Prediction of Carbon BTEX Adsorption Capacity Using Field Monitoring Data

The need for predicting adsorption capacity for benzene, toluene, ethylbenzene, and xylenes (BTEX) onto granular-activated carbon (GAC) is a problem commonly associated with petroleum-spill remediation. In this study, monitoring data are compiled from operational records of ground-water pump and treat remediation sites where GAC adsorption is utilized as a primary treatment mechanism for BTEX. The monitoring data are reduced to adsorbed and equilibrium concentrations from which Freundlich isotherms and various linear and multivariate models are calibrated for prediction of BTEX capacity on GAC. The models are employed by themselves and with Ideal Adsorbed Solution Theory to predict capacity for total BTEX and benzene. Several models are selected based on prediction ability and are tested with independent data. Two simple models, a multivariate model and a Freundlich isotherm, are recommended. Complex empirical models and Ideal Adsorbed Solution Theory did not perform as well as the selected models and were rejected. From the Freundlich isotherm, new Freundlich constants are reported that describe adsorption of total BTEX on GAC from gasoline-contaminated ground water.     

Adsorption of 1,1,1,2-Tetrafluoroethane by Various Adsorbents

Experiments have been conducted to investigate gas-phase adsorption characteristics of 1,1,1,2-tetrafluoroethane (HFC-134a) by activated carbon fiber, extruded activated carbon, granular activated carbon, activated alumina, and molecular sieve. HFC-134a is currently regarded as an excellent replacement for chlorofluorocarbon-12, a refrigerating and cooling agent extensively used previously in all automobiles and many cooling systems. Performances of HFC-134a adsorption were characterized by the equilibrium adsorption capacity, time to reach equilibrium, and desorption efficiency of exhausted adsorbent. A simple thermal treatment process with proper operating temperature and treatment duration was found to be effective for the regeneration of exhausted adsorbents. Adsorption isotherms of the empirical Freundlich and Jossens types were observed to adequately represent the equilibrium adsorption data. A mass transfer model based on the pseudo steady state squared driving force was adopted to describe the mass transfer process of HFC-134a adsorption.     

Overall Adsorption Isotherm of Natural Organic Matter

Adsorption equilibrium data in lumped water quality indices obtained for diluted solutions of a peat water and effluents from a wastewater treatment were analyzed using the ideal adsorbed solution theory with the Freundlich equation. The use of the same value for Freundlich exponent 1∕n in the ideal adsorbed solution theory resulted in a straightforward and less computationally demanding expression to describe an overall batch adsorption isotherm. A fictive component approach, assuming a logarithmic normal distribution of Freundlich K and a nonadsorbable fraction, adequately described and predicted the overall isotherms for different initial concentrations of diluted solutions presented as a lumped water quality index. The parameters in the distributed fictive component approach were independently sensitive to each portion of an isotherm curvature. Preferential adsorption of the smaller molecular weight (MW) components was observed by a size-exclusion high-performance liquid chromatography. Two-dimensional distribution analysis of organics in terms of Freundlich K and MW revealed a weak tendency of the adsorptive strength to decrease with the increase of the MW.     

Determination and Correlation of Binary Gas Adsorption Equilibria of VOCs

Highly porous activated carbon is used in the removal of volatile organic compounds (VOCs) and the purification of room air. Since the activated carbon must be capable of removing VOCs at low concentrations through adsorption, studies on the adsorption equilibrium of trace-level concentrations of VOCs are essential. To determine the adsorption isotherm, a headspace gas chromatography (HSGC) method was used, with analysis carried out using gas chromatography or gas chromatography-mass spectroscopy. The reliability of this method was confirmed by comparison of the adsorption isotherms of methanol measured by the HSGC method with those measured by the volumetric method. Isotherms for three different types of activated carbon and eight types of VOCs were determined over a wide range of concentrations. Furthermore, the results of the HSGC method for two systems of binary adsorption equilibria (dichloromethane+trichloroethylene) and (benzene+toluene), were found to be correlated with those of the ideal adsorbed solution theory.     

Applicability of Equilibrium Isotherm Models for the Biosorptive Uptakes in Comparison to Activated Carbon-Based Adsorption

The adsorption isotherm models available in the literature have generally developed for sorption onto metallic surfaces or activated carbon-based sorbents. However, biosorptive uptakes involve interactions of biopolymer-based surfaces with different types of pollutants, which are quite different from metal surfaces or activated carbon. So, in the present study, 16 different types of adsorption isotherm models have been studied. For a ready reference both types of sorbents, i.e., a biosorbent and activated carbon have been employed. Results show that in general the accuracy of models to fit experimental data improves with the degree of freedom. The Fritz–Schluender model gives the most accurate fit (R2?0.85–0.99) to all experimental data in comparison to other models used both for activated carbon and the biosorbent. However, most widely used isotherm models, i.e., Langmuir and Freundlich, could be used to describe the sorption equilibrium of biosorptive processes with a fair degree of accuracy, owing to the mathematical ease in the use of these models. Trends of the applicability of various sorption equilibrium models to biosorptive uptakes are similar to those of activated carbon-based sorptions. Comprehensive equilibrium analysis has assisted in understanding the mechanistic aspects associated with different types of sorbents.     

Adsorption of carbon dioxide by coconut activated carbon modified with Cu/Ce

A series of the coconut activated carbons(CAC) based absorbents modified with Cu and Ce(Cu/CAC,Cu/Ce/CAC) were prepared by impregnation technology for carbon dioxide capture.The adsocrption equilibriums of CO2 on Cu/CAC and Cu/Ce/CAC were measured.The results showed that the adsorption capacity of CO2 onto the activated carbon modified with Cu/Ce increased with the decreasing temperature in the same pressure.The adsorption capacity of CO2 on Cu/CAC was higher than that of the blank CAC,and compared with the Cu/CAC,the adsorption capacity of CO2 of Cu/Ce/CAC with the mass ratio of Cu/Ce=30 was improved at 298 and 303 K.In addition,the adsorption equilibrium data for CO2 at various temperatures was fitted to Langmuir,Freundlich and D-R isotherm models.It was found that the D-R equation was the best model for fitting the adsorption data on Cu/Ce/CAC at different temperatures.     

Adsorption of Perfluorinated Compounds onto Activated Carbon and Activated Sludge

The adsorption of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) onto powdered activated carbon (PAC) was investigated in the presence and absence of effluent organic matter (EfOM) at an environmentally relevant concentration range (0.1–500??μg/L). Adsorption of PFOS and PFOA to PAC fitted the Freundlich model well (r2>0.98), and adsorption capacity of PFOS (KF = 17.48) and PFOA (KF = 10.03) in the absence of EfOM was more than one order of magnitude higher than that in the presence of EfOM (KF = 0.66 for PFOS, KF = 0.20 for PFOA), indicating that EfOM greatly reduces the adsorption capacity of PAC. Moreover, EfOM was characterized by ultrafiltration, and fractions of nominal molecular weights were obtained to investigate their effect on the PFOS and PFOA adsorption. The fraction of <1??kDa had greater effect on adsorption than the fraction of >30??kDa, indicating that the similar molecular size of target compounds was the major contributor to adsorption competition. Additionally, biosorption of PFOS and PFOA to activated sludge fitted the linear isotherm (r2>0.9) within a concentration range of 50–400??μg/L. On the basis of our data, the estimated partition coefficient, Kd, was 729??L/kg for PFOS and 154??L/kg for PFOA, respectively, suggesting that PFOS and especially PFOA have a low tendency to partition onto sludge.     

Equilibrium Adsorption of Phenol-, Tire-, and Coal-Derived Activated Carbons for Organic Vapors

Adsorption isotherms for alkane, aromatic, and ketone vapors were determined for activated carbon fiber cloth, tire-derived activated carbon and coal-derived activated carbon adsorbents. Physical and chemical properties of the vapors and adsorbents were used to interpret these results that were obtained from 20 to 50°C, with a more limited data set at 125 and 175°C and relative pressures between 0 and 0.99. Fitted isotherms using the Freundlich and Dubinin–Radushkevich adsorption models had mean total relative errors <5.6 and 9.2% for the microporous and mesoporous/macroporous adsorbents, respectively, at the temperature range from 20 to 50°C. The predictive direct quantitative structure activity relationship model had mean total relative errors <9.7 and 61% for the microporous and mesoporous/macroporous adsorbents, respectively, at the temperature range from 20 to 50°C without requiring experimental input.     

Adsorption of carbon dioxide by coconut activated carbon modified with Cu/Ce

A series of the coconut activated carbons (CAC) based absorbents modified with Cu and Ce (Cu/CAC, Cu/Ce/CAC) were prepared by impregnation technology for carbon dioxide capture. The adsocrption equilibriums of CO₂ on Cu/CAC and Cu/Ce/CAC were measured. The results showed that the adsorption capacity of CO₂ onto the activated carbon modified with Cu/Ce increased with the decreasing temperature in the same pressure. The adsorption capacity of CO₂ on Cu/CAC was higher than that of the blank CAC, and compared with the Cu/CAC, the adsorption capacity of CO₂ of Cu/Ce/CAC with the mass ratio of Cu/Ce=30 was improved at 298 and 303 K. In addition, the adsorption equilibrium data for CO₂ at various temperatures was fitted to Langmuir, Freundlich and D-R isotherm models. It was found that the D-R equation was the best model for fitting the adsorption data on Cu/Ce/CAC at different temperatures.     

A significant improvement in adsorption behavior of mesoporous TUD-1 silica through neodymium incorporation

Neodymium was incorporated into the three-dimensional mesoporous siliceous material TUD-1.In order to understand the chemical and morphological structure of the prepared material,several characterization techniques were performed.The characterization results show the formation of highly distributed isolated Nd3+ions incorporated in the silica matrix in tetrahedrally coordinated structure,moreover no aggregation of separate phase(s)was/were observed.The prepared material was investigated as an adsorbent for methyl green(MG)dye in aqueous solution as a model cationic dye.The results show higher adsorption capacity for Nd-TUD-1 by almost 24 times higher than the neat parent TUD-1 material and more than 100 times higher than bulky Nd₂O₃under neutral pH.The adsorption results were fitted perfectly with pseudo-second-order model.Moreover,the adsorption isotherms were perfectly fitted with Freundlich isotherm model which indicates the formation of a multilayer of the dye molecules onto the Nd-TUD-1 surface as a physisorption with endothermic nature.     

An Enhanced Study on Adsorption of Al(iii) onto Bentonite and Kaolin: Kinetics,Isotherms, and Mechanisms

In order to remove aluminum ions in bauxite processing wastewater, two natural clay minerals (bentonite and kaolin) were used as adsorbents. The adsorption behaviors including kinetics and isotherms were studied at much broader pH range, higher temperature, and higher Al(III) concentration by batch experiments. The adsorption mechanisms were investigated by optical microscope, zeta potential testing, and XRD analysis. The results show that Al(III) adsorption is strongly pH dependent and increases clearly with increasing pH. The pseudo-second-order kinetic model can best describe the adsorption process, and the intra-particle diffusion was not the sole rate-controlling step. The Langmuir–Freundlich model can fit best the adsorption equilibrium data, and the maximum capacities of Al(III) adsorbed on bentonite and kaolin reach to 8.52 mg g^–1 and 0.58 mg g^–1, respectively, at 35°C. Thermodynamic studies display that the adsorption of Al(III) onto clay minerals is non-spontaneous. The adsorption of Al(III) onto bentonite is endothermic and causes an increase in the entropy, while kaolin is exothermic and causes a decrease in the entropy. The interaction mechanisms of Al(III) with bentonite and kaolin involve electrostatic attraction, cation exchange, surface complex, and precipitation. Bentonite as adsorbent has more potential to remove Al(III) than kaolin.     

Equilibrium and Kinetic Study on Reactive Dyes Adsorption by Palm Kernel Shell-Based Activated Carbon: In Single and Binary Systems

The adsorption of two reactive dyes, Reactive Black 5 and Reactive Red E, onto palm kernel shell-activated carbon (PKSAC) was studied. The effect of the presence of more than one dye in solution on the equilibrium and kinetics of adsorption was investigated. Equilibrium isotherm models were applied to describe the adsorption capacities of single and binary systems. Adsorption of reactive dyes for single system can be represented by the Freundlich and the Redlich-Peterson models. For binary system, the equilibrium was described successfully by the modified extended Freundlich model. Experimental data showed that competitive adsorption for active sites on the carbon surface resulted in a reduction in the overall uptake capacity of the reactive dyes. The rates of adsorption in single system were found to agree well with the pseudosecond-order kinetic model. Finally, the chemical oxygen demand (COD) of the treated reactive dye solutions from single and binary systems showed that a minimum of 4 g/L dosage of PKSAC was needed to reduce the COD to an acceptable level according to the Water Quality Guidelines and the Pollutant Fact Sheets Guidelines.     

An Overview of the Studies about Heavy Metal Adsorption Process by Microorganisms on the Lab. Scale in Turkey

Abstract

Heavy metal ions, Cr(VI), Pb(II), Cu(II), Fe(III) and Ni(II) were removed from synthetic aqueous solutions by using Z. ramigem, an activated sludge bacterium, and R. arrhizus, a filamentous fungus. The adsorption isotherms were developed and it was seen that the adsorption equilibrium data fit both Freundlich and Langmuir isotherms. Heavy metal adsorption on free and immobilized cells was also investigated in various reactor types such as stirred tank reactors (single and multi-stage) and packed bed reactors.     

Modeling Volatile Organic Compound Sorption in Activated Carbon. II: Multicomponent Equilibrium

A new approach is presented for modeling multicomponent volatile organic compound (VOC) sorption equilibrium in ultra- and supernanoporous activated carbons. The model uses “Dubinin–Astakhov thermal equation of equilibrium adsorption” (DA-TEEA) for single-component adsorption thermodynamics and “ideal/real adsorbed solution theories” (IAST/RAST) for the multicomponent mixing rules. Use of the Henry’s Law adsorption isotherm resolves the singularity of DA-TEEA at zero-coverage conditions. The introduced method predicts multicomponent adsorption equilibria of VOCs based on equilibrium data of only one similar component. Single and binary adsorption equilibria of acetone and benzene vapors in Kynol ACFC-5092-20 activated-carbon-fiber-cloth adsorbents are predicted with the presented models and compared with modeled and measured characterization data available in the literature. The Wilson model for nonideal binary solution mixtures is used to predict the activity coefficients needed in DA-TEEA/RAST. Modeled results are compared against measured characterization data. The selected Henry’s Law upper-bound pressure (HUBP) is found to be an important factor controlling the accuracy of the multicomponent equilibrium models. An optimum HUBP can generate highly accurate results from both DA-TEEA/IAST and DA-TEEA/RAST. The accuracy realized by applying this method to acetone–benzene mixtures is sufficient for engineering design and development purposes.     

Adsorption of Sulfur Dioxide on Activated Carbon from Oil-Palm Waste

Adsorption of sulfur dioxide (SO2) onto activated carbons prepared from oil-palm shells was investigated in this paper. Experimental results showed that the adsorption temperature and SO2 concentration significantly determined the amount of SO2 adsorbed and the equilibrium time. However, sample particle size had minimum effect on the equilibrium time. For a fixed SO2 concentration, the adsorption rate and adsorption kinetic parameters (activation energy and frequency factor) were obtained. A linearly proportional relationship between the Brunauer-Emmett-Teller surface area and the adsorptive capacity of the activated carbon from oil-palm shells was observed. An intraparticle Knudsen diffusion model based on a Freundlich isotherm was developed for predicting the amount of SO2 adsorbed and the SO2 concentration profile within the particle. Based on the estimated isotherm parameters and diffusion coefficients by experimental data fitting, this model could predict the amount adsorbed under different concentrations very well. However, this model was unsuitable for the activated carbon prepared from oil-palm shells by chemical activation because of the occurrence of chemisorption, which was related to the nature of the sample surface functional groups.     

Neural Network Modeling of Organics Removal by Activated Carbon Cloths

The adsorption of organic compounds onto an activated carbon cloth is studied in a dynamic reactor. An experimental design is carried out to investigate the influence of operating conditions (initial concentration C0, flow velocity U0, and bed thickness Z) and adsorbate's characteristics. A slow intraparticular diffusion is shown by flattened breakthrough curves, and adsorption capacities are high and range between 50 and 250 mg g?1. The transfer zone Z0, assessed by the Adams and Bohart equation, is low (3 mm). All experimental results are modeled by a neural network to take into account the specific diffusion of cloths. Parameters related to the adsorbate-adsorbent affinity in a batch reactor are consequently introduced in the input layer of the neural network (intraparticular coefficient Kw and Freundlich parameters Kf and l∕n), added to operating conditions whose influence was shown (C0, U0, and Z) and time t. The statistical quality of the neural network modeling is high (r2 = 0.956). Furthermore, the Garson connection weight method allows the relative influence of input neurons to be determined. This analysis confirms the influence of parameters relative to adsorbant-adsorbate affinity.     

Adsorption Isotherms for Methyl Tert-Butyl Ether and Other Fuel Oxygenates on Two Bituminous-Coal Activated Carbons

Methyl tert-butyl ether (MTBE) is frequently used as a gasoline additive to reduce carbon monoxide emissions from vehicles. Alternative fuel oxygenates are also used separately or in conjunction with MTBE including ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), diisopropyl ether (DIPE), tert-butyl alcohol (TBA), and ethanol (EtOH). Granular activated carbon (GAC) sorption is a proven technology for the removal of the ether oxygenates while the alcohols are not well adsorbed. In this research, Freundlich and Langmuir isotherms coefficients were developed based on linearized forms of the models for MTBE, ETBE, TAME, and DIPE (R2>0.97) on two common bituminous coal GACs:Calgon F400 and F600. No significant adsorption of either TBA or EtOH was observed on these carbons. The relative capacities on both Calgon F400 and F600 were DIPE>TAME>ETBE>MTBE>TBA, EtOH.     

Effect of Moisture on the Adsorption of Volatile Organic Compounds by Zeolite 13×

The adsorption of volatile methanol, acetone, and benzene onto zeolite 13× was studied in the presence of water vapor. Breakthrough curves for these volatile organic compounds (VOCs) were measured by using a gas-phase Fourier transformation infrared (FT-IR) spectrometer instead of a gas chromatograph (GC) because a gas-phase FT-IR spectrometer provides a more rapid response to the change of gas concentration than that of GC. To observe the influences of humidity (i.e., water vapor) on the performance of zeolite 13× during the VOC adsorption, the adsorption experiments were carried out at three different initial concentrations and two humidity conditions for each VOC. The results showed a significant influence of increased humidity on the breakthrough time, the shapes of breakthrough curves, and the uptake of VOCs. For the case of the benzene and water vapor coadsorption system, the presence of the moisture caused a greater decrease in the VOC uptake as well as the breakthrough time than for the other VOC–water coadsorption systems. A modified Freundlich-type isotherm was introduced in this study to describe the decrease in the uptake of VOCs in the presence of the moisture. This modified empirical equation provided a good fit to experimental results, with an average error of 8%.     

Modeling of Adsorption and Regeneration of Volatile Organic Compounds on Activated Carbon Fiber Cloth

A mathematical model is developed to predict continuous adsorption-regeneration cycling of volatile organic compounds (VOCs) on activated carbon fiber cloth (ACFC) at the indoor VOC concentration levels. The adsorption-regeneration model incorporates both the adsorption equilibrium and mass transfer fundamentals. It assumes local equilibrium between the gas-phase and the solid-phase, and axially dispersed-flow, film transfer, and intraparticle transport by surface and pore diffusion. Successful agreement between model simulations and experimental data was obtained and the kinetic properties of the adsorption/regeneration cycling on the ACFC were characterized. For the adsorption process, the film transfer is the dominant factor for mass transfer at low flow rates (45–184 L/min), and the intraparticle mass transfer rate controls over the gas-phase rate as the flow rates increase. The regeneration concentration profiles are most sensitive to the adsorption isotherms at the temperatures of interest, especially as desorption is initiated. The surface diffusivity also contributes to the shape of the regeneration profile: the tailing of desorption profile shifts up with the increase of surface diffusivity.