Effect Of Pore Size Distribution Research Articles

Effects of Pore-Size Distribution on the Gas Diffusion Coefficient and Gas Permeability of Compacted Manufactured Sand Tailing–Bentonite Mixtures

Effects of Pore-Size Distribution on the Gas Diffusion Coefficient and Gas Permeability of Compacted Manufactured Sand Tailing–Bentonite Mixtures

Simulation of densification behavior of nano-powder in final sintering stage: Effect of pore-size distribution

In the final sintering stage, nano-sized powder frequently forms a pore structure where most pores are surrounded by more than 5 grains. The pore structure is different from that of coarse powder. In this study, the densification behavior of nano-sized powder is modelled and simulated in the final sintering stage. The porous body has the initial size distribution of pores, represented as a Weibull function. The mechanical interaction between pores is analyzed to simulate the evolution of porosity characteristics as well as densification kinetics. The densification rate for the size-distributed pores is lower than that for single-sized ones. The experimental relationship between the densification rate and the porosity could well be reproduced by choosing appropriate pore-size distributions. The simulation also shows that the sintering stress with densification may increase or decrease depending on the size distribution, but is remarkably lower than that for single-sized pores.

Effect of pore-size distribution on Ru/ZSM-5 catalyst for enhanced N2 activation to ammonia via dissociative mechanism

In the present study, a series of Ru/ZSM-5 catalysts with different pore-size distributions were prepared and investigated for NH3 synthesis. Our studies indicate that Ru/ZSM-5-Mic with micropore structure exhibits superior NH3 synthesis rate, which is much higher than those of Ru/ZSM-5-Mac (with macroporous structure) and Ru/ZSM-5-Mes (with mesoporous structure) catalysts. A series of TPD experiments demonstrate that pore-size distributions play an important role in N2 adsorption and activation over Ru/ZSM-5. Moreover, the addition of La significantly promotes the NH3 synthesis performance over Ru/ZSM-5-Mic. Additionally, in situ DRIFTS studies indicate that the main intermediate species over Ru/ZSM-5-Mic are –NH2, and most of the surface hydrogen species desorb following the H2O-formation pathway.

A Novel Relative Permeability Model for Gas and Water Flow in Hydrate-Bearing Sediments With Laboratory and Field-Scale Application

In a producing gas hydrate reservoir the effective porosity available for fluid flow constantly changes with dissociation of gas hydrate. Therefore, accurate prediction of relative permeability using legacy models (e.g. Brooks-Corey (B-C), van Genuchten, etc.) that were developed for conventional oil and gas reservoirs would require empirical parameters to be calibrated at various Sh over its range of variation, but such calibrations are precluded because of lack of experimental relative permeability data. This study proposes a new relative permeability model for gas hydrate-bearing media that is a function of maximum capillary pressure, capillary entry pressure, pore size distribution index, residual saturations, hydrate saturation, and four other constants. The three novel features of the proposed model are: (i) requires fitting its six empirical parameters only once using experimental data from any single Sh, and the same set of empirical parameters predict relative permeability at all Sh, (ii) includes the effect of capillarity, and (iii) includes the effect of pore-size distribution. From practical standpoint, the model can be used to simulate multiphase flow in gas hydrate-bearing sediments where the proposed relative permeability can account for the evolving hydrate saturation. The proposed model is implemented in a numerical simulator and the wall time required to perform simulations using the proposed model is shown to be similar to the time it takes to run same simulations with the B-C model. The proposed model is a step forward towards achieving the goal of physically accurate modeling of multiphase flow for gas hydrate-bearing sediments that accounts for the effect of gas hydrate saturation change on relative permeability.

Multiscale Fluid-Phase-Behavior Simulation in Shale Reservoirs Using a Pore-Size-Dependent Equation of State

Summary The phase behavior of reservoir fluids plays a fundamental role in predicting well performance and ultimate recovery. The uncertainty in phase behavior is currently one of the greatest challenges in developing unconventional shale resources. The complex phase behavior is attributed to the broad range of pore sizes in shale. In macroscale geometries such as fractures and macropores, the fluid behavior is bulk-like; in nanoscale pores, the fluid behavior is significantly altered by confinement effects. The overall phase behavior of fluids in porous media of mixed pore sizes is yet to be understood. In this paper, we present a study on the effect of pore-size distribution on the phase behavior of shale-reservoir fluids in a multiscale-pore system. The global fluid-phase equilibria among different sizes of pores are simulated. A pore-size-dependent equation of state (EOS) is used to describe the fluid by the confining pore diameter. The EOS confinement parameters for fluid/pore-wall surface interaction are determined by experimental results from differential-scanning calorimetry (DSC) and isothermal adsorption of species C1–14. The multiscale phase equilibria are simulated by directly minimizing the total Helmholtz free energy. A modified Eagle Ford oil is used for the case study. Constant-composition expansions (CCEs) of dual-scale (bulk and 15 nm) and triple-scale (bulk, 15 nm, and 5 nm) systems are simulated. The first bubble emerges from the bulk region at a lightly suppressed “apparent” bubblepoint pressure. Below the bubblepoint, the liquid saturation in the bulk region drops sharply, but the fluids in the nanopores are undersaturated throughout the multistage expansions. In the end, large amounts of intermediate-to-heavy hydrocarbons are retained in nanopores, implying a significant oil-recovery loss in shale. The confinement effect also leads to near-critical phase behavior in small-scale nanopores (<5 nm).

Pore-size distribution effects on the thermal conductivity of the fired clay body from lightweight bricks

This study investigated the effects of three pore-forming agents on the properties of the fired clay body applied in the production of lightweight bricks for the building envelopes. Test samples were made from clay raw material already containing two combustible pore-forming agents (sawdust and cellulose sludge). A part of this research was focused on studying the influence of adding two combustible pore-forming agents (molasses and cornstarch) and a chemical additive Vuppor to the claw raw material. Testing of the material properties showed that although the three samples had almost the same pore volume, their thermal conductivities varied. These findings led to an important conclusion. The pore size of 1–200 µm (filled with not only air but also biomass ash) reduced the thermal conductivity, and conversely, an increase in the small pore size less than 1 µm increased the thermal conductivity of the fired clay body.

Effect of pore-size distribution on the collapse behaviour of anthropogenic sandy soil deposits

In the former open-pit mines of the Lusatian region in Germany, several liquefaction events have occurred during the recent years in the anthropogenic deposits made of very loose sandy soils. These events are related to the rising ground water table after the stop of controlled ground water lowering. The very loose state is due to the formation of sand aggregates (pseudo-grains) during the deposition process. The pseudo-grains enclose larger voids of dimension greater than the single sand grain. Wetting induced collapse of the pseudo-grains is presumed to be one of the possible mechanisms triggering liquefaction. In the present study, the effect of larger voids on the wetting induced deformation behaviour of sandy soils is experimentally investigated by laboratory box tests. The deformation field in the sample during wetting was measured using Digital Image Correlation (DIC) technique. The results show that the observed deformations are affected by the pore size distribution, thus the amount of voids between the pseudo-grains (macro-void ratio) and the voids inside the pseudo-grains (matrix void ratio). The global void ratio of a sandy soil is not sufficient as single state parameter, but the pore size distribution has to be taken into account, experimentally as well as in modelling.

Effect of pore-size distribution in cathodic gas diffusion layers on the electricity generation of microbial fuel cells (MFCs)

A simple approximate proportional relationship was found between the increases of electricity generation of microbial fuel cells and the volume fraction of mesopores in gas diffusion layers.

Mechanical and structural properties of polylactide/chitosan scaffolds reinforced with nano-calcium phosphate

In this study, chitosan/polylactide scaffolds reinforced with nano-calcium phosphate (average crystallite size of 16.5 nm) (CP) were fabricated to create a material with excellent properties for bone tissue engineering applications via freeze-casting method. The structural and mechanical properties of nanocomposite scaffolds were studied by increasing amount of chitosan/poly lactide ratio and nano-CP content in both dry and hydrate states, which reflected the exact status of scaffolds in a real biomechanical environment. The morphologies of the nanocomposite scaffolds were viewed using scanning electron microscopy (SEM) and all the scaffolds exhibited a high porosity (up to 92 %) with open pores of 38–387 μm average diameters, which decreased with increased chitosan/polylactide ratio and nano-CP content. Also, SEM photograph of the cross-sectional area of the scaffold showed nano-CP was dispersed all over the polymer matrix thoroughly. The results of mechanical tests showed that the compressive modulus (E) and compressive stress (σ) enhanced, when chitosan and nano-CP increased. X-ray diffraction analysis indicated typical chitosan, polylactic acid and nano-CP peaks and showed that the increase in nano-CP weight percentage increased its peak intensities. In addition, the effect of pore-size distributions of the scaffolds with the same composition was studied in relation to mechanical properties. The results showed substantial differences in the pore-size distributions of scaffolds with the same composition prepared, which have no effect on their dry states.

Effect of Pore-Size Distribution on Shrinkage of Concretes

The effects of pore structure of concrete made with slag-blended cement on shrinkage behavior of concrete when exposed to drying were presented in this paper. The investigated parameters were the length of curing (1-day and 7-day curing), slag and gypsum contents in mixtures. Pore structure analysis was studied by conducting mercury intrusion porosimetry and nitrogen gas adsorption technique tests. The results show that 65% slag concrete with 7-day curing exhibited the lowest shrinkage evolution compared to 0, 35, 50% slag mixes. This is attributed to the highest pore radius where meniscus forms when drying in these concretes. It was found that addition of gypsum in slag mixes tend to reduce the nanopores (within the range from 4 to 20 nm pore size) and decrease the proportion of mesopores. The higher proportion of mesopores and the lower value of meniscus pore radius could explain the increase in drying shrinkage of concrete made with 65% slag cement containing 0% added gypsum.

Removal of cyanocobalamine from aqueous solution using mesoporous activated carbon

The adsorption of cyanocobalamine was studied using coal-based mesoporous activated carbon (AC). The ACs tested showed a comparable pore volume, around 0.5 cm 3 g −1, but different contribution of mesopores ranging from 0.53 to 0.82 cm 3 g −1. The adsorption of cyanocobalamine was carried out in slightly alkaline solution in static conditions. Three kinetic models including a first-order Lagergren model, a pseudo-second-order model, and an intraparticle diffusion model were applied to describe the kinetics and mechanism of adsorption. The adsorption of cyanocobalamine on mesoporous carbons followed the pseudo-second-order model. The diffusion of cyanocobalamine molecule within smaller mesopores was identified to be the rate-limiting step. The analysis of adsorption equilibrium data indicates that the adsorption of cyanocobalamine better fits the Langmuir equation than the Freundlich equation. The Langmuir adsorption capacity of the carbon is strongly related to the degree of mesoporosity development. Among ACs tested, the carbon with the highest mesopore volume and mesopore width of 10–50 nm shows the greater ability to remove cyanocobalamine from aqueous solution. The effect of pore-size distribution on the kinetics and mechanism of adsorption has been discussed.

Hydrodynamic dispersion in perfusion chromatography—a network model analysis

A network model was used to simulate the hydrodynamic dispersion, which occurs in perfusion chromatography for proteins under non-retained conditions. In order to elucidate the details of the velocity dependency of the hydrodynamic dispersion coefficient in a perfusive bed, the effects of pore-size distribution (PSD), pore inter-connectivity (PI), and solute molecular size were incorporated into the simulations. It was found that, for purification of proteins on a perfusive column, among these parameters, PI affected the dispersion results most significantly over the whole range of Peclet numbers investigated. POROS media were postulated to possibly have a very high PI, of around 4.77–5.37. PSD also played a very important role in determining the dispersion results; POROS R1 and POROS R2 behaved quite differently, although both of them possess bi-modal PSDs. At higher PI (connected-pore fraction higher than 0.8), the D L / UL curve for POROS R1 showed double plateaus, whereas that for POROS R2 gave only one plateau. Under the experimental conditions investigated, only the macropore size distribution contributed to the dispersion results in POROS R1, whereas the composite bi-modal PSD contributed to the results in POROS R2. Based on the simulation results, size exclusion was also found to affect the dispersion results, giving rise to low dispersion coefficient in the molecular diffusion controlled region and high dispersion coefficient in the convection region. However, in the case of a perfusive column, size exclusion effects were rather insignificant. It was also found that hindered diffusion resulted in sharp increase in the dispersion data at very high Peclet number ( Pe>10 4), which was more significant for POROS R2. The simulation results corroborated the experimental data very well. These indicate that the use of a network model to obtain the hydrodynamic dispersion coefficient is a more realistic representation of the column efficiency in perfusion chromatography, one which accounts directly for microscopic information, such as pore structure and solute molecular size.

Effect of Pore-Size Distribution on the Catalytic Performance for Coal Liquefaction. II. Carbonaceous and Metallic Deposition on the Catalyst

Abstract The behavior of carbonaceous and metallic depositions on catalysts during hydroliquefaction of coal was investigated by using several kinds of catalyst supports with different pore-size distribution values in order to obtain the fundamental data for designing long-life catalysts. Higher concentration of carbonaceous deposition was observed on large-pore and bimodal catalysts than was observed on the comparative small pore and unimodal catalysts, respectively. However, the carbonaceous deposit was distributed more evenly inside large pores than it was inside small pores. The micropores of the bimodal catalysts were more effectively used than were those of the unimodal catalysts. Thus, the unimodal catalysts with small pores suffered more severe pore-mouth poisoning than the bimodal or the large-pore catalysts. The penetration behavior of the metallic components was found to be different for each metal. Discrete minerals such as clay could not penetrate into the catalyst pores and were deposited on the external surface of the catalyst particle. While, the metallic components coordinated with organic compounds such as phenolates or chelates deposited inside the macro- and mesopores. Easy access of the large asphaltenic molecules to the active sites resulted in high coal-liquefaction activity for the catalyst. This was accompanied by large amounts of both carbonaceous and metallic depositions. It is concluded that large-pore or bimodal pore structure is required for both high liquefaction activity and suppression of pore-mouth poisoning.