Texture mercury porosimetry

Since the porosity of carbons is responsible for their adsorption properties, the analysis of the different types of pores (size and shape), as well as the PSD, is very important to foresee the behavior of these porous solids in final applications. We can state that the complete characterization of the porous carbons is complex and needs a combination of techniques, due to the heterogeneity in the chemistry and structure of these materials. There exist several techniques for the analysis of the porous texture, from which we can underline the physical adsorption of gases, mercury porosimetry, small angle scattering (SAS) (either neutrons—SANS or x-rays—SAXS), transmission and scanning electron microscopy (TEM and SEM), scanning tunnel microscopy, immersion calorimetry, etc. 

Two epoxy-activated related supports, Sepabeads EC-EP3 and EC-EP5 (Figure 11.3), were assayed for the immobilization of A. aculeatus fructosyltransferase. By combination of nitrogen isotherms and mercury porosimetry analyses, the textural properties of both carriers were determined (Table 11.3). As shown, both samples... 

Incorporation of appropriate contact angles in textural characterization by mercury porosimetry... 

For description of textural properties of carbonaceous adsorbents, adsorption/desorption isotherms of vapours and gases in static conditions as well as mercury porosimetry are used. The latter method often leads to destruction of porous structure of investigated materials while the usage of the former one is affected by the specific properties of molecular sieves described above. Taking into account these limitations, in this work the authors have made an attempt of determination of porous structure of carbon molecular sieves with the used of the pycnometric technique. 

As a conclusion, image analysis, impedance spectroscopy and microtomography are nondestructive methods able to provide valuable information on the texture of porous materials. These three techniques are complementary to mercury porosimetry, which does not allow the analysis of morphological details. 

The texture properties of the ultrathin porous glass membranes prepared in our laboratory were initially characterized by the equilibrium based methods nitrogen gas adsorption and mercury porosimetry. The nitrogen sorption isotherms of two membranes are shown in Fig. 1. The fully reversible isotherm of the membrane in Fig. 1 (A) can be classified as a type I isotherm according to the lUPAC nomenclature which is characteristic for microporous materials. The membrane in Fig. 1 (B) shows a typical type IV isotherm shape with hysteresis of type FIl (lUPAC classification). This indicates the presence of fairly uniform mesopores. The texture characteristics of selected porous glass membranes are summarized in Tab. 1. The variable texture demanded the application of various characterization techniques and methods of evaluation. 

Cylindrical pellets of four industrial and laboratory prepared catalysts with mono- and bidisperse pore structure were tested. Selected pellets have different pore-size distribution with most frequent pore radii (rmax) in the range 8 - 2500 nm. Their textural properties were determined by mercury porosimetry and helium pycnometry (AutoPore III, AccuPyc 1330, Micromeritics, USA). Description, textural properties of catalysts pellets, diameters of (equivalent) spheres, 2R, (with the same volume to geometric surface ratio) and column void fractions, a, (calculated from the column volume and volume of packed pellets) are summarized in Table 1. Cylindrical brass pellets with the same height and diameter as porous catalysts were used as nonporous packing. 

Textural characterisation of the samples was carried out by measuring apparent density (mercury at 0.1 MPa), mercury porosimetry and N2 and CO2 adsorption isotherms, at -196 and 0 °C, respectively. The apparent surface areas of the samples were obtained by using the BET equation [5]. The micropore size analysis was performed by means of the t-plot and the Dubinin-Astakhov methods [6]. 

We will provide a succinct introduction to the main textural characterisation techniques for catalysts. As a heterogeneous catalyst comprises a support and an active phase, we will distinguish between techniques intended for studying the support, which will be presented in a first section (Physisorption isotherms and mercury porosimetry) and techniques used to characterise the active phase, in the strict sense of the term, shown in a second section (Chemical adsorption). For each technique, we will show the theoretical principle, the way in which the measurement is carried out and the equipment used. Finally, examples will be used to illustrate the type of response that can be given using these characterisation techniques. 

The aim of this study is to eompare pore structure characteristics of two industrial catalysts determined by standard methods of textural analysis (physical adsorption of nitrogen and mercury porosimetry) and selected methods for obtaining parameters relevant to transport processes (multicomponent diffusion and permeation of gases). 

Catalysts were characterised by two standard textural-analysis methods mercury porosimetry (AutoPore 9200, Micromeritics, USA) and physical adsorption of nitrogen (ASAP2010M, Micromeritics, USA). 

Alumina membranes containing monodispersed cylindrical pores have been characterised by a combination of three ditferent techniques Field emission scanning electron microscopy, mercury porosimetry and small angle neutron scattering (SANS). SANS is a method which can provide details of the highly anisotropic texture in such model porous materials. 

The highly anisotropic porous texture of alumina membranes containing monodispersed cylindrical pores has been characterised using a combination of three techniques SEM, mercury porosimetry and SANS. The SANS technique is a promising and very sensitive method for the analysis of such anisotropic pore structures. Further quantitative analysis of these membranes, which contain uniform macropores, will require SANS measurements at much lower Q. 

Several determination methods of a porous texture can be used for characterizing the supports. Certain of these methods (i.e., scanning electron microscopy, mercury porosimetry) are described in other chapters of this book. We shall only report here the specific methods of support characterization. 

Several traditional techniques have been used to determine the composition, structure and texture of the catalysts. These include X-ray fluorescence. X-ray diffraction, specific surface-area measurements, mercury porosimetry, and electron microscopy. The application of each technique is straightforward and will not be discussed here. For descriptions of these techniques see the respective sections in Part A of this volume. 

The composition, the textural and surface properties of the catalysts were studied by AAS, mercury porosimetry, XRD, XPS and TG-DTA [16,17]. The amount of metallic copper on the surface of catalyst was determined by titration with N2O [18]. The characterization of bulk and surface properties of the catalysts is given elsewhere [14,16,17]. 

In this work, nanocomposite supports formed by nanometric domains of alumina dispersed on a-Al203 beads were synthesized by a modified incipient wetness impregnation method in order to improve specific surface area and surface reactivily of a-Al203 large porosity precursor. The obtained composites were characterized by conventional physical methods like N2 adsorption-desorption, mercury porosimetry, TEM and SEM, in order to describe the evolution of the composite textural properties with the impregnated phase morphology. 

R. Pirard, C. Alie, and J.-P. Pirard, Characterization of Porous Texture of Hyper-porous Materials by Mercury Porosimetry Using Densification Equation, Powder TechnoL, 128, pp. 242 7, 2002. 

Pirard R, Rigacci A, Marechal JC, Achard P, Quenard D, Pirard JP (2003) Characterization of porous texture of hyperporous polyurethane based xerogels and aerogels by mercury porosimetry using densification equation. Polymer 44 4881 887. 

Non-intrusive mercury porosimetry Characterization technique to study the porous texture of a material by collapsing this material under an isostatic mercury pressure, at pressures low enough to not induce mercury intrusion in the pores... 

The specific surface area of the activated catalyst was found to increase with alumina content up to about 20 m /g at around 2% AI2O3 and then to remain constant (10), demonstrating the role of this additive as structural promoter that (together with other nonreducible phases such as hercynite and calcium ferrite) prevents sintering of the metallic iron particles into low surface area material. These values are compatible with the mean particle sizes of around 30 nm, as determined by mercury porosimetry and seen directly in the scanning electron microscope (Fig. 2) (11). This agreement further shows that the texture of the catalyst permits the N2 molecules of the BET analysis to reach essentially the whole internal surface. 

Whatever the catalyst precursor, the intrusion volume is 40 to 50% that of the pure support indicating that mercury porosimetry also detects some texture modifications in the catalyst, as compared to the original carrier. However, if we take into account that 60% of the mass in the calcined catalyst is due to nickel, we reach the conclusion that the total pore volume of the carrier in the supported precursor is not different from that in the pure carrier. 

The coke diameter Dc is derived from the molecular mass, assuming a spherical shape of the coke molecule. In the fraction y of pores with a diameter smaller than Dc, the coke diameter equals the pore diameter. Values for the textural parameters were obtained from physical measurements electron microscopy, nitrogen desorption, and mercury porosimetry. 

The mechanical bdbiaviour of two series of silica and of resorcinol xerogels is analyzel by mercury porosimetry. The data are expressed as pressure-density curves, which enables textural infinmation to be obtained. In particular, it is shown that some of the analyzed samples exhibit a maik lowering of their mechanical stiffiiras upon compression, lliis observation is analyzed in terms of tte collapse of the sample s porosity and of the heterogeneity of die microstructure. 

The texture of two series of silica and organic xerogels was analyzed by mercury porosimetry. The samples are mainly compressed but not intruded by mercury in the porosimeter, and flie information obtained is therefore purely mechanical. A textural information can however be extracted from the data by analyzing the way in which a given microstructme should resist a compressive stress. 

Two standard methods (mercury porosimetry and helium pycnometry) together with liquid expulsion permporometry (that takes into account only flow-through pores) were used for determination of textural properties. Pore structure characteristics relevant to transport processes were evaluated fiom multicomponent gas counter-current difhision and gas permeation. For data analysis the Mean Transport-Pore Model (MTPM) based on Maxwell-Stefan diffusion equation and a simplified form of the Weber permeation equation was used. 

All porous materials were chosen to cover as wide as possible range of pore sizes and to represent both monodisperse and bidisperse PSD. Textural properties were determined by mercury porosimetry (AutoPore 111, Micromeritics, USA) and helium pycnometry (AccuPyc 1330, Micromeritics, USA) are summarized in Table 1. 

Mercury porosimetry is a method currently used to characterize the texture of porous materials. It enables determining pore volume, specific surface area and also distributions of pore volume and surface area versus pore size. It can be applied to powders, as weU as to monolithic porous materials. The basic hypothesis usually accepted is that mercury penetrates into narrower and narrower cavities or pores as pressure increases. Data analysis is performed using the intrusion equation proposed by Washburn (1921) ... 

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