Removal of nitrogen oxides from air by chemicals-impregnated carbons

Fixation of nitrogen oxides (NO_x) in air onto granular activated carbon impregnated with chemicals was attempted to improve removal efficiency of NO_x by activated carbon adsorption. Nitric oxide (NO) and nitrogen dioxide (NO₂), were tried to remove by a flow test. Fixed-bed adsorption breakthrough curves were obtained when some kinds of carbon were used. The amount adsorbed of NO₂ changed with the amount and kinds of metallic salts impregnated. Chemicals-impregnated carbons were prepared from a commercial activated carbon. Among obtained carbons, the one which showed the highest selectivity for NO_x was chosen, and its performance with the change in humidity was determined. Removal mechanism of NO₂ was estimated, and the carbon impregnated with potassium hydroxide was found to be superior to any other carbon tested. The amount of the adsorbed NO and that produced by the reduction of NO₂ were determined from the breakthrough curves.     

Enhanced mercury adsorption in activated carbons from biomass materials and waste tires

Agricultural residues and waste tires constitute an important source of precursors for activated carbon production. Activated carbons offer a potential tool for mercury emissions control. In this work, pine and oak wood, olive seed and tire wastes have been used for the preparation of activated carbons, in order to be examined for their mercury removal capacity. In the case of activated carbons produced from pine/oak woods and tire wastes, a two stage physical activation procedure was applied. Activated carbons derived from olive seeds were prepared by chemical activation using KOH. Pore structure of the samples was characterized by N₂ and CO₂ adsorption, while TPD-IR experiments were performed in order to determine surface oxygen groups. Hg° adsorption experiments were realized in a bench-scale adsorption unit consisting of a fixed-bed reactor. The influence of activation technique and conditions on the resulted activated carbon properties was examined. The effects of pore structure and surface chemistry of activated carbons were also investigated. Activated carbons produced from olive seeds with chemical activation possessed the highest BET surface area with well-developed micropore structure, and the highest Hg° adsorptive capacity. Oxygen surface functional groups (mainly lactones) seem to be involved in Hg° adsorption mechanism.     

The adsorptive properties of carbonised olive stones

Olive stones were carbonised to 1120°K and activated in carbon dioxide at 1100°K to 20% burn-off. Adsorptive properties were measured by adsorption of nitrogen (77°K) and carbon dioxide (195°K, 273°K) using the Langmuir and Dubinin equations of adsorption to deduce effective surface areas. The extents of development, with activation of meso- and macro-porosity were monitored by mercury porosimetry; the surface textures of the parent olive stones, and carbonised and activated products were described by scanning electron microscopy. The carbonised stones had a surface area of 500 k(m)² kg⁻¹ in microporosity increasing to 1500 k(m)² kg⁻¹ at twenty per cent burn-off. This sample had a micropore volume of 600 cm³ kg⁻¹ and 600 cm³ kg⁻¹ in the meso- and macro-porosity. The activation process did not occur evenly, but selectivity. There was no strong evidence for catalytic initiation of the selective gasification. The activated carbons were pseudomorphs of the parent olive stones and did not abraid easily. Their purity (0·21% ash) and low sulphur content (less than 0·1%) may make these active carbons commercially attractive.     

Preparation and characterization of active carbons from olive stones

Olive stones have been carbonized under a flow of nitogen in the temperature range from 700 to 900°C and activated in a CO₂ flow in the range from 675 to 875°C. ZnCl₂ was used in some of the activation processes. The adsoptive characteristics of the carbonized and activated samples have been determined by adsorption of nitrogen (77 and 90 K), carbon dioxide (195 and 273 K), n-butane (273 K) and methylene blue (aqueous solution at 298 K). Meso and macroporosity have been followed by mercury porosimetry. The resulting activated carbons have very large surface areas as well as a highly developed microporosity. The most adequate experimental conditions for the preparation of active carbons, highly microporous but with a well developed meso and macroporosity, are discussed. All active carbons prepared have a very low ash content and complete absence of sulphur, both very attractive characteristics.     

The effect of activation method on the properties of pecan shell‐activated carbons

Pecan shell chars were activated using steam, carbon dioxide (CO₂), or phosphoric acid (H₃PO₄) to produce granular activated carbons (GACs). The GACs were characterized for select physical, chemical and adsorption properties. Air oxidation of the GACs was used to increase copper ion (Cu²⁺) adsorption. BET surface areas of pecan carbons were equal to or greater than commercial GACs. Carbon dioxide activation favored microporosity, while the other activations increased both mesoporosity and microporosity. Bulk densities and particle attrition of the pecan shell GACs were generally similar to the commercial carbons. Air oxidation of steam‐and CO₂‐activated GACs increased copper ion adsorption, although not to the same extent as GACs made by H₃PO₄ activation. Copper ion adsorption and the amount of titratable functional groups greatly exceeded the values for the commercial GACs. Steam‐and CO₂‐activated pecan shell carbons were similar to but in some cases exceeded the ability of commercial GACs to remove certain organic compounds from water. GACs from pecan shells showed considerable commercial potential to remove metal ions and organic contaminants from water. © 1999 Society of Chemical Industry     

Adsorption of sulfur dioxide onto activated carbons prepared from oil‐palm shells impregnated with potassium hydroxide

Adsorption of sulfur dioxide (SO₂), a gaseous pollutant, onto activated carbons prepared from oil‐palm shells pre‐treated with potassium hydroxide (KOH) impregnation was studied. Experimental results showed that SO₂ concentration and adsorption temperature affected significantly the amount of SO₂ adsorbed and the equilibrium time. However, sample particle sizes influenced the equilibrium time (due to effect of diffusion rate) only. Desorption at the same temperature of adsorption and a higher temperature of 200 °C confirmed the presence of chemisorption due to pre‐impregnation. Impregnation with different activation agents was found to have limited effect on the inorganic components of the sample. Compared with the activated carbon pre‐treated with 30% phosphoric acid (H₃PO₄) that had larger BET and micropore surface areas, the sample impregnated with 10% KOH had a higher adsorptive capacity for SO₂, which was closely related to the surface organic functional groups of the sample. In general, the activated carbon prepared from oil‐palm shell impregnated with KOH was more effective for SO₂ adsorption and its adsorptive capacity was comparable to some commercial activated carbons. © 2000 Society of Chemical Industry     

The effect of commercial carbon de‐ashing on its thermal stability and porosity

The influence of Korver's de‐ashing procedure on the changes in the thermal stability and porosity of three commercial granular activated carbons: D43/1 (Carbo‐Tech, Essen, Germany), AHD, and WD‐extra (Hajnówka, Poland) was investigated. For original carbons, carbons treated only with concentrated HCl, and completely de‐ashed carbons (treated with concentrated HCl and HF) the thermogravimetric results in air and helium, apparent and true densities, low‐temperature nitrogen adsorption, and mercury porosimetry are reported and compared. The changes in thermal stability and porosity are discussed together with the mechanism of carbon de‐ashing. © 1999 Society of Chemical Industry     

Adsorption of lead on activated carbons from olive stones

Studies on the adsorption of lead on activated carbons from aqueous solutions are described. Olive stones have been used as raw material to prepare the activated carbon samples. The porous texture and the chemical nature of the surface of the carbon samples were studied. The adsorption yield as a function of pH, salinity and presence of different cations has been investigated. The results obtained by using these activated carbons have been compared with those corresponding to a commercial activated carbon. All samples show a high adsorption capacity against lead ions.     

Non-porous reference carbon for N2 (77.4 K) and Ar (87.3 K) adsorption

A new non-porous carbon material from granular olive stones has been prepared to be used as a reference material for the characterization of the pore structure of activated carbons. The high precision adsorption isotherms of nitrogen at 77.4 K and argon at 87.3 K on the newly developed sample have been measured, providing the standard data for a more accurate comparative analysis to characterize disordered porous carbons using comparative methods such as t- and α_S-methods.     

On the nature of surface acid sites of chlorinated activated carbons

Two activated carbons containing different amounts of chlorine were obtained by chlorination of an activated carbon prepared from olive stones. Variations in surface physics and chemistry of the samples were studied by N₂ and CO₂ adsorption, mercury porosimetry, TPD, XPS, pH_PZC measurements, and by testing their behaviour as catalysts in the decomposition reaction of isopropanol. Our results indicate that chlorination of activated carbon increases its Lewis acidity but decreases its Brönsted acidity, which can be explained by the resonance effect introduced into the aromatic rings of graphene layers by the chlorine atoms covalently bound to their edges. This resonance effect could also explain the changes observed in the thermal stability of C-Cl and C-O bonds.     

Surface modified granular activated carbon for enhancement of nickel adsorption from aqueous solution

Coal-based granular activated carbon was modified with acetates of sodium, potassium and lithium at concentrations of 10 and 15% and used as adsorbents to explore the adsorption mechanism of nickel ion in aqueous solution. Acetate treatment reduced surface area and pore volume of the activated carbons, but the adsorption amount of Ni(II) on the modified activated carbons (MAC) was greater than that on the virgin activated carbon. The adsorption depended on pH of the solution with an optimum at 4.5 and the adsorbed nickel could be fully desorbed by using 0.05M HCl solution. The maximum adsorption capacity of nickel ion on Li (15 wt%) modified activated carbon was 151.3 mg/g and the adsorption isotherm follows Langmuir, Sips, and Redlich-Peterson isotherm models better than the Freundlich isotherm model. The kinetic data was better fitted by a non-linear form of the pseudo-first order than the pseudo-second order, but the difference between two kinetic models was small.     

Removal of elemental mercury from coal combustion flue gas by chloride-impregnated activated carbon

In this work, adsorption of vapour-phase elemental mercury (Hg⁰) from pulverised-coal combustion flue gas by commercially available granular activated carbons treated with zinc chloride (ZnCl₂) impregnation was investigated. The experiment results showed that ZnCl₂ impregnation significantly enhanced the adsorptive capacity for mercury vapour, but decreased the specific surface area of the activated carbon. This could be explained by the occurrence of chemisorption, which was confirmed by adsorption tests over a wide range of temperatures. The influence of ZnCl₂ solution concentration on the mercury removal performance was also studied. Mechanisms of mercury adsorption onto the Cl-impregnated activated carbon were proposed.     

Adsorption of copper(II) and EDTA‐chelated copper(II) onto granular activated carbons

Waste streams generated by electroless copper plating in the printed circuit boards manufacturing industry often contain copper complexed by strong chelating agents such as EDTA. The consequence of metal complexation by chelating agents is that alternative treatment to chemical precipitation is often necessary to achieve the low metal concentrations required by increasingly stringent environmental regulations. This paper examines the feasibility of using activated carbon to remove EDTA‐chelated copper(II) species as well as free copper(II) ions from aqueous solution. The adsorption characteristics of copper(II) and EDTA‐chelated copper(II) on two granular activated carbons prepared from coal and coconut shell were evaluated. Adsorption equilibrium data of copper(II) on the two carbons corresponded well to the Langmuir model. The coconut shell‐based carbon exhibited a greater adsorption capacity for copper(II) than the coal‐based carbon under similar experimental conditions. Solution pH had a considerable influence on copper(II) adsorption by the two carbons. Low adsorption levels of copper(II) at pH 3 and high adsorption levels in the pH range of 4–6 were observed. However, a reverse adsorption trend was observed when the chelating agent EDTA was added to the copper(II) solution. Adsorption of EDTA‐chelated copper(II) by the two carbons was higher at pH 3 than at pH 6. The contrasting adsorption behaviour of copper(II) ions and EDTA‐chelated copper(II) species can be readily explained in terms of electrostatic interaction in that solution pH influences the surface charge of the carbons as well as the charge property of copper(II) ions and EDTA‐chelated copper(II) species. © 2000 Society of Chemical Industry     

Removal of CO from process gas with Sn–activated carbon in pressure swing adsorption

A pressure swing adsorption (PSA) system using activated carbon impregnated with SnCl ₂·2H ₂ O and pure activated carbon was used to remove CO from a model H ₂/CO mixture representing the steam reformer process gas. On comparing PSA results for both carbons, the CO adsorptive capacity of impregnated carbon was found to be superior to that of the pure carbon. This was confirmed by the fact that the concentration of CO, initially at 1000 ppm, was successfully reduced to 4.02% and 1.04% of its initial concentration by the pure and the impregnated activated carbons respectively in the PSA system. The species in the impregnated carbon responsible for the improved gas phase CO adsorption was found to be SnO ₂. Simulation results at a cyclic time of 600 s in the PSA operating at 10 atmospheres gave a product recovery and purity of 99.99% and 57.48%, respectively. At 6 atmospheres, the product recovery and purity were 92.17% and 77.12%, respectively. © 2000 Society of Chemical Industry     

Gas-phase mercury removal through sulfur impregnated porous carbon

Gas phase mercury removal is a vital unit operation in gas processing industries. The present work attempts to prepare a sulfur impregnated carbon at optimized experimental conditions and compares its elemental adsorption capacity with the number of commercially available carbon based adsorbents. The effect of adsorption temperature on mercury adsorption capacity has been estimated for the prepared sulfur impregnated carbon. The adsorption capacity was found to increase with increase in adsorption temperature owing to the chemisorption nature of the adsorption. The adsorption isotherms were generated at three different temperatures and were found to close adhere to the Langmuir Isotherm model. The adsorption capacity was found to increase until 140 °C, while decrease beyond, which was attributed to the softening and agglomeration of sulfur. The maximum adsorption capacity of 4325 μg/g was observed at a temperature of 140 °C. A comparison of the relative adsorption capacity of various adsorbent at 30 °C, revealed the adsorption capacity of the sulfur impregnated carbon prepared in the present work much higher than the commercially available carbons. The high adsorption capacities with simple preparation techniques favor the commercial mercury adoption process.     

Microwave irradiated and thermally heated olive stone activated carbon for nickel adsorption from synthetic wastewater: A comparative study

In attempt to compare the removal efficiency and yield of the activated carbon prepared using the conventional and microwave‐assisted heating is the focus of this work. Toward this olive stone (a biomass precursor) is activated using the popular activating agent potassium hydroxide. The process optimization exercise is carried out by using the standard full factorial statistical design of experiments (response surface methodology). The activated carbons prepared under the optimized conditions are compared based on the adsorption capacity and yield. The adsorption capacity was found higher using microwave heating as compared with conventional heating. The microwave heating requires significantly lesser holding time as compared to conventional heating method to produce activated carbon of comparable quality, with higher yield. The BET surface area of carbon using microwave heating is significantly higher than the conventional heating. Although the mesopore surface area of carbon is not vary significantly, the activation time, power, and nitrogen gas consumption are significantly lower than the conventional heating rendering that the activation process via microwave is more economical than that via conventional heating. The adsorption isotherm data fitted the Langmuir isotherm well and the monolayer adsorption capacity was found to be 12.0 and 8.42 mg/g for microwave and thermally heated activated carbon, respectively. Regeneration studies showed that microwave‐irradiated and thermally heated olive stone could be used several times by desorption with an HCl reagent. Both carbons can be used for the efficient removal of Ni²⁺ (>99%) from contaminated wastewater. © 2013 American Institute of Chemical Engineers AIChE J, 60: 237–250, 2014     

Licorice residue and Pistachio-nut shell mixture: A promising precursor for activated carbon

As a continuation of previous research concerning preparation of activated carbon from agricultural by-products, applying a mixture of two kinds of lignocellulosic by-products with complementary properties as the parent material is investigated. Two kinds of activated carbons are prepared by chemical activation of the parent mixture – including residues of licorice and pistachio-nut shells – with H₃PO₄ and ZnCl₂ solutions, separately. The produced activated carbons have the surface areas comparable to the commercial ones. The lower ash content, higher bulk density and surface area of mix-based activated carbons in comparison with licorice-based ones, and also the highest mercury adsorption capacity of the mix-based ones confirm that it would be possible to modify the properties of an activated carbon using several complementary raw materials. The comparison of mercury adsorption capacities among mixed-based and the commercial activated carbons reveals that mix-based ones are effective and economical adsorbents for industrial wastewater treatment.     

Comprehensive Methodology for the Investigation of Mercury Adsorption on Activated Carbons

In mercury adsorption on activated carbons both physisorptive and chemisorptive mechanisms play a role. The systematic investigation of Hg⁰ chemisorption is difficult because equilibrium capacities cannot be determined due to slow adsorption mechanisms. Therefore, the present publication suggests a three‐step approach: 1) Breakthrough curves are used to assess the dynamics of Hg⁰ adsorption. 2) The contributions of physisorption and chemisorption can be distinguished by coupled adsorption and desorption experiments. 3) Temperature programmed desorption (TPD) experiments are performed to get information about specific chemisorptive binding sites on the surface. This approach was tested on four characteristic examples of impregnated and non‐impregnated activated carbons.     

Activated carbons prepared from biogas residue: characterization and methylene blue adsorption capacity

BACKGROUND: In China, some biogas residue, which cannot be utilized by microbes in the anaerobic process, has been used as fertilizer. More has been deposited in biogas plants or on land around the plants. This has an effect on the environmental protection of the biogas plant, especially if the high lignin content in the biogas residue is not handled properly. RESULTS: In this study biogas residue has been used for the preparation of activated carbons by phosphoric acid activation. Textural characterization and feasibility of employing the prepared activated carbon to remove methylene blue (MB) from aqueous solution were investigated. The results show that the activated carbons have high surface area (1950 m² g^?1) and pore volume (1.232 cm³ g^?1). Equilibrium data were best described by the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 344.83 mg g^?1 at 25 °C. Among the kinetic models studied, the pseudo‐first‐order model was found to be the most applicable to describe the adsorption of MB. CONCLUSIONS: The adsorption performance of activated carbons prepared from biogas residues (BR‐AC) was comparable with that of commercial material and other adsorbents reported in earlier studies and presents a high value added application for biogas residues. Copyright © 2010 Society of Chemical Industry     

Mechanisms of Cr(VI) removal from water by various types of activated carbons

The removal mechanisms of Cr(VI) from water using different types of activated carbons, produced from coconut shell, wood and dust coal, were investigated in this project. Different types of activated carbons have different surface characteristics. The coconut shell and dust coal activated carbons have protonated hydroxyl groups on the surface (H‐type carbons), while the surface of the wood‐based activated carbon has ionised hydroxyl groups (L‐type carbons). The adsorption kinetics of chromium onto the activated carbons at pH values ranging from 2 to 6 were investigated. It was found that the optimum pH to remove total chromium was 2 for wood‐based activated carbon, while for coconut shell and dust coal activated carbons, the optimum pH was around 3–4. The difference in the optimum pH for different activated carbons to remove Cr(VI) from water can be explained by the different surface characteristics and capacity of the activated carbons to reduce Cr(VI) to Cr(III). © 1999 Society of Chemical Industry