Development of porosity in brown-coal chars on activation with carbon dioxide

Two petrographic types of Tertiary brown coals, xylitic and earthy, were carbonized, and activated with carbon dioxide between 1123 and 1273 K. The development of porosity in the activated chars was studied by adsorption of benzene and carbon dioxide at 298 K and by mercury porosimetry. The type of brown coal exerts a dominant influence on the properties of the activated chars. The xylitic brown-coal, when compared with the earthy brown-coal, yields products with a higher pore volume and better sorptive properties. Activated chars from the xylitic brown-coal reach a surface area of 800 m² g^?1, contained principally in micropores and very narrow mesopores (radius below 3.0 nm). Dimensions of pores in the activated chars from the earthy brown-coal are less uniform, the mesopores are broader (an important part of them has a radius between 5.0 and 100.0 nm), and micropores are present to a smaller extent; the surface area of these products is between 200 and 350 m² g^?1. Activated chars from both types of brown coals have a well developed system of macropores.     

The adsorptive properties of activated plum stone chars

Plum stones were carbonized to 1173 K and activated in carbon dioxide at 1143 K to 50% burn-off. Adsorptive properties were measured by adsorption of benzene (298 K) and carbon dioxide (273 K) using the BET and Dubinin-Radushkevich equations of adsorption to deduce effective surface areas. Extents of development, with activation, of meso- and macro-porosity were monitored by mercury porosimetry; the surface textures of the carbonized and activated plum stones were monitored by scanning electron microscopy, and an elemental analysis of mineral matter accumulated during activation was made using the EDAX system. The carbonized stones had effective surface areas of 10m²g^?1 (from benzene adsorption) increasing to 850 m²g^?1 at 50% burn-off. The corresponding areas deduced from the carbon dioxide isotherms were 550 and 830 m²g^?1. There was roughening of surfaces during activation leading to pit formation with accumulation of mineral matter rich in calcium and iron at these positions. The carbonized and activated plum stones contain as much as 10% of oxygen.     

Textural study of a coal from villanueva de rio y minas (sevilla,spain) and of samples prepared from it by acid and heat treatments

A coal with high inorganic matter content from the mine of Villanueva de Rio y Minas (Sevilla, Spain) (VRMO) was classified by following the ASTM norms as a high volatile matter A bituminous coal. The starting coal was treated either with HCl (VRMH) or thermally at 1000°C for 2 h (VRMOC), the resultant yield values (referred to as VRMO, dry) being, respectively, 97 and 79%; also VRMH was either treated with HNO₃ (VRMN) or HF (VRMF), and the yield values (referred to as VRMH, dry) of the process were then 95 and 59%. The textural characterization of samples was effected by adsorption of CO₂ at 273 K and of N₂ at 77 K, as well as by mercury porosimetry. VRMN presents the highest value of the apparent surface area (S_D-R=219 m² g^?1) (CO₂, 273 K) and of the specific surface area of mesopores and macropores (S_me+ma=5.2 m² g^?1) (N₂, 77 K), while the greatest value of the cumulative specific surface area of macropores (S_ma=1.2 m² g^?1) (mercury porosimetry) corresponds to VRMOC; S values are expressed on a per gram of original sample basis. The micropore volume accessible to CO₂ at 273 K increases in both the HCl and the HNO₃ treatment and decreases in the HF and heat treatments. The HCl and HNO₃ treatments produce an increase of the mesoporosity; the HF treatment seems to affect in a special way the mesoporous texture. Furthermore, the heat treatment gives rise to a notable development of the macroporosity.     

Effects of activation temperature on the properties and structure of PAN‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of activation temperature of a precursor fiber on the microstructure, specific surface, pore‐size distribution, and adsorption properties of PAN‐based activated carbon hollow fibers (PAN‐ACHF) were studied in this work. After the activation process, the BET surface area of the PAN‐ACHF and surface area of mesopores in the PAN‐ACHF increased very remarkably and reached 1422 m² g^?1 and 1234 m² g^?1, respectively, when activation temperature is 1000°C. The adsorptions to creatinine and VB₁₂ of PAN‐ACHF were much high and reached 99 and 84% respectively. In PAN‐ACHF which went through the activation at 700°C and 800°C, the micropore filling mainly occurred at low relative pressures, multimolecular layer adsorption occurred with the increasing of relative pressure, and the filling and emptying of the mesopores by capillary condensation occurred at high relative pressures. But in PAN‐ACHF which went through the activation at 900°C, a mass of mesopores resulted in the large pore filling by capillary condensation. The dominant pore sizes of mesopores in PAN‐ACHF are from 2 nm to 5 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3778–3783, 2006     

A Non-Conventional Adsorbent for the Removal of Clofibric Acid from Aqueous Phase

The adsorption of Clofibric acid, one of the most frequently prescribed high environmental risk drugs, was studied using H₃PO₄ activated Schumannianthus dichotomus (ASD). The chemical characteristics of the adsorbent were established by Bohem’s titration, pH_PZC, FTIR, SEM, XRD, porosity, and surface area analysis. It was observed that the adsorbent was microporous-mesoporous in nature with BET surface area of 1199.98 m².g^?1. The influence of temperature (303-323 K), pH (2-10), textural properties, adsorbent load, and contact time was studied. The Langmuir equation was found to best represent the equilibrium data for clofibric acid-adsorbent system, yielding monolayer adsorption capacity of 258.39 mg.g^?1 at 303 K. The pseudo-second order model best explained (R² > 0.999) the adsorption kinetics with rate constant 0.037 g.mg^?1min^?1. The thermodynamics parameters, ΔG°, ΔH°, and ΔS°, evaluated as ?8.14 kJmol^?1, ?34.07 kJmol^?1, and ?85.5 JK^?1mol^?1, respectively, revealed that the adsorption process is feasible, spontaneous, and exothermic in nature. In the column mode, the adsorption capacity of ASD (267.93 mg.g^?1) was found to be higher than the batch mode of operation (258.39 mg.g^?1). The cost incurred per kg of the developed adsorbent was USD 14.36.     

The effects of iron sulphide surface area variations on coal liquefaction

The purpose of this work was to determine the effects of surface area variations of iron sulphides on coal liquefaction. Several iron sulphides were synthesized including pyrites (FeS₂) with 46.6 wt% Fe, pyrrhotites (Fe_1?xS) with ~ 60 wt% Fe and iron-sulphur compounds of unknown composition. Surface areas of the synthetic pyrites varied from 2 to ? 10 m² g^?1, pyrrhotite surface areas were 6 and 10 m² g^?1, and the surface areas of the iron-sulphur compounds were 40 and 80 m² g^?1. These iron sulphides were tested for catalytic activity in tubing reactor runs with West Virginia Blacksville no. 2 coal and SRC-II heavy distillate. All these sulphides showed catalytic effects as compared to runs with only coal and solvent, although the effects were not as large as those obtained with a cobalt-molybdenum on alumina catalyst. Large differences in surface areas before reactor testing did not cause any significant differences in conversion. The results from an additional series of tubing reactor runs, which was carried out to determine how iron sulphide surface areas change during liquefaction, showed that the surface areas were drastically changed during the two-minute heat-up of the reactor. Robena pyrite with a surface area of 2.0 m² g^?1 and the iron-sulphur compound with a surface area of 80 m² g^?1 yielded iron sulphides with surface areas of 5.2 and 10.8 m² g^?1 after a two-minute heat-up to 425°C and subsequent one-minute quench.     

Formation of porous structures in activated brown-coal chars using O2, CO2 and H2O as activating agents

Two brown coals, xylitic and earthy, carbonized at 1173 K were activated with water vapour, carbon dioxide and oxygen, each producing a different distribution of porosity. In the xylitic coke, activated in the range of burn-offs from 1 to 70%, the action of water vapour results in the development of pores of all dimensions. At the highest burn-off the product has an effective surface area of 920 m² g^?1 and a total sorptive pore volume of 0.83 cm³ g^?1, 33% of which is in micropores. Carbon dioxide creates, from the xylitic coke at the burn-off of 70%, a highly microporous adsorbent with about the same surface area (890 m² g^?1) as the corresponding water-vapour activated product. The pore volume of the carbon dioxide sample is lower (0.49 cm³ g^?1) but these contain 63% of micropores, which amounts to a contribution of 92% of these pores to the effective total surface area. The activation of the xylitic coke with oxygen leads to a high development of porosity at low burn-offs, but becomes ineffective on continuation of the process to medium and high burn-offs. This is thought to be due to a blocking of the entrances of the micropores by surface oxygen complexes formed on the surface of the coke. Oxygen gives, at a high burn-off, a product with the lowest total adsorptive volume (0.45 cm³ g^?1) and surface area (650 m² g^?1). All the activated products obtained from the xylitic coke can be regarded, when effective surface areas are considered, as microporous adsorbents. With the earthy coke a total adsorptive pore volume (consisting mainly of wide mesopores) is developed which is higher than with the corresponding xylitic coke, but this result is difficult to reproduce, because the earthy coke samples are easily influenced by temperature in the process of activation, especially that by oxygen.     

Characterization of activated carbon produced from almond shell and hazelnut shell

Ammonium chloride-impregnated and untreated almond shell and hazelnut shell samples were carbonized in a flow of nitrogen at relatively low temperatures. Pore structure characterization and sorption capacities of activated carbons prepared from shells of almond and hazelnut indicated that treatment with NH₄Cl increased the total surface area and improved sorption characteristics. Chemical activation carried out at 350°C gave products with surface area values above 500 m² g^?1. On the other hand, the surface area values observed for the products obtained from untreated raw materials were about half of this value. The surface area of products obtained from NH₄Cl-impregnated samples reached values of over 700 m² g^?1 when the carbonization temperature was increased 700°C.     

Effects of activation time on the properties and structure of polyacrylonitrile‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of activation time of a precursor fiber on the microstructure, specific surface area, pore‐size distribution, and adsorption properties of PAN‐based activated carbon hollow fibers (PAN‐ACHF) were studied in this work. The BET surface area of PAN‐ACHF and surface area of mesopores gradually increase with activation time extending, and reach the maximum values, 780 and 180 m² g^?1, respectively, when fibers are activated at 800°C for 100 min. The adsorption ratio to creatinine changes little with activation time extending and all values over all activation time are above 90%. The adsorption ratio to VB₁₂ gradually increases with activation time extending before 60 min, and then becomes relatively constant from 60 to 100 min. The number of pores on the surface of PAN‐ACHF increases with activation time extending. The amount of mesopores in PAN‐ACHF made of fibers activated for different time increases with activation time extending and the dominant pore sizes of mesopores in PAN‐ACHF range from 2 to 5 nm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2565–2569, 2006     

Preparation of ordered porous carbon from tea by chemical activation and its use in Cr(VI) adsorption

Ordered porous carbon was prepared from a new carbon precursor??the tea leaves, the most widely used beverage worldwide by a chemical activation process. We obtained well developed spherical interlinked meso and micro pores with uniform pore morphology and high surface area from green, black and waste tea by NaOH as well as H₃PO₄ activation process. The carbon obtained from green tea by H₃PO₄ activation had the highest BET surface area of 1,285?m²g^?1 with total pore volume of 0.6243?mL?g^?1. The as prepared porous carbon showed high adsorption efficiency of Cr(VI) adsorption from aqueous solution.     

Surface area variations of coal during solvent extraction

Changes in the surface area of a Wyoming sub-bituminous coal with progressive extraction have been investigated. Surface areas were determined from CO₂ adsorption isotherms at 196 K using the BET equation with 0.234 nm² for the molecular cross-sectional area of the CO₂ molecule at 196 K. Surface areas of the extracted coal varied with extraction time, yield and with the nature of the solvent. A maximum surface area of 265 m²/g was obtained from a four-hour treatment using tetralin at 350 °C as the solvent. The raw coal had a surface area of 99 m²/g.     

Carbons of high surface area. A study by adsorption and high resolution electron microscopy

Five carbons of high surface area, ~ 2000–3000 m²g^?1 are studied by adsorption of carbon dioxide at 195 and 273 K. Effective surface areas are calculated using Langmuir and Dubinin- Radushkevich equations. Structure in these carbons is assessed by phase contrast high resolution transmission electron microscopy. The lamellae or constituent layers of these carbons are resolved as fringe images. Careful examination of thin sections of these carbons shows significant differences in separation distances of lamellae which indicate differences in the size and shape of the supermicroporosity which exists as the space between the lamellae. These differences correlate closely with the effective surface areas. The supermicroporosity consists of cage-like voids 1–5 nm dia., the cages being separated by walls of 1–3 carbonaceous layers in thickness. The filling of such supermicroporosity by a mechanism of increasing adsorption potential or cooperative adsorption adequately accounts for high internal volumes of up to 1.7cm³g^?1 and of effective surface areas of about 3000 m²g^?1. The size and shape of supermicroporosity can be deduced from micrographs.     

Superior carbon-based CO2 adsorbents prepared from poplar anthers

A series of renewable nitrogen-containing granular porous carbons with developed porosities and controlled surface chemical properties were prepared from poplar anthers. The preparation conditions such as pre-carbonization and activation temperatures and KOH amount significantly influence the structures and chemical compositions of the porous carbons, the CO₂ adsorption capacities of which are highly dependent on their pore structures, surface areas, nitrogen contents and adsorption conditions. The sample with developed microporosity, especially with the pores between 0.43 and 1 nm and high nitrogen content shows high CO₂ adsorption capacity at 1 bar and 25 °C. In contrast, when the adsorption pressure is higher than 5 bar, its CO₂ adsorption capacity is dominated by its surface area, and more accurately by its pore volume. Irrespective of this, if the pressure was decreased to 0.1 bar, its CO₂ capture ability is closely correlated to its nitrogen content but not to its porosity. By optimizing the preparation conditions, a porous carbon with a surface area of 3322 m² g⁻¹ and a CO₂ adsorption capacity as high as 51.3 mmol g⁻¹ at 50 bar and 25 °C was prepared.     

Investigation of equilibrium and kinetic parameters of methylene blue adsorption onto MCM-41

Mesoporous MCM-41 was synthesized at room temperature using tetraethoxysilane (TEOS) with cetyltrimethylammonium bromide (CTAB) and employed as an effective adsorbent for the adsorption of methylene blue dye from aqueous solution. The as-synthesized MCM-41 was calcined at 250 and 550°C to study the relation between the surface area and pore volume with surfactant removal. The synthesized MCM-41 was characterized using thermo gravimetric analysis (TGA), X-ray diffraction (XRD) patterns, nitrogen adsorption/desorption isotherms and Fourier transform infrared (FT-IR) spectroscopy. The MCM-41 calcined at 550°C showed higher surface area (1,059 m² g^?1) with pore volume of 0.89 ml g^?1 and was used for the investigation of adsorption isotherms and kinetics. The experimental results indicated that the Freundlich and Redlich-Peterson models expressed the adsorption isotherm better than the Langmuir model. In addition, the influence of temperature and pH on adsorption was also investigated. The decrease in temperature or the increase in pH enhanced the adsorption of dye onto MCM-41. A maximum adsorption capacity of 1.5×10^?4 mol g^?1 was obtained at 30°C. The kinetic studies showed that the adsorption of dye on MCM-41 follows the pseudo-second-order kinetics.     

Development of porosity and surface heterogeneity upon air activation of graphitized carbon black

One graphitized carbon black (Vulcan 3G) and three samples prepared by its activation in air at 978K have been used as supports for platinum catalysts. Surface characteristics of the four supports have been studied by physical adsorption of N₂ at 77 and 90K. Surface area increases smoothly with burn-off from 62 m² g^?1 (original V3G) to 121 m²g^?1 (52.8% burn-off sample). Porosity and surface heterogeneity develop upon activation but all samples have a large degree of surface homogeneity and low porosity.     

Activated carbon from sewage sludge for removal of sodium diclofenac and nimesulide from aqueous solutions

Sludge based activated carbons (ACs) were used to remove selected pharmaceuticals such as diclofenac (DCF) and nimesulide (NM) from aqueous solutions. The powered sewage sludge was mixed with different proportions of ZnCl₂. The mixture was pyrolyzed in a conventional oven using three different temperatures under inert atmosphere. Afterwards, in order to increase the specific surface area and uptake capacity the carbonized materials were acidified with 6mol L^?1 HCl under reflux at 80 °C for 3 hours. The characterization of ACs was achieved by scanning electron microscopy, FTIR, TGA, hydrophobicity index by water, n-heptane vapor adsorption and nitrogen adsorption/desorption curves. The specific surface area (S _BET ) of adsorbents varied between 21.2 and 679.3m²g^?1. According to the water and n-heptane analysis data all ACs had hydrophobic surface. Experimental variables such as pH, mass of adsorbent and temperature on the adsorption capacities were studied. The optimum pH, mass of adsorbent and temperature for adsorption of DCF and NM onto ACs were found to be 7.0 (DCF) and 10.0 (NM), 30mg and 25 °C, respectively. The kinetic adsorption was investigated using general-order, pseudo-first order and pseudo-second order kinetic models, while the general-order model described the adsorption process most suitably. The maximum amounts of DCF and NM adsorbed were 156.7 and 66.4mg g^?1 for sample 1(500-15-0.5), respectively.     

Adsorption of CO2, CH4, CO2/N2 and CO2/CH4 in novel activated carbon beads: Preparation,measurements and simulation

A series of high performance carbonaceous mesoporous materials: activated carbon beads (ACBs), have been prepared in this work. Among the samples, ACB‐5 possesses the BET specific surface area of 3537 m² g^?1 and ACB‐2 has the pore volume of 3.18 cm³ g^?1. Experimental measurements were carried out on the intelligent gravimetric analyzer (IGA‐003, Hiden). Carbon dioxide adsorption capacity of 909 mg g^?1 has been achieved in ACB‐5 at 298 K and 18 bar, which is superior to the existing carbonaceous porous materials and comparable to metal‐organic framework (MOF)‐177 (1232 mg g^?1, at 298 K and 20 bar) and covalent‐organic framework (COF)‐102 (1050 mg g^?1 at 298 K and 20 bar) reported in the literature. Moreover, methane uptake reaches 15.23 wt % in ACB‐5 at 298 K and 18 bar, which is better than MOF‐5. To predict the performances of the samples ACB‐2 and ACB‐5 at high pressures, modeling of the samples and grand canonical Monte Carlo simulation have been conducted, as is presented in our previous work. The adsorption isotherms of CO₂/N₂ and CO₂/CH₄ in our samples ACB‐2 and 5 have been measured at 298 and 348 K and different compositions, corresponding to the pre‐ and postcombustion conditions for CO₂ capture. The Dual‐Site Langmuir‐Freundlich (DSLF) model‐based ideal‐adsorbed solution theory (IAST) was also used to solve the selectivity of CO₂ over N₂ and CH₄. The selectivities of ACBs for CO₂/CH₄ are in the range of 2–2.5, while they remain in the range of 6.0–8.0 for CO₂/N₂ at T = 298 K. In summary, this work presents a new type of adsorbent‐ACBs, which are not only good candidates for CO₂ and CH₄ storage but also for the capture of carbon dioxide in pre‐ and postcombustion processes. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Aspects of gasification and structure in cokes from coals

Cokes were prepared from nine coals of different rank and characterized by surface area measurement, reactivity to carbon dioxide at 1473K and Raman-laser spectroscopy. Rates of gasification of cokes on a unit surlface area basis (K¹ = g m^?2 min^?1) decreased with increasing rank of parent coal based on maximum oil reflectances. However rates of gasification could not be related to coke structure as measured by Raman-laser spectroscopy.     

Physical adsorption and heat of immersion studies of microporous carbons

Physisorption and heat of immersion measurements have been made with two microporous carbons—a sample of charcoal cloth (BET area, 1250 m² g^?1; pore volume, 0.59 cm³ g^?1 having predominantly narrow micropores and a sample of Amoco carbon (BET area, 3700 m² g^?1; pore volume, 1.9 cm³ g^?1), having a wider distribution of micropores extending into the supermicropore range (pore width, ca. 1–2 nm). The adsorption isotherms of nitrogen and toluene are of Type 1 and reveal that the external surface of both samples is very small. The heat of immersion measurements were carried out with the aid of a Tian-Calvet microcalorimeter and with the following liquids: n-hexane, cyclohexane, neo-hexane, toluene, mesitylene and isodurene. A sample of non-porous graphitized carbon black (Vulcan 3G: BET area, 71.1 m² g^?1) was studied. Immersion calorimetry shows that in spite of the larger adsorptive capacity of the Amoco carbon, the sample of charcoal cloth has a higher adsorption affinity. The differences in the corresponding heats of immersion and in the adsorptive properties indicate that many of the pores in charcoal cloth are slit-shaped, whereas those in the Amoco carbon appear to be more cylindrical in shape.     

Correlation of the reactivity,the active surface area and the total surface area of thin films of pyrolytic carbon

Using thin films of pyrolytic carbon the rate of the reaction with oxygen has been measured over the temperature range 625–740°C and at pressures of oxygen from 6–100 torr. The active surface area (ASA) of the films was measured from the total concentration of strongly-bound complexes with oxygen on the surface and the relative total surface area (TSA) was measured by low-temperature adsorption of nitrogen. A maximum in reactivity and in ASA was observed for films of average thickness of about 20 nm with a TSA of about 30 m² g^?1. At the maximum the ASA and TSA were essentially equal. The results are interpreted in terms of the mechanism of formation of pyrolytic carbon in the initial stages.