Selective Water Sorbents for Multiple Applications, 10. Energy Storage Ability

The application of new selective water sorbents for storage of low temperature heat is analyzed. Values of energy storage ability E are measured by a DSC technique for more than fifteen samples of selective water sorbents based on silica gels, aluminas, carbon Sibunit and aerogels as host matrices and CaCl₂, LiBr, MgCl₂ as impregnated salts. E-values up to 8.4 kJ/g and 4.0 kJ/g are found for forced and naturally saturated sorbents, which are much higher than for common sorbents, like zeolites and unimpregnated silica gels. The temperature dependence of E gives an estimation of sensible and latent heat contributions as well as the average heat of water desorption and average specific heat of dry sorbents. A comparison between the SWSs and others materials proposed in literature is done.     

Water desorption isotherms of cellulose-acetate membranes

 The water desorption isotherms are determined in three cellulose acetate membranes with different acetyl content as a function of p/p ₀ at 10–40 °C. The partition coefficients (adsorbed water over water pressure) show a minimum at p/p ₀=0.5–0.6. This indicates a two energy mechanism. The agreement of our results with the BET adsorption isotherms only till p/p ₀<0.3 shows that a two energy adsorption mechanism is valid only for small water contents, probably one hydrate layer and a second more liquid-like water layer. At large p/p ₀, the adsorbed water becomes more and more liquid like by polarization of the hydrogen bonds. The heat of desorption is larger than the vaporization heat of water ΔH _vap(H₂O). It decreases with increasing water content asymptotically to ΔH _vap(H₂O). The cause may be a larger van der Waals interaction of the hydrate layer due to coordination numbers larger than 4.4 as in liquid water. Additionally, we found a hole adsorption process by sorbing unpolar solvents. The water and methonal adsorption are 100 times larger due to a swelling mechanism depending on the number of acetyl groups in the membranes. The amounts of n-alcohols sorbed decrease with their chain length. Received: 25 April 1997 Accepted: 10 June 1997     

Evaluation of adsorbent materials for heat pump and thermal energy storage applications in open systems

The evaluation of solid adsorbents in open sorption systems for heating, cooling and thermal energy storage (TES) applications is crucial for the ecological and economical performance of these systems. An appropriate adsorbent has to reach the temperature limit given by the heating/cooling system of the consumer. It has to provide high energy efficiency and a high energy density for storage applications. A method for an easy evaluation of different adsorbents for a specific application has been developed. The method is based on the adsorption equilibrium of the adsorbent and water vapor. The crucial property for the discussed field of applications is the differential heat of adsorption. Criteria for the evaluation of the adsorbent are the breakthrough curves (responsible for the dynamics of the process), the possible temperature lift (or the dehumidification) of the air, the thermal COP and the storage capacity.     

Dynamics and isotherms of water vapor sorption on mesoporous silica gels modified by different salts

The mesoporous silica gels impregnated with different metal salts were prepared and studied. The pore structure and specific surface area of adsorbents were evaluated using nitrogen adsorption. Then, the sorption isotherms and dynamics of water vapor were carried out at 303 K and different relative humidity (RH). The temperature programmed desorption experiments were conducted to estimate the activation energy (E _d) of water desorption on the silica gels. The results showed that the sorption capacity for water decreased with the increase of the ionic radius (except the calcium ion) and that CaCl₂ and LiCl were particularly suitable for use in modification of the mesoporous silica gel to improve their sorption rates and capacities for water vapor at the lower and medium RH (RH < 80%). The larger the average pore diameter and pore volume of the initial silica gels, higher the accrual rates of the water vapor sorption rate and capacity were after modification with hygroscopic salts. The activation energy of the water desorption on the mesoporous silica gel modified by CaCl₂ were much higher than that on the silica gel modified by LiCl, because the polarizability of the Ca²⁺ was higher than that of Li⁺.     

Adsorption of Gases, Vapors and Liquids by Microporous Adsorbents

Adsorption of Xe, Kr, Ar, N₂, O₂, H₂ CH₄, CO₂, He, and freons by PAU-10 and ACC microporous carbon adsorbents as well as by A and X zeolites was investigated over a wide range of pressures (0.1 Pa – 20 MPa) and temperatures (77, 120–600 K). The amount of gases, vapors and liquids adsorbed by microporous adsorbents increases steadily with increasing pressure and does not change dramatically if phase transitions occur in the adsorptive. Isosteres of adsorption constructed as a curve of ln P against f(1/T)_a retain a linear form over a wide range of pressures and temperatures. The slope of isosteres does not vary on going through the critical temperature of the gaseous phase. At high pressures, due to non-ideality of the gaseous phase and non-inert behavior of the adsorbent the differential molar heat of adsorption is dependent on temperature. At high fillings of micropores the differential molar isosteric heat capacities of adsorption systems show maxima that indicate the occurrence of structural rearrangements in the adsorbate.     

Synthesis of amine-modified mesoporous materials for CO2 capture by a one-pot template-free method

A one-pot template-free route was developed for the synthesis of novel tetraethylenepentamine modified porous silica as CO₂ adsorbents, the obtained materials were characterized by N₂ adsorption/desorption, thermogravimetry, elemental analysis, Fourier transform infrared spectrometry,scanning electron microscopy and transmission electron microscopy. It was found that the amine species were inserted into the silica skeleton, which considerably enhanced their dispersion. Compared with similar materials derived from impregnation, the porous structure of the silica can be better reserved, leading to a promising CO₂ adsorption capacity of 3.98 mmol CO₂/g-adsorbent and a fast adsorption kinetic in simulated flue gas at 348 K. The resulted adsorbents could also be easily regenerated and showed a good durability in multiple adsorption–desorption cycles. All these features make this method a promising option for the preparation of CO₂ adsorbents.     

Dependence of the energy of surface-active substances/metal interaction on their ionization potentials. Evaluation of hydrophilicity of metal

The function Δ(ΔG _A ⁰), which is the difference of Gibbs energies characterizing surface-active substance (surfactant, SAS) adsorption at metal/solution and air/solution surfaces, has been introduced. The equation connecting the function Δ(ΔG _A ⁰) with SAS ionization potential has been obtained using the elementary theory of donor-acceptor interactions. Published experimental data on SAS adsorption at mercury, bismuth and gold have been used for Δ(ΔG _A ⁰) calculation. The dependence of Δ(ΔG _A ⁰) on ionization potentials can be described by an equation derived in this work. It has been demonstrated that the value of the hydrophilicity of gold is much higher than the values for mercury and bismuth. The lifetime of SAS molecules at a metal surface has been estimated. The question of the possibility of theoretica l estimation of standard energies ΔG _A ⁰ characterizing SAS adsorption at a metal/solution surface has been discussed. Received: 9 December 1996 / Accepted: 13 January 1997     

Enhanced CO2 Adsorption over Polymeric Amines Supported on Heteroatom‐Incorporated SBA‐15 Silica: Impact of Heteroatom Type and Loading on Sorbent Structure and Adsorption Performance

Silica supported amine materials are promising compositions that can be used to effectively remove CO₂ from large stationary sources, such as flue gas generated from coal‐fired power plants (ca. 10 % CO₂) and potentially from ambient air (ca. 400 ppm CO₂). The CO₂ adsorption characteristics of prototypical poly(ethyleneimine)–silica composite adsorbents can be significantly enhanced by altering the acid/base properties of the silica support by heteroatom incorporation into the silica matrix. In this study, an array of poly(ethyleneimine)‐impregnated mesoporous silica SBA‐15 materials containing heteroatoms (Al, Ti, Zr, and Ce) in their silica matrices are prepared and examined in adsorption experiments under conditions simulating flue gas (10 % CO₂ in Ar) and ambient air (400 ppm CO₂ in Ar) to assess the effects of heteroatom incorporation on the CO₂ adsorption properties. The structure of the composite adsorbents, including local information concerning the state of the incorporated heteroatoms and the overall surface properties of the silicate supports, are investigated in detail to draw a relationship between the adsorbent structure and CO₂ adsorption/desorption performance. The CO₂ adsorption/desorption kinetics are assessed by thermogravimetric analysis and in situ FT‐IR measurements. These combined results, coupled with data on adsorbent regenerability, demonstrate a stabilizing effect of the heteroatoms on the poly(ethyleneimine), enhancing adsorbent capacity, adsorption kinetics, regenerability, and stability of the supported aminopolymers over continued cycling. It is suggested that the CO₂ adsorption performance of silica–aminopolymer composites may be further enhanced in the future by more precisely tuning the acid/base properties of the support.     

Characterization of Titania/Silica Gel by Means of Low-Pressure Nitrogen Adsorption

Adsorbents synthesized by grafting of titania onto mesoporous silica gel surfaces at different temperatures were studied by means of nitrogen adsorption–desorption and water desorption. The pore size distribution f(R_p) of titania/silica gel depends on the titania concentration (C_TiO2) and the temperature of titania synthesis. Nonuniformity of TiO₂ phase is maximal at a low C_TiO2 value (3.2 wt.% anatase deposited at 473 K), and two peaks of the fractal dimension distribution f(D) are observed at such a concentration of titania, but at larger C_TiO2 values, only one f(D) peak is seen. More ordered filling of pores and adsorption sites by nitrogen, reflecting in the shape of adsorption energy distributions f(E) at different pressures of adsorbate, is observed for adsorbent with titania (rutile+anatase) grafted on silica gel at a higher temperature (673 K).     

Effect of Heat Treatment and Additives on the Photochromic and Mechanical Properties of Sol-Gel Derived Photochromic Coatings Containing Spirooxazine

The experimental results on the photochromic and mechanical properties of coatings containing 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3′-(3H)-naphth(2,1-b)(1,4) oxazine] (SO) derived from 3-glycidyl-oxypropyltrimethoxysilane (GPTMS), bisphenolA (BPA) and 1-methylimidazole (MI) by sol-gel processing are presented. It is shown that heat treatment temperature is a conflicting factor to the photochromic intensity (ΔA ₀), photostability and abrasion resistance of the photochromic coatings. With increasing densification temperature the matrix rigidity increases leading to a decrease of ΔA ₀ and at the same time an enhancement of both abrasion resistance and photostability, the optimum heat treatment temperature is 110°C under our experimental conditions. By the use of certain additives, e.g., fluorosilanes (FAS), not only ΔA ₀ but also the photostability and the abrasion resistance of the photochromic coatings have been further improved.     

Determination of the surface properties of untreated and chemically treated kaolinites by inverse gas chromatography

Inverse gas chromatography is used to study the surface properties of the untreated and chemically treated kaolinite samples. Changes in the enthalpy of adsorption for a variety of probes and in the surface energy of clays are measured and the effect of modification of the natural clay after chemical treatment with Na₂CO₃ is determined. The surface energy of the natural clay increased by the modification due to an increase in the surface area. It can be concluded that the dispersive component of surface free energy, γ _s ^d , decreases with temperature in the 200–275°C temperature range for both samples. Temperature coefficients of γ _s ^d for untreated and modified kaolinites are −0.1185 and −0.3966 mJ/(m² °C) with the correlation coefficients (R ²) of 0.8479 and 0.965, respectively. From the retention data for polar probes at infinite dilution, information on the accessibility of surface sites to the probes and on the acid-base character of the surface is obtained. The specific free energy of adsorption, the specific enthalpy of adsorption (ΔH ^sp), and the specific entropy of adsorption of polar probes on initial and modified kaolinites are determined. The ΔH ^sp values correlated with the donor numbers and modified acceptor numbers of the probes to quantify the acidity (K _A) and basicity (K _D) parameters of clay surfaces. The values of K _A and K _D for initial and modified kaolinites are determined to be 0.1202 and 0.2803; 0.0130 and 0.0408 with the correlation coefficients of −0.9805 and −0.9782, respectively. The unmodified clay sample indicated a more acidic character, while the modified clay sample conferred a largely basic character. Consequently, the predominant surface basicity of the modified kaolinite agrees with expectation, bearing in mind the treatment with Na₂CO₃, taking into consideration that such a modification contributes to a decrease in the hydrophilicity of the surface and also results in the surface showing only weak Lewis acidity. The text was submitted by the authors in English.     

Ce3+ adsorption on hydrated MnO2

The adsorption of Ce³⁺ on hydrated manganese dioxide (HMD) was studied as a function of concentration, temperature and pH of the cerium solution labelled with¹⁴¹Ce. The steady state values of cerium adsorption at various concentrations fit well with the classical Freundlich isotherm. The effect of temperature on equilibrium adsorption values was utilized to determine the change in the standard enthalpy ΔH ^o of the cerium uptake process and its value (ΔH ^o=10.57) indicates that the uptake process proceeds via ion exchange.¹⁴¹Ce desorption studies, from HMD in water, HCl and unlabelled CeCl₃ solution, confirmed the ion exchange nature of the cerium uptake process as well as its reversibility.     

Heating effects on morphological and textural characteristics of individual and composite nanooxides

Morphological, structural and adsorption characteristics of nanooxides (fumed individual silica, alumina and titania, and composite silica/alumina, silica/titania and alumina/silica/titania) were compared after different treatments (wetting/drying, ball-milling, suspending/drying, heating) at different temperatures (373–1173 K) using low-temperature nitrogen adsorption data. The structural characteristics such as specific surface area (S _BET), pore volume (V _p), pore (PSD) and particle (PaSD) size distributions (calculated using self-consisting regularization procedure with respect to both PSD and PaSD), fractality, adsorption energy distributions depend differently on heating temperature because desorption of water molecularly and dissociatively adsorbed at a surface and in bulk of primary nanoparticles occurs over a wide temperature range at different rates. These processes affect both structural and energetic characteristics of nanooxides.     

Structural and Adsorptive Characteristics of Pyrocarbon/Silica Gel Si-60

Pyrocarbon/silica gel adsorbents (carbosils, CS) with mesoporous Si-60 (Merck, granule size 0.2–0.5 mm) modified by pyrolysis of CH₂Cl₂ at 823 K and reaction time from 0.5 to 6 h and then hydrothermally treated at 473 K for 6 h were studied by means of TEM, adsorption and ¹H NMR methods. Changes in the structural and adsorptive characteristics of hybrid adsorbents before and after hydrothermal treatment, which depend on pyrocarbon content (C _C), were analyzed on the basis of TEM micrographs and p-nitrophenol and nitrogen adsorption isotherms treated using a constrained regularization method. Interfacial water layers in aqueous suspension of CS were investigated by means of ¹H NMR with freezing-out of bulk water at T < 273 K showing nonlinear changes in the Gibbs free energy of interfacial water with increasing C _C because of nonlinear dependence of the structural characteristics of pyrocarbon deposits and CS as a whole on C _C.     

Removal of Th(IV) ions from aqueous solution using bi-functionalized algae-yeast biosorbent

Composites could be more effective adsorbents than inorganic and organic components individually. In the present study, the red macro marine algae, Jania Rubens and yeast, Saccharomyces cerevisiae immobilized on silica gel were used as a constituent of bi-functionalized biosorbent to remove thorium ions from aqueous solution. Optimum biosorption conditions were determined as a function of pH, initial Th(IV) concentration, contact time, temperature, volume/mass ratio and co-ion effect. The morphological analysis of the biocomposite was performed by the scanning electron microscopy and functional groups in the biosorbent were determined by FT-IR spectroscopy. In order to find the adsorption characteristics, Langmuir, Freundlich, and Dubinin–Radushkevich adsorption isotherms were applied to the adsorption data. The data were well described by Langmuir adsorption isotherms while the fit of Freundlich adsorption isotherms and Dubinin–Radushkevich equation to adsorption data was poor. Using the equilibrium constant value obtained at different temperature, the thermodynamics properties of the biosorption (ΔG°, ΔH° and ΔS°) were also determined. The results show that biosorption of Th(IV) ions onto biocomposite was exothermic nature, spontaneous and more favorable at lower temperature under examined conditions.     

Systematik des Adsorptionsverhaltens homologer aliphatischer Amine an der Grenzfläche Quecksilber/Elektrolyt

Zusammenfassung Dutch die wechselstrompolarographische Kapazitäts-Potential-und Kapazitäts-Zeit-Messungen (E _m = konstant) als Funktion der Aminkonzentration wurden die Adsorptionsisothermen homologer Amine und Amin-Hydrochloride beiT = 25 °C undT = 50 °C experimentell bestimmt.Die Ads orptionsisothermen wurden mittels dimensionsloser Adsorptionstherme nachFrumkin-Damaskin ausgewertet und in Form folgender Adsorptionsparameter diskutiert und verglichen: Attraktionskonstantea; Adsorptionskoeffizientb und freie StandardadsorptionsenthalpieG _A .Der Zuwachs in denG _A -Werten pro CH₂-Gruppe läßt sich zuG _A /CH₂0,3–0,5 kcal. Mol^–1 abschätzen. Bis auf wenige Ausnahmen sind die Adsorptionsparametera, b, undG _A Temperaturfunktionen

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Summary The adsorption isotherms of homologous amines and some of their hydrochlorides were obtained from capacity-potential- und capacity-time measurements atT = 25 °C andT = 50 °C.From the adsorption isotherms we computed the thermodynamic adsorption parameters according toFrumkin andDamaskin. On the basis of the adsorption parameters attraction constant (a), adsorption coefficient (b) and free standard energy of adsorptionG _A , the results have been discussed und compared.The increase ofG _A per CH₂-group is aboutG _A /CH₂ 0,3 to 0,5 Kcal Mol^–1. In most cases the adsorption parametersa, b andG _A are temperature functions.

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Mit 3 Abbildungen und 1 Tabelle     

Charge-transfer interactions between nucleophilic compounds and chromatographic packings containing chemically bonded Cu(II) complexes

Summary Results are presented of studies of packings containing copper (II) acetylacetonate (acac), hexafluoroacetylacetonate (hfac), and chloride, chemically bonded via β-dik-etonate groups. The retention parameters retention factor (k) specific retention volume (V _g), and molecular retention index (M _e) were measured and used to calculate the thermodynamic parameters free energy of adsorption (ΔG _a) heat of adsorption (−ΔH _a), and entropy of adsorption (ΔS _a). These parameters enable, characterization of specific interactions between aromatic and cyclic hydrocarbons, ethers and thioethers and metal complexes chemically bonded, to a silica surface.     

Adsorption of uranium(VI) onto <Emphasis Type="Italic">Ulva sp.</Emphasis>-sepiolite composite

Ulva sp. and sepiolite were used to prepare composite adsorbent. The adsorption of uranium(VI) from aqueous solutions onto Ulva sp.-sepiolite has been studied by using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as solution pH, initial uranium(VI) concentration, and temperature, have been investigated and the optimum conditions determined. The adsorption patterns of uranium on the composite adsorbent followed the Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model. The sorption is physical in nature (sorption energy, E = 4.01 kJ/mol). The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK _d vs. 1/T plots. Thermodynamic parameters (ΔH _ads = −22.17 kJ/mol, ΔS _ads = −17.47 J/mol·K, ΔG ^o _ads (298.15 K) = −16.96 kJ/mol) show the exothermic heat of adsorption and the feasibility of the process. The results suggested that the Ulva sp-sepiolite composite adsorbent is suitable as a sorbent material for recovery and biosorption/adsorption of uranium ions from aqueous solutions.     

Hydrogen storage in porous structures of adamantane‐based nitrogen‐heterocyclic ring with diamond‐like structure

Using the density functional theory and molecular mechanics methods, we calculated the binding energy and parameters about the primitive cell designed by us with the adamantane and the nitrogen heterocyclic ring, the vibrational frequencies about the small complexes. Grand canonical Monte Carlo simulations were performed to predict the capacities for the hydrogen storage and adsorption isotherms. The results show the positive effects of bigger specific surface area and pore volume on hydrogen storage and isosteric heat. The gravimetric hydrogen uptake of adamantane‐based nitrogen‐heterocyclic ring of quaterpyridyl can reach 9.02 wt % at room temperature and 100 bar. But the volumetric H₂ capacities of the four materials are low at T = 298 K because of weak interaction between the materials and H₂ molecule. © 2014 Wiley Periodicals, Inc.     

吸附法制备CuO-Ag/SiO2纳米复合物

利用吸附法原位制备CuO/SiO2、CuO-Ag/SiO2纳米复合物,研究了不同吸附质体系中预负载的纳米Ag粒子对CuO的影响。结果表明:Ag粒子对CuO的影响因吸附质的不同而不同。以Cu(Ac)2为吸附质,纳米Ag几乎没有影响;以NaOH为吸附质,纳米Ag使得CuO的晶粒粒径增大。这一结果与铜物种对Ag晶粒粒径的影响规律完全不同。通过比较不同吸附质的吸附行为,Cu(OH)2与硅胶表面的相互作用被认为是导致这一现象的原因。