Desorption Model Research Articles

A self-similarity transport model of gas desorption inside high maturity shale under thermal enhanced conditions

Thermal stimulation methods have been investigated to enhance gas extraction from the high maturity shale recently. In this paper, a Longmaxi shale core sample, with vitrinite reflectance = 2.8%, was selected for canister tests to investigate the gas desorption process first at 55 °C and then switched to 110 °C. A mathematical model (self-similarity) was proposed to mimic the gas decaying process in nano-sized pore system. Gas adsorption/desorption incorporated advection and Knudsen flow were considered in this model. For high Knudsen number flow, the effective diffusion coefficient of the gas in the model was assumed to be a power law of density gradient. From the experiment, when heating temperature was raised from 55 °C to 110 °C, more adsorbed gas started desorbing to the porous media. It was found that the gas production rate increased significantly (20 times) and the cumulative gas production also raised considerably (11 times). By selecting an appropriate exponent m for effective diffusion coefficient, the gas production rate decayed as 1t at 55 °C and declined as 1t2 at 110 °C, which fit well with experimental data. The scaling results indicated that Knudsen flow was the dominant source of the gas flow in the whole heating process. In conclusion, Knudsen flow is the dominant gas transport form during the heating process. Thermal stimulation can significantly promote gas production rate. Moreover, the developed mathematical model can well predict the gas production rate in the heating process.

Sorption and Desorption of CO2 and CH4 in Vitrinite- and Inertinite-Rich Polish Low-Rank Coal

Low-pressure sorption tests were carried out on samples of selected Polish bituminous coal in coal–methane and coal–carbon dioxide systems. The purpose was to determine the relationship between the petrographic composition of low-rank coal and the amount of gas stored in its porous structure and desorbed from it. The influence of the degree of coalification on the amount of sorbed gas was reduced to minimum, because isotherms of deposition and evacuation of gases were determined on the base coal samples and two concentrates of lithotypes, vitrain and durain, isolated from the original coal. It was found that the sorption capacity of carbon dioxide was related to the pertographic composition, but no such correlation was observed in regard to methane. Langmuir and Dubinin–Radushkevich sorption isotherms and the modified desorption model based on Langmuir equation were chosen. The applied equations gave a very good fit to the experimental data. Calculated parameters corresponding to free adsorption energy in the Dubinin–Radushkevich equation allow concluding on the independence of its mechanism from coal petrography and on the preference of carbon dioxide sorption. Calculated adsorption equilibrium constants in Langmuir’s equation show variability with petrographic composition of coal and have lower values for methane than for carbon dioxide. It was shown that the size of the hysteresis loop depends on the petrographic composition of coal and increases with increase in vitrinite content for both sorbates, which was confirmed by values of areal hysteresis index and hysteresis parameter.

Kinetic study of subcritical water extraction of flavonoids from citrus unshiu peel

Citrus peels are the main source of many important flavonoids, flavanones (hesperidin and narirutin) and polymethoxyflavones (PMFs; sinensetin, nobiletin, and tangeretin), which have antioxidant, anti-inflammatory, anticancer, and cardioprotective properties. In this study, the mechanisms controlling the extraction rates of flavonoids from Citrus unshiu peel using subcritical water (SW) were studied at different temperatures (120–180 °C) and flow rates (1.0–2.0 mL/min). The extraction yields increased from 40.9, 69.0, and 67.4% at 120 °C to 79.6, 81.9, and 89.0% at 160 °C for hesperidin, narirutin, and PMFs, respectively, while decomposition occurred at 180 °C. The extraction rate curves at different flow rates were used to determine whether the extraction was best described by a thermodynamic partitioning or kinetic desorption model. The extraction rate curves showed that the initial extraction phase is fast, while the subsequent phase is slow. The thermodynamic partitioning model did not match with the experimental data for the latter part of the extraction period. The two-site kinetic desorption model fit the entire extraction period very well, suggesting that the extraction of citrus flavonoids was mainly controlled by intra-particle diffusion. Interestingly, this model fit well even at the pyrolysis temperature (180 °C). Therefore, the two-site kinetic model can well describe both the decomposition mechanism and extraction mechanism of citrus flavonoids when using SW. The diffusion coefficient of hesperidin increased about 9.8-fold at 160 °C and 2 mL/min relative to 120 °C and 1 mL/min. The activation energy of hesperidin (37.2–43.8 kJ/mol) was higher than those of narirutin and PMFs (8.2–36.8 kJ/mol). This study showed that the extraction mechanism is mainly affected by intra-particle diffusion, and that use of small amounts of SW, an environmentally friendly solvent, promotes good recovery of flavonoids from citrus peel in a short time.

Effective Model of NOx Adsorption and Desorption on PtPd/CeO2-ZrO2 Passive NOx Adsorber

An effective model for describing NOx adsorption and desorption on a PtPd/CeO2-ZrO2 passive NOx adsorber is presented. The kinetic parameters are evaluated from the available experimental data obtained during NOx adsorption/desorption experiments including CO2 and H2O in the feed, performed at 80, 120 and 160 °C both in the presence and in the absence of reducing agents (CO or C2H4 ). The model describes the temperature dependence of the NOx adsorption rate and capacity, the impact of CO, and dynamics of the NOx desorption events. The model predicts formation of nitrites, nitrates, and additional storage enabled in the presence of CO. Thermal decomposition of the stored NOx species results in two main desorption peaks. Nitrites are desorbed at lower temperatures while nitrates are thermally more stable. The evolution of nitrite and nitrate species in the model corresponds with the measured DRIFTS spectra of the catalyst surface. The presence of CO significantly improves the rate of NOx adsorption and storage efficiency at low temperatures, most probably due to reduction of oxidic Pt and Pd nanoparticles. The developed model captures well the observed trends and can be utilized for simulations of PNA performance under real operating conditions.

Physical Properties of MEA + Water + CO2 Mixtures in Postcombustion CO2 Capture: A Review of Correlations and Experimental Studies

The knowledge of physicochemical properties of a mixture of amine, water, and CO2 is beneficial in evaluating the postcombustion CO2 capture process and process equipment design. This study reviews the literature of density, viscosity, and surface tension measurements with the evaluated measurement uncertainties and proposed correlations for monoethanol amine (MEA), water, and CO2 mixtures. Adequate research has been performed to measure and develop correlations for pure MEA and aqueous MEA mixtures, but further studies are required for CO2-loaded aqueous MEA mixtures. The correlations fit measured properties with an acceptable accuracy, and they are recommended to use in process equipment design, mathematical modelling, and simulations of absorption and desorption.

Exploration on self-equilibrium rule and adsorption-desorption model between pine nut (Pinus koraiensis) peptide molecules and environmental moisture molecules

The storage of pine nut (Pinus koraiensis) peptide (PNP) powder involves hygroscopic phenomena. To investigate the adsorption and self-equilibrium rules between these peptides and the environmental moisture molecules, several studies such as low-field nuclear magnetic resonance (LF-NMR), dynamic vapor sorption (DVS) and adsorption-desorption models were done. The results showed that the outward moisture migration occurred during storage as 7.80% and 16.68% moisture were respectively constrained by the original sample and 90 days after lyophilization, by chemical bonding. Additionally, 1.79% moisture was lost in PNP powder at day 90. The optimized adsorption model for PNP powder was changed from Henderson’s to Oswin’s model during the 90 days’ storage whereas the optimized desorption model was changed from Halsey’s to GAB’s model. The PNP powder at day 90 presented smaller particles with an average diameter and height of 15.645 nm and 50 nm, respectively, and it contained more molecular moisture which cannot be removed. The free thiol of the PNP powder at day 0 and day 90 was 1.75 ± 0.16 μM SH/g and 1.95 ± 0.16 μM SH/g, respectively, and the total sulfhydryl was 101.46 ± 1.06 μM SH/g and 118.44 ± 1.27 μM SH/g. The registered increased sulfhydryl content contributed to the generation of off-flavor.

Temperature- and pressure-dependent gas diffusion in coal particles: Numerical model and experiments

The diffusion coefficient is a key parameter related to gas migration in coalbed methane extraction and CO2 geologic sequestration applications. Isothermal assumptions are usually used in diffusion models and experimental tests, in which the thermal effect and its impact on gas adsorption/desorption are neglected. Coal powder gas diffusion tests are not exactly reflective of an isothermal process, in fact, due to gas-desorption-induced decreases in temperature. In this study, a coupled thermal-diffused-mechanical model for gas desorption–diffusion under non-isothermal conditions is developed in which the effects of gas pressure, temperature, and coal porosity on the gas diffusion coefficient are considered. The effect of gas-desorption-induced temperature variation is also included. Gas desorption–diffusion tests are conducted on coal powder under isothermal and adiabatic conditions, respectively. The developed model is then used to simulate the gas desorption–diffusion process under adiabatic conditions and the results are compared against the test data. The proposed non-isothermal model with varying diffusion coefficient, which can be regarded as an improvement of the classical unipore diffusion model, is shown to replicate the whole desorption–diffusion process and back-calculate a relatively consistent diffusion coefficient value range for all scenarios. The results also show that the assumption of isothermal conditions in a diffusion model significantly overestimates the accumulated gas diffusion content throughout the gas desorption–diffusion process. The assumption of constant diffusion coefficient partially underestimates the gas diffusion rate and accumulated gas diffusion content in the later stages.

Clean technology for synchronous sequestration of charged organic micro-pollutant onto microwave-assisted hybrid clay materials.

The Sustainable Development Goal 6 (SDG #6) of the United Nations (UN) is hinged on the provision, availability, and sustainability of water for the global populace by 2030. In a bid to achieve this goal, the quest to seek for ubiquitous and low-cost adsorbents to treat effluents laden with industrial dyes, such as methylene blue (MB), is on the increase in recent years. Acute exposure of humans to (MB) dye causes cyanosis, necrosis, and jaundice and even leads to death. In this research, zinc-modified hybrid clay composite adsorbent (materials from kaolinite and biomass (crushedCarica papaya seeds and/or plantain peel)) was developed via microwave route. This adsorbent was characterized using field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray (EDX), and high-resolution transmission electron microscopy (HR-TEM). These characterization techniques confirmed the success achieved in doping hybrid clay with Zn. These adsorbents were used to sequester cationic dye (MB) from aqueous solutions and textile effluent under various experimental conditions. The adsorption and desorption data obtained were analyzed using various kinetic models, which are two-step kinetics, pseudo-first order, pseudo-second order, fractal kinetics, first-order desorption, second-order desorption, and modified statistical rate theory (MSRT) desorption models. Results showed that the adsorption of the dye occurred via several chemical interactions, while the latter models (for desorption) indicated that desorption occurred in two different desorption sites on the adsorbent surfaces, which showed that the adsorption of MB dyeonto the adsorbents was stable without the emergence of any secondary pollution. Adsorption of MB was achieved within 15min for aqueous solutions and 900min for textile effluent, which is an improvement on previous results from other studies. The three adsorption-desorption cycles for MB uptake by the adsorbents showed that it is pragmatically applicable to treat textile effluents. Hence, low-cost composite adsorbents have a potential for the effective remediation of MB dyefrom textile effluents as this study confirmed.

Десорбция атомов калия, стимулированная электронным облучением системы K/K-=SUB=-x-=/SUB=-Au-=SUB=-y-=/SUB=-

Electron-stimulated desorption of K atoms from the surface of potassium atoms on KxAuy was discovered. A KxAuy layer on a tungsten substrate with a gold film deposited on it with a thickness of not more than 5 atomic layers of gold. A quasi-resonant dependence on the energy of the exciting electrons of the electron-stimulated desorption was found. The quasi-resonance dependence is due to the excitation of core levels of Au 5p3/2 and Au 5p1/2. A model of electron-stimulated desorption of K atoms in the K/KxAuy system is proposed that adequately describes the processes that occur during electron-stimulated desorption of potassium atoms. The processes of electron-stimulated desorption excitation of potassium atoms occur at the K/KxAuy interface.

Modelling of Desorption from Surface Effective Sites Formed on Nanosized Metal Clusters

Modelling of Desorption from Surface Effective Sites Formed on Nanosized Metal Clusters

Modeling post-fumigation desorption of phosphine in bulk stored grain

Phosphine is a dangerous gas commonly used in fumigations of stored grains throughout the world. Grain that has not fully released the phosphine it absorbed during fumigation may continue to desorb phosphine into the headspace of a shipping container or storage. USOSHA standards for handling phosphine state the acceptable Threshold Limit Value (TLV) of 0.3 ppm. In many cases, during grain transport and handling, the level of phosphine in work environments can exceed the 0.3 ppm TLV which resulted from desorption of phosphine from fumigated grains. It is also important to note that desorbing grain, with low concentrations of phosphine, can facilitate insect resistance. Therefore, it is important to understand the process of phosphine venting and desorption in order to ensure safe handling of fumigated grain. In order to achieve this, the venting and release of phosphine was studied on location in a well-sealed grain silo in Lake Grace, Western Australia. The data set served for verification of a 3D finite element ecosystem model and were compared to the predicted results. Results were calculated using two different fumigant desorption models based on previous literature, i.e., a reversed sorption model and an air-grain equilibrium model. Simulations reproduced accurate trends of desorption but did not accurately reproduce the quantity of fumigant, with 55.5% error for the model based on reversed sorption equations, and 86.3% error for the air-grain equilibrium based model. For both models, additional simulations were conducted to compare the effectiveness of existing grain venting regulations at producing grain that is within post-fumigation safe handling limits. Results revealed that current U.S. standards may be insufficient to guarantee safety based on minimum venting times needed. These results highlight the necessity for continued research into phosphine desorption and the importance for establishing realistic post-fumigation venting guidelines.

Numerical modelling of adsorption and desorption of water vapor in zeolite 13X using a two-temperature model and mixed-hybrid finite element method numerical solver

In this paper, we present a new two-temperature mathematical model for a thermo-chemical energy storage based on the adsorption and desorption of the water vapor in zeolite 13X. The adsorption process is modelled using the Linear Driving Force (LDF) model and the Langmuir-Freundlich isotherms. A numerical solver based on the mixed-hybrid finite element method and operator splitting technique is proposed. Furthermore, we present a computational study of the charging and discharging processes of the thermo-chemical energy storage emphasising the behaviour of the two temperatures: fluid temperature and zeolite temperature.

A model of gas desorption and radiation during initial high voltage conditioning in vacuum

Large quantities of gas are desorbed from the anode electrode during initial high-voltage conditioning of broad-area electrodes in a vacuum, equivalent to many monolayers and consist mostly of neutral molecules with an ionic component of a few percent. The ions are accelerated to the cathode, producing secondary electrons from the cathode and x-rays. There is still no reasonable explanation of these phenomena. Experiments have been performed to try to understand the source of the gas and radiation by using a residual gas analyzer to examine the desorption products from copper electrodes during initial high-voltage conditioning. The desorption products produced during initial high-voltage conditioning were then compared with those from thermal desorption of the same electrodes and surface preparation as they were heated in vacuum to about 600 °C, both with and without a high electric field present. Thermal desorption with an applied field showed a significant difference in the desorption spectrum compared with no applied field and produced a modest source of radiation that did not appear to be produced by field emission. At electrode temperatures beyond 450 °C, radiation production increased exponentially with temperature, likely produced by surface ionization of minor contaminants with a low ionization potential. These observations have been used as input to propose that the radiation and gas desorption observed during initial high-voltage conditioning is initiated by surface ionization from the many projections with high field enhancement factors on the anode surface.

Hierarchical quantum master equation approach to vibronic reaction dynamics at metal surfaces.

A novel quantum dynamical method to simulate vibronic reaction dynamics in molecules at metal surfaces is proposed. The method is based on the hierarchical quantum master equation approach and uses a discrete variable representation of the nuclear degrees of freedom in combination with complex absorbing potentials and an auxiliary source term. It provides numerically exact results for a range of models. By taking the coupling to the continuum of electronic states of the surface properly into account, nonadiabatic processes can be described and the effect of electronic friction is included in a nonperturbative and non-Markovian way. Illustrative applications to models for desorption of a molecule at a surface and the current-induced bond rupture in single-molecule junctions demonstrate the performance and versatility of the method.

Development and environmental implication of pedotransfer functions of Cd desorption rate coefficients in historically polluted soils

The desorption rate is an important factor determining cadmium (Cd) ecotoxicity and pollution remediation in soils. The pedotransfer functions (PTFs) of desorption rate coefficients of fresh Cd in soils have been developed in literature. We hypothesized that the aging of Cd pollution would alter Cd desorption process. Taking historically polluted soils as the object, this study aimed at testing the hypothesis and developing new PTFs of desorption rate coefficients for historical Cd. 15 d batch extraction experiments and 13 kinetic models were employed to define Cd desorption rate coefficients in 27 historically polluted soil samples. Compared with fresh Cd, the desorption rate coefficients of historical Cd were lower, and the break time of biphasic desorption processes was retarded to 3 d (4320 min). Different with the usual models for fresh Cd desorption (e.g. parabolic diffusion and two constant rate models), the best models to mimic the historical Cd desorption processes were the pseudo first order, logarithmic, Elovich, and simple Elovich models. The rate-limiting step controlling Cd desorption was changed from the intraparticle diffusion to the interface reaction with aging of pollution. New PTFs of desorption rate coefficients of historical Cd were established (R2 ≥ 0.71). Cd desorption rate coefficients increased with organic matter and clay contents, but decreased with oxalate extractable Fe content, solution pH, cation exchange capacity, and silt content. The key soil properties influencing desorption rate coefficients were not altered by the aging of pollution. The developed PTFs could guide us to adjusting the ecotoxicity and pollution remediation of Cd in historically polluted field soils.

Extraction of aromatic abietane diterpenoids from Salvia officinalis leaves by petroleum ether: Data resolution analysis

Salvia officinalis is the source of a vast variety of compounds valuable for pharmaceutical and food industry. The extractability of lipophilic diterpenoids from S. officinalis(L.) by petroleum ether is studied using Soxhlet, reflux, and percolation methods. The binding of the solute to the plant matrix is described by the Hill-Langmuir desorption model. The Monte Carlo sampling method is used to constrain the parameters of the extraction model and perform the resolution analysis of the extraction data. The percolation, followed by extraction at reflux, is demonstrated to be the most efficient method of extraction. The freely available content is estimated to be ye = 20.0 ± 2.9 mg g–1, while the total content in our case is shown to be 50–55 mg g–1 or higher. For engineering applications, the estimate of 60–70 mg g–1 is suggested as the upper limit.

Effects of particle mixing on characteristics of gas desorption and non-constant dynamic diffusion in coal

ABSTRACT Gas drainage technology is closely related to the flow of methane in coal. Desorption and diffusion of gas in coal is an important basic research area, and particle size is one of the influencing factors. In this study, the desorption and diffusion characteristics of coal samples mixed with different particle sizes over time were measured under constant temperature and pressure. The results show that in the initial stage, the desorption volume and desorption rate of coal samples are relatively large. The improved desorption model can well fit the data and the order of desorption volume is negatively correlated to the mean particle size of coal samples. The single small particle coal sample has the largest desorption volume which reached 3.77ml/g. Both the unipore model and the constructed unsteady dynamic diffusion model can well describe the diffusion of gas in coal, the diffusion coefficient of coal sample decreases with time, and the decay rate decreases gradually with time until it remains unchanged. The calculation results of the two models show that the diffusion coefficient ranges of gas in coal between 10−10m2/s and 10−12m2/s. For single-particle coal samples, the diffusion coefficient is positively correlated with particle size. The diffusion coefficient D is affected by the particle size and the degree of compaction between coal particles. These observations indicate that coal samples with different particle sizes will affect the desorption and diffusion of gas, and it has a positive impact on methane recovery.

Development and identification of a mathematical model of the process of continuous autoclave desorption of noble metals in moving-bed apparatus

The process of continuous autoclave desorption is the most promising for the intensification of coal-sorption technology for extracting noble metals by active carbons from solutions and pulps. The article presents a mathematical model of continuous autoclave desorption of gold from active carbons, which is based on the physicochemical regularities of the process and describes its dynamics. The developed mathematical model of the dynamics of the continuous desorption process allows analyzing the influence of the main parameters on the degree of extraction of gold and silver from activated carbons. It has been established that such parameters as temperature, phase ratio, processing time and pH of the elution solution have the greatest influence. Identification of the mathematical model showed satisfactory agreement between the experimental and the data obtained as a result of the simulation, which confirms the possibility of using it for analyzing and optimizing the process.

Modeling and experiment of gas desorption of bubble column with an external loop in the heterogeneous flow regime

This work introduces an external loop to a bubble column and presents enhanced gas exchange in the heterogeneous flow regime. Gas exchange experiments under the same amount of gas input were carried out with varying gas velocity to understand the difference of bubble characteristic between the bubble column (BCR) and the bubble column with an external loop (BCR-EL). The observation of rise and descending velocity of bubbles in the BCR-EL showed that the fraction of bubbles passing the downcomer continuously increases with the incremental superficial gas velocity. A gas molecule in the liquid phase is desorbed by another gas molecule, and this gas exchange was assumed to be a phenomenon that a reactant in the liquid phase is converted to a product. To test the validity of the assumed gas exchange as a reaction in the experiments with the BCR-EL, a modeling study was performed using Fisher-Tropsch synthesis. It prevailed that the syngas conversion was higher in the BCR at the homogeneous flow regime, while the BCR-EL at the heterogeneous flow regime (above 0.08 m/s) had higher syngas conversion than the BCR due to higher gas recycle to the downcomer.

Derivation of site-specific remediation goals by incorporating the bioaccessibility of polycyclic aromatic hydrocarbons with the probabilistic analysis method

Incorporating bioaccessibility into human health risk assessment is recognized as a valid way to reduce the conservative properties of conventional results, where the total concentration of a contaminant analysed by exhaustive chemical extraction is applied. Taking a coke production site in Beijing as an example, a mild chemical extraction technology was employed to profile the bioaccessibility of benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IcP) and dibenz[ah]anthracene (DBA) in soils. The results that were regressed using two bi-phase desorption models (Karickhoff and Weibull) revealed that the rapid desorption fractions of BaP, IcP and DBA, which are taken for bioaccessible fractions, were basically less than half of the total contents in the soils. Probabilistic analysis (PA) was carried out with pre-set distributions of the exposure parameters to characterize the uncertainty in the assessment. The results incorporating bioaccessibility and PA were several times higher than the generic remediation goals which equal to national screening levels, and orders of magnitude higher than the baselines of the region and nation. The results of the Weibull fit were finally recommended as site-specific remediation goals (SSRGs) (10.59 mg/kg, 95.48 mg/kg and 9.24 mg/kg). Over-remediation was avoided while contributing to considerable economic and environmental benefits.