Preparation and characterization of activated carbon spheres from polystyrene sulphonate beads by steam and carbon dioxide activation

The polymeric precursor polystyrene sulphonate beads were used to produce activated carbon spheres (ACSs). ACSs were prepared by carbonization of polymeric precursor at 800°C followed by activation of resultant char with steam and carbon dioxide activation processes. The resulting ACSs were characterized for N₂ adsorption, Raman spectrometry, and scanning electron microscope (SEM). The adsorption properties such as, BET surface area (S_BET), pore volume (V_pore), and micropore volume (V_micro) of ACSs produced at different gasification time and temperature with steam and carbon dioxide activation were investigated in this study. It is found that porosity of ACSs produced from steam and carbon dioxide activation increases with increasing activation time. The results exhibited that ACSs produced from above carbon dioxide activation have shown high S_BET and V_pore 1266 m²/g and 1.13 cm³/g respectively compared to ACSs from steam activation S_BET 949 m²/g and V_pore 0.98 cm³/g, respectively. SEM study revealed that ACSs produced from carbon dioxide activation have exhibited a smooth surface and better microstructure as compared to ACSs from steam activation process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Porous properties of activated carbon produced from Eucalyptus and Wattle wood by carbon dioxide activation

This work focused on the preparation of activated carbon from eucalyptus and wattle wood by physical activation with CO₂. The preparation process consisted of carbonization of the wood samples under the flow of N₂ at 400°C and 60 min followed by activating the derived chars with CO₂. The activation temperature was varied from 600 to 900°C and activation time from 60 to 300 min, giving char burn-off in the range of 20/2-83%. The effect of CO₂ concentration during activation was also studied. The porous properties of the resultant activated carbons were characterized based on the analysis of N2 adsorption isotherms at −196°C. Experimental results showed that surface area, micropore volume and total pore volume of the activated carbon increased with the increase in activation time and temperature with temperature exerting the larger effect. The activated carbons produced from eucalyptus and wattle wood had the BET surface area ranging from 460 to 1,490 m²/g and 430 to 1,030 m²/g, respectively. The optimum activation conditions that gave the maximum in surface area and total pore volume occurred at 900°C and 60 min for eucalyptus and 800°C and 300 min for wattle wood. Under the conditions tested, the obtained activated carbons were dominated with micropore structure (∼80% of total pore volume).     

Preparation and characterization of mesoporous activated carbon from waste tires

Activated carbons were produced from waste tires and their characteristics were investigated. Rubber separated from waste tires was first carbonized at 500 °C in N₂ atmosphere. Next, the obtained chars were activated with steam at 850 °C. As a result, fairly mesoporous activated carbons with mesopore volumes and BET surface areas up to 1.09 cm³/g and 737 m²/g, respectively, were obtained. To further improve the porous properties of the activated carbons, the char was treated with 1 M HCl at room temperature for 1 day prior to steam activation. This treatment increased mesopore volumes and BET surface areas of the activated carbons up to 1.62 cm³/g and 1119 m²/g, respectively. Furthermore, adsorption characteristics of phenol and a dye, Black 5, on the activated carbon prepared via acid treatment were compared with those of a commercial activated carbon in the liquid phase. Although the prepared carbon had a larger micropore volume than the commercial carbon, it showed a slightly lower phenol adsorption capacity. On the other hand, the prepared carbon showed an obviously larger dye adsorption capacity than the commercial carbon, because of its larger mesopore volume.     

Potassium salt-assisted synthesis of highly microporous carbon spheres for CO2 adsorption

Highly microporous carbon spheres for CO₂ adsorption were prepared by using a slightly modified one-pot Stöber synthesis in the presence of potassium oxalate. Formaldehyde and resorcinol were used as carbon precursors, ammonia as a catalyst, and potassium oxalate as an activating agent. The resulting potassium salt-containing phenolic resin spheres were simultaneously carbonized and activated at 800 °C in flowing nitrogen. Carbonization of the aforementioned polymeric spheres was accompanied by their activation, which resulted in almost five-time higher specific surface area and total pore volume, and almost four-time higher micropore volume as compared to analogous properties of the carbon sample prepared without the salt. The proposed synthesis resulted in microporous carbon spheres having the surface area of 2130 m² g⁻¹, total pore volume of 1.10 cm³ g⁻¹, and the micropore volume of 0.78 cm³ g⁻¹, and led to the substantial enlargement of microporosity in these spheres, especially in relation to fine micropores (pores below 1 nm), which enhance CO₂ adsorption. These carbon spheres showed three-time higher volume of fine micropores, which resulted in the CO₂ adsorption of 6.6 mmol g⁻¹ at 0 °C and 1 atm.     

Laboratory studies of the rapid pyrolysis and desulphurization of a Texas lignite

Rapid heating of Alcoa D lignite particles during ‘free-fall’ through a counterflowing pyrolysis gas is an effective method of producing a low sulphur char. For 200 μm particles with residence times of seconds in steam, the organic sulphur of the lignite is reduced from ? 1.3 wt % to ? 0.8 wt % over a temperature range ≈ 700–800 °C. Similar levels of desulphurization were achieved with particles as large as 550 μm, even with shorter residence times. Devolatilization is rapid and substantial with the production of significant quantities of olefins. Steam gasification becomes important above 700 °C for the 200 μm particles. By 820 °C, the conversion of coal to gas is twice as large with steam as for nitrogen, and by 870 °C, it is about four times larger. Chars are reactive and of high surface area. Limited testing suggests that the reduced sulphur chars can be burned directly with emissions of SO₂ below 0.5 g/10⁶J (1.2 lb/10⁶ Btu).     

Ether linkage in poly(1,2-propylene carbonate), a key structure factor to tune its performances

As an alternating copolymer of CO₂ and propylene oxide, poly(1,2-propylene carbonate) (PPC) should be composed of fully carbonate structure, whereas it generally contains certain ether linkage due to the existence of competitive formation of ether linkage by consecutive epoxide enchainment. Though the ether linkage was not always the dominant structure in PPC, a new understanding was provided in that the ether linkage was crucial structure factor on the PPC performances, especially for oxygen barrier property, transparency, thermal and mechanical properties. The gas barrier properties and transparency of PPC film became worse with increasing ether linkages, the oxygen, nitrogen and carbon dioxide permeability of PPC with ether linkage of 0.6 % were 14 cm³/m²/24 h/0.1 MPa, 11 cm³/m²/24 h/0.1 MPa and 220 cm³/m²/24 h/0.1 MPa, respectively, while for PPC with ether linkage of 54.1 %, they became 116 cm³/m²/24 h/0.1 MPa, 108 cm³/m²/24 h/0.1 MPa and 599 cm³/m²/24 h/0.1 MPa, respectively. When the ether linkage in PPC increased from 0.6 % to 54.1 %, the thermal decomposition temperature at 5 wt% loss(T _d-5% ) increased from 218.6 °C to 241.0 °C, while the glass-transition temperature(T _g ) decreased from 45.2 °C to 11.1 °C, meanwhile, the room temperature tensile strength decreased from 55.4 MPa to 2.3 MPa, and the elongation at break increased from 8.5 % to 1558.2 %.     

Adsorptive removal of sulfur dioxide by Saskatchewan lignite and its derivatives

A non-equilibrium method using fixed bed microreactor was used to measure SO₂ adsorption characteristics of chars and activated carbons derived from Saskatchewan lignite. SO₂ breakthrough times and profiles were measured using lignite at a variety of temperatures, particle sizes and SO₂ concentrations of 75–175 °C; 2–5.6 mm and 1000–5000 ppm, respectively. Adsorption was found to be a strong function of residence time and feed SO₂ concentration, a moderate function of particle size and a weak function of temperature. There was a marginal difference in the adsorption capacity between lignite (15 mg SO₂/g lignite) and the char obtained from the same starting amount of lignite (26 mg SO₂/g char, or 17 mg SO₂/g original lignite). Activation of lignite with steam resulted in an activated carbon, which had highest adsorption capacity of 93 mg SO₂/g activated carbon.     

Indirect electrochemical reduction of carbon dioxide to carbon nanopowders in molten alkali carbonates: Process variables and product properties

Carbon was deposited on a mild steel cathode during electrolysis in the molten mixture of Li₂CO₃ and K₂CO₃ (mole ratio: 62:38) under CO₂ or mixed N₂ and CO₂ atmospheres at 3.0–5.0 V and 540–700 °C. In a three-electrode cell, cyclic voltammetry was applied on a platinum working electrode to study the reduction and deposition processes. A two-electrode cell helped correlate electrolysis variables, e.g. temperature and voltage, with the deposition rate, current efficiency, and properties of the deposited carbon powders. High current efficiency (>90%) and deposition rate (>0.11 g cm⁻² h⁻¹) were achieved in the study. Elemental analysis of the electro-deposits, following washing with HCl solutions (2.3–7.8 mol L⁻¹), showed carbon as the dominant element (75–95 wt.%) plus oxygen (5–10 wt.%) and small amounts of other elements related to materials of the electrolytic cell. Thermogravimetry detected fairly low onset combustion temperatures (310–430 °C), depending on the electrolysis and acid washing conditions. Amorphous and various nanostructures (sheet, rings and quasi-spheres) were revealed by electron microscopy in carbon samples deposited under different process conditions. The specific surface area of the carbon deposited at 5.0 V and 540 °C was as high as 585 m² g⁻¹. An analysis of the energy consumption suggests several ways for efficiency improvement so that the electrolytic carbon from CO₂ will become commercially attractive.     

Preparation of ultra-thin PAN-based activated carbon fibers with physical activation

This study elucidates the stabilization and activation in forming activated carbon fibers (ACFs) from ultra-thin polyacrylonitrile (PAN) fibers. The effect of stabilization time on the properties and structure of resultant stabilized fibers was investigated by thermal analysis, X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy (SEM). Stabilization was optimized by the pyrolysis of ultra-thin PAN fibers in air atmosphere at 280°C for 15 min, and subsequent activation in steam at 1000°C for 0.75 to 15 min. Resultant ACFs were characterized by N₂ adsorption at 77 K to evaluate pore parameters, XRD to evaluate structure parameters, and field emission scanning electron microscopy (FESEM) to elucidate surface morphology. The produced ACFs had surface areas of 668–1408 m²/g and a micropore volume to total pore volume ratio from 78 to 88%. Experimental results demonstrate the surface area and micropore volume of 1408 m²/g and 0.687 cm³/g, respectively, following activation at 1000°C for 10 min. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of activated carbon from oil sands coke

Several million tonnes of oil sands coke are generated each year in Alberta, Canada as a by-product of bitumen upgrading. Due to its high carbon content, oil sands coke can be a suitable precursor for the preparation of activated carbon. In this study, delayed and fluid oil sands coke were physically activated in a muffle furnace under select conditions of activation time (2–6 h), temperature (800–900 °C), steam rate (0.3–0.5 mL/min), and activation atmosphere (CO₂, CO₂ + steam, and N₂ + steam). The activated products were characterized using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, nitrogen adsorption, iodine and methylene blue tests. An increase in activation time and temperature resulted in higher surface areas in both delayed and fluid coke due to an enhanced etching of pores. An increase in steam rate led to the production of the highest specific surface area (577 m²/g) and iodine number (670 mg/g) within delayed coke; whereas, a lower steam rate resulted in the production of the highest specific surface area (533 m²/g) and iodine number (530 mg/g) in activated fluid coke samples.     

Highly CO2RR activity and electrochemical performance of A-site deficient symmetrical electrode materials (La0.6Sr0.4)1−xFe0.8Ni0.2O3-δ for CO2 electrolysis

A-site deficient (La_0.6Sr_0.4)_1−xFe_0.8Ni_0.2O_3-δ (x = 0, 0.05, 0.1) perovskite oxide materials (LSFN100, LSFN95, and LSFN90) are evaluated as symmetrical electrode materials for CO₂ electrolysis. All three perovskite oxides display pure cubic perovskite structure. The introduction of A-site deficiency results in greater tendency of in-situ exsolution and stronger CO₂ adsorption capacity, which are verified by temperature-programmed reduction of H₂ and temperature-programmed desorption of CO₂. Furthermore, the current densities with LSNF90 symmetrical cell are 1.72, 1.18 and 0.72 A·cm⁻² under the applied voltage of 1.8 V at 850, 800 and 750 °C to electrolysis CO₂, respectively. Low polarization resistance of 0.186, 0.267 and 0.454 Ω·cm² is also observed under open circuit conditions at 850, 800 and 750 °C, respectively. A-site deficiency of perovskite materials reduces the activation energy of oxygen evolution reaction (OER) and carbon dioxide reduction reaction (CO₂RR). Symmetrical cell with LSFN90 electrode shows good electrochemical performance and long-term stability for CO₂ electrolysis.     

Molded micro- and mesoporous carbon/silica composite from rice husk and beet sugar

A molded carbon/silica composite with high micro- and mesoporosity, as well as a high bulk density, was fabricated by activating a disk-molded precursor made from carbonized rice husk (RH) and beet sugar (BS) at 875 °C in CO₂. The pore structure of the RH- and BS-based carbon/silica composite (RBC) was analysed in relation to the bulk density. An activation time of 2.0 h provided the largest BET specific surface area (1027 m²/g) and total pore volume (0.68 cm³/g) and a low bulk density (0.54 g/cm³). An RBC that was first activated for 1 h was immersed again in BS syrup and then activated in CO₂ for 1 h. This two-step activation process provided both a high bulk density (0.69 g/cm³) and a highly textured structure (BET specific surface area, 943 m²/g; total pore volume, 0.56 cm³/g). The immersion in BS syrup was useful for improving the texture without reducing the bulk density, in comparison to one-step activation for 1.0 h. The suspension of the RBCs was basic because of the residual inorganic compounds of potassium and calcium. However, the basicity of the suspension was alleviated by washing the RBCs with water.     

Microstructural variations of lignite,subbituminous and bituminous coals and their high temperature chars

Microstructure of a North Dakota lignite, a Washington subbituminous and a New Mexico bituminous coal and their chars produced by devolatilization in nitrogen at 1000 to 1300°C was investigated in this work using the CO₂ adsorption method conducted at 25°C. For each coal and char, specific surface area, micropore volume, micropore surface area, mean equivalent radius of micropores and characteristic energy of adsorption, as well as micropore volume distribution, were determined, and their variations with devolatilization temperature studied and interpreted. It was found that, overall, specific surface areas, micropore volumes and micropore surface areas of chars decreased monotonically as devolatilization temperature was raised from 1000 to 1300°C, although most of these values were much larger than that of their parent coals. The micropore volume distributions of the three coals and their high temperature chars were interpreted and found to provide an interesting insight into the micro structural variations of these coals and chars.     

Template-free synthesis of N-doped porous carbons and their gas sorption properties

Nitrogen-rich carbon precursors are prepared and subsequently used for the preparation of N-doped porous carbons (NPCs). Two carbon precursors (CPs), CP-60 and CP-40, are prepared at different temperatures, 60 °C and 40 °C, respectively. The obtained CP materials are almost nonporous based on the N₂ adsorption/desorption analysis. These nonporous CP materials are converted into NPC materials through a carbonization at 800 °C. Porous NPC-60-800 and NPC-40-800 are prepared from CP-60 and CP-40, respectively. In contrast to the CP materials, the NPC materials exhibit higher surface areas. The surface areas of NPC-60-800 and NPC-40-800 are 422.9 m² g⁻¹ and 520.8 m² g⁻¹, respectively. The respective N-contents of NPC-60-800 and NPC-40-800 materials are 4.30 and 3.54 wt.% based on the elemental analysis. The types of N-containing groups of NPC materials are investigated by X-ray photoelectron spectroscopy (XPS) analysis. The NPC materials are good sorbents for CO₂ storage. The heats of CO₂ adsorption (Q_st) are 48.4 kJ mol⁻¹ for NPC-60-800 and 47.0 kJ mol⁻¹ for NPC-40-800. Both materials are also good H₂ sorbents at 77 K: 1.23 wt.% (NPC-60-800) and 1.22 wt.% (NPC-40-800).     

Investigation of sorption and diffusion of supercritical carbon dioxide into poly(vinyl chloride)

The interaction of supercritical carbon dioxide (scCO₂) with poly(vinyl chloride) (PVC) was systematically investigated. PVC films of 0.5 mm thickness were treated with CO₂ at pressures between 5 and 40 MPa, at temperatures between 40 and 70°C and soaking times between 0.5 and 7 h. The gravimetric desorption data were kinetically and thermodynamically evaluated assuming Fickian diffusion and the morphology changes due to the CO₂ treatment investigated by microscopic methods. The sorbed amount of CO₂, q (q=g_CO2/g_polymer) ranged between 0.03 (5 MPa, 70°C) and 0.13 (15 MPa, 40°C). The desorption diffusivities, D_d, were in the order of 0.1×10⁻¹¹ m²/s and decreased with decreasing amounts of CO₂. In contrast, the sorption diffusivities, D_s, were markedly higher and varied between 0.7×10⁻¹¹ and 2.5×10⁻¹¹ m²/s (20 MPa, 40–70°C). The CO₂ treatment changed the polymer chain structure, macroscopically visualized by the film opaqueness and by the density decrease to 1.05 g/cm³. Microcellular structures were not detected.     

Supercritical CO2-assisted extrusion foaming: A suitable process to produce very lightweight acrylic polymer micro foams

A strategy of CO₂-assisted extrusion foaming of PMMA-based materials was established to minimize both foam density and porosities dimension. First a highly CO₂-philic block copolymer (MAM: PMMA-PBA-PMMA) was added in PMMA in order to improve CO₂ saturation before foaming. Then the extruding conditions were optimized to maximize CO₂ uptake and prevent coalescence. The extruding temperature reduction led to an increase of pressure in the barrel, favorable to cell size reduction. With the combination of material formulation and extruding strategy, very lightweight homogeneous foams with small porosities have been produced. Lightest PMMA micro foams (ρ = 0.06 g cm⁻³) are demonstrated with 7 wt% CO₂ at 130°C and lightest blend micro foams (ρ = 0.04 g cm⁻³) are obtained at lower temperature (110°C, 7.7 wt% CO₂). If MAM allows a reduction of T^foaming, it also allows a much better cell homogeneity, an increase in cell density (e.g., from 3.6 10⁷ cells cm⁻³ to 2 to 6 10⁸ cells cm⁻³) and an overall decrease in cell size (from 100 to 40 μm). These acrylic foams produced through scCO₂-assisted extrusion has a much lower density than those ever produced in batch (ρ ≥ 0.2 g cm⁻³).     

Reaction,densification, and mechanical properties of Ti2AlCx ceramics at low applied pressure and temperature

Ti₂AlC_x ceramic was produced by reactive hot pressing (RHP) of Ti:Al:C powder mixtures with a molar ratio of 2:1:1–.5 at 10–20 MPa, 1200–1300°C for 60 min. X-ray diffraction analysis confirmed the Ti₂AlC with TiC, Ti₃Al as minor phases in samples produced at 10–20 MPa, 1200°C. The samples RHPed at 10 MPa, 1300°C exhibited ≥95 vol.% Ti₂AlC with TiC as a minor phase. The density of samples increased from 3.69 to 4.04 g/cm³ at 10 MPa, 1200°C, whereas an increase of pressure to 20 MPa resulted from 3.84 to 4.07 g/cm³ (2:1:1 to 2:1:.5). The samples made at 10 MPa, 1300°C exhibited a density from 3.95 to 4.07 g/cm³. Reaction and densification were studied for 2Ti–Al–.67C composition at 10 MPa, 700–1300°C for 5 min showed the formation of Ti–Al intermetallic and TiC phases up to 900°C with Ti, Al, and carbon. The appearance of the Ti₂AlC phase was ≥1000°C; further, as the temperature increased, Ti₂AlC peak intensity was raised, and other phase intensities were reduced. The sample made at 700°C showed a density of 2.87 g/cm³, whereas at 1300°C it exhibited 3.98 g/cm³; further, soaking for 60 min resulted in a density of 4.07 g/cm³. Microhardness and flexural strength of Ti₂AlC_0.8 sample were 5.81 ± .21 GPa and 445 ± 35 MPa.     

Tailoring the surface chemistry and porosity of activated carbons: Evidence of reorganization and mobility of oxygenated surface groups

An activated carbon with developed porosity and surface area (S_BET = 2387 m² g⁻¹) was prepared by chemical activation and then oxidized with ammonium peroxydisulfate. The oxidation treatment destroyed mesopore walls leading to a severe surface area reduction. Specific thermal treatments were carried out in different portions of the oxidized sample to selectively remove the oxygenated surface complexes. The combination of different techniques revealed that thermal treatment between 300 and 500 °C produces a strong reorganization of oxygenated groups on the chemical structure of carbons. CO₂-evolving groups (around 75 wt.%) are selectively transformed into CO-evolving groups. These processes only occur inside the pores, and involve CO₂ desorption and re-adsorption in this temperature range. At a higher treatment temperature (700 °C), re-oxidation is prevented and the surface chemistry becomes quite similar to the original activated carbon.     

Preparation of Activated Carbons from Tobacco Stems by Potassium Hydroxide Activation and Phosphine Adsorption

Activated carbon preparation from tobacco stems by KOH activation at different activation temperatures and KOH/char mass ratios were investigated in this study. The effects of preparation parameters on activated carbon pore structure, morphometrics, microcrystallinities, and surface functional groups were characterized by N₂ adsorption, SEM, XRD, and FTIR technologies, respectively. The optimum preparation condition of activated carbon was activation temperature of 850°C, and KOH/char mass ratio of 2. Under this condition, the BET surface area of 2215 m²/g, and the pore volume of 1.343 cm³/g can be obtained. Prepared activated carbon showed clearly honeycomb holes, and a predominated amorphous structure. With increase of activation temperature and KOH/char mass ratio, decrease of surface oxygen functional group, and aromatization of the carbon structure was found. The activated carbon was subject to PH₃ purification, and the maximum PH₃ adsorption capacity of 253 mg/g can be realized based on well prepared KOH-AC with modification of 2.5% Cu. It seems that the activated carbon produced from chemical activation of tobacco stem would be an effective and alternative adsorbent for PH₃ adsorption because of its high surface area, adsorption capacity, and low cost.     

Grafting of styrene/maleic anhydride copolymer onto PVDF membrane by supercritical carbon dioxide: Preparation,characterization and biocompatibility

Herein we report the surface modification of poly(vinylidene fluoride) (PVDF) microporous membrane via thermally induced graft copolymerization with maleic anhydride (Man)/styrene (St) in supercritical carbon dioxide (SC CO₂). SC CO₂, as a solvent and carrier agent, could accelerate mass transfer of monomers inside polymer matrixes and then facilitate the graft copolymerization on the surface of the membrane and within membrane pores, which were confirmed by FT-IR/ATR and XPS spectra together with SEM photographs. The effects of SC CO₂ pressure and temperature and the monomer concentration on the graft copolymerization were investigated. The modified PVDF membranes containing from 0 to 7 wt.% of grafted St–Man copolymer (SMA) were prepared and analysed in terms of surface microstructure, composition, hydrophilicity and biocompatibility. Solid-state ¹³C CP/MAS NMR and DSC indicated that the grafted SMA on the PVDF membrane had the alternative sequence structure and formed the different phases in the modified membrane, where the grafted SMA was associated with T_g of 122.8 °C and the PVDF matrix with T_m of 161.2 °C. The static contact angle measurements revealed that remarkable and permanent hydrophilicity was obtained upon grafting SMA. The experiments of BSA adsorption and cell growth also showed that the surface of SMA-based PVDF membrane has excellent biocompatibility.