Desorption Model Research Articles

CBM Desorption Model and Stages Based on a Natural Desorption Experiment.

Coalbed methane (CBM) desorption modeling is critical for understanding CBM desorption mechanisms and objectively analyzing the production characteristics of CBM wells. According to the CBM natural desorption experimental data of 64 coal samples taken from the Qinshui Basin, we established a CBM desorption model, quantitatively identified the CBM desorption stages, and discussed the relationship between CBM desorption characteristics and well productivity. The results indicated a very significant functional relationship between the CBM natural desorption time and cumulative desorption quantity, which could be accurately described by the model V = aLt/(t + bL). On the basis of this model and the numerical description of the desorption data, the CBM natural desorption process was divided into four stages: the desorption startup stage, desorption sensitive stage, desorption steady stage, and desorption decay stage. As indicated by analogical reasoning of the CBM well production process, the desorption startup stage corresponded to the drainage-based pressure drop stage, the desorption sensitive and steady stages corresponded to the steady production stage, and the desorption decay stage corresponded to the production declining stage. The CBM adsorption time exponentially decreased with the increase in the average CBM desorption rate and with the increase in the CBM gas content and vitrinite/inertinite ratio. Furthermore, within a certain range of desorption pressure, a high ratio between the adsorption time and gas content corresponded to the extension of the steady production stage of CBM wells, whereas higher or lower ratios were adverse to steady production.

Desorption and transfer processes in different classes of dyes

AbstractWe report an analytical approach to study dye desorption and transfer processes in aqueous environment. The study was conducted simulating standard laundry washes using two different donor textiles, a polyester textile dyed with Disperse Blue 79 and a cotton textile dyed with Reactive Red 239, and two acceptor textiles, undyed cotton and polyester, respectively. Dye bleeding/solubilization from a donor textile to the solution was investigated through UV–visible absorbance analysis, while the dye absorption onto acceptor textile was quantified by UV–visible reflectance analysis. Dye desorption and transfer processes were investigated in water and surfactant solutions at different concentrations. A desorption and transfer model for the two classes of dyes was hypothesized by performing kinetic experiments. The results show that both processes depend on the presence of surfactants for the disperse dye. Conversely, the presence of surfactants has little effect on the reactive dye. Finally, the presence of an acceptor polyester significantly increases the bleeding of the disperse dye, while the presence of an acceptor textiles less influences the total release of the reactive dye.

Towards a better understanding of ice mantle desorption by cosmic rays

ABSTRACT The standard model of cosmic ray heating-induced desorption of interstellar ices is based on a continuous representation of the sporadic desorption of ice mantle components from classical ($0.1\, \mu$m) dust grains. This has been re-evaluated and developed to include tracking the desorption through (extended) grain cooling profiles, consideration of grain size-dependencies and constraints to the efficiencies. A model was then constructed to study the true, sporadic, nature of the process with possible allowances from species co-desorption and whole mantle desorption from very small grains. The key results from the study are that the desorption rates are highly uncertain, but almost certainly significantly larger than have been previously determined. For typical interstellar grain size distributions it is found that the desorption is dominated by the contributions from the smallest grains. The sporadic desorption model shows that, if the interval between cosmic ray impacts is comparable to, or less than, the freeze-out time-scale, the continuous representation is inapplicable; chemical changes may occur on very long time-scales, resulting in strong gas phase chemical enrichments that have very non-linear dependences on the cosmic ray flux. The inclusion of even limited levels of species co-desorption and/or the contribution from very small grains further enhances the rates, especially for species such as H2O. In general, we find that cosmic ray heating is the dominant desorption mechanism in dark environments. These results may have important chemical implications for protostellar and protoplanetary environments.

Direct simulation Monte Carlo of the gas-adsorption of particles in gas–particle flows

The acceleration and heating of particles in gas–particle flows represents a general question in fluid mechanics and has been widely studied since the 1920s. However, studies on the gas adsorption–desorption process of a particle in a gas–particle flow are still lacking. In this paper, we aim to introduce a framework with which to explain the gas adsorption–desorption kinetic equilibrium of a spherical particle in a gas–particle flow. We also explore the potential influences of gas adsorption and desorption on the heating and acceleration of a particle in such a flow. We study the gas adsorption–desorption process using the Langmuir adsorption model and the flow method presented by Brancher in a Direct Simulation Monte Carlo simulation. We develop a new model to consider the gas adsorption–desorption kinetic equilibrium on the surfaces of spherical particles in the calculation of the Thermal Accommodation Coefficient. We observe from the simulations that the trend of gas adsorption is opposite to that of the particle surface temperature. We also find that the efficiency of the convective heat transfer and acceleration of a particle is higher for a particle with a higher adsorption probability on its surface. This paper provides a new framework with which to study the gas adsorption–desorption processes of particles in gas–particle flows. It also inspires for future work on the potential applications of the particle gas adsorption–desorption model in astrophysics.

A desorption model for the code SOLIDUSS and its experimental benchmarking

The code SOLIDUSS is a Monte Carlo based solid-state diffusion software for radiation protection. It was developed to accurately estimate the amount of radionuclides that could escape activated material affected by an accidental fire. A desorption model based on the computation of the desorption probability of those radionuclides reaching the surface of an object was introduced to upgrade the software, proven to be a significant improvement with respect to earlier stages of the code.A set of experiments was performed at CERN to estimate the out-diffusion of radionuclides from activated materials typically used in accelerator environments when exposed to high temperatures. In particular, a 49.3 µm thick Cu foil containing 60Co and a 94 µm thick Al foil with 22Na were exposed to approximately 1000 °C and 600 °C respectively for different time periods. Out-diffusion fractions of 1.5 ± 5.5% for 60Co after 5 h and 22.5 ± 3.1% for 22Na after 4 h were obtained.A set of SOLIDUSS simulations was carried out replicating the experimental setup and using literature diffusion and desorption activation parameters. The results obtained are in good agreement with the experimental data within error bars. A high sensitivity of the simulation results to changes in the input parameters was observed.

Initial Desorption of Reaction Beech Wood

The research aimed to obtain empirical data for modeling the initial desorption in reaction wood from the cross-section of the green beech (Fagus sylvatica L.) log. Firstly, we analyzed the chemical composition, macro and microscopic structure of tension and opposite wood tissue. Then, the Equilibrium Moisture Content (EMC) was measured by the Dynamic Vapor Sorption method during the initial desorption. The used air parameters were specific for the mild drying schedule of green beech timber (t = 20, 35, and 50 °C, Relative Humidity (RH) ranging from 95 to 0 %). Relationships between the EMC of reaction wood and drying parameters were modeled using the Response Surface Method (RSM). The tests revealed: different hygroscopic properties of tension and opposite wood, the dependence of EMC value on temperature, and differences between EMC values for initial (first) and second desorption. Moreover, it was confirmed that, during initial desorption, the EMCs of reaction wood are significantly higher than reference EMC data. The differences in the EMC value are up to 0.14 kg/kg (for air with RH above 90 %). The presented polynomial model of the initial desorption of reaction beech wood can improve drying schedules for beech sawn timber with a high amount of reaction tissue.

Mechanism of Methane Adsorption/Desorption in Low-Rank Vitrain and Durain Coal Affected by Pore Structure and Wettability: A Case Study in Dafosi Area, South Ordos Basin, China

Water content and water–coal interface wettability are always the difficult issues of coalbed methane adsorption/desorption. In order to study the effects of the pore structure and wettability of different macro coal components on methane adsorption and desorption, we compared and analyzed the wettability difference between vitrain and durain, and revealed the influence of wettability on methane adsorption and desorption through a pore structure analysis, wettability measurements, an adsorption–desorption experiment and adsorption heat calculations under different conditions, taking the No. 4 coal in Dafosi Coal Mine of the Huanglong coalfield as the research object. The results show that both vitrain and durain are relatively hydrophilic substances. However, vitrain has a low ash content, high volatility, and less oxygen, and the pores are mainly semi-closed pores compared with dark coal. Vitrain also has poor connectivity, poor sorting, a small pore diameter, and a coarser surface, resulting in poor surface wettability. The large specific surface area (SSA) and relatively poor wettability of vitrain leads to more adsorption sites in methane, which makes the adsorption capacity of vitrain greater than that of durain, but the good pore connectivity of durain causes the strong desorption capacity of durain. The isosteric adsorption heat of the adsorption process is greater than that of the desorption process, indicating that there is a desorption hysteresis phenomenon which is essentially due to the lack of energy in desorption. Surfactants change the wettability of the coal surface, and different surfactants have different effects on methane adsorption and desorption. Relatively speaking, the methane desorption of coal samples treated with G502 and 6501 are better. The research results provide scientific reference for the study of gas–water transport in the desorption process of low-rank CBM, and provide evidence for the methane desorption model of vitrain and durain.

Spatially and temporally heterothermic kinetic model of hydrogen absorption and desorption in metals with heat transport

Numerical modelling of hydrogen transport is effective for designing and optimizing various energy systems, including hydrogen storage devices, fuel cells, and nuclear fusion reactors. In the present study, we propose and demonstrate a spatiotemporally heterothermic, autonomous kinetic model of hydrogen absorption and desorption in metals for precise simulations. Our bidirectional transport model comprises elementary mass transfer processes of surface adsorption and desorption, subsurface transport, and bulk diffusion. Also implemented are heat generation and conduction stemming from the absorption enthalpy, to determine the evolution of temperature distribution in the metal body, as well as the hydrogen concentration profile. Simulations by our transport model reproduce experimental hydrogen absorption and desorption curves for various temperature levels and metal scales with a single identical set of numerical equations and kinetic parameters, to thus verify the validity of the model.

How Stickiness Can Speed Up Diffusion in Confined Systems.

The paradigmatic model for heterogeneous media used in diffusion studies is built from reflecting obstacles and surfaces. It is well known that the crowding effect produced by these reflecting surfaces slows the dispersion of Brownian tracers. Here, using a general adsorption desorption model with surface diffusion, we show analytically that making surfaces or obstacles attractive can accelerate dispersion. In particular, we show that this enhancement of diffusion can exist even when the surface diffusion constant is smaller than that in the bulk. Even more remarkably, this enhancement effect occurs when the effective diffusion constant, when restricted to surfaces only, is lower than the effective diffusivity with purely reflecting boundaries. We give analytical formulas for this intriguing effect in periodic arrays of spheres as well as undulating microchannels. Our results are confirmed by numerical calculations and MonteCarlo simulations.

A Numerical Evaluation of Coal Seam Permeability Derived from Borehole Gas Flow Rate

Coal seam permeability is a critical factor in coal seam gas extraction and gas outburst control. In Australian coal mines, coal seam permeability is normally estimated using a packer test or drill stem test. In contrast, Chinese coal mines generally estimate a parameter called the “gas conductivity coefficient” by measuring natural gas flow rates from an underground borehole drilled through a coal seam. With this method, it has been frequently reported that the permeability of many Chinese coal seams is between 0.0001 mD and 0.01 mD, which is extremely low compared to that of Australian coal seams (1–100 mD). It is therefore natural to wonder how closely the Chinese method measures permeability. Resolving this question will allow knowledge and experience in outburst management to be shared between Australian and Chinese coal mines. This question is investigated by the numerical modelling of gas desorption and flow through a seam of known permeability and by using the model’s borehole gas flow rate to estimate the permeability using the Chinese method. A total of 126 simulations were run with various input reservoir parameters. The results suggest that the Chinese method estimates permeability at an accuracy of 85% to 100%, which is adequate for mine pre-drainage design and outburst control. For the high diffusion rate (e.g., high gas content and short desorption time) and low Darcy flow rates (e.g., low permeability), these errors are reduced.

Experimental study of water-sorption and desorption of several varieties of oil palm mesocarp fibers

The availability and mechanical performance of palm nut mesocarp fibers make them a serious alternative to synthetic fibers for certain textile and composite applications. However, their use can be limited by the lack of knowledge of the process of water absorption and moisture recovery of these fibers as well as the mechanisms of desorption. This work highlights the porous character of palm nut mesocarp fibers (OPMF) by SEM analysis; this character is amplified by NaOH treatment. X-ray diffraction, Thermogravimetric Analysis and Infrared spectrometry of OPMF are also performed. The study of the drying kinetics of OPMF shows that the desorption model of Verna et al. best describes their drying process at three desorption isotherms (60, 70 and 80 °C). The diffusion coefficient is lower for the interior fibers than the exterior ones at all isotherms. The activation energy of the outer Tenera fibers (21.3 kJ/mol) is twice that of the Dura variety (10.2 kJ/mol). Moisture uptake is about 10% for Dura and inner Tenera varieties and 7% for outer Tenera fibers while water uptake is about 160% for Dura and Tenera varieties and 114% for outer Tenera fibers. The models of Sikame et al. and Mohsenin best describe the water and moisture uptake kinetics of OPMF. The moisture diffusion coefficient varies from 2.31 × 10−12 m2/s to 5.26 × 10−12 m2/s while the water diffusion coefficient varies from 3.32 × 10−10 m2/s for external Tenera fibers to 4.85 × 10−10 m2/s for internal Tenera fibers. There is great versatility between the water and moisture diffusion parameters from one variety of OPMF to another as well as within the same variety between external and internal fibers.

Experimental study on ultrasonic irradiation for enhancing coalbed methane recovery

The present study proposes the use of a new ultrasonic irradiation method to enhance permeability and desorption for gas recovery from low-permeability coal reservoirs. A triaxial stress ultrasonic irradiation test apparatus was developed specifically for coal, considering the properties of gas adsorption, migration, and sound intensity, and providing a simultaneous measurement of gas flux, to investigated the deformation and temperature of coal samples obtained from the Fuxin coal field by permeability and desorption experiments. With the ultrasonic irradiation duration, the permeability of coal improved gradually with unequal variation, accompanied by the Klinkenberg effect where it decreased rapidly and then increased slowly with increasing gas pressure. The ability to desorb coal was enhanced by higher sound intensity ultrasound irradiation, and the volume of gas desorption was much greater than that of the sample without mange, the temperature and strain were demonstrated as a “J shaped” curve. An X-ray computer tomography (CT) technique was used to visualise the meso- or macro-cracks in the coal sample at pre- and post- ultrasonic irradiation, consequently, fractures expanded under the irradiation of ultrasonic waves. A permeability and desorption model was developed to describe the improvement of coal seam gas production capacity under ultrasonic irradiation, which introduced effective sound pressure.

Last developments in polymers for wearable energy storage devices

Last developments in polymers for wearable energy storage devices

Adsorption of Zerovalent Iron Nanoparticles in the Inorganic Fraction of Volcanic Soils

Zerovalent (ZVI) iron has been used in environmental remediation, but the environmental fate of its nanoparticles (NZVI) is hard to find. The present study aimed to characterise the adsorption processes of commercial ZVI in the inorganic fraction of volcanic soils, contributing to the knowledge of the adsorption process on the whole soil. Volcanic soil samples were obtained by calcination method and characterised. A nano-ZVI stable suspension is prepared and characterised to know its size-particle distribution. Adsorption points (kinetical and isothermal) were obtained by adapting the procedure for homogeneous analyte adsorption. Kinetical, solute transport and isothermal adsorption and desorption models were adjusted to obtain more conclusive information about the process. Analysis of the results revealed that adsorption is a fast process. The inorganic fraction of an Andisol presented pH-dependant surface charge, requiring highly consistent control of the working pH to obtain proper adsorption points. Isothermal adsorption indicates that a combination of physical and chemical mechanisms contributes to the NZVI adsorption process. Desorption studies suggested chemisorption on specific surface-active sites of adsorbents, with the inorganic fraction of soil irreversibly retaining most of the NZVI particles. NZVI become irreversibly adsorbed over the inorganic fraction of soils, extending particle reactivity through time, affecting the stability of organic matter and microbial communities. In turn, this increases the possibility for plant uptake. Nevertheless, there is a low risk for the transport of NZVI through soil profiles or co-transport of other components that becomes adsorbed over iron, lowering the risk of aquifer pollution.

Hydroalcoholic extraction of bioactive compounds from expeller soybean meal under subcritical conditions

The extraction of bioactive compounds from expeller soybean meal (ESM) was performed using different ethanol + water mixtures under subcritical conditions in a dynamic mode. The influence of temperature, solvent mass flow rate, solvent mixture composition, ionic strength, and particle size of the matrix on the extraction yield and the extract characteristics (total phenol and total flavonoid content and antioxidant activity) was evaluated using a screening design. Extracts that showed better results were analyzed by ORAC and TEAC tests. Finally, to predict the extraction kinetics of the bioactive compounds, the one-site desorption model and the thermodynamic partition model were compared. The results show that it was possible to obtain extracts with a high phenols and flavonoids content (23.04 mg GAE/g ESM and 7.34 mg QCE/g ESM, respectively) with good antioxidant capacity compared to extracts obtained from other vegetable matrices.

Evaluating isotherms and isosteric heat utilization during sorption characteristics of feed barley

A well-formulated sorption model defines the grain moisture and also the energy expenses associated with drying and/or rehydration. Though literature contains adsorption and desorption models that are used to identify the hysteresis, they are not efficient to implement in sensors simultaneously when monitoring stored grain transient conditions. This study modifies the existing sorption model to fit transient monitoring criteria based on harvest moisture conditions between 11.3 and 85.9% RH at three temperatures (15, 25 and 35 °C). Feed barley was taken for the sorption study and fitted with equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) equations of five widely used isotherm models, respectively. Model was fitted with EMC's attained at individual temperatures and the transfer phases between them.Sorption isotherms showed a non-smooth Type II sigmoidal trend with positive correlation between RH and EMC. The time taken to reach EMC irrespective of RH was inversely proportional to the temperature difference noted from the transfer phase. The Modified-Oswin equation (EMC) was found to be appropriate to represent the sorption isotherm of feed barley. For the transfer phases, EMC at higher temperature showed negligible difference with initial EMC phase except at 15 °C with higher RH (adsorption). Heat of sorption showed a decreasing trend with moisture and was 27% (average) higher than the latent heat of vaporization. Sorption heats for transfer phases were higher than initial EMC phases but not significantly different. Energy difference went up to 250 kJ kg−1 between 9 and 14% db moisture showing a normal distribution below and above the moisture range, respectively. Thus, future storage models should consider sorption heats for proper estimation of energy expenses during drying and rehydration.

Adsorption and desorption of Cd in reclaimed soil under the influence of humic acid: characteristics and mechanisms

Exogenous humus can change the content and migration activity of cadmium (Cd) in soil. Humic acid (HA) is an important soluble humus component in soil. In order to explore the relationship between cadmium pollution mechanism and ecological environment of humic acid in reclaimed soil, the characteristics of humic acid adsorbing cadmium in alkaline conditions were studied. This study employed reclaimed soil from the Huainan mining area, China. The adsorption and desorption characteristics as well as influence mechanisms on the heavy metal cadmium (Cd) were explored under the influence of HA. The results show that: (1) When Cd concentration was low (0.2–10 mg/L), HA had little effect on Cd adsorption and desorption in reclaimed soil. When the Cd concentration was high (15–80 mg/L), HA had a great influence on the adsorption and desorption of Cd in reclaimed soil. The addition of HA can inhibit the adsorption of Cd by reclaimed soil and effectively improve the desorption capacity of Cd by reclaimed soil. (2) The kinetic curves of Cd adsorption and desorption of reclaimed soil with added HA show that both processes (adsorption and desorption) include two stages: rapid reaction and slow reaction. The adsorption of Cd by reclaimed soil under the influence of HA was 18.18% lower than that of normal reclaimed soil, and the increase of Cd desorption was 50.29%. (3) The factors affecting the adsorption and desorption of Cd in the soil were analyzed with gray theory, and their importance can be ordered as follows: Cd concentration > HA concentration > pH > temperature. Considering the influence of HA, a multi-factor coupling function model of adsorption and desorption of Cd in soil is established. This model provides theoretical guidance for the scientific prediction and evaluation of Cd environmental pollution risks in soil and will be useful for developing a new solution for engineering remediation of high concentration Cd contaminated soil.

Furfural hydrogenation over Cu, Ni, Pd, Pt, Re, Rh and Ru catalysts: Ab initio modelling of adsorption, desorption and reaction micro-kinetics

Hydrogenation, hydrodeoxygenation and ring opening of biomass-derived furfural were studied by using Pd/C, Pt/C, Re/C, Ru/C, Rh/C, Ni/C and Cu/C catalysts. Based on experiments, a generalized micro-kinetic model was developed, describing kinetics of tested catalysts well. Pd/C could unselectively hydrogenate furfural’s ring, aldehyde group or both and was the most active tested catalyst. Selective aldehyde group hydrogenation, followed by deoxygenation was observed with other catalysts. This route was also favorable thermodynamically according to density functional theory (DFT) calculations. Only Ru/C could form methyltetrahydrofuran (45.3 % yield) and ring opening products at 200 °C. Reaction conditions were optimized in silico for most promising catalysts (Pd, Pt, Re, Ni on carbon), by fixing the kinetic parameters obtained by regression analysis and subsequently maximizing the objective function, i.e. the yield of the product of interest. Validation experiments confirmed a high Pd/C hydrogenation activity already at 40 °C, forming predominantly tetrahydrofurfural (85 % yield), while 95 % yield of 2-methyltetrahydrofuran was obtained by using a cheap Ni/C at 212 °C.

Quantifying the Chemical Desorption of H2S and PH3 from Amorphous Water-ice Surfaces

Abstract Nonthermal desorption of molecules from icy grain surfaces is required to explain molecular line observations in the cold gas of star-forming regions. Chemical desorption is one of the nonthermal desorption processes and is driven by the energy released by chemical reactions. After an exothermic surface reaction, the excess energy is transferred to products’ translational energy in the direction perpendicular to the surface, leading to desorption. The desorption probability of product species, especially that of product species from water-ice surfaces, is not well understood. This uncertainty limits our understanding of the interplay between gas-phase and ice-surface chemistry. In the present work, we constrain the desorption probability of H2S and PH3 per reaction event on porous amorphous solid water (ASW) by numerically simulating previous laboratory experiments. Adopting the microscopic kinetic Monte Carlo method, we find that the desorption probabilities of H2S and PH3 from porous ASW per hydrogen-addition event of the precursor species are 3% ± 1.5% and 4% ± 2%, respectively. These probabilities are consistent with a theoretical model of chemical desorption proposed in the literature if ∼7% of energy released by the reactions is transferred to the translational excitation of the products. As a byproduct, we find that approximately 70% (40%) of adsorption sites for atomic H on porous ASW should have a binding energy lower than ∼300 K (∼200 K). The astrochemical implications of our findings are briefly discussed.

Modeling desorption and adsorption kinetics of reactive red 195 in washing microenvironment

The faded-on stains of cotton clothes are a common daily phenomenon. The desorption and adsorption of reactive dyes are theoretically responsible for the faded-on stains on cotton clothes in the washing microenvironment, especially when the light color cotton fabrics ( LCFs) are washed together with the cotton fabrics dyed in highly saturated color ( CFSCs). However, the effects of washing parameters on the desorption and adsorption kinetics of reactive dyes and the mitigation of faded-on stains in the washing microenvironment through washing parameter optimization are poorly understood. This study thoroughly discusses the desorption and adsorption behaviors of reactive red 195 in the washing microenvironment from the inhibition of color transfer. Firstly, CFSCs and LCFs were prepared by using reactive red 195 and cotton fabrics. Secondly, the effects of washing parameters, washing temperature, washing liquor ratio, and washing solution pH, on the dye desorption and adsorption rate were studied with the simulated washing device ( SWD), followed by the response surface analysis of washing parameters. Thirdly, the modeling of desorption and adsorption kinetics and velocity were detailed. Finally, the model of dye desorption and adsorption was validated in a drum washing machine ( DWM). The results are helpful for the design of scientific washing procedures to curb the faded-on stains of cotton clothes effectively.