scholarly journals Pore Structures of ZSM-5 Synthesized in the Mesopore Spaces of a Carbon Aerogel

2003 ◽  
Vol 21 (2) ◽  
pp. 199-203 ◽  
Author(s):  
Yousheng Tao ◽  
H. Tanaka ◽  
T. Ohkubo ◽  
H. Kanoh ◽  
K. Kaneko
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Nitrogen Adsorption ◽  
Carbon Aerogel ◽  
Template Method ◽  
Pore System ◽  
Average Pore ◽  
Pore Structures ◽  
Uniform Mesopores

A mesoporous ZSM-5 monolith several millimetres in size has been synthesized employing the template method and using a carbon aerogel with uniform mesopores. Measurement of the pore-size distribution using nitrogen adsorption showed a bimodal pore system of mesopores and micropores whose average pore widths were 8 nm and 0.51 nm, and whose volumes were 0.09 cm3/g and 0.34 cm3/g, respectively.

scholarly journals Comparison of Nitrogen Adsorption and Mercury Penetration Results: II. Pore size Distributions Calculated from Type IV Isotherm Data

1988 ◽  
Vol 5 (3) ◽  
pp. 168-190 ◽  
Author(s):  
Bruce D. Adkins ◽  
Burtron H. Davis
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Nitrogen Adsorption ◽  
Type Iv ◽  
Pore Size Distributions ◽  
Nitrogen Desorption ◽  
The Difference ◽  
Penetration Data ◽  
Packed Sphere

The pore distributions calculated from nitrogen desorption and from mercury penetration data are similar for the four materials utilized in this study. While there are small differences in the distributions calculated using different models (Cohan. Foster or Broekhoff-deBoer) with nitrogen adsorption or desorption isotherm data, all three show reasonable agreement with distributions calculated from mercury penetration data. Frequently practical catalysts have such a broad pore size distribution that neither method alone is adequate to measure the total pore size range. The present results suggest a direct comparison, without recourse to a scaling factor, is appropriate when comparing results from the two methods even though the pore size distribution maximum may vary by at least 50% depending upon the model chosen for the calculation. Better agreement may be obtained between the two experimental techniques by adjusting either the nitrogen adsorption data using a packed sphere model or the mercury penetration data by an earlier reported correction ratio. The difference between the two methods becomes less than 20% when a correction procedure is used; however, further studies are needed to define the range of material shaped that these procedures are applicable to.

scholarly journals The structural porosity in soil hydraulic functions – a review

2008 ◽  
Vol 3 (Special Issue No. 1) ◽  
pp. S7-S20 ◽  
Author(s):  
M. Kutílek ◽  
L. Jendele
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Soil Structure ◽  
Water Retention ◽  
Retention Function ◽  
Pore System ◽  
Conductivity Function ◽  
Soil Hydraulic ◽  
Matrix Domains

Products of biological processes are the dominant factor of soil structure formation in A horizons, while in B horizons their role is less expressed. Soil structure influences dominantly the structural domain of the pore system in bimodal soils thus affecting soil hydraulic functions. The form of soil hydraulic functions depends upon the pore size distribution and generally upon configuration of the soil pore system. We used the functions derived for the lognormal pore size distribution and modified them to bi-modal soils. The derived equations were tested by experimental data of catalogued soils. The procedure leads to the separation of two mutually different domains of structural and matrix pores. The value of the pressure head (potential) separating the two domains is not constant and varies in a broad range. For each domain we obtained its water retention function and unsaturated hydraulic conductivity function. The separation of hydraulic functions for the two domains is a key problem in the solution of preferential flow and in controlling lateral flow between the structural and matrix domains. Water retention function is fully physically based while the conductivity function still keeps fitting parameters, too. Their simple relationship to tortuosity and pores connectivity was not confirmed. Since they differ substantially for matrix and structural domains, we suppose that there exists a great difference in configuration of porous systems in structural and matrix domains. The use of uniform fitting conductivity parameters for the whole range of pores is not justifiable.

A rate equation theory for the pore size distribution of calcined CaCO3 in calcium looping

2016 ◽  
Vol 192 ◽  
pp. 197-216 ◽  
Author(s):  
Z. S. Li ◽  
P. T. Liang ◽  
N. S. Cai
Keyword(s):  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Rate Equation ◽  
Bimodal Distribution ◽  
Adsorption Method ◽  
Average Pore ◽  
Calcium Looping ◽  
Pore Evolution

CaCO3 calcination is an important step in calcium looping, and the formed pore structure of porous CaO is critical for subsequent carbonation towards carbon dioxide. Therefore, it is necessary to investigate the evolution of the pore structure of the sorbent in the calcination step. A mathematical model describing the pore size distribution during the calcination of the CaCO3 particle was developed. CaCO3 calcination is calculated following a shrinking core model at the CaO–CaCO3 interface, and CO2 diffuses through the porous CaO layers. During the decomposition of CaCO3, after the departure of the CO2 molecule from its original lattice, a vacancy will be formed that will diffuse inside the solid, and the collision and coagulation of the vacancy results in pore formation. A rate equation theory was proposed to describe the vacancy coagulation and pore evolution inside the solid, with rate expressions derived for the pore size distribution function with time evolution. To validate the developed model, the evolution of the pore size distribution during CaCO3 calcination was experimentally measured in a high-temperature furnace combined with the nitrogen adsorption method. It was found that there is a characteristic bimodal distribution for the pore structure of calcined CaCO3, with average pore sizes of ∼2.8 nm and ∼50 nm. The calculated results agree well with the experimental data, and the relative importance of growth and coagulation was discussed.

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