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Porosity development of templated porous carbons dried by vacuum as carbon electrodes for electric double-layer capacitors
(2023-03-15)
Kraiwattanawong, Kriangsak
Resorcinol and formaldehyde (RF) resin serves as the carbon precursor for porous carbons and carbon/carbon composites possessing a high specific surface area (SSA). This work presents the porosity improvement by the elimination of cotton fibers (CF) from CF/RF composite hydrogels subsequently exchanged by tertiary butyl alcohol (TBA), dried by vacuum, and carbonized. This route contributes the templated porous carbons (TPC) with an asymmetric structure comprising micropores, mesopores, and macropores. At 0.25 of the CF/RF weight ratio, TPC dried by vacuum apparatus has SSA of 2,102 m2 g−1, whereas TPC dried by evaporation only offers SSA of 663 m2 g−1. Using the vacuum acts as pseudo-freeze drying during TBA removal, forming sponge-like carbon and allowing ultra-high SSA. The electrochemical properties of vacuumed TPCs were analyzed, showing that TPC at 0.25 of the CF/RF weight ratio possessed 626 F g−1 more than TPC at 0.00 of the CF/RF weight ratio which had 392 F g−1 at 200 mA g−1.
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Palm oil conversion to bio-jet and green diesel fuels over cobalt phosphide on porous carbons derived from palm male flowers
(2020-06-01)
Kaewtrakulchai, Napat
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Kaewmeesri, Rungnapa
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Itthibenchapong, Vorranutch
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Eiad-Ua, Apiluck
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Faungnawakij, Kajornsak
Porous carbon was successfully synthesized from palm male flowers (PMFs), using microwave-assisted potassium hydroxide (KOH) activation and was used as a catalyst support for the conversion of palm oil into bio-hydrocarbons, in fractions of green diesel and bio-jet fuel. Palm male flower-derived porous carbon (PC), consolidated with well dispersed cobalt phosphide (CoP) nanoparticles, was synthesized by simple wet-impregnation with subsequent thermal treatment. The physicochemical properties of the synthesized CoP/PC catalysts were evaluated by various techniques including proximate and ultimate elemental analysis, FTIR, XRD, N<inf>2</inf> sorption, SEM, TEM–EDS, and NH<inf>3</inf>-temperature programmed desorption (TPD). The effects of the pyrolysis temperatures (600−900◦ C), used for the impregnated samples before the reduction process, on catalyst properties and catalytic performance were investigated. Moreover, the effect of a liquid hourly space velocity of 0.5–1.5 h−1 and reaction temperatures of 340–420◦ C was studied in the palm oil conversion. The catalyst pyrolyzed at 600◦ C possessed the greatest particle dispersion and surface area, and showed the highest yield of liquid hydrocarbon product (C9–C18). We also found that the high pyrolysis temperature above 800◦ C partially transformed the Co<inf>2</inf> P phase into CoP one which significantly exhibited higher cracking activity and bio-jet selectivity, due to the improved acidity of the catalyst.
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Transformation of waste marigold flowers into porous carbons via hydrothermal carbonization
(2019-01-01)
Chaiammart, Nattapat
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Wongcharoen, Sittan
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Eiad-Ua, Apiluck
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Ishizaki, Takahiro
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Panomsuwan, Gasidit
Vast quantities of marigold flowers are often discarded as waste at sacred places and temples after religious ceremonies in Thailand. This has motivated us to examine the utilization of waste marigold flowers as a precursor for the synthesis of porous carbons by hydrothermal carbonization (HTC) and pyrolysis. Waste marigold flowers were hydrothermally treated at 180 °C for 2, 12, and 24 h. The resultant hydrochars were subsequently pyrolyzed at 800 °C under argon (Ar) atmosphere. Based on X-ray diffraction and Raman spectroscopy analyses, the samples exhibited an amorphous phase regardless of HTC time. With increasing HTC time, the marigold surface became rougher and more ruptured. This resulted in the development of a porous structure, thereby increasing surface area. The specific surface area of carbon samples increased from 118 to 281 m2 /g with HTC increasing from 2 to 24 h, respectively. Increase of specific surface area mainly resulted from the development of a microporous structure at longer HTC times. Our results offer guidelines to control surface area and porosity through the adjustment of HTC conditions.
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Control of mesoporous properties of carbon cryogels prepared from wattle tannin and furfural
(2008-12-01)
Kraiwattanawong, Kriangsak
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Mukai, Shin R.
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Tamon, Hajime
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Lothongkum, Anchaleeporn W.
Wattle tannin-furfural (TFu) carbon cryogels are synthesized by sol-gel polycondensation of wattle tannin with furfural by using sodium hydroxide (NaOH) as a catalyst, dried by freeze-drying technique and then pyrolyzed under inert atmosphere, respectively. The amounts of wattle tannin (T), furfural (Fu), NaOH (C) and distilled water (W) are changed for preparing the mesoporous TFu carbon cryogels. The mole ratio of tannin to catalyst T/C plays a crucial role for the synthesis of TFu organic and carbon cryogels. The results suggest that the T/C ratio should be above 0.25 but <1.0 to prepare the mesoporous and homogeneous cryogels. Although TFu carbon cryogels have the broad mesopore size distribution, the mesoporous structure is controllable by the synthesis conditions. The carbon cryogels possess the mesopore volume less than 0.56 cm3/g and the BET surface area less than 600 m2/g. Moreover, the ratio of catalyst to water C/W can be used to prepare the homogeneous and mesoporous carbon cryogels, and to control the mesopore radius of carbon cryogels in the range of 1.6-9.6 nm. © 2007 Springer Science+Business Media, LLC.
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Improvement of mesoporosity of carbon cryogels by acid treatment of hydrogels
(2008-11-01)
Kraiwattanawong, Kriangsak
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Mukai, Shin R.
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Tamon, Hajime
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Lothongkum, Anchaleeporn W.
Wattle tannin-furfural (TFu) gels are synthesized by the sol-gel polycondensation of wattle tannin with furfural by using sodium hydroxide as a catalyst and cured at 363 K. After cured, the TFu hydrogels are treated in hydrochloric acid (HCl) solutions with various variables as follows: aging temperature, HCl concentration and pH. TFu cryogels aged are then freeze-dried and pyrolyzed under an inert atmosphere to obtain TFu carbon cryogels. The TFu and carbon cryogels were characterized by N<inf>2</inf> adsorption and scanning electron microscope. The high HCl concentration yields the increase of mesopore volume almost twice especially at high temperature and the mesopore size distribution can be greatly developed sharper and narrower when the high concentration of HCl or/and the high temperature are used. Moreover, this method is the versatile approach for developing the mesopore structure of the low and high porous TFu hydrogels and has no serious problem of weight loss after treatment. © 2008 Elsevier Inc. All rights reserved.
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Improvement of mesopore structure of resorcinol and formaldehyde carbon cryogels by acid solution
(2008-01-01)
Kraiwattanawong, K.
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Kitchaiya, P.
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Neramittagapong, A.
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Praserthdam, P.
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Tamon, H.
Resorcinol and formaldehyde (RF) carbon cryogels are prepared by sol-gel polycondensation by using sodium carbonate (C) as a catalyst with water (W) as solvent, immersed in acid solution, hydrochloric acid (HC1), dried by freeze-drying technique and then carbonized under inert atmosphere, respectively. Compared with their carbon precursors, both V<inf>mes</inf> and mesopore size distributions of all carbon cryogels can be developed since the pore shrinkage is the crucial role in the change of pore structure of carbon gels. HC1 may promote the strength of small pore structure and increase the pore shrinkage of large pore structure. Consequently, the treatment of HC1 does not only enhance the partial collapse of large pore structure, the treatment also increases the strength of small pore structure to inhibit the shrinkage of this structure during carbonization as well. © 2008 Trans Tech Publications, Switzerland.
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Preparation of carbon cryogels from wattle tannin and furfural
(2007-01-05)
Kraiwattanawong, K.
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Mukai, S. R.
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Tamon, H.
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Lothongkum, A. W.
Wattle tannin-furfural (TFu) hydrogels were synthesized by the sol-gel polycondensation of wattle tannin with furfural by using three types of base catalysts (NaOH, Na<inf>2</inf>CO<inf>3</inf> and NaHCO<inf>3</inf>). TFu cryogels were prepared by freeze drying of the hydrogels and TFu carbon cryogels were obtained by pyrolysis of the cryogels in an inert atmosphere. The TFu and carbon cryogels were characterized by N<inf>2</inf> adsorption and scanning electron microscope (SEM). The effect of catalysts on porous properties of carbon cryogels resulted in different ways: (1) NaOH enhances increasing mesopore volumes and surface area of carbon cryogels and (2) Na<inf>2</inf>CO<inf>3</inf> and NaHCO<inf>3</inf> cause decreasing those of carbon cryogels. The TFu and carbon cryogels prepared by using NaOH as a catalyst possessed large mesopore volumes comparing with micropore volumes. Even though the TFu cryogels have surface area and mesopore volumes smaller than the resorcinol-formaldehyde (RF) cryogels, the carbon cryogels have unique porous properties differed from the RF carbon gels. The properties are summarized as follows: (1) the mesopore volume changes insignificantly after pyrolysis, (2) the pore radius is increased after pyrolysis and (3) micropores are not greatly developed during pyrolysis. © 2006 Elsevier Inc. All rights reserved.

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