scholarly journals Study on the Separation of H2 from CO2 Using a ZIF-8 Membrane by Molecular Simulation and Maxwell-Stefan Model

Molecules ◽  
2019 ◽  
Vol 24 (23) ◽  
pp. 4350 ◽  
Author(s):  
Behrouz Bayati ◽  
Asma Ghorbani ◽  
Kamran Ghasemzadeh ◽  
Adolfo Iulianelli ◽  
Angelo Basile
Keyword(s):  
Molecular Simulation ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Langmuir Model ◽  
Separation Process ◽  
Point Of View ◽  
Theoretical Point ◽  
Zeolitic Imidazolate Framework ◽  
Adsorption Of Co2 ◽  
And Diffusion

The purification of H2-rich streams using membranes represents an important separation process, particularly important in the viewpoint of pre-combustion CO2 capture. In this study, the separation of H2 from a mixture containing H2 and CO2 using a zeolitic imidazolate framework (ZIF)-8 membrane is proposed from a theoretical point of view. For this purpose, the adsorption and diffusion coefficients of H2 and CO2 were considered by molecular simulation. The adsorption of these gases followed the Langmuir model, and the diffusion coefficient of H2 was much higher than that of CO2. Then, using the Maxwell–Stefan model, the H2 and CO2 permeances and H2/CO2 permselectivities in the H2–CO2 mixtures were evaluated. Despite the fact that adsorption of CO2 was higher than H2, owing to the simultaneous interference of adsorption and diffusion processes in the membrane, H2 permeation was more pronounced than CO2. The modeling results showed that, for a ZIF-8 membrane, the H2/CO2 permselectivity for the H2–CO2 binary mixture 80/20 ranges between 28 and 32 at ambient temperature.

Estimation for discretely observed diffusions using transform functions

2004 ◽  
Vol 41 (A) ◽  
pp. 99-118 ◽  
Author(s):  
Leah Kelly ◽  
Eckhard Platen ◽  
Michael Sørensen
Keyword(s):  
Asymptotic Normality ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Estimation Technique ◽  
Consistency And Asymptotic Normality ◽  
And Diffusion ◽  
Explicit Estimators

This paper introduces a new estimation technique for discretely observed diffusion processes. Transform functions are applied to transform the data to obtain good and easily calculated estimators of both the drift and diffusion coefficients. Consistency and asymptotic normality of the resulting estimators is investigated. Power transforms are used to estimate the parameters of affine diffusions, for which explicit estimators are obtained.

scholarly journals Carbon Quantum Dots from Lemon Waste Enable Communication among Biodevices

Chemosensors ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 202
Author(s):  
Federico Calì ◽  
Valentina Cantaro ◽  
Luca Fichera ◽  
Roberta Ruffino ◽  
Giuseppe Trusso Sfrazzetto ◽  
...  
Keyword(s):  
Carbon Dots ◽  
Electromagnetic Waves ◽  
Carbon Quantum Dots ◽  
Point Of View ◽  
Fluorescence Properties ◽  
Fluorescent Nanoparticles ◽  
Theoretical Point ◽  
Molecular Communication ◽  
Chemical Systems ◽  
And Diffusion

A bioinspired method of communication among biodevices based on fluorescent nanoparticles is herein presented. This approach does not use electromagnetic waves but rather the exchange of chemical systems—a method known as molecular communication. The example outlined was based on the fluorescence properties of carbon dots and follows a circular economy approach as the method involves preparation from the juice of lemon waste. The synthesis is herein presented, and the fluorescence properties and diffusion coefficient are evaluated. The application of carbon dots to molecular communication was studied from a theoretical point of view by numerically solving the differential equation that governs the phenomenon. The theoretical results were used to develop a prototype molecular communication platform that enables the communication of simple messages via aqueous fluids to a fluorescence-detecting biodevice receiver.

Estimation for discretely observed diffusions using transform functions

2004 ◽  
Vol 41 (A) ◽  
pp. 99-118 ◽  
Author(s):  
Leah Kelly ◽  
Eckhard Platen ◽  
Michael Sørensen
Keyword(s):  
Asymptotic Normality ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Estimation Technique ◽  
Consistency And Asymptotic Normality ◽  
And Diffusion ◽  
Explicit Estimators

This paper introduces a new estimation technique for discretely observed diffusion processes. Transform functions are applied to transform the data to obtain good and easily calculated estimators of both the drift and diffusion coefficients. Consistency and asymptotic normality of the resulting estimators is investigated. Power transforms are used to estimate the parameters of affine diffusions, for which explicit estimators are obtained.

scholarly journals A Necessary Characteristic Equation of Diffusion Processes Having Gaussian Marginals

2012 ◽  
Vol 2012 ◽  
pp. 1-9
Author(s):  
Syeda Rabab Mudakkar
Keyword(s):  
Fourier Transform ◽  
Diffusion Process ◽  
Characteristic Equation ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Kolmogorov Equation ◽  
Marginal Density ◽  
Operator Approach ◽  
One Dimensional ◽  
And Diffusion

The aim of this work is to characterize one-dimensional homogeneous diffusion process, under the assumption that marginal density of the process is Gaussian. The method considers the forward Kolmogorov equation and Fourier transform operator approach. The result establishes the necessary characteristic equation between drift and diffusion coefficients for homogeneous and nonhomogeneous diffusion processes. The equation for homogeneous diffusion process leads to characterize the possible diffusion processes that can exist. Two well-known examples using the necessary characteristic equation are also given.

scholarly journals Cs Retention and Diffusion in C-S-H at Different Ca/Si Ratios

2018 ◽  
Author(s):  
Eduardo Duque-Redondo ◽  
Kazuo Yamada ◽  
Iñigo López-Arbeloa ◽  
Hegoi Manzano
Keyword(s):  
Diffusion Coefficients ◽  
Alkaline Earth ◽  
Diffusion Processes ◽  
Hydration Product ◽  
Cement Matrix ◽  
Water Molecules ◽  
Average Diffusion ◽  
Dynamics Simulations ◽  
And Diffusion

<div>Cement and concrete have been widely used as a barrier to isolate many types of contaminants, including radioactive waste, in repository sites. Nevertheless, the intrusion of groundwater in those nuclear repositories may release those contaminants by leaching mechanisms. Because of this, the retention and diffusion processes in cement matrix require to be analyzed in depth. The adsorption in cement and C‐S-H gel, its main hydration product, is influenced by factors as the pH, the composition or the alkali and alkaline earth content. In this work, molecular dynamics simulations were employed to study the role of Ca/Si ratio of the C‐S‐H in the capacity to retain Cs and diffusivity of these ions in gel pores. For that purpose, we built four different C‐S‐H models with Ca/Si ratios from 1.1 to 2.0. The results indicate better cationic retention at low Ca/Si ratios due to the interaction of the cations with the bridging silicate tetrahedrons. However, the average diffusion coefficients of the cations decrease at higher Ca/Si ratios because the high ionic constraint in the nanopore that induces a longrange ordering of the water molecules.</div>

scholarly journals The use of underground thermal gradients as technique for soil radon mitigation

2021 ◽  
Author(s):  
Francisco J. Arias ◽  
Salvador De Las Heras
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Thermal Gradient ◽  
Short Note ◽  
Point Of View ◽  
Thermal Gradients ◽  
Theoretical Point ◽  
Cold Regions ◽  
Standard Temperature ◽  
Soil Radon

Diffusion coefficients of radon through minerals and rocks are characterised by Arrhenius linear plots, i.e., increasing with temperature. It has been observed, for example, that rocks with a mild heating (<100°C) translate into a radon release that can be enhanced 100–1,000 times than the normal release at STP (Standard Temperature Pressure (STP). Therefore, it is reasonable to think that if the soil is deliberately heated creating a thermal gradient, it could be possible, at least from a theoretical point of view, to thermally pump radon from soil because the radon atoms will escape preferentially from cold regions (low diffusion coefficient) towards hot regions (high diffusion coefficients) if a radon sink is located. In this short note, this approach for soil radon removal is investigated.

scholarly journals Cs Retention and Diffusion in C-S-H at Different Ca/Si Ratios

2018 ◽  
Author(s):  
Eduardo Duque-Redondo ◽  
Kazuo Yamada ◽  
Iñigo López-Arbeloa ◽  
Hegoi Manzano
Keyword(s):  
Diffusion Coefficients ◽  
Alkaline Earth ◽  
Diffusion Processes ◽  
Hydration Product ◽  
Cement Matrix ◽  
Water Molecules ◽  
Average Diffusion ◽  
Dynamics Simulations ◽  
And Diffusion

<div>Cement and concrete have been widely used as a barrier to isolate many types of contaminants, including radioactive waste, in repository sites. Nevertheless, the intrusion of groundwater in those nuclear repositories may release those contaminants by leaching mechanisms. Because of this, the retention and diffusion processes in cement matrix require to be analyzed in depth. The adsorption in cement and C‐S-H gel, its main hydration product, is influenced by factors as the pH, the composition or the alkali and alkaline earth content. In this work, molecular dynamics simulations were employed to study the role of Ca/Si ratio of the C‐S‐H in the capacity to retain Cs and diffusivity of these ions in gel pores. For that purpose, we built four different C‐S‐H models with Ca/Si ratios from 1.1 to 2.0. The results indicate better cationic retention at low Ca/Si ratios due to the interaction of the cations with the bridging silicate tetrahedrons. However, the average diffusion coefficients of the cations decrease at higher Ca/Si ratios because the high ionic constraint in the nanopore that induces a longrange ordering of the water molecules.</div>

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