The preparation of activated carbon from macadamia nutshell by chemical activation

Different structured activated carbons were prepared from macadamia nutshell by chemical activation with potassium hydroxide and zinc chloride. The influence of process variables on the carbons' pore structure was studied in order to optimise these parameters. The results were also compared with those previously obtained on the chemical activation of coal. The most important parameter in chemical activation with both chemical agents was found to be the impregnation ratio. Carbonization temperature is the second important variable which had significant effect on pore volume evolution. Under the experimental circumstances studied, the optimum conditions in preparation of carbons with high surface area and pore volumes with both chemical agents are identified.     

Influence of pore size distribution on methane storage at relatively low pressure: preparation of activated carbon with optimum pore size

Activated carbons prepared by KOH activation of an anthracite were studied for methane storage applications. The effect of the different variables of the activation process (KOH/anthracite ratio, pyrolysis temperature and time) on methane storage and methane delivery was analyzed. Methane delivery was obtained in two different ways: calculated from the isotherm and measuring the volume of methane delivered from a carbon-filled vessel (5 cm³). Both methods give similar values. In addition to the well-known effect of the micropore volume and packing density, special attention was paid to the effect that the micropore size distribution has in methane storage performance. It was shown that this parameter is also a key parameter in the application of activated carbons for methane storage applications. Activated carbons prepared from a cheap raw material and using a single stage activation process have reached very high values of methane storage (155 V/V) and delivery (145 V/V).     

浅谈无剥离微负压废旧轮胎热解技术产业化

结合工程实践，详细介绍了无剥离、微负压废旧轮胎热解技术的技术特点、工艺流程、主要设备选型及主要技术指标。并分析了废旧轮胎热解技术产业化的前景。     

Recycling polymeric wastes by means of pyrolysis

Different polymeric wastes, which include materials from the automobile industry, such as tyres, automobile shredder residues (ASR) and sheet moulding compound (SMC), and materials from municipal solid wastes (MSW), such as cardboard, tetrabrik and plastics (LDPE, PP, PS, PET and PVC), pure and mixed, have been pyrolysed in a 3.5 dm³ autoclave at 500 °C for 30 min in a nitrogen atmosphere. The amount and characteristics of the solid, liquids and gases obtained are presented. The suitability of the different materials for the pyrolysis recycling process is discussed. It is concluded that pyrolysis is a very promising technique for recycling tyres, SMC, one type of ASR (heavy ASR), and LDPE, PP and PS, either pure or mixed; with all of them valuable solid, liquid and gaseous products are obtained in pyrolysis. On the contrary, light ASR, tetrabrik and cardboard do not yield valuable products in the pyrolysis process and therefore their recycling by pyrolysis is not of interest, except as a way of volume reduction. PET and PVC turned out to be troublesome in the pyrolysis experiments; for a proper study of their recycling by pyrolysis other operating conditions and installations are required. © 2002 Society of Chemical Industry     

Influence of HNO3 oxidation on the structure and adsorptive properties of corncob-based activated carbon

An investigation of the impact of strong oxidation with HNO₃ on the porosity and adsorption characteristics of char and activated carbons, derived from corncobs, is presented. Texture parameters, as obtained from N₂ adsorption at 77 K, showed a considerable decrease in surface area of the activated carbons with enhanced pore widening. The extent of porosity modification was found to depend on the scheme of activation of the precursor, simple carbonization, steam pyrolysis, steam gasification of the char, or chemical activation with H₃PO₄. Surface-chemical changes were detected by FTIR spectroscopy, where absorption bands assigned to carboxyl, carboxylate, carbonyl, and phenolic groups were observed. A SEM study demonstrated the erosive effect of HNO₃, detected by the presence of disintegration of the carbon grains, with the porous structure probably containing very large macropores. As a consequence of the oxidation process, elemental analysis showed high contents of O, H and N, and TG confirmed that the weight loss distribution in the thermogram becomes slower at higher temperatures. The removal of phenol decreased as a result of the formation of oxygen functionalities. Mono-nitrophenols were adsorbed in smaller amounts than phenol, and p-nitrophenol showed a relatively higher uptake than the other two mono-nitrophenols, whereas the uptake of Methylene Blue was improved. Removal of Pb²⁺ from aqueous non-buffered solution was considerably enhanced by chemical oxidation, which may be related to pore widening, increased cation-exchange capacity by oxygen groups, and the promoted hydrophilicity of the carbon surface.     

Preparation and characterization of porous carbons from PAN-based preoxidized cloth by KOH activation

Porous carbons (PCs) were prepared from PAN-based preoxidized cloth with potassium hydroxide (KOH) as active reagent by the chemical activation method. The PCs have been systematically studied by the adsorptions of nitrogen, benzene and iodine. It has been found that the process parameters such as weight ratio of KOH to the starting material, activation temperature and activation time are crucial for preparing high quality PCs. A series of PCs with high BET surface area and well-developed porous structure in which micropores are dominant were obtained with less KOH and shorter activation time in comparison to the traditional methods. The optimum conditions for preparing PCs with high BET surface area from PAN-based preoxidized cloth were given, and the relationships between pore structure and adsorption property of PCs were explored.     

Relationship between pyrolysis activation energy and graphitizability

Characteristics of the carbonization process of various carbons are compared with the structures of the resulting carbons. A relationship is obtained between the effective activation energy for pyrolysis and the interlayer spacing after treatment to 2700°. A quantitative evaluation of graphitizability of carbon materials on this basis is proposed.     

Synthesis of activated carbons by chemical activation of new anthracene oil-based pitches and their optimization by response surface methodology

This paper deals with the synthesis of new anthracene oil-based activated carbons by chemical activation with KOH. It focuses on the optimization of the processing conditions involved by means of surface response methodology. A factorial design (2³+3) in one block with four degrees of freedom was used to optimize the process, based on the responses BET surface area, total pore volume, mesopore volume, micropore volume and mol ratio CO:CO₂. The variables measured include KOH to pitch ratio (1:1, 3:1 and 5:1), activation temperature (700 up to 1000 °C) and pitch characteristics. The activation of anthracene oil-based pitch led to activated carbons with BET surface area values of 2880 m² g⁻¹. The factorial design expresses every response factor as a mathematical equation using the experimental variables. The most critical factor for each experiment design response has been identified from the analysis of variance (ANOVA). These mathematical models were also used to obtain the optimum processing conditions for the production of activated carbon with controlled properties. The experimental processing of the optimized activated carbons gave rise to a sample with BET, total pore volume, mesopore volume, micropore volume values which were in good agreement with those predicted by statistical analysis.     

Aromaticity and ring condensation in pyrolyzed pitches

The process of pyrolysis of different pitches is studied by high resolution solid state ¹³C NMR. Two possible models are used to take into account the aliphatic carbons that may be attached to polycondensed pyrolyzed structures, to match the aromatic quaternary over tertiary ratio and stay within reasonable range of size for the aromatic structures. It was found that the most highly aromatic pitches have the biggest structures and probably small aliphatic chains.     

Vanadium(V) Removal by Adsorption onto Activated Carbon Derived from Starch Industry Waste Sludge

This study examines the adsorption potential of activated carbons for vanadium (V) removal from aqueous solution. Activated carbons were produced via chemical activation of waste treatment sludge from the starch industry. Specific surface area and pore sizes of waste sludge samples were determined through chemical activation and pyrolysis. Experimental data indicated that sludge samples had micropore structure and specific surface area of up to 1196 m²/g. First-order and second-order models were applied to determine adsorption kinetics. Freundlich, Langmuir, and Dubinin–Radushkevich isotherms were used to analyze equilibrium data of adsorption. Equilibrium adsorption data showed the best fit to the Freundlich isotherm. Adsorption of vanadium (V) follows second-order kinetic models. Maximum adsorption was observed at pH 4.0. Langmuir adsorption capacity was found to be 37.17 mg/g. The results of the study indicated that activated carbon obtained from industrial sewage sludge was effective in removing vanadium from aqueous solutions, which creates a significant advantage for treatment of industrial wastewaters and management of solid wastes.     

Steam-activated carbons from a bituminous coal in a continuous multistage fluidized bed pilot plant

A vertical three-stage fluidized bed pilot plant, with downcomers, was designed and built in order to study the continuous process of the production of activated carbons from a high-volatile bituminous coal from the Puertollano basin (Spain), by steam activation. The pilot plant can operate with a production of up to 40 kg per day. Very good activated carbons were produced at the selected operating conditions. The effect of the following operating conditions on the reactivity and adsorption characteristics of the activated carbons was analyzed: (1) carbonization conditions (one- and two-step activation), (2) activation temperature (800–850 °C), and (3) steam gas velocity (1.5–3 times the minimum fluidization velocity). Carbonization conditions considerably affect the reactivity of the chars obtained; the faster the carbonization process, the higher the reactivity. Nevertheless, the effect of this variable on the development of porosity is not very relevant, and consequently the direct activation process is an attractive alternative to the two-step (carbonization and activation) process. On the other hand, both temperature and steam flow rate (affecting the reaction rate) have a marked effect on the development of porosity.     

Characterization and application of activated carbon produced by H3PO4 and water vapor activation

Activated carbons have been prepared from woody biomass birch by using various activation procedures: a) treatment with phosphoric acid and pyrolysis at 600 °C in inert atmosphere, b) the same as in (a) followed by steam activation at the same temperature and c) treatment with phosphoric acid and direct pyrolysis in a stream of water vapor at 700 °C. The surface area and the porosity of the activated carbons were strongly dependent on the treatment after impregnation with H₃PO₄ (pyrolysis in inert atmosphere, steam pyrolysis or combination of both).Activated carbon, prepared by impregnation with phosphoric acid followed by steam pyrolysis (steam activation) had highly developed porous structure and the largest surface area among all prepared carbons (iodine number 1280 mg/g and BET surface area 1360 m²/g). The adsorption capacity of this sample for Hg(II) from aqueous solution was studied in varying treatment conditions: contact time, metal ion concentration and pH. The adsorption followed Langmuir isotherms and the adsorption capacity for Hg(II) at 293 K was 160 mg/g.     

The effect of activated carbon surface moisture on low temperature mercury adsorption

Experiments with elemental mercury (Hg⁰) adsorption by activated carbons were performed using a bench-scale fixed-bed reactor at room temperature (27°C) to determine the role of surface moisture in capturing Hg⁰. A bituminous-coal-based activated carbon (BPL) and an activated carbon fiber (ACN) were tested for Hg⁰ adsorption capacity. About 75-85% reduction in Hg⁰ adsorption was observed when both carbon samples’ moisture (∼2 wt.% as received) was removed by heating at 110°C prior to the Hg⁰ adsorption experiments. These observations strongly suggest that the moisture contained in activated carbons plays a critical role in retaining Hg⁰ under these conditions. The common effect of moisture on Hg⁰ adsorption was observed for both carbons, despite extreme differences in their ash contents. Temperature programmed desorption (TPD) experiments performed on the two carbons after adsorption indicated that chemisorption of Hg⁰ is a dominant process over physisorption for the moisture-containing samples. The nature of the mercury bonding on carbon surface was examined by X-ray absorption fine structure (XAFS) spectroscopy. XAFS results provide evidence that mercury bonding on the carbon surface was associated with oxygen. The results of this study suggest that surface oxygen complexes provide the active sites for mercury bonding. The adsorbed H₂O is closely associated with surface oxygen complexes and the removal of the H₂O from the carbon surface by low-temperature heat treatment reduces the number of active sites that can chemically bond Hg⁰ or eliminates the reactive surface conditions that favor Hg⁰ adsorption.     

Developing ash-free high-strength spherical carbon catalyst supports

The possibility of using furfurol for the production of ash-free high-strength active carbons with spheroidal particles as adsorbents and catalyst supports is substantiated. A single-stage process that incorporates the resinification of furfurol, the molding of a spherical product, and its hardening while allowing the process cycle time and the cost of equipment to be reduced is developed. Derivatographic, X-ray diffraction, mercury porometric, and adsorption studies of the carbonization of the molded spherical product are performed to characterize the development of the primary and porous structures of carbon residues. Ash-free active carbons with spheroidal particles, a full volume of sorbing micro- and mesopores (up to 1.50 cm³/g), and a uniquely high mechanical strength (its abrasion rate is three orders of magnitude lower than that of industrial active carbons) are obtained via the vapor-gas activation of a carbonized product. The obtained active carbons are superior to all known foreign and domestic analogues and are promising for the production of catalysts that operate under severe regimes, i.e., in moving and fluidized beds.     

A comparison of surface morphology and chemistry of pyrolytic carbon blacks with commercial carbon blacks

The surface morphology and chemistry of CBp obtained by pyrolysis of waste tyres at 500 and 700 °C, respectively was studied compared with a commercial tyre carbon blacks by laser particle size analyzer, X-ray diffractogram (XRD) and electron spectroscopy for chemical analysis (ESCA). The distribution of CBp aggregates was the mixed particle distribution of commercial carbon blacks added to tyres in fabrication. The concentration of inorganic compounds and carbonaceous deposits (the organic compounds deposited on the surface of the CBp) depends on the pyrolysis temperature. The chemical nature of the CBp from pyrolysis at 700 °C was found to be closer to the commercial tyre carbon blacks than the CBp from pyrolysis at 500 °C.     

Active carbon from scrap tyres

The possibility of producing active carbon by activation at 850 °C of the char obtained from the pyrolysis (at 450 and 600 °C) of scrap tyres has been studied. The activated char showed good adsorbing characteristics, similar to those of typical commercial grades. The yield and the desired adsorbing capacity depend on the activation time. However, the ash content and friability are quite high; therefore the activated char is suitable for applications in powder form in which the ash does not cause problems.     

Preparation of porous carbons from petroleum coke by different activation methods

Porous carbons were prepared from Shengli petroleum coke (SPC) and Minxi petroleum coke (MPC) by different activation methods with H₂O, KOH and/or KOH+H₂O as active agents. The porous carbons were characterized by nitrogen adsorption at 77 K. It has been found that activation method and component of petroleum coke, of which different kinds of transitional metals on petroleum coke are crucial for preparing high quality porous carbons. Under the identical experimental conditions, the co-activation with KOH and H₂O as active agents in the same activation process, which has been rarely reported in literature, is the easiest method for the preparation of porous carbons with high surface area. The sequence of active agents in terms of difficulty in the preparation of porous carbons with high surface area is as follows: KOH+H₂O>KOH>H₂O. A drawback of KOH+H₂O activation in the preparation of porous carbon in this work is found to be its low carbon yield in comparison to KOH activation. Compared with the SPC coke, the MPC coke with higher contents of transitional metal and carbon and lower content of nitrogen is more suitable for making high surface area porous carbons, which is believed to be mainly due to the difference in the contents of transitional metals. Porous carbon with surface area around 2500–3000 m²/g and carbon yield about 25–30% has been obtained from MPC coke by KOH+H₂O activation with less KOH and shorter activation time in comparison to the traditional methods.     

The effects of demineralization and swelling in producing active carbon from Turkish lignites

In this study, active carbon was obtained through chemical activation methods using some pretreatment to Gölbaşı (Adıyaman) and Kangal (Sivas) lignites. For both lignites, pretreatment was carried out in three steps. In the first step, demineralization was achieved by applying HCl–HF pretreatment to raw lignites. In the second one, raw and demineralized lignites were swollen not only with benzene but also with THF (tetrahydrofurane). Later, these two samples at 85 °C were exposed to chemical activation by impregnation with ZnCl₂. Chemical activation processes were carried out in a situation where samples on quartz board in a quartz tube in a cylindrical furnace were kept for 1 h at 500 °C, 100 ml/min N₂ flow speed and 30 °C/min heating rate. The active carbons produced were washed with 10% HCl and later with demineralized water. BET surface area of the active carbon samples was generally higher than 1000 m²/g. The surface area value of the Gölbaşı lignite was relatively higher than that of Kangal lignites. Similarly, the surface area value of the active carbons produced at the end of pretreatment with THF was higher than that of active carbon produced through pre-swelling using benzene. For all active carbon samples, ash, total sulfur and iodine adsorption values were different.     

A study of porosity in active surface in modified carbon fibres

Conclusions -- The primary adsorption center content of modified ÉLUR-M carbon fibres depends on the conditions of the surface activation process: after electrochemical treatment, more of them are contained than after treatment with ozone.-- In electrochemical treatment of carbon fibres, an optimum zone of intensity of this process is observed, for which the formation of the largest number of active centers is characteristic.-- The number of active centers which are formed on the surface of type LU carbon fibres depends on the final pyrolysis temperature and is caused by structural—chemical processes during carbonization of the material.-- The investigated carbon fibres are ultramicroporous materials with a pore diameter no greater than 6–7 Å and a total pore volume of 0.03–0.09 cm³/g.VNIIPV. Translated from Khimicheskie Volokna, No. 3, pp. 33–35, May–June, 1991.