Microporous Carbons Obtained via Solvent-Free Mechanochemical Processing, Carbonization and Activation with Potassium Citrate and Zinc Chloride for CO2 Adsorption (original) (raw)
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Nanomaterials
Mechanochemical synthesis of ordered mesoporous carbons with tunable mesopores and well-developed irregular microporosity is investigated. This synthesis was carried out by the self-assembly of ecofriendly chemicals such as tannin and glyoxal used as carbon precursors, and triblock copolymer as a soft templating agent. The structural properties of the resulting carbons were tailored by using different block copolymers (Pluronic F127, and P123) as soft templates. The various weight ratios of tannin and block copolymer were employed to tune the textural properties of these carbons. The tannin: Pluronic F127 ratios (1:0.75, 1:1, 1:1.1) gave the ordered mesoporous carbons among a wide variety of the samples studied. The ordered mesoporosity was not observed in the case of Pluronic P123 templated mesoporous carbons. The CO2-activated carbon samples obtained for both Pluronic templates showed a high specific surface area (close to 900 m2/g), large pore volume (about 0.6–0.7 cm3g−1), narro...
Emergent Materials
A simple one step chemical activation involving a relatively mild chemical potassium citrate and inexpensive chitosan as a carbon source is presented for the synthesis of microporous carbons with a high specific surface area. The synthesis avoids the use of a highly corrosive and unfriendly activating agent, KOH, which is generally used for the creation of the porosity. The obtained microporous carbons display a high specific surface area which can be tuned by varying the amount of activating agent (1784-2278 m 2 g −1). The optimized material exhibits a high surface area of 2278m 2 g −1 and a pore volume of 1.00 cm 3 g −1. As high microporosity is beneficial for CO 2 adsorption, the prepared materials are employed as adsorbents for the capture of CO 2. The optimized sample displays excellent CO 2 uptakes at 0°C/0.15 bar (1.1-1.8 mmol g −1) and 0°C/1 bar (4.3-6.1 mmol g −1). The high surface area of the materials allows for high CO 2 uptakes at 0°C/30 bar (17.3-22.0 mmol g −1). The microporosity of these high surface area carbons is further decorated with strontium carbonate nanoparticles. The adsorption capacity per unit surface area is increased significantly upon the incorporation of the nanoparticles, revealing the role of the nanoparticles on the enhancement of the CO 2 adsorption capacity. A similar strategy could be extended for the fabrication of a series of microporous carbons derived from biomass for many applications including CO 2 capture.
Journal of Environmental Chemical Engineering, 2018
Design of an optimum adsorbent for carbon dioxide (CO 2) capture is likely one of the most important challenges of our time. In the present study, we report for the first time the fabrication of walnut shell-derived nanoporous carbon with chemical adsorption sites for CO 2 adsorption at mediate (1 bar) and high pressures (10 bar) under room temperature by varying the preparation parameters. Based on the results, KOH activation through reaction with N groups of urea results in a great development of the pore structure, furthermore micropores are formed better by decreasing KOH/C mass ratio and activation temperature, and increasing the activation time, which cause higher adsorption at 1 bar. However, contrariwise conditions can form mesopores, leading to higher adsorption at higher pressures. Consequently, the value of CO 2 adsorption capacity reached 7.42 and 14.03 mmol/g under optimum conditions at 1 and 10 bar, respectively. It was found that the CO 2 adsorption capacity is dependent on both the nitrogen loading amount and the porous properties of adsorbent, and in specific the average pore diameter showed more effective role than surface area. Finally, the optimum adsorbents with heterogeneous surfaces and interactions represented promising choices to separate CO 2 from CO 2 /CH 4 and CO 2 /N 2 binary mixtures.
Chemical Engineering Journal
There is a growing interest in developing renewable biomass-based adsorbents to be used in numerous applications, including CO2 capture in postcombustion conditions. In the present study, several activated carbons (ACs) were produced from vine shoots-derived biochar through both physical and chemical activation using CO2 and KOH, respectively. The performance of these ACs was tested in terms of CO2 uptake capacity at an absolute pressure of 15 kPa and at different temperatures (0, 25, and 75 °C), apparent selectivity towards CO2 over N2, and isosteric heat of adsorption. At 25 °C, the chemically ACs with KOH impregnation exhibited the highest CO2 adsorption capacity, which was similar or even higher than those recently reported for a number of carbon-based adsorbents. However, the AC prepared through physical activation with CO2 at 800 °C and a soaking time of 1 h appears as the most promising adsorbent analyzed here, due to its higher CO2 uptake capacity and adsorption rate at relatively high temperature (75 °C), its relatively high selectivity at this temperature, and its apparently low energy demand for regeneration. Given that physical activation with CO2 is more feasible at industrial scale than chemical activation using corrosive alkalis, the results reported here are encouraging for further development of vine shootsderived adsorbents.
Increase the Microporosity and CO2 Adsorption of a Commercial Activated Carbon
Applied Mechanics and Materials, 2015
Microporous carbons prepared from commercial activated carbon WG12 by KOH and/or ZnCl 2 treatment were examined as adsorbents for CO 2 capture. The micropore volume and specific surface area of the resulting carbons varied from 0.52 cm3/g (1374 m 2 /g) to 0.70 cm3/g (1800 m 2 /g), respectively. The obtained microporous carbon materials showed high CO 2 adsorption capacities at 40 bar pressure reaching 16.4 mmol/g.
Biomass Conversion and Biorefinery, 2019
Cashew nutshell (CNS)-based biochar is obtained as a by-product in a pilot scale (20 kg/h) gas-fired auger pyrolysis reactor at 500°C during bio oil production. This pyrolytic biochar has low BET surface area (BET SA 0.80 m 2 /g) and poor porosity as the fast pyrolysis conditions are set to augment the bio oil yield over other products. To value add to this carbon, downstream activation is performed in an externally heated lab scale reactor. Formation of activated carbon with BET SA between 300 and 700 m 2 /g with moderate improvement in porosity ensued from CO 2 and steam activation, while chemical activation with K 2 CO 3 enhanced the BET SA to 1225 m 2 /g and Langmuir surface area to 1707 m 2 /g in addition to significant enhancement of porosity. CNS-based activated carbons predominantly possess narrow pore size distribution with small-sized micropores and ultra-micropores limiting the presence of mesopores. The effect of equilibrium time (10 s and 45 s) on N 2 adsorption is extensively studied, and it is found to have a significant role in detection of ultra-micropores below 0.8 nm (at very low pressures). The CO 2 absorptivity of K 2 CO 3activated CNS carbon is found to be between 4.16 and 6.22 mmol/g (i.e. 183.04-273.6 mg/g) at atmospheric pressure and 0°C. These activated CNS carbons possess ultra-micropores between 0.46 and 0.8 nm suitable for CO 2 uptake. This study shows the sustainable path of making CO 2 adsorbent from a low-cost renewable biomass precursor like CNS. Keywords Cashew nutshell. Pyrolytic biochar. Activated carbon. K 2 CO 3 activation. CO 2 adsorption. DR plot
CO2 capture on KOH-activated carbons derived from yellow mombin fruit stones
Journal of Environmental Chemical Engineering, 2016
Activated carbons derived from the stones of yellow mombin, an abundant tropical fruit, were prepared at 500 and 700 C (referred to here as BP5 and BP7, respectively). The carbons were further activated with KOH and the resulting materials (referred to as CAK5 and CAK7) were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman scattering measurements. The microporous network architecture was evaluated by the Dubinin-Astakhov equation and the non-local density functional theory, assuming slit-shaped pores. In general, the graphitization process of the activated carbons decreased and the microporous volume increased significantly when the pyrolysis temperature was elevated from 500 to 700 C. The temperature of 500 C favored the production of activated carbons with high pore volumes in the range of 0.85-1.0 nm, which has been considered a key feature affecting CO 2 capture at low pressures. Therefore, the carbon sample activated with KOH at 500 C (i.e. CAK5) adsorbed 10.5 mmol CO 2 /g at 0 C, 7.3 mmol CO 2 /g at 25 C and 4.9 mmol CO 2 /g at 75 C. The adsorption efficiency of the samples increased as: BP5 < BP7 < CAK7 < CAK5, with values ranging from 30.8 to 46.2%. CO 2 capture on activated carbons proved highly stable after 10 adsorption-desorption cycles at 75 C.
Journal of the Taiwan Institute of Chemical Engineers, 2014
A series of activated carbons (ACs) were prepared from Eucalyptus camaldulensis wood by chemical activation with H 3 PO 4 , ZnCl 2 at different impregnation ratios as well as by pyrolysis, followed by activation with KOH. The porosity characteristics of these ACs were determined by N 2 adsorption isotherms. Through varying the H 3 PO 4 /biomass ratio from 1.5 to 2.5, the prepared ACs displayed BET surface areas in the range of 1875-2117 m 2 /g with micropores content of 69-97%. For the ZnCl 2 activated series, BET surface areas varying from 1274.8 to 2107.9 m 2 /g with micropores content of 93-100% were obtained from impregnation ratios of 0.75-2.0. The AC obtained by KOH had the largest BET surface area of 2594 m 2 /g and the high micropore content of 98%. In addition, the FTIR and SEM analyses conducted for characterizing the ACs and the CO 2 adsorption onto all series of the eucalyptus wood based ACs at pressures ranging from 0 to 16 bar using a volumetric method were investigated. Also the effect of temperature (15-75 8C) on the amount of CO 2 adsorbed by the ACs that was prepared with H 3 PO 4 , KOH and ZnCl 2 was studied. The CO 2 adsorption capacity on the AC prepared with KOH was up to 4.10 mmol/g at 1 bar and 303 K, having an increase of about 63% in comparison with the commercial AC.
Synthesis and Characterization of Bio-Based Porous Carbons by Two Step Physical Activation with CO2
2014
Porous carbons were synthesized from coconut shell using two step CO2 activation and their characteristics were investigated. Nitrogen adsorption test for Brunauer-Emmett-Teller (BET) specific surface area and pore volume of the adsorbent produced were carried out. The Langmuir surface area, BET surface area and pore volume of the synthesized carbon are 533 m 2 /g, 361 m 2 /g and 0.19 cm 3 /g respectively. Micropores are predominant constituting 88% of the total surface area. From the Fourier Transform Infrared Spectroscopy (FTIR) analysis, hydroxyls, alkenes, carbonyls and aromatics functional groups were identified. Thermogravimetric analysis (TGA) results gives thermal analysis whereby moisture pyrolysis occurred at 105 o C, the pyrolysis of hemicellulose and cellulose occurred at 160-390 o C. However, lignin decomposition occurred in a wider temperature range (390-650 o C). The proximate and ultimate analysis shows high percentage of carbon and less ash content which indicates a good precursor material for porous carbon.
Biomass derived carbon materials: Synthesis and application towards CO2 and H2S adsorption
Nano Select, 2021
Porous carbon materials derived from palm date seeds, guava seeds and winged beans are proposed as environmentally friendly and efficient adsorbents for CO2 and H2S adsorption. The feedstock is converted into hydrochar via hydrothermal carbonization (HTC), at 200°C, for several hours, and the textural properties are tuned using the chemical activation approach with KOH. The activated carbons (ACs) prepared in here are characterized by high surface areas, more than 2000 m2 g‐1, and large pore volumes (1.23 cm3 g‐1). It is observed that a lower concentration of KOH results in a larger number of micropores, leading to improved gas uptake properties. The carbons obtained in here present sponge‐like structure with particle sizes in the range of 5–100 µm. Their morphology is characterized by irregular particle shape with large conchoidal cavities and smooth surfaces. The samples display significant gas adsorption capacity, with 5.47 mmol g‐1 CO2 uptake at 0°C, 1 bar and 4.36 mmol g‐1 at r...