Gas Sorption Process Research Articles

Functionalized nanofibers in gas sorption process: a critical review on the challenges and prospective research.

Air pollution has become the most important environmental and human health threat as it is accounting for about 7 million deaths across the globe every year. Particulate matter (PM) derived from the combustion of fossil fuels, biomass, and other agricultural residues pollutes the atmospheric air which affects the quality of the environment and poses a great threat to human health. Ecological imbalance, climatic variation, and cardiovascular and respiratory problems among humans are significant extortions due to PM pollution. Scientific approaches were initiated to limit the levels of PM in the atmospheric air and the use of nanofiber mats has received wide attention as these possess versatile properties including nanoscale-sized pore structure, homogeneity in their size distribution with high specific surface area, and low basis weight. To exploit their filtration potential towards wide classes of pollutants and also to enhance the capturing efficacy, functionalized nanofibers are currently in practice with tailor-made modifications on the surface. The present review provides a comprehensive report on the different fabrication processes of functionalized nanofibers along with the controlling factors affecting the efficacy of the gas separation process. Also, it provides technical insights on the mass transfer aspects of PM filtration by elucidation their mechanism which can provide vital information on the rate-controlling diffusive flux(es). Conclusively, the practical challenges encountered in the large-scale air filtration systems such as filter cleaning, flow-rate regulation, pressure drop, and extent of reusability are discussed, and the review has identified potential gaps in the current research and can be considered for the prospective research in the area of PM separation process.

Deformation kinetics of coal–gas system during isothermal and dynamic non-isothermal processes

Gas-induced coal deformation plays a crucial role in fields like potential CO2 sequestration in coal and coalbed methane production. Since the gas sorption process in coal has an exothermic nature, temperature changes can inherently impact sorption and induced deformation behavior in coal. The current research aims to study the evolution of deformation behavior in terms of kinetics over time under isothermal (318 K) and non-isothermal (318→298 K) conditions for coal exposed to different gases (CO2, CH4, and He). The results indicate that sorption deformation kinetics are influenced by gas types, gas pressures, and coal composition inhomogeneity. Four linear strains measuring strain kinetics in various micro-regions on coal surfaces reveal heterogeneous behaviors linked to the distribution of macerals. Regarding the non-isothermal process, deformation kinetics display distinct patterns for the three gases. A temperature decrease causes sample shrinkage when exposed to CH4 and He, while swelling occurs with CO2 exposure, which may result from a combined effect of temperature change and differing sorption mechanisms of these gases in coal. Additionally, the temperature decrease leads to a phase state change in CO2, transitioning from supercritical to gas to liquid. The study shows continuous deformation kinetics, with no significant impact of the phase change on the deformation behavior observed.

Modeling of Gas Sorption Process by Dispersed Liquid Flow

A mathematical model of the process of gas propagation in the atmosphere and its sorption by fine flow has been developed. The use of the finite difference method in modeling allows to obtain numerical solutions of the spatial distribution of gas concentration during its deposition by a jet of arbitrary intensity and shape. The proposed method of mathematical description of the process of sorption of hazardous gases allows you to choose an arbitrary number and spatial location of nodal points that satisfy the Courant-Friedrichs-Levy condition. The developed model allows to predict the intensity of gas sorption in technological processes and in the elimination of the consequences of emergencies. The use of the developed model will increase the efficiency of emergency management and choose effective methods of sorption of hazardous gases in the atmosphere. The results of numerical calculations confirmed the efficiency of the developed model and theoretically demonstrated the effectiveness of using water curtains for the sorption of ammonia from the atmosphere. According to the simulation results, it is established that the use of fine spray jets can significantly reduce the distance of distribution of hazardous gas.

Research of the Chlorine Sorption Processes when its Deposition by Water Aerosol

Modified stepwise model of gas sorption process with finely dispersed water flow. The sorption model allows forecasting the intensity of hazardous gases deposition with adequate for the emergency recovery conditions accuracy using minimum input parameters. This allows using the sorption model under the conditions of emergency and increasing the forecasting promptness. Use of chemical neutralizer is proposed to increase the effectiveness of chlorine hazardous gas deposition. Use of sodium hydroxide is proposed as the chlorine chemical neutralizer, which is easily dissolved in water, non-toxic and easy to store. An experimental laboratory facility was developed and created with the purpose of experimental verification of the sorption processes, which allows researching the sorption processes by liquid aerosols within a wide range of dispersity. Adequacy of the existing models as well as the modified one was verified experimentally. The verification results showed a 5% indicator of the theoretical and experimental results compliance.

A Review on Ionic Liquid Gas Separation Membranes.

Ionic liquids have attracted the attention of the industry and research community as versatile solvents with unique properties, such as ionic conductivity, low volatility, high solubility of gases and vapors, thermal stability, and the possibility to combine anions and cations to yield an almost endless list of different structures. These features open perspectives for numerous applications, such as the reaction medium for chemical synthesis, electrolytes for batteries, solvent for gas sorption processes, and also membranes for gas separation. In the search for better-performing membrane materials and membranes for gas and vapor separation, ionic liquids have been investigated extensively in the last decade and a half. This review gives a complete overview of the main developments in the field of ionic liquid membranes since their first introduction. It covers all different materials, membrane types, their preparation, pure and mixed gas transport properties, and examples of potential gas separation applications. Special systems will also be discussed, including facilitated transport membranes and mixed matrix membranes. The main strengths and weaknesses of the different membrane types will be discussed, subdividing them into supported ionic liquid membranes (SILMs), poly(ionic liquids) or polymerized ionic liquids (PILs), polymer/ionic liquid blends (physically or chemically cross-linked ‘ion-gels’), and PIL/IL blends. Since membrane processes are advancing as an energy-efficient alternative to traditional separation processes, having shown promising results for complex new separation challenges like carbon capture as well, they may be the key to developing a more sustainable future society. In this light, this review presents the state-of-the-art of ionic liquid membranes, to analyze their potential in the gas separation processes of the future.

Fiber-Based Gas Filter Assembled via In Situ Synthesis of ZIF-8 Metal Organic Frameworks for an Optimal Adsorption of SO2: Experimental and Theoretical Approaches.

For environmental protection from exposure to airborne toxic gases, metal organic frameworks (MOFs) have drawn great attention as gas adsorbent options, with their advantages in chemical tailorability and large porosity. To develop a fiber-based gas filter that is effective against SO2 gas, zeolite imidazole framework-8 (ZIF-8) was applied to polypropylene nonwoven by various methods. Among the tested methods, the sol-gel impregnation method showed the highest ZIF-8 loading efficiency. There existed an optimal loading of ZIF-8 for the maximum adsorption efficiency, and it was associated with the accessibility of gas molecules to the ZIF-8 pores and active sites. Dominant adsorption processes and mechanisms were investigated by fitting the theoretical sorption models to experimental data. The results demonstrate that the increased ZIF-8 loading to fibers, beyond a certain level, may hinder the diffusivity and increase the barrier effect, eventually decreasing the adsorption efficiency. This study is novel and significant in that a multifaceted approach, including experimental analysis, theoretical investigation, and computational modeling, was made for scrutinizing the intricate phenomena occurring in the gas sorption process. The results of this study provide the fundamental yet practical information on the manufacturing considerations for the optimal design of MOF-loaded fibrous adsorbents.

Cellular-automaton modeling of gas sorption kinetics in the finite volume of coal

The work is devoted to cellular-automaton modeling based on a class of cellular automata with Margolus neighborhood. Modeling of the gas sorption process by coal particle was carried out. To organize this kind of evolutionary process, the method of cellular automata modeling was supplemented by the Monte Carlo method to implement the boundary conditions at the solid – gas interface.

Laser-induced silicon nanocolumns by ablation technique

High-purity silicon wafers were irradiated in ultrapure water environment by laser ablation (LA). Columnar structures were induced on the surface using multiple pulses from Nd:YAG laser. Nd:YAG pulsed laser irradiance with 1.3 × 109 W/cm2 operated at 266 nm wavelength, 6 ns pulse duration, and 10 mJ pulse energy with different repetition rates 10 Hz and 20 Hz. Shape, structure, and size distribution of silicon nanocolumns were determined by scanning electron microscope and particle counting method. High populations of silicon nanoparticles were formed on the surfaces of the substrates after LA process. Elemental composition analysis was performed by energy dispersive x-ray spectrometer for the silicon targets and the deposited nanoparticles. Surface area of the silicon nanoparticles was measured by gas sorption process. UV-Visible spectrophotometer was used to detect the scattered light from the nanocolumns structure on the silicon target.

Characterization analysis of activated carbon derived from the carbonization process of plane tree (Platanus orientalis) seeds

In this work, plane tree seed-based activated carbons were characterized in detail for a variety of applications. The particularly important area of application would be in the artificial photosynthesis. After carbonization process of biomass precursor at 650°C, the resulting preliminary activated carbons were activated at various temperatures. The activated carbons were characterized by oxygen functionalities (a particularly important role has ester oxygen groups) which provide a unique microstructure. The chemical compositions of as-prepared activated carbons were analyzed through Fourier transform infrared and Raman spectra as well as gas chromatography–mass spectroscopy analysis, while morphology was observed by scanning electron microscopy analysis. Applied analysis showed that detected graphite mainly becomes uniformly nanocrystalline system. The current study also explored the applicability of carbon material obtained from plane tree seed as a potential gaseous adsorbent. The characterization showed that the tested material contains both mesopores and micropores, and this should be advantageous for the gas sorption process, since mesopores may provide low-resistant pathways for the diffusion of CO2 molecules, while the micropores are the most suitable for trapping of CO2. The sorption process analysis (including adsorption/desorption isotherms behavior) shows indication that the rate-limiting step of CO2 adsorption onto activated carbon is probably governed by diffusion-controlled process, especially at temperatures below 850°C.

An innovative method to characterize sorption-induced kerogen swelling in organic-rich shales

Matrix swelling due to the gas sorption has not been properly accounted in the organic-rich shale formations. In general, the adsorbed gas attaches on the pore surface in the kerogen and clay minerals and occupies the pore volume. Meanwhile, the absorbed gas dissolves or diffuses into the matrix (solid lattice) of kerogen, resulting in the swelling of kerogen. As a result, the increase of the adsorbed and absorbed gases leads to a reduction of the pore volume for the free gas. Thus, it is essential to appropriately characterize the kerogen swelling caused by gas sorption so that to accurately determine the nanopore structure and the gas transport behavior in shale kerogen.In this study, an innovative method is developed to evaluate the swelling behavior of kerogen ascribed to the methane sorption. The method aims at characterizing the regions of adsorbed gas, absorbed gas, and free gas in the slit-shaped nanopores in shale kerogen based on the density profile determined using the Simplified Local-Density (SLD) model. Results for Barnett and Eagle Ford shale kerogens reveal that the gas adsorption prevails when the pore pressure is less than 6 MPa, whereas the gas absorption dominates the gas sorption process when the pore pressure is larger than 6 MPa. In addition, the ratio of absorption thickness to adsorption thickness increases with the pore pressure and such ratio reaches the 34.4% and 25.4% at the pore pressure around 20 MPa for the Barnett and Eagle Ford shale kerogens, respectively. Furthermore, the bulk and pore volumetric strains of the kerogen in the Barnett and Eagle Ford shale core samples are calculated based on the swelling length of kerogen caused by the methane sorption. The calculated strains of kerogen are in line with the measured strains of the shale and coal samples published in the literature, which verifies the reliability of the proposed innovative method. Finally, the impacts of methane sorption on the surface diffusion and the gas slippage in the slit nanopores of kerogen are also discussed.The proposed method provides a practical approach to characterize the sorption-induced kerogen swelling in shales, which is difficult to measure in the laboratory. The findings of this study advance the understanding of gas sorption process and give insight into the characterization of nanopore structure and gas transport mechanism in shale kerogen.

CO2 and CH4 sorption properties of granular coal briquettes under in situ states

The aim of this work was an experimental research into the sorption properties of coal briquettes under the various states of stress. The present state of knowledge when it comes to the impact of stress on the CO2 and CH4 sorption properties of coal is limited. Hence, in situ sorption capacity or sorption-induced deformation may vary considerably from these specified in the unloaded conditions. As part of this paper, a research device that enables the sorption measurements for coal samples submitted to loads of up to 40 MPa is presented. Sorption experiments with pure CO2 and pure CH4 were carried out by means of the volumetric method, under isobaric-isothermal conditions. Dry coal material in the form of granular coal briquettes was used. Presented results aimed to prove the existence of a relation between the stress state, sorption capacity and volumetric deformation of coal. Gas sorption and desorption processes on coal may be triggered by the action of mechanical factor. The mechanical load applied to the coal sorbent reduces its sorption capacity but has no direct effect on swelling. The sorption or desorption induced volumetric changes of coal occur regardless of the stress state and regardless of the mechanism of the sorption process itself. Deeper coal seams with reduced CO2 and CH4 sorption capacity may not be as useful for ECBM techniques as the shallower coal seams. Reduction of the sorption capacity with depth may also explain the growing threat of coal and methane outbursts in the USCB mines observed in recent years.

Development and Characterization of Non-Evaporable Getter Thin Films with Ru Seeding Layer for MEMS Applications.

Mastering non-evaporable getter (NEG) thin films by elucidating their activation mechanisms and predicting their sorption performances will contribute to facilitating their integration into micro-electro-mechanical systems (MEMS). For this aim, thin film based getters structured in single and multi-metallic layered configurations deposited on silicon substrates such as Ti/Si, Ti/Ru/Si, and Zr/Ti/Ru/Si were investigated. Multilayered NEGs with an inserted Ru seed sub-layer exhibited a lower temperature in priming the activation process and a higher sorption performance compared to the unseeded single Ti/Si NEG. To reveal the gettering processes and mechanisms in the investigated getter structures, thermal activation effect on the getter surface chemical state change was analyzed with in-situ temperature XPS measurements, getter sorption behavior was measured by static pressure method, and getter dynamic sorption performance characteristics was measured by standard conductance (ASTM F798–97) method. The correlation between these measurements allowed elucidating residual gas trapping mechanism and prediction of sorption efficiency based on the getter surface poisoning. The gettering properties were found to be directly dependent on the different changes of the getter surface chemical state generated by the activation process. Thus, it was demonstrated that the improved sorption properties, obtained with Ru sub-layer based multi-layered NEGs, were related to a gettering process mechanism controlled simultaneously by gas adsorption and diffusion effects, contrarily to the single layer Ti/Si NEG structure in which the gettering behavior was controlled sequentially by surface gas adsorption until reaching saturation followed then by bulk diffusion controlled gas sorption process.

Free energy study of H2O, N2O5, SO2, and O3 gas sorption by water droplets/slabs

Understanding gas sorption by water in the atmosphere is an active research area because the gases can significantly alter the radiation and chemical properties of the atmosphere. We attempt to elucidate the molecular details of the gas sorption of water and three common atmospheric gases (N2O5, SO2, and O3) by water droplets/slabs in molecular dynamics simulations. The system size effects are investigated, and we show that the calculated solvation free energy decreases linearly as a function of the reciprocal of the number of water molecules from 1/215 to 1/1000 in both the slab and the droplet systems. By analyzing the infinitely large system size limit by extrapolation, we find that all our droplet results are more accurate than the slab results when compared to the experimental values. We also show how the choice of restraints in umbrella sampling can affect the sampling efficiency for the droplet systems. The free energy changes were decomposed into the energetic ΔU and entropic -TΔS contributions to reveal the molecular details of the gas sorption processes. By further decomposing ΔU into Lennard-Jones and Coulombic interactions, we observe that the ΔU trends are primarily determined by local effects due to the size of the gas molecule, charge distribution, and solvation structure around the gas molecule. Moreover, we find that there is a strong correlation between the change in the entropic contribution and the mean residence time of water, which is spatially nonlocal and related to the mobility of water.

Switching of Adsorption Properties in a Zwitterionic Metal–Organic Framework Triggered by Photogenerated Radical Triplets

A new metal–organic framework (MOF) that features photoreactive zwitterionic pyridinium 4-carboxylate units has been designed. Upon UV light irradiation, these units form radical triplets permitted by intramolecular electron transfer between anionic carboxylate and cationic pyridinium groups. This reversible light-responsive behavior creates on/off switchable charge gradients localized at the MOF’s major adsorption sites and, thus, allows significant control of the gas sorption process. It is shown that this strategy offers new design routes for accessing stimulus-responsive materials.

Development of sorption thermal battery for low-grade waste heat recovery and combined cold and heat energy storage

A promising compact sorption thermal battery is developed for low-grade waste heat recovery and combined cold and heat energy storage. Thermal energy is stored in the form of bond energy of sorption potential during the charging phase and the stored thermal energy is released in the form of heat energy and cold energy during the discharging phase. The operating principle and conceptual design of sorption thermal battery based on solid–gas sorption processes is firstly introduced, and then the working performance of sorption thermal battery using consolidated composite sorbent of expanded graphite/manganese chloride is investigated. Experimental verification showed that sorption thermal battery is an effective method to achieve combined deep-freezing cold and heat energy storage, and its working temperature can be easily adjusted by changing system pressure. The cold and heat energy densities are as high as 600 kJ/kg and 1498 kJ/kg, respectively. Moreover, energy densities of different energy storage methods and sorption working pairs are compared and analyzed. It appears that sorption thermal battery is a promising compact high-performance energy storage technology for waste heat recovery and renewable energy utilization due to its distinct advantage of high energy density and broad range of working temperature.

Solid–gas thermochemical sorption thermal battery for solar cooling and heating energy storage and heat transformer

Thermal energy storage plays a vital role in the sustainable utilization of solar energy for heating and cooling applications due to its inherent instability and discontinuity. An advanced high-performance solid–gas thermochemical sorption thermal battery is developed for solar cooling and heating energy storage and heat transformer. Solar thermal energy is stored in the form of bond energy during the charging phase and the stored energy is released in the form of heat and cold energy during the discharging phase based on the energy conversion between thermal energy and bond energy of sorption potential during the solid–gas sorption process of working pair. The heat and cold energy storage densities are as high as 1300–1600 kJ/kg and 640–720 kJ/kg respectively when the sorption thermal battery using working pair of SrCl2–NH3 works as short-term and long-term seasonal energy storage. Moreover, the working temperature of stored energy can be effectively upgraded by using the sorption thermal battery. It appears that the proposed sorption thermal battery is an effective method for the short-term and long-term storage of solar thermal energy, and it has distinct advantages of combined cold and heat storage, high energy density, integrated energy storage and energy upgrade in comparison with conventional energy storage methods.

In-situ analysis of gas-loaded porous materials

In order to understand gas sorption processes at the molecular level it is important to correlate physico-chemical data (e.g. sorption isotherms and calorimetric analysis) with structural data. It is therefore desirable to carry out structural elucidation and calorimetric analysis under conditions that closely mimic those of the sorption/desorption experiments. However, the crystallographic analysis of samples under controlled gas environments poses significant technical challenges, particularly given the limited space associated with the sample compartment of standard commercial diffractometer. In this regard, an environmental gas cell has been developed in parallel with a pressure-programmed differential scanning calorimeter. Use of these complementary techniques has provided new insight into features such as pressure-induced phase transformations that give rise to inflections and hysteresis in sorption isotherms. The influence of guest molecules on aspects such as structural flexibility, linear thermal expansion and changes in network interpenetration will be discussed.

Molecular Mechanism of Gas Adsorption into Ionic Liquids: A Molecular Dynamics Study

Room-temperature ionic liquids (RTILs) have been shown to be versatile and tunable solvents that can be used in many chemical applications. In this Perspective, we developed a dynamic, molecular-scale picture of the gas dissolution and interfacial processes in RTILs using molecular simulations. These simulations can provide the free energies associated with transporting a gas solute across various RTIL interfaces and physical insights into the interfacial properties and transport molecular mechanism of gas sorption processes. For CO2 sorption, the features in the potential of mean force (PMF) of CO2 using both polarizable and nonpolarizable force fields are similar qualitatively. However, we observed some quantitative differences, and we describe the causes of these differences in this paper. We also show the significant impact of ionic liquid chemical structures on the gas sorption process, and we discuss their influence on the H2O transport mechanism.

Water sorption characteristics of carbon nanostructures calculated on the basis of the Ornstein–Zernike equation

Molecular systems in contact with the bounding surfaces are examined. New apparatus describing adequately quasi–two-dimensional structures whose cross sectional dimensions are comparable with the correlation length is suggested. It is based on the modified method of the Wigner distribution functions and the system of Ornstein–Zernike equations generalized for one- and two-particle distribution functions. Modeling of the physical gas sorption process in carbon nanofibers and nanotubes allows local microstructure, sorption characteristics, effective sizes, and optimal technological filling parameters to be calculated.

Favorable Hydrogen Storage Properties of M(HBTC)(4,4′-bipy)·3DMF (M = Ni and Co)

Two metal-organic frameworks of M(HBTC)(4,4'-bipy).3DMF (M = Ni and Co; H 3BTC = 1,3,5-benzenetricarboxylic acid; 4,4'-bipy = 4,4'-bipyridine; DMF = N,N'-dimethylformamide) were synthesized by a one-pot solution reaction and a solvothermal method, respectively. The as-prepared samples have high specific surface areas of 1590 m (2)/g and 887 m (2)/g. The activation at different temperatures for the guest removal prior to gas loading obviously affects the gas sorption process. Ni(HBTC)(4,4'-bipy).3DMF shows high hydrogen storage capacities of 1.20 wt % at room temperature and 3.42 wt % at 77 K. Co(HBTC)(4,4'-bipy).3DMF shows capacities of 0.96 wt % at 298 K and 2.05 wt % at 77 K. The hydrogen adsorption heats in the two compounds decrease slightly as a function of the amount adsorbed, and it confirms that the H 2 molecules are combined with stronger sites preferentially. Research on the kinetics of hydrogen adsorption shows a fast saturation process (80 s) and no obvious capacity loss after 20 cycles.