Alumina Gel Research Articles

Single and Binary Mixture Adsorption Behaviors of C6–C8 Hydrocarbons on Silica–Alumina Gel

To ensure the technical use of natural gas, heavy hydrocarbons and other components must be separated. Therefore, in this work the adsorption of C6–C8 hydrocarbons n-hexane, n-heptane, n-octane, benzene, toluene, and cyclohexane on a commercial silica–alumina gel (Sorbead H) was investigated in experiments and dynamic simulations. Single and binary mixture equilibrium isotherms were determined from cumulative breakthrough curve experiments on a fixed bed adsorber at 25–75 °C and 1.3 bar (abs) in the trace range up to approximately 5000 ppmmol. The adsorption behavior is interpreted on the basis of the molecular structure of the adsorptive, the surface chemistry, and the pore structure of the adsorbents. Binary mixture isotherms were calculated using the theory of the ideal adsorbed solution (IAST). The results were in good agreement with experimental data. The adsorption dynamics was investigated by breakthrough curve experiments and simulated dynamically using an isothermal model based on mass balances a...

Fabrication of α-alumina by a combination of a hydrothermal process and a seeding technique

This paper describes a method for producing [Formula: see text]-Al2O3 at low temperatures by a combination of a hydrothermal process and a seeding technique. White aluminum hydroxide precipitate was prepared by a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution. Peptization of the precipitate by acetic acid at room temperature transformed it into a transparent alumina sol. The alumina sol was treated with a hydrothermal process. [Formula: see text]-Al2O3 particles serving as seeds were added to the hydrothermally treated alumina sol. The sol containing the [Formula: see text]-Al2O3 particles was transformed into an [Formula: see text]-Al2O3-seeded alumina gel by drying at room temperature. The non-seeded alumina gel was amorphous or showed fine crystallites and began to crystallize into [Formula: see text]-Al2O3 at 900[Formula: see text]C. The [Formula: see text]-Al2O3-seeding promoted the crystallization of the alumina gel to [Formula: see text]-Al2O3. A remarkable [Formula: see text]-Al2O3 crystallinity was achieved with an increase in [Formula: see text]-Al2O3 particle content by weight in the final seeded alumina gel. For an [Formula: see text]-Al2O3 particle content of 5%, the seeded alumina gel was partially crystallized to [Formula: see text]-Al2O3 by annealing at temperatures as low as 600[Formula: see text]C.

Development and validation of a high-performance thin-layer chromatographic method for the simultaneous determination of levamisole and cocaine in seized cocaine sample

Cocaine is the second most illicit drug worldwide. Levamisole, an anthelminthic drug, has been identified as a cocaine adulterant in the United States since the last decade. Now, its presence has increasingly been discovered in street cocaine samples seized in India. Recently, it has been observed in many street cocaine samples seized by investigation agencies in India. Due to the incidence of toxicity caused by this contamination which has been increasing rapidly since 2002, it is important to understand the chemical separation, identification, and quantification of this drug. In the present study, an attempt has been made to develop a new high-performance thin-layer chromatographic (HPTLC) method for the simultaneous discrimination and quantification of levamisole in seized cocaine samples. Chromatography was performed using a pre-coated silica gel aluminum plate as the stationary phase, and the mobile phase cyclohexane—toluene—diethyl amine (75:15:10) was able to discriminate between cocaine hydrochloride and levamisole hydrochloride significantly. Densitometric analysis was performed in the absorbance mode at 230 nm. The linear regression analysis of data for the calibration curve showed good linearity over a concentration range of 100–1200 ng per band and 200–2400 ng per band with a regression value of 0.997 and 0.995 for levamisole hydrochloride and cocaine hydrochloride, respectively. The developed method is used to quantify cocaine content as well as to estimate the concentration of adulterant levamisole. The method was validated according to the International Conference on Harmonization (ICH) guidelines and can be used in the identification and quantification of levamisole and cocaine in seized cocaine samples. The present method is simple, reproducible, and repeatable, which can easily be performed in any laboratory.

A comparative study for the extraction methods and solvent selection for isolation, quantitative estimation and validation of ursolic acid in the leaves of Lantana camara by HPTLC method

To select the best organic solvent and ideal extraction technique for isolation and quantitative estimation of ursolic acid from the leaves of Lantana camara (L. camara) by high performance thin layer chromatography (HPTLC). A sensitive, fast and reproducible HPTLC method was developed and validated for estimation of ursolic acid from the leaves of L. camara. Different leaves extracts of L. camara were prepared through different extraction methods (maceration, reflux, soxhlet and ultrasound assisted extraction technique) by using four different solvents of varying polarity such as ethanol, methanol, acetone and chloroform. The maximum % extract yield was obtained in methanol, so we select methonolic extract for HPTLC evaluation. The calibration plot of standard ursolic acid with respect to peak area showed an tremendous linear relationship in the concentration range of 1000–4000 ng/spot with a correlation coefficient r2 = 0.994. The separation was completed on precoated silica gel aluminium plates 60F254 using Toluene: Acetone: Formic Acid (7.8:2.2:0.15) as mobile phase which gives a compact spot of ursolic acid (Rf value 0.49). For the proposed method (Limit of Detection) LOD (561.85 ng/spot), (Limit of Quantification) LOQ (1702.58 ng/spt), recovery of drug (99.02–101.43%) and precision (0.4303–2.1576% RSD) was found to be satisfactory. It can be concluded on the basis of HPTLC results that methanol was found to be the best solvent and Soxhlet was found to be an ideal extraction technique for the isolation of ursolic acid from L. camara leaves for routine analysis.

Extraction of water particles from atmospheric air through a Scheffler reflector using different solid desiccants

ABSTRACT In this article, an attempt has been made to extract water particles from atmospheric air by using silica gel, molecular sieve13× and activated alumina. The cycle consists of two phases, first is a nocturnal phase (night) and other is a diurnal phase (day time). In the nocturnal phase, adsorption process takes place, regeneration and condensation processes take place in the diurnal phase. The water production rate depends upon the regeneration rate of the material. A newly designed fixed focus Scheffler reflector of surface area 1.54 m2 is used to regenerate the desiccant materials. The water produced from this method is clean and can be used for potable purposes. The production rate of water is 43, 38 and 155 ml/day from 1 kg each of the molecular sieve, activated alumina and silica gel, respectively; furthermore, the adsorption rate, regeneration rate and cost analysis are also carried out.

The water resistance stability of marine lubricating oil

The marine lubricating oil was emulsified when water penetrated into it, the detergent dispersant in the lubricating oil were decomposed, emulsification could cause worse performance of detergent dispersing property, water preventive function and abrasion resistance. In this study, rubber membrane dialysis and silica gel alumina column chromatography were used for analysis of the oil phase after the water resistance test, combined with a solvent washing system with increased polarity. The results had shown that the structure of sulfurized alkylphenol salt detergent dispersant in marine oil was destroyed by water, large amount of calcium carbonate micelles was destroyed into the water phase, which caused the decrease of the total base number of the marine lubricating oil.

Stability Indicating HPTLC Method for Simultaneous Estimation of Sacubitril and Valsartan in their Pharmaceutical Dosage Form

A simple, precise, accurate and rapid high performance thin layer chromatographic method has been developed and completely validated for the estimation of Valsartan and Sacubitril in pharmaceutical dosage forms. Quantification of Valsartan and Sacubitril were carried out with precoated silica gel aluminum Plate 60 F254, (20 cm ×10 cm) 100 μm thickness as stationary phase. Toluene: Methanol: Ethyl Acetate: Glacial Acetic acid (8:2:1:1 % v/v/v). The optimized chamber saturation time before chromatographic development was 20 min at room temperature (25ºC ± 2). The length of chromatographic run was 8 cm which took average 15 min to develop. Densitometry scanning was performed using Camag TLC scanner IV with Win CATS software (V 1.4.6.2002, Camag). Optimized chromatogram of Valsartan and Sacubitril having Rf of 0.43 and 0.33, respectively. Linear relationship between peak area and concentration of standard was evaluated over the concentration range expressed in ng/band by making five replicate measurements in the concentrations range of 400-1400 ng/band and 4000-14,000 ng/band, respectively for Valsartan and Sacubitril. Literature reveals that there was no any method developed using HPTLC in simultaneous estimation of Valsartan and Sacubitril in their pharmaceutical dosage form. The proposed method can be successfully applied for the estimation of drug content of different marketed formulations.

Сорбционное концентрирование и определение методом ГКР-спектроскопии пирена с использовани- ем алюмогелей, содержащих наночастицы серебра

Получены алюмогели, содержащие наночастицы (НЧ) серебра, и оценено их использование в качестве материалов для одновременного концентрирования пирена и его детектирования методом гигантского комбинационного рассеяния света (ГКР). НЧ серебра предварительно подвергали искусственной агрегации с помощью хлорида натрия. Изучены сорбционные свойства полученных алюмогелей по отношению к пирену, и показано повышение степени извлечения пирена на сорбентах, модифицированных додецилсульфатом натрия (ДДС). Оценена возможность определения пирена, выделенного на сорбенте, методом ГКР-спектроскопии.

Adjuvant-perfluorocarbon based approach for improving the effectiveness of cryosurgery in gel phantoms

The current study suggests novel methods to enhance freezing inside the tissue mimicking gel phantoms during the cryosurgery process. In this study, freezing of gel phantoms is carried out by a cryosurgery setup and the temperature is measured in real time using a data acquisition system. Alumina is used as an adjuvant and the variation of the alumina concentration in the gel phantoms results in a decrease of end temperature achieved after cryosurgery. However, the lowest end temperature is attained when the alumina concentration in the gel phantom is 1% (w/v) and for further studies this optimal concentration is utilised. It is observed that with the increase in insertion depth of the cryoprobe (from 1 to 1.5 cm), there is a decrease in end temperature at each thermocouple location in these alumina gel phantoms. The cooling of these alumina containing gel phantoms in presence of a perfluorohexane layer reveals that there is an inhibition of freezing due to this low thermal conductivity barrier (the axial ice ball depth is reduced from 2 cm to 1.5 cm). Furthermore, with the addition of glycine (i.e. 1% (w/v) alumina 5% (w/v) glycine gel phantom), a substantial end temperature decrease is observed at the thermocouples placed nearer to the cryoprobe, thus indicating the usefulness of this strategy in enhancing localised freezing. In conclusion, this study provides various new approaches that enhance the efficacy of cryosurgery immensely.

Analysis of Pore Structure Characteristics of Carbonated Low-Clinker Cements

In this study, changes in transport properties of low-clinker cements on carbonation are investigated. Cement paste and concrete samples were cast using ordinary Portland cement and four types of blended cement. The samples were exposed to 3 ± 0.2% carbon dioxide concentration, 60 ± 5% relative humidity and 27 ± 2 °C temperature to undergo carbonation. The transport properties of uncarbonated and carbonated samples were assessed by measuring water absorption, rate of water absorption and pore structure characteristics. Elemental mapping using scanning electron microscope was carried out to investigate the changes occurring in the microstructure of cement paste on carbonation. Also, volume change occurring on carbonation of different hydration phases was computed theoretically. Irrespective of the type of blended cement, increase in porosity and restructuring of pores are observed on carbonation. The rate of water absorption in concrete is also found to be increased on carbonation. Decalcification of C–S–H and an outward migration of calcium ions from inner C–S–H and clinker grains are observed in elemental maps on carbonation. The volume change calculations show maximum reduction in solid volume on carbonation of alumina-bearing phases like AFt and AFm. The decalcified C–S–H formed on carbonation of C–S–H is found to be hydrous in nature, and the specific gravities of decalcified C–S–H and alumina gel formed on carbonation are found to lie between 2–2.15 and 2.00–2.30, respectively.

Retardation effect of elevated temperature on the setting of calcium sulfoaluminate cement clinker

The hydration of calcium sulfoaluminate (CSA) clinker at 5, 20 and 40 °C was characterized by a combination of XRD, DTA-TG and ESEM analysis (also with backscattered electron imaging, BEI). Meanwhile, the setting times and compressive strength development were studied. It was interesting to notice that elevated temperature retards the setting of CSA clinker and decreases compressive strength prominently, while it promotes the hydration heat releasement and hydration degree. With the temperature rising from 5 °C to 40 °C, the amount of ettringite formed after 1 d decreases by half, but alumina gel increases by more than 4 times, accompanying with a more inhomogeneous microstructure and higher porosity. ESEM observations indicate that such massive alumina gel covers on the unreacted particles and other hydrates, which could account for the retardation of elevated temperature on the setting of CSA clinker.

The effect of sol–gel boehmite coatings on the corrosion and decarburization of C45 steel

Sol–gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45carbon steel by dip coating. After the deposition the coatings were heat treated by drying at RT, 150 and 200 °C. It was found that for crack-free coatings, the drying temperature needs to be ≥150 °C. Properly heat-treated boehmite coatings then improve the corrosion resistance of steel, while proposed alumina coatings derived from the boehmite coatings during annealing of the steel affect the decarburization. The coated steel samples were annealed at temperatures that are typical for the heat-treatment and thermomechanical process of C45 steel, i.e., AC3 (austenitization, thermomechanical process). The sol–gel alumina coating decreased the decarburization rate of the quenched steel during the tempering (≤600 °C), which meant that the hardness reduction on the steel surface was smaller. Alumina coatings have a smaller effect on the decarburization at higher temperatures; however, the metallographic analyses indicate that the coatings can retard the oxidation rate in comparison to the decarburization rate and thus, somewhat increase the visual level of the decarburization. Under annealing conditions (T = 950 °C, t = 0.5–2 h) at which the oxidation rate is higher than the decarburization rate the decarburization process is not important since the decarburized layer is peeled off the steel surface together with the scale. No visual decarburization is then observed.

Size and Morphology Controlled Synthesis of Boehmite Nanoplates and Crystal Growth Mechanisms

The aluminum oxyhydroxide boehmite is an important crystalline phase in nature and industry. We report development of a flexible additive-free hydrothermal synthesis method to prepare high quality boehmite nanoplates with sizes ranging from under 20 nm to 5 μm via using hydrated alumina gels and aluminum hydroxide amorphous powders as precursors. The size and morphology of the boehmite nanoplates was systematically varied between hexagonal and rhombic by adjusting precursor concentrations, pH, and the synthesis temperature, due to face-specific effects. The transformation mechanism is consistent with dissolution and reprecipitation, and involves transitory initial appearance of metastable gibbsite that is later consumed upon nucleation of boehmite. Detailed X-ray pair distribution characterization of the solids over time showed similarities in short-range order that suggest linkages in local chemistry and bonding topology between the precursors and product boehmite, yet also that precursor-specific differ...

RP-HPLC AND HPTLC STABILITY INDICATING ASSAY METHODS FOR IVERMECTIN IN BULK AND TABLET DOSAGE FORM

Simple, rapid, precise, accurate RP-HPLC and HPTLC methods have been developed and validated for ivermectin in bulk and its marketed formulation. RP-HPLC method for drug was achieved on Grace C18 (250 mm X 4.6 ID, Particle size; 5 μ) column using mobile phase acetonitrile: 10 mM phosphate buffer (95:05 v/v) pH adjusted to 3 with o-phosphoric acid. Detection of drug was done at 245 nm. The retention time was found to be 5.83 min. HPTLC method for ivermectin was accomplished on a precoated silica gel aluminium plate 60F-254 (CAMAG Linomat 5), using toluene: methanol: glacial acetic acid (8:2:0.1 v/v/v) as a mobile phase. The densitometric scanning was performed at 245 nm which showed Rf 0.46 for ivermectin. The stress testing of the drug individually was carried out under acidic, alkaline, oxidation, photo-stability and thermal degradation conditions. The proposed methods were successfully applied for the determination of drug in bulk and its marketed formulation.

Load-dependent heat of adsorption of C6 hydrocarbons on silica alumina gel

In natural gas processing, adsorptive units remove higher hydrocarbons from the crude gas, for example to avoid freezing in consecutive cryogenic units. This article describes a detailed investigation on the adsorption of C6 hydrocarbons (benzene, cyclohexane, n-hexane) at low concentrations up to 5000 ppmmol in a N2 carrier gas on two industrial produced silica alumina gels. Adsorption isotherms were derived from cumulative breakthrough experiments in a fixed-bed adsorber between 25 °C and 75 °C and 1.3 bar (abs.). The isosteric heat of adsorption was determined from the temperature-dependent isotherms. Furthermore an adsorption potential model was developed to describe the temperature dependency of equilibrium capacity and heat of adsorption. The paper discusses the experimental data with respect to molecular structure of the adsorptives as well as surface chemistry and pore structure of the adsorbents.In comparison to the other adsorptives, the aromatic benzene exhibits the highest loadings and the highest heat of adsorption. In addition it shows the strongest load- and temperature-dependency of the heat of adsorption.

29Si{27Al}, 27Al{29Si} and 27Al{1H} double-resonance NMR spectroscopy study of cementitious sodium aluminosilicate gels (geopolymers) and gel-zeolite composites.

The influence of starting materials and synthesis route on the properties and the structure of cementitious sodium aluminosilicate gels is not fully understood, partly due their amorphous nature and the fact that they often contain residual reactants, which can make the results of single-pulse NMR spectroscopy applied to these materials difficult to interpret or ambiguous. To overcome some of these limitations, 29Si{27Al} TRAPDOR NMR as well as 27Al{29Si} and 27Al{1H} REDOR NMR spectroscopy were applied to materials synthesized by the one-part alkali-activation route from three different amorphous silica starting materials, including rice husk ash. The latter led to formation of a fully amorphous sodium aluminosilicate gel (geopolymer), while the materials produced from the other silicas contained amorphous phase and crystalline zeolites. Application of the double-resonance NMR methods allowed to identify hydrous alumina gel domains in the rice husk ash-based material as well as significantly differing amounts of residual silica in the three cured materials. Four-coordinated Al existed not only in the aluminosilicate gel framework but also in a water-rich chemical environment with only a small amount of Si in proximity, likely in the alumina gel or possibly present as extra-framework Al in the aluminosilicate gel. The results demonstrate how the employment of different silica starting materials determines the phase assemblage of one-part alkali-activated materials, which in turn influences their engineering properties such as the resistance against chemically/biologically aggressive media.

Highly porous and surface-expanded spinel hydrogen manganese oxide (HMO)/Al2O3 composite for effective lithium (Li) recovery from seawater

Lithium (Li) recovery from seawater is currently attracting great attention due to increasing industrial demand. Hydrogen manganese oxide (HMO) is a promising adsorbent for Li recovery from seawater, but powder-type HMO is difficult to apply and it is essential to obtain a granulated material for practical application. To minimize Li adsorption capacity loss and to obtain high mechanical stability in seawater, highly porous cylindrical HMO/Al2O3 composites have been synthesized, and their Li adsorption behavior has been investigated in seawater. Various ratios (1:4, 1:5, 1:9, 1:19, and 1:39) of lithium manganese oxide (LMO):alumina gel were tested for the synthesis of HMO/Al2O3 composites. All of the LMO/Al2O3 composites exhibited large surface area owing to the mesoporous character of γ-Al2O3. By increasing the Al2O3content in the composite, the surface area is expanded and a more porous structure is obtained, but the crystallinity of the spinel phase of LMO is decreased.After delithiation, the HMO/Al2O3 composite was applied for Li adsorption from seawater. HMO/Al2O3 composites exhibited similar Li uptakes compared to HMO powder (ca. 9 mg Li/g HMO) due to their highly expanded surface area and porous structure. During the recovery of Li adsorbed on the HMO/Al2O3 composites by acid treatment, more manganese (Mn) was dissolved from composites containing more Al2O3 due to the low crystallinity of the spinel HMO. Finally, it was found that HMO/Al2O3 containing 25% Al2O3 exhibited less than 1% Mn dissolution, and its Li adsorption performance did not decrease over five Li adsorption–desorption cycles.

Low temperature synthesis of α-alumina through a hydrothermal process combined with a seeding technique

This paper reports a method for producing α-Al2O3 at low temperatures by using a hydrothermal process and a seeding technique. White aluminum hydroxide precipitate prepared through a homogeneous precipitation method using aluminum nitrate and urea was peptized by using formic acid at room temperature to transform it into a transparent alumina sol. After the sol was hydrothermally treated, α-Al2O3 nanoparticle seeds were added to the sol. The sol containing the α-Al2O3 nanoparticles was transformed into an α-Al2O3-seeded alumina gel by drying at room temperature. The non-seeded alumina gel began to crystallize into α-Al2O3 at 500 °C. The α-Al2O3-seeding promoted the crystallization of the alumina gel to α-Al2O3. A remarkable α-Al2O3 crystallinity was achieved with an increase in α-Al2O3 content by weight in the final seeded alumina gel. Even with a content as low as 1%, the seeded alumina gel was partially crystallized to α-Al2O3 at a temperature as low as 400 °C.

Assessment of white layer in hardened AISI 52100 steel and its prediction using grinding power

ABSTRACTIn the present work, the effect of various grinding mechanisms on white layer (WL) formation in AISI 52100 steel is studied using two types of alumina grains, one produced by sol–gel process and the other by conventional fusion. Further, a novel approach is proposed on predicting the WL formation using grinding power. This study correlates the power variation with the change in the metallurgical aspects of the work material. WL of about 56 µm thickness is observed in the material ground by worn out sol–gel alumina wheel. However, no WL is present in the material ground by fused alumina wheel. High toughness in sol–gel alumina led to generation of wear flats with increasing grinding passes and transformed the dominant grinding mechanism from shearing to plowing and sliding. This increases the temperature in the grinding zone, which was the reason for WL formation. Change in the dominant grinding mechanisms from shearing is found to increase the grinding power. Since the change in dominant grinding mechanisms is the cause for WL formation, the increase in grinding power is found to be a good measure in predicting the WL formation. The predictability of WL formation by grinding power is further validated by comparing the power variation in grinding process by both the grinding wheels.

Correlation of Sol–Gel Alumina‐Supported Cobalt Catalyst Processing to Cobalt Speciation, Ethanol Steam Reforming Activity, and Stability

AbstractThe effect of sol–gel alumina characteristics on the supported Co catalyst properties was investigated at the different steps of catalyst preparation. Porous alumina with variable surface reactivity were prepared from the sol–gel transition and the spinodal decomposition induced by polymers. The hydrophobicity of polymer or the calcination temperature controls the amount of the hydroxyl groups. The dried catalysts are composed of cobalt alumina hydrotalcite‐like compounds up to 64 %. After calcination, higher proportions of CoAl2O4 are observed in the alumina presenting a greater content of hydroxyl and hydrotalcite. The Co speciation during activation investigated by Quick X‐ray absorption spectroscopy evidences that both Co3O4 and CoAl2O4 are first fully reduced to CoO and then partially transformed into point‐like Co0 nucleus. The catalysts were highly active in the ethanol steam reforming reaction; however, coke deposition leads to deactivation. This deleterious effect was minimized for catalysts operating with a CoO/Co0 ratio close to 1:3.