Water sorption by the calcium chloride/silica gel composite: The accelerating effect of the salt solution present in the pores

The kinetics of isothermal water sorption by the CaCl₂/silica gel composite initiated by a small stepwise pressure rise over the sample has been investigated at a constant underlying plate temperature of 35°C. The initial portion of the kinetic curves is consistent with Fick’s diffusion model: the amount of sorbed water increases in proportion to the square root of the sorption time. This makes it possible to determine the effective diffusivity of water (D _eff). At small amounts of sorbed water (w < 0.19 g/g), D _eff changes slightly. The diffusivity of water in the composite pores (D) calculated for the same conditions is close to the Knudsen diffusivity of water vapor in mesopores. The D _eff value grows with an increasing water content of the composite; that is, sorbed water accelerates water transport in the pores. This is likely due to the appearance of an extra diffusion channel, namely, diffusion through the aqueous solution of the salt, whose formation begins on the silica gel surface at w > 0.1 g/g. The contribution from this channel increases markedly when the amount of adsorbed water is above 0.25 g/g. This can be explained by the formation of the “connected” phase of the solution in the pores.     

Adsorption of acid and basic dyes on NiO-SiO2 composites

A series of composites containing 2.5–21.0% NiO on a surface of macroporous silica is synthesized. The specific surface area of the composites measured by the thermal desorption of nitrogen decreases with an increase in the NiO content from 24 for the original silica carrier to 16 m²/g the for composite containing 21.0% NiO. The basic dye, methylene blue (MB), is only adsorbed on SiO₂ in water solutions, while acid blue anthraquinone (ABA) is only adsorbed on the NiO. The effective specific surface area Seff and effective diameters D _eff of NiO nanoparticles are calculated from the adsorption isotherms of ABA on NiO composites and on NiO synthesized without a carrier. S _eff of NiO nanoparticles decreases from 76 to 42 m²/g and D _eff increases from 8 to 14 nm with rising NiO content in the composites. The NiO nanoparticles synthesized without a carrier are characterized by the lowest S _eff (30 m²/g) and the largest D _eff (20 nm).     

Selective water sorbents for multiple applications. 12. Water sorption equilibrium at elevated temperature

In this communication we present the experimental data on water sorption equilibrium for SWS-1L (CaCl₂ in mesoporous silica) measured at an elevated temperature of 150^o to 260^oC and the corresponding vapor pressure P_H2O of 1.1 to 9.2 bar. A comparison of these data with those obtained at lower T (30-150^oC) and P_H2O (8-130 mbar) is made. All experimental data appear to fall on the same temperature-independent curve «water sorption vs. relative vapor pressure» which indicates a universal mechanism of water sorption over the whole T-P range.     

Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40?10^?6 m–1000?10^?6 m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D _p (60 Å) =1.95?10^?10 [m²/s] and D _p (90 Å) =5.8?10^?10 [m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.     

Block carbon articles of cellular structure: Special processing features,range of applications

In catalytic and sorption processes mineral and carbon-mineral block articles find at present growing application. In the Institute of Problems of Hydrocarbons Processing, Siberian Division, Russian Academy of Sciences, a process was developed for production of blocks of cellular structure containing 99 wt% of carbon with a developed porous structure of adjustable pore volume V _Σ = 0.2–0.5 cm³ g^?1, specific area ABET = 5–500 m² g^?1, pore radius 4–40 nm, and mechanical strength 40–120 kg cm^?2.     

Diffusion of n-alkanes in mesoporous 5A zeolites by ZLC method

Diffusion properties of mesostructured zeolite 5A were investigated by employing n-alkanes as probe molecules using the zero length column (ZLC) method. The mesopores were found to enhance molecule diffusion. Moreover, the effective diffusion time constant (D _eff/R ²) increased with mesoporosity in the zeolites between 308 K and 393 K, whereas the activation energy decreased with increasing mesopore volume. The effective diffusivity values of n-alkanes in mesoporous zeolite 5A were generally higher than that the microporous zeolite 5A sample. This clearly implied the important role of the mesopore in zeolites crystals in facilitating the transport of reaction molecules due to shorter average diffusion path length and less steric hindrance.     

Sorption kinetics of 1-fluoro-1,1-dichloroethane in vinylidene chloride-acrylonitrile-styrene terpolymer

The sorption kinetics of liquid 1-fluoro-1,1-dichloroethane (HCFC-141b) and its vapor in vinylidene chloride (VDC)-acrylonitrile (AN)-styrene (St) terpolymers were investigated by weight gain method. It was found that the sequence of the effect of monomer unit on the barrier property for HCFC-141b is AN>VDC>St at the same molar content. The diffusion mechanism of HCFC-141b in VDC-AN-St terpolymer depends on the glass transition temperature (T_g) of VDC terpolymers, sorption temperature, vapor pressure and so on. For Fickian diffusion, the diffusivity (D) is exponential function of vapor pressure at the same temperature. A quantitative relationship between D in terms of HCFC-141b in VDC-AN-St terpolymer with composition VDC/AN/St=55.7/12.9/31.4 (wt), temperature and activity was obtained, and the activation energy of diffusion is 37.68 KJ/mol.     

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⁺.     

Preparation,characterization and crystal structure of N,N-dimethylanilinium β-octamolybdate dihydrate

N,N-dimethylanilinium β-ocatmolybdate dihydrate has been synthesized in acidic aqueous solution. The compound has been identified by using TG, DTG, IR and ¹H NMR techniques. It crystallizes in the triclinic system, space group PĪ, Z = 1, a = 11.755(3) Å, b = 11.836(5) Å, c = 10.498(2) Å, α = 105.29(2)°, β = 81.56(3)°, γ = 115.24(3)°, V = d1273.4(8) Å, D_o = 2.23(1) Mg m⁻³, D_x = 2.23 Mg m⁻³, R = 0.029 and R₂ = 0.032 for 5259 observed reflexions. Two crystallographically independent [C₈H₁₂N]⁺ cations, one water molecule and one centrosymmetric β-octamolybdate polyanion are present in the asymmetric unit. Hydrogen bonds of types NH ···O and OH···O seem to stabilize the structure.     

Selective water sorbents for multiple applications, 4. CaCl2 confined in silica gel pores: Sorption/desorption kinetics

This paper presents experimental data on water sorption/desorption kinetics on composite SWS-1L and SWS-1S materials, bulk aqueous CaCl₂ solutions and pure KSKG silica gel. Desorption kinetic curves are measured in the temperature range of 328–363 K at different vapor pressures. First order kinetics is found for both SWS materials and the bulk aqueous solution with the apparent activation energies of the water desorption equal to 23.5 kJ/mol and 48.6 kJ/mol, respectively. The difference in the kinetic behavior of the bulk and disperse systems is discussed.     

Effects of supercritical CO2 exposure on diffusion and adsorption kinetics of CH4, CO2 and water vapor in various rank coals

The physico-chemical effects caused by supercritical CO₂ (ScCO₂) exposure is one of the leading problems for CO₂ storage in deep coal seams as it will significantly alter the flow behaviors of gases. The main objective of this study was to investigate the effects of ScCO₂ injection on diffusion and adsorption kinetics of CH₄, CO₂ and water vapor in various rank coals. The powdered coal samples were immersed in ScCO₂ for 30 days using a high-pressure sealed reactor. Then, the diffusion and adsorption kinetics of CH₄, CO₂ and water vapor in the coals both before and after exposure were examined. Results indicate that the diffusivities of CH₄ and CO₂ are significantly increased due to the combined matrix swelling and solvent effect caused by ScCO₂ exposure, which may induce secondary faults and remove some volatile matters that block the pore throats. On the other hand, the diffusivities of water vapor are reduced due to the elimination of surface functional groups with ScCO₂ exposure. It is concluded that density of the surface function groups is the controlling factor for water vapor diffusion rather than the pore properties. The unipore model and pseudo-first-order equation can simulate the diffusion and adsorption kinetics of CH₄ and CO₂ very well, but the unipore model is not capable of well describing water vapor diffusion. The effective diffusivity (D_e), diffusion coefficient (D) and adsorption rates (k₁) of CH₄ and CO₂ are significantly increased after ScCO₂ exposure, while the values of water vapor are decreased notably. Thus, the injection of ScCO₂ will efficiently improve the transport properties of CH₄ and CO₂ but hinder the movement of water molecules in coal seams.     

Surface energetics of calcium carbonates using inverse gas chromatography

Various calcium carbonate samples were characterized by inverse gas chromatography (IGC) at infinite dilution. The interactions between the samples and hydrocarbon probes, C₅–C₁₀ were related to the retention volume in gas chromatographic experiments. The surface energetics of chalk, marble and precipitated calcium carbonate (PCC) were determined in terms of the apolar component of the surface free energy γ_S^LW and the differential enthalpy of adsorption, −ΔH_A^∘. These results were evaluated with respect to bulk chemical composition, BET surface area and pore structure. The results suggest that physi- and chemisorbed water bound at surface sites and within the pore structure significantly influence the surface properties of the calcium carbonates. The values of γ_S^LW and −△H_A^∘ after redeposition of the water adlayer suggested reversibility of the water sorption process and the resulting changes in the energetics of the surfaces. Values of γ_S^LW for the chalk samples in the initial state were 140–180 mJ m⁻², whereas the marble and PCC were ≈55mJ m⁻². Removal of bound and pore water by heating at elevated temperatures caused a progressive increase in the γ_S^LW to ≈250 mJ m⁻² for the PCC sample. The γ_S^LW of the chalk sample also increased but to a much lesser extent. △H_A^∘ values for the samples followed the trend chalk>marble>PCC.     

Sorption equilibria of CO2 on silica-gels in the presence of water

The sorption equilibria of carbon dioxide on three types of silica gel (SG) with different pore size distributions in the presence of water were studied experimentally using a volumetric method at 275?K with pressures from 0 to 3.7?MPa. Both the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO₂ hydrates. For wet silicon gel A(SG-A) with water loading ratio of 0.75, the highest CO₂ sorption was about 2.5?mmol of CO₂ per gram of dry sorbent at 275?K. Similarly, the highest sorption was about 2.7?mmol for wet SG-B with R _w =0.81. However, CO₂ hydrate did not form on the wet surface of SG-C due to its large pore sizes.     

Substructure of a rubidium-ion-exchanged form of the silicate nepheline hydrate I

X-Ray structure analysis of a nepheline hydrate I crystal, Rb⁺-exchanged at 80°C, was performed making use only of the main diffractions. The resulting substructure was found to be orthorhombic with a = 8.0802(8), b = 15.259(2), c = 5.1584(5) Å, V = 636.0ų, space group Pnm2₁. Fourier and least-squares techniques gave the residuals R = 0.048 and R_w = 0.058, and a tentative formula of RbNa₂Al₃Si₃O₁₂ · H₂O (Z = 2, D_c = 2.65 g cm^?3). Tetrahedral distances were consistent with Al,Si alternation in the framework. Of the channel species, Na(1) and Na(2) were found not to be exchangeable at the current temperature. These sodium atoms are located in the small cages, formed by 6-rings of O atoms which connect the 8-ring channels parallel to c into two-dimensional pore systems. In the larger tunnels the replacement was complete and these contain a Rb⁺ ion and probably a water molecule in symmetry-related positions. According to this model, Rb⁺ coordinates four oxygens of an 8-ring and two water molecules, with RbO distances in the range 2.81–3.36 Å. Additional O atoms are found at greater distances.     

Development of procedures for preparing sorbents with improved structural characteristics from anthracite mining waste

Various procedures were suggested for activating anthracite mining waste (fine fraction) to obtain microporous sorbents with 60% (by weight) yield of the final product and pore structure characteristics (SBET = 400–600 m² g^?1, sorption pore volume 0.26 cm³ g^?1) close to those of commercial activated coals.     

Effective moisture diffusivity and activation energy during convective drying of bread containing clove oil/orange oil

The aim of present study was to investigate the characteristic drying behaviour of bread with the convective drying method for increasing bread shelf life. Effective moisture diffusivity and activation energy were compared in detail. According to the results, bread samples were dried between 0 and 450 min for 40 °C, 0–180 min for 50 °C and 60 °C, respectively. The experimental data with high coefficient of determination (R²) changed between 0.889 and 0.998. The values of D_eff were obtained between 1.21 × 10^?9-1.22 × 10^?8 m²/s. Also, E_a values were found to be in range of 82.47–100.49 kJ/mol for bread samples which had additive-free and additive. When the bread samples without additives and the breads with essential oils were compared, it was found that the activation energy increased with the use of additives. Moisture content values decreased with the increase in time. Drying rate and moisture content relation showed the expected behaviour, thermally and morphologically.     

The admittance of an electrochemical cell with adsorption of electroactive species at the DME

Equations for the electrode admittance in, the case of adsorption of electroactive species have been derived, considering both a.c. and d.c. aspects of adsorption. It was shown that due to the d.c. aspects the function also contains a drop-time dependent term f(t_m): =c_OD_O^1/2+c_RD_R^1/2 +f(t_m)?s Under normal polarographic conditions the value of is constant, so c_O and c_R are drop-time dependent and consequently also the value of the Warburg coefficient σ, as well as the adsorption parameters C_LF and C_HF.     

Influence of the structure and morphology of ultrathin poly(3-hydroxybutyrate) fibers on the diffusion kinetics and transport of drugs

Ultrathin fibers of a biodegradable polymer poly(3-hydroxybutyrate) with an encapsulated drug (dipyridamole, 0–5% of poly(3-hydroxybutyrate) mass) are obtained by electrospinning. Introduction of the drug substantially affects the geometric shape and crystallinity of individual filaments as well as the total porosity of the fibrillar film on their basis. As follows from the SEM data, in the absence of the drug or at its low concentration (<3%), poly(3-hydroxybutyrate) fibers appear as ellipse-like fragments alternating with cylindrical ones. At a higher content of the drug (3–5%), the abnormal ellipse-like structures are practically absent and the fiber acquires the cylindrical shape. A set of morphological and crystallinity characteristics of the fibers determines the absorption of water and the rate of the diffusion transport of the drug as well as the corresponding profiles of its controlled release. A simplified model of drug desorption from the fibrillar film is advanced which considers two sequential stages of the process: (i) diffusion of the drug in the polymer fiber with coefficient D _f ~ 10^–12 cm²/s and dimeter φ_f ~ 2–4 μm and (ii) transport of the drug in the interfibrillar porous space filled by solvent with diffusion coefficient D _w = 5.5 × 10^–6 cm²/s. Using the characteristics of porosity, crystallinity, and geometry of the fibers and diffusion effective coefficients D _eff calculated from the profile of drug release, it is shown that the limiting stage of the transport of the drug is its diffusion in the volume of the cylindrical fiber. The model makes it possible to turn from the experimental values of D _eff to partial diffusion coefficients D _f and to calculate the kinetic profile of drug release with allowance made for the above-listed factors.     

Continuous sorption of synthetic dyes on dried biomass of microalga Chlorella pyrenoidosa

The sorption of thioflavine T (TT) and malachite green (MG) cationic synthetic dyes on dried biomass of green microalga (Chlorella pyrenoidosa) immobilised in polyurethane foam under continuous column systems conditions using spectrophotometric methods of detection was investigated. Data characterising the sorption of TT and MG on microalgal biomass immobilised in polyurethane foam in a column system from single (C ₀ = 25 μmol dm^?3) or binary equimolar (C ₀ = 25 μmol dm^?3) dye solutions in the form of breakthrough curves were well described by the Thomas (R ² = 0.994–0.912), Yoon-Nelson (R ² = 0.994–0.911), and Clark (R ² = 0.993–0.911) models. Useful parameters characterising the sorption column system were obtained from these mathematical models. The Thomas model, in particular, provided the Q _max (maximal sorption capacity in μmol g^?1) parameter for characterisation of biosorbent and also for evaluation of competitive effects in the TT and MG dyes sorption. For the purposes of biomass regeneration, a one-step desorption of the dyes studied from the microalgal biomass in batch and continuous column systems was performed. Efficiency of TT desorption from microalgal biomass increased in the order: deionised H₂O (50.7 %), 99.5 vol. % 1,4-dioxane (67 %), 20 mmol dm^?3 NiCl₂ (83 %), 96 vol. % ethanol (85 %), 0.1 mol dm^?3 HCl (89 %), 1 mol dm^?3 acetic acid (89 %). In the case of MG, the desorption efficiency increased in the order: deionised H₂O (13 %), 20 mmol dm^?3 NiCl₂ (50 %), 0.1 mol dm^?3 HCl (91 %), 99.5 vol. % 1,4-dioxane (94 %), 1 mol dm^?3 acetic acid (99 %), 96 vol. % ethanol (> 99 %). The presence of carboxyl, phosphoryl, amino, and hydroxyl groups, the important functional groups for sorption of cationic xenobiotics, was also confirmed on the algae biomass surface by potentiometric titration and ProtoFit modelling software. The data obtained showed that the dried immobilised algae biomass could be used as a sorbent for removing toxic xenobiotics from liquid wastewaters or contaminated waters and also presenting the possibilities of mathematical modelling of sorption processes in continuous column systems in order to obtain important parameters for use in practice.     

Molecular interactions and structures in ethylene glycol-ethanol and ethylene glycol-water solutions at 303 K on densities, viscosities, and refractive indices data

Molecular interactions and structural fittings in binary ethylene glycol + ethanol (EGE, x _EG = 0.4111–0.0418) and ethylene glycol + water (EGW, x _EG = 0.1771–0.0133) mixtures were studied through the measurement of densities (ρ), viscosities (η), and refractive indices (n _D ) at 303.15 K. Excess viscosities (η ^E ), molar volumes (V _m ), excess molar volumes (V _m ^E ), and molar retractions (R _M ) of the both binary systems were computed from measured properties. The measured and computed properties have been used to understand the molecular interactions in unlike solvents and structural fittings in these binary mixtures.