Density Of Adsorbed Layer Research Articles

Molecular simulation of the impact of surface roughness on carbon dioxide adsorption in organic-rich shales

This study investigates the adsorption behavior of carbon dioxide in organic nanopores with different surface roughness. The nanopores are constructed by sinusoidally corrugating the graphite slit pore walls. By computing the density distributions, adsorption quantities and orientation of carbon dioxide under various pressure and roughness conditions, we elucidate the impacts of surface roughness on carbon dioxide adsorption in organic nanopores. The Langmuir-Freundlich adsorption model is utilized to fit the isotherms of CO2 adsorption under three different roughness conditions. the results show that increasing surface roughness led to the increase in the adsorption of carbon dioxide, as the relative roughness increased from 0% to 12.92%, the average CO2 adsorption capacity increased by 0.003 mmol/m2. Both the adsorbed layer density and monolayer maximum adsorption capacity increased concurrently with escalating roughness. Moreover, carbon dioxide molecules preferentially aligned parallel to the rough organic surface within the adsorption layer, consistent with the smooth graphitic wall configuration. All simulations, observations, and calculations were performed through grand canonical Monte Carlo (GCMC) simulations. These findings provide insights into the influence of surface roughness on CO2 adsorption, especially in organic nanopores, which has substantial implications for carbon capture and geological sequestration applications. The results could facilitate optimization of strategies for efficient, secure geological CO2 storage.

Absolute adsorption of light hydrocarbons on organic-rich shale: An efficient determination method

Absolute adsorption has been found being more accurate than directly measured excess adsorption value for estimating the in-situ shale gas-in-place storage. To obtain accurate absolute adsorption, traditional methods determined the adsorbed gas density using complicated molecular simulation methods, which is employed to correct the measured excess value. In this work, excess adsorption, which is deemed to be inaccurate in previous work, of CH4 and C3H8 is first measured on three typical shale rocks. The adsorbed-layer density is then reasonably calculated using the simplified local density theory (SLD) to obtain corresponding absolute adsorption of CH4 and C3H8. It is found that the adsorbed layer density calculated from SLD theory is comparable to that obtained from molecular simulation methods, while it is more efficient for the density computation. Compared to CH4, C3H8 presents stronger adsorption capacity on shale rocks, suggesting that C3H8 is more affinity to organic shale. The CH4′s absolute adsorption is stronger than its excess value and their deviation enlarges as pressure increases, while absolute adsorption for C3H8 is found to be more or less the same with the measured excess value. The importance of this work lies in that we propose a new method for efficiently obtaining the adsorbed-layer density, which is crucial for accurately determining gas and oil storage in shale reservoirs.

High pressure sorption of various hydrocarbons and carbon dioxide in Kimmeridge Blackstone and isolated kerogen

We have measured adsorption and desorption of methane, ethane, propane, n-butane, iso-butane and carbon dioxide in Kimmeridge Blackstone at high pressures at temperatures of 60, 90 and 120 °C. Sorption of various light hydrocarbons and carbon dioxide in the isolated kerogen at 60 °C was also investigated. In our measurements, we used the gravimetric method. Physical and chemical properties of samples were measured to provide insight into sorption. Methane, ethane and carbon dioxide sorption was measured to 150 bar. Due to low vapor pressure of propane at 60 and 90 °C, the sorption was measured to 15 bar at 60 °C and 30 bar at 90 °C, respectively. At 120 °C, propane sorption was measured to 30 bar. Similarly, n-butane and iso-butane sorption was studied to 5, 9.5 and 15 bar at 60, 90 and 120 °C, respectively. Compared to sorption of these gases at moderate pressure in our recent work, high pressure sorption shows more pronounced hysteresis and non-monotonic excess sorption. In this work, we use the adsorbed layer density, estimated from grand canonical Monte Carlo (GCMC) simulations, and the liquid density to compute the absolute adsorption and examine the difference between the two. The results show that the absolute adsorption estimated with the two densities is significantly different in methane but similar in the other species. The butanes, n-butane and iso-butane, despite close bulk densities have very different adsorption. The adsorbed layer densities by GCMC simulations are different by about 10% which partly account for the adsorption difference. Other mechanisms may be at play due to different shape of the two molecules.

Neutron Reflectivity Study of Alkylated Azacrown Ether at the Air−Liquid and the Liquid−Liquid Interfaces

We report the neutron reflectometry study of partially deuterated di-hexadecyl-diaza-18-crown-6 ether (d-ACE-16) at the air-water and the oil-water interfaces. At the air-water interface, the thickness of the monolayer is smaller than that for a fully stretched d-ACE-16 molecule, suggesting a tilt of the alkyl chains with respect to the normal. At the oil-water interface, the same molecules were found to form a more diffuse layer distribution stretching across both sides of the interface. On the oil side, the molecules are densely packed within a thickness of 17 A, the hydrophilic part of the molecule with the azacrown ether ring being immersed in the adjacent aqueous side of the interface. The latter consists of a thick 38 A layer comprising staggered, loosely adsorbed d-ACE-16 molecules. With increasing spread amount, the adsorbed layer density increases at the oil side until saturation at ca. 2.25 x 10(-6) mol m(-2), above which the layer collapses.

Structure of mixed β-lactoglobulin/pectin adsorbed layers at air/water interfaces; a spectroscopy study

Based on earlier reported surface rheological behaviour two factors appeared to be important for the functional behaviour of mixed protein/polysaccharide adsorbed layers at air/water interfaces: (1) protein/polysaccharide mixing ratio and (2) formation history of the layers. In this study complexes of β-lactoglobulin (positively charged at pH 4.5) and low methoxyl pectin (negatively charged) were formed at two mixing ratios, resulting in negatively charged and nearly neutral complexes. Neutron reflection showed that adsorption of negative complexes leads to more diffuse layers at the air/water interface than adsorption of neutral complexes. Besides (simultaneous) adsorption of protein/polysaccharide complexes, a mixed layer can also be formed by adsorption of (protein/)polysaccharide (complexes) to a pre-formed protein layer (sequential adsorption). Despite similar bulk concentrations, adsorbed layer density profiles of simultaneously and sequentially formed layers were persistently different, as illustrated by neutron reflection analysis. Time resolved fluorescence anisotropy showed that the mobility of protein molecules at an air/water interface is hampered by the presence of pectin. This hampered mobility of protein through a complex layer could account for differences observed in density profiles of simultaneously and sequentially formed layers. These insights substantiated the previously proposed organisations of the different adsorbed layers based on surface rheological data.

Direct Evidence of Carbon Dioxide Sorption on Argonne Premium Coals Using Attenuated Total Reflectance−Fourier Transform Infrared Spectroscopy

The direct interaction between CO2 and two Argonne Premium Coals [Pocahontas No. 3 (low-volatile bituminous) and Beulah-Zap (lignite)] was probed by use of attenuated total reflectance−Fourier transform infrared (ATR−FTIR) spectroscopy at 328 K and pressures up to 8.0 MPa. Sorbed CO2 on Argonne Coals was detected at 2335 cm-1 for Beulah-Zap coal and 2332 cm-1 for Pocahontas No. 3 coal. The energy of adsorption (18.8−20.5 kJ/mol), estimated from the Langmuir equation, was consistent with physisorption. The spectral data indicated that only one type of site was available for sorption. No evidence could be found for specific interactions between CO2 and oxygen functional groups in the coals. The CO2−coal sorption isotherm was derived without estimating the CO2 compressibility and adsorbed layer density, both of which are needed in manometric techniques.

Classification of supercritical gas adsorption isotherms based on fluid–fluid interaction

Based on an increase in fluid–fluid interaction, supercritical gas adsorption isotherms can be classified into three types, Henry-type isotherms, virial isotherms, and cooperative isotherms. The isotherms of the three types differ in terms of the compression factor and the adsorbed layer density. The goodness of this classification is supported by calculations based on the density functional theory. This classification is used for hydrogen adsorption isotherms on a single-wall carbon nanohorn obtained at different temperatures.

Effect of polyethylene oxide on the viscosity of dispersions of charged silica particles: interplay between rheology, adsorption, and surface charge

In this study a systematic investigation on the adsorption of polyethylene oxide (PEO) onto the surface of silica particles and the viscosity behavior of concentrated dispersions of silica particles with adsorbed PEO has been performed. The variation of shear viscosity with the adsorbed layer density, concentration of free polymer in the solution (depletion forces), polymer molecular weight, and adsorbed layer thickness at different salt concentrations (range of the electrostatic repulsion between particles) is presented and discussed. Adsorption and rheological studies were performed on suspensions of silica particles dispersed in solutions of 10−2 M and 10−4 M NaNO3 containing PEO of molecular weights 7,500 and 18,500 of different concentrations. Adsorption measurements gave evidence of a primary plateau in the adsorption density of 7,500 MW PEO at an electrolyte concentration of 10−2 M NaNO3. Results indicate that the range of the electrostatic repulsion between the suspended particles affects both adsorption density of the polymer onto the surface of the particles and the viscosity behavior of the system. The adsorbed layer thickness was estimated from the values of zeta potential in the presence and absence of the polymer and was found to decrease with decreasing the range of the electrostatic repulsive forces between the particles. Experimental results show that even though there is a direct relation between the viscosity of the suspension and the adsorption density of the polymer onto the surface of the particles, variation of viscosity with adsorption density, equilibrium concentration of the polymer, and range of the electrostatic repulsion cannot be explained just in term of the effective volume fraction of the particles and needs to be further investigated.

Effect of Adsorbed Polyethylene Oxide on the Rheology of Colloidal Silica Suspensions

The viscosity behavior of aqueous suspensions of silica particles with physically adsorbed polyethylene oxide (PEO) molecules was investigated in relation to the adsorbed layer density and concentration of nonadsorbed polymer in the suspending fluid. Adsorption studies revealed the presence of two plateaus in the adsorption isotherm, which was attributed to a change in conformation from a flat, “pancake”-type, to a more elongated “brush”-type conformation of the adsorbed polymer, where the terminal hydroxyl groups remained bound to the silica surface. Adsorption and rheological studies were performed on suspensions of silica particles of three different sizes dispersed in solutions of 0.01 M NaNO3 containing PEO of different concentrations and different molecular weights. The variation of shear viscosity with the adsorbed layer density, concentration of free polymer in the suspending media (depletion forces), and particle size are discussed. Results on the role of particle size on the viscosity of electrostatically and sterically stabilized suspensions indicate that sterically stabilized systems may be treated as hard spheres at high shear rates depending upon the adsorbed layer density and concentration of nonadsorbed polymer in the suspending media. Electrostatically stabilized suspensions may show deviation from hard sphere behavior even at high shear rates depending on the range of electrostatic repulsion between the suspended particles. Further investigation must be performed to be able to explain the difference between the behavior of electrostatically and sterically stabilized systems in terms of the deformability of the layers, i.e., “softness” of the electrical double layers around the particles as compared with the “stiffness” of the adsorbed layers of the polymer.