Silica Gel System Research Articles

Highly efficient separation and equilibrium recovery of H2/CO2 in hydrate-based pre-combustion CO2 capture

Gas hydrate-based CO2 capture processes have attracted considerable attention due to their potentials for energy-efficient pre-combustion CO2 capture. Recent investigations have explored the use of tailored-wettability porous silica gels, highlighting benefits in thermodynamic and kinetic efficiencies, specifically characterized by low energy requirements and rapid formation. However, achieving high purity levels for both H2 and CO2 is crucial for practical implementation. Consequently, identifying and optimizing an effective separation route becomes imperative. In this study, we examined the thermodynamic stability, gas uptake, and separation factors of THF (5.56 mol%) + H2 + CO2 hydrates with varying compositions (H2:CO2 = 80:20, 60:40, 30:70, or 20:80 mol%) in C0 and C1 silica gel (functionalized by monofunctional alkylsilanes (X-(CH3)2-Si-Cn)) systems with SDS (0 or 500 ppm). Pressure-composition diagrams for THF + H2 + CO2 systems in C0 and C1 silica gel were meticulously measured. Notably, the C1 silica gel system without SDS demonstrated good thermodynamic stability, substantial gas uptake, and a significant separation factor. Based on the pressure-composition diagram of the C1 silica gel system, we proposed a highly efficient route for separating H2 and CO2. This proposed cyclic process involves a three-stage reactor and achieve to gas hydrate-based pre-combustion CO2 capture, yielding a purity of approximately 91 % H2 and 94 % CO2. The present findings provide valuable insights into optimizing the wettability of porous media and efficient separation routes, demonstrating the feasibility of a gas hydrate-based pre-combustion carbon dioxide capture process.

Thin-layer chromatography of DNS amino acids derivatives in systems with silica gel and silanized silica gel plates

Abstract Investigations into separation selectivity of High-Performance Thin-layer chromatography (HPTLC) of dansyl (DNS) derivatives of amino acids in silica gel (Silica gel 60 F254s plates) and silanized silica gel (RP-18 W plates) systems are presented. The results have been obtained for mobile phases containing different concentrations of acetonitrile (ACN) in formic acid (FA) water solution (final concentration of FA in the mobile phase was equal to 265 mmol/dm3). The data obtained show differences in separation selectivity of the solutes between employment of HPTLC silica gel and RP-18 W systems.

Investigation of relaxation processes and phase transitions in the silica gel-undecylenic acid system using IR spectra in a wide temperature range

The study of relaxation processes in porous inhomogeneous systems via dielectric and mechanical spectroscopy methods is associated with methodological difficulties. To understand how IR spectroscopy can be used to elucidate the temperature-dependent changes that take place in the undecylenic acid - porous silica gel systems, such as phase transition and relaxation processes, we compare IR spectroscopic data with previously obtained dielectric spectroscopy data for the bulk undecylenic acid and undecylenic acid embedded in silica gel matrices of different pore sizes. We demonstrate that the topological soliton model can be used for both bulk undecylenic acid, and the undecylenic acid in nanoporous silica gel matrices.

Long-term dechlorination of cis-DCE to ethene with co-immobilized Dehalococcoides mccartyi BAV1 and Clostridium butyricum in silica gel system

Chloroethenes are common groundwater pollutants, and have been classified as toxic and carcinogenic to humans. The metabolites of chloroethenes, cis-dichloroethene (cis-DCE) and vinyl chloride (VC) commonly accumulate in groundwater due to their recalcitrant reductive dechlorination under anaerobic conditions. Dehalococcoides mccartyi (Dhc) is the key anaerobic bacteria for complete dechlorination of chloroethene, and Clostridium butyricum (C. butyricum) can provide hydrogen for supporting the growth of Dhc. In this study, we co-immobilized Dhc strain BAV1 and C. butyricum in a silica gel to determine the ability of the complete dechlorination of cis-DCE. Our results showed that our immobilized system could protect BAV1 from a high concentration (8 mM) of cis-DCE to carry out complete dechlorination. After the long-term use of our immobilized system, the activity of complete dechlorination was maintained for more than 180 consecutive days. Furthermore, we applied the immobilized system to remediate contaminated groundwater and uncovered the complete dechlorination of cis-DCE into ethene, a non-toxic product, within 28 days. Therefore, this novel co-immobilized system could serve a solution for bioremediation at chloroethene-contaminated sites.

하이브리드 데시컨트 제습기의 해석 모델

An analytical model is presented for a hybrid desiccant dehumidifier where a vapor compression refrigeration dehumidifier is augmented with a desiccant wheel in order to provide improved dehumidification performance. The performance indices of a hybrid desiccant dehumidifier are expressed explicitly in terms of its general design and operating parameters so that various combinations of refrigerants and desiccant wheels can be evaluated. The model is validated through the prediction of the performance of a commercial hybrid dehumidifier with a polymer desiccant wheel. In comparison with refrigeration dehumidifiers, the hybrid dehumidifier is predicted to have 26~ 55% higher efficiency. In comparison with a silica gel system, the polymer system is predicted to have 20% higher efficiency.

Performance of a solar adsorption cooling and desalination system using aluminum fumarate and silica gel

• Aluminum Fumarate is evaluated in a solar hybrid cooling and desalination system. • The comparison with silica gel spotlights the net effects of a dynamic heat source. • Interrelated effects of thermal and adsorption characteristics are critical issues. • Aluminum Fumarate performance is affected negatively by the cumulative heat stored. • Silica gel system is more responsive to changes in the initial heating temperature. This paper numerically investigated the influence of adsorbent materials’ thermal and adsorption characteristics on the overall performance of solar adsorption cooling cum desalination systems. A case study using an array of solar collectors was conducted to compare the emerging Aluminum Fumarate metal–organic framework (Al-Fum) with conventional silica gel (SG) under typical meteorological data at a selected site. Although the adsorption characteristics of Al-Fum outperforms SG at the material level, the former’s low thermal characteristics increased the cumulative heat stored and limited the integrated-system performance. The low thermal diffusivity of Al-Fum slowed down the integrated system’s response, providing that the average solar COPs of the SG-based system over different months were higher by 83%, 43%, and 22% at inlet chilled water temperatures of 15 °C, 20 °C, and 25 °C, respectively, and 1 mm fin spacing. However, the best specific cooling power of the AF-based system were higher than those of the SG-based system by − 16.6%, 16.8%, and 30.5% at these temperatures. Furthermore, the SG-based system was more negatively affected by reducing the heat storage initial temperature from 70 °C to 50 °C, but it attained COP and solar COP higher than those of the AF-based system by 14.9%–63%, respectively.

Pressurized planar electrochromatography of DNS amino acids derivatives in silica gel and silanized silica gel systems with formic acid addition to the water mobile phase

Pressurized planar electrochromatography (PPEC) of dansyl (DNS) derivatives of amino acids in normal- and reversed-phase systems is presented. The results have been obtained for mobile phases with different acetonitrile (ACN) concentrations (0–85%). The data obtained show differences in separation selectivity between high-performance thin-layer chromatography (HPTLC) and PPEC systems. These differences originate from the electrophoretic effect which is involved in the PPEC system, contrary to the HPTLC one.

Rhamonolipids produced by Pseudomonas aeruginosa promotes methane hydrates formation in fixed bed silica gel medium

Natural gas hydrates are seen as an alternative future energy source. They have also been valued for their carbon dioxide capturing capability, gas separation, desalination, natural gas storage and transportation. Developing economical and viable gas hydrate based technology is one of the most promising research areas of present decade. Successful commercialization of gas hydrate based technology is often curtailed due to slow formation rate. The present study evaluates biosurfactant as a kinetic promoter of methane hydrates formation in a fixed bed C type silica gel medium. Biosurfactant was produced by growing Pseudomonas aeruginosa strain A11 in glycerol supplemented mineral salt medium. Biosurfactant characterization with FTIR, NMR and MALDI-TOF spectroscopy reveled it to be a glycolipids type biosurfactant namely rhamnolipids. Saturating C type silica gel with of 100 ppm rhamnolipids solution enhanced the rate of methane hydrates formation by reducing the induction time. Mole of methane consumed and percentage of water to hydrate conversion was observed to be more in 1000 ppm rhamnolipids saturated C type silica gel as compared to quiescent water system and water saturated silica gel system. Overall results suggest that rhamonolipids produced by strain A11 in combination with silica gel can be utilized as environmentally safe kinetic promoter for methane hydrate formation.

Comprehensive exploration of the ultraviolet degradation of polychlorinated biphenyls in different media

As one of the most important natural transformation processes, photodegradation deserves more attention and research. In the current work, we comprehensively explored the photochemical behaviors of polychlorinated biphenyls (PCBs) in n-hexane (Hex), methanol/water, and silica gel under UV-irradiation. Photodegradation rates were found to be faster in methanol/water than in Hex. All of the three photochemical systems generated sigmatropic rearrangement products. The dominant photodegradation pathways were dechlorination, dechlorination/methoxylation/hydroxylation, and hydroxylation in Hex, methanol/water, and silica gel systems, respectively. Furthermore, some new photodegradation products, such as polychlorinated biphenyl ethers, polychlorinated dibenzofurans, polychlorinated biphenylenes, and methylated polychlorinated biphenyls, are reported for the first time. These findings would provide deeper insight into the phototransformation behaviors of PCBs.

Evaluation on performance of solar adsorption cooling of silica gel and SAPO-34 zeolite

As a technology of the green energy utilization, solar adsorption cooling is a promising way to make use of the solar energy in the future. Aiming to the efficiency improvement of such kind system, the performance of the solar adsorption cooling system that employed the silica gel-water as the working pair was evaluated experimentally. With a mono-axial solar collector of tracking parabolic trough to provide the heat supply to the adsorption bed, the effect of the adsorption time on the system performance was mainly addressed in the study. The experimental results revealed that the performance of the system reached the maximum as the adsorption time was 45 min. Correspondingly, the coefficient of performance of the system reached 0.258. In addition, a comparison of the optimal performance of the silica gel system to the SAPO-34 zeolite system was conducted. It was revealed that both the cooling capacity and the performance coefficient of the silica gel system depended more strongly on the adsorption time than those of the SAPO-34 zeolite system did. At the optimal adsorption time, the coefficient of performance of the silica gel system was 1.93 times as that of the SAPO-34 zeolite system. In general, the silica gel-water pair has shown better performance as compared to the SAPO-34 zeolite-water pair as used in the solar adsorption cooling system.

SF6 Hydrate Formation in Various Reaction Media: A Preliminary Study on Hydrate-Based Greenhouse Gas Separation.

SF6 hydrate formation behaviors in various reaction media, such as bulk water, porous silica gel, and hollow silica, were investigated for hydrate-based SF6 separation with a primary focus on thermodynamic stability and formation kinetics. The measured three-phase (H-LW-V) equilibria demonstrated that the types of reaction media used in this study had no effect on the thermodynamic stability of SF6 hydrates. The dissociation enthalpy (ΔHd) of SF6 hydrate was measured using a high-pressure micro-differential scanning calorimeter, and it corresponded well with estimates from the Clausius-Clapeyron equation. The unstirred porous silica gel system showed a larger gas uptake and a higher growth rate at the early stage of SF6 hydrate formation. However, the gas uptake and growth rate of SF6 hydrates in stirred bulk water and unstirred hollow silica were significantly increased at a larger temperature driving force or in the presence of sodium dodecyl sulfate. The experimental results obtained in this study will be very helpful for a better understanding of the thermodynamic and kinetic characteristics of SF6 hydrate formed in various reaction media and in surfactant-added solution, and are expected to contribute to further development of the hydrate-based SF6 separation process.

Photon Upconverted Emission Based on Dye-Sensitized Triplet–Triplet Annihilation in Silica Sol–Gel System

Photon upconverted emission based on dye-sensitized triplet–triplet annihilation was observed in silica gel systems containing Pt(II) octaethylporphyrin (triplet sensitizer) and 9,10-diphenylanthracene (singlet emitter). The triplet sensitizer was encapsulated and highly dispersed in the silica gels prepared by the sol–gel method. The singlet emitter was adsorbed on the silica gel pores accessible to the outside. Phosphorescence of the triplet sensitizer was partially quenched, and the singlet emission was enhanced with an increase in the concentration of the singlet emitter. The emission intensity increased in proportion to the approximate square of the irradiation power. The triplet energy transfer from some of the encapsulated triplet sensitizer molecules to the adsorbed singlet emitter molecules was observed in the silica gels followed by the triplet–triplet annihilation and upconverted singlet emission. The phosphorescence quenching and upconverted singlet emission were more significantly observed in the gel dried at a lower temperature (wetter gel). The wetter gel contained higher amounts of solvent and water molecules, in which the triplet sensitizer and singlet emitter should collide and then the sensitized emitters should collide between themselves during their excited-state lifetime. The photon upconversion process required the triplet sensitizer and singlet emitter molecules to be in an environment similar to the solvents.

Interfacial Structure and Evolution of the Water–Silica Gel System by Reactive Force-Field-Based Molecular Dynamics Simulations

Nanoporous silica gel structures and associated interfaces formed on the surface of silicate and borosilicate glasses play an important role in understanding the dissolution mechanisms of these glasses. Interfacial models that consist of bulk silica, nanoporous hydrated silica gel, and bulk water were constructed and their evolution was studied to understand the water–glass reaction fronts using the Reactive Force Field (ReaxFF)-based molecular dynamics simulations. The short- and medium-range structures of the gel and the interfaces as well as water diffusion and silica dissolution behaviors were studied in detail. It was found that the gel region exhibited an increase in Si–O network connectivity with time, consistent with recent NMR results, due to cross-linking of siloxane bonds in the gel and the dissolution of less connected [SiO4] groups into the water region. Higher network connectivity of the silica gel can regulate transport of ions and plays the role of passivation. Dissolved silica clusters in...

Methodology for Rapid Isolation of Moringin: Potential Anticancer Compound from the Seeds of Moringa stenopetala

The seeds of Moringa stenopetala which are known to be rich sources of glucosinolates, primarily glucomoringin, have been shown to have limited anticancer effects when tested in vitro. In the present study, however, the water extract of the seeds obtained following defatting by hexane displayed potent cytotoxic activity against HepG2 (IC50, 6.28 ± 0.55 μg/ml) and the SH-SY5Y human neuroblastoma (IC50, 9.81 ± 1.30 μg/ml) cells. The methanol extract displayed a weak cytotoxic activity against the HepG2 human hepatocellular cancer cells when tested upto 500 μg/ml, while extraction with hexane yielded the non-cytotoxic fixed oil which fatty acid composition was primarily oleic acid (75%). By monitoring the constituents of the water extract by HPLC and a one-step combiflash chromatographic system using C-18 silica gel system, the principal active constituent (glucomoringin isothiocyanate or moringin; 4(α-L-rhamnosyloxy)-benzyl isothiocyanate) was isolated. Moringin was 6.3 and 2.4 times more potent than etoposide in the HepG2 and SH-Sy5Y cell lines respectively. The isolation of this potent potential anticancer compound from the seeds of M. stenopetala without the need for multi-step chromatographic and enzyme-digestionbased purification steps are discussed.

A fractal approach on modeling gas hydrate phase equilibria in porous media

A thermodynamic model based on the reaction-adsorption two-step formation mechanism was improved by introducing fractal theory to predict hydrate phase equilibria in porous media. The surface effect on phase equilibrium of porous media system was modified by considering the shape of the pore edge, which was supposed to hold a fractal feature as von Koch curve. A fractional dimension Laplace equation was established in describing the phase equilibrium conditions of methane, ethane, propane, and carbon dioxide hydrates in silica gel pores. The calculated results showed that when the shape of the pore edge is assumed as spherical, the calculations by the thermodynamics model developed are close or a little superior to those of traditional van der Waals-Platteeuw type models. When the surface effect of the pore edge shape is introduced, the absolute average deviations for silica gel systems can be further decreased.

Thin-layer chromatographic method for separation of wheatgrass pigments on sucrose impregnated silica gel plates

One of the most important aspects of the selected analytical method is avoiding the degradation of the target compounds during the analysis of the samples. Chromatographic techniques, particularly thin-layer chromatography (TLC), are widespread in this field. However, difficulties arise in applying chromatographic methods, such as separation efficiency, and stability of target compounds. The application of silica gel as stationary phase might be an appropriate choice [2], but at the same time, the degradation of the pigment compounds is fast, so the analysis has to be done relatively quickly [3]. In order to avoid degradation, a column filled with sucrose was used as adsorbent for isolation of chlorophylls [4, 5] and home-made thin-layer plates for analysis [6–8]. However, the resolution was rather limited. The aim of this investigation was to find a rapid and simple analytical method for the separation of the pigments originated from commercial wheat grass extracts without any degradation product generated during the analysis of the samples. The sucrose immersed silica gel system fulfilled all of these requirements. 2 Experimental

Fractionation of an Extract ofPluchea odorataSeparates a Property Indicative for the Induction of Cell Plasticity from One That Inhibits a Neoplastic Phenotype

Introduction. Several studies demonstrated that anti-inflammatory remedies exhibit excellent anti-neoplastic properties. An extract of Pluchea odorata (Asteraceae), which is used for wound healing and against inflammatory conditions, was fractionated and properties correlating to anti-neoplastic and wound healing effects were separated. Methods. Up to six fractionation steps using silica gel, Sephadex columns, and distinct solvent systems were used, and eluted fractions were analysed by thin layer chromatography, apoptosis, and proliferation assays. The expression of oncogenes and proteins regulating cell migration was investigated by immunoblotting after treating HL60 cells with the most active fractions. Results. Sequential fractionations enriched anti-neoplastic activities which suppressed oncogene expression of JunB, c-Jun, c-Myc, and Stat3. Furthermore, a fraction (F4.6.3) inducing or keeping up expression of the mobility markers MYPT, ROCK1, and paxillin could be separated from another fraction (F4.3.7), which inhibited these markers. Conclusions. Wound healing builds up scar or specific tissue, and hence, compounds enhancing cell migration support this process. In contrast, successful anti-neoplastic therapy combats tumour progression, and thus, suppression of cell migration is mandatory.

Fabrication of a Novel Catalyst Support with Hierarchical Pore Structure

A novel catalyst support with trimodal pore structure was hydrothermally synthesized by building up nano-particles of titanium silicalite-1 inside the macroporous system of silica gel using the tetrapropylammonium hydroxide (TPAOH) as template, titanium (IV) tetrabutoxide monomer (TBOT) as titanium source and the silica gel with macropores as in situ silicon source as well as matrices. The prepared support exhibited intrinsic pore of TS-1, intercrystalline mesopores and residual macropores of silica gel, accomplishing the interconnection of micro-, meso-, and macrpores.

Trimodal pore catalyst preparation method by growth of zeolite inside macroporous matrices of silica

In this paper, a novel catalyst support with trimodal pore structure was hydrothermally synthesized by building up nano-particles of titanium silicalite-1 inside the macroporous system of silica gel using the tetrapropylammonium hydroxide (TPAOH) as template, titanium (IV) tetrabutoxide monomer (TBOT) as titanium source and the silica gel with macropores as in situ silicon source as well as matrices. The prepared support exhibited intrinsic pore of TS-1, intercrystalline mesopores and residual macropores of silica gel. When loaded with Co, the trimodal catalyst was employed to catalyze the methanation of carbon monoxide, showing higher CO conversion and CH 4 selectivity than the bimodal and unimodal catalysts due to the favored metallic Co surface area and dispersion.

Regulation of Potassium Aminocarboxylates on Calcium Oxalate Crystal Growth and Its Relationship with Molecular Structure

The effect of potassium aminocarboxylates on crystallization of calcium oxalate (CaOxa) was investigated in silica gel system by means of scanning electron microscopy and X-ray diffraction. These aminocarboxylates included potassium aminoacetate (KGLY), dipotassium glycoletherdiaminotetraacetate (K2EGTA), dipotassium aminotriacetate (K2NTA), dipotassium diethylenetriaminepenteacetate (K2DTPA), dipotassium ethylene diamine tetraacetate (K2EDTA) and dipotassium cyclohexanediamine tetraacetate (K2CDTA). All these aminocarboxylates could induce the formation of calcium oxalate dihydrate (COD), inhibit the aggregation of calcium oxalate monohydrate (COM) and decrease the specific surface area of COM aggregates. The ability to induce COD formation follows the order: K2DTPA (55wt%) > K2EDTA ≈K2CDTA (50wt%) > K2NTA (43wt%) >> K2EGTA (4wt%) > KGLY (2wt%), and the ability to inhibit COM aggregation follows the sequence: K2DTPA>K2NTA > K2CDTA≈ K2EDTA > K2EGTA > KGLY. These results are discussed in terms of their molecular structure, relative content of carboxylic groups, spatial location of carboxyl groups in aminocarboxylates, and their coordination capacity and modes with Ca ions. It is proved that K2NTA and K2DTPA can be the potential drugs for preventing the formation of CaOxa stones.