Chunfei Wu

Chunfei Wu

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CO2 adsorption - solid materials - High-temperature CO2 adsorption - CaO-based - Influence of CaO development

Limestone-Derived Porous Rod Hierarchical Ca-based Metal–Organic Framework

https://doi.org/10.3390/ma13194297

In this work, Limestone-Derived Porous Rod Hierarchical Ca-based Metal–Organic Framework have been developed, in order to enhance the efficiency of CO2 capture. CO2 capture capacity in unit of mmol/g is normally used. However, in this work, this value is not reported. Also, only 10 cycles of CO2 capture was performed to indicate the material’s stability, which is not sufficient. There might also be issues related to the stability of MOF. Nevertheless, the following content is from this reference, which might provide an alternative for developing CaO sorbents, which could be used for other applications.

“Limestone is a relatively abundant and low-cost material used for producing calcium oxide as a CO2 adsorbent. However, the CO2 capture capacity of limestone decreases rapidly after multiple carbonation/calcination cycles. To improve the CO2 capture performance, we developed a process using limestone to transform the material into a rod Ca-based metal–organic framework (Ca-MOF) via a hydrothermal process with the assistance of acetic acid and terephthalic acid (H2BDC). The structural formation of rod Ca-MOF may result from the (200) face-oriented attachment growth of Ca-MOF sheets. Upon heat treatment, a highly stable porous rod network with a calcined Ca-MOF-O structure was generated with a pore distribution of 50–100 nm, which allowed the rapid diffusion of CO2 into the interior of the sorbent and enhanced the CO2 capture capacity with high multiple carbonation–calcination cycle stability compared to limestone alone at the intermediate temperature of 450 °C. The CO2 capture capacity of the calcined porous Ca-MOF-O network reached 52 wt% with a CO2 capture stability of 80% after 10 cycles. The above results demonstrated that rod Ca-MOF can be synthesized from a limestone precursor to form a porous network structure as a CO2 capture sorbent to improve CO2 capture performance at an intermediate temperature, thus suggesting its potential in environmental applications.”

“Hydrothermal Synthesis of Rod Ca–Metal–Organic Framework

The rod Ca-MOFs were synthesized from limestone (CaCO3, Ilan, Taiwan) by a hydrothermal process via the assistance of acetic acid. The morphology and composition of nature limestone are illustrated in Figure S1. First, the ligand solution of 6 mmole terephthalic acid (H2BDC, 98%, Alfa Aesar (Ward Hill, MA, USA)) was dissolved in 20 mL of pre-heated N,N-dimethylacetamide (C4H9NO, DMA, 99.5%, J.T.Baker (Delaware, PA, USA)) at 90 °C until the powders were completely dissolved in 30 min. The metal solution of 6 mmole limestone was then acidified in various concentrations of acetic acid including 1, 5 and 10 M in DI water for 24 h. Next, the ligand solution was added into the metal solution and stirred for 10 min. Finally, the mixture solution was poured into a Teflon-lined stainless-steel autoclave and reacted at 120 °C from 1 to 18 h. In order to collect the powders and remove unreacted ions, the reacted solution was washed with ethanol through high-speed centrifugation 4 times and dried at 60 °C in an oven for 12 h. All the samples were ground to fine powders. The as-synthesized Ca-MOFs were denoted as Ca-MOF-xh-y, where x and y indicated the acidification time of limestone and the concentration of acetic acid, respectively. Subsequently, the raw powders were calcined at 750 °C in an air environment to convert MOF precursors into CaO-based sorbents denoted as Ca-MOF-xh-y-O.”
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“Figure 8. (a) CO2 capture kinetics at 450 °C and (b) multiple carbonation–calcination cycles of Ca-MOF-24h-y-O and calcined limestone.” CO2 adsorption tests were carried out using TGA. It is noted that the unit (g-CO2/g-sorbent %) used for CO2 uptake capacity is confusing.

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