Synthesis of carbon molecular sieves from palm shell by carbon vapor deposition

A series of experiments were conducted to produce carbon molecular sieves (CMS) through carbon deposition from a locally available palm shell of Tenera type for separating gaseous mixtures. The process involves three stages; carbonization, physical activation with steam, and carbon deposition by using benzene cracking technique. Carbonization of the dried palm shells was occurred at 900°C for duration of 1 h followed by steam activation at 830°C for 30–420 min to obtain activated carbons with different degree of burn-offs. The highest micropore volume of activated carbon obtained at 53.2% burn-off was used as a precursor for CMS production. Subsequent carbon deposition of the activated sample at temperature range from 600 to 900°C for 30 min has resulted in a series of CMSs with different selectivities of CO₂/CH₄ and O₂/N₂. The kinetic adsorption isotherm of CO₂, CH₄, O₂ and N₂ at room temperature also presented in this work.     

Growth of carbon nanofibers on activated carbon fiber fabrics

Activated carbon fiber fabrics, an excellent adsorbent, were used as catalyst supports to grow carbon nanofibers. Because of the microporous structure of the activated carbon fibers, the catalysts could be distributed uniformly on the carbon surface. Based on this concept, the carbon nanofibers can be grown directly on the activated carbon fiber fabrics. We demonstrate that carbon nanofibers with a diameter between 20 and 50 nm for most of the fibers can be synthesized uniformly and densely on activated carbon fiber fabrics, impregnated by nickel nitrate catalyst precursor, using catalytic chemical vapor deposition. Although the carbon nanofibers are not straight with a crooked morphology, they form a three-dimensional network structure. Structure characterizations by TEM and XRD indicate that the carbon nanofibers have a turbostratic graphite structure and the graphite layers are stacked with a herringbone structure.     

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.     

Adsorption properties of carbon molecular sieves prepared from an activated carbon by pitch pyrolysis

In this study a heat-treatment process using an activated carbon and coal-tar pitch was developed to prepare carbon molecular sieves (CMSs) for CH₄/CO₂ separation. This process results in a partial blockage of the pores of the activated carbon precursor, so that a reduction in the pore size takes place. Equilibrium CO₂ adsorption measurements at different temperatures, and CO₂ and CH₄ kinetic measurements at different temperatures and feed pressures were carried out using the TEOM technique for a carbon molecular sieve (CMS) prepared by this process (sample CB3) and a commercial CMS (Takeda 3A, sampleT3A). The overall diffusion for CO₂ in sample CB3 was faster than that in T3A and a slightly higher CO₂ adsorption capacity of CB3 was obtained. The transient uptake profiles in both samples at different temperatures and different CO₂ partial pressures were described in some cases by a micropore diffusion model, and in other cases by a dual resistance model. Both equilibrium and kinetic results demonstrate a better CO₂/CH₄ separation performance for the CMS prepared in the present study (CB3) than for the commercial CMS (Takeda 3A), due to the existence of slightly wider pore-mouth openings in sample CB3. This study demonstrates that the process used in this work is an interesting and reproducible approach to prepare CMS for CO₂/CH₄ separation.     

Thermocatalytic decomposition of methane using palm shell based activated carbon: Kinetic and deactivation studies

Catalytic characteristics of activated carbon manufactured from palm shell (ACPS) for methane decomposition was studied using a thermobalance by measuring thee mass gain with time. A reaction order of 0.5 is obtained for methane decomposition over the activated carbon and the activation energy is 210 KJ mol^− 1. The activity of the activated carbon had decreased in almost a linear relationship with the amount of carbon deposited at 800 °C, which indicates that the carbon deposition occurred uniformly on to the carbon surface, while diffusion effect appeared to occur significantly at the last stage of the process at reaction temperatures up to 950 °C. The study of mass gain using different particle sizes indicates the existence of mass transfer effect and the pore mouth blocking which seem to take place particularly in large particles. Comparison between ACPS and commercial based activated carbon (AC) shows almost similar values with regard to change of mass gain with time, maximum amount of carbon deposited before deactivation and the deactivation time.     

煤层气变压吸附用炭分子筛的制备研究

为解决煤层抽放气中CH4/N2的分离问题,以椰壳炭化料为原料,采用炭化、活化和炭沉积相结合的方法,以苯为沉积剂,改变工艺条件,制备了不同性能的炭分子筛,研究了炭分子筛前驱体的种类、苯流量对炭分子筛分离效果的影响,结果表明,在炭化温度450℃,炭化时间40 min,活化温度850℃,活化时间120 min时制备的炭分子筛前驱体,进一步制成炭分子筛对CH4/N2的分离效果最好;在750℃,沉积时间30 min,苯流量0.45 m L/min时制备的炭分子筛对CH4/N2的分离效果最好。     

Preparation of carbon molecular sieves from carbon micro and nanofibers for sequestration of CO2

In this study, a hierarchal web of carbon micro and nanofibers was used as a precursor for the synthesis of a carbon molecular sieve (CMS). CMSs were prepared by thermal treatment of carbon fibers using a microwave heating device. The heating power and treatment time were optimized for the maximum performance of the prepared CMS for the separation of CO₂ at low concentrations from the gaseous mixture of CO₂ and air under dynamic (flow) conditions. Based on the experimental data, microwave power input of 240 W and treatment time of 15 min were found to be suitable for the maximum uptake of CO₂ by CMS. Adsorption breakthrough curves were obtained at different gas flow rates and CO₂ concentrations. CMSs prepared from the hierarchal web of carbon micro and nanofibers were found to be superior to those prepared from ACF. The CO₂ uptake was determined to be approximately 0.88 mg/g and 10 mg/g at concentrations of 500 ppm and 5000 ppm, respectively, in air.     

TiO2 photocatalyst deposition by MOCVD on activated carbon

Activated carbon modified by HNO₃ was used as the support during the production of TiO₂ by metal organic chemical vapor deposition (MOCVD). The HNO₃ modification increased mesopores surface area of activated carbon indicating the size of pores increased. The concentration of surface oxygen bearing groups on the HNO₃ modified activated carbon was much higher than that of the original activated carbon. It was found that a modification of activated carbon by 6 mol/L HNO₃ increased the deposition rate of TiO₂ by 4.5 times. The modification of activated carbon by HNO₃ significantly raised the photocatalytic activity of TiO₂ resulting from the formation of smaller-sized TiO₂ particles well dispersed confirmed by the results of XRD patterns and N₂ adsorption-desorption isotherms.     

炭纤维基复合吸附材料的制备及其气体分离性能研究

活性炭纤维基复合炭分子筛材料作为一种新型的吸附材料,具有丰富而发达的微孔结构、大的比表面积和优异的导电性能,这些性质使其具有独特的气体分离性能。本文以沥青基活性炭纤维和酚醛树脂为原料制备复合炭分子筛材料,用扫描电镜和氮吸附等温线法研究其外观型态和孔隙结构,在变电吸附工艺条件下以CO2为探针考察了此类复合吸附材料的分离性能。     

Adsorption of methane on corn cobs based activated carbon

Activated carbon was prepared with corn cobs and potassium hydroxide under optimized variables. Due to their botanical origin, corn cobs can be an excellent starting material to produce nanoporous carbon for natural gas storage. Samples with different BET surface areas were chosen to perform methane adsorption experiments. Methane adsorptions on corn cob based activated carbon were studied at four different pressures (500, 1000, 1500 and 2000 psi) and two different temperatures (298 K and 323 K) in a volumetric adsorption apparatus. The volume based methane adsorption results specified an ‘increase in the methane adsorption capacities of activated carbon with increasing surface area and showed that adsorption capacity of methane depends on pressure and temperature. The highest methane storage capacity was found to be 160 (v/v) at 298 K and 1500 psi. The applications include use in the transportation of natural gas, natural gas based vehicles, and adsorption of gas from landfills.     

煤层气浓缩用碳分子筛的研制及性能研究

为评价分析碳分子筛(Carbon Molecular Sieves,CMS)产品性能,以酚醛树脂废料为主要原料,通过添加助剂,采用炭化/气相沉积一体化工艺,制备了专用于煤层气提浓的BM碳分子筛(记为BMCMS)。采用CO_2吸附法、加压热重法及四塔变压吸附法对BMCMS及商业碳分子筛(记为JCCMS)的孔隙结构、CH_4和N_2的吸附容量、速度以及对煤层气的实际分离性能等进行研究。结果表明,BMCMS碳分子筛的孔隙以0.85 nm以下微孔为主,主要分布在0.4~0.65 nm,其比例占整个孔隙的66%以上,高于JCCMS的65%;碳分子筛的孔隙直径为N_2分子的1.1~1.8倍时,该类孔隙适宜吸附N_2,而对CH_4的吸附具有阻碍作用;当用于PSA浓缩抽采煤层气时,可将煤层气中CH_4浓度提高25.6%,实际运行指标优于JCCMS。     

Preparation of photocatalytic TiO2 coatings of nanosized particles on activated carbon by AP-MOCVD

Anatase TiO₂ coatings on highly porous activated carbon were prepared by a novel method—atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). At a source temperature of 423 K, the TiO₂ particles were mostly coated on the external surface of activated carbon. These particles were well dispersed with their sizes ranging from 10 to 50 nm. The optimum loading of TiO₂ was found to be 12 wt%. The TiO₂ photocatalysts so prepared behave similarly to that of the pure commercial TiO₂ powder. The activated carbon supported TiO₂ catalyst could be easily separated from the treated water with its catalytic performance maintained even after 10 cycles, indicating that the TiO₂ coating was stable. It was observed that TiO₂ supported on activated carbon had a high capacity to mineralize pollutants. Consequently, activated carbon supported TiO₂ by AP-MOCVD is a promising photocatalyst for the photodegradation of pollutants in water.     

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).     

Molecular sieve properties obtained by cracking of methane on activated carbon fibers

Molecular sieve properties of activated carbon fibers modified by cracking treatment with methane are studied herein. The effect of methane treatment on the porous texture of the samples has been studied while varying temperature and time. These materials have been evaluated for their selectivity during CO₂ and CH₄ separation; their uptakes have been compared with non-treated activated carbon fibers (studied previously), which were considered suitable to be used as molecular sieves. Kinetics of CO₂ and CH₄ uptake have also been investigated in this research. The treatment produced materials exhibiting fast kinetics and high selectivity during CO₂ and CH₄ separation; at the same time however, the CO₂ uptake capacity was diminished.     

Improved activated carbon by thermal treatment in methane and steam: Physicochemical influences on MIB sorption capacity

Thermal treatment by steam or by methane plus steam altered the physicochemical properties of a commercial lignite-based activated carbon; and improved the carbon’s sorption capacity for the odorant 2-methylisoborneol (MIB). Rapid small scale column tests (RSSCTs) revealed that favorable thermal treatment allowed an activated carbon to remove this odorant for up to six times longer before initial MIB breakthrough than did its commercial lignite counterpart. For these RSSCTs (135 ppt), clarified water from a water treatment plant (2.07 mg/L TOC) was spiked with ¹⁴C-MIB; and liquid scintillation protocols facilitated ¹⁴C-MIB detection at 1-3 ppt. The more favorable thermal treatment at 1000 °C increased pore volumes with 5-400 Å widths by twofold; and the bed volume to initial MIB breakthrough correlated fairly well (R² = 0.9) with pore volume in the range of 5-60 or 5-400 Å. Thermal tailoring altered the carbon’s apparent point of zero charge: from pH 6.5 for the commercial lignite carbon, to pH 9.2 for tailored carbon. When methane and steam were used together, the C, H, N and O contents were virtually the same as for the commercial lignite. In contrast, when steam was employed alone, the percent of oxygen increased, and the percent of H, C and N therefore decreased slightly.     

Comparative study of the textural characteristics of oil palm shell activated carbon produced by chemical and physical activation for methane adsorption

The objective of this study is to relate textural and surface characteristics of microporous activated carbon to their methane adsorption capacity. Oil palm shell was used as a raw material for the preparation of pore size controlled activated carbon adsorbents. The chemical treatment was followed by further physical activation with CO₂. Samples were treated with CO₂ flow at 850 °C by varying activation time to achieve different burn-off activated carbon. H₃PO₄ chemically activated samples under CO₂ blanket showed higher activation rates, surface area and micropore volume compared to other activation methods, though this sample did not present high methane adsorption. Moreover, it was shown that using small proportion of ZnCl₂ and H₃PO₄ creates an initial narrow microporosity. Further physical activation grantees better development of pore structure. In terms of pore size distribution the combined preparation method resulted in a better and more homogenous pore size distribution than the conventional physical activation method. Controlling the pore size of activated carbon by this combined activation technique can be utilized for tuning the pore size distribution. It was concluded that the high surface area and micropore volume of activated carbons do not unequivocally determine methane capacities.     

Preparation,modification and industrial application of activated carbon from almond shell

Almond shell was used to prepare activated carbon using physical activation method, consisted of carbon dioxide (CO₂) gasification. The effects of the preparation variables which were activation temperature, activation time and carbon dioxide flow rate on the adsorption capacity of iodine and methylene blue solution were investigated. The optimal activated carbon was obtained by these conditions as follows: 800 °C activation temperature, 100 cm³/min carbon dioxide flow rate and 120 min activation time. The characterization of carbon materials is performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ¹³C (CP/MAS and MAS) solid-state NMR, nitrogen adsorption (BET) and Boehm's titration method. For an industrial application, the optimal activated carbon was ammoxidated to improve its adsorption capacity toward total organic carbon from Tunisian industrial phosphoric acid. The influence of experimental parameters such as specific consumption, initial concentration, contact time, agitation speed and temperature on TOC removal was studied.     

Preparation and modification of activated carbon fibres by microwave heating

Thermal treatment of activated carbon fibres (ACF) has been carried out using a microwave device, instead of a conventional furnace. The results show that microwave treatment affects the porosity of the ACFs, causing a reduction in micropore volume and micropore size. More importantly, the results also show that microwave treatment is a very effective method for modifying the surface chemistry of the ACFs with the production of pyrone groups, detected by FTIR. As a result very basic carbons, with points of zero charge approximately equal to 11, are readily obtained.     

Mechanism of carbon nanotube growth from camphor and camphor analogs by chemical vapor deposition

Single walled nanotubes have been synthesized by chemical vapor deposition from camphor, camphor analogs (camphorquinone, norcamphor, norbornane, camphene, fenchone), and various other precursors (menthone, 2-decanone, benzene, methane). The high temperature conditions (865 °C) and Fe/Mo alumina catalyst used in the syntheses are archetypal conditions for the production of single walled carbon nanotubes. It has been shown that the mechanism of tube growth is unlikely to depend upon the production of reactive five- and six-member rings, as has been previously suggested. The results suggest that the presence of oxygen in the precursor does not significantly improve the quality of tubes by etching amorphous carbon: it is suggested that the control of the flux of the precursor to the catalyst is more important in the production of high quality tubes. There is, however, evidence for different distributions of tube diameter being produced from different precursors.     

Effect of activation temperature on pore development in activated carbon produced from palm shell

A series of experiments were conducted to investigate the effect of activation temperature on pore development of activated carbon produced from palm shell. Activation of the samples was carried out at 800, 850 and 900 °C for different durations ranging from 10 to 180 min. The samples were characterized using N₂ adsorption for evaluation of micropores and the mercury intrusion technique for mesopore and macropore analysis. Within the range of activation temperatures studied, high burn‐off products derived from high activation temperatures tend to have larger micropore development. However, an increase in the activation temperature has no remarkable effect on mesopore and macropore development. © 2002 Society of Chemical Industry