Screening of Porous Materials by Thermal Response Measurements

Adsorption thermal response screening by optical adsorption calorimetry was recently demonstrated to be a versatile tool for rapid surface area and adsorption capacity testing of porous materials. Beyond the high throughput approach, further insight in possibilities and application examples for the method will be presented. Especially a rapid classification of porous materials regarding their pore properties and the possibility to evaluate adsorption kinetics by using thermal response measurements will be discussed.     

Adsorption of organic molecules from aqueous solutions on carbon materials

Adsorption of organic molecules from dilute aqueous solutions on carbon materials is a complex interplay between non-electrostatic and electrostatic interactions. Non-electrostatic interactions are essentially due to dispersion and hydrophobic interactions, whereas the electrostatic or coulombic interactions appear with electrolytes when they are ionized at the experimental conditions used. Both interactions depend on the characteristics of the adsorbent and the adsorptive and the solution chemistry. Among them the carbon surface chemistry has a great influence on both electrostatic and non-electrostatic interactions, and can be considered one of the main factors in the adsorption mechanism from dilute aqueous solutions. In this paper the current knowledge about the fundamental factors that control the adsorption process from aqueous phase will be presented.     

脱硫吸附剂与吸附脱硫技术

综述了国内外原料气和燃料油吸附脱硫技术在吸附脱硫材料和吸附脱硫工艺方面的研究与开发进展。介绍了分子筛类、金属氧化物类、活性炭类等脱硫吸附剂。分别评述了物理吸附、活化吸附、选择性吸附等燃料油吸附脱硫技术的机理和工艺。     

基于模式搜索加速遗传算法的逆向法确定竞争吸附等温线

基于局部优化算法的逆向法,被广泛应用于确定吸竞争附等温线模型,但其存在的主要问题是:不能保证结果的广义收敛性和低下的计算效率.本文提出了一种基于模式搜索加速遗传算法的反晨向法.并将该算法成功应用于柠檬酸/葡萄糖的竞争吸附等温线的确定,在保证了计算结果的广义收敛性的前提下,算法执行效率相对传统遗传算法提高了一倍以上.     

Adsorption of zinc onto anionic ion-exchange resin from cyanide barren solution☆

Removal of zinc from cyanide barren solution is obligatory for its reuse in leach process. Batch experiments were carried out to evaluate the adsorption capacity of resins under different experimental conditions, including con-centration, resin amount, initial pH, contact time and temperature. More than 99%of adsorption was achieved under the optimal condition. High adsorption rates on the resin were observed at the beginning and plateau values were obtalned in 60 min. The thermodynamic parameters (free energy changeΔG, enthalpy changeΔS and entropy changeΔH) for the adsorption were evaluated. The adsorption kinetic mechanism was studied with four models. The experimental results show that the adsorption follows the Langmuir isotherm and the kinetics follows the pseudo-second-order model.     

Characterization of adsorbent materials supported on polyurethane foams by nitrogen and toluene adsorption

Different composite adsorbent materials were obtained by supporting three activated carbons, one zeolite and one pillared clay, in a polyurethane foam. Adsorption isotherms of nitrogen and toluene were determined to evaluate the influence of the supporting process in the adsorption capacity of the different adsorbent materials. The results indicate that the activated carbons in form of pellets presented the best results with a decrease of about 20% in the nitrogen adsorption capacity but maintaining the same toluene adsorption capacity. The inorganic adsorbents presented a decrease of about 73% for the zeolite and 97% for the pillared clay in the nitrogen adsorption capacity and also a pronounced decrease in the toluene adsorption capacity. Two materials, one activated carbon and one zeolite, with different particle sizes were supported in the polyurethane foam. The decrease in the adsorption capacity of nitrogen and toluene was more pronounced when solids with smaller particles were used. This was an indication that the decrease in the adsorption capacity is related to the impregnation of the surface of the solid particles by the polyurethane during the synthesis of the composite material, which was observed by scanning electron microscopy. Nevertheless, the supporting method, in a one step procedure, presented itself with good possibilities for applications with activated carbons in the form of pellets.     

ADSORPTION OF A LEATHER DYE ON MESOPOROUS STRUVITE OBTAINED FROM SWINE WASTEWATER

Struvite powder obtained from swine wastewater was used as adsorbent to remove an azo leather dye from aqueous solution. The material was characterized by X-ray diffraction, surface area, and atomic force microscopy. The sample presented a single phase having a mesoporous structure and surface area of 35.63 m² g^?1. Langmuir and Freundlich isotherm models were fitted to the adsorption data and both satisfactorily represented the process. The maximum adsorption capacity was 38.14 mg g^?1. From the analysis of thermodynamic parameters such as free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) it was verified that the adsorption process is very fast, spontaneous, and exothermic in nature, with weak forces acting.     

Prediction of adsorption equilibrium using a modified D-R equation: organic-water vapor mixtures on BPL carbon

Methods to describe and predict adsorption equilibrium using the D-R equation are presented in this paper. We focus on adsorption of organic-water vapor binary mixtures on BPL activated carbon. By adjusting the partial pressure of the organic component in the binary mixture, the effects of the presence of water vapor on adsorption of the organic component are quantitatively expressed using one term in a modified form of the D-R equation. The developed models have broad application ranges that are not limited by organic type and the loadings of the organic and water vapor. They can be used for coadsorption of water-immiscible or water-miscible organic compounds with water vapor on BPL activated carbon in the cases of small or large organic loading with low or near-saturation relative humidity. Compared with other methods for the adsorption of organic-water vapor binary mixtures, our models are simple and do not require iteration.     

Adsorption enthalpies of sodium dodecyl sulphate onto carbon blacks in the low concentration range

Adsorption enthalpies of sodium dodecyl sulphate onto a set of carbon blacks from aqueous solutions in the low concentration range are presented. The surfactant was found to adsorb on the carbon surface exothermally in the whole studied coverage. From the calorimetric results and the analysis of the adsorption isotherms by a double Langmuir equation, a model of the adsorption mechanism in these systems is suggested. The adsorption of the surfactant onto the carbon blacks can be explained by two energetically distinct steps corresponding to the adsorption of SDS in two different types of porosity.     

Performance of a synthetic resin for lithium adsorption in waste liquid of extracting aluminum from fly-ash

In this study, we investigated the performance of a synthetic resin for the adsorption of Li from pre-desilicated solution which is the waste liquid produced by extracting aluminum from fly ash. The adsorption kinetics and isotherms of the resin were obtained and analyzed. The saturated adsorption sites of the resin were in agreement with the quasi-second-order kinetic model. Then, the pore diffusion model (PDM) was applied to represent the lithium adsorption kinetics which confirming that the external mass is the limiting step. Moreover, we evaluated the adsorption properties of this resin in fixed-bed mode. We established a feasible extraction process for Li from strong alkaline solutions with low Li concentrations. The process parameters, such as the flow rate, initial adsorption solution concentration, water washing process, desorption agent concentration, and flow rate were studied. The desorption rate of the Li⁺ ions was directly proportional with the concentration of the desorption agent. The time required to accumulate Li decreased as the hydrochloric acid concentration and flow rate increased. Time of the peak appeared increased from 0.5 bed volume (BV) to 2.5 BV as the concentration was increased from 1 to 3 mol·L^-1, and the peak increased from 231 to 394 mg·L^-1. The resin presented good selectivity for Li⁺ ions and could effectively separate impurity ions from the pre-desilication solution.     

Adsorption of benzoic acid by CTAB exchanged montmorillonite

This paper reports the adsorption of benzoic acid from water on cetyl trimethylammonium exchanged montmorillonite (CTAB-montmorillonite). Important factors are the adsorbent concentration, ionic strength, equilibrium time and pH. The largest adsorption is at pH 9. The adsorption kinetics data fitted the pseudo-second-order equation. The adsorption isotherms at different pH were linear indicating a partition mechanism. Up to about 61% of the dissolved benzoic acid was adsorbed by CTAB-montmorillonite. These results indicate that CTAB-montmorillonite is a potential adsorbent for benzoic acid.     

Prediction of adsorption equilibrium using a modified D-R equation: pure organic compounds on BPL carbon

A method for predicting adsorption equilibrium using a modified Dubinin-Radushkevich (D-R) equation is presented in this paper. We focus on adsorption of pure organic compounds on BPL-activated carbon. We introduce a new variable k_v, a volume adjusting coefficient, and simply use V_b, the constant molar volume of the adsorbate at its normal boiling temperature, instead of V_m, the temperature-dependent molar volume of the adsorbate at the adsorption temperature. The model parameters in the modified D-R equation for an adsorbate are predicted from V_b. Overall, the modified D-R equation gives more accurate results than the traditional one.     

Applying a Gouy–Chapman–Stern model for adsorption of organic cations to soils

An effective adsorption model was developed by S. Nir in 1978 for predicting adsorption to synthetic membranes and was also adapted by him afterwards to clay minerals. The main principles of the model are the solution of the electrostatic Gouy–Chapman equations while calculating the adsorbed amounts of the cations as the sum of those residing in the double-layer region and the cations that are chemically bound in a closed system. Thus, the equilibrium concentration in solution is influenced by the adsorption as the function of the amounts bound. The model was later developed and adapted for the adsorption of organic cations, and, in most cases, the fit of calculated results to measured adsorbed amounts of cations was very good, after calibrating the model for the chemical tested, with only two adjustable parameters for each chemical. In the current work, we tested the applicability of this model for the adsorption of a monovalent and a divalent organic cation by several soils, by considering the cation exchange capacities (CEC) and the specific surface areas (SSA) of the soils. For three out of four soils, a very good fit was obtained by using the required parameters for the calculations from previous studies of cation adsorption on clay minerals. The main advantage of the presented model over Langmuir and Freundlich adsorption isotherms is that no additional changes in the parameters were needed when the background concentration of salts in the suspensions was increased from 10 to 50 or 500 mM.     

A SIMPLE METHOD OF DETERMINING PORE AND SURFACE DIFFUSIVITIES IN ADSORPTION STUDIES

In this paper, a new graphical method of determining pore and surface diffusivities in adsorption systems is presented. The method involves only a simple linear plot of the inverse of half time of adsorption versus a concentration factor. The pore diffusivity and the surface diffusivity are determined directly from the intercept and the slope of the straight line, respectively. Experimental data of n-butane on Ajax activated carbon are used to illustrate the potential application of this new technique in the diffusivity parameter determination.     

Effect of ZnO loading to activated carbon on Pb(II) adsorption from aqueous solution

The effect of zinc oxide loading to granular activated carbon on Pb(II) adsorption from aqueous solution was studied in comparison with zinc oxide particles and oxidized activated carbon. Cu(II), Cd(II) and nitrobenzene were used as reference adsorbates to investigate the adsorption. The BET surface area and point of zero charge (pH_PZC) in the aqueous solution were measured for the adsorbents. The adsorption isotherms were examined to characterize the adsorption of heavy metals and organic molecules. The heavy metal adsorption was improved by both the zinc oxide loading and the oxidation of activated carbon. In contrast, the adsorption of nitrobenzene was considerably reduced by the oxidation, and slightly decreased by the zinc oxide loading. The zinc oxide loading to the activated carbon was found to be effectively used for the Pb(II) adsorption whereas only a part of surface functional groups was used for the zinc oxide particles and the oxidized activated carbon. From the experimental results, the surface functional groups responsible for the Pb(II) adsorption on the zinc oxide loaded activated carbon were considered to be hydroxyl groups that formed on the oxide, while those on the oxidized activated carbon were considered to be carboxylic groups.     

变压吸附制氮装置用于工业生产中的惰性保护

简要介绍变压吸附制氮技术的基本原理、变压吸附制氮装置以及用于工业生产中的惰性保护     

ADSORPTION OF ORGANIC SOLUTES INTO ACTIVATED CARBONS-BATCH STUDIES

In this paper, a new model is proposed for the adsorption of organic solutes into solids having a bimodal pore size distribution. This model takes into account, the pore and surface diffusion in the macropore and also the adsorption capacities in both macropore and micropore. The model equations are solved numerically (Crank-Nicholson) and in special cases, the asymptotic solutions for micropore uptake control and macropore uptake control are presented. This model is applied to data obtained by Peel, Benedek and Crowe (1981) and is shown to describe the experimental data well. It has been observed that surface diffusion plays a significant role in the adsorption of phenol on activated carbon.     

Effektive Stofftrennung in Gas‐ und Flüssigphase durch selektive Adsorption

Adsorption is a versatile tool for the separation of low abundant molecules from complex mixtures. The affinity and selectivity of the adsorbents are crucial parameters for the efficiency of the separation process. This work provides an overview of the basic adsorption mechanisms and illustrates their relevance for technical applications based on own experimental data in bioprocess, environmental and safety engineering. Distinctive features between the adsorption from the gas and fluid phase, respectively, the differences between small molecules and interacting biomacromolecules are presented.     

LOCAL EQUILIBRIUM THEORY FOR THE DYNAMICS OF NONISOTHERMAL MIXED GAS ADSORPTION OF HIGH-CONCENTRATION COMPONENTS

A local equilibrium theory for nonisothermal gas adsorption is developed which accounts for variations in interstitial gas velocity induced by adsorption. Also presented are expressions describing the entropy admissibility criterion. A solution is developed for a Riemann's problem involving adiabatic gas-phase adsorption where there is no inert diluent and where Langmuir isotherms apply.     

Effects of Electrolyte Concentration on Surfactant Adsorption to a QCM Immersed in Surfactant + Electrolyte Solutions

Abstract

Surfactant adsorption from aqueous electrolyte solutions onto metal surfaces was characterized through the use of a Quartz Crystal Microbalance (QCM). The need for a better understanding of the surfactant adsorption process became apparent in previous studies by Morton et al., directed toward the development of a thermodynamically-based model of oil removal from metal surfaces. These modeling efforts utilized existing data on surfactant adsorption data, yet required the estimation of surfactant adsorption phenomena, such as the transition between monolayer adsorption and multi-layer adsorption and the location of the critical micelle concentration (CMC). Experimental techniques utilizing the quartz crystal microbalance (QCM) have been shown to be highly reliable for measuring slight changes, on the order of a nanogram, in the adsorption behavior of surfactants from aqueous solutions. The current study demonstrates that the addition of low concentrations (< 100 mM) of sodium chloride to aqueous solutions of ionic surfactant can have a significant effect on the adsorption of the surfactant to a gold surface. An analysis of the QCM measurements as well as a discussion of the effects of salt addition on various solution properties will be presented. Impacts of the current results to previously published work as well as potential applications will be discussed.