Adsorption/desorption of toluene on a hypercrosslinked polymeric resin in a highly humid gas stream

In many sources of volatile organic compounds (VOCs), large amounts of water vapor come from the air and the reactors. The relative humidity (RH) of exhaust gas is normally >60% and is supersaturated. Maintaining the property of adsorbent on VOCs in a highly humid gas stream is a serious industrial problem. In this study, the adsorption/desorption behavior of toluene in a micro-mesoporous polymeric resin was investigated in a highly humid environment to explore the influence of abound water vapor on resin adsorption and regeneration. This resin could selectively adsorb toluene at an RH of 80%, and its adsorption property was unaffected by the presence of water vapor. In the case of humidity saturation, the resin displayed a high adsorption capacity at a moisture content of <30%. Therefore, the polymer resin is an excellent water-resistant adsorbent of VOCs. In the regenerative experiment, the resin maintained its original adsorption capability after four adsorption/ desorption cycles of toluene purging with nitrogen gas at 120℃. The resin exhibited excellent regeneration performance at high humidity.

Mechanism model for shale gas transport considering diffusion, adsorption/desorption and Darcy flow

To improve the understanding of the transport mechanism in shale gas reservoirs and build a theoretical basic for further researches on productivity evaluation and efficient exploitation, various gas transport mechanisms within a shale gas reservoir exploited by a horizontal well were thoroughly investigated, which took diffusion, adsorption/desorption and Darcy flow into account. The characteristics of diffusion in nano-scale pores in matrix and desorption on the matrix surface were both considered in the improved differential equations for seepage flow. By integrating the Langmuir isotherm desorption items into the new total dimensionless compression coefficient in matrix, the transport function and seepage flow could be formalized, simplified and consistent with the conventional form of diffusion equation. Furthermore, by utilizing the Laplace change and Sethfest inversion changes, the calculated results were obtained and further discussions indicated that transfer mechanisms were influenced by diffusion, adsorption/desorption. The research shows that when the matrix permeability is closed to magnitude of 10^-9D, the matrix flow only occurs near the surfacial matrix; as to the actual production, the central matrix blocks are barely involved in the production; the closer to the surface of matrix, the lower the pressure is and the more obvious the diffusion effect is; the behavior of adsorption/desorption can increase the matrix flow rate significantly and slow down the pressure of horizontal well obviously.

Oxygen adsorption/desorption behavior of YBaCo4O7+δ and its application to oxygen removal from nitrogen

A new medium-temperature (200-400 °C) adsorbent material for oxygen removal and air separation, YBaCo4O7+δ, was prepared by the solid-state reaction method. This new adsorbent could adsorb a large quantity of oxygen in the temperature range of 200-370 °C. Adsorbed oxygen could be released by raising temperature over 400 °C or by switching the atmosphere from oxygen to nitrogen. This oxygen adsorption and desorption process had good reproducibility. Taking advantage of this unique oxygen intake/release behavior, a nitrogen purification process was investigated. The results showed that YBaCo4O7+δ material was a promising candidate for the oxygen sorption process and could be used to produce high-purity nitrogen or to remove trace oxygen from other gases.

Thermogravimetric Study on Oxygen Adsorption/Desorption Properties of Double Perovskite Structure Oxides REBaCo_2O_(5+δ)(RE= Pr,Gd,Y)

The oxygen adsorption/desorption properties of double perovskite structure oxides PrBaCo2O5＋δ,GdBaCo2O5＋δ,and YBaCo2O5＋δ were investigated by the thermogravimetry（TG）method in the temperature range of 400~900 ℃.The calculated oxygen adsorption/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides,such as Ba0.95Ca0.05Co0.8Fe0.2O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ,whereas,the oxygen permeation flux was comparable to that of the latter,which was attributed to the smaller difference of oxygen vacancy in oxygen and nitrogen atmosphere（Δδ/Vmol）in these double perovskite structure oxides.The large oxygen adsorption/desorption rate constants of GdBaCo2O5＋δ and PrBaCo2O5＋δ made them nice catalyst coating materials,on other membrane surfaces,to improve the oxygen permeability.

Time-Resolved Measurements of the Adsorption/Desorption of Rb Atoms on Octadecyltrichlorosilane Coated Surfaces

We carry out the first time-resolved measurement of Rb atoms desorbing from octadecyltrichlorosilane coated sur- faces by polarizing the atoms near the surface using an evanescent wave pump pulse and watching the subsequent intensity change of another evanescent wave probe beam, and find the mean adsorption （dwell） time to be about 400ns at a cell body temperature of 112℃. The adsorption energy is found to be 0.19eV from the surface tem- perature dependence of the adsorption time. This method can be extended to study the adsorption/desorption process of other alkali atoms on other surfaces of transparent substrates with an ultimate time resolution limited by the flight time of atoms in the evanescent wave which is of the order of nanoseconds.

Adsorption/Desorption of Low-density Lipoprotein on a Heparinized Surface of Gold Sensors

Heparin has been considered to be a potentially useful ligand for low-density lipoprotein（LDL） detection and analysis in a clinical context.In order to construct an affinity surface for preferential adsorption of LDL,heparin-modified gold surface（GS-Hep） was fabricated by a self-assembling method and hydrophobic-modified gold surfaces（GS-Hydro） was used as a control.The morphologies of the modified gold surfaces were investigated by atomic force microscopy（AFM） and the quantity of heparin bound to gold surface was assayed by the toluidine blue（TB） colorimetric method.Water contact angles were determined to investigate wettability on GS-Hep and GS-Hydro.Surface plasmon resonance（SPR） technique was used subsequently to detect the selective binding of LDL with heparin.And the investigation on the effect of pH on LDL adsorption suggests that lower pH lead to higher quantities of LDL adsorption on GS-Hep.Compared with GS-Hydro,GS-Hep is selective for LDL from both single and binary protein solutions.Moreover,adsorbed LDL on GS-Hep could be washed off by injecting elution solution,such as NaCl solution,for the purpose of the regeneration of GS-Hep for further LDL adsorption.

Determination of Energetic and Geometric Properties of Plant Roots Specific Surface from Adsorption/Desorption Ishoterm

Background and Aims: Structure and composition of plant roots surfaces are extremely complicated. Water vapor adsorption/desorption isotherm is a powerful tool to characterize such surfaces. The aim of this paper is to present theoretical approach for calculating roots surface parameters as adsorption energy, distribution of surface adsorption centers, as well as roots geometric and structure parameters as surface fractal dimension, nanopore sizes and size distributions on example of experimental isotherms of roots of barley taken from the literature. This approach was up to date practically not applied to study plant roots. Methods: Simplest tools of theoretical analysis of adsorption/desorption isotherms are applied. Results: Parameters characterizing energy of water binding, surface complexity and nanopore system of the studied roots were calculated and compared to these of the soils. Some possible applications of root surface parameters to study plant-soil interactions are outlined. Conclusions: Physicochemical surface parameters may be important for characterizing root surface properties, their changes in stress conditions, as well as for study and model plant processes. Physicochemical and geometrical properties of plant roots differ from these of the soils.

Adsorption/desorption behavior between a novel amphoteric granular lignin adsorbent and reactive red K-3B in aqueous solutions

A novel amphoteric granular lignin adsorbent(AGLA) was prepared using magnesium lignosulfonate as a raw material which was provided by a straw sulfite pulp mill in Guangdong Province, China. A reactive dye(red K-3B) was used as an adsorbate to investigate the adsorption behavior by static and mobile ways. The removal of reactive red K-3B was found to be initially pH and concentration dependent. Moreover, an increase of solution temperature ranging from 5℃ to 60℃ helped to enhance the rate of intraparticle diffusion of adsorbate and changes in the size of the pores of the adsorbent and thus to reduce the adsorption time. The total breakthrough adsorption capacity was 531 mg/g, and the saturated adsorption capacity was 560 mg/g, which prevailed over the activated carbons evidently. The reactive red K-3B adsorbed on AGLA could be recovered with a mixture of alcohol, NaCl and HCl aqueous solutions. The recovery percentage could reach 92.4%.

Removal of Toluene by Adsorption/Desorption Using Ultra-stable Y Zeolite

The adsorption performance of toluene on ultra-stable Y zeolite (USY) was studied via dynamic adsorption. The eff ects of bed temperature, initial concentration, and feed fl ow rate on adsorption were investigated. The Yoon-Nelson model was used to fi t the toluene breakthrough curves. The length of mass transfer zone was calculated based on breakthrough curves. The Langmuir-Freundlich model fi t the adsorption isotherms of toluene on USY, which indicated that the surface of USY was heterogeneous. The adsorption isosteric heat calculated from adsorption isotherms ranged from 54.3 to 69.8 kJ/mol, indicating physical adsorption. The combined technique of temperature swing adsorption with vacuum swing adsorption (TVSA) exhibited excellent desorption performance, which was attributed to the low desorption activation energy. Under optimized TVSA conditions, the desorption rate of toluene reached 90.6% within 10 min. The long-term cyclic utilization results indicated that the adsorption capacity of USY was stable.

Particle concentration effect in adsorption/desorption of Zn(Ⅱ) on anatase type nano TiO_2

Adsorption/desorption in a new Zn（Ⅱ）-TiO2 adsorption system was investigated at different particle concentrations （Cp）. TEM, SEM and XRD analyses revealed that the TiO2 particles were an aggregation of nano-sized （approximately 10 nm） pure anatase-type TiO2. Adsorption experiments were carried out with particle concentrations of 100, 400 and 1000 mg/L, and their adsorption isotherms were found to decline successively, showing an obvious Cp effect. Desorption experiments indicated that adsorption in this system was irreversible, and the irreversibility increased with increasing Cp. These phenomena could be explained by the MEA （metastable equilibrium adsorption） theory and the Cp effect could be modeled well with an MEA-Freundlich-type Cp effect isotherm equation. This study may heln understand environmental behavior of contaminants on ultrafine natural particles.

Insights into the adsorption/desorption of CO_(2) and CO on single-atom Fe-nitrogen-graphene catalyst under electrochemical environment

Single-atom metal-nitrogen-graphene(M-N-Gra) catalysts are promising materials for electrocatalytic CO_(2) reduction reaction(CO_(2) RR). However, theoretical explorations on such systems were greatly hindered because of the complexity in modeling solid/liquid interface and electrochemical environment. In the current work, we investigated two crucial processes in CO_(2) RR, i.e. adsorption and desorption of CO_(2) and CO at Fe-N_(4) center, with an explicit aqueous model. We used the ab initio molecular dynamics simulations associated with free energy sampling methods and electrode potential analysis to estimate the energetics under electrochemical environment, and found significant difference in aqueous solution compared with the same process in vacuum. The effect of applied electrode potential on the adsorption structures,charge transfer and free energies of both CO_(2) and CO on Fe-N-Gra was thoroughly discussed. These findings bring insights in fundamental understandings of the CO_(2) RR process under realistic conditions, and facilitate future design of efficient M-N-Gra-based CO_2 RR catalysts.

Comparison of dynamic adsorption/desorption characteristics of toluene on different porous materials

Four different types of adsorbents, SBA-15, MCM-41, NaY and SiO2, were used to study the dynamic adsorption/desorption of toluene. To further investigate the influence of pore structure on its adsorption performance, two SBA-15 samples with different microspores were also selected. It is shown that microporous material NaY has the largest adsorption capacity of 0.2873 mL/g, and the amorphous SiO2 exhibits the least capacity of 0.1003 mL/g. MCM-41 also shows a lower break through capacity in spite of the relatively small pore diameter, because it can not provide the necessary small geometric confinement for the tiny adsorbates. However, the mesoporous SBA-15 silica with certain micropore volume shows relatively higher adsorption capacity than that of MCM-41 silica. The presence of micropores directly leads to an increase in the dynamic adsorption capacity of toluene. Although NaY has the highest adsorption capacity for toluene, its complete desorption temperature for toluene is high （〉 350°C）, which limits its wide application. On the contrary, mesoporous silica materials exhibits a good desorption performance for volatile organic compounds at lower temperatures. Among these materials mesoporous SBA-15 samples, with a larger amount micropores and a lower desorption temperature, are a potentially interesting adsorbent for the removal of volatile organic compounds. This behavior should been related with the best synergetic effect of mesopores and micropores.

Molecular mechanism of adsorption/desorption hysteresis:dynamics of shale gas in nanopores

Understanding the adsorption and desorption behavior of methane has received considerable attention since it is one of the crucial aspects of the exploitation of shale gas.Unexpectedly,obvious hysteresis is observed from the ideally reversible physical sorption of methane in some experiments.However,the underlying mechanism still remains an open problem.In this study,Monte Carlo(MC) and molecular dynamics(MD) simulations are carried out to explore the molecular mechanisms of adsorption/desorption hysteresis.First,a detailed analysis about the capillary condensation of methane in micropores is presented.The influence of pore width,surface strength,and temperature on the hysteresis loop is further investigated.It is found that a disappearance of hysteresis occurs above a temperature threshold.Combined with the phase diagram of methane,we explicitly point out that capillary condensation is inapplicable for the hysteresis of shale gas under normal temperature conditions.Second,a new mechanism,variation of pore throat size,is proposed and studied.For methane to pass through the throat,a certain energy is required due to the repulsive interaction.The required energy increases with shrinkage of the throat,such that the originally adsorbed methane cannot escape through the narrowed throat.These trapped methane molecules account for the hysteresis.Furthermore,the hysteresis loop is found to increase with the increasing pressure and decreasing temperature.We suggest that the variation of pore throat size can explain the adsorption/desorption hysteresis of shale gas.Our conclusions and findings are of great significance for guiding the efficient exploitation of shale gas.

Review of Molecular Simulation Method for Gas Adsorption/desorption and Diffusion in Shale Matrix

Shale gas is becoming an increasingly promising alternative energy resource because of its high efficiency and environment-friendly characteristic. The amount of adsorbed gas on the shale matrix surfaces and dissolved gas in the shale matrix bulk is the dominant factor in the long-term productivity of shale reservoir. Although experimental measurements have been extensively carried out to investigate the gas adsorption and diffusion properties in the shale matrix, they cannot provide the detailed information on the microscopic transport mechanism of shale gas during the gas production process. Molecular simulation can accurately visualize the gas adsorption/desorption and diffusion processes in the shale matrix. In the present study, the recent research advances of molecular simulation on gas adsorption/desorption and diffusion in the shale matrix are reviewed. Firstly, the density functional theory(DFT) for shale gas molecule desorption/adsorption on the surface of the matrix crystal is illustrated. Then, the grand canonical Monte Carlo(GCMC) method predicting the amount of shale gas desorption/adsorption in the shale matrix crystal is introduced. Finally, molecular dynamics simulation(MD) for gas diffusion in the shale matrix is elucidated. Further developments of the molecular simulation method in shale gas production are also discussed.

Study on the Effects of Polyacrylamide on Phosphorus Adsorption and Desorption Characteristics of Soil Aggregates

[Objective]The research aimed to provide scientific reference for reasonable utilization of polyacrylamide(PAM).[Method]After PAM treatment,the soil aggregates were classified through dry sieve analysis and the adsorption capacity and desorption capacity of all soil aggregates to phosphorus at different phosphorus concentrations were analyzed.[Result] The phosphorus adsorption and desorption of soil sample treated by PAM declined. The amount of phosphorus adsorption increased with the increase of phosphorus concentration and this increase was fast in low phosphorus concentration area but slow in high phosphorus concentration area.At different phosphorus concentrations,adsorption showed a へ shape changing trend.The phosphorus adsorption was related to phosphorus concentration and the 2-3 mm aggregate had the highest desorption rate while 0.1-0.25 mm aggregate and 0.45-1 mm aggregate had lowest desorption rate.[Conclusion]The PAM treatment generated significant influence on phosphorus adsorption and analytic features of aggregate in all size fractions.

Adsorption and Desorption Characteristics of Cadmium and Lead in Typical Paddy Soils of Jiangxi Province and Its Environmental Risk Assessment

[Objective] This study aimed to investigate the adsorption and desorption characteristics of cadmium and lead in typical paddy soils of Jiangxi Province. [Method] Gleyed paddy soil and waterloggogenic paddy soil were collected from Jiangxi Province and used as experimental materials to investigate single and com- petitive adsorption and desorption behaviors of cadmium and lead by batch equilib- rium method. The environmental risk of the presence of cadmium and lead in paddy soils was assessed using distribution coefficients. [Result] Under equal ratio condi- tions, the adsorption capacity of lead by two types of paddy soils was higher than that of cadmium, and the adsorption rate in waterloggogenic paddy soil was higher than that in gleyed paddy soil. The desorption capacity of cadmium by two types of paddy soils was higher than that of lead, and the desorption rate in gleyed paddy soil was higher than that in waterloggogenic paddy soil. Under competitive condi- tions, the adsorption capacity of cadmium and lead by paddy soils was significantly reduced compared with single ion system, while the desorption rate was remarkably improved. The potential environmental risk of cadmium contamination was greater than that of lead in paddy soils. Moreover, environmental risks of cadmium and lead were reduced with the increase of pH, which increased significantly under the coex- istence state. [Conclusion] In the coexistence of cadmium and lead, cadmium con- tamination should be controlled and avoided compared with lead contamination in paddy soils.

Adsorption and Desorption of Natural Zeolite on NH_4^+

The adsorption and desorption kinetic of natural zeolite on NH4＋ was stud-ied by lab analysis. The results showed that the adsorption and desorption kinetic of natural zeolite on NH4＋ coincided with the first-order kinetics, modified Freundlich equation, parabolic diffusion model, and heterogeneous diffusion model. The desorp-tion of the adsorbed NH4＋ was far rapider than the adsorption, which can be fin-ished within 60 min.