Carbonization and CO<Subscript>2</Subscript> activation of scrap tires: Optimization of specific surface area by the Taguchi method

This research demonstrates the production of activated carbon from scrap tires via physical activation with carbon dioxide. A newly constructed apparatus was utilized for uninterrupted carbonization and activation processes. Taguchi experimental design (L16) was applied to conduct the experiments at different levels by altering six operating parameters. Carbonization temperature (550–700 °C), activation temperature (800–950 °C), process duration (30–120 min), CO₂ flow rate (400 and 600 cc/min) and heating rate (5 and 10 °C/min) were the variables examined in this study. The effect of parameters on the specific surface area (SSA) of activated carbon was studied, and the influential parameters were identified employing analysis of variance (ANOVA). The optimum conditions for maximum SSA were: carbonization temperature=650 °C, carbonization time=60 min, heating rate=5 °C/min, activation temperature= 900 °C, activation time=60 min and CO₂ flow rate=400 cc/min. The most effective parameter was activation temperature with an estimated impact of 49%. The activated carbon produced under optimum conditions was characterized by pore and surface structure analysis, iodine adsorption test, ash content, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The process yield for optimized activated carbon was 13.2% with the following properties: specific surface area=437 m²/g, total pore volume=0.353 cc/g, iodine number=404.7 mg/g and ash content=13.9% along with an amorphous structure and a lot of oxygen functional groups. These properties are comparable to those of commercial activated carbons.     

Coconut kernel-derived activated carbon as electrode material for electrical double-layer capacitors

Carbonization of milk-free coconut kernel pulp is carried out at low temperatures. The carbon samples are activated using KOH, and electrical double-layer capacitor (EDLC) properties are studied. Among the several samples prepared, activated carbon prepared at 600 °C has a large surface area (1,200 m² g^?1). There is a decrease in surface area with increasing temperature of preparation. Cyclic voltammetry and galvanostatic charge–discharge studies suggest that activated carbons derived from coconut kernel pulp are appropriate materials for EDLC studies in acidic, alkaline, and non-aqueous electrolytes. Specific capacitance of 173 F g^?1 is obtained in 1 M H₂SO₄ electrolyte for the activated carbon prepared at 600 °C. The supercapacitor properties of activated carbon sample prepared at 600 °C are superior to the samples prepared at higher temperatures.     

Kinetics and reaction mechanism of hydrogen sulfide oxidation over activated carbon in the temperature range of 125–200°c

The kinetics and reaction mechanism of the oxidation of hydrogen sulfide over activated carbon were studied in the temperature range 125–200°C. The heats of adsorption of oxygen and H₂S were found to be 73.8 and 16.0 kJ/mol, respectively, in the above temperature range. The sorption constants and the reaction constant have been expressed as a function of temperature. The role of water in the oxidation reaction has been clarified. No evidence was found to show that sulfur catalyzes the oxidation reaction.     

Oxidation of low concentrations of hydrogen sulphide: Process optimization and kinetic studies

Low concentrations (e.g. < 3) of H₂ S in natural gas can be selectively oxidized over an “granular Hydrodarco” activated carbon catalyst to elemental sulphur, water and a small fraction of by-product sulphur dioxide, SO₂. To optimize the H₂ S catalytic oxidation process, the process was conducted in the temperature range 125—200 °C, at pressures 230—3200 kPa, with the O/H₂ S ratio being varied from 1.05 to 1.20 and using different types of sour and acid gases as feed. The optimum temperature was determined to be approximately 175 °C for high H₂ S conversion and low SO₂ production with an O/H₂ S ratio 1.05 times the stoichiometric ratio. The life of the activated carbon catalyst has been extended by removing heavy hydrocarbons from the feed gas. The process has been performed at elevated pressures to increase H₂ S conversion, to maintain it for a longer period and to minimize SO₂ production. The process is not impeded by water vapour up to 10 mol% in the feed gas containing low concentrations of CO₂ (< 1.0). A decrease in H₂ S conversion and an increase in SO₂ production were obtained with an increase in water vapour in the feed gas containing a high percentage of CO₂. The process works well with “sour natural gas” containing approximately 1% H₂ S and with “acid gas” containing both H₂ S and CO₂. It gives somewhat higher H₂ S conversion and low SO₂ production with feed gas containing low concentrations of CO₂. A kinetics study to determine the rate-controlling step for the H₂ S catalytic oxidation reaction over “granular Hydrodarco” activated carbon has been conducted. It was concluded that either adsorption of O₂ or H₂ S from the bulk phase onto the catalyst surface is the rate-controlling step of the H₂ S catalytic oxidation reaction.     

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).     

Sequestration of carbon dioxide by m-xylylenediamine with forming a crystalline adduct

The reaction of m-xylylenediamine (mXD) with carbon dioxide was examined and its feasibility as a sequestration material of carbon dioxide was discussed. The reaction was monitored by using the FT-IR and gravitational methods, while the crystalline structure of the reaction product was investigated with elemental analysis, powder Xray diffraction, single crystallography, and ¹³C MAS NMR spectroscopy. Even at ambient temperature, mXD reacted with carbon dioxide of low partial pressure in the atmosphere and produced a 1: 1 molar adduct which appeared as a white crystalline material. The hydrogen bonds that formed between the adduct molecules resulted in the formation of a stable crystal. The sequestration capacity of mXD was very great, ～280 mg g _mXD ^?1 below 50 °C. An adsorbent prepared by dispersing mXD on silica was capable of capturing carbon dioxide, but it could be regenerated by evacuating at 25 °C.     

Stannous chloride—an effective reducing agent for the removal of selenium(IV) from acidic solution

BACKGROUND: Selenium removal from aqueous solutions can be a significant industrial problem, particularly in the metallurgical industry. In order to evaluate new reducing agents for this application, the reduction of selenious acid (H₂SeO₃) species with stannous ions (Sn²⁺) from weakly acidic sulfate solutions containing 300 mg L^?1 of selenium at 23 °C was studied. RESULTS: At initial pH values < 1.3 and molar ratio ≥ 2, less than 0.5 µg L^?1 of selenium(IV) remained in solution after reduction. The reductive precipitation reaction started as soon as the stannous ions were added to the selenium‐bearing solution and was completed in less than 5 min. The reaction products, characterized using X‐ray diffraction, electron microscopy, particle and surface area measurements, X‐ray photoelectron spectroscopy and chemical analysis, were composed of approximately equal amounts of tin selenide and tin dioxide. In addition to tin selenide a minor amount of selenium(IV) was found to be removed via adsorption on the tin dioxide formed in situ. Tests with a complex industrial solution also resulted in full and stable selenium precipitation. CONCLUSION: Stannous ions were found to be very effective in removing selenious ions from synthetic and industrial solutions, producing very stable precipitates. Copyright © 2012 Society of Chemical Industry     

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     

Effects of the oxidation temperature on the structure and properties of polyacrylonitrile‐based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The effects of the oxidation temperature of the PAN hollow fiber precursor on the microstructure, specific surface, pore size distribution, and adsorption properties of PAN‐based activated carbon hollow fiber (PAN‐ACHF) were studied. When PAN hollow fibers were oxidized at 270°C, because of drastic oxidation, chain scission occurred, and the number of pores within and on the surface of the resultant PAN‐ACHF increased, but the pores were just in the thinner region of the skin of PAN‐ACHF. The surface area of PAN‐ACHF reached a maximum when the oxidation temperature was 270°C. The adsorption ratios to creatinine were all higher than 90% at all oxidation temperatures, and the adsorption ratio to VB₁₂ reached a maximum (97%) at 230°C. The dominant pore sizes of the mesopores in PAN‐ACHF ranged from 2 to 5 nm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 203–207, 2005     

Influence of activation temperature on the properties of polyacrylonitrile-based activated carbon hollow fiber

In this work, polyacrylonitrile hollow fiber was oxidized, carbonized, and activated by carbon dioxide into activated hollow carbon fiber. The effects of the activation temperature on the characteristics of the resulting activated hollow carbon fiber, including the mechanical properties, the surface area, and pore size distribution, were studied. The results show that by activating for 40 min at 800°C, the mechanical properties was better, the surface area was larger, and the pore size was distributed in three ranges. Higher activation temperature led to the decrease in the mechanical strength, the increase in the burn-off degree of the surface, the reduce of the portion of micropores, and the greatly broadening the pore size distribution. Lower activation temperature can only produce pleading on the surface of the fiber instead of open pores, due to the milder attack of CO₂. Therefore, the characteristics of the activated hollow carbon fiber can be controlled by the activation temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1331–1336, 1998     

Rapid solvothermal synthesis of microporous UiO-66 particles for carbon dioxide capture

One of the important metal-organic frameworks known as UiO-66 has received significant attention recently due to its unprecedented chemical and thermal stability, with exceptionally high surface area. We prepared UiO-66 particles by a rapid solvothermal method which took only 30 min at 120 °C to prepare, compared to the previous work which took longer than 12 h. Changing the precursor’s concentration ratio from 0.5 to 1.5 and reaction temperature from 80 °C to 140 °C resulted in the increase of UiO-66 particle size from 30 to 150 nm. The highest surface area of ca. 1,300 m²/g was achieved at concentration ratio of 1 and temperature of 120 °C with bi-modal pore sizes of ca 0.60 nm and 1.25 nm, respectively. The UiO-66 particles with the highest surface area were then employed to capture carbon dioxide from a binary gas mixture. Results from CO₂ adsorption capacity measurement using UiO-66 indicate that the adsorbent was capable of capturing 1.3611 mmol/g at pressure of 1.5-1.7 bar and flowrate of 300 cm³/min.     

Surface properties of carbons from poly(vinyl chloride)

Non-activated carbons were prepared by the thermal degradation of poly(vinyl chloride) (PVC) in air or nitrogen atmosphere in the temperature range 600-1000°C. Carbon dioxide-activated carbons from PVC were also obtained by gasification of non-activated carbon from PVC at 900°C burn-off (4-50%). Thermal degradation in air atmosphere gave high carbon yield because the oxygen of air increased crosslinking at lower temperature and chemisorbed on the carbon surface at high temperatures. Thermal degradation in air and gasification with carbon dioxide created carbon-oxygen surface groups which increased the hydrophilicity of the carbon surface and consequently increased water adsorption capacity. Gasification with carbon dioxide to high burn-off created new pores and widened already existing pores.     

Preparation and CO2 adsorption of amine modified Mg–Al LDH via exfoliation route

In response to the recent focus on reducing carbon dioxide emission, the preparation and characterization of organically functionalized materials for use in carbon capture have received considerable attention. In this paper the synthesis of amine modified layered double hydroxides (LDHs) via an exfoliation and grafting synthetic route is reported. The materials were characterized by elemental analysis (EA), powder x-ray diffraction (PXRD), diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) and thermogravimetric analysis (TGA). Adsorption of carbon dioxide on modified layered double hydroxides was investigated by TGA at 25–80 °C. 3-[2-(2-Aminoethylamino) ethylamino]propyl-trimethoxysilane modified MgAl LDH showed a maximum CO₂ adsorption capacity of 1.76 mmol g^?1 at 80 °C. The influence of primary and secondary amines on carbon dioxide adsorption is discussed. The carbon dioxide adsorption isotherms presented were closely fitted to the Avrami kinetic model.     

Low temperature atomic layer deposition of SiO2 thin films using di-isopropylaminosilane and ozone

Silicon dioxide (SiO₂) films are deposited by atomic layer deposition (ALD) at low temperatures from 100 to 200 °C using di-isopropylaminosilane (SiH₃N(C₃H₇)₂, DIPAS) as the Si precursor and ozone as the reactant. The SiO₂ films exhibit saturated growth behavior confirming the ALD process, showing a growth rate of 1.2 Å/cycle at 150 °C, which increases to 2.3 Å/cycle at 250 °C. The activation energy of 0.24 eV, extracted from temperature range of 100–200 °C, corresponds to the reported energy barrier for reaction between DIPAS and surface –OH. The temperature dependence of the growth rate can be explained in terms of the coverage and chemical reactivity of the thermally activated precursor on the surface. The ALD-SiO₂ films deposited at 200 °C show properties such as refractive index, density, and roughness comparable to those of conventionally deposited SiO₂, as well as low leakage current and high breakdown field. The fraction of Si–O bond increases at the expense of Si–OH at higher deposition temperature.     

Diuron Multilayer Adsorption on Activated Carbon from CO2 Activation of Grape Seeds

Granular activated carbons were obtained from grape seeds by pyrolysis at 600°C and subsequent physical activation with CO₂ (750–900°C, 1–3 h, 25–74% burn-off). The carbon and ash content increased during the activation, reaching values of 79.0% and 11.4%, respectively. Essentially microporous materials with BET surface areas between 380 and 714 m²/g were obtained. The performance of the activated carbon in the adsorption of diuron in aqueous phase was studied within the 15–45°C temperature range. Equilibrium data showed that the maximum uptake increased with temperature from 120 to 470 µmol/g, also evidencing some dependence of the adsorption mechanism on temperature. Data were fitted to five isotherm models [Langmuir, Freundlich, Dubinin–Radushkevich, BET, and GAB (Guggenheim, Anderson, and de Boer)]. Kinetic data were analyzed using first- and second-order rate equations and intraparticle diffusion model. The second-order rate constant values obtained (2.8–13.5 × 10^?3 g/µmol min) showed that the hollow core morphology of the material favors the adsorption kinetics.     

Effects of Thermal Treatment on Gas Transport Through Porous Silica Membranes

Abstract

The effects of thermal treatment from 180°C to 1150°C on the gas transport properties of porous silica membranes were systematically studied for various gases. The permeance of all gases, except for CO₂, has a maximum at 800°C. The CO₂ permeance was constant from 180°C to 600°C and then decreased monotonically. Membranes thermally treated at 1150°C did not exhibit any gas permeation because of pore collapse. The gas transport behavior follows a combination of Knudsen diffusion and surface diffusion for all gases tested except for carbon dioxide. The permeation of carbon dioxide is strongly affected by capillary condensation. We propose a new transport model composed of two components; that is, the Knudsen diffusion factor, α, and the surface diffusion factor, β. A transition was observed for α and β at around 800–900°C, which is close to the strain point of the membrane. This transition treatment temperature can be correlated with the changes in gas permeance. The model allows qualitative evaluation of gas transport through porous membranes regardless of their actual microporous structures.     

Interfacial tension and density measurement of the system corn germ oil – carbon dioxide at low temperatures

In this article, the physical properties of corn germ oil at high pressures of up to 30 MPa and at low temperatures from ?10 °C to 22 °C are presented. We measured the interfacial tension of the commercially available corn germ oil Mazola® and of unrefined corn germ oil in contact with carbon dioxide, as well as the density of carbon dioxide‐saturated corn germ oil. The interfacial tension of refined and unrefined corn germ oil in contact with gaseous carbon dioxide at temperatures above ?10 °C depends on time, while at higher pressures the equilibrium value of the interfacial tension is reached immediately after the formation of the drops or bubbles. The interfacial tension of unrefined corn germ oil in contact with carbon dioxide is higher than the interfacial tension of refined corn germ oil. This fact is explained in this article. The interfacial tension of refined and of unrefined corn germ oil in contact with carbon dioxide decrease with rising pressure and can be described as a function of the carbon dioxide density for the examined temperature range. The density of carbon dioxide‐saturated corn germ oil is linearly dependent on pressure, with a high slope if carbon dioxide is gaseous and with a low slope if carbon dioxide is liquid.     

Effect of KI and KOH Impregnations over Activated Carbon on H2S Adsorption Performance at Low and High Temperatures

In the present work, commercial-grade activated carbon was modified by steam activation to improve its surface properties for high temperature desulfurization. The modified sample was also further upgraded by impregnating with KOH and KI to promote the chemisorption with of H₂S. The H₂S adsorption performance was tested under the temperature range of 30–550°C using the temperature program adsorption technique to understand the effect of adsorption temperature on the material adsorption characteristic. It was found that at ambient temperature, the impregnation of activated carbon with KOH can promote the H₂S adsorption capacity of activated carbon, whereas the impregnation with KI does not provide a significant beneficial effect. At high adsorption temperature (upto 550°C), both KOH and KI impregnation considerably improve the H₂S adsorption performance of activated carbon in terms of the adsorption capacity and breakthrough time. It was revealed from N₂ adsorption, SEM and EDS measurement that the chemical reactions between H₂S and alkaline compounds (KOH and KI) are promoted at high temperature. Based on all experimental results, the equilibrium adsorption model using the linear isotherm was developed to predict the adsorption behavior of these sorbents in terms of equilibrium isotherm constant and mass transfer coefficient for later scaling-up process.     

Enlargement of the micropores of a caking bituminous coal by controlled oxidation

In a study of the enlargement of pores of coals it has been found that treatment of a bituminous coal (PSOC No. 371, from the Pennsylvania State University Coal Section) with a 5:95 O₂:N₂ stream 4 h at 400 °C increases the surface area as measured by nitrogen adsorption at 77K by a factor of at least 50 to a value 52 m² g^?1. The increase in pore size was accompanied by a 9.7% weight loss. Simultaneously, the area as measured by carbon dioxide at 195K increased from 61 to 136 m² g^?1 and that measured by carbon dioxide at room temperature increased from 125 to 237 m² g^?1. Attempts to enlarge the pores by oxidation with hydrogen peroxide or ozone were unsuccessful. A Pittsburgh coal subject to a small percentage of oxygen in nitrogen or steam at 300 to 400 °C showed a surface area as measured by nitrogen adsorption of less than 1 m² g^?1 both before and after such pretreatment. This same coal with a 5:95 O₂:N₂ stream for 4 h at 450 °C showed a surface area of 110 m² g^?1 measured by nitrogen adsorption at 77K.     

Influence of Activated Carbon on the Thermal Decomposition of Hydroxylammonium Nitrate

This paper presents experimental results for the thermal decomposition of hydroxylammonium nitrate (HAN) in the presence of activated carbon with a high specific surface (up to 3000 m²/g) obtained by activation of rice husk with potassium hydroxide at a temperature of 700°C in a rotating spherical furnace. The addition of activated carbon reduces the temperature of the onset of decomposition of HAN from 185 to 86 ± 0.5°C. The burning rate of HAN doped with activated carbon increases to 400 mm/s at an overpressure of 6 MPa. It has been shown that the addition of activated carbon reduces the amount of NO _x gases produced by decomposition to 30%.