Isoconversional Kinetic Analysis of Isothermal Selective Ethanol Adsorption on Zeolite Type NaZSM‐5

The kinetic parameters of the selective isothermal adsorption of ethanol from an aqueous solution onto a hydrophobic zeolite type NaZSM‐5 were determined using a series of the so‐called standard methods (the initial rate, the saturation rate and the maximum rate methods). The kinetic model of ethanol adsorption was determined by the “model fitting” method. The dependence of the kinetic parameters on the degree of adsorption and the presence of a compensation effect were determined by the isoconversional method. The complex changes of the activation energy and pre‐exponential factor with the degree of adsorption were explained by the model of the activation energy distribution of elemental adsorption processes.     

Kinetics of Isothermal Ethanol Adsorption onto a Carbon Molecular Sieve under Conventional and Microwave Heating

The isothermal kinetics of ethanol adsorption from aqueous solution onto a zeolite type carbon molecular sieve (CMS‐3A) under conventional heating (CH) and microwave heating (MWH) was investigated. The adsorption kinetics is described by the model of a phase‐boundary controlled reaction for both heating modes. The activation energy (E_a) for the adsorption process under MWH is lower than under CH while the preexponential factor (lnA) is higher. Ethanol adsorption is a kinetically complex process whose complexity changes with the mode of heating. The established decrease in E_a and increase in lnA under MWH compared to CH is explained with the increase in the ground vibrational level of the – OH twisting vibrations in the ethanol molecule and with the decrease in its anharmonicity factor which is caused by the selective resonant transfer of energy from CMS‐3A to the OH oscillators.     

Determination of Kinetics and Equilibria for Adsorption of Water Vapor on Single Zeolite Particles by a Magnetic Suspension Balance

In order to obtain kinetic and equilibrium data for the adsorption of water vapor on zeolite for use in packed bed adsorber simulations, experimental investigations have been conducted on single zeolite particles with the help of a magnetic suspension balance. The objective was, first, to present such data in a form that is accurate enough and as simple as possible for easier application of the packed bed model and, second, to investigate and discuss the potential of the magnetic suspension balance technique, comparing with more conventional methods.     

A Simple Determination Method of Adsorption Kinetics from a Liquid Phase Fixed‐Bed Breakthrough Curve

The mass transfer zone (MTZ) method using the linear driving force (LDF) approximation is the most common and frequently used technique for the analysis of adsorption kinetics from a fixed‐bed breakthrough curve and for adsorptive process design. However, the adsorption kinetics obtained by the MTZ method includes approximations and estimation errors. This report describes a new analytical method for determining the intraparticle diffusivity (D_S) and the fluid‐film mass transfer coefficient (k_F) from an experimental breakthrough curve without using the LDF approximation and empirical correlations for estimating k_F . The proposed method has the advantage of less trial and error on the curve‐fitting process and helps better determine D_S and k_F . The estimation procedure of the Biot number that represents the ratio of D_S to k_F is the key of this method. The values of D_S and k_F for the adsorption of phenols onto activated carbon were determined from experimental breakthrough curves using the new analytical method. The results indicate that the method presented in this study yields reliable values.     

Kinetics,Isotherms and Equilibrium Study of Co(II) Adsorption from Single and Binary Aqueous Solutions by Acacia nilotica Leaf Carbon

The removal of cobalt ion from aqueous solution by Acacia nilotica leaf carbon (HAN), is described. Effect of pH, agitation time and initial concentration on adsorption capacities of HAN was investigat...     

Heterogeneity of Adsorption Sites and Adsorption Kinetics of n-Hexane on Metal-Organic Framework MIL-101(Cr)

abstract The heterogeneity of adsorption sites and adsorption kinetics of n-hexane on a chromium terephthalate-based metal-organic framework MIL-101(Cr) were studied by gravimetric method and temperatu...     

Kinetics and Equilibrium Modeling of Sterol Adsorption on Styrene‐Divinylbenzene Cation‐Exchange Resins

The potential of recovering phytosterols from fatty acid methyl esters by an adsorption‐desorption process is demonstrated using a strong‐acid ion‐exchange styrene‐divinylbenzene resin (SA‐R) as an adsorbent and ethanol as a desorbent. Since the operating cost of the overall process significantly depends on the efficiency of SA‐R in the adsorption step, the behavior of SA‐R in sterol adsorption is investigated in detail using a model solution of stigmasterol in n‐heptane. The results indicate that stigmasterol was associatively and exothermically adsorbed on SA‐R. Based on the experimental results, a simple pseudo‐second‐order model and a modified Langmuir isotherm with their parameters, which well predicted kinetics and adsorption capacity of SA‐R, are proposed.     

Equilibrium and Kinetics of the Extraction of Propionic Acid Using Tri‐n‐Octylphosphineoxide

Organophosphorous compounds have been widely used in inorganic analysis for the extraction and separation of inorganic acids or metal species. Since these compounds can form hydrogen bonds to proton donors, they can also be used for the extraction of acidic organic compounds. Therefore, the reactive extraction of propionic acid using tri‐n‐octylphosphine oxide (TOPO) in hexane was studied. Equilibrium and kinetics experiments were performed. The extraction of propionic acid using n‐heptane, light liquid paraffin, heavy liquid paraffin and hexane was studied and hexane was found to be most suitable diluent. The equilibrium complexation constant for the propionic acid‐TOPO complex was determined to be 0.702 m³/kmol. The extraction was found to be first order in propionic acid and first order in TOPO with the overall rate constant as 46.91 (m³/kmol)²/s.     

Thermal Behavior and Thermolysis Kinetics of the Explosive Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD)

Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD), a cyclic nitroamine, has been studied with regard to the kinetics and mechanism of thermal decomposition, using thermogravimetry (TG), IR spectroscopy, and pressure differential scanning calorimetry (PDSC). The IR spectra of TNAD have also been recorded, and the kinetics of thermolysis has been followed by non‐isothermal TG. The activation energy of the solid‐state process was determined by using the Flynn‐Wall‐Ozawa method. Compared with the activation energy obtained from the Ozawa method, the reaction mechanism of the exothermic process of TNAD was classified by the Coats‐Redfern method as a nucleation and nuclear growth (Avrami equation 1) chemical reaction (α=0.30–0.60) and a 2D diffusion (Valensi equation) chemical reaction (α=0.60–0.90). E_a and ln A were established to be 330.14 kJ mol⁻¹ and 29.93 (α=0.30–0.60) or 250.30 kJ mol⁻¹ and 21.62 (α=0.60–0.90).     

Adsorption of Organic Solutes on Membrane Filters during Aqueous Phase Filtration. I. Basic Rate and Equilibrium Studies Using Toluidine Blue

Abstract

Membrane filters are made from a wide variety of polymeric materials, in a wide range of pore sizes, and are used in large numbers (several hundred million per year) to filter particulates from many types of solutions. However, during filtration, organic solutes are adsorbed by these membranes, often quite extensively. Thus, the composition of the filtrate can be very different from that of the original solution. A systematic study has been initiated to quantify and explain the adsorption of organic solutes during membrane filtration as affected by membrane type (material, pore size, presence/absence of wetting agents), solute type, pH, ionic strength, and filtration flow rate. Our first studies have employed a dye (toluidine blue) as the dissolved organic solute, and 11 membrane filters made of mixed cellulose esters, polyvinylidene difluoride, polytetrafluoroethylene, and polycarbonate. The results of these studies, which are both equilibrium and kinetic in nature, are presented. These results indicate how adsorption effects may be minimized.     

Selective Catalytic Reduction of NO by Ammonia over Raney‐Ni Supported Cu‐ZSM–5 I. Catalyst Activity and Stability

Composite materials containing Raney Ni and Cu‐ZSM‐5 are highly active catalysts for the selective catalytic reduction (SCR) of NO by NH₃. Their catalytic properties were studied with particular attention to the influence of moisture and SO₂ in the feed, and to effects of catalyst shaping operations. Composite materials (16–20 wt‐% zeolite) were prepared by mixing the components, with different degree of segregation in the resulting pressed particles, or by growing ZSM‐5 crystallites on the surface of leached Raney Ni, which were then exchanged with Cu ions. Catalytic tests were performed with 1000 ppm NO, 1000 ppm NH₃, 2 % O₂ in He, at 3–6.5 · 10⁵ h^–1 (related to zeolite component). With physical mixtures, the catalytic behaviour strongly depended on the mixing strategy, particles containing both Ni and zeolite being inferior to mixed Ni‐only and zeolite‐only particles. The SCR activity was promoted by 2 % H₂O in the feed, SO₂ (200 ppm) was a moderate poison at low temperatures, but indifferent or slightly promoting at high temperatures. A catalyst prepared from ZSM‐5 grown on Raney Ni, which was ranked intermediate in dry feed, was promoted to excellent performance in H₂O and SO₂ containing feed at T > 700 K and was stable for 38 h at 845 K. The results suggest that SCR catalysts containing highly active zeolites should be produced avoiding shaping operations e.g. by use of zeolite crystallites grown on wire packings.     

Adsorption of chromium (III) ion from aqueous solution using rice hull ash

Rice hull was calcined to rice hull ash (RHA) at 500 °C under 20 mL air/s for 50 min. The RHA thus prepared has been found to be able to remove chromium (III) ion from aqueous solution, though not very efficient. The experiments indicated that the rate of removal of Cr³⁺ and the removal of Cr³⁺ at equilibrium was increased upon decreasing the RHA dosage. The removal could also be enhanced upon increasing the initial chromium concentration, or adsorption temperature. However, pH in the range of 2.5-5.4 or stroke speed higher than 120 stroke/min could not change the removal. The dependence of the RHA dosage and the initial chromium concentration on the removal have been found to be strong, while that of adsorption temperature is mild. An empirical equation correlating the relationship between the removal of Cr³⁺ and the adsorption time was determined.     

Selective Adsorption of Phenol and Nitrobenzene by β‐Cyclodextrin‐Intercalated Layered Double Hydroxide: Equilibrium and Kinetic Study

The composite of carboxymethyl‐modified β‐cyclodextrin‐intercalated ZnAl‐layered double hydroxide (CMCD‐LDH) was investigated for selective adsorption of phenol (Ph) and nitrobenzene (NB). The Freundlich model can be used to describe satisfactorily the adsorption isotherms of Ph and NB. The adsorption capacity of CMCD‐LDH for Ph and NB increases with the increase of temperature, indicating the endothermic nature of this sorption process. CMCD‐LDH exhibits preferential adsorption for Ph over NB at pH 6.5 due to the selective recognition of the interlayer CMCD cavity. Pseudo‐first‐order and pseudo‐second‐order kinetic models were applied to simulate the kinetics of the adsorption process. The calculated q_e values based on the pseudo‐second‐order model are much closer to the experimental data q_e,exp. As a result, the pseudo‐second‐order kinetic model is more reasonable to describe the adsorption process of Ph and NB onto the CMCD‐LDH composite. CMCD‐LDH can be potentially applied in selective adsorption and separation of wastewater pollutants.     

The Potential of Energy Saving by Gas‐Phase Adsorption Processes

In large chemical plants multicomponent fluid mixtures are separated in fractions or in pure components. Dealing with gaseous mixtures, separations can be carried out by cryogenic distillation, adsorption followed by temperature swing adsorption (TSA) or pressure swing adsorption (PSA) or membrane processes, as gas permeation or pervaporation. When separation is carried out with membrane processes, the purification efficiency is often not sufficient if ultrapure products are the objective of the process. In the case of cryogenic distillation and adsorption product purity is not a problem. The investment cost of membrane as well as cryogenic separation processes are high in comparison to adsorption separation plants but the increase of investment cost versus capacity is smaller for cryogenic plants compared to membrane and adsorption units [1]. Therefore, the installation of a cryogenic process may be advantageous in very large plants designed for ultrapure products whereas adsorption is often the domain for plants with medium capacity. The future of membrane separation depends on the development of more efficient membranes.     

四氢呋喃水溶液在3(A)分子筛上的吸附平衡与动力学研究

研究了四氢呋喃水溶液在间歇搅拌槽内3 A分子筛上的吸附平衡和动力学,用Langmuir方程拟合了吸附等温线,并用粒内表面扩散模型和Langmuir方程对吸附动力学曲线进行拟合.求取了表面扩散系数Ds,并研究了温度、初始浓度和粒径的变化对Ds的影响.Ds在25℃下C0为6.5%、dp为1 46～1.97mm时为7.83×10-7(cm2·s-1),并随着温度的升高及随着浓度的加大而增加,但不受粒径变化的影响.此外还求取了表面扩散指前因子Dso为1.85×10-5(cm2·s-1)和不同浓度下的活化能E.     

Calcined tetrabutylammonium kaolinite and montmorillonite and adsorption of Fe(II), Co(II) and Ni(II) from solution

Kaolinite and montmorillonite were modified with tetrabutylammonium (TBA) bromide, followed by calcination. The structural changes were monitored with XRD, FTIR, surface area and cation exchange capacity measurements. The modified clay minerals were used for adsorption of Fe(III), Co(II) and Ni(II) ions from aqueous solution under different conditions of pH, time and temperature. The uptake of the metal ions took place by a second order kinetics. The modified montmorillonite had a higher adsorption capacity than the corresponding kaolinite. The Langmuir monolayer capacities for the modified kaolinite and montmorillonite were Fe(III): 9.3 mg g^− 1 and 22.6 mg g^− 1; Co(II): 9.0 mg g^− 1 and 22.3 mg g^− 1; and Ni(II): 8.4 mg g^− 1 and 19.7 mg g^− 1. The modified kaolinite interacted with Co(II) in an endothermic manner, but all the other interactions were exothermic. The decrease of the Gibbs energy in all the cases indicated spontaneous adsorption.     

Kinetics and Thermodynamics of Lead (II) Adsorption on Vermiculite

Abstract

The kinetics and thermodynamics of Pb(II) adsorption on vermiculite have been studied by the sets of experiments at various conditions (temperature, initial lead concentration and adsorption time). The structures of the vermiculite before and after Pb(II) adsorption were measured using X‐ray diffraction (XRD), thermogravimetric analysis (TA), and X‐ray photoelectron spectroscopy (XPS). Adsorption of Pb(II) was strongly affected by pH. First order kinetics model best described the reaction rate, and the adsorption capacity calculated by the model was consistent with that actual measurement. Isotherms for the adsorption of Pb(II) on vermiculite were developed and the equilibrium data fitted well to the Langmuir and Freundlich models. Thermodynamic parameters such as enthalpy, entropy, and free energy were calculated using the Van't Hoff equations. The thermodynamics of Pb(II) on vermiculite indicates the spontaneous and endothermic nature of adsorption. Quantitative desorption of Pb(II) from vermiculite was found to be more than 40% which facilitates the sorption of metal by ion exchange