Adsorption of organics on activated carbon cloth at zero surface coverage

Summary Adsorption properties of activated carbon cloth were investigated by gas-solid chromatography. Retention of several organic compounds was measured in the temperature range from 200 to 250°C. The gas/solid distribution coefficients and the related thermodynamic function of adsorption at zero surface coverage were determined. The obtained experimental data were used to explain the adsorbent-adsorbate interaction.     

Competitive adsorption and desorption of a bi-solute mixture: effect of activated carbon type

This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorption capacity and desorption capacity of a bi-solute mixture of phenol and 2-chlorophenol (2-CP). For this purpose, two different PACs; thermally activated Norit SA4 and chemically activated Norit CA1, and their granular countertypes with similar physical characteristics, thermally activated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better adsorbers for phenol and 2-CP compared with chemically activated carbons, but adsorption was more reversible in the latter case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption. The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed to higher energies of 2-CP adsorption.     

Kinetic and equilibrium studies of urea adsorption onto activated carbon: Adsorption mechanism

We found that activated carbon effectively removed urea from solution and that urea adsorption onto activated carbon followed a pseudo-second-order kinetic model. We classified the urea adsorption on activated carbon as physical adsorption and found that it was best described by the Halsey adsorption isotherm, suggesting that the multilayer adsorption of urea molecules on the adsorption sites of activated carbon best characterized the adsorption system. The mechanism of adsorption of urea by activated carbon involved two steps. First, an amino (–NH₂) group of urea interacted with a carbonyl (–C?O) group and a hydroxyl (?OH) group on the surface of activated carbon via dipole–dipole interactions. Next, the –C?O group of the urea molecule adsorbed to the activated carbon interacted with another –NH₂ group from a second urea molecule, leading to multilayer adsorption.     

Preparation and characterization of activated carbon from bagasse fly ash

Activated carbons from bagasse fly ash (BFA) were prepared by one step chemical activation using ZnCl₂ as activating agent, or combination method of chemical with CO₂ physical activation (physicochemical activation). The development of porosity was studied in correlation with the method of activation, activation temperature, and also the chemical weight ratio. A typical sample by the combination method at 600 °C and weight ratio of ZnCl₂:BFA = 2 exhibited micropore volume of 0.528 cc/g, mesopore volume of 0.106 cc/g and surface area of 1200 m²/g. For determining the adsorption capacity of the carbon samples in solutions, phenol and methylene blue equilibrium adsorption experiments were conducted. The properties and adsorption capacity of the synthesized activated carbons has been compared to commercial activated carbon (Norit^® SX Plus).     

Kinetics of adsorption and desorption of Pb(II) in aqueous solution on activated carbon by two-site adsorption model

The adsorption and desorption equilibrium and kinetics of lead ions from aqueous solutions on a granular activated carbon (GAC) were examined. Rapid increase followed by slow increase in Pb(II) amount on the GAC was observed as a function of time for the adsorption, while rapid decrease and consecutive very slow decrease was observed in desorption. Based on the experimental results, a two-site adsorption model was proposed for the adsorption and the desorption of Pb(II) under the study conditions. The Pb(II) adsorption on the GAC was estimated to have simultaneously occurred on the strong and the weak adsorption sites. Conventional Langmuir-type kinetic equations were introduced to quantitatively predict the adsorption and desorption with the two-site model by optimizing the parameters to fit the equilibrium and the kinetic experimental results. The equilibrium and kinetic experimental results could be represented by the equations by using one set of the common Langmuir parameters. Resultant kinetic parameters revealed that the adsorption equilibrium constant was two orders of magnitude greater for strong adsorption site than for weak adsorption site, though the maximum number of weak adsorption site was 1.5 times as great as that of strong adsorption site. The strong adsorption equilibrium constant resulted from a small desorption rate constant for the site. The equations were demonstrated to be applicable for predicting other desorption performances as well.     

甲烷在石墨化热解碳黑和活性炭上的吸附

为研究影响碳基吸附剂吸附超临界温度气体的主要因素,选择石墨化热解碳黑BP280和Ajax活性炭,分析超临界温度高压甲烷在其上的吸附平衡。应用容积法,在压力0~20.5 MPa、温度253 K~313 K测定甲烷的吸附平衡数据,并由等量吸附线标绘和亨利定律常数确定等量吸附热。引入通用吸附等温方程,再由方程的Langmuir标绘确定最大吸附容量,进而通过方程的线性化计算吸附平衡态中甲烷分子的作用能。结果表明,甲烷在两种吸附剂上的最大吸附容量均随温度而变化,并都小于液态甲烷的密度;甲烷在碳黑和活性炭上的等量吸附热分别为11.9 kJ/mol~12.5 kJ/mol和17.5 kJ/mol~22.5 kJ/mol,体现了两种吸附剂不同的表面能量分布;甲烷分子间作用能随吸附量的变化特点反映了超临界温度甲烷以类似于压缩气体状态聚集的特点和吸附剂结构上的差异。碳基吸附剂的比表面积和微孔容积是影响其储存甲烷容量的重要因素。     

Removal of ionic liquids and ibuprofen by adsorption on a microporous activated carbon: Kinetics,isotherms, and pore sites

Ionic liquids (ILs) are considered as emergent pollutants as their synthesis and further use at a large scale might generate environmental problems. The adsorption on activated carbons represents one of the most effective methods to remove ionic liquids and other micropollutants from wastewater. In this work, the adsorption properties on an activated carbon cloth of two pyridinium ionic liquids (4-tert-butyl-1-propylpyridinium bromide (IL1) and 4-tert-butyl-1-(2-carboxyethyl)pyridinium bromide (IL2)) newly synthesized, were compared with the ones of ibuprofen. The adsorption kinetics and isotherms were studied at pH 3 and 7.5. The adsorption thermodynamic parameters calculated from the isotherms indicate an exothermic process, typical of physisorption. The adsorption kinetics of a mixture of the molecules show a competition between ibuprofen and IL2. The location of each adsorbed ionic liquid and ibuprofen into the porosity of the activated carbon cloth was determined from N₂ (at 77 K) and CO₂ adsorption isotherms (at 273 K). The purification process of an effluent containing the ionic liquids and the ibuprofen in mixture or in single solute could be workable by adsorption on an activated cloth.     

Kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode: effects of pore length distribution and solution resistance

The effects of pore length distribution (PLD) and solution resistance, R_sol, on the kinetics of double-layer charging/discharging of the activated carbon fiber cloth electrode (ACFCE) were investigated in a 30 wt% H₂SO₄ solution using nitrogen gas adsorption, a.c. impedance spectroscopy, the current transient technique, and cyclic voltammetry. The impedance spectra of the ACFCE were theoretically calculated based upon the transmission line model in consideration of the pore size distribution (PSD) and the PLD. From comparison of both the experimental and theoretical impedance spectra of the ACFCE, it is suggested that the deviation from the ideal impedance behavior of a cylindrical pore in the experimental impedance spectrum of the ACFCE is mainly ascribed to PLD, rather than to PSD. The cathodic current transients and cyclic voltammograms were theoretically calculated based upon the transmission line model as functions of the standard deviation of the PLD and R_sol. From the results, it is concluded that ion penetration into the pores is closely related to both and R_sol during double-layer charging/discharging of the ACFCE, that is, the larger and R_sol, the lower is the rate capability, thus causing higher retardation of ion penetration into the pores.     

Carbon dioxide-methane mixture adsorption on activated carbon

In this work, we report new experimental data of pure and binary adsorption equilibria of carbon dioxide and methane on the activated carbon RB2 at 273 and 298 K. The pressure range studied were 0–3.5 MPa for pure gases and 0–0.1 MPa for mixtures. The combination of the generalized Dubinin model to describe the pure CO₂ and CH₄ isotherms with the IAST (Ideal Adsorbed Solution Theory) for the mixtures provide a method for the calculation of the binary adsorption equilibria. This formulation predicts with acceptable accuracy the binary adsorption data and can easily be integrated in general dynamic simulation of PSA (pressure swing adsorption process) adsorption columns. It involves only three parameters, independent of the temperature, and directly determined with only one adsorption isotherm of CO₂.     

Adsorption of methyl mercaptan on surface modified activated carbon

The influence of surface modification of activated carbon on the adsorption of methyl mercaptan in N(2) was investigated. The modification of the activated carbon was carried out by treatment with HNO(3)/H(2)SO(4) solutions, heat-treatment in Ar, and adsorption of cetylamine. Acid-treatment increased the adsorption of methyl mercaptan compared with the original activated carbon, and the adsorbed amounts increased with ratio of H(2)SO(4) in HNO(3)/H(2)SO(4) solutions. This result suggests that hydrogen bonding between acidic groups formed by acid-treatment and thiol groups of methyl mercaptan plays a role in adsorption of methyl mercaptan on activated carbon.     

Liquid-phase adsorption: Characterization and use of activated carbon prepared from diosgenin production residue

The adsorption behavior of activated carbon (AC) prepared from the residue of diosgenin by-product was characterized. The adsorption capacities of AC such as iodine, phenol and methylene blue (MB) are 933.28, 145.38 and 165 mg/g, respectively. The results of MP analysis and BJH method show AC has developed micropore and mesopore volumes, which are 0.1621 and 0.2623 cm³/g respectively, with the mean pore diameter of 1.49 nm. Comparison of the liquid phase adsorption capacities of AC to the standard activated carbon (SAC) and the commercial activated carbon (CAC) for wastewater treatment showed AC was superior to SAC and CAC. Experiments on phenol and MB adsorption and COD and chroma removal from diosgenin wastewater were carried out under different conditions of contact time, temperature, concentration, adsorbent dose and pH. The removal of COD and chroma of 10-multiple wastewater is 92.46 mg/g and 88 %, respectively. Adsorption parameters for the Langmuir and Freundlich isotherm models were determined. At lower temperatures, the data for phenol and COD fitted Freundlich model better than Langmuir model and vise versa for MB and chroma. Adsorption followed second-order kinetics. The study proves that AC prepared from the residue of diosgenin by-product can be used as adsorbent for the treatment of diosogenin wastewater as a cost-effective approach of resource recycle of Discorea zingiberensis C.H. Wright.     

Molecular dynamics study of selective adsorption of PCB on activated carbon

The selectivity of PCB adsorption from fish oil onto activated carbon (AC) was investigated by means of molecular dynamics to determine the importance of molecular planarity. PCB congeners 77 and 118 were selected for comparison purposes due to pronounced differences in mean adsorption efficiency and molecular geometry; triolein, a triacylglycerol of oleic acid (C18:1), was used as the representative fish oil component. Graphitic carbon structure was set up to serve as activated carbon model. Molecular force fields employed in the simulations combined short-range parameters from the OPLS with partial atomic charges obtained via quantum chemical calculations using DFT/B3LYP/6-31**G+ and Solvation Model 6. We modified the dihedral angle potential between the PCB aromatic rings and applied Schrödinger's Jaguar package to evaluate the required force field constants. Our complete system comprised a number of PCB molecules dissolved in triacylglycerol that overlaid and filled the pores of an AC structure. The production run of 4 ns provided strong indications that smaller pores will be conductive to better selectivity though also resulted in certain doubts concerning the estimation and assignment of partial atomic charges on the activated carbon. The majority of PCB molecules trapped in pores were attached via cl-AC “bonding”, leaving the main part of the PCB molecule free to interact with triolein. The cl-AC adsorption energy was found to surpass the energy criteria conventionally used for hydrogen bonds. Planar orientation assumed by a PCB molecule in a very energetically favored position on top of the graphite sheet clearly supported the π-cloud overlap hypothesis.     

Chromium adsorption in olive stone activated carbon

In this work, Cr(III) adsorption on activated carbon obtained from olive stones in an upflow fixed-bed column at 30^∘C was studied. The flow rate influence on the breakthrough curves at a feed concentration of 0.87 meq/L was investigated in an attempt to minimize the diffusional resistances. Breakthrough curves for a flow range of 2–8 mL/min were obtained at 10.5 cm bed height and inlet diameter of 0.9 cm. The mass transfer parameters indicated that the bed minimal resistance was attained at 2 mL/min. Therefore, the data equilibrium was carried out until the bed was saturated at 2 mL/min. The dynamic system generated a favorable isotherm with a maximum chromium uptake of 0.45 meq/g. A column sorption mathematical model was created considering the axial dispersion in the column and the intraparticle diffusion rate-controlling steps. The isotherm was successfully modeled by the Langmuir equation and the mathematical model described the experimental dynamic data adequately for feed concentrations from 0.26 to 3.29 meq/L.     

Nitrogen adsorption on fluorinated activated carbon fiber

Nitrogen adsorption isotherms for fluorinated activated carbon fiber (F-ACF) and fluorinated carbon black (F-CB) were measured at 77 K. Surface structures of F-ACF and F-CB were examined by _s -plot analysis using the adsorption data on the nonporous carbon black (CB) and F-CB. The surface energy of F-ACF was lower than that of ACF. The micropore structure of ACF was preserved even after fluorination, although the limiting adsorption amount and the micropore width decreased with fluorination.     

甲烷在活性炭上吸附平衡模型的研究

比较吸附模型分析甲烷在活性炭上吸附平衡的适用性,为吸附式天然气(ANG)的工程应用提供准确的预测模型。基于在温度268.15～338.15 K、压力0～12.5 MPa测试的甲烷在Ajax活性炭上的吸附平衡数据,选择Langmuir、Langmuir-Freundlich和Toth方程,应用非线性回归拟合方程参数后,确定绝对吸附量和甲烷吸附相态,并比较方程在不同压力区域内的预测精度。结果表明,甲烷吸附相密度随平衡温度和压力变化;由绝对吸附量确定的甲烷在Ajax活性炭上的平均等量吸附热为15.72 kJ/mol,小于由过剩吸附量的标绘结果;Langmuir、Langmuir-Freundlich和Toth方程预测结果在0～0.025 MPa的累积相对误差为6.449 8%、7.918 4%和0.910 0%,在1～10 MPa为0.491 1%、0.161 3%和0.369 4%。Toth方程在整个压力范围内的预测结果最为准确,但Langmuir-Freundlich方程在较高压力区域内具有较高的预测精度。     

Kinetic,equilibrium and thermodynamic study of 2-chlorophenol adsorption onto Ricinus communis pericarp activated carbon from aqueous solutions

ABSTRACT

This study reports on the adsorption of 2-chlorophenol from an aqueous solution using activated carbon prepared by H₂SO₄ activation of the pericarp of Ricinus communis (RCAC). The pericarp was carbonized and activated by treating with H₂SO₄ solution followed by heating in an oven at 105°C for 12 hrs. Batch adsorption experiments were carried out as a function of pH, contact time, initial concentration of the adsorbate, adsorbent dosage and temperature of the solution. Kinetic data were best fit to a pseudo-first-order rate equation for the adsorption of 2-chlorophenol on RCAC. Thermodynamic parameters ΔH^o, ΔS^o and ΔG^o for the adsorption were also determined which shows that adsorption on the surface of RCAC was spontaneous in nature, and exothermic between temperatures of 20°C and 80°C. The equilibrium data better fit the Langmuir isotherm model for 2-chlorophenol adsorption on RCAC. IR spectrum for loaded and unloaded RCAC was obtained and found to be in good agreement.     

Critical evaluation and comparison of enrichment efficiency of multi-walled carbon nanotubes, C18 silica and activated carbon towards some pesticides from environmental waters

In this work, optimization of multi-residue solid phase extraction (SPE) procedures coupled with high-performance liquid chromatography for the determination of Propoxur, Atrazine and Methidathion from environmental waters is reported. Three different sorbents were used in this work: multi-walled carbon nanotubes (MWCNTs), C18 silica and activated carbon (AC). The three optimized SPE procedures were compared in terms of analytical performance, application to environmental waters, cartridge re-use, adsorption capacity and cost of adsorbent. Although the adsorption capacity of MWCNT was larger than AC and C18, however, the analytical performance of AC could be made close to the other sorbents by appropriate optimization of the SPE procedures. A sample of AC was then oxidized with various oxidizing agents to show that ACs of various surface properties has different enrichment efficiencies. Thus researchers are advised to try AC of various surface properties in SPE of pollutants prior to using expensive sorbents (such as MWCNT and C18 silica).     

Synthesis of nitrogen doped activated carbon/polyaniline material for CO2 adsorption

The equilibrium adsorption isotherms of carbon dioxide and nitrogen on the nitrogen doped activated carbon (NAC) prepared by the chemical activation of a pine cone‐based char/polyaniline composite were measured using a volumetric technique. CO₂ and N₂ adsorption experiments were done at three different temperatures (298, 308, and 318 K) and pressures up to 16 bar, and correlated with the Langmuir, Freundlich, and Sips models. The Sips isotherm model presented the best fit to the experimental data. The N‐doped adsorbent showed CO₂ and N₂ adsorption capacity of 3.96 mmol·g⁻¹ and 0.86 mmol·g⁻¹, respectively, at 298 K and 1 bar. The selectivity predicted by ideal adsorbed solution theory (IAST) model was achieved 47.17 for NAC at 1 bar and y_N2 = 0.85 which is a composition similar to flue gas. The results showed that NAC adsorbent has a high CO₂‐over‐N₂ selectivity in a binary mixture. The relatively fast sorption rate of CO₂ on NAC compared to N₂ indicates the stronger affinity between CO₂ and amine groups. The isosteric heat of adsorption of CO₂ by the NAC demonstrated the physico‐chemical adsorption of CO₂ on the adsorbent surface. These data showed that prepared NAC could be successfully applied in separation of CO₂ from N₂.     

Atenolol sequestration using activated carbon derived from gasified Glyricidia sepium

Activated carbon (AC) derived from gasified Glyricidia sepium woodchip (GGSWAC) was prepared using KOH and CO₂ activation via microwave radiation technique to remove atenolol (ATN) from aqueous solution. The surface area (S_BET) and total pore volume (TPV) of GGSWAC were 483.07 m²/g and 0.255 cm³, respectively. The n-BET model fits well with the isothermal data indicating a multilayer adsorption with the saturation capacity of 121, 143 and 163 mg/g at 30, 45 and 60 °C, respectively. The kinetic study showed that ATN adsorption followed Avrami model equation (R² ≅ 0.99). Based on the thermodynamic parameters, the adsorption of ATN onto GGSWAC was endothermic (ΔH_S = 234.17 kJ/mol) in the first layer of adsorption and exothermic in the subsequent layer (ΔH_L = −165.62 kJ/mol). The ATN adsorption was controlled by both diffusion and chemisorption. In continuous operation, the Thomas (R² = 0.9822) and Yoon–Nelson (R² = 0.9817) models successfully predicted the ATN adsorption.     

Selective adsorption and removal ability of pine needle-based activated carbon towards Al(III) from La(III)

Rare earth elements are an important strategic resource. As one of the most valuable member, lanthanum plays a key role in lanthanide. However, trace Al(III) impurity in lanthanum materials can seriously damage the performance of lanthanum materials. In this paper, a nitrogen-containing activated carbon, AC-PN-700, was synthesized using pine needle as raw material and KOH as activator. The AC-PN-700 was characterized by surface area analyzer, elemental analysis and FT-IR. The adsorption and selective ability of AC-PN-700 towards Al(III) were investigated. The BET specific surface area of AC-PN-700 was 596.4 m².g^?1, and the average pore diameter was 2.7?nm. Depend on its large specific surface, well-developed internal pore structure and abundant nitrogen-containing functional groups, the AC-PN-700 possesses strong adsorption affinity and excellent recognition selectivity towards Al(III). The adsorption capacity of AC-PN-700 towards Al(III) could reach to 3.89?mg.g^?1, removal rate towards Al(III) was almost 100%, and relative selectivity coefficients with respect to La(III) is 9.5. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. In addition, AC-PN-700 possesses better regeneration ability and reusability.