concentrations (CO(2)/N(2)=10%). Approximately 95.6% of the initial CO(2) adsorption capacity of the adsorbent is retained after 30 cycles of carbonationcalcination. TEM analysis indicates that carbonation-promoted CaCO(3) formation in the Ca-Al-O oxide matrix at 600 degrees C, but a subsequent desorption in N(2) at 700 degrees C, caused the formation CaO nanocrystals of approximately 10 nm. The CaO nanocrystals are widely distributed in the weakly crystalline Ca-Al-O oxide matrix and are present during the carbonationcalcination cycles. This demonstrates that Ca-Al-O sorbents that developed through the synthesis and calcination of Ca-rich Ca-Al LDH phases are suitable for long-term cyclic operation in severe temperature environments.
Characterization and Structure Evolution of Ca-Al-CO(3) Hydrotalcite Film for High Temperature CO(2) Adsorption
(2010-07-01)
Wu, Chih-Hsiang
;
Chang, Yen-Po
;
Chen, San-Yuan
;
Liu, Dean-Mo
;
Yu, Ching-Tsung
In this work, monodispersed layered double hydroxide (Ca-Al LDHs) nanoparticles were synthesized by hydrothermal coprecipitation. Uniform thin films of layered double hydroxide on porous anodic aluminum oxide (AAO) substrates were formed by a direct precipitation process in a homogeneous suspension containing monodispersed Ca-Al layered double hydroxide nanoparticles. It was found that the formation of a designed hydrotalcite-like phase is strongly dependent on the [Ca2-]/ [Al(3+)] ratios, and that a minor CaCO(3) phase could possibly form simultaneously, which is attributed to the greater insolubility of CaCO(3) and the incompatibility of the ionic size of Al and Ca. The optimal CO(2) adsorption capacity appears in the layered Ca-OH-Al structure with the composition ratio of 3:1. Furthermore, the CO(2) adsorption mechanism varies with treatment temperature. Below 400 degrees C, the CO(2) adsorption is attributed to the LDH structure with a large surface area and pore volume, but above that the adsorption is due to the formation of CaCO(3) and CaO. The permeation behavior and CO(2) absorption can be explained by a preferable chemical and physical absorption of CO(2) on the layered double hydroxide and porous structure of the membrane.
Characterization and Structure Evolution of Ca-Al-CO3 Hydrotalcite Film for High Temperature CO2 Adsorption
(2010-07-01)
Wu, Chih-Hsiang
;
Chang, Yen-Po
;
Chen, San-Yuan
;
Liu, Dean-Mo
;
Yu, Ching-Tsung
In this work, monodispersed layered double hydroxide (Ca-Al LDHs) nanoparticles were synthesized by hydrothermal coprecipitation. Uniform thin films of layered double hydroxide on porous anodic aluminum oxide (AAO) substrates were formed by a direct precipitation process in a homogeneous suspension containing monodispersed Ca-Al layered double hydroxide nanoparticles. It was found that the formation of a designed hydrotalcite-like phase is strongly dependent on the [Ca2-]/ [Al3+] ratios, and that a minor CaCO3 phase could possibly form simultaneously, which is attributed to the greater insolubility of CaCO3 and the incompatibility of the ionic size of Al and Ca. The optimal CO2 adsorption capacity appears in the layered Ca-OH-Al structure with the composition ratio of 3:1. Furthermore, the CO2 adsorption mechanism varies with treatment temperature. Below 400 degrees C, the CO2 adsorption is attributed to the LDH structure with a large surface area and pore volume, but above that the adsorption is due to the formation of CaCO3 and CaO. The permeation behavior and CO2 absorption can be explained by a preferable chemical and physical absorption of CO2 on the layered double hydroxide and porous structure of the membrane.
Synthesis of Calcium Aluminates Granule with TiO2 Binder for High-temperature CO2 Capture
(2013-01-01)
Yu, Ching-Tsung
;
Chen, Wei-chin
;
Chyou, Yau-Pin
;
Chen, San-Yuan
;
材料科學與工程學系
High-temperature CO2 captures using powder and granule is investigated using thermogravimetric analyzer (TGA) and fixed-bed reactor (FBR). The CO2 sorbent, Ca-Al-CO3 powder was prepared using co-precipitation method of Ca+2, Al+3 and CO32- under alkaline conditions. The granule was fabricated by mixing Ca-Al-CO3 powder, H2O and w/or w/o TiO2 binder, followed by granulation and calcinations at 600 degrees C. In TGA experiment, high CO2 capacity of 45 similar to 50 wt% after 100 cycles can be achieved with powder at 750 degrees C, while it was dramatically decayed to 40-50% only after 2-5 cycles in FBR. Alternatively, using Ca/Ti granule exhibited recovery of 80-90% for 15 cycles in TGA and 70-80% for 10 cycles in FBR, respectively. This outcome indicates that calcium aluminates granule with TiO2 binder is competitive CO2 sorbent. (C) 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of GHGT
Synthesis, characterization and high temperature CO2 capture capacity of nanoscale Ca-based layered double hydroxides via reverse microemulsion
(2014-02-15)
Chang, Po-Hsueh
;
Chang, Yen-Po
;
Lai, Yen-Ho
;
Chen, San-Yuan
;
Yu, Ching-Tsung
In this study, we report a reverse microemulsion method to prepare stable homogeneous suspensions containing dispersed Ca-Al layered double hydroxide (LDH) nanoparticles. By changing the concentration, reaction time and temperature, the nano-particles with different structural morphology was developed from amorphous aggregation to platelet, regular hexagon and hydrangea-like hierarchical structure. The crystallization and growth of Ca-Al LDH nanoparticles were involved with a nucleation and growth process under nonaqueous polar solvent/surfactant system. After calcination at 700 degrees C, the calcined nano-sized Cal-Al LDH powders synthesized from the reverse microemulsion display remarkable CO2 capture behavior at 600 degrees C, which is strongly dependent on the reaction conditions (concentration, time and temperature). The calcined powder synthesized at 80 degrees C exhibits a faster rate of CO2 absorption and higher CO2 capture capacity of 44 wt% CO2 without apparent degradation under multiple cycles of carbonation-calcination. (C) 2013 Elsevier B. V. All rights reserved.