Sorption properties of activated carbons obtained from corn cobs by chemical and physical activation

The paper presents results of a study on obtaining activated carbon from common corn cobs and on its use as adsorbent for removal of pollution from liquid and gas phases. The crushed precursor was subjected to pyrolysis at 500 and 800?°C in argon atmosphere and next to physical or chemical activation by CO₂ and KOH respectively. The effect of pyrolysis conditions and activation method on the physicochemical properties of the materials obtained was tested. The sorption properties of the carbonaceous adsorbents obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide sorption from gas stream in dry and wet conditions as well as by iodine and methylene blue removal from aqueous solution. The final products were microporous activated carbons of well-developed surface area varying from 337 to 1213 m²/g and showing diverse acid-base character of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for corn cobs permits production of cheap adsorbents with high sorption capacity toward toxic gases of acidic character as well as different pollutants from liquid phase.     

The use of microwave radiation for obtaining carbonaceous adsorbents from biomass and their use in elimination of inorganic pollutants

A new technology of obtaining activated carbons by physical and direct activation of biomass with the use of microwave radiation is described. The effect of activation temperature (700 and 800 °C) and two periods of time (15 and 30 min) on the textural parameters, acid–base character of the surface and sorption properties of activated carbons was tested. The resulting carbons were characterized by low-temperature nitrogen sorption and determination of pH as well as the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide adsorption in dry and wet conditions as well as by iodine removal from aqueous solution. The final products were adsorbents of surface area ranging from 291 to 368 m²/g and pore volume from 0.20 to 0.26 cm³/g, showing basic character of the surface. The results obtained in our study have proved that suitable choice of the pyrolysis and activation procedure for hay with the use of microwave radiation permit producing adsorbents with good capacity toward toxic gases of acidic character as well as inorganic pollutants of molecules of size similar to that of iodine molecules.     

Removal of NO<Subscript>2</Subscript> by carbonaceous adsorbents obtained from residue after supercritical extraction of marigold

Carbonaceous adsorbents were obtained from the residue after supercritical extraction of marigold subjected to physical activation and used as nitrogen dioxide and iodine adsorbents. The effect of carbonisation and activation temperature on the textural parameters, acid–base character of the surface and sorption properties of the activated carbons was tested. The materials obtained were activated carbons of low-developed surface area varying from 2 to 206 m²/g, showing clearly basic character of the surface. The results proved that proper selection of the carbonisation and activation procedure of the residue after supercritical extraction of marigold permitted obtaining carbonaceous adsorbents with good capacity toward liquid as well as gas inorganic pollutants. The effectiveness of NO₂ removal was found to depend to large extent on the conditions of adsorption. The preliminary wetting of the adsorbent bed was shown to significantly increase the amount of pollutants removed.     

The effect of chemical activation method on properties of activated carbons obtained from pine cones

A method for obtaining carbonaceous adsorbents from pine cones by chemical activation with NaOH is described. Activated carbons were obtained by two methods of activation (physical mixing and impregnation) and two variants of thermal treatment. It has been shown that pine cones can be successfully used as cheap precursor of carbonaceous adsorbents of well-developed surface area, large pore volume and good sorption properties. All activated carbon samples obtained show strongly microporous structure and surface of acidic character. The best physicochemical properties and greatest sorption capacity towards iodine were found for the carbon samples obtained by physical mixing of the precursor with the activating agent and then subjected to thermal activation at 600°C.     

Production of activated carbons from biodegradable waste materials as an alternative way of their utilisation

New carbonaceous adsorbents were prepared by means of direct, physical and chemical activation of corn cobs and cherry stones as well as coffee and tobacco industry waste materials. The effect of activation method on the textural parameters, acid-base character of the surface and sorption properties toward toxic gases of the materials obtained was tested. Depending on the precursor as well as method of preparation, the final products were micro/mesoporous activated carbons of surface area reaching to 1426 m²/g, showing largely different acid-base properties of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for industrial and agricultural biodegradable waste materials permits production of cheap carbonaceous adsorbents with very high sorption capacity towards nitrogen dioxide and hydrogen sulphide reaching to 83 mg NO₂/g_ads and 215 mg H₂S/g_ads, respectively.     

NO2 removal on adsorbents prepared from coffee industry waste materials

A technology for obtaining carbonaceous adsorbents by physical and chemical activation of waste materials from coffee industry is described. The effect of pyrolysis temperature and type of activation procedure on the textural parameters, acid–base character of the surface and sorption properties of activated carbons has been tested. The resulting carbons were characterized by low-temperature nitrogen sorption, determination of pH and the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by evaluation of nitrogen dioxide adsorption in dry and wet conditions. The final products were adsorbents of specific surface area ranging from 5 to 2,076 m²/g and pore volume from 0.03 to 1.25 cm³/g, showing very diverse acidic–basic character of the surface. The results obtained in our study have proved that a suitable choice of the pyrolysis and activation procedure for coffee industry wastes permits production of adsorbents with high sorption capacity of nitrogen dioxide, reaching to 44.5 and 84.1 mg NO₂/g in dry and wet conditions, respectively.     

Importance of structural and chemical heterogeneity of activated carbon surfaces for adsorption of dibenzothiophene

The performance of various activated carbons obtained from different carbon precursors (i.e., plastic waste, coal, and wood) as adsorbents for the desulfurization of liquid hydrocarbon fuels was evaluated. To increase surface heterogeneity, the carbon surface was modified by oxidation with ammonium persulfate. The results showed the importance of activated carbon pore sizes and surface chemistry for the adsorption of dibenzothiophene (DBT) from liquid phase. Adsorption of DBT on activated carbons is governed by two types of contributions: physical and chemical interactions. The former include dispersive interactions in the microporous network of the carbons. While the volume of micropores governs the amount physisorbed, mesopores control the kinetics of the process. On the other hand, introduction of surface functional groups enhances the performance of the activated carbons as a result of specific interactions between the acidic centers of the carbon and the basic structure of DBT molecule as well as sulfur-sulfur interactions.     

Adsorption of NH3 onto activated carbon prepared from palm shells impregnated with H2SO4

Adsorption of ammonia (NH3) onto activated carbons prepared from palm shells impregnated with sulfuric acid (H2SO4) was investigated. The effects of activation temperature and acid concentration on pore surface area development were studied. The relatively large micropore surface areas of the palm-shell activated carbons prepared by H2SO4 activation suggest their potential applications in gas adsorption. Adsorption experiments at a fixed temperature showed that the amounts of NH3 adsorbed onto the chemically activated carbons, unlike those prepared by CO2 thermal activation, were not solely dependent on the specific pore surface areas of the adsorbents. Further adsorption tests for a wide range of temperatures suggested combined physisorption and chemisorption of NH3. Desorption tests at the same temperature as adsorption and at an elevated temperature were carried out to confirm the occurrence of chemisorption due to the interaction between NH3 and some oxygen functional groups via hydrogen bonding. The surface functional groups on the adsorbent surface were detected by Fourier transform infrared spectroscopy. The amounts of NH3 adsorbed by chemisorption were correlated with the contents of elemental oxygen present in the adsorbents. Mechanisms for chemical activation and adsorption processes are proposed based on the observed phenomena.     

Synthesis of spherically shaped granulated carbon sorbent

New technological procedure for obtaining spherical carbon sorbents was considered. The method is based on oil granulation in the technology of coal benefication. The coal dust of 2SS brand and coal tar were used to obtain spherical activated carbons with high sorption and strength characteristics. The influence exerted by the introduction of surfactants in the course of molding on the quality parameters of activated carbons was examined. The basic physicochemical and sorption characteristics of the carbons being developed were analyzed and it was shown that spherical carbon adsorbents with micropore volume of up to 0.31 cm³ g^–1 and abrasion strength of up to 91% can be obtained.     

Biochars and Activated Biocarbons Prepared via Conventional Pyrolysis and Chemical or Physical Activation of Mugwort Herb as Potential Adsorbents and Renewable Fuels

The main objective of this study was to prepare a series of biochars and activated biocarbons via conventional pyrolysis as well as chemical or physical activation of solid residue after solvent extraction of wild growing plant (popular weed)–mugwort. The influence of the variant of the thermochemical treatment of the precursor on such parameters as elemental composition, textural parameters, acidic-basic character of the surface as well as adsorption abilities of the prepared carbonaceous materials was checked. Moreover, the suitability of the biochars prepared as renewable fuels was also investigated. It has been shown that the products obtained from the mugwort stems differ in many respects from the analogous materials obtained from mugwort leaves. The products were micro/mesoporous materials with surface area reaching 974.4 m²/g and total pore volume–1.190 cm³/g. Surface characterization showed that chemical activation with H₃PO₄ results in the acidic character of the adsorbents surface, whereas products of pyrolysis and especially physical activation show strongly alkaline surface properties. All the adsorbents were used for methylene blue and iodine adsorption from the aquatic environment. To understand the nature of the sorption process, the Langmuir, Freundlich and Temkin isotherm models were employed. The Langmuir model best described the experimental results, and the maximum sorption capacity calculated for this model reached 164.14 mg of methylene blue per gram of adsorbent. In case of iodine removal, the maximum capacity reached 948.00 mg/g. The research carried out for the biochars prepared via conventional pyrolysis showed that the value of their heat of combustion varies in the range from 21.74 to 30.27 MJ/kg, so they can be applied as the renewable fuels.     

On the adsorption/oxidation of hydrogen sulfide on activated carbons at ambient temperatures

Activated carbons of various origins (bituminous coal, wood, coconut shells, and peat) were studied as adsorbents of hydrogen sulfide. Before the experiments the surface of the adsorbents was characterized by using the sorption of nitrogen, Boehm and potentiometric titrations, thermal analysis, and FTIR. The adsorbents were chosen to differ in their surface areas, pore volumes, and surface acidities. To broaden the spectrum of surface acidity, carbons were oxidized by using nitric acid and ammonium persulfate. After hydrogen sulfide adsorption the species present on the surface were analyzed using thermal analysis, ion chromatography, and elemental analysis. The H(2)S breakthrough capacity tests showed that the performances of different carbons differ significantly. For a good performance of carbons as hydrogen sulfide adsorbents a proper combination of surface chemistry of carbon and porosity is needed. It was demonstrated that a more acidic environment promotes the formation of sulfur oxides and sulfuric acid despite yielding small H(2)S removal capacities. On the other hand, a basic environment favors the formation of elemental sulfur (sulfur radicals) and yields high capacities. The presence of a sufficient amount of water preadsorbed on the carbon surface to facilitate dissociation also plays an important role in the process of H(2)S adsorption/oxidation. The results showed that there is a critical value in carbon surface acidity, which when exceeded results in a negligible hydrogen sulfide breakthrough capacity. This is consistent with the mechanism of H(2)S adsorption on unmodified carbons, where the rate-limiting step is the reaction of adsorbed hydrogen sulfide ion with dissociatively adsorbed oxygen. When the acidity is expressed as pH, its value should be higher than 5 to ensure the effective removal of hydrogen sulfide from the gas phase. Study of carbon regeneration using water washing and heat treatment showed that the adsorbents can be regenerated to about 40% of their initial capacity.     

Nonlinear gas chromatography as a way of studying inhomogeneous sorbents

A way of organizing and processing the results from gas–chromatographic experiments to obtain chromatographic retention characteristics for a fixed concentration of sorbate in the gas phase or on the surface of the sorbent is proposed and substantiated. The suitability and expediency of such retention characteristics for describing the sorption properties of inhomogenous sorbents is demonstrated using a wide variety of adsorbents of different natures (activated carbons, swelling and nonswelling polymers, silicas and their silver derivatives) as examples.

     

Preparation of steam-activated carbons as catalyst supports

A series of activated carbons prepared from a low-rank Spanish coal has been prepared in order to evaluate the influence of the activation conditions in the porous structure and in the surface chemistry of the resulting material. This optimization was performed with the main aim of obtaining an appropriate activated carbon that would suit the desirable features of a catalyst support, as this study is a part of a work that accomplishes the production of carbon-based catalysts for the selective reduction of nitrogen oxides. The carbons were activated with steam in a fluidized bed reactor. The influence of the temperature of activation, the total gas flow, the steam percentage and the residence time was evaluated.     

杉木活性炭吸附处理水溶液中的尼古丁

用不同孔径及化学性质的活性炭对尼古丁水溶液进行吸附研究. 以杉木屑为原料, 分别用氯化锌化学活化法和水蒸气物理活化法制备活性炭, 并分别命名为AC-Z和AC-H. 同时选用椰壳基商品活性炭作为对比吸附剂, 命名为AC-C. 采用比表面积孔径测定分析仪及Boehm滴定法对活性炭进行表征, 分别测定其比表面积、孔径分布和表面官能团含量. 吸附实验主要考虑吸附时间、温度和尼古丁溶液的初始浓度三个因素, 实验数据分析结果表明微孔有利于物理吸附的进行, 而表面酸性官能团及金属原子作为吸附活性位的作用更加重要. 由改变温度对各样品的吸附量影响也能说明活性位在吸附中的作用. AC-Z拥有较多的活性位, 温度变化时尼古丁的吸附量先升高后减小, 这主要是由于适合的温度能加快尼古丁分子的离解并促使其与活性位相结合, 而过高的温度会造成尼古丁分子动能增加, 导致分子间碰撞的机率和强度增大, 使吸附在活性炭表面的尼古丁分子脱落. AC-H和AC-C由较多的微孔和不同程度的活性位组成, 优先发生物理吸附, 并且伴随发生吸附剂表面分子团簇现象, 其吸附趋势与AC-Z相反. 动力学研究表明活性炭对尼古丁的吸附反应非常迅速, 并且符合准二阶动力学程模型. 各热力学参数ΔG⁰, ΔH⁰和ΔS⁰的计算结果表明吸附剂对尼古丁的吸附为吸热和自发性过程.AC-Z和AC-H的ΔH⁰值远低于AC-C, 说明吸附剂表面的活性位对尼古丁分子有强烈的吸引作用, 所以吸附相同数量吸附质分子所需的吸附热更小, 这也说明了活性位在吸附过程中发生作用.     

Creation of active sites by impregnation of carbon fibers: application to the fixation of hydrogen sulfide

Activated carbon fibers, which exhibit high specific area and numerous active surface sites, constitute very powerful adsorbents and are widely used in filtration to eliminate pollutants from liquid or gaseous effluents. The fibers studied in this work are devoted to the filtration of gaseous effluent containing very small amounts (few vpm) of hydrogen sulfide. Preliminary experiments evidenced that these fibers weakly adsorb hydrogen sulfide. To improve their fixation capacity toward H(2)S the activated fibers are impregnated in an aqueous solution of potassium hydroxide. The impregnation treatment usually takes place before activation but in this work it occurs at room temperature after activation of the fibers. A further thermal treatment is performed to increase the efficiency of the system. The overall treatment leads to the creation of basic sites showing a great activity for H(2)S gas in the presence of water vapor. The mechanism has been established by a series of characterizations before, during, and after the different operation units. The KOH deposited after impregnation is carbonated into KHCO(3) at room temperature and then decomposed into K(2)CO(3) during the thermal treatment. K(2)CO(3) and H(2)S dissolve in a liquid aqueous solution formed on the fiber surface. Then carbonate ions and H(2)S molecules react together almost completely to yield HS(-) species. As a consequence the sorption capacities of hydrogen sulfide on the impregnated fibers are much higher, even for small hydrogen sulfide volume fractions.     

Cadmium ion adsorption on different carbon adsorbents from aqueous solutions. Effect of surface chemistry, pore texture, ionic strength, and dissolved natural organic matter

Adsorption of Cd(II) species at pH = 5 was studied on three carbon adsorbents: granular activated carbon, activated carbon fiber, and activated carbon cloth. As-received and oxidized adsorbents were used. Cd(II) adsorption greatly increased after oxidation due to the introduction of carboxyl groups. The use of a buffer solution to control the pH introduced some changes in the surface chemistry of carbons through the adsorption of one of the compounds used, biphthalate anions. The increase in ionic strength reduced Cd(II) uptake on both as-received and oxidized carbons due to a screening of the electrostatic attractions between the Cd(II) positive species and the negative surface charge, which in the case of as-received carbons derived from the biphthalate anions adsorbed and in the oxidized ones from the carboxyl groups. Tannic acid was used as a model compound for natural organic matter. Its adsorption was greatly reduced after oxidation, and most of the carbon adsorbents preadsorbed with tannic acid showed an increase in Cd(II) uptake. In the case of competitive adsorption between Cd(II) species and tannic acid molecules, there was a decrease in Cd(II) uptake on the as-received carbon whereas the contrary occurred with the oxidized carbons. These results illustrate the great importance of carbon surface chemistry in this competitive adsorption process. Finally, under all experimental conditions used, when the adsorption capacity of carbons was compared under the same conditions it increased in the following order: granular activated carbon < activated carbon fiber < activated carbon cloth.     

Activated carbon prepared by physical activation of olive stones for the removal of NO2 at ambient temperature

Activated carbon was prepared from olive stones by physical activation using water vapor at 750 °C. Textural, morphology and surface chemistry characterizations were achieved (nitrogen adsorption, SEM, FTIR and TPD–MS). NO₂ adsorption was performed for different inlet gas compositions and temperatures. NO₂ may adsorb directly on the oxygenated surface groups, and can also be reduced to NO. Therefore, a second NO₂ molecule adsorbs on the oxygen left on the carbon surface. TPD performed after NO₂ adsorption showed the presence of various surface groups. The adsorption capacity was about 131 mg/g, which is higher than with several activated carbon prepared from classical lignocellulosic biomass. NO₂ reduction into NO decreased with increasing the inlet oxygen concentration. In contrast, a slight decrease in the NO₂ adsorption capacity was observed with increasing temperature. It seems that the activated carbons prepared from olive stones by steam activation could be used as efficient adsorbents for NO₂ removal.     

Modification of Activated Carbon Fibers and Their Characterizes of Adsorption for Xenon

Activated carbon fibers (ACFs) are characterizes by their highly developed internal surface area and porosity. Especially the development of micro- and mesopores is of great importance because it allows the carbons to adsorb large amounts and various types of chemicals from gases or liquids. Due to such a valuable feature, activated carbon fibers have been in use for many years. Porous carbon materials have now become extremely versatile adsorbents of major industrial significance. The high surface area and porosity of activated carbon fibers are the result of the activation process; physical or chemical activation. However, the complexity of the carbon structure, although voluminous research has been done and great effort has been made toward the control of pore size and its distribution^[1-3]. The recent development of industrial technology provides new application fields for porous carbons and,at the same time, requires the carbon to have a desired pore structure. To meet such a requirement, many novel approaches to control pore structure have been proposed.     

Porous properties of activated carbons from waste newspaper prepared by chemical and physical activation

Activated carbons were prepared from old newspaper and paper prepared from simulated paper sludge by chemical activation using various alkali carbonates and hydroxides as activating reagents and also by physical activation using steam. In the chemical activation, the influence of oxidation, carbonization, and activation on the porous properties of the resulting activated carbons was investigated. The specific surface areas (S(BET)) of the activated carbons prepared by single-step activation (direct activation without oxidation and carbonization) were higher than those resulting from two-step activation (oxidation-activation and carbonization-activation) and three-step activation (oxidation-carbonization-activation) methods. The S(BET) values were strongly dependent on the activating reagents and the activating conditions, being >1000 m(2)/g using K(2)CO(3), Rb(2)CO(3), Cs(2)CO(3), and KOH as activating reagents but <1000 m(2)/g using Li(2)CO(3), Na(2)CO(3), and NaOH. These differences in S(BET) values are suggested to be related to the ionic radii of the alkalis used as activating reagents. The microstructures of the higher S(BET) samples show a complete loss of fiber shape but those of the lower S(BET) samples maintain the shape. In the physical activation, the porous properties of the activated carbons prepared by the single-step method were examined as a function of the production conditions such as activation temperature, activation time, steam concentration, and flow rate of the carrier gas. The maximum S(BET) and total pore volume (V(P)) were 1086 m(2)/g and 1.01 ml/g, obtained by activation at 850 degrees C for 2 h, flowing 20 mol% of steam in nitrogen gas at 0.5 l/min. A correlation was found between S(BET) and the yield of the product, the maximum S(BET) value corresponding to a product yield of about 10%. This result is suggested to result from competition between pore formation and surface erosion. Compared with chemically activated carbons using K(2)CO(3), the porous properties of the physically activated carbons have lower S(BET) and V(P) values because of the smaller size and lower volume of their micropores. On the other hand, they retain the original fiber shape and the paper sheet morphology after activation.     

Adsorption of toluene and toluene–water vapor mixture on almond shell based activated carbons

The aim of work is to study the adsorption of a common volatile organic compound such as toluene using activated carbons prepared by chemical activation with phosphoric acid of a lignocellulosic precursor, almond shell, under different conditions. The Impregnation ratio, temperature and time of activation were modified to obtain activated carbons with different characteristics. Regarding the characteristics of the activated carbons, the effects of porous structure and surface chemistry on the toluene adsorption capacity from toluene isotherms have been analysed. Results show that the control of properties of the activated carbons, particularly porous structure, highly dependent on the preparation conditions, plays a decisive role on the toluene adsorption capacity of the activated carbons. Concerning the experiments of toluene adsorption conducted in dynamic mode, activated carbons prepared at low temperatures of activation show higher breakthrough times than those obtained for activated carbons prepared at higher activation temperatures. The amount of toluene adsorbed in presence of water vapor in the gas stream lead to a decrease ranging from 33 to 46 % except for carbons prepared at higher temperatures activated that show only a slight decrease in the amount of toluene adsorbed. Activated carbons can be regenerated with soft heat treatment showing a slight decrease in the adsorption capacity. The high toluene adsorption capacities as well as the high breakthrough times obtained in presence of water vapor make these activated carbons suitable for commercial applications.