Adsorption characteristics of binary vapors among acetone, MEK, benzene, and toluene

Adsorption dynamics of single and binary vapor systems on the activated carbon bed were studied by using acetone, methylethyketone (MEK), benzene, and toluene. Relationships between the equilibrium adsorption capacity and the characteristics of vapors such as molecular weight, density, boiling point, vapor pressure, molecular diameter, and polarity index were also investigated. From breakthrough experiments, toluene had the strongest affinity with activated carbon in the single and binary vapor systems. The shape of the breakthrough curves of vapor with higher affinity in the binary system was similar to that of the single vapor. On the other hand, the vapor with lower affinity showed a roll-up phenomenon, but the level of roll-up became lower and wider with the increase in fraction in the binary system.     

Comparison of vapor adsorption characteristics of acetone and toluene based on polarity in activated carbon fixed-bed reactor

Adsorption characteristics according to polarity of acetone and toluene vapors on coconut based activated carbon were investigated by using a fixed bed reactor. Single vapor and binary vapor adsorption of acetone and toluene were conducted. In the single vapor system, the equilibrium adsorption capacity of toluene vapor on activated carbon was five times higher than that of acetone vapor because of polarity difference between adsorbent and adsorbate. The breakthrough curve of acetone vapor in the binary vapor was quite different from that of single acetone vapor. Acetone adsorbed in the binary vapor was substituted with toluene due to the affinity difference during adsorption process and its outlet concentration increased to 1.6 times than inlet concentration. The temperature changes in activated carbon bed during adsorption of acetone vapor and toluene vapor occurred in the time ranges of 10–30 min. The temperature change for acetone vapor adsorption was about 3 °C; however, that for toluene vapor adsorption was increased to 33 °C maximally.     

酸、碱改性活性炭对甲醇、甲苯吸附性能

分别采用硝酸和氢氧化钠对活性炭进行改性,利用比表面积及孔径分析仪（BET）、扫描电镜（SEM）、Boehm滴定法对活性炭物化性质进行表征,测试改性活性炭对甲醇、甲苯吸附性能。结果表明,经过酸、碱改性后的活性炭比表面积、总孔容、微孔孔容均有所增大。酸改性表面酸性基团增加,碱改性后活性炭酸性基团减少。酸改性后的活性炭对甲醇、甲苯吸附能力有所下降,后经碱改性的活性炭吸附能力均有不同程度的提高。单组分吸附实验时,甲醇穿透曲线斜率要大于甲苯,穿透时间早于甲苯。在多组分吸附过程中会出现甲苯取代甲醇的吸附现象,使得已经被吸附的甲醇发生脱附,此时甲醇的出口浓度大于进口浓度,形成峰值效应。     

活性炭吸附苯、甲苯废气的研究

研究了苯、甲苯组成的混合溶剂系统的吸附平衡关系及动力学性质。采用动态吸附法对纯组分、混合组分的吸附情况进行了测定。 根据Langmuir方程拟合出相应的平衡常数qe和K。通过对二组分吸附的穿透曲线进行分析,发现吸附能力强的甲苯能从活性炭中置换出吸附能力弱的苯。整个吸附过程分为三个阶段进行。分别利用E-L方程和IAST理论进行理论预测分析,并与实验结果进行了比较。结果表明,虽然E-L方程对吸附总量的预测与实验结果较为吻合,但对各个组分吸附量的预测却经常产生正负偏差;而IAST引入竞争模型,较好地消除了这种正负偏差,平均误差不超过10%,与实验结果更为吻合。     

Breakthrough data analysis of adsorption of volatile organic compounds on granular activated carbon

Volatile Organic Compounds (VOCs) such as methanol, ethanol, methyl ethyl keton, benzene, n-propanol, toluene, and o-xylene were adsorbed in a laboratory-scale packed-bed adsorber using granular activated carbon (GAC) at 101.3 kPa. The adsorber was operated batchwise to obtain the breakthrough curves of VOCs under the adsorption conditions such as adsorption temperatures (298–323 K), flow rates of nitrogen (60×10⁻⁶-150×10⁻⁶m³/min), GAC amount of 0.002 kg, and concentration of VOCs (3,000–6,000 ppmv). The adsorption kinetics was obtained by fitting the experimental breakthrough data to the deactivation model, combining the adsorption of VOCs and the deactivation of GAC. The adsorption isotherm, and adsorbed amount and adsorption heat of VOCs were obtained using the breakthrough curve: the former for comparison with the conventional isotherm models, the latter for correlation with the physical properties of VOCs.     

Competitive adsorption of a benzene-toluene mixture on activated carbons at low concentration

Previous studies of the adsorption of benzene and toluene at low concentration showed that both porosity and surface chemistry of the activated carbon play an important role. This paper analyses the adsorption behaviour of a mixture of VOCs (benzene-toluene) on AC, due to the lack of information regarding the adsorption of mixtures. Thus, the performance of chemically activated carbons, physically activated carbon with steam and commercial samples is studied. This study shows that chemically activated carbons have better performance than the other samples, showing much higher adsorption capacities, breakthrough times and separation times. Porosity is a key factor and those activated carbons with higher volumes of micropores exhibit higher adsorption capacities and breakthrough times. This work also analyses the state of the adsorbed phase resulting from the mixture adsorption and comparison of the composition of the adsorbed hydrocarbons with that predicted by the ideal adsorption solution theory (IAST), shows good agreement.     

Evaluating isotherm models for the prediction of flue gas adsorption equilibrium and dynamics

We evaluated isotherm models for the precise prediction of adsorption equilibrium and breakthrough dynamics. Adsorption experiments were performed using pure N₂, CO₂ and their binary mixture with an activated carbon (AC) material as an adsorbent. Both BET and breakthrough measurements were conducted at various conditions of temperature and pressure. The corresponding uptake amount of pure component adsorption was experimentally determined, and parameters of the four different isotherm models, Langmuir, Langmuir-Freundlich, Sips, and Toth, were calculated from the experimental data. The predictive capability of each isotherm model was also evaluated with the binary experimental results of binary N₂/CO₂ mixtures, by means of sum of square errors (SSE). As a result, the Toth model was the most precise isotherm model in describing CO₂ adsorption equilibrium on the AC. Based on the breakthrough experimental result from the binary mixture adsorption, non-isothermal modeling for the adsorption bed was performed. The breakthrough results with all of the isotherm models were examined by rigorous dynamic simulations, and the Toth model was also the most accurate model for describing the dynamics.     

Adsorption of multicomponent volatile organic compounds on semi-coke

Experimental and theoretical studies were made on the adsorption of toluene, ethyl acetate, benzene and their binary and ternary mixtures by semi-coke in an isothermal condition of 293 K. Breakthrough curves of these volatile organic compounds (VOCs) were measured by a gas chromatograph. The results showed that the adsorptive orders of these three VOCs were: toluene > ethyl acetate > benzene. The phenomenon of “roll-up” was observed in the breakthrough curves and under this condition, the more strongly adsorbed species displace the weaker ones. H₂O₂ was used to activate the semi-coke and the activation enhanced the adsorption capacity of semi-coke to all the three VOCs, especially to toluene. The extended Langmuir equation agrees well with the experimental isotherm data for binary and ternary mixtures and the error is below 5%.     

Column Dynamics for Multicomponent Adsorption–Constant Pattern Formation

Abstract

A mathematical model for predicting adsorption breakthrough time for an N-component mixture from a carrier gas is described. Formation of constant pattern fronts is assumed, and the model accounts for roll-up of each species. Mixture equilibrium isotherms for all the species and length of the mass transfer zone, only for the least strongly adsorbed component, are needed for prediction.     

Study of Adsorption Equilibrium and Dynamics of Benzene,Toluene, and Xylene on Zeolite NaY

The equilibrium and dynamics of low concentrations of benzene, toluene, and xylene in heptane adsorbed by zeolite NaY at 30, 40, and 50 °C were studied. The Langmuir equation was suggested to simulate the isotherms. Based on isotherms and material balances, multi‐component competitive adsorption isotherms can be successfully predicted by mono‐component adsorption isotherm parameters. A series of column adsorption experiments were conducted to study the adsorption dynamics. The mass transfer equations were solved by numerical analysis and used to describe the breakthrough curves, and the mass transfer coefficients in the adsorption column were obtained as well.     

An experimental study of adsorption of polymers on activated carbon: Butadiene—styrene polymers and poly(methyl methacrylate)

An experimental study of the extents and rates of adsorption of several polymers from various solvents onto activated carbon has been carried out. The polymers studied included polystyrene, polybutadiene, butadiene–styrene copolymers and poly(methyl methacrylate). The solvents included toluene, cumene, decalin, 2-pentanone, and methyl ethyl ketone (MEK). Polystyrene is adsorbed from the different solvents in the order MEK, 2-pentanone, cumene, toluene, decalin. The adsorption from toluene, decalin, and cumene is in the order polystyrene, polybutadiene butadiene—styrene copolymer. The fact that the copolymer is adsorbed less than either homopolymer is striking. The variation of molecular weight distribution with extent of adsorption has been studied. It was found that low molecular weight polymer was preferentially adsorbed in the early stages of the experiment, but high molecular weight polymer was adsorbed at longer times. The apparent adsorption rate constants have been evaluated for the various systems and resolved into external mass transfer, internal (intraparticle) mass transfer, and adsorption rate constants. The experimental data have been applied to the prediction of the elution of the polymers from chromatographic columns packed with activated carbon.     

Propane/Propylene Separation by Simulated Moving Bed II. Measurement and Prediction of Binary Adsorption Equilibria of Propane,Propylene, Isobutane,and 1-Butene on 13X Zeolite

Abstract

The design of a simulated moving bed (SMB) process relies on valid thermodynamic predictions of multicomponent adsorption built up from accurate binary adsorption equilibrium data. Experimental adsorption equilibria of binary mixtures constituted by propane, propylene, isobutane and 1-butene on 13X zeolite were determined using breakthrough experiments at 373 K and 150 kPa. In addition, these binary adsorption experiments allow to confirm the choice of isobutane as an interesting desorbent for the separation of propane-propylene by SMB, since it has an intermediate selectivity between the two species to separate. Various prediction models are available in the literature but only a few of them have both physical and thermodynamical consistency. The ideal adsorbed solution theory (IAST), the thermodynamically consistent extended Toth model (TCET), and the physically-consistent extended Toth isotherm (PCET) were used to predict binary adsorption equilibria from pure component adsorption isotherms parameters. The PCET model was found suitable for representing the adsorption equilibrium of the different hydrocarbon mixtures with a reasonably good accuracy.     

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Abstract

Pure component adsorption equilibrium of CH₄ and CO₂ on activated carbon have been studied at three different temperatures, 298, 323, and 348?K within a pressure range of 10–2000?kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO₂/CH₄ (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800?kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO₂/CH₄, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800?kPa, extended Sips model underestimated significantly the CO₂ adsorbed amount and overestimated the CH₄ adsorbed amount.     

Dual mode roll-up effect in multicomponent non-isothermal adsorption processes with multilayered bed packing

Roll-up is a common phenomenon occurring in multicomponent adsorption processes when the concentrations of some components at the outlet of the adsorber exceed their inlet levels. Previous investigations attributed the roll-up effect typically to the displacement of one component by another because of the difference in adsorption affinities or diffusivities. In this work, we report the existence of a peculiar type of roll-up caused by thermal effect solely in our multicomponent non-isothermal breakthrough experiments where the light component CO₂ was swept off by a pure thermal wave developed from water vapour adsorption. Even though, the formation of a pure thermal wave is well known, it does not lead to the above roll-up without a multilayered bed packing. To our surprise, a secondary roll-up of CO₂ caused by H₂O displacement was also observed, since the front of the water concentration wave ran behind its thermal wave in our case. The parameters affecting the formation of this special dual mode roll-up were investigated and summarised. This work will give guidance to the design of multilayered cyclic adsorption processes, e.g. determination of layering ratios and duration of the feed step.     

Modeling of adsorption isotherm of a binary mixture with real adsorbed solution theory and nonrandom two‐liquid model

Gas‐phase adsorption equilibria of diluted mixtures of methyl‐ethyl‐ketone and isopropylanol on activated carbon were investigated. Experimental isotherms were determined by a constant volume method. Single‐component adsorption isotherms were fitted by the frequently used Toth model with good accuracy. Then adsorption isotherms were determined for different binary mixtures (with different initial ratio of the two components). Binary mixtures adsorption isotherms were calculated using the adsorbed solution theory. Ideal adsorbed solution theory (IAST) could not represent experimental data, but it was observed that increasing amount of MEK led to higher nonideality of the mixture. Then UNIversal QUAsi Chemical (UNIQUAC) and nonrandom two‐liquids (NRTL) models were considered to describe activity coefficients of the adsorbed phase. The fitted parameters of UNIQUAC model depend on the ratio of the two components, whereas the NRTL model is able to fit all experiments with the same parameters, whatever the initial ratio may be. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Multicomponent mass transfer in fixed-bed carbon adsorption columns

The technique based upon the constant pattern model was extended to evaluate mass transfer coefficients for multicomponent (binary) adsorption by carbons. The mass transfer coefficient of the lesser adsorbed component was essentially the same for both single component and binary systems. The mass transfer coefficient of the more strongly adsorbed component was significantly lower in the binary case, indicating interference between components. The mass transfer coefficients obtained were used in a computer simulation of fixed bed adsorption columns, and experimental data were successfully predicted.     

Silylated rice husk MCM-41 and its binary adsorption of water–toluene mixture

Mesoporous material, MCM-41, synthesized from rice husk (RH-MCM-41) was modified by loading silylating agent (either trimethylchlorosilane (TMCS), dimethyl-dichlorosilane (DMCS) or phenyl-trichlorosilane (PTCS)) with different concentrations (1–9 wt.%), and aging times, varied between 1, 6, 9, and 24 h. Properties of the silylated MCM-41 samples were characterized by XRD, FTIR, N₂ adsorption, and the binary adsorption of a water–toluene mixture for the breakthrough curves; afterwards, the hydrophobicity indices were determined. Silylating agent caused RH-MCM-41 to possess smaller average pore size and surface area, compared to parent RH-MCM-41. Using a silylating condition of 1 wt.% TMCS for 1 h, modified RH-MCM-41 showed satisfactory enhancement its of hydrophobicity without any significant surface modification. Due to the substitution of silane group onto RH-MCM-41, the hydrophobicity index was increased.     

湿度对油烟中易挥发有机化合物吸附的影响

主要研究了甲醛、乙醛和苯在有机硅烷KH560和1706改性活性炭(AC)表面的脱附活化能,并通过透过曲线实验测定了不同湿度对三者在改性活性炭上吸附的影响,最后用光电子能谱(XPS)分析材料表面的亲水基团和憎水基团比例的变化。结果表明,采用有机硅烷改性活性炭可提高材料的憎水性,在较高湿度下(RH60%),三者在未改性活性炭固定床穿透时间减少得最多,1706/AC固定床次之,KH560/AC固定床最小;程序升温脱附(TPD)实验表明,用有机硅烷改性活性炭可以削弱水和活性炭表面的结合力,增强与甲醛、乙醛和苯的结合力。通过XPS分析,与未改性活性炭相比,经有机硅烷改性的活性炭,其憎水性得到提高。     

Breakthrough Data Analysis of Adsorption of Toluene Vapor in a Fixed‐Bed of Granular Activated Carbon

Abstract

Toluene vapor was adsorbed in a laboratory‐scale packed‐bed adsorber using granular activated carbon (GAC) at constant pressure (101.3 kPa). The adsorber was operated batchwise with the charge of GAC in the range of 2–4 g to obtain the breakthrough curves of toluene vapor. Experiments were carried out at different adsorption temperatures (25–50°C), sparger temperatures (20–30°C), and the flow rates of nitrogen (80–150 cm³/min) to investigate the effects of these experimental variables on the breakthrough curves. The deactivation model was tested for these curves by combining the adsorption of toluene vapor and the deactivation of adsorbent particles. The observed values of the adsorption rate constant and the deactivation rate constant were evaluated through analysis of the experimental breakthrough data using a nonlinear least squares technique. The experimental breakthrough data were fitted very well to the deactivation model than the adsorption isotherm models in the literature.     

New phenomenon in competitive hydrogenation of binary mixtures of activated ketones over unmodified and cinchonidine-modified Pt/alumina catalyst

Competitive hydrogenations of eight binary mixtures of ethyl pyruvate (EP), methyl benzoylformate (MBF), ketopantolactone (KPL), pyruvic aldehyde dimethyl acetal (PA) and trifluoroacetophenone (TFAP) on platinum/alumina catalysts unmodified (racemic hydrogenation) and modified by cinchonidine (chiral hydrogenation) were studied under the experimental conditions of the Orito reaction. Reaction rates of chiral and racemic hydrogenations were determined and relative adsorption coefficients were calculated. In the competitive chiral hydrogenation of EP + MBF, EP + TFAP and KPL + MBF binary mixtures a new phenomenon was observed: namely the EP and KPL are hydrogenated faster than MBF and TFAP, whereas in racemic one the MBF and TFAP are hydrogenated faster than EP or KPL. Effects of the activated ketones structure on their reactivity and the stability of the surface complexes are discussed. It was found that differences in rate enhancement are caused by the differences both in the adsorptivity and in the reactivity of adsorbed substrates and adsorbed intermediate complexes.