Desorption Stage Research Articles

Kinetics of gas desorption during the thermal dissociation of iron(III) oxide

The kinetics of desorption and the subsequent thermal dissociation of iron(III) oxide are studied by thermogravimetric analysis with programmed heating at a constant rate of 3–10 K/min and chromatographic analysis of a gas phase. The sequence of desorption stages is experimentally established. The data obtained are processed, a formal description is performed, and the kinetic parameters of desorption and dissociation stages are determined.

Solid-State NMR Studies of the Local Structure of NaAlH4/C Nanocomposites at Different Stages of Hydrogen Desorption and Rehydrogenation

Structural properties of NaAlH4/C nanocomposites were studied using 23Na and 27Al solid-state NMR. The samples were synthesized by melt infiltration of a highly porous carbon support, with typical pore sizes of 2−3 nm. Physical mixtures of high surface carbon with alanates in different stages of hydrogen desorption show somewhat broadened resonances and a small negative chemical shift compared to pure alanates. This is most likely caused by a susceptibility effect of the carbon support material, which shields and distorts the applied magnetic field. After melt infiltration, 23Na and 27Al spectra are broadened with a small downfield average shift, which is mainly caused by a chemical shift distribution and is explained by a larger disorder in the nanoconfined materials and a possible charge transfer to the carbon. Our measurements show that the local structure of the nanoconfined alanate is the similar to bulk alanate because a comparable chemical shift and average quadrupolar coupling constant is found. In contrast to bulk alanates, in partly desorbed nanocomposite samples no Na3AlH6 is detected. Together with a single release peak observed by dehydrogenation experiments, this points toward a desorption in one single step. 23Na spectra of completely desorbed NaAlH4/C and NaH/C nanocomposites confirm the formation of metallic sodium at lower temperatures than those observed for bulk alanates. The structural properties observed with solid-state NMR of the nanoconfined alanate are restored after a rehydrogenation cycle. This demonstrates that the dehydrogenation of the NaAlH4/C nanocomposite is reversible, even without a Ti-based catalyst.

Functions of LiBH4 in the hydrogen sorption reactions of the 2LiH–Mg(NH2)2 system

LiBH(4) is an effective additive in enhancing hydrogen desorption and absorption properties for the 2LiH-Mg(NH(2))(2) hydrogen storage system. The improving factors brought by LiBH(4) were studied experimentally. Although a minimum in activation energy was observed in the middle stage of hydrogen desorption for the samples with and without LiBH(4) doping, a reduction in the activation energy was manifest in the overall conversion range due to the LiBH(4) introduction. In contrast to the pure 2LiH-Mg(NH(2))(2), the system component Mg(NH(2))(2) crystallized in the presence of LiBH(4) at about 150 °C in situ from the post-milled amorphous mixture prior to hydrogen desorption. We believe the formation of the N-atom matrix by the crystalline Mg(NH(2))(2) is relevant to the subsequent dehydrogenation as it shares a similar sublattice structure with the desorption product. The formation and disappearance of Li(4)(BH(4))(NH(2))(3) in the dehydrogenation step witnessed the capturing and releasing of LiNH(2) that is generated from the dehydrogenation of 2LiH-Mg(NH(2))(2), which alters not only the kinetics but also thermodynamics in favor of an improved hydrogen sorption performance. The reaction mechanism could be further clarified by the refinement of powder neutron diffraction data of the intermediate compound Li(4)(BD(4))(NH(2))(3).

Oxidation of CO Catalyzed by a Cu Cluster: Influence of an Electric Field

Adsorption ability and reaction rate are two essential parameters that define the efficiency of a catalyst. Herein, we implement density functional theory (DFT) and report that CO can be oxidized by a pyramidal Cu cluster with an associated reaction barrier E(b)=1.317 eV. In this case, our transition state calculations reveal that the barrier can be significantly lowered after superimposing a negative electric field. Moreover, when the field intensity corresponds to F=-0.010 au, the magnitude of E(b)=0.698 eV is equivalent to-or lower than-those of typical catalysts such as Pt, Rh, and Pd. The superimposition of a positive field is found to enhance the release of the nascent CO(2) molecule. Our study demonstrates that small Cu clusters have better adsorption ability than the corresponding flat surface while the field can be used to enhance the purification of the exhaust gas.

Trapping behaviour of deuterium ions implanted into tungsten simultaneously with carbon ions

The trapping behaviour of deuterium ions implanted into tungsten simultaneously with carbon ions was investigated by thermal desorption spectroscopy (TDS) and x-ray photoelectron spectroscopy (XPS). The D2 TDS spectrum consisted of three desorption stages, namely desorption of deuterium trapped by intrinsic defects, ion-induced defects and carbon with the formation of the C–D bond. Although the deuterium retention trapped by intrinsic defects was almost constant, that by ion-induced defects increased as the ion fluence increased. The retention of deuterium with the formation of the C–D bond was saturated at an ion fluence of 0.5×1022 D+ m–2, where the major process was changed from the sputtering of tungsten with the formation of a W–C mixture to the formation of a C–C layer, and deuterium retention as the C–D bond decreased. It was concluded that the C–C layer would enhance the chemical sputtering of carbon with deuterium with the formation of CDx and the chemical state of carbon would control the deuterium retention in tungsten under C+–D2+ implantation.

Continuous O2-CO2 production using a Co-based oxygen carrier in two parallel fixed-bed reactors

Oxygen-enriched carbon dioxide stream with oxygen concentration higher than 20 vol% was produced continuously by using a Co-based oxygen carrier packed in two parallel fixed-bed reactors operated in a cyclic manner. Oxygen was absorbed by the oxygen carrier with air being fed. An oxygen-enriched carbon dioxide stream was ob- tained when the fixed-bed was regenerated with carbon dioxide as a purge gas. Multiple absorption and desorption cycles indicated that the Co-based oxygen carrier had high cyclic stability. XRD analysis determined the absorbed and desorbed products were Co3O4 and CoO, respectively. The TGA results indicated that Co-based oxygen carrier did not react with NO or SO2 during the desorption stage. This Co-based oxygen carrier offers potential for applications in the O2-CO2 production for the oxy-fuel coal combustion process. La0.1Sr0.9Co0.5Fe0.5O2.6+0.9CO2⇔ 0.9SrCO3+0.05La2O3+0.5CoO+0.25Fe2O3+0.15O2 (1) Sr0.5Ca0.5Co0.5Fe0.5O2.47+CO2⇔ 0.5SrCO3+0.5CaCO3+0.5CoO+0.25Fe2O3+0.11O2 (2) This reversible process makes perovskite material react with CO2 to form carbonate when using CO2 to release O2. In the next step, O2 storage step, the carbonate formed will decompose and gas prod- uct CO2 will be released into air, diluted by N2. This will result into failing to capture CO2 from flue gas (11). So oxygen carrier with high reactivity, high reaction rate, high stability and not reacting with CO2 is critical for CAR O2 production process. It is found that cobalt oxide can be used as oxygen carrier and has all these good characters mentioned above. The storage and release of O2 are based on the following reversible reaction:

Remoção de níquel(II) de soluções aquosas pela biomassa <em>Sargassum filipendula</em> em múltiplos ciclos de sorção-dessorção

The behavior of seaweed Sargassum filipendula during a removal of nickel from a 50 mg/L aqueous solution at pH 3.5 in fixed-bed columns operating in adsorption/desorption cycles has been studied. Two elution systems were tested; the first one operating with the direct passage of eluant and the second one with the solution recycle.Then, ten consecutive sorption-desorption cycles were investigated in two packed-bed columns, the first column was regenerated with H2SO4 (0.1 M) and the second one with MgSO4 / H2SO4 (3.5% in pH 3) in eluant recycle system. The sorption and desorption stages were carried out for about 30h and 2 h, respectively, representing 20 days of a continuous use of the biomass. A high quantity of recovered nickel was observed in the elution stages (approximately 97%). After 10 cycles, it was verified that the Sargassum filipendula biomass continued accomplishing elevated values of nickel removal from the solution, showing to be an efficient alternative treatment of wastewaters containing metals. The biomass is easily found and the regeneration presented low cost besides having facilitated the treatment process dispensing successive biomass changes.

Deuterium retention and release in tungsten co-deposited layers

A systematic study of the influence of the deposition conditions on the deuterium retention in co-deposited tungsten layers formed both by magnetron sputtering and in the PISCES-B linear device has been carried out. Experimental parameters such as the tungsten deposition rate, the incident particle energy and the substrate temperature are shown to affect the level of deuterium retention in the layers. A decreased retention for increased substrate temperature and deposition rates, and an increased retention for increasing incident deuterium particle energy are observed. A scaling equation is proposed to describe the influence of the conditions during the co-deposition process (surface temperature, incident particle energy and deposition flux) on the deuterium retention. In addition, the desorption kinetics of deuterium has been studied by TDS. Two desorption stages at 473–573 K and at 1073 K have been observed.

Impedance of faradeic process with partial charge transfer

The electrochemical impedance of charge-transfer reaction involving the stages of adsorption and desorption of intermediate partially charged substance is analyzed theoretically in the frequency-potential plane in order to study the possibility for measuring the partial charge transfer. The simplest case of adsorption two-electron transfer, namely, the Langmuir adsorption with liner dependence of reaction rate on the coverage, is considered. It is assumed that the partial charge transfer is independent of the electrode potential.

Selective hydrogenation of ethyl-benzoylacetate to 3-hydroxy-3-phenyl-propionate catalyzed by Pd/C in EtOH as a solvent in the presence of KOH: The role of the enolate ion on the reaction mechanism

Abstract The selective hydrogenation of ethyl-benzoylacetate to 3-hydroxy-3-phenyl-propionate catalyzed by Pd/C in EtOH in a solution of KOH has been investigated. Mass transfers as well as adsorption and desorption stages do not influence reaction kinetics. A kinetic model is proposed based on the best fitting of the experimental data with Langmuir–Hinshelwood type kinetics equation. The mechanism implies that the enolate of the ethyl-benzoylacetate adsorbs strongly on two sites, thus occupying a large part of the surface Pd atoms without any reaction. The ethyl-benzoylacetate adsorbs also on two sites but with adsorption equilibrium constant almost three order of magnitude lower than that of the enolate anions. Also the hydrogen is poorly adsorbed, however, it forms Pd–H and reacts with the adsorbed keto-ester by a step hydrogenation mechanism in which the first hydride insertion is the rate-determining step. Furthermore, due to the low surface Pd–H availability and the fast desorption of the 3-hydroxy-3-phenyl-propionate the consecutive hydrogenolysis of the C–OH bond of the product is practically suppressed, thus achieving selectivity close to 100%.

Structure-dependent deuterium release from ion implanted beryllium: Comparison between Be(1 1 [formula omitted] 0) and Be(poly)

The temperature-driven release of deuterium implanted as keV ions into metallic beryllium is measured by temperature-programmed desorption (TPD). TPD spectra from single and polycrystalline Be implanted with 1keV ions are compared. The high-temperature desorption stage (T>700K) is attributed to the release of deuterium trapped at several types of energetically different ion-induced defects. A release peak around 850K is recorded in the single crystal, while in the polycrystal all deuterium desorbs below this temperature. An increase in the maximum release temperature is observed after implantation of the polycrystal with higher ion energies (2 and 3keV). We propose an interpretation of the experimental results based on two types of traps, with depth distributions adapted to the implantation energy. Preliminary TMAP7 calculations qualitatively reproduce the shifts in the maximum desorption temperature, observed in the polycrystal at different implantation energies. The difference between the single and the polycrystal is explained by a higher density of surviving defects in the single crystal. Diffusion of mobile defects to grain boundaries and subsequent annihilation is proposed as the dominant mechanism for differences in deuterium desorption from Be(112¯0) and Be(poly).

Tests of membrane-sorption decontamination of the reservoir cascade of the Techa river

Results are reported from a comprehensive test, under real conditions, of technology for removal of 90Sr from the waters of the Techa reservoir cascade. This technology includes stages of preliminary decontamination, ion exchange softening with desorption and carbonate precipitation of hardening salts and 90Sr from the desorbates, sorption cleanup on natural zeolites, and concentration of the strontium-containing carbonate precipitates. After the precipitates are removed, the solutions are reused in the desorption stage. The quality of the decontaminated water meets all the requirements for discharge into open drainage network in terms of all indicators. (The specific activity of 90Sr is 3–5 Bq/liter in the filtrates.) The 90Sr is concentrated by a factor of about 900 as solid radioactive waste in the form of a sediment with a moisture content of 50% and by about 1700 as air-dried solids. As a preliminary estimate, the operating cost of decontaminating 1 m3 of water in the V-11 reservoir is 200 rubles.

Preliminary Assessment of a Concept of Looping Combustion of Carbon

A novel concept of looping combustion of carbon (CarboLoop) is presented. It is based on the feature of carbons to extensively uptake oxygen upon exposure to air at moderate temperatures. Surface oxides of carbon are eventually released as combustion products (CO, CO2) as the oxidized fuel is brought to moderate-to-high temperature in an oxygen-free atmosphere. This concept is pursued to the formulation of a preliminary scheme of a looping combustor of carbons based on a dual interconnected bed reactor system. One of the reactors is air-blown and acts as the fuel oxidizer. The second reactor, operated with partial recycle of gaseous effluents (CO2 + impurities), acts as the fuel desorber. Operating conditions of the oxidation and desorption stages may be properly tuned, leading to alternative looping strategies. The present study lays down the basic mechanistic background for analyzing the process, based on a simplified semiglobal approach to combustion and oxidation of solid carbons. The soundness of the CarboLoop concept has been verified by purposely designed experiments. The alternated oxidation/desorption stages typical of a looping combustor are simulated in a thermogravimetric analyzer. Experiments were directed to monitoring the oxidation and desorption steps under simulated looping conditions. Graphitized coke has been used as a surrogate carbon fuel. The experimental results confirm the soundness and potential of the CarboLoop concept and lay the path for its further development.

Kinetics of Peach Clarified Juice Discoloration Process with an Adsorbent Resin

This paper deals with the effects of adsorbent resin upon kinetic process of peach juice adsorption de-coloration at different temperatures ranged from 10 °C to 50 °C. The adsorption equilibrium was quantified by means of adsorption isotherms in the range from 10 °C to 50 °C. Absorbance data at 420 nm were used to plot all the isotherms, which correlated reasonable well with the Freundlich and Langmuir isotherms. Also, the efficiency of the adsorption process was studied for different resin/juice ratios at different temperatures, from which it was observed that there was a notable improvement in efficiency as the resin content increased, while the increase in temperature was not so important in the process. The adsorption kinetics was also studied at 30 °C, for relationships of 1, 2, and 3 g resin/100g juice. A kinetic adsorption— desorption model in two simultaneous steps was proposed, where the adsorption step is considered as zero order and the desorption step as first order. This allows a global expression to be obtained that fits the experimental data appropriately to this kinetic type equation. The initial adsorption rate depended on the resin/juice relationship in such a way that the higher its value, the lower this relationship was. It was also shown that the equilibrium constant showed a similar tendency, its value being superior to the unit, which indicates that the retention stage over the resin prevails over the colored product desorption stage.

Chemically modified silver nanoparticles as a new sorbent for preconcentration of polycyclic aromatic hydrocarbons from aqueous solutions

236 Currently, considerable attention is paid to determination of compounds contaminating the environment, in particular, polycyclic aromatic hydrocarbons (PAHs) due to their high carcinogenic activity [1]. Determination of PAH concentrations in aqueous media poses great difficulty. This stimulates the development of highly sensitive and highly selective methods of analysis. Usually, analysis of environmental objects for PAHs includes preconcentration followed by identification and quantitative determination. In recent years, alternative methods based on sorption preconcentration followed by luminescence determination of PAHs at room temperature have been developed [2, 3]. The sorption methods are more practicable than other preconcentration methods, for example, liquid and supercritical fluid extraction. In this study, PAHs were preconcentrated from aqueous solutions using chemically modified silver nanoparticles as sorbents. PAH are sorbed on them under static conditions, i.e., by mere stirring of the analyte with the sorbent, and then determined based on sensitized fluorescence intensity of silver nanoparticles at room temperature. A specific feature of this approach is the absence of the stage of desorption of the analytes, which is most often incomplete. Pyrene was chosen as the model PAH. This choice was due to the fact that this compound is often used as a fluorescence probe for the study of the state of sorbates and physicochemical properties of sorbents owing to the high sensitivity of its fluorescence spectra to change in the local environment [4, 5]. The fluorescence spectra of pyrene and the absorption spectra of silver nanoparticles lie in the same region, which is a necessary condition for the appearance of sensitized fluorescence of silver nanoparticles [6]. Chemically modified silver nanoparticles were prepared by reduction of silver nitrate in an aqueous solution with an excess of sodium borohydride in the presence of cetyltrimethylammonium bromide (CTAB). CTAB (0.44 g) was dissolved in doubly distilled water (20 mL), silver nitrate (0.17 g) was added, and an aqueous solution (5 mL) containing sodium borohydride (0.08 g) was added dropwise. The mixture was stirred at room temperature for 30 min. The aqueous sol of silver nanoparticles was used as the sorbent either directly (concentrated sol) or after 10-fold dilution with doubly

Experimental Study of O2−CO2 Production for the Oxyfuel Combustion Using a Co-Based Oxygen Carrier

Production of O2−CO2 mixed gases for the oxyfuel combustion using a Co-based oxygen carrier packed in a fixed bed reactor was investigated. The reaction kinetics of CoO with O2 and the decomposition kinetics of Co3O4 in CO2 atmosphere at different temperatures were studied using thermogravimetric analysis (TGA). Both desorption and sorption processes exhibit a high reaction rate. Multiple sorption and desorption cycles indicated that Co-based oxygen carrier has high reactivity and cyclic stability. The results of X-ray diffraction indicated that Co-based oxygen carrier does not react with CO2 during the desorption stage, and this is especially important for oxyfuel combustion. The high temperature sorption process for production of O2−CO2 gas mixtures in a fixed bed reactor packed with Co-based oxygen carrier particles through air separation with carbon dioxide as the purge gas is investigated. Oxygen is absorbed, and heat is stored by the Co-based oxygen carrier particles with air being fed. An O2−CO2 stream can be obtained when the fixed bed is regenerated with carbon dioxide as the desorption gas. O2 fraction in the O2−CO2 gas mixtures can be controlled by adjusting the flow rate of CO2 regeneration gas. This Co-based oxygen carrier offers potential for further study in the O2−CO2 production for the oxyfuel coal combustion process.

Kinetics of water adsorption on loose grains of SWS-1L under isobaric stages of adsorption heat pumps: The effect of residual air

In this paper we studied the effect of a non-adsorbable gas (air) on kinetics of water adsorption on loose grains of the composite adsorbent SWS-1L (silica modified by calcium chloride) (grain size 0.8–0.9 and 1.4–1.6 mm). The adsorbent grains were placed on the surface of isothermal metal plate at T = 60 °C and equilibrated with the mixture of water vapor at P H 2O = 10.3 mbar and air at a certain partial pressure P A. After that the metal plate was subjected to a temperature drop down to 35 °C at almost constant pressure over the grains. Reduction of the adsorption rate was revealed even at the partial pressure of residual air P A as low as 0.06 mbar. At P A > 0.4 mbar the kinetic curves were near-exponential and the characteristic adsorption time τ did not depend on the grain size and increased as τ = τ 0 + AP A, where A = 700 ± 50 s/mbar. Desorption stage was less affected by the residual air. The specific cooling power generated during the isobaric adsorption stage was estimated as a function of the residual air pressure.

Temperature-dependent activation energy for silicon desorption processes

A theoretical analysis is presented of the temperature dependence of the activation energy for thermal desorption of silicon from textured tantalum tape. The curves derived from experimental data for the initial stages of desorption are in qualitative agreement with calculation results, which makes it possible to estimate lateral interaction forces and the adatom-substrate interaction energy as a function of surface coverage and to predict structural changes in the film.

Structure of Ternary Imide Li2Ca(NH)2 and Hydrogen Storage Mechanisms in Amide−Hydride System

The crystal structure of the ternary imide Li 2Ca(NH) 2 has been determined using neutron powder diffraction data on a deuterated sample. The structure consists of infinite layers of edge-shared Ca[NH] 6 octahedra, which are separated by Li cations. The mobile Li (+) ions in such two-dimensional channels defined by Ca[NH] 6 octahedra layers are shown to have a great impact on the hydrogenation properties of the imide. Through detailed structural analysis on the products at various stages of desorption and absorption of the amide-hydride mixture, we proposed a dehydrogenation mechanism involving the mobile small ions in both amide and hydride and a hydrogen storage mechanism for the ternary imide.

Precise Depth Control and Low-Damage Atomic-Layer Etching of HfO[sub 2] using BCl[sub 3] and Ar Neutral Beam

The etch characteristics of HfO 2 by atomic-layer etching (ALET) were investigated using a BCl 3 /Ar neutral beam. The effect of ALET on surface modification and etch-depth control was also examined. Self-limited etching of HfO 2 could be obtained using BCl 3 ALET. This was attributed to the absorption of BCl 3 by the Langmuir isotherm during the absorption stage and the vaporization of hafnium-chlorides/boron oxychlorides formed on the surface during the desorption stage. In addition, the surface composition of HfO 2 was not altered by etching during ALET.