Intelligent Gravimetric Analyzer Research Articles

Experiment and Modeling of Pure and Binary Adsorption of n-Butane and Butene-1 on ZSM-5 Zeolites with Different Si/Al Ratios

Four ZSM-5 zeolite catalysts with different Si/Al ratios for the catalytic cracking of C 4 fractions to produce ethylene and propylene were prepared in this study. First, the adsorption isotherms of pure n-butane and butene-1 and their mixtures on these catalysts at 300K and p=0–100kPa were measured using the intelligent gravimetric analyzer. The experimental results indicate that the presence of Al can significantly affect the adsorption of butene-1 than that of n-butane on ZSM-5 zeolites. Then, the double Langmuir (DL) model was applied to study the pure gas adsorption on ZSM-5 zeolites for pure n-butane and butene-1. By combining the DL model with the ideal adsorbed solution theory (IAST), the IAST-DL model was applied to model the butene-1 (1)/ n-butane (2) binary mixture adsorption on ZSM-5 zeolites with different Si/Al ratios. The calculated results are in good agreement with the experimental data, indicating that the IAST-DL model is effective for the present systems. Finally, the adsorption over a wide range of variables was predicted at low pressure and 300K by the model proposed. It is found that the selectivity of butene-1 over n-butane increases linearly with the decrease of Si/Al ratio. A correlation between the selectivity and Si/Al ratio of the sample was proposed at 300K and p=0.08MPa.

Experimental measurements and computer simulation of methane adsorption on activated carbon fibers

Three activated carbon fibers (ACFs) with different BET specific surface areas (SSAs) were prepared. Experimental characterization and methane adsorption on the ACFs were measured by the intelligent gravimetric analyzer (IGA-003, Hiden) at 258 and 298 K. Correlations proposed between the methane adsorption capacity and SSA indicate that the SSA plays an important role on storage amount at a given temperature. A detailed experimental investigation was focused on the sample ACF3 of the highest SSF of 1511 m 2/g at five temperatures, from 258 to 298 K. The temperature dependence for methane adsorption amount on ACF3 at 1.8 MPa is proposed. It shows that temperature is vital to methane storage capacity for ACF3, and adsorption storage at the temperatures below 280 K is recommended for favorite uptakes. To model ACF3, the pores are described as slit-shaped with a pore size distribution that was determined by molecular simulation and the statistics integral equation. Predictions of methane adsorption, carried out at 258 and 298 K and high pressures by molecular simulation, indicate that our sample ACF3 can reach the uptake of 14.99 wt% at 4.0 MPa and 298 K, which is comparable with the best result in the literature.

Neutron scattering and gravimetric study ofBI2Sr2CaCu2O8+x high-temperature superconductors

We analysed some of the structural properties ofBI2Sr2CaCu2O8+x superconductors using neutron scattering and intelligent gravimetric analyser instruments from roomtemperature to 750 °C. Both of the experiments showed that the oxygen content of the compound is temperaturedependent and decreases as the temperature increases. Neutron experiment results showedthat the lattice parameters of the compound are a function of oxygen content and theyincrease as the oxygen content decreases.

Sorption of hydrocarbons in silicalite-1 studied by intelligent gravimetry

Adsorption and desorption isotherms, adsorption kinetics and TG (thermogravimetry) curves of cyclopentane, cyclohexane, benzene, and p-xylene in silicalite-1 have been measured by using intelligent gravimetric analyzer (IGA). The thermodynamic and kinetic properties of the systems, such as the heats of sorption, free energies of sorption, entropy changes, and the diffusion coefficients, have been derived from these measurements. The results suggest that the size and configuration of sorbate molecules play a critical role on the adsorption and diffusion behaviour of the systems. Tiny changes in the size and the shape of sorbate molecules can result in a significant difference in the adsorption properties.

On the prediction of adsorption isotherms of methanol/water vapour mixtures on microporous activated carbon

It is well known that the adsorption of organic vapours on activated carbons (AC) can be disturbed in the presence of water vapour. When the adsorbed solutions are miscible, different theories, based on the pioneering Dubinin–Radushkevich (D–R) and Dubinin– Astakhov (D–A) equations are used to describe the experimental data. Among recent works, Linders et al. [1] showed that the isotherm of multicomponents can be modeled by using the ideal adsorbed solution theory (IAST), D–R and D–A equations. This model fits well with the experimental data up to a relative pressure of 0.1 (methanol adsorption at 60% RH) but shows discrepancies beyond these value. No explanation was given by the authors. Taqvi et al. [2] proposed to estimate the binary equilibria using the virial mixture coefficient approach (VMC). The observed trends are explained in terms of molecular interactions and, in particular, water was found to promote the adsorption of methanol. This is explained by the ability of alcohol to form H bond with water. To sum up, it seems that if some points such as the state of the phase adsorbed (homogeneous solution) are well established, other points such as the over-adsorption of methanol or the lack of models for the high methanol relative pressures, need further explanation. In this work, we report our results obtained for the co-adsorption of methanol and water vapours on a commercial activated microporous carbon (AC). The relative humidity (RH) ranges from 25% to 74% and the methanol concentration from 0% to saturation. The obtained results lead us to propose a thermodynamical approach that explains the isotherms of methanol adsorption at constant RH. Furthermore, our approach fits well with several results in the literature. Adsorption isotherms were collected in dynamic flow conditions at 298 K using an intelligent gravimetric analyzer (IGA) supplied by Hiden Analytical Ltd. This apparatus is fully computer controlled and measures gravimetric adsorption on a microbalance. The sample temperature was constantly monitored throughout the experiment, and the variation was found to be ±0.05 K. Further details about the acquisition procedure can be found elsewhere [3]. The AC studied has been obtained by activation of coconut shell in steam at 1123 K. The porosity characterization was determined by benzene adsorption using a procedure described elsewhere [4]. The sample is mainly considered as microporous (Vmic = 0.585 cm 3 /g; Vmes = 0.082 cm 3 /g) with specific surface area close to 1500 m 2 /g and having a poor surface chemistry (acidic groups = 0.06 meq/g and basic groups = 0.5 meq/g as determined by Boehm titration). The isotherms of pure methanol and water adsorption are presented in Fig. 1. The adsorption of methanol, that exhibits type I isotherm, is characterized by strong dispersive interactions of the methyl groups with the carbon pore walls [3]. As a result, a large part of the pore volume is already filled at low relative pressures. The water isotherm is of type V. Then the carbon surface is evaluated to be extremely hydrophobic. The sharp increase of the adsorbed water is attributed to the condensation of water into the micropores. The adsorption isotherms of binary mixtures, presented in Fig. 2, were obtained for a relative humidity of 25%, 50%, 60% and 74% respectively. It should be noted that the number of data for each isotherm decreases with increasing RH due to limitations of our experimental set-up. Moreover, all the isotherms are of type I. The slope at low partial pressure in methanol increases with increasing RH before reaching a plateau that corresponds to the capacity near saturation. The total mass uptake is higher when RH = 25% than for pure methanol, and it then decreases with increasing RH.

Adsorption Study of Methane on Activated Meso‐carbon Microbeads by Density Functional Theory

AbstractA combined method of density functional theory (DFT) and statistics integral equation (SIE) for the determination of the pore size distribution (PSD) is developed based on the experimental adsorption data of nitrogen on activated mesocarbon microbead (AMCMB) at 77 K. The pores of AMCMB are described as slit‐shaped with PSD. Based on the PSD, methane adsorption and phase behavior are studied by the DR method. Both nitrogen and methane molecules are modeled as Lennard‐Jones spherical molecules. and the well‐known Steele's 10–4–3 potential is used to represent the interaction between the fluid molecule and the solid wall. In order to test the combined method and the PSD model, the Intelligent Gravimetric Analyzer (IGA‐003) was used to measure the adsorption of methane on the AMCMB. The DFT results are in good agreement with the experimental data. Based on these facts, we predict the adsorption amount of methane, which can reach 32.3 w at 299 K and 4 MPa. The results indicate that the AMCMBs are a good candidate for adsorptive storage of methane and natural gas. In addition, the capillary condensation and hysteresis phenomenon of methane are also observed at 74.05 K.

Study of sorption/desorption of water and organic vapors on poly(ethylene maleate)‐based sensor‐coating materials using an automated gravimetric analyzer

AbstractHydrophobic comonomers bisphenol‐A and hexafluorobisphenol‐A were incorporated as diol components in the sensor‐coating material poly(ethylene maleate) (PEM), resulting in modified polymers, HCPEM and HFPEM, respectively. To assess the suitability of these polymers as sensor interfaces, the sorption/desorption isotherms and kinetics of water and a range of volatile organic vapors were obtained over the entire relative pressure range of 0.1 to 1.0, using an automated intelligent gravimetric sorption analyzer. The extent and rate of sorption of organic vapors were higher in the modified polymers compared to those of the parent polymer. Sorption hysteresis was observed at high relative pressures, especially with water and other hydrogen‐bonded polar organic vapors. Polarizable vapors like toluene and benzene were sorbed more than nonpolarizable cyclohexane vapors. The sorption results were interpreted in terms of semiempirical models based on concepts of thermodynamic interaction parameter, partition coefficient, and linear solvation energy relationship. The study reveals the potential of sorption/desorption isotherms and kinetics in characterizing the sorption properties of coating materials that are used as an interface in acoustic wave sensors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1760–1767, 2003

The characterisation of different forms of water in low rank coals and some hydrothermally dried products ☆

Equilibrium moisture contents were determined at 30 °C for a range of coals (raw and acid-washed) and hydrothermally dried (HTD) coals in desiccators at various relative humidities maintained by saturated salt solutions. The equilibrium moisture content at 15% relative humidity for a Loy Yang Low Ash coal was the same within the limits of error as that obtained from an isotherm generated by a microbalance (Intelligent Gravimetric Analyser). Total non-freezing water values for the coals and HTD products were measured using both 1H NMR and differential scanning calorimetry (DSC). Higher values for the non-freezing water contents were obtained from DSC measurements, possibly because the calculation assumes that the enthalpy of the non-freezing water is constant and equivalent to that of the bulk water. This assumption is almost certainly erroneous and is not made in the calculation of non-freezing water from the 1H NMR results. The values obtained by the 1H NMR method corresponded to relative humidity values equal to about 92% for the raw coals and ≥96% for the HTD products.

Contribution of Mineral Matter to Water Associated with Bituminous Coals

The effect of mineral matter on the moisture-binding capacity of samples from two Australian bituminous coal seams was investigated by gravimetric sorption and nuclear magnetic resonance (NMR) techniques. The water uptake contributions from the mineral matter (predominantly clay) and organic components of the coal samples were determined from precise isothermal sorption measurements at relative pressures up to 0.9 using a Hiden intelligent gravimetric analyzer. Also, water interacting with the coal samples, such that it is unfrozen at −3 °C during heating, was quantified using a proton NMR technique. Water uptake (per unit mass of dry solids) at a relative pressure of 0.9 by the mineral matter in the coal samples studied was assessed to be 2.3−2.8 times the uptake by the organic material. Coal mineral matter containing 26 wt % of montmorillinite, a swelling type clay, had more than twice the water uptake per unit surface area when compared to mineral matter in which clay was present only as kaolinite. For...

Deuterium Absorption in Pd 0.9Y 0.1 Alloy

Microgravimetric measurements are reported of the pressure–concentration dependence of deuterium in the palladium solid–solution alloy, Pd 0.9Y 0.1. An Intelligent Gravimetric Analyzer (IGA) was used and the measurements were made in the temperature range (60 °C≤ T≤100 °C). The results obtained revealed a hitherto unseen hysteresis effect in the absorption–desorption isotherm. This hysteresis is believed to be due to a reordering of the palladium–yttrium lattice driven by the hydrogen (deuterium) absorption. The second absorption/desorption cycle shows a wider hysteresis loop than the first but further cycles repeat the shape of the second loop. In-situ neutron diffraction measurements were also made on deuterated Pd 0.9Y 0.1 at 303 K. These data support the hypothesis that the hysteresis is due to an order–disorder transition involving the yttrium atoms in the metal lattice.