Adsorption equilibria of binary ethylmercaptan/hydrocarbon mixtures on a NaX zeolite

We present here coadsorption data of ethylmercaptan with n-heptane or toluene on NaX at 298 K in the aim to use this adsorbent for removing mercaptans from natural gas. Results show that NaX has an adsorption affinity for sulphur compound strong enough to perform a deep desulphurization. NaX adsorbs preferentially ethylmercaptan over a large domain of pore filling. A displacement of n-heptane by ethylmercaptan is even observed. However, toluene becomes preferentially adsorbed at high filling. The dependence of filling and composition on selectivities and failed prediction of coadsorption equilibria by the IAS Theory indicate that the adsorbed mixture behaves as a non-ideal solution. Calorimetric measurements of coadsorption heats show that the coadsorption process is not governed by enthalpic effects but by entropic effects consecutive to steric hindrance of molecules in confined spaces.     

Modeling of water vapor adsorption isotherms onto polyacrylic polymer

The adsorbed amounts of water vapor onto polyacrylic polymer (polymer ×10) were measured using a thermogravimetry method as a function of pressure at 298 and 313 K. The adsorption isotherms are categorized to type II isotherms by IUPAC classification leading to a hysteresis loop between adsorption and desorption branches. The current study was completed by the measurement of the adsorption heats at 298 K using a differential scanning calorimetry. The calorimetric curves showed two adsorption heats domains. These domains have been attributed to the adsorption of “equivalent monolayer” and the condensation of water between polymeric chains. The correlation of experimental data to some chosen theoretical models shows that the GAB model is the most adequate to describe water vapor sorption isotherms.     

Sorption of n‐hexane in amorphous polystyrene

Sorption properties of pure n‐hexane vapor in amorphous polystyrene (PS) were studied at 298 K by thermogravimetry under controlled vapor pressure. Two sorption–desorption cycles were performed by varying the relative pressure between 0 and 0.91. Mixing of PS with n‐hexane resulted in a strong plasticization, which was evidenced by quite significant depression in the glass transition temperature of the polymer as shown by differential scanning calorimetry. Maximum quantity of n‐hexane sorbed in the PS at 298 K and at a pressure close to saturation was about 12.4 wt %. The thermogravimetry yielded an isotherm with a strong hysteresis loop, explanation of which was hypothesized with the help of (a) Flory–Huggins sorption model extended by Vrentas, (b) analysis in terms of modification in the glass transition temperature of the n‐hexane/PS system as a function of sorbed quantity, and (c) change in total volume of the system. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1252–1258     

Sticking probability on zeolites

The sticking coefficient, i.e., the probability that, on hitting the surface of a nanoporous particle (zeolite), a molecule shall be able to enter the intracrystalline space, is a key quantity for the application of such materials in heterogeneous catalysis and molecular sieving. On the basis of pulsed field gradient NMR diffusion measurements and molecular dynamics simulations, typical values of this probability are found to be close to one. They exceed previous estimates on the basis of IR uptake measurements by many orders of magnitude.     

Supramolecular Open‐Framework of a Bipyridinium‐Carboxylate Based Copper Complex with High and Reversible Water Uptake

The rigid zwitterionic ligand 1,1′‐bis(4‐carboxylatphenyl)‐(4,4′‐bipyridinium) (pc1) and copper(II) ions give rise to a linear complex [Cu(pc1)₂(H₂O)₄]²⁺, which self assembles in a pseudo tetragonal supramolecular arrangement leading to the supramolecular open‐framework [Cu(pc1)₂(H₂O)₄](Cl)₂ · 8H₂O exhibiting an open structure including water molecules and chlorides in pores. The dehydration of this material occurs at relatively low temperature (70 °C) and results in structure modification accompanied by shrinking of the crystals. Characterization of the obtained material by FT‐IR spectroscopy reveals appearance of coordinated carboxylates groups, which may indicate the formation of coordination polymer after dehydration. Water adsorption (maximum uptake 0.23 g H₂O per g) on dehydrated material allows to restore the initial structure. A large hysteresis in water adsorption‐desorption isotherm is characteristic of a significant modification of the structure during the hydration‐dehydration cycle which is in line with the structural transition determined from thermodiffractometry and FT‐IR spectroscopy.     

A Robust Nanoporous Supramolecular Metal–Organic Framework Based on Ionic Hydrogen Bonds

Hydrogen‐bond assembly of tripod‐like organic cations [H₃‐MeTrip]³⁺ (1,2,3‐tri(4′‐pyridinium‐oxyl)‐2‐methylpropane) and the hexa‐anionic complex [Zr₂(oxalate)₇]^6? leads to a structurally, thermally, and chemically robust porous 3D supramolecular framework showing channels of 1 nm in width. Permanent porosity has been ascertained by analyzing the material at the single‐crystal level during a sorption cycle. The framework crystal structure was found to remain the same for the native compound, its activated phase, and after guest resorption. The channels exhibit affinities for polar organic molecules ranging from simple alcohols to aniline. Halogenated molecules and I₂ are also taken up from hexane solutions by this unique supramolecular framework.     

Interaction Mechanisms between guaiacols and lignin: the conjugated double bond makes the difference

Lignin is considered to be responsible for a selective sorption of phenolic compounds on wood. In order to investigate the mechanisms involved, two similar guaiacol compounds--only differing by the nature of the para side chain--were adsorbed on oak wood extracted lignin. Vapor sorption-desorption isotherms indicated that about 3.5 wt % of 4-vinylguaiacol is adsorbed near saturation whereas it is only 0.8% for 4-ethylguaiacol. For both compounds, the isotherms displayed a hysteresis though significantly greater for 4-vinylguaiacol. Analyses of the hydroxyl stretching region of FTIR spectra of the lignin/4-ethylguaiacol and lignin/4-vinylguaiacol complexes indicated that physisorption via hydrogen bonds occurs for both sorbates with lignin phenolic hydroxyl groups but which would be more condensed for the former than for the latter. According to NMR spectra, these phenolic hydroxyl groups correspond to non-etherified guaiacyl subunits. In contrast with other para substituents, the conjugated vinyl bond favors not only physisorption but also chemisorption as witnessed by the fact that upon desorption in the vapor phase, even after pumping under dynamic vacuum for several days, about 1 wt % of 4-vinylguaiacol remains adsorbed onto lignin.     

Investigation of hydrolysis of lithium oxide by thermogravimetry,calorimetry and in situ FTIR spectroscopy

Journal of Thermal Analysis and Calorimetry - The mechanism of hydrolysis of lithium oxide (Li2O) was studied by thermogravimetry, calorimetry and in situ infrared spectroscopy under water (H2O)...     

Differential calorimetric enthalpies of adsorption ofp-xylene andm-xylene on y faujasites at 25°C

The differential enthalpies of adsorption ofp-xylene andm-xylene on NaY, KY and BaY zeolites were measured by isothermal calorimetry coupled with isothermal volumetry at 25C. Whatever the zeolite, the enthalpies of adsorption ofp-xylene andm-xylene at low filling were of the same order of magnitude. They did not show significantly the effect of the dipolar moment ofm-xylene. Their absolute values varied in the sequence Q ₀(pX/NaY)<Q ₀(pX/KY) =Q ₀(mX/KY)<Q ₀(pX/BaY)<Q ₀(mX/NaY) =Q ₀(mX/BaY)During the adsorption of the third molecule of xylene per -cage, BaY zeolite exhibited specific behaviour: the differential enthalpies of adsorption decreased with the filling of the -cages in such a way that they became lower than those of the other two zeolites. Some arguments concerning the structures of the zeolite and xylene molecules can explain such behaviour. Whatever the zeolite, the adsorption capacity of the -cages was 3.5 molec.^–1. For relative pressures ranging from 0.2 to 0.5, an additional adsorption of about 0.1 molec.^–1 occurred on the external surface.     

Adsorption of water vapor by poly(styrenesulfonic acid), sodium salt: isothermal and isobaric adsorption equilibria

Air conditioning and dehumidifying systems based on sorption on solids are of great interest, especially in humid climates, because they allow reduction of thermal loads and use of chlorofluorocarbons. Previous studies have shown that hydrophilic polymers such as sulfonic polymers can have very high performance in water adsorption from air. The aim of this study was to characterize the water vapor adsorption properties of fully sulfonated and monosulfonated poly(styrenesulfonic acid), sodium salt, and to elucidate the mechanism of adsorption on these materials. Adsorption isotherms have been determined by TGA between 298 and 317 K for pressures ranging from 0.1 to 45 hPa. They have type II of the IUPAC classification and a small hysteresis loop between adsorption and desorption processes was observed only for the monosulfonated sample. Water content is up to 80% weight at 80% relative humidity. Adsorption isotherms have been well fitted with the FHH model. Adsorption–desorption isobars have been determined by TGA under 37 hPa in the temperature range 298–373 K. They show that these polymers can be completely regenerated by heating at 313 K under humidified air. No degradation of the adsorption properties has been observed after several regenerations. Adsorption enthalpies and entropies have been deduced from the Clapeyron equation and from DSC measurements. A good agreement was found. A mechanism of adsorption is proposed considering two kinds of adsorbate: bounded water in electrostatic interaction with functional groups and free water resulting from condensation.