Initial Desorption Research Articles

Infrared linear dichroism as a tool to evaluate volatile guest partition between amorphous and nanoporous-crystalline polymer phases

Desorption kinetics of ethene, propene, and butadiene from films exhibiting axially oriented nanoporous-crystalline δ phases of syndiotactic polystyrene (s-PS) have been followed by gravimetric and infrared linear dichroism measurements. The reported data can be rationalized by assuming that, after the initial desorption mainly involving molecules absorbed in the amorphous phase, most gaseous molecules are included as guest in the nanoporous-crystalline phase. This allows establishing a simple method to evaluate guest partition between nanoporous-crystalline and amorphous polymeric phases, which possibly can be applied for most volatile guest molecules. The described method also allows establishing the presence of one guest molecule (ethene, propene, or butadiene) per cavity of the nanoporous δ form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Effect of rapid solidification on phase structure and hydrogen storage properties of Mg70(Ni0.75La0.25)30 alloy

The hydrogen absorption/desorption kinetics and P–C isotherm of Mg70(Ni0.75La0.25)30 alloy, both the as-melt and rapid solidification were carried out on a sievert-type apparatus. The experimental data of initial hydrogen absorption and desorption kinetics at 573 K are in good agreement with Avrami–Erofeev equation, which indicated a three-dimensional interface reaction process of nucleation and growth for the initial hydrogenation kinetics and ‘‘geometrical contraction model’’ for dehydrogenation kinetics. However, the third absorption process seems to have a different hydriding mechanism as chemical reaction. P–C isotherm curves show that the as-melt alloy has two distinct hydrogen absorption plateaus, while the rapid solidification alloy has only one, which attribute to the absent of LaMg3 phase by rapid solidification. It can be confirmed by DSC analysis that the as-melt alloy has two endothermic peaks, compared to one for the rapid solidification alloy. The dehydrogenation activation energies of Mg70(Ni0.75La0.25)30 alloy were calculated by Kissinger method, showing the values of 128.60 ± 13.79 and 112.89 ± 9.94 kJ/mol for the as-melt sample and 61.09 ± 6.28 kJ/mol for rapid solidification alloy respectively.

Water retention and gas relative permeability of two industrial concretes

This experimental study aims at identifying the water retention properties of two industrial concretes to be used for long term underground nuclear waste storage structures. Together with water retention, gas transfer properties are identified at varying water saturation level, i.e. relative gas permeability is assessed directly as a function of water saturation level Sw. The influence of the initial de-sorption path and of the subsequent re-saturation are analysed both in terms of water retention and gas transfer properties. Also, the influence of concrete microstructure upon water retention and relative gas permeability is assessed, using porosity measurements, analysis of the BET theory from water retention properties, and MIP. Finally, a single relative gas permeability curve is proposed for each concrete, based on Van Genuchten–Mualem's statistical model, to be used for continuous modelling approaches of concrete structures, both during drying and imbibition.

Desorption of Asphaltenes from Silica-Coated Quartz Crystal Surfaces in Low Saline Aqueous Solutions

The quartz crystal microbalance (QCM) was used to study desorption of asphaltenes from silica-coated quartz crystals upon exposure to various aqueous low saline solutions of different salt concentrations and cationic valency. Ultraviolet (UV) spectroscopy measurements confirmed desorption in selected experiments. The amount of desorption was related to the type and concentration of electrolyte and the sequence of injecting the electrolyte solutions. Initial desorption upon exposure to solutions with high ionic strength was likely due to repulsion between negatively charged sites acquired at the silica and the asphaltenes. During the injection of low saline aqueous solutions, a critical expansion of the diffuse double layer was required for desorption to occur. Comparatively lower desorption of asphaltenes was observed in the CaCl2 solutions than in NaCl and seawater solutions.

A New Coal Sampling System for Measurement of Gas Content in Soft Coal Seams

Core samples or drill cuttings from boreholes drilled in coal seams are used in direct measurements of gas content in coal. In soft coal seams, core samples are difficult or sometimes impossible to obtain due to poor borehole stability such as large borehole deformation and borehole collapse, drill cuttings have to be taken and used. Due to their faster initial gas desorption rates, drill cuttings need to be taken rapidly and accurately at given positions during borehole drilling to ensure the accuracy of gas content measurements. To meet these sampling requirements of drill cuttings, a new sampling-while-drilling (SWD) system has been developed. The SWD system is based on a special design of double-tubing drill rods and a reversed circulation of pressurized air. A field test of the SWD system was carried out with satisfactory results. This paper presents the principle and results of the field test of the SWD system.

Enhanced volumetric hydrogen density in sodium alanate by compaction

Powder compaction is a potential process for the enhancement of the volumetric and gravimetric capacities of hydrogen storage systems based on metal hydrides. This paper presents the hydrogen absorption and desorption behaviour of compacts of sodium alanate material prepared under different levels of compaction pressure. It is shown that even at high compaction levels and low initial porosities, hydrogen absorption and desorption kinetics can proceed comparatively fast in compacted material. Furthermore, experimental hydrogen weight capacities of compacted material are higher than the experimental values obtained in case of loose powder. It is demonstrated that the kinetic behaviour of the compacted material during cycling is directly associated to the volumetric expansion of the compact, which is quantitatively measured and analyzed during both hydrogen absorption and desorption processes. The cycling behaviour and dimensional changes of compacted sodium alanate material are a key consideration point if it is used as hydrogen storage materials in practical tank systems.

Equilibrium moisture content (EMC) in Norway spruce during the first and second desorptions

Abstract It is a commonly accepted notion that the equilibrium moisture content (EMC) of wood at a given relative humidity (RH) is highest during initial desorption of green wood due to an irreversible loss of hygroscopicity during the 1st desorption. The basis for this notion is investigated by assessing how drying and saturation procedures influence the differences between the 1st and the 2nd desorption curves for Norway spruce (Picea abies (L.) Karst.) sapwood. The study establishes 1st and 2nd desorption isotherms for a variety of initial conditions and it covers the RH range from 60.1% to 99.9%. The state of the water is not affected by oven-drying and rewetting as demonstrated by time domain low field NMR relaxometry. The results challenge the conclusions of earlier studies and indicate that in these studies the 2nd desorption was initiated at much too low EMC and therefore fails to describe a boundary desorption isotherm. Instead, it becomes an intermediate desorption isotherm starting at the adsorption boundary curve and crossing over to eventually meet the desorption boundary curve. The results also show that vacuum drying at room temperature only gives a modest loss of hygroscopicity compared to the green state. Conversely, oven-drying at 103°C results in a more significant loss of hygroscopicity, except for RH above 96% where an increase in EMC surprisingly is seen.

Protein release parameters estimated with a flow system on zinc-containing apatite

Adsorption and desorption properties of proteins on zinc-containing apatite were successively monitored with a newly-developed flow system, and sustained-release ability of the apatite with different zinc contents was evaluated using protein release parameters we suggested. Three sustained-release parameters; initial desorption rate (rinit), time of desorption-completed (Tdes), and desorption constant (kd) were estimated with graphical analysis of dynamic desorption curves in a flow of 20 mM phosphate-buffered solution (PBS). Bovine serum albumin (BSA) of isoelectric point (pI) 4.8 and egg white lysozyme (LSZ) of pI 11.2 were employed as model protein drugs. Incorporation of zinc into hydroxyapatite changed desorption responses of the proteins. Zn(0.15), where the number in parentheses denoted the preparing molar ratio of Zn/Ca, showed the most sustained-release ability: less rinit, longer Tdes, and smaller kd. Furthermore, the adsorbed amounts of the proteins for Zn(0.15) were 1.5 ~ 4 times larger than Zn(0), which suggested that Zn(0.15) would be promising as a sustained-release carrier of protein drugs.

Comparison of hydrogen cycling kinetics in NaAlH 4–carbon aerogel composites synthesized by melt infusion or ball milling

This work compares the initial desorption and hydrogen cycling kinetics of NaAlH 4 melt infused into carbon aerogel with NaAlH 4–carbon aerogel composite synthesized by ball milling. Samples having comparable carbon content (47.4 wt%) prepared by either method yield virtually identical desorption and cycling behavior. Furthermore, the ball milled material can be made with lower carbon content and still maintain only slightly reduced kinetic improvements. Surprisingly, there is no evidence for mixed infused-like and bulk-like behavior even for carbon content as low as 9.1 wt%. Unlike melt infused NaAlH 4, where co-infusion of TiCl 3 catalyst has proven difficult, the ball milled material can easily accommodate co-doping with both carbon and TiCl 3. The inclusion of carbon with TiCl 3 results in a modest but significant improvement in kinetics compared to NaAlH 4 doped with TiCl 3 alone, especially for rehydrogenation. Ball milling with activated carbon produces an improvement very similar to that of carbon aerogel, whereas graphene and graphite have smaller effects, in that order. During cycling of the second stage NaAlH 4 reaction, i.e., Na 3AlH 6 ↔ 3NaH + Al + (3/2)H 2, addition of either activated carbon or carbon aerogel at 23.1 wt%, but without TiCl 3, results in kinetic performance as good as or better than NaAlH 4 doped with TiCl 3.

2Mg-Fe Alloy Processed by Hot Extrusion: Influence of Particle Size and Extrusion Reduction Ratio on Hydrogenation Properties

Samples of a 2Mg-Fe (at.%) mixture were produced by high energy ball-milling (HEBM) with ball to powder ratio = 20:1, in an argon gas atmosphere, in 190 ml vials (sample-1) to produce powders and in 300 ml vials (sample-2) to produce plates. Both samples were cold-pressed into preforms. The preforms were then extruded at 300°C at a ram speed of 1mm/min., with the following extrusion ratios: sample-1 at 3/1 to ensure porosity and sample-2 at 5/1 to increase the adhesion of the plates. The resulting bulks from samples 1 and 2 were hydrogenated for 24h in a reactor under 15 bar of H2to produce the Mg2FeH6complex hydride, and at 11 bar of H2to produce both the complex hydride and MgH2hydride. In addition, sample-1 was severely temperature-hydrogen cycled to verify its microstructural stability and the influence of grain size on the sorption properties. XRD patterns showed Mg(hc), Fe(ccc) and Mg2FeH6in both samples, and sample-2 also contained MgH2and MgO (attributed to processing contamination). DSC results demonstrated that the initial desorption temperature of sample-1 was lower than that of sample-2. However, sample-2 showed faster desorption kinetics, presenting a desorption peak about 73°C below that of sample-1. This could be attributed to the activation/catalyst effect of the MgH2hydride. The improvement in sorption properties was attributed mainly to porosity and to the type of employed catalysts.

Adsorption and solvent desorption behavior of ion-exchanged modified Y zeolites for sulfur removal and for fuel cell applications

Typical ion-exchanged modified Y zeolites (AgY and CeY) were prepared for sulfur removal. The adsorption and desorption behavior of typical sulfur and hydrocarbon molecules in various Y zeolites has been investigated by the adsorption breakthrough and on site solvent washing experiments, as well as computer simulation. Breakthrough experiments showed that the adsorption capacity for thiophenic sulfur increased for the studied adsorbents as follows: CeY>AgY>NaY. The higher initial sulfur concentration accelerated the appearance of breakthrough, and the outlet sulfur concentration, in all cases, cannot reach the corresponding initial sulfur level. The concentration profile of washing solvent during desorption process showed that most of the sulfur compounds could be recovered at initial desorption stage. The desorption rates of typical Y zeolites follow the order: NaY>AgY>CeY, which is the reverse as that found in adsorption capacity. The distinct adsorption and desorption behavior of CeY, AgY, and NaY zeolites was markedly related with their various binding force (S–M coordination, π-complexation, and Van der Waals force) with sulfur compounds. The adsorption isotherms and density distribution snapshots study by computer simulation confirmed the preferential adsorption of thiophenic sulfur.

Hydrogen desorption behavior of vanadium borohydride synthesized by modified mechano-chemical process

The vanadium borohydride was synthesized by a mechano-chemical milling method and its hydrogen desorption performance was evaluated. The effect of cooling during milling process on the hydrogen desorption behavior was also investigated. Nearly pure hydrogen was detected using a mass spectrometer coupled with a simultaneous thermal analyzer. Thermogravimetric method was conducted to determine the initial desorption temperature and the amount of hydrogen released from the hydride. The initial desorption temperature of vanadium borohydride was found below 100 °C, with an enthalpy change of 25.4 kJ/mol V(BH 4) 3. The amount of hydrogen released from the hydride prepared by milling but without cooling was 0.25 wt%, while that prepared with controlled cooling at 20 °C was 1 wt%. A beneficial effect of enhanced hydrogen release to 2.2 wt% from borohydride was found if multi-walled carbon nanotubes (MWCNTs) were added as an additive.

Water desorption behavior of desiccant rotor under microwave irradiation

Microwave heating is expected to be a novel regeneration method of desiccant rotor in desiccant humidity conditioner, because it has advantages of direct and rapid heating of material. In this study, desorption experiments were conducted by using the practical desiccant rotor coated with zeolite in the microwave power ranging from 200 to 800 W and desiccant rotor length of 60–180 mm. As a result, both desorption ratio in a desorption equilibrium and initial desorption rate were found to increase linearly with microwave power. Concerning the effect of rotor length, it was found that initial desorption rate and desorption ratio at 600 s also increased with rotor length. However, experimental desorption ratio in a desorption equilibrium was much lower than estimated value, which was calculated on the basis of change in relative humidity involved by temperature increase of rotor, and the deviation increased with microwave power and rotor length. From the temperature measurement in the rotor, a noticeable temperature distribution was observed in the radial and axial directions of rotor even though water desorption attained an equilibrium state. Consequently, it was indicated that nonuniform heating of the rotor mainly caused decrease in desorption ratio. ► Water desorption of zeolite desiccant rotor was conducted with microwave heating. ► Initial desorption rate and equilibrium ratio rose linearly with microwave power. ► Initial desorption rate and equilibrium ratio increased with rotor length. ► Experimental desorption ratio was much lower than theoretically estimated value. ► A big temperature distribution existed in the radial and axial directions of rotor.

A pyridine adduct of bis(di-iso-butyldithiocarbamato-S,S′)cadmium(II): Multinuclear (13C, 15N, 113Cd) CP/MAS NMR spectroscopy, crystal and molecular structure, and thermal behaviour

Crystalline bis(N,N-di-iso-butyldithiocarbamato-S,S′)(pyridine)cadmium(II) – adduct 1 was prepared and studied by means of multinuclear 13C, 15N, 113Cd CP/MAS NMR spectroscopy, single-crystal X-ray diffraction and simultaneous thermal analysis (STA). In molecular structure 1, the cadmium atom coordinates with four sulphur atoms and one nitrogen atom of pyridine, forming a coordination polyhedron [CdS4N], whose geometry is an almost ideal tetragonal pyramidal (C4v). The coordinated py molecule is in the apical position, while two structurally non-equivalent di-iso-butyldithiocarbamate ligands, playing the same terminal S,S′-chelating function, define the basal plane. To characterise additionally the structural state of the cadmium atom in this fivefold coordination, 113Cd chemical shift anisotropy (CSA) parameters, δaniso and η, were calculated from experimental MAS NMR spectra that revealed an almost axially symmetric 113Cd chemical shift tensor. From a combination of TG and DSC measurements taken under an argon atmosphere, we found that the mass of adduct 1 is lost in two steps involving initial desorption of coordinated py molecules with subsequent thermal destruction of liberated cadmium(II) di-iso-butyldithiocarbamate, with yellow-orange, fine-powdered solid CdS as the final product.

Hydrogen absorption/desorption properties of Li–Al–N–H composite

Li 3AlH 6 and LiNH 2 at a 1:3 molar ratio were mechanically milled to yield a Li–Al–N–H composite. The hydrogen storage properties of the composite were studied using thermogravimetry, differential scanning calorimetry, mass spectrometry, and X-ray diffraction. Addition of LiNH 2 lowered the decomposition temperature of Li 3AlH 6. The Li–Al–N–H composite began to release hydrogen at around 110 °C, which was 90 °C lower than the initial desorption temperature of Li 3AlH 6. About 7.46 wt% of hydrogen was released from the composite after heating from room temperature to 500 °C. A total hydrogen desorption capacity of 8.15 wt% was obtained after accounting for hydrogen released in the ball-milling process. The resulting dehydrogenated composite absorbed 3.56 wt% of hydrogen at 400 °C under a hydrogen pressure of 110 bar. The hydrogen absorption capacity and kinetic properties of the Li–Al–N–H composite significantly improved when CeF 3 was added to the composite. A maximum hydrogen absorption capacity of 4.8 wt% was reached when the composite was doped with 2 mol% CeF 3.

Adsorption of Ammonia on Ozonated Activated Carbon

In this theoretical research, we investigated ozonated granular activated carbon (OGAC) as an ammonia adsorbent in aqueous systems. Research objectives were to determine the (1) effectiveness of ozone loading on adsorption capacity of activated carbon in aqueous ammonia solutions, (2) kinetics and adsorption isotherms of ammonia adsorption, and (3) effect of volatile organic compounds on adsorption of ammonia from the aqueous phase. Batch experiments indicated that ozonation for 30 min enhanced the adsorption capacity of granular activated carbon from 0.47 0.065 mg g-1 to 1.02 0.099 mg g-1 due to increased surface oxygen species on activated carbon. These results suggested that activated carbon could be chemically modified to enhance the adsorption of ammonia from aqueous systems. Analysis of the rate data suggested that the adsorption of ammonia on OGAC followed an Elovich model with initial adsorption rate (a) and desorption constants () between 0.146 and 1.06 mg g-1 min-1 and 5.5 and 7.75 g mg-1, respectively (25C to 45C). The effect of temperature (25C to 45C) on adsorption was not found to be significant, suggesting that adsorption on OGAC was non-activated. However, presence of volatile organic compounds (VOCs) such as p-cresol and acetic acid inhibited adsorption of ammonia on OGAC. Future research is needed to synthesize activated carbon that can absorb ammonia and VOCs simultaneously.

Experiment on small size coal sample's methane desorption law based on Sun Chong-Xu Formula

Abstract The calculated methane content keeps away from real loss methane content with the increasing of loss time and initial desorption velocity data. Small size coal sample's methane absorption and desorption experimental study is carried out under the condition of a certain methane adsorption balance pressure and constant temperature, which the small size coal sample is collected from different coal mines. The experimental data is studied with the methane desorption law of Sun Chong-Xu formula (Q=ati). Relations among coal sample's methane desorption quantity, exposure time and methane desorption velocity are studied. Then eigenvalues (i) in desorption law (Q=ati) of coal samples with different exposure time is calculated. So the same group coal samples’ Eigenvalues calculated with different exposure time are studied. This study provides according for small size coal sample's methane loss value accurate calculation.

Experimental Study on Inhibitory Effect of Gas Desorption by Injecting Water into Coal-sample

Abstract In order to further study inhibitory effect of gas desorption in coal seam water infusion, the laboratory test method is used in this paper, which experiments on coal sample that is fully adsorbed methane before being injected water into. By the experiments, gas desorption isotherms, gas desorption rate and residual gas content after water injection are obtained. And also, the following test results are got: the first, with water being injected, coal gas desorption isotherms moves upward, that is, gas content in coal sample increases under a certain balance pressure; the second, with water being injected, it can lower both the initial desorption rate and the attenuation speed of gas adsorption in coal sample, that is, coal gas desorption rate curve becomes more smooth; the third, with water being injected, it increases residual gas content in coal, and residual gas content increases with injection pressure and water content. Through these experiments, the following conclusions can be drawn: with high pressure water being injected into pores of coal, residual water in coal has inhibitory effect to adsorption methane, ultimately, reducing gas desorption rate and desorption volume; so that, water injection is benefit for gas outburst, and the inhibitory effect is an important role in mechanism of water injection to prevent coal and gas outburst.

Sorption and Desorption of Pyrethroid Insecticide Permethrin on Concrete

Use of pesticides around residential homes is linked to contamination of urban waterways, where impervious surfaces like concrete are considered as sources or facilitators of the contamination. However, the fate of pesticides on urban hard surfaces is poorly understood. We characterized sorption and desorption of permethrin, the most used pyrethroid insecticide, on concrete surfaces, to understand its availability for contaminating runoff water. Sorption of (14)C-permethrin to concrete was rapid, and the sorption isotherm was linear, with surface area-normalized K(d) of 1.91 ± 0.1 mL/cm(2). When small permethrin-treated concrete cubes (14 × 14 × 8 mm) were subjected to 300 h sequential desorption, both the parent compound and total (14)C showed an initial rapid desorption, followed by prolonged slow desorption. Meanwhile, permethrin became more resistant to desorption as the pesticide contact time on the concrete increased. When desorption was performed 1 and 7 d after the treatment, the desorbed permethrin after 300 h was 34.1 ± 3.2% and 23.7 ± 1.1% of the spiked amount, respectively, as compared to 56.2 ± 6.1% for the freshly spiked samples. The decreased desorption was partially attributed to permethrin decomposition on the alkaline concrete. However, even after 300 h, over 20% of the applied (14)C still remained in the concrete. Therefore, when pesticide-treated concrete surfaces come in contact with runoff water, elevated concentrations may be expected initially, while the extended desorption implies a potential for sustained contamination.

Quantifying hysteresis of atrazine desorption from a sandy loam soil

Batch experiments were carried out to investigate the effects of initial atrazine concentrations and consecutive desorption steps on the desorption characteristics of atrazine from a sandy loam soil. As initial atrazine concentration increased, the average percentage of atrazine desorption on the sandy loam soil ranged gradually from 23.1% to 38.5% after five consecutive desorption steps. The values of the Freundlich capacity parameter, k des, derived from the initial concentration and time-dependent desorption isotherm were consistently higher than those associated with sorption. The opposite trend was observed only for the values of nonlinear parameter, n des, from the initial concentration-dependent desorption isotherms. Atrazine hydrolysis to hydroxyatrazine and bound residue formation were mainly responsible for the observed hysteresis in its sorption and desorption isotherms. For the initial concentration-dependent desorption isotherms, as initial atrazine concentration increased, the values of hysteretic coefficients ω and λ decreased, and H values increased. However, the relationships between initial atrazine concentration and hysteretic coefficients were not pronounced for ω, H, or λ. For the time-dependent desorption isotherms, λ and H values increased as the atrazine desorption step proceeded. The correlation between hysteretic coefficient and desorption step was highly significant for λ ( P < 0.0001), but not for H.