热处理对憎水硅胶吸附水蒸气的影响

用甲基氯硅烷蒸气或溶液处理硅胶,均可制成憎水硅胶。关于憎水硅胶的吸附性能和热稳定性的研究,文献中时有报道。本文主要探讨以下3个问题:(1)在水蒸气吸附中,硅胶表面自由羟基和缔合羟基究竟哪种起主要作用;(2)从吸附水蒸气等数据讨论硅胶表面有机基团—OSi(CH_3)_3的热稳定性;(3)用二甲基二氯硅烷(DMCS)和三甲基氯硅烷(TMCS)处理的憎水硅胶,哪种硅胶的热稳定性较高。这些基本问题,不仅具有学术意义,对研究氧化物表面改性也有参考价值。     

Effect of pore size on the performance of composite adsorbent

Three kinds of commercial silica gels with pore size of 2–3, 4–7 and 8–10 nm respectively are used for preparing composite adsorbents by soaking them into the aqueous solution of calcium chloride. The test result indicates that both the water uptake and adsorption rate of composite adsorbents prepared from 4–7 and 8–10 nm silica gels improve greatly compared to pure silica gels, but they do not for 2–3 nm silica gels. The silica gel with pore size of 2–3 nm is not suitable for preparing the composite adsorbent by impregnation method due to the pore blockage because of the small pore size. The SCP and COP of the adsorption chiller with sample SA50 are 128.3 Wkg^?1 and 0.27 respectively at the hot source temperature of 90 °C, which are largely superior to that of SA0. Hence using the composite adsorbent instead of the pure silica gel can reduce the size of the adsorption chiller.     

Energetics of small molecule and water complexation in hydrophobic calixarene cavities

Calixarenes grafted on silica are energetically uniform hosts that bind aromatic guests with 1:1 stoichiometry, as shown by binding energies that depend upon the calixarene upper rim composition but not on their grafted surface density (0.02-0.23 nm(-2)). These materials are unique in maintaining a hydrophilic silica surface, as probed by H2O physisorption measurements, while possessing a high density of hydrophobic binding sites that are orthogonal to the silica surface below them. The covalently enforced cone-shaped cavities and complete accessibility of these rigidly grafted calixarenes allow the first unambiguous measurements of the thermodynamics of guest interaction with the same calixarene cavities in aqueous solution and vapor phase. Similar to adsorption into nonpolar protein cavities, adsorption into these hydrophobic cavities from aqueous solution is enthalpy-driven, which is in contrast to entropy-driven adsorption into water-soluble hydrophobic hosts such as beta cyclodextrin. The adsorption thermodynamics of several substituted aromatics from vapor and liquid are compared by (i) describing guest chemical potentials relative to pure guest, which removes differences among guests because of aqueous solvation and van der Waals contacts in the pure condensed phase, and (ii) passivating residual guest binding sites on exposed silica, titrated by water during adsorption from aqueous solution, using inorganic salts before vapor adsorption. Adsorption isotherms depend only upon the saturation vapor pressure of each guest, indicating that guest binding from aqueous or vapor media is controlled by van der Waals contacts with hydrophobic calixarene cavities acting as covalently assembled condensation nuclei, without apparent contributions from CH-pi or other directional interactions. These data also provide the first direct quantification of free energies for interactions of water with the calixarene cavity interior. The calixarene-water interface is stabilized by approximately 20 kJ/mol relative to the water-vapor interface, indicating that water significantly competes with the aromatic guests for adsorption at these ostensibly hydrophobic cavities. This result is useful for understanding models of water interactions with other concave hydrophobic surfaces, including those commonly observed within proteins.     

苯基化硅胶的物理结构和表面性质的研究

本文利用苯基三氯硅烷和硅胶表面羟基反应制备了苯基化硅胶。测定了苯基化硅胶的物理结构、水蒸气吸附等温线、润湿热、差热分析(DTA)和红外光谱(IR)。结果表明,所有苯基化硅胶的真密度(dT)、比表面(S)和比孔体积(V)均减少, 而表观密度(dA)增加, 但苯基化对不同硅胶的平均孔半径(r)有不同的影响; 苯基化硅胶对水蒸气吸附, 对水、苯和环己烷的润湿热均显著减少; 苯基化硅胶的热稳定性大于甲基化硅胶, 甲基化硅胶的表面是高度憎水的, 但苯基化硅胶的憎水性则很弱。     

Using near-infrared spectroscopy and differential adsorption bed method to study adsorption kinetics of orthoxylene on silica gel

This paper has demonstrated the study on the adsorption kinetics of orthoxylene on silica gel with a novel experimental methodology. In the method, there was a differential adsorption bed (DAB) where the solid adsorbent always contacted with the same bulk concentration of the adsorbate vapor, and the DAB was monitored with near-infrared diffuse reflectance spectroscopy (NIRDRS) continuously as well as non-invasively. Local partial least squares (PLS) algorithm was suggested to replace normal global PLS method in multivariate calibration models for processing NIRDRS data, because the concentration of the adsorbate on the adsorbent varied greatly as the adsorption process was going on. In this way, we, conveniently as well as promptly, obtained instantaneous adsorption rates of several orthoxylene/silica gel adsorption processes under different conditions like partial pressure of orthoxylene vapor and velocity of gas, and discovered that the adsorption process was physical adsorption, and mainly controlled by external diffusion.     

二组分气体在固体上吸附的研究(IV)

测定了丙酮－正己烷、甲苯－正己烷、苯－正己烷、正戊烷－正己烷四个二组分气体在部分石墨化的灯黑上的吸附等温线,并测定了单组分气体吸附等温线．对比了上述四个二组分气体,分别在硅胶、硅烷化硅胶和灯黑上吸附的十二个吸附体系的吸附规律．结果表明,二组分气体在吸附剂上的竞争吸附的强弱,基本上可以通过它们的纯组分气体在吸附剂上第一层吸附热Q1数值的大小加以预测．     

INVESTIGATION OF THE INTERACTIONS BETWEEN WATER AND MODIFIED SILICA GEL BY IGC AND TPD

In this work, the thermodynamic parameters for the adsorption of water vapor on untreated silica gel and silica gel treated with hygroscopic salts and silane coupling agent were determined by Inverse Gas Chromatography (IGC) in the infinite dilution region. The desorption activation energies of the water vapor on virgin and modified silica gels were estimated by using the Temperature Programmed Desorption (TPD) technique. The interactions between the water and the virgin and modified silica gels were discussed. Results showed that the thermodynamic parameters and desorption activation energy of water vapour on the silica gels increase with decreasing pore size and increasing the surface hydrophilic properties. The desorption activation energy of virgin and modified silica gels was found to increase with increasing the thermodynamic parameters. The larger the adsorption parameters and the desorption activation energy were, the interactions between water and virgin and modified silica gels were.     

INVESTIGATION OF THE INTERACTIONS BETWEEN WATER AND MODIFIED SILICA GEL BY IGC AND TPD

1. INTRODUCTIONSilica gel is an amorphous inorganic polymer composed of siloxane (Si-O-Si) groups in the inner region and silanol (Si-OH) groups distributed on the surface [1]. Silanol groups can be easily functionalized by different chemical procedures. …     

二组分气体在固体上吸附的研究(Ⅳ)

测定了丙酮－正己烷、甲苯－正己烷、苯－正己烷、正戊烷－正己烷四个二组分气体在部分石墨化的灯黑上的吸附等温线，并测定了单组分气体吸附等温线．对比了上述四个二组分气体，分别在硅胶、硅烷化硅胶和灯黑上吸附的十二个吸附体系的吸附规律．结果表明，二组分气体在吸附剂上的竞争吸附的强弱，基本上可以通过它们的纯组分气体在吸附剂上第一层吸附热Q1数值的大小加以预测．     

硅胶的表面硅烷化处理及其吸附性能研究

为研究改性硅胶对挥发性有机废气的吸附性能,分别采用十六烷基三甲氧基硅烷、辛基三乙氧基硅烷、苯基三甲氧基硅烷、一甲基三乙氧基硅烷对硅胶进行气相改性处理,试验研究了不同改性剂、改性时间对硅胶饱和吸附率的影响,考察了改性硅胶对甲苯、水二组分体系的吸附选择性.结果表明,硅胶对甲苯的吸附主要为物理吸附,长链的硅烷改性剂在60℃、...     

Composite Water Sorbents of the Salt in Silica Gel Pores Type: The Effect of the Interaction between the Salt and the Silica Gel Surface on the Chemical and Phase Compositions and Sorption Properties

The influence of the inorganic salt-silica gel surface interaction on the chemical and phase compositions and sorption properties of composites of the salt in silica gel pores type is studied. Two possible interaction mechanisms are considered: (1) the ion-exchange adsorption of metal cations on the silica gel surface from a solution of a salt (CaCl₂, CuSO₄, MgSO₄, Na₂SO₄, and LiBr) and (2) the solid-phase spreading of a salt (CaCl₂) over the silica gel surface. The adsorption of metal cations on the silica gel surface in the impregnation step affords ≡Si-OM ⁿ⁺¹ surface complexes in the composites. As a result, two salt phases are formed in silica gel pores at the composite drying stage, namely, an amorphous phase on the surface and a crystalline phase in the bulk. The sorption equilibrium between the CaCl₂/SiO₂ system and water vapor depends on the ratio of the crystalline phase to the amorphous phase in the composite.     

The hydroxyl content of silica gel

Thermogravimetric analysis of silica gel has shown that the loss in weight between 30° and 910°C can be quantitatively explained on the basis of water being lost from three distinct and different populations of sites on the silica gel surface. The results indicate that the site energies of the three different populations are randomly distributed and, consequently, the resulting weight loss steps from each population can be described by the integral of a simple normal distribution with temperature. The calculated weight loss obtained by assuming three different site-groups having randomly distributed adsorption energies is, within experimental error, coincident with the experimental data. It is also shown that the water evolved from the second population of sites originates from strongly bound water and may also contain water generated by the condensation of (geminal) silanol groups contained in the overlapping and neighbouring population.     

在不同覆盖度下二组分气体在硅胶上的吸附规律

The composition adsorption isotherms (ya~xg curve) for acetone-n-hexane, benzene-n-hexane, toluene-n-hexane and n-pentance-n-hexane vapor mixtures on silica gel with different surface coverage (θ) at 25℃ were measured. The experimental results indicated that the ya ~ xg curves approached gradually down to corresponding binary liquid-vapor equllibrium curves with increasing of surface coverage. Therefore, the binary adsorbed phases are similarly with the binary liquid phase. Except for acetone-n-hexane system, which had a minimum boiling point, the composition adsorption isotherms of the other three binary systems could be simulated by equation of relative volatility.     

Improvement of water vapor adsorption ability of natural mesoporous material by impregnating with chloride salts for development of a new desiccant filter

The aim of this study is the development of a new adsorbent for the desiccant material which can be regenerated by the domestic exhaust heat by using natural mesoporous material, Wakkanai siliceous shale. To improve this shale’s performance to adsorb/desorb the water vapor, lithium chloride, calcium chloride or sodium chloride was supported into the mesopores by impregnating with each chloride solution. Especially sodium chloride was effective to increase the water vapor adsorption amount 5–7 times of that of natural shale in the relative humidity range from 50 to 70%. Moreover, the appropriate impregnating concentrations were determined as 5wt% from the relationship between the maximum water vapor adsorption amount and the mesopore volume. Based on these results, a new desiccant filter has been developed by impregnated original paper with lithium chloride and sodium chloride. This paper contained shale powder in the synthetic fibers. The dehumidification performance of this filter was evaluated under the simulated summer condition in Tokyo. From the cyclic adsorption/regeneration test, this shale and chlorides filter could adsorb and desorb 60 g/h water vapor repeatedly at the regeneration temperature of 40°C. On the other hand, a silica gel filter and a zeolite filter adsorbed and desorbed only 10 g/h and 25 g/h, respectively. These results suggested that the shale impregnated with the chlorides has the best dehumidification ability as a new desiccant material. Further, the desiccant filter made from the shale will achieve the effective use of the low temperature exhaust heat.     

二组分气体在固体上吸附的研究(Ⅱ)──丙酮-正己烷、甲苯-正己烷、苯-正己烷、正戊烷-正己烷分别在硅胶上的吸附

测定了丙酮-正己烷、甲苯-正己烷、苯-正己烷、正戊烷-正己烷4个二组分以及各单组分气体在硅胶上的吸附等温线.实验结果表明二组分气体在硅胶上的竞争吸附的强弱,可以通过比较它们的纯组分气体在硅胶上第一层吸附热Q₁数值的大小加以预测.     

二组分气体在固体上吸附的研究(Ⅲ)──丙酮-正己烷、甲苯-正己烷、苯-正己烷、正戊烷-正己烷分别在硅烷化硅胶上的吸附

测定了丙酮-正己烷、甲苯-正己烷、苯-正己烷、正戊烷-正己烷4个二组分气体在硅烷化硅胶上的吸附等温线,并测定了单组分气体吸附等温线。实验结果表明:二组分气体在硅烷化硅胶上的竞争吸附的强弱可以通过其单组分气体在硅烷化硅胶上第一层吸附热Q_1数值的大小预测。     

The Thermal Stability and Adsorbability of the Mechylated Silica Gel

The methylated silica gel has been produced by the reaction between the surface silanol groups and Clsi(CH3)3 vapor.The adsorption isotherms of acetic acid from carbon tetrachloride onto silica gel and emthylated silica gel heated at various temperatures have been determined at 25℃,and the above mentioned silica gels have been studied by TC and IR.The results indicate:(1) The adsorption of acetic acid from carbon tetrachloried onto methylated silica gel decreased greatly,probably because the concentration of the free hydroxyl groups for methylated silica gel decreased greatly as the IR shows.(2) As the methylated surface was destroyed at 450℃,the adsorption ability was restored when the methylated silica gel treated at>500℃.(3) So long as the methylated silica gel was treated at high temperature,the adsorption ability could be restored owing to that surface free hydroxyl groups were reproduced.     

Thermal Diffusivity and Adsorption Kinetics of Silica-Gel/Water

There have been performed experimental measurements of effective thermal conductivity of silica-gel for a stagnant cylindrical fixed bed under transient and steady state conditions in the presence of dry air at different pressures and for different amounts of adsorbed water. The Bauer-Schlünder and Kunii-Smith models have been used to identify the thermal solid conductivity of silica gel pellets from measurements of the conductivity in an adsorbent bed. Sorption rates of water vapor in silica gel were measured using a single-step thermal method by monitoring the sample surface temperature by infrared detection. In order to obtain the mass diffusivity it is necessary to match the numerical solution of the mathematical model to the experimental data.     

On the Behavior of Nonionic Surfactants at the N-Heptane/Silica Gel Interface: Influence of the Presence of Interfacial Water Inferred from Adsorption Isotherms and Calorimetric Data

The behavior of two polydisperse nonionic surfactants, poly (oxyethylene) glycol alkylphenyl ether TX-35 and TX-100, at the prewetted silica gel/n-heptane and dried silica gel/n-heptane interfaces has been compared by the determination of the average adsorption isotherms of the polydisperse surfactants and of displacement enthalpies. From HPLC experiments, we could also separately quantify the adsorption of each ethyleneoxide (EO) fractions for silica gel from the polydisperse surfactant solution. The adsorption isotherms clearly indicate an incomplete preferential adsorption of the large (EO) chains over the small ones, as well on dried silica gel as on a prehydrated sample. This preferential adsorption and its driving force follow the solubility rules of the poly(oxyethylene) glycol alkylphenyl ether in an apolar solvent and support the idea of a solubility-limited adsorption: solubility in organic solvents of the smaller (EO) chains is much more significant than that of the longer ones and hence prevents adsorption of the smaller species. Consequently, it is observed that the presence of interfacial water decreases the affinity of TX-35 molecules for the hydrophilic silica surface due to the hydration of (EO) chains. In contrast, for TX-100 adsorption after the prewetting treatment the clearest trend is a drastic increase of the adsorption ascribed to the additional solubilization (and micellization) of the TX-100 molecules in the interfacial aqueous phase. The differential molar enthalpies of displacement show a change in the adsorption mechanism, depending on the presence of molecular water on the surface. In the initial part of the adsorption isotherm, a prevailing exothermic process is obtained with prehydrated silica and suggests that hydration of the polar heads of TX-35 and the solubilization of the TX-35 in interfacial water are occurring. For higher equilibrium concentrations, the enthalpies of displacement observed with the prehydrated adsorbent become slightly lower than those obtained with dry silica gel. It may be that this difference is due to the micellization phenomenon of the surfactant species with longer EO chains in interfacial water. These features emphasize the influence of interfacial water on the adsorption of EO fractions from organic solvent. Copyright 2000 Academic Press.     

Influence of Water Vapor on Silica Membrane: Adsorption Properties and Percolation Effect

The influence of water vapor on silica membrane with pore size of 4 ? has been investigated in terms of adsorption properties and percolation effect at 50 and 90 oC. Two methods are employed: spectroscopic ellipsometry for water vapor adsorption and gas permeation of binary mixture of helium and H₂O. The adsorption behaviors on the silica membrane comply with the first-order Langmuir isotherm. The investigation demonstrates that helium flux through the silica membrane decreases dramatically in presence of H₂O molecules. The transport of gas molecules through such small pores is believed not to be continuous any more, whereas it is reasonably assumed that the gas molecules hop from one occupied site to another unoccupied one under the potential gradient. When the coverage of H₂O molecules on the silica surface increases, the dramatic decrease of helium flux could be related to percolation effect, where the adsorbed H₂O molecules on the silica surface block the hopping of helium molecules.