Hexane Desorption Research Articles

In Situ X‐Ray and Infrared Measurements of Alkane Absorption and Desorption Processes of Isotactic Poly(4‐Methyl‐1‐Pentene) Film

AbstractSmall molecules are absorbed selectively in the amorphous regions in semicrystalline polymers, except for some specific polymeric systems forming host‐guest cocrystals such as syndiotactic polystyrene. The crystalline density of isotactic poly(4‐methyl‐1‐pentene) (P4MP1) is substantially lower than those of analogs, and it is even slightly lower than the amorphous density. This study is investigated the absorption/desorption behaviors of short alkanes in P4MP1 in situ, and found that the alkanes are mainly absorbed in its amorphous region. Infrared spectroscopy measurements reveal that the P4MP1 film with low crystallinity absorbs higher amount of decane than the high crystallinity film does. Also it is found by small‐angle X‐ray scattering (SAXS) that, when hexane is dropped onto the P4MP1 as‐cast film, a lamellar long‐spacing peak appears at 0.16 nm−1 which disappears with the spontaneous desorption of hexane. Because the pristine P4MP1 films give no obvious SAXS peak due to the close density of crystalline and amorphous regions, the appearance of the SAXS peak indicates that an X‐ray contrast is obtained by the preferential absorption to amorphous region. The disappearance of the peak is thus reasonably understood by the loss of the contrast due to desorption.

Coupled Hydrocarbon Desorption in Zeolite Beta-Containing Monolithic Catalyst

The 3-D, large-pore zeolite beta (BEA) is effective in trapping large hydrocarbons (HCs). We conducted temperature-programmed desorption (TPD) experiments of a BEA-containing monolithic catalyst prestored with various mixtures of propylene, hexane, and toluene. The addition of propylene to a hexane + toluene mixture results in an unusual interaction during TPD. A rather small concentration of propylene increases the desorption temperature of the hexane from a weakly held into a stronger bound component. A variation in the propylene concentration leads to the nonmonotonic dependence of a high temperature hexane desorption peak. The data suggest that the blockage of hexane desorption by propylene depends on the uptake time. The findings complicate the analysis and design of HC traps used in applications such as vehicle aftertreatment systems.

Se-C Cleavage of Hexane Selenol at Steps on Au(111).

Selenols are considered as an alternative to thiols in self-assembled monolayers, but the Se-C bond is one limiting factor for their usefulness. In this study, we address the stability of the Se-C bond by a combined experimental and theoretical investigation of gas-phase-deposited hexane selenol (CH3(CH2)5SeH) on Au(111) using photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory (DFT). Experimentally, we find that initial adsorption leaves atomic Se on the surface without any carbon left on the surface, whereas further adsorption generates a saturated selenolate layer. The Se 3d component from atomic Se appears at 0.85 eV lower binding energy than the selenolate-related component. DFT calculations show that the most stable structure of selenols on Au(111) is in the form of RSe-Au-SeR complexes adsorbed on the unreconstructed Au(111) surface. This is similar to thiols on Au(111). Calculated Se 3d core-level shifts between elemental Se and selenolate in this structure nicely reproduce the experimentally recorded shifts. Dissociation of RSeH and subsequent formation of RH are found to proceed with high barriers on defect-free Au(111) terraces, with the highest barrier for scissoring R-Se. However, at steps, these barriers are considerably lower, allowing for Se-C bond breaking and hexane desorption, leaving elemental Se at the surface. Hexane is formed by replacing the Se-C bond with a H-C bond by using the hydrogen liberated from the selenol to selenolate transformation.

Adsorption of surfactants and proteins at the interface between their aqueous solution drop and air saturated by hexane vapour

The adsorption of proteins (β-lactoglobulin, β-casein) and the oxyethylated non-ionic surfactants C10EO8 and C14EO8 at the aqueous solution/air interface is strongly enhanced and accelerated by the presence of hexane vapour in the air phase caused by the co-adsorption of hexane molecules. Due to this hexane co-adsorption, the dependence of dilational visco-elasticity modulus on surface pressure is shifted towards larger surface pressure values. The adsorption kinetics of the studied non-ionic surfactants shows the same picture as that observed for the two proteins. In contrast, the desorption process of the hexane molecules from a pre-adsorbed mixed adsorption layer is very slow. This decelerated desorption is explained by a rather large desorption energy required by the hexane molecules. The experimental data are compared with several theoretical models developed earlier. The results allow estimating the activation energy for the hexane desorption from adsorption layers of the two studied non-ionic surfactants.

Application of Pseudomonas putida TISTR152 Immobilized on Plant Leaves for Benzene Adsorption

Dieffenbachia picta, Acrostichum aureum, Ficus religiosa, Lagerstroemia macrocarpa, Alstonia scholaris, and Dracaena sanderiana leaf materials have high benzene removal efficiency. So, these six plant leaf materials were investigated for continuous adsorption systems. In adsorption systems, A. aureum and A. scholaris leaf materials were found to have the highest benzene removal capacity. Physical sorption was confirmed by hexane desorption and Fourier transform infrared spectrometry (FT–IR). Pseudomonas putida immobilized on A. aureum and A. scholaris leaf cassava‐beads were used as biofilters. A total of 1.2–1.5 min with an enrichment medium was shown to be the suitable retention time and suitable nutrients for the biofilter system.

Kinetics of desorption of hexane from the microporous metal organic framework RPM-1

The kinetics of desorption of hexane from the microporous metal framework RPM-1 has been studied using a pulse mass analyzer. In this method a small sample of organic liquid was injected into a heated carrier gas that passes through a packed bed of adsorbent. The change in mass of the bed with time was observed following the adsorption of the pulse. RPM-1 is a microporous material of the general formula [M3(bpdc)3(bpy)] · 4DMF · H2O, where M is either Co or Zn, bpdc is biphenyl dicarboxylate and bpy is 4,4′-bipyridine. The pores are channels of larger supercages (11 × 11 × 5 Å) connected by smaller windows of approximately 8 Å diameter. The desorption of hexane was well represented by a combination of two first order processes. Activation energies determined for the two processes over a temperature range of 373–473 K were 56 and 63 kJ/mol for RPM-1 (Co). The two activation energies are similar to isosteric heats of adsorption measured independently in earlier work at corresponding coverages. Similar values were found for RPM-1 (Zn). The pulse mass analyzer was found to be an effective way to investigate the dynamics of adsorption processes.

Adsorption and desorption of a wetting fluid in Vycor studied by acoustic and optical techniques.

We study the adsorption and desorption of hexane in porous Vycor, as the ambient vapor pressure is varied, through sorption isotherm, ultrasonic velocity and attenuation, and light scattering measurements. On adsorption, we show that the fluid fills the pore space uniformly until capillary condensation occurs; however, small, randomly distributed, vapor bubbles remain, as detected by a large increase in the attenuation of the ultrasound. On desorption, the mismatch in the index of refraction between the empty pores and the surrounding filled pores leads to intense scattering of light that reveals the presence of long-range correlations in the pore space. These correlations have a fractal dimension of 2.6, which is very near the value predicted for invasion percolation. Finally, we also investigate the time dependence of the changes in the adsorbed fluid mass and use these measurements to identify three distinct regimes with vastly differing mechanisms for mass transport. The results presented here provide information on the differences in pore-space correlations on filling and drainage, and highlight the critical role of the connectivity of the pores to the surface in determining the desorption behavior.

Effect of pressing on the diffusional properties of polyacetylene

AbstractPressing of polyacetylene films before (or after) sorption of dopant can reduce significantly the rate of sorption (or desorption) due to reduced effective surface area and pore size, as is found in the experiments of vapour sorption and desorption of hexane and iodine. On exposure to air, the pressed films have significantly lower oxidation rates at 120°C than the unpressed ones.

Residual hexane in meals

AbstractIt is now possible to determine in a reliable way the residual hexane in meals. In the case of rapeseed, tests performed in the experimental pilot plant of GERDOC have revealed three parameters, which to our knowledge have not previously been studied, and which have a favorable influence on the desorption of hexane: drying the seeds with hot air before they are crushed, dehulling the seeds, and decreasing the length of the extraction time.