Adsorption of Acetaldehyde,Propionaldehyde, and Butyraldehyde on Silica Gel

Abstract

Adsorption isotherms of acetaldehyde, propionaldehyde, and butyraldehyde on Davison silica gel were determined gravimetrically at three temperatures. The isoteric heat of adsorption initially increased at low loading and then decreased monotonically with an increase in loading. The equilibrium adsorption data were successfully correlated by Polanyi's potential theory. The equilibrium data were also correlated with the Langmuir, BET, Freundlich, and the Hines et al. models. The Freundlich and the Hines et al. models provided the best fit to the data, while the BET equation was found to be applicable only for a relative pressure range of 0.05 to 0.2. The monolayer surface coverages of silica gel by all of the aldehydes estimated by the Langmuir equation were found to be consistently higher than those calculated from the BET equation, except for acetaldehyde at 306.5 K.     

Adsorption equilibria of chloropentafluoroethane on activated carbon powder

An equilibrium study was conducted on the adsorption of chloropentafluoroethane (CFC-115, CF₃CF₂Cl) on activated carbon powder between 298.15 K and 373.15 K. Experimental data were fitted with several isotherm equations. Among the twoparameter equations, the BET equation showed the best results over the entire relative pressure range studied. When the pressure range was divided into two regions, a better result was obtained by applying the Langmuir equation in the lower pressure range and the BET equation in the higher relative pressure region. Among the threeparameter equations, the Langmuir-Freundlich equation gave better results than the RedrichPeterson equation. The isosteric heat of adsorption of CFC-115 on the activated carbon powder was estimated. It was found to have the same order of magnitude with the heat of condensation, which indicates that the adsorption was primarily due to physical forces.     

AN EVALUATION OF ISOTHERMS IN THE DESCRIPTION OF COMPETITIVE ADSORPTION EQUILIBRIA

Since adsorption isotherm equations are widely used in the industry to model adsorption on substances like activated carbon, an investigation was done to determine the applicability of three of these equations, viz, the multi-component Freundlich, multi-component Langmuir and the isotherm equation proposed by Fritz and Schluender. Based on statistical thermodynamic principles a discrete adsorption model was recently proposed. This model was used to create sets of binary adsorption data with some non-ideal characteristics. These data sets were used to evaluate the isotherm equations

It was found that the Langmuir isotherm gave the best fits, except where the visible adsorption energy changes with the surface loading or where selective adsorption occurs. Under these conditions, the Freundlich equation or that proposed by Fritz and Schluender should be used. It is recommended that these equations should be used to model low coverage-low concentration regions, while the high coverage-high concentration regions should be modelled using the Langmuir isotherm if possible

Some recommendations are made in connection with the procedure to estimate parameters for these isotherm equations.     

Determination of Specific Surface Area of Granular Activated Carbon by Aqueous Phase Adsorption of Phenol and from Pore Size Distribution Measurements

Abstract

Adsorption of phenol from the aqueous phase onto six grades of granular activated carbon (GAC) was studied at 35°C. The adsorption equilibrium data for all the GAC-phenol systems were analyzed by Langmuir, BET, and John's adsorption isotherm equations to estimate the specific surface area of each adsorbent. Pore size distribution measurements were also carried out for all the GAC samples. The surface area values obtained by both Langmuir and BET methods are in close agreement in the micromolar concentration range such as those present in waste-water. Pore size distribution measurement shows that for all the GAC samples used in this investigation, more than 97% of the surface area is located in the micropores below 35 Å in radius.     

分形吸附模型

在对ＢＥＴ公式、Ｈｅｎｒｙ吸附定律和ＦＨＨ吸附等温式的分形形式进行综合评述的基础上,根据分形ＢＥＴ公式的特殊情况得到了极低压力下的分形Ｌａｎｇｍｕｉｒ公式。由Ｌａｎｇｍｕｉｒ方程的推导过程提出了经验性的分形Ｌａｎｇｍｕｉｒ方程,并利用文献数据进行了验证,针对分形Ｆｒｅｕｎｄｌｉｃｈ公式的不足,得出了分形Ｆｒｅｕｎｄｉｃｈ经验方程,该方程适合于描述煤对碘及Ｃｒ＾６＋的吸附过程。     

Retention and Release of Lead by a Very Fine Sandy Loam. I. Isotherm Modeling

Abstract

The retention of lead by a very fine sandy loam was investigated. Aqueous lead concentrations between 10 and 1000 mg/L and soil concentrations ranging from 10 to 167 g/L were used. Lead retention by the soil was a strong function of pH. The width of the pH—adsorption edge decreased with increasing lead concentration. Experimental results were modeled using the Langmuir, Freundlich, and BET isotherms. Only the Langmuir and Freundlich isotherms successfully represented the experimental results. The role of surface precipitation was assumed to be small because of the failure of the BET isotherm to adequately predict metal retention. The Freundlich isotherm provided the best fit because a maximum surface concentration was usually not observed. Langmuir and Freundlich isotherms parameters varied in a way that suggested that the average binding energy and the distribution of bond strengths increased with increasing pH. The isotherm expressions determined in this study can be used as source-sink terms in the generalized mass transport model.     

Effect of Complexation on the Adsorption of Cadmium by Activated Carbon

Abstract

The adsorption of Cd²⁺ in the absence and presence of two chelating agents was examined as a function of pH. Fits of the data to the Freundlich and Langmuir equations were compared as were results with Zn and Pb using four different activated carbons. In general, adsorption increased with increasing pH and was not extensive, particularly for Cd. At low cadmium to carbon ratios, EDTA appeared to enhance adsorption. With more realistic loadings, when competition for surface sites is greatest, the presence of EDTA is shown to be detrimental to the process. 1,10-Phenanthroline, the second chelating agent studied, was more effective for promoting the removal of Cd. The uncomplexed Cd and Cd-EDTA systems were best described by the simple Langmuir adsorption isotherm. The adsorption of 1,10-phenanthroline and its Cd complex were modeled using a modified form of the Langmuir equation.     

甲烷、乙烷、丙烷和丁烷在中孔活性炭上的吸附平衡

以活性炭AC1为吸附剂,在体积法实验装置上分别测定了其对甲烷、乙烷、丙烷和丁烷4种气体的吸附等温线,吸附温度分别为283、293、303和313 K。利用77 K吸附氮气数据表征AC1,得到其比表面积为956 m²·g^-1,孔体积为1.36 mL·g^-1,孔径分布在1~5 nm,中孔的比例达到了61%。AC1对4种气体的吸附等温线均为I型等温线,分别采用Langmuir方程和Langmuir-Freundlich方程(简称L-F方程)对吸附平衡数据进行拟合,结果表明,L-F方程具有更好的拟合效果,为后序的多组分吸附平衡研究提供了基础数据。AC1对乙烷/丙烷的吸附平衡选择性系数在1.7~2.5,吸附选择性随吸附压力的增大而减小,吸附温度对吸附选择性无明显影响。     

Adsorption characteristics of carbonized bark for phenol and pentachlorophenol

The potential of using carbonized slash pine bark as a substitute for activated carbon was examined in this study. The bark was carbonized by slow heating in nitrogen for 6·5 h to 672°C. The BET-N₂ surface area, average micropore and mesopore diameter, and micropore volume were 332 m² g⁻¹ 21·7 Å, and 0·125 cm³ g⁻¹, respectively. The adsorption capacities for phenol and pentachlorophenol (PCP) at pH 2 and pH 8 were evaluated. The Langmuir equation provided a slightly better fit than the Freundlich equation to two sets of phenol data. The calculated Freundlich constants, K = 0·41–0·58 mmol/g/(mmol dm⁻³)^1/n and 1/n = 0·30–0·41, were lower and higher, respectively, than literature values for activated carbons. The adsorption capacity of the carbonized bark was much lower for PCP than for phenol. The protonated and anionic PCP isotherms were Type II or III, respectively, in the Brunauer classification. The BET equation provided the best fit to protonated PCP isotherm data. The anionic PCP data were fitted to both the BET model and an equation used in the literature to represent phosphate adsorption on activated carbons. Non-linear regression of the data for both phenol and PCP adsorption with the Freundlich, Langmuir and BET equations generally gave more accurate param-eters, compared with the use of linearized equations to obtain the parameters. © 1998 SCI.     

铁改性杭锦土对磷的吸附及对沉积物磷释放的控制

以天然粘土矿物杭锦土(HJ)为原料,采用浸渍法制备表面负载铁氧化物的铁改性杭锦土(FHJ)吸附剂.采用BET、SEM、XRD等技术对其进行表征,并考察了铁负载比例、pH、共存离子对FHJ除磷的影响.结果表明,浸渍法成功将铁氧化物负载在杭锦土表面;溶液pH越低越有利于FHJ对磷酸盐的吸附;除磷性能受CO32-、SiO32...     

An isotherm model for adsorption of gases and vapours on heterogeneous adsorbents

The adsorption of gases and vapours on heterogeneous adsorbents is generally described by assuming that the surface of an adsorbent consists of several energetic sites or patches. The adsorption on a site or a patch can be described by a local isotherm, such as the Langmuir, BET or Jovanovich equations, whereas the heterogeneity or the energy distribution on the adsorbent is expressed by a probability density function such as normal distribution, gamma distribution and exponential distribution. The overall adsorption isotherm is then derived by summing the contributions of all sites. Although the parameters of the energy distribution are generally related to the heat of adsorption, the overall adsorption isotherm is often insensitive to the parameters of the probability density functions, which are assumed on statistical grounds. In the present work, a new isotherm model is derived for the adsorption of gases and vapours on heterogeneous adsorbents, which combines the Jovanovich local isotherm and an exponential-six type energy potential function. The new model can correlate both Type I and Type II isotherms and has been tested successfully with the literature data for the adsorption of various gases and vapours on several different heterogeneous adsorbents. The absolute average error for most of the systems is below 3%. A comparison of the present model with other models for heterogeneous surfaces is presented.     

From Langmuir isotherm to Brunauer–Emmett–Teller isotherm

Developed for multilayer adsorption, the Brunauer–Emmett–Teller ( BET) isotherm considers the adsorption of the first layer as an equilibrium chemical reaction between adsorbate molecules and adsorption sites and the adsorption of the second and subsequent layers as a condensation–evaporation process. Following the recent development of an activity-based formulation for the Langmuir isotherm for monolayer adsorption, we present an activity-based formulation for the BET isotherm in which species concentrations are replaced with species activities. Capturing the adsorbent surface heterogeneity for the adsorption of the first layer, the resulting thermodynamic BET isotherm is shown to accurately represent pure component adsorption isotherms over the relative pressure range of zero to unity or prior to the onset of capillary condensation. The thermodynamic BET isotherm should facilitate accurate estimation of monolayer adsorption capacity and the corresponding adsorbent surface area.     

Humic acid-immobilized polymer/bentonite composite as an adsorbent for the removal of copper(II) ions from aqueous solutions and electroplating industry wastewater

In this study, humic acid (HA) was immobilized onto amine-modified polyacrylamide/bentonite composite (Am-PAA-B) which was prepared by direct intercalation polymerization technique and the product (HA-Am-PAA-B) was used as an adsorbent for the removal of copper(II) ions from aqueous solutions. The surface characteristics of bentonite, Am-PAA-B and HA-Am-PAA-B were investigated. The adsorbent behaved like a cation exchanger and more than 99.0% Cu(II) ions’ removal was observed at the pH range 5.0–6.0. Kinetic and isotherm experiments showed that amount of Cu(II) ions adsorbed increases with increase of the initial concentration and temperature. The adsorption kinetic data were interpreted by pseudo-first-order and pseudo-second-order rate equations. The suitability of Langmuir, Freundlich and Dubinin–Radushkevich (D-R) adsorption models to the equilibrium data was investigated. The Langmuir isotherm was found to provide the best theoretical correlation of the experimental equilibrium data. The thermodynamic and kinetic activation parameters were derived to predict the nature of adsorption process and discussed in detail. The isosteric heat of adsorption was constant even after increase in surface loading. The removal efficiency of HA-Am-PAA-B was tested using electroplating industry wastewater. The desorption of adsorbed Cu(II) ions was achieved by 0.1 M HCl and four adsorption/desorption cycles were performed without significant decrease in the adsorption capacity.     

紫竹竹叶提取物作为盐酸中锌的缓蚀剂的研究

用失重法研究了紫竹(Phyllostachys nigra Munro)竹叶提取物PMLE在0.01~0.05 mol/LHCl溶液中对锌的缓蚀作用。结果表明:PMLE对锌在0.01 mol/LHCl溶液中具有良好的缓蚀作用,且在锌表面的吸附符合Langmuir吸附等温式。缓蚀率随缓蚀剂浓度的增加而增大,但随温度和盐酸浓度的增加而减小。通过Van't Hoff方程和Mathur经验动力学公式分别求出了吸附焓ΔHads和腐蚀动力学参数(速率常数k,动力学常数B),并据此参数讨论了PMLE的缓蚀行为。     

Moisture adsorption isotherms and thermodynamics properties of sucuk (Turkish dry-fermented sausage)

Moisture adsorption isotherms of sucuk were determined using the isopiestic method at 10 °C, 20 °C and 30 °C and within the range of 0.2-0.9 water activity. The isotherms of sucuk exhibited Type II behavior according to BET classification. The adsorption data were analyzed using mathematical equations of Halsey, Caurie, Peleg, Smith, Oswin, Henderson, Modified-BET, GAB, Ferro-Fontan and Harkins-Jura. The best fit of experimental data was obtained with Peleg equation in the range of temperatures and water activities investigated. Thermodynamic properties such as differential enthalpy and entropy, enthalpy-entropy compensation, spreading pressure, net integral enthalpy and entropy were determined from moisture adsorption isotherm data of sucuk. The net isosteric heat of sorption and differential entropy decreased with increasing moisture contents in an exponential function. The spreading pressure increased with increasing water activity, and decreased with increasing temperature. The net integral enthalpy decreased with increased moisture content. The integral entropy increased with moisture content, but it was negative in value. The enthalpy-entropy compensation theory was applied to water adsorption of sucuk.     

Separation of Ni (II) Ions From Aqueous Solution onto Maghemite Nanoparticle (γ-Fe3O4) Enriched with Clay

Ni(II) ions removal using maghemite nanoparticle on bentonite-clay was investigated. Adsorbent was synthesized using the sol-gel method characterized by the surface area Brunauer, Emmett, and Teller (BET), scanning electron microscopy and energy dispersive X-Ray spectrometer, transmission electron microscopy, FTIR spectroscopy, and zero-point-charge. Experiments were done as a function of solute concentration and temperature. Various kinetic models were evaluated and effective diffusion coefficient, activation energy, and entropy of activation were determined. The adsorption isotherm data were fitted to the Langmuir and Freundlich equations, and the Langmuir adsorption capacity was found to be 114.9 mg/g. These results showed that the adsorbent is an attractive option for Ni(II) removal.     

Experimental and theoretical study of methane adsorption on granular activated carbons

The experimental and theoretical study of methane adsorption on granular activated carbons is presented. The adsorption data are modeled by various isotherm equations. Toth equation is found to have the best fit. The isosteric heat decreases with loading and increases weakly with temperature, which is an indication of heterogeneity of the methane and granular activated carbon system. Using optimized parameters from Toth equation, a novel procedure is developed to calculate the integral heat of adsorption, which is the total amount of isosteric heat of adsorption at a given temperature and pressure during the adsorption process. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Comparative study of methylene blue dye adsorption onto activated carbon,graphene oxide,and carbon nanotubes

Three different carbonaceous materials, activated carbon, graphene oxide, and multi-walled carbon nanotubes, were modified by nitric acid and used as adsorbents for the removal of methylene blue dye from aqueous solution. The adsorbents were characterized by N₂ adsorption/desorption isotherms, infrared spectroscopy, particle size, and zeta potential measurements. Batch adsorption experiments were carried out to study the effect of solution pH and contact time on dye adsorption properties. The kinetic studies showed that the adsorption data followed a pseudo second-order kinetic model. The isotherm analysis indicated that the adsorption data can be represented by Langmuir isotherm model. The remarkably strong adsorption capacity normalized by the BET surface area of graphene oxide and carbon nanotubes can be attributed to π–π electron donor acceptor interaction and electrostatic attraction.     

Generalization of thermodynamic Langmuir isotherm for mixed-gas adsorption equilibria

This work presents a comprehensive thermodynamic model for both pure component isotherms and mixed-gas adsorption equilibria. A generalization of thermodynamic Langmuir isotherm, the proposed model assumes competitive adsorption of multiple adsorbates on adsorbent surface for mixed-gas adsorption equilibria, and it applies an area-based adsorption nonrandom two-liquid activity coefficient model in the activity coefficient calculations for the adsorbate phase. The resulting generalized Langmuir isotherm properly captures both surface loading dependence and adsorbate phase composition dependence for mixed-gas adsorption equilibria. The model is validated with accurate representations of gas adsorption equilibrium data for varieties of unary, binary, and ternary gas systems. The model results are further compared with those calculated from extended Langmuir isotherm and Ideal Adsorbed Solution Theory.     

新型口服活性炭微球对内源性分子肌酐的吸附性能研究

对活性炭微球吸附肌酐的行为进行研究,以探讨其治疗尿毒症等疾病的可能性。在不同吸附时间、不同pH环境以及不同浓度等条件下,测定自制活性炭微球对肌酐的吸附量,根据Langmuir和Freundlich等温线方程对吸附等温线数据进行处理,检验实验数据与方程的吻合度,确定方程参数。吸附在三小时内达到平衡,pH在2～10范围有减少趋势但无有意义相差,平衡吸附量随肌酐浓度的升高而增加,等温线的数据与Langmuir方程吻合。活性炭微球对肌酐的吸附属L型吸附,说明该吸附为微孔填充机制,在稀溶液中属单分子层吸附。另外,此样品如用于体内,胃肠道的酸碱性对其吸附性能影响很小。