Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties

High surface area activated carbons were prepared by simple thermo-chemical activation of Jatropha curcas fruit shell with NaOH as a chemical activating agent. The effects of the preparation variables, which were impregnation ratio (NaOH:char), activation temperature and activation time, on the adsorption capacity of iodine and methylene blue solution were investigated. The activated carbon which had the highest iodine and methylene blue numbers was obtained by these conditions as follows: 4:1 (w/w) NaOH to char ratio, 800 °C activation temperature and 120 min activation time. Characterization of the activated carbon obtained was performed by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption isotherm as BET. The results present that the activated carbon possesses a large apparent surface area (S_BET = 1873 m²/g) and high total pore volume (1.312 cm³/g) with average pore size diameter of 28.0 Å.     

Preparation of granular activated carbon from oil palm shell by microwave-induced chemical activation: Optimisation using surface response methodology

In this study, waste palm shell was used to produce activated carbon (AC) using microwave radiation and zinc chloride as a chemical agent. The operating parameters of the preparation process were optimised by a combination of response surface methodology (RSM) and central composite design (CCD). The influence of the four major parameters, namely, microwave power, activation time, chemical impregnation ratio and particle size, on methylene blue (MB) adsorption capacity and AC yield were investigated. Based on the analysis of variance, microwave power and microwave radiation time were identified as the most influential factors for AC yield and MB adsorption capacity, respectively. The optimum preparation conditions are a microwave power of 1200 W, an activation time of 15 min, a ZnCl₂ impregnation ratio of 1.65 (g Zn/g precursor) and a particle size of 2 mm. The prepared AC under the optimised condition had a BET surface area (S_BET) of 1253.5 m²/g with a total pore volume (V_tot) of 0.83 cm³/g, which 56% of it was contributed to the micropore volume (V_mic).     

微波加热核桃壳制取活性炭及孔结构表征

以核桃壳为原料,采用微波加热-水蒸汽活化法制备了活性炭。研究了微波功率、活化时间和水蒸汽流量等因素对吸附性能的影响。最佳工艺条件为：微波功率600 W、活化时间7 min、水蒸汽流量5 mL/min,活性炭产品的碘吸附值1076．57 mg/g,亚甲基蓝吸附值195 mg/g,得率25．11%。该工艺将常规加热方法的炭化和活化简化为一个过程,所需加热时间仅为传统方法的1/21,产品活性炭的亚甲基蓝吸附值为国家一级品标准的1．44倍。同时测定了该活性炭的氮吸附等温线,通过BET计算了活性炭的比表面积,并通过H—K方程和密度函数理论表征了活性炭的孔结构。结果表明,该活性炭为微孔型,BET 比表面积1 154．91 m~2/g,总孔体积0．564 9 mL/g,微孔占总孔体积(体积分数,下同) 79．86%,中孔体积分数19．97%,大孔占0．17%。     

Regeneration of spent catalyst from vinyl acetate synthesis as porous carbon: Process optimization using RSM

Optimization of the process of regeneration of spent catalyst from vinyl acetate synthesis was attempted using response surface methodology (RSM) based on the central composite design (CCD). The optimization was performed to maximize the response variables of methylene blue (MB) adsorption capacity as well as the yield of the porous carbon, with the process variables being regeneration temperature, regeneration duration and steam flow rate. The two factor interaction model and quadratic model were developed to correlate the process variables with the response variables. Based on the analysis of variance (ANOVA), all the three process parameters were found to be significant. The optimized process conditions were identified to be activation temperature of 946 °C, activation time of 30 min and steam flow rate of 2.4 g min⁻¹ with MB adsorption capacity of 420 mg/g and a yield of 50.7%. The MB adsorption capacity as compared with the majority of the literature reported values, along with high yield of the regenerated carbon, certify the economic feasibility of the process, with potential application in variety of liquid phase adsorption processes.     

The factors affecting the performance of activated carbon prepared from oil palm empty fruit bunches for adsorption of phenol

Powdered activated carbons (PACs) were produced from oil palm empty fruit bunches (EFB) by varying the operating parameters of temperatures, CO₂ gas flow rates and activation times using 2-level full factorial experimental design. The EFB samples were first carbonized for 30 min using nitrogen gas followed by physical activation using CO₂ to optimize best production conditions. The optimum conditions for PACs produced were investigated through adsorption tests on aqueous solution of phenol. The results of this study demonstrated that the activation temperature with the range of 800–900 °C had the most significant effect on the adsorption characteristics as well as the yield of the activated carbon produced. Based on the analysis of variance (ANOVA) and model equation developed, the optimum production conditions for the EFB PAC were found to be at the activation temperature of 900 °C with CO₂ gas flow rate of 0.1 L/min and activation time of 15 min. Characterization of PAC produced showed that the activation conditions would find good-quality adsorbent with the BTE surface area of 345.1 m²/g and well forming pores distribution.     

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.     

Preparation and characterization of mesoporous activated carbon from waste tires

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

Carbon nanofibres and activated carbon nanofibres as electrodes in supercapacitors

Carbon nanofibres have been prepared by a floating catalyst procedure at industrial scale in a metallic furnace. The nanofibres (50-500 nm diameter and 5-200 μm length) are grown from the Fe particles used as catalyst. Soot appears together with the carbon nanofibres. The sample has been chemically activated using KOH as activating agent. Scanning electron microscopy has shown a smooth surface for the as-prepared carbon nanofibres but a rough surface for the activated ones. The specific surface area increases from 13 to 212 m²/g due to the activation. The volume of the micropores (in the 1-2 nm range) and the mesopores (2-5 nm range), as deduced by density functional theory methods, also increases after the activation. Electrochemical behaviour of the as-prepared and activated carbon nanofibres has been tested in a supercapacitor at laboratory scale using 6 M KOH aqueous solution as electrolyte. The specific capacitance, which is less than 1 F/g for the as-prepared sample, increase up to ≈60 F/g for the activated sample. Only a slight decrease in capacitance has been observed as the current density increases. Specific power of ≈100 W/kg at specific energy of 1 Wh/kg has been found in some particular cases. We have compared the electrochemical parameters of our activated carbon nanofibres with those of activated carbon nanofibres coming from a commercial sample; the latter was activated by the same way as our sample.     

Spherical activated carbons for low concentration toluene adsorption

The activation process of a spherical activated carbon (SAC) from Kureha Carbon was analysed and the behaviour of these materials to adsorb low concentration volatile organic compounds was studied. Two series of activated carbons were prepared using CO₂ or steam as activating atmospheres at 880 and 840 °C, respectively. Activation times between 45 min and 24 h were selected, leading to burn-offs between 21 and 60%. The results show, for similar burn-off percentages, that the porosity development is similar for the two activating gases at moderate burn-off percentages, and larger for CO₂ than for steam at high burn-off percentages. For similar burn-offs, steam leads to SACs with slightly larger bed densities than CO₂. In general, a low and similar increase in the total surface oxygen groups’ content is noted after activation with both activating agents. Toluene adsorption capacities as large as 46 g toluene/100 g SAC can be achieved with some of these spherical activated carbons in a continuous flow-through SAC bed, when influent air-phase toluene was 200 ppmv. Considering that these SACs have quite high bed densities, their toluene adsorption capacities per unit of volume reach remarkably high values.     

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

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

Preparation and characterization of chars and activated carbons from Saskatchewan lignite

Saskatchewan lignite was used as a precursor to prepare carbonaceous adsorbents for use as SO₂ adsorbent from flue gases. The lignite was carbonized producing char in a fixed bed microreactor system at different temperatures from 350 to 550 ^°C in nitrogen atmosphere. The chars obtained at 475 ^°C for 120 min exhibited the highest micropore surface area (136 m²/g) and volume (0.062 cm³/g) and the smallest median pore diameter (∼ 0.7 nm). Carbon dioxide and steam were used as activating agents. Activation of char at optimum conditions of 650–675 ^°C for 15 min with carbon dioxide and steam resulted in a further increase in micropore surface area (220 and 186 m²/g for CO₂ and steam, respectively) and volume (0.090 and 0.085 cm³/g for CO₂ and steam, respectively). The yield of char was 64 wt.%, while the yields of activated carbon were 60 and 57 wt.% for CO₂ and steam activation, respectively; all based on the mass of original lignite.     

Porous structure and adsorptive properties of pineapple peel based activated carbons prepared via microwave assisted KOH and K2CO3 activation

The present research explores the feasibility of microwave irradiation for preparation of high surface area activated carbon from pineapple peel (PPAC), an agricultural effluent emitted from the food can processing industries via KOH and K₂CO₃ activation. The activation process was performed at the microwave power of 600 W and irradiation time of 6 min. The equilibrium behavior of PPAC was investigated by performing batch adsorption experiments using methylene blue as adsorbate. Nonlinear adsorption isotherm models, Langmuir, Freundlich and Temkin were used to simulate the equilibrium data. KOH activated sample demonstrated a better development of pore structure, with the BET surface area, total pore volume and average pore size of 1006 m²/g, 0.59 m³/g and 23.44 Å, respectively, while the monolayer adsorption capacity of methylene blue was determined to be 462.10 mg/g. The findings support the potential use of microwave assisted KOH and K₂CO₃ activation as a promising activation technique.     

HEMP-derived activated carbon fibers by chemical activation with phosphoric acid

Activated carbon fibers were prepared by chemical activation of hemp fibers with phosphoric acid at different carbonization temperatures and impregnation ratios. Surface properties of the activated carbons fibers were significantly influenced by the activation temperature and the impregnation ratio. An increase of either of these parameters produced a high development of the porous structure of the fibers. Activated carbon fibers with apparent surface area of 1350 m²/g and mesopore volume of 1.25 cm³/g were obtained at 550 °C with an impregnation ratio of 3. The activated carbon fibers presented a high oxidation resistance, due to the presence of phosphorus compounds on the carbon surface. The oxidation resistance results suggest that C-O-PO₃ and mainly C-PO₃ and C-P groups act as a physical barrier, blocking the active carbon sites for the oxidation reaction.     

Production of microporous palm shell based activated carbon for methane adsorption: Modeling and optimization using response surface methodology

In this study, the optimization of the palm shell based activated carbon production using combination of chemical and physical activation for methane adsorption is investigated. response surface methodology (RSM) in combination with central composite design (CCD) was used to optimize the operating parameters of the production process. Physical activation temperature, chemical impregnation ratio and physical activation time were chosen as the main process variables and the amount of methane adsorption was selected as the investigated response. Phosphoric acid and carbon dioxide were used as chemical and physical agents, respectively. The optimum reaction conditions were found to be a physical activation temperature of 855 °C, H₃PO₄ impregnation ratio of 9.42 g of phosphorous per gram palm shell and physical activation time of 135 min. The results exhibited significant increase in methane adsorption after physio-chemical activation.     

Thermal regeneration of spent coal‐based activated carbon using carbon dioxide: process optimisation,Methylene Blue decolorisation isotherms and kinetics

Spent coal‐based activated carbon from the silicon industry has been used as raw material for the regeneration of activated carbon, with carbon dioxide as the regenerating agent. The regeneration process was optimised using response surface methodology and the optimum regeneration conditions were: regeneration temperature 985 °C; regeneration time 120 min; and carbon dioxide flow rate of 600 ml/min. The iodine number and yield of the activated carbon obtained under the optimum regeneration conditions were 1071 mg/g and 67%, with a Brunauer–Emmet–Teller surface area of 1270 m²/g and pore volume of 0.91 cm³/g. The regenerated carbon was tested for the removal of Methylene Blue dyes. The maximum adsorption capacity was found to be 395 mg/g and the equilibrium data fitted to the Langmuir isotherm model. The kinetic data indicated that the best fit corresponds to the pseudo‐second‐order kinetic model.     

水蒸气活化再生乙酸乙烯合成触媒载体活性炭

探讨了活化温度、活化时间、水蒸气流量对再生后活性炭吸附性能和得率的影响,得到了最佳工艺条件:活化温度1 000℃,活化时间60 min,水蒸气流量2.23 g/min。该工艺条件下再生活性炭的碘吸附值1 174.37 mg/g,亚甲基蓝吸附值200 mL/g,得率为62.87%。再生后活性炭的吸附指标达到国家一级品的标准,其中亚甲基蓝吸附值是国家一级品标准的2.22倍。同时,测定了该活性炭氮吸附,通过BET计算了活性炭的比表面积,通过密度函数理论(DFT)表征了活性炭的孔结构。结果表明:该活性炭为微孔型,BET比表面积为1 254.51 m2/g,总孔容为0.592 6 mL/g。     

XPS study and physico-chemical properties of nitrogen-enriched microporous activated carbon from high volatile bituminous coal

N-enriched microporous active carbons of different physico-chemical parameters have been obtained from high volatile bituminous coal subjected to the processes of ammoxidation, carbonisation and activation in different sequences. Ammoxidation was performed by a mixture of ammonia and air at the ratio 1:3 (flow ratio 250 ml/min:750 ml/min) at 350 °C, at each stage of production i.e. that of precursor, carbonisate and active carbon. Ammoxidation performed at the stage of demineralised coal or carbonisate has been shown to lead to a significant nitrogen enrichment and to have beneficial effect on the porous structure of the carbon during activation, allowing obtaining samples of the surface area of 2600-2800 m²/g and pore volume 1.29-1.60 cm³/g to be obtained with the yield of about 50%. The amount of nitrogen introduced into the carbon structure was found to depend on the sequence of the processes applied. The greatest amount of nitrogen was introduced for the processes in the sequence carbonisation → activation → ammoxidation. The introduction of nitrogen at the stage of active carbon leads to a reduction in the surface area and lowering of its sorption capacity. From the XPS study, ammoxidation introduces nitrogen mainly in the form of imines, amines, amides, N-5 and N-6, irrespective of the processing stage at which it is applied.     

KOH activation of ordered mesoporous carbons prepared by a soft-templating method and their enhanced electrochemical properties

Ordered mesoporous carbon (COU-2) was synthesized by a soft-templating method. The COU-2 mesoporous carbon was activated by using KOH to improve its porosity. The mesopore size of COU-2 was 5.5 nm and did not change by the KOH activation. But, the BET surface area of COU-2 largely increased from 694 to 1685 m²/g and total pore volume was increased from 0.54 to 0.94 cm³/g after the KOH activation. The large increase of micropore volume is due to the increase of the surface area. Electrochemical cyclic voltammetry measurements were conducted in aqueous (1 M sulfuric acid) and organic (1 M tetraethyl ammonium tetrafluoroborate/polypropylene carbonate) electrolyte solutions. The KOH-activated COU-2 carbon shows superior capacitances over the COU-2 carbon and a commercial microporous carbon both in aqueous and organic electrolyte solutions. These results suggest that the carbons having regularly-interconnected uniform mesopores and micropores in thin pore walls are desirable for the electrodes in electrochemical double-layer capacitors.     

Adsorption of Cd(II), Hg(II) and Zn(II) from aqueous solution using mesoporous activated carbon produced from Bambusa vulgaris striata

Mesoporous activated carbon (surface area of 608 m²/g) has achieved high efficiency in removal of cadmium, mercury and zinc ions from water solution. The proposed low-cost adsorbent was physically activated with water steam from the bamboo species Bambusa vulgaris striata. The batch studies suggested an activated carbon dose of 0.6 g/L, solution pH of 9 and an equilibrium time of 16 h in static conditions. The pseudo-second order equations represented the adsorption kinetics with high correlation. Fitting of the experimental results to the Langmuir, Freundlich, Redlich–Peterson and Toth isotherm models showed an almost homogeneous surface coverage and presence of physical adsorption. The highest adsorption capacities, calculated from the Langmuir model, are 239.45, 248.05 and 254.39 mg/g of cadmium, mercury and zinc, respectively.     

Activation of coal tar derived needle coke with K2CO3 into an active carbon of low surface area and its performance as unique electrode of electric double-layer capacitor

Raw needle coke from coal tar pitch was activated with K₂CO₃ at a coke:carbonate weight ratio of 1:4, to prepare an electrode for an electric double-layer capacitor (EDLC). Although the surface area of the coke activated at 900 °C for 3 h was as small as 20 m²/g, with a very high yield, the coke achieved capacitances per weight and volume of 20 F/g and 20 F/ml, respectively, in the two-electrode system, by charging at 2.7 V. The surface area of KOH-activated coke with a similar ratio (coke:hydroxide = 1:4, wt:wt) was over 2300 m²/g, and it exhibited capacitance per weight and volume values of 42 F/g and 17 F/ml, respectively. The coke activated by K₂CO₃ was found to be further activated by the charging. This electrochemical activation, which has been reported as activation in an electric field, was investigated by cyclic voltammetry in order to clarify it. The graphitic and pore structures of the coke after the electrochemical activation were analyzed by XRD to confirm retention of the graphene structure. Xe-NMR showed that the formation of small new pores was induced in the cathode material, increasing the surface area from 6 m²/g to 18 m²/g before use, although the pore volume was around 0.015-0.017 m³/g both before and after the charging. This activation with K₂CO₃ and a deeper understanding of the activation on charging suggest future directions for the preparation of electrode carbon for EDLCs.