Methane sorption on ordered mesoporous carbon in the presence of water

An ordered mesoporous carbon was synthesized using SBA-15 as the template. The sorption isotherms of methane on the synthesized carbon material were collected. Its ordered structure was confirmed by the XRD, SEM and TEM examinations. The BET surface area is 1100-1200 m²/g, the total pore volume is 1.24-1.30 cm³/g, and the pore size distribution is very narrow and centered at 2-5 nm. As high as 41.2 wt.% of methane was stored per unit mass of carbon at 275 K and pressures less than 7 MPa in the presence of 3.86 times more water. This sorption amount is 31% higher than the largest sorption capacity reached by activated carbon in the presence of water, which was equal to or higher than the storage capacity of compression till 20 MPa. The enthalpy change corresponding to the sudden change of isotherms was equal to the enthalpy change of methane hydrate formation; therefore, the mechanism of the enhanced methane storage was considered due to the formation of methane hydrate in the porous carbon material.     

Adsorption of CO2 from dry gases on MCM-41 silica at ambient temperature and high pressure. 2: Adsorption of CO2/N2, CO2/CH4 and CO2/H2 binary mixtures

Adsorption equilibrium capacity of CO₂, CH₄, N₂, H₂ and O₂ on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO₂/N₂, CO₂/CH₄, CO₂/H₂ binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO₂ adsorption in comparison to the other gases, in agreement with CO₂/N₂, CO₂/CH₄, CO₂/H₂ selectivity determined using IAST. In comparison to well known benchmark CO₂ adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO₂ separation performances from CO₂/N₂, CO₂/CH₄ and CO₂/H₂ binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO₂ capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons.     

Control of mesoporous properties of carbon cryogels prepared from wattle tannin and furfural

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.     

Synthesis of ordered carbon replicas by using Y-zeolite as template in a batch reactor

Ordered carbon material that preserves the structural regularity of the parent zeolite template was synthesized by using ethylene as carbon source and HY-zeolite in a batch reactor. The obtained carbons exhibit a high degree of microporosity having BET surface areas between 1400 and 2400 m²/g. The morphology and structure of the prepared carbon materials were investigated by elemental analysis, X-ray diffraction measurements, scanning electron microscopy and nitrogen adsorption. The results were compared with the parent zeolite template. The carbonization procedure of precursor-encapsulated samples was investigated by thermal analysis and it has been found that the resulting quality of the ordered carbons strongly depends on the heat treatment of the composite material.     

Templated synthesis of mesoporous carbon from sucrose—the way from the silica pore filling to the carbon material

Mesoporous carbon materials were synthesized using sucrose as carbon precursor and commercial silica as template. Every step of the synthesis such as pore filling, loss of carbon precursor during carbonization and development of the carbon pore system during silica removal have been investigated in detail. As a criterion for the quality of the obtained carbon materials, the pore size distribution estimated by applying density functional theory was used.     

Examination of synthesis conditions for graphite-derived nanoporous carbon-silica composites

A soft chemical method was used to insert silica bridging species between the layers of a graphite oxide precursor to form nanoporous graphitic composites (NPGC) and the effect of various synthetic conditions including colloidal dispersion, interlayer pre-expansion, and hydrolysis of silica source on the pore formation of NPGC was examined. It was found that an optimal alkali concentration for GO dispersion and surfactant concentration for pre-expansion exists for obtaining NPGC with very high porosity. Water content in surfactant-pre-expanded GO and the tetraethoxysilane hydrolyzing time and temperature influence the porosities of NPGC. The pore formation mechanism of NPGC is discussed based on these examinations, indicating the important roles of those conditions giving higher Si content and good composition state of carbon layers and silica in NPGC porosities.     

Capacitance limits of high surface area activated carbons for double layer capacitors

A large specific surface area (SSA) of carbon materials used for electrochemical double layer capacitors (EDLC) is the most important parameter leading to a large gravimetric capacitance (C_g). However, for a SSA determined with the differential functional theory (DFT) model above a value of 1200 m²/g the plot of C_g versus S_DFT exhibits a plateau. We suggest that this limitation of C_g can be ascribed to a space constriction for charge accommodation inside the pore walls. As a consequence, the use of extremely high surface area carbons for EDLCs may be unprofitable.     

Molecular modeling and adsorption properties of porous carbons

In this work, we calculate the adsorption isotherms and isosteric heat of argon in molecular models of saccharose coke obtained via the Hybrid Reverse Monte Carlo method. In the first route (method A), the molecular models were built by considering only carbon atoms, and all other heteroatoms present were neglected. In the second route (method B), the molecular models were built by considering carbon and hydrogen atoms. We find that the models obtained via method B have smaller pores as compared to the models obtained via method A. This is reflected in the adsorption properties. The amount adsorbed is less in models obtained via method B as compared to method A. We also find that the isosteric heat calculated in the models obtained via method B match the experimental data more closely as compared to models obtained from method A.     

Imaging the structure and porosity of active carbons by scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been employed for a comparative structural characterization, down to the atomic scale, of a representative set of porous carbons with different adsorption characteristics and prepared either by activation (physical or chemical) or templating techniques. The studied materials included a chemically activated, supermicroporous high surface area carbon, two activated carbons containing both micro- and mesopores synthesized by physical activation, an ultramicroporous carbon molecular sieve, and an ordered microporous carbon templated in the nanochannels of zeolite Y. In general, good agreement was found between the porous structures as imaged by STM and the porous texture derived from gas adsorption data for all the carbons investigated. The activated carbon samples were dominated by networks of slit type micropores and, in some cases, by mesopores of varied morphologies. By contrast, the zeolite-templated carbon exhibited rounded micropore morphology, and the carbon molecular sieve displayed a rather featureless conformation dominated by voids only below 1 nm wide. The structural differences observed by STM were interpreted in terms of the different preparation procedures of the studied carbons. In particular, the templated carbon consisted of minute clusters about 1 nm in diameter that were interpreted to be formed within the extremely confined, microporous spaces of the zeolite Y template.     

ADSORPTION OF LIGHT HYDROCARBONS ON SPENT SHALE PRODUCED IN A COMBUSTION RETORT

Adsorption isotherms of ethane, propane, and n-butane on two different retorted oil shales were determined gravimetrically at 284.3, 293.7, and 303.2 K. The equilibrium data for these hydrocarbons were correlated with the Langmuir isotherm equation. The equilibrium adsorption data for all the hydrocarbons studied were also correlated by the modified Polanyi potential theory. A single generalized characteristic curve which correlates the equilibrium adsorption data for all three hydrocarbons was obtained by using the ratio of characteristic free energies.     

MIGRATION AND DIFFUSION OF BINARY ELECTROLYTES UNDER A CONSTANT CURRENT II

The problem in title is analyzed for dilute solutions with no substantial intenonic effects and with the diffusivity and the electrophoretic mobility being related via the Nernst-Einslein equation. The case is considered of only the positive ion reacting at the electrodes, being produced at the anode and consumed at the cathode, With the electroneutrality condition as a first approximation, the equations for the average concentration and the electric field are decoupled and solved analytically. Then the deviation from electroneutrality is calculated in the second approximation via Poisson' s equation. The problem has a steady state if the current is smaller than a certain value. With this analysis and measurements of concentrations at different times, electrophoretic mobilities of the two ions can be calculated. The implications for interpreting measurements in microelectrophoresis and electrophoretic mass transport analysis are discussed     

Electrical double-layer characteristics of novel carbide-derived carbon materials

A variety of nanoporous carbide-derived carbon materials possessing improved pore size distributions were synthesised from a mixture of titanium carbide and titanium dioxide. It was observed that TiO₂ caused partial oxidation of the carbon particles created during high-temperature chlorination of the TiC/TiO₂ mixture. The resulting carbon powder is characterised by narrow pore size distribution with a peak pore size of around 8 Å and a noticeably smaller amount of pores below 6-7 Å compared to the carbon derived from pure TiC. Electrochemical and electrical double-layer characteristics of novel carbon materials in the acetonitrile solution of triethylmethylammonium tetrafluoroborate were obtained by using cyclic voltammetry and constant current methods. Carbon electrode materials of this study were tested over the temperature range from −10 °C to +60 °C. Results of this study affirmed a great potential of the synthesised advanced carbide-derived carbon, whose specific double-layer capacitance reaches approximately 90 F cm⁻³ and 125 F g⁻¹.     

Improvement of mesoporosity of carbon cryogels by acid treatment of hydrogels

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 N₂ 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.     

Catalytic graphitization of templated mesoporous carbons

Graphitic porous carbons with a wide variety of textural properties were obtained by using a silica xerogel as template and a phenolic resin as carbon precursor. The synthetic procedure used to prepare them was as follows: (a) infiltration of the porosity of silica by a solution containing phenolic resin, (b) carbonization of the silica-resin composite, (c) removal of the silica skeleton, (d) impregnation of the templated porous carbon with a metallic salt and (e) catalytic graphitization of the impregnated carbon by heat treatment at 900 °C. The graphitization of the carbons thus prepared varies as a function of the carbonization temperature used and the type of metal employed as catalyst (Fe, Ni or Mn). The porous characteristics of these materials change greatly with the temperatures used during the carbonization step. These graphitized carbons exhibit high electrical conductivities up to two orders larger than those obtained for the non-graphitized samples.