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  • 1
    Electronic Resource
    Electronic Resource
    Modification of the Porosity of Pillared Clays by Carbon Deposition II. Hydrocarbon Cracking (1997)
    Springer
    Journal of porous materials 4 (1997), S. 5-15 
    Details
    ISSN: 1573-4854
    Keywords: pillared clay ; pore size modification ; adsorption ; cracking ; carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract To enhance the adsorption selectivity of pillared clays an attempt is made to modify the initial pore size by a controlled deposition of carbon. Cracking of hydrocarbons in the pores of the pillared clay results in coke deposits which can alter the pore size. Based on the evaluation of the amount of coke, the coke density, the decrease in micropore volume, changes in the micropore size distribution and the acidity it was possible to distinguish between pore-blocking, pore-filling and pore-narrowing effects. The modification mechanisms strongly depend on the initial porous structure, the acidity (Brönsted/Lewis), the cracking conditions (static or flow) and the hydrocarbons used. The carbon deposition results in a decrease in pore volume due to pore-filling (Ti-PILC) and pore-blocking (Al-PILC) without achieving a controlled pore-narrowing but some indications for pore-entrance narrowing were found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009663020550
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical evaluation of pillared clay adsorbents: Part I. The microporosity of Al- and Ti-pillared montmorillonite (1996)
    Springer
    Journal of porous materials 3 (1996), S. 47-59 
    Details
    ISSN: 1573-4854
    Keywords: theoretical calculations ; microporosity ; pillared clays ; adsorbents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Fillared clays have become a well known class of porous materials. Due to the versatile porosity they seem to be complementary to zeolites and can be very useful for adsorption and catalytic processes. Despite intensive research, real industrial applications are still lacking. Somehow, the porosity of these pillared clays is not what was expected. The present study reports theoretical calculations, based on simple geometrical models in combination with experimental data, in order to obtain a better insight in the PILC structure and its limiting factors. Parameters such as interpillar free distance and maximum micropore volume were calculated and compared to experimental or literature data. The final goal is to find out the potential of pillared clays as adsorbents to be used as substituents or complements for zeolites. This part reports calculations, in terms of microporosity, performed for two types of pillared clays having completely different porosity properties: Al- and Ti-PILC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01135361
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  • 3
    Electronic Resource
    Electronic Resource
    The use of the logarithmic adsorption isotherm for the determination of the micropore-size distribution (1995)
    Springer
    Journal of porous materials 2 (1995), S. 97-105 
    Details
    ISSN: 1573-4854
    Keywords: pore-size distribution ; micropores ; PILC ; adsorption potential ; N2-adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The determination of the micropore-size distribution of microporous materials is of major importance in the field of adsorption and catalysis. This new method to derive the micropore-size distribution for Pillared Clays (PILC) is based on the logarithmic adsorption isotherm. When a N2-adsorption isotherm is replotted on a log P/P 0 scale, a curve representing the adsorption potential is obtained. Because the adsorption potential is highly dependent on the pore-size, this curve contains all the information on the pore structure. These curves often exhibit steps, large increases in volume adsorbed by small changes in adsorption potential. These are thermodynamically related to the filling of pores of a certain size. The relative pressures where these steps appear are dependent on the pore-size. Taking the derivative, dV/d log (P/P 0), the location of these steps becomes more clear. These derivative curves give a lot of information on the pore-size distribution. The presence of several maxima and their sharpness informs about the number of different pore-sizes present and the homogeneity. Assuming that N2-adsorption in the micropores is ruled by the amount of N2-layers which can fit in, the micropore range can be subdivided in five pore groups adsorbing 1–5 layers. By locating the main maxima in the derivative curves of pillared clays with known but different slit widths, we can correlate a pore-size range to a certain P/P 0 range where these pores will fill. In this way a micropore-size distribution based on the adsorption potential can be constructed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486576
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical evaluation of pillared clay adsorbents: Part III: The total porosity and the macrostructure of Al-pillared montmorillonite and hectorite (1996)
    Springer
    Journal of porous materials 3 (1996), S. 207-216 
    Details
    ISSN: 1573-4854
    Keywords: theoretical calculations ; total porosity ; macrostructure ; pillared clays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract As a new class of porous materials, pillared clays have been more and more investigated as a potential substituent or complement to zeolite materials. Despite of intensive research, real industrial applications are still lacking. Somehow, the porosity of these materials is lower than what was expected. To evaluate the potential of the pillared clays as adsorbent, theoretical calculations were carried out to obtain a better insight of the influence of the PILC's macrostructure on the micro- and mesoporosity. Assuming the layers to stack in a 3-dimensional brick-like fashion, the micro- and mesoporosity and interpillar free distance were calculated taking into account: the clay layer dimensions, interlayer free spacing, lateral distance between adjacent layers, partial pillaring/collapse and pillar symmetry. The calculations were performed for Al-pillared montmorillonite and hectorite and validated with experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01137909
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  • 5
    Electronic Resource
    Electronic Resource
    Modification of the porosity of pillared clays by carbon deposition. I. Polymer carbonization (1996)
    Springer
    Journal of porous materials 3 (1996), S. 257-266 
    Details
    ISSN: 1573-4854
    Keywords: pillared clay ; pore size modification ; adsorption ; polymers ; carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In order to use pillared clays (PILC) for selective adsorption, further modifications of the porous structure are necessary. The deposition of carbon residues onto the porous structure of pillared clays by the carbonization of polymers (polyvinylalcohol) was proposed to achieve a controlled modification of the pore size. Ti and Al-pillared clays (calcined and non-calcined) were impregnated with PVA (different grades and different concentrations and subsequently carbonized to form carbon phases. The effect of the carbon deposits on the porosity of Ti- and Al-PILC is discussed in terms of pore-blocking, pore-filling and pore-narrowing. The deposition of carbon using PVA resulted in a complete pore-blocking for Al-PILC and in a narrowing of the pore size distribution for Ti-PILC, without achieving a controlled pore-narrowing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01137915
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical Evaluation of the Microporosity of Pillared Layered Double Hydroxides (1999)
    Springer
    Journal of porous materials 6 (1999), S. 307-321 
    Details
    ISSN: 1573-4854
    Keywords: layered double hydroxides (LDHs) ; theoretical calculations ; microporosity ; Fe(CN)6-MgAl-LDHs ; [PV2W10O40]-ZnAl-LDHs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Over the last ten years, the concept of pillaring has frequently been applied on layered double hydroxides (LDHs). Due to the variety of possible anionic pillaring species and the adjustable layer charge density, LDHs offer good perspectives with regard to the creation of porous adsorbents and catalysts. But despite these possibilities, their porosity properties can still not compete with those of industrially applicable materials like zeolites. In this study, theoretical calculations based on geometrical models and performed on both Fe(CN)6-MgAl-LDHs (A) and [PV2W10 O40]-ZnAl-LDHs (B) were reported. Properties such as the micropore volume and the interpillar distance were calculated, and compared to experimental data. For a M(II)/M(III) ratio in the layers of 3, the theoretical maximum micropore volumes were 0.3843 cm3/g (A) and 0.1497 cm3/g (B), respectively. By implementing parameters like the stack size, pillars on the outside of the stacks and the possibility of collapse, the model was adjusted in order to create a realistic picture of the microstructure of pillared LDHs. This led to a better understanding of the limiting factors, and gave an explanation for the relatively low micropore volumes of pillared LDHs. For the Fe(CN)6-MgAl-LDHs, small interpillar distances were responsible for the partial inaccessibility of the interlayer regions by N2. This effect was the most pronounced for high charge density LDHs. The situation for the [PV2W10O40]-ZnAl-LDHs is more complex. Probably due to an incomplete pillaring process, the theoretical maximum values are not reached.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009692925326
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular probe technique for the assessment of the carbon molecular sieve structure (1995)
    Springer
    Journal of porous materials 2 (1995), S. 19-23 
    Details
    ISSN: 1573-4854
    Keywords: carbon molecular sieve ; adsorption ; micropore size distribution ; molecular probe ; DR equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Nitrogen adsorption at 77 K is the most common technique for defining the surface area and pore volume of a porous material. However it is not adequate to assess the microporosity of carbon molecular sieves (CMS), because of activated diffusion effects. In this paper, a molecular probe technique was used to defining the pore size of CMS materials. Adsorption of gases (vapors) with different molecular sizes, were measured by a gravimetric method using a spring balance. The amount adsorbed at room temperature was recorded over a 24-h period. The following molecular probes were chosen: CO2 (0.33 nm), C2H6 (0.4 nm), n-C4H10 (0.43 nm), i-C5H112 (0.5 nm), and CCl4 (0.6 nm). The micropore volumes were estimated by the Dubinin-Raduhkevich (DR) equation. Assuming that the diameters of the micropores are larger than those of the adsorbed molecules, the micropore volume distribution of each sample was estimated. The results demonstrated that the main pore size of the studied CMSs are less than 0.5 nm. One of the samples had a narrow pore size distribution in the range of 0.33–0.43 nm, which is the critical pore size for kinetic separation of oxygen from nitrogen. It is concluded that the molecular probe technique is an effective mean to assess the CMS adsorbents structure, which is not currently possible using conventional approaches with a single adsorbate, such as nitrogen or argon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486566
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical evaluation of pillared clay adsorbents: Part II: Differences in porosity between Al-pillared laponite and hectorite (1996)
    Springer
    Journal of porous materials 3 (1996), S. 157-168 
    Details
    ISSN: 1573-4854
    Keywords: pillared clays ; laponite ; theoretical calculations ; microporosity ; macrostructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Pillared Clays are proposed as a new class of sorbents with properties which exceed those of zeolites. However, despite of intense research, the materials are still not used as substituents of zeolites. By the present study a better understanding of the potential and limiting factors of pillared clays is achieved by means of geometric models. These models take into account interlayer distance, pillar symmetry, collapse, partial pillaring, layer size and layer stacking. The results are evaluated on microporosity and interpillar distance and compared to experimental data. Because of the important contribution of mesopores to the pore volume of PILCs, a macrostructure in which the experimental mesopore volume has been approximated, is proposed. This paper reports the evaluation of two Al-pillared hectorites, natural and synthetic (laponite), having completely different macrostructures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01134027
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical evaluation of pillared clay adsorbents: Part IV: The microporosity of Fe- and mixed Fe-Zr-pillared montmorillonite (1996)
    Springer
    Journal of porous materials 3 (1996), S. 217-225 
    Details
    ISSN: 1573-4854
    Keywords: pillared clays ; montmorillonite ; theoretical calculations ; microporosity ; Fe-PILC ; Fe-Zr-PILC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Pillared clays are proposed as a new class of sorbents with properties similar to zeolites. However, despite extensive research, zeolites have not yet been replaced by pillared clays for industrial applications. In the present study a better understanding of the potential and limiting factors of Fe and mixed Fe-Zr pillared clays is focused by theoretical modelling calculations including interlayer distance, pillar symmetry, collapse and partial pillaring. The results are evaluated on microporosity and interpillar distance and are compared to experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01137910
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  • 10
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    An improved model for through-diffusion experiments: application to strontium and tritiated water (HTO) diffusion in Boom Clay and compacted illite (2016)
    Geological Society (of London)
    Details
    Publication Date: 2016-06-26
    Description: Through-diffusion experiments are conventional experiments to measure the transport parameters of radionuclides in clays. Typically, a regular replacement of the outlet volume by a tracer-free volume is performed. In the classical approach, this type of through-diffusion experiment is modelled by assuming a zero concentration in the outlet volume. Nonetheless, this assumption is not always correct, usually because the outlet volume is insufficiently large or the time between two consecutive replacements of the outlet volume is too long. Therefore, a model was developed disregarding this assumption and, instead, considers the tracer concentration in the outlet volume to evolve, as in the experiments: the flux into the outlet volume increases the tracer concentration and, at each replacement, the tracer concentration in the outlet volume is set to zero. The model was used to reproduce the diffusion of strontium (Sr) and tritiated water (HTO) in illite and Boom Clay. Model results yielded good matches with the tracer evolution in the inlet and the outlet, and the tracer profile in the core at the end of the experiment.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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