Adsorption Of N-heptane Research Articles

An Optimized Procedure for the Synthesis of AlSBA-15 with Large Pore Diameter and High Aluminum Content

A series of AlSBA-15 materials with different nSi/nAl ratio have been synthesized by simply adjusting the molar water to hydrochloric acid ratio (nH2O/nHCl). It was possible to control the nSi/nAl ratio, location, and coordination of Al atom in the SBA-15 silica matrix by the above method. Moreover, AlSBA-15 with nSi/nAl ratio up to 7 can be successfully prepared by adjusting the nSi/nAl ratio in the synthesis gel at nH2O/nHCl of 276. The effect of the nature of Al source in the AlSBA-15 synthesis has been investigated using different aluminum source, viz., aluminum sulfate, aluminum nitrate, aluminum hydroxide, and aluminum isopropoxide. Aluminum isopropoxide was found to be the good aluminum source for AlSBA-15 material synthesis and enhanced the amount of aluminum incorporation, location, and coordination in the SBA-15 silica walls. The effect of synthesis temperature of AlSBA-15 materials has also been reported. Nitrogen adsorption measurement shows that the pore diameter of AlSBA-15 can be tuned from 9.7 to 12.5 nm by simply adjusting crystallization temperature from 100 to 130 °C. The pore volume increases from 1.35 to 1.55 cm3/g with a concomitant decrease of the surface area from 930 to 783 m2/g. For the first time, the mechanical stability of hexagonal AlSBA-15 materials was studied by applying different pelletizing pressures and subsequent characterization by XRD, N2 adsorption, and mercury porosimetry. n-Heptane adsorption isotherms were recorded to evaluate the uptake of organics of the compressed materials. It has been found that mechanical stability of AlSBA-15 is lower compared to that of pure silica SBA-15 materials.

TEOM analysis of the equilibria and kinetics of n-hexane and n-heptane adsorption on FCC catalyst/silicalite

A tapered element oscillatory microbalance is used for the measurement of uptake rates of n-hexane and n-heptane on fluid catalytic cracking catalyst and silicalite adsorbent. Investigations are considered over the temperature range of 373 to 513 K , and adsorbate partial pressures up to 0.12 bar . Based on measured adsorption isotherms, and through mechanistic descriptions of the diffusion process, a mathematical model is developed to describe the transient response of the microbalance, and subsequently the kinetics of adsorption and desorption. For example, for the hexane-silicalite system at a temperature of 473 K , the diffusion coefficient at zero-surface coverage is estimated as 2.9×10 −11 m 2/ s , with an activation energy of 17 kJ/ mol . This is consistent with published data based on other transient analysis methods. At relatively low temperatures of operation, i.e. less than 450 K , a single resistance model for mass transfer failed to accurately predict the desorption profiles for hexane on silicalite. As a means of quantifying the observed desorption rates, a dual-resistance model is introduced in which two different diffusion rates are assumed to take place above and below a threshold value of adsorbate concentration. Such a model may be used to account for silicalite phase transitions at high adsorbate loading.

Mechanical Stability and Porosity Analysis of Large-Pore SBA-15 Mesoporous Molecular Sieves by Mercury Porosimetry and Organics Adsorption

The mechanical stability of SBA-15 mesoporous silicas has been assessed using powder X-ray diffraction; nitrogen, benzene, and n-heptane adsorption; and mercury porosimetry. SBA-15 was found to possess rather low mechanical stability as compared to other mesoporous materials, viz., MCM-41 and MCM-48. These results can be explained by a simple mechanical model, which shows that SBA-15 has an unfavorable ratio between pore diameter and wall thickness. This ratio is more favorable for MCM-41 despite its smaller wall thickness. Our study confirmed that SBA-15 contains a significant amount of micropores in addition to the hexagonal arrangement of large mesopores. The amount (represented by the additional pore volume and surface area) of these complementary pores is tunable by variation of the synthesis temperature. It was shown that SBA-15 synthesized at temperatures higher than 120 °C contains almost no micropores. However, the pore size distribution of these materials is broader compared to materials synthesized at a lower temperature. The observed structural properties of the different SBA-15 materials are attributed to the changes in the degree of penetration of the poly(ethylene oxide) chains of the triblock copolymer within the silica walls of SBA-15.

Low temperature hydrocracking of n-heptane over Ni-supported catalysts: study of global kinetics

Two kinetic models were applied to n-heptane hydrocracking on a Ni-Re/ZSM-5 catalyst over a wide range of operating experimental conditions (temperature=433–493 K, and pressure=760 mm Hg). In the first model, the hydrogen is adsorbed on the catalyst surface without dissociation, while the second model assumes hydrogen dissociation. Both models assume that the adsorption follows Langmuir isotherm. The molecular hydrogen associated with an active site is most likely involved in the CC bond rupture, which is concluded to be the rate controlling step in this work. The extracted intrinsic kinetics were estimated via the derivation of the reactor model. The apparent activation energy for n-heptane cracking is found to be 83 kJ/mol. Both models describe well the n-heptane consumption rate. The simulation results revealed that the hydrogen adsorption constant is smaller than the n-heptane adsorption constant.

Adsorption isotherms for the system n-heptane/ethanol/HDPE

The equilibrium isotherms for the adsorption of n-heptane and ethanol on high density polyethylene (HDPE) are reported at 27–110°C and at 20–100 mmHg. The experimental apparatus and procedures are described for three methods, namely flow, static and chromatographic. The obtained results are discussed on the basis of the Henry law for adsorbates at low coverage on solids.

Theoretical study of then-heptane-HZSM-5 ring structure model interaction

We present a theoretical analysis for the interaction of the n-heptane molecule with an HZSM-5 zeolite, modeled as a ring structure. The Turbomole program, which is a density functional theory based method, was used. Quantum mechanical (QM) calculations were all-electron using the gradient-corrected BLYP approach. We employed orbital basis sets of DZP quality for all atoms. Two coordination modes were studied for the n-heptane–zeolite interaction: a reference structure with the n-heptane moiety located at the center of the ring, and a structure where n-heptane is close either to a Broensted acid site (the region around the Al atom) or to a Lewis acid site. Although the chosen ring represents a minimal model for a zeolitic cavity, the obtained results give insight about the formation of the carbocationic species, proposed as intermediaries during the catalytic cracking reactions. The key electronic effects such as charge transfers and frontier molecular orbitals, involved in the adsorption of n-heptane over the inner surface of the HZSM-5 cavity are presented and discussed for the representative coordination modes studied. The Mulliken and the Roby-Davidson population analysis were done. They are very useful, particularly the second one, to identify the catalytic sites, nucleophilic and/or electrophilic centers, as well as to locate the possible intermediates or transition states with a carbocation character, which are of considerable importance in the hydrocarbon catalytic cracking chemistry. Lastly, we have studied some of the effects that the surroundings produce on the chosen rings–hydrocarbon systems. This was accomplished through the use of a QM/MM(molecular mechanics) methodology. In this way, the embedded QM region representing the cavity it is described more properly for these host–guest interactions. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 725–740, 1999

Thermodynamics of Adsorption ofn-Alkanes on Maleated Wood Fibers by Inverse Gas Chromatography

The adsorption ofn-heptane,n-octane,n-nonane, andn-decane on untreated wood fiber and wood fiber treated with maleated polypropylene was studied by inverse gas chromatography (IGC) at infinite dilution or zero surface coverage. The specific retention volume increased with increasing probe chain length, decreased with increasing column temperature, and increased with increasing maleated polypropylene concentration. The enthalpy of adsorption increased with increasing chain length of the probe vapors. The enthalpy of adsorption remained constant after the treatment of wood fiber. The London dispersive component of the surface free energy decreased with the column temperature and showed no dependency with either the type of wood fiber or the maleated polypropylene concentration.

Isomerization of n-Heptane over Pd-Loaded Silico-Alumino-Phosphate Molecular Sieves

Isomerization of n-heptane was studied on a series of bifunctional SAPO-based catalysts with contents of 0.1 wt% Pd. From results on temperature programmed desorption of NH 3 it is deduced that the different molecular sieve structures contain nearly identical amounts of silicon substituting for phosphorus in the framework (0.3 to 0.5 silicon atoms per unit cell). Best activities and selectivities for branched heptane isomers are achieved with SAPO-11 and SAPO-31. SAPO-17 and SAPO-5 show substantially lower activities. With SAPO-5, there is a high cracking selectivity which is assumed to be caused by the reduced accessibility of parts of the bridged hydroxyl groups within the molecular sieve framework. Different locations of these acid sites are evidenced by infrared OH vibration spectra recorded after adsorption of n-heptane.

Steam reforming of n-heptane using a Rh/MgAl: I. Support and kinetics 2O 4 catalyst

A Rh/MgAl 2O 4 catalyst was found to be active for the steam reforming of n-heptane in the range 400–500°C. The MgAl 2O 4 support was prepared by calcining of a mixture of α-alumina and magnesia powders at 1420°C. The development of pore structure in MgAl 2O 4 support was examined with SEM, XRD and porosimetry before and during calcination. The pores are found to originate from voids among MgAl 2O 4 particles produced by solid reaction that magnesia was diffusing to alumina particles. Therefore, the pore size is able to control as a result of control of alumina particle size. In order to clarify the role of this support, a kinetic study on the reaction between n-heptane and steam was conducted at 500°C and 1 atm. The initial reaction rate, r 0 (mol g −1h −1), obtained experimentally is best expressed by the following equation: r 0=k( KP 0 C 7H 16 1+KP 0 C 7H 16 )( K′P 0 H 2O 1 +K′P 0 H 2O ) where k (0.071 mol/g h) is the apparent rate constant, p 0 j are the partial pressures of reactants j in the feed gas and K (111 atm −1) and K′ (0.712 atm −1) are the adsorption equilibrium constants for n-heptane and water, respectively. It is confirmed that steam reforming of n-heptane proceeds through the adsorption of n-heptane on rhodium metal and of steam on the support surface. The characteristics of the composition distribution of products shows that carbon monoxide is a primary product in the reaction system and both carbon dioxide and methane are the secondary products.

Thermodynamics of adsorption from binary liquid mixtures on heterogeneous adsorbents

The surface excess isotherms for adsorption of n-heptane–cyclohexane mixtures on graphon and benzene–cyclohexane mixtures on silica gel at three different temperatures have been analysed by a simple analytical model which accounts for the effects of the liquid-phase non-ideality, the dissimilarity of the adsorbate sizes and the adsorbent heterogeneity on the isotherm. The adsorbents are found to be substantially heterogenous for these mixtures. An analytical expression for the heat of immersion of the heterogeneous adsorbent as a function of the equilibrium liquid-phase composition has been derived. It is shown that the adsorbent heterogeneity has a much more pronounced effect on the shape of the surface excess isotherm than on the heat of immersion.

Study of the adsorption of n-heptane and 1-heptane by aerosil

Adsorption isotherms of 1-heptene and n-heptane were determined at three near-ambient temperatures on a nonporous silica (Aerosil 200 They appear to lend support to the hypothesis that the double bond of the olefins contributes to specific interactions with hydroxyl groups. In addition, the differential enthalpies and entropies of adsorption of each hydrocarbon were determined as a function of the amount adsorbed showing restricted mobility for 1-heptene and a high surface mobility for n-heptane.

Studies in the synthesis of ZSM-5 zeolites

ZSM-5 zeolites have been synthesized using tri-ethyl-n-propylammonium (TEPA) cations as the source of the organic base. X-ray diffraction, framework i.r. spectroscopy, scanning electron microscopy, adsorption of n-heptane and cyclohexane and product distribution in the conversion of methanol to hydrocarbons have been utilized in characterizing the synthesized zeolite. The rates of both nucleation and growth of ZSM-5 crystals are lower when TEPA rather than tetrapropylammonium (TPA) cation is used. The amount of cyclohexane (but not n-heptane) adsorbed on the ZSM-5 zeolite (prepared by the TEPA route) decreases at increased SiO 2 /Al 2 O 3 ratios. Under certain conditions, the ZSM-5 zeolite (in both the TPA and TEPA systems) undergoes transformation into α -quartz.

The adsorption of hydrocarbons on cellophane

The adsorption of n-heptane, n-octane, n-nonane, and n-decane on cellophane was studied in the Henry's law region by elution gas chromatography. The heat, entropy, and free energy of adsorption, calculated from retention data, varied linearly with the number of carbon atoms. The low adsorption heats at zero coverage indicated a virtual absence of high energy sites. A London dispersion force contribution to the cellophane surface free energy was estimated to be ∼42 mN m−1 from the free energy of adsorption per methylene group, in good agreement with estimates based on contact angle measurements.

Infrared study of the adsorption of hydrocarbons on rutile at the solid–vapour and solid–liquid interfaces

The adsorption of n-heptane, toluene and 1,4-dimethylbenzene vapours on to the surface of rutile has been studied by infrared spectroscopy. Surface hydroxyl groups were perturbed to a lesser extent by weak interactions with physically adsorbed n-heptane molecules than by stronger hydrogen-bonding interactions with the aromatic nuclei of toluene or 1,4-dimethylbenzene. Hydroxyl groups responsible for an infrared band at 3410 cm–1 in spectra of rutile were unaffected by the adsorption of hydrocarbons and are thought to be at sub-surface lattice sites. Two types of surface hydroxyl group were replaced by a chemisorbed oxidation product, possibly acetate anions, when rutile was exposed to 1,4-dimethylbenzene vapour.

Studies on Catalysts for Low-Temperature Steam-Reforming of Hydrocarbons (IV)

In order to clarify the main basic cause of the unique supporting property of MgWO4, a kinetic study on the reaction between n-heptane and steam over a Rh-MgWO4 catalyst was carried out at 500°C and 1atm.It has been shown that the initial rate r0(mol/g•min) experimentally obtained is best expressed by the rate equationr0=kp0C7p0H2O/(1+Kp0C7), where k(=3.4±0.2mol/g•min•atm) is the apparent rate constant, p0j is the partial pressure of j-component in the feed vapor and K(=230atm-1) is the adsorption equilibrium constant for n-heptane (C7).From the relation between r0 and p0C7 it has been suggested that the high activity of the Rh-MgWO4 catalyst would be ascribed to the moderately strong adsorption of n-heptane onto the surface of this catalyst. Further, the characteristics of the composition of the evolved gas have been discussed in terms of kinetic equilibrium.

Thermodynamics and kinetics of the adsorption of n-heptane on type 5A molecular sieves

Adsorption isotherms of n-heptane on type 5A zeolite were determined in the temperature range 150–400°C and the kinetics of desorption was measured The heat of adsorption, determined chromatographically, was 10.9 kcal/mole in the temperature range below the critical temperature of n-heptane and about 3 kcal/mole above. Experimental data can be well described by the Riekert isotherm with two molecules per cell below the critical temperature and one molecule (Langmuir isotherm) above. Desorption can be described by a first order rate equation with an activation energy of 5.8 kcal/mole.

Studies on the Surface Properties of the Surface-Treated Silica Gels by the n-Pentanol through the Adsorption of Various Kinds of Vapours and the Heat of Immersion

The surface properties of silica gels treated with n-pentanol were investigated by the adsorption of argon at 77°K, water vapour at 288°K and n-heptane at 273°K and by the heat of immersion of water and n-heptane at 298°K on the samples having various numbers of surface groups. The following results were confirmed: (1) For the silica gel samples which were untreated or had a small number of surface groups, the shape of isotherms of water vapour adsorption was the type II in BET classification, whereas it was the type I for the samples with a large number of surface groups. (2) The shape of isotherms of n-heptane adsorption was the type II for both the untreated and surface-treated samples. The existence of many capillary pores less than 20Å in diameter was suggested, since the volume of pores larger than 20Å in diameter appeared to be exactly the same for both the untreated and surface-treated silica gels. (3) The surface areas obtained from the absorption of argon, water and n-heptane showed a linear dependence on the number of surface groups. From their slopes, it was concluded that each of the surface groups covered 1.5 unreacted silanol and these surface groups would presumably be distributed on the surface of silica gels uniformly. (4) The heat of immersion of water showed a linear relation with the monolayer adsorption value obtained from water vapour adsorption.

Studies on the Surface Properties of the Organophilic Silica Gels through the Vapor Adsorption and the Heat of Immersiont

メタノール,エタノール,ブタノール,ペンタノール,ヘキサノール,オ久タノール,デカノール,ドデカノール,テトラデカノールで表面処理した親油性シリカゲルの表面特性を77rKアルゴン,288。K水蒸気,273rK%-ヘプタン吸着等温平衡および水,かヘプタンへの湿潤熱から検討した結果つぎのことが認められた。(1)未処理シリカゲルおよびメタノール,エタノール処理シリカゲルの水蒸気吸着等温線はB￡TIII型であるが,付着基炭素鎖の長い場合にはBETI型である。表面処理シリカゲルによる水蒸気吸着量は未処理シリカゲルのそれにくらべいちじるしく小さい。(2)未処理シリカゲルのアルゴン表面積は水蒸気表面積にほぼ等しく,ヘプタン表面積は分子の大きさの相違を考慮すれば妥当な値と認められる。アルゴン表面積は親油,親水性表面のいずれに対しても合理的な表面積を与える。(3)表面処理シリカゲルの水蒸気表面積とヘプタン表面積を加えたものはアルゴン表面積に等しい。(4)処理シリカゲルの表面は付着基による親油性表面と,未反応でかつ吸着点となり得る親水性表面からなり,また未反応であるが付着基でおおわれて吸着点となり得ない付着基に近接したシラノールが存在する。(5)処理シリカゲルのヘプタンへの湿潤熱は付着基炭素鎖の長くなるにつれて大きくなる。処理シリカゲルの水への湿潤熱とそれぞれの水蒸気表面積との間には直線関係が成立する。

Catalysts for the polymerization of ethylene oxide

THE authors have previously [1] found that the oxides and hydroxides of the alkaline earth metals possess a high catalytic activity for the polymerization of ethylene oxide. In view of the fact that this reaction is one of the few polymerization reactions in which polymers with a molecular weight of 10t-107 are formed on ordinary (non-complex) catalysts, it was of interest to s tudy the rules for the selection of catalysts for this reaction. Recently, information on some new catalysts for this reaction has appeared in scientific [2-4] and patent [5-6] l i terature, but in the majority of published papers [7-10] data are given only on the kinetics of the process on already known polymerization catalysts and no information on the rules for selecting catalysts is given. In the present work, the polymerization of ethylene oxide has been studied by the method of our previous paper [1]. Tubes with a thin internal partition were used for polymerization. The catalyst (0.2-0.5 g) was placed in One part of the tube and was pumped out at a vacuum of 10 -5 mm at a high temperature (the t ime of vacuum conditioning amounted to from 0.5 to 10 hr and the teml~rature from 75 to450 °, depending on the catalysts). After conditioning had been completed, the oven was removed and the tube with the catalyst was sealed off. Ethylene oxide (5 ml) and solvent -benzene -(also 5 ml) were condensed into the other half of the tube. The tube was sealed and was then shaken vigorously, a striker placed in the tube breaking the thin partition. The moment of mixing of the monomer -e thy lene oxide--and the solvent with the catalyst was taken as the start of the reaction. Fur ther polymerization was carried out in a thermostat ted bath fixed in a shaking apparatus (40 oscillations per rain). After the completion of the polymerization, the block polymer ~ catalyst -~solvent were treated with dichloroethane. The catalyst was separated by centrifuging. The polymer was precipitated from the solution by adding n-hexane and was dried at 50-60 °, i.e. somewhat below its melting point. The molecular weights of the polymers were determined as indicated in our previous paper [1]. The surfaces of the catalysts were determined by a weight method from the adsorption of n-heptane or by a volume method

The adsorption of n-heptane on solids at low pressure

The adsorption of n-heptane on solids at low pressure