Bimodal pore distribution

The bimodal pore distribution model used by Gibilaro et aL may also be used to analyze the results of this type of experiment. If it is assumed that all extraneous effects due to mixing in the interstices between the pellets have been eliminated by means of a control experiment, the results corresponding to equations (10.39) and (10.40) are now... 

The shape of the porosimetry curve provides information about the pores. The diagram in Fig. 5a represents a sample that contains essentially one pore size, as indicated by only one increase in volume. As diagrammed in Fig. 5b, two volume increases in the intrusion curve are observed, which is indicative of a bimodal pore distribution. Figure 5c is an example of a curve demonstrating a continuous range of pore sizes. 

The extra pore system in A1MCM-41 (both with Si/Al = 16 and 32) is evident due to the pore size distribution plot (Figure IB). At the higher content of aluminum, not only was a bimodal pore distribution registered, but also a main XRD peak at 2.0 nm was broadened. 

Typical pore size distribution data are shown in Fig. 5, where the integral penetration of mercury into the pores is plotted as a function of applied pressure. The calculated pore diameters in angstroms are shown across the top. The integral curve clearly shows a bimodal pore distribution with mean pore diameters at 20,000 and 50 A. The latter is at the lower limit of the technique. A nitrogen desorption isotherm is required to obtain an accurate measure in the region below 100 A. 

Liapis and McCoy [63] have assumed that the bimodal pore structure of per-fusive adsorbent particles is made of a macroporous region, in which mass transfer takes place through intraparticle convection and pore diffusion, and a microp-orous region made of spherical microparticles in which mass transfer takes place through pure diffusion. Frey et al. [61] developed a model for the analysis of mass transfer in spherical particles having a bimodal pore distribution and derived the following expression for h nt in perfusion chromatography. 

One additional feature occurs when this catalyst is used with extremely heavy residua feedstocks. With proper preparational techniques, bimodal pore distributions are produced in which constrictions at the openings inhibit diffusion of large asphaltenic, coke producing molecules, whereas smaller sulfur compounds have easy access. This effectively reduces excessive coking which otherwise occurs. ... 

These Sylox or precipitated silicas often display bimodal pore distributions, and the cause can be seen in Scheme 29. Small pores are formed between the primary particles within an agglomerate, and large pores by the space between the agglomerates. Therefore, the measured pore... 

The molecular diffusivities were calculated from a weighted average of the binary diffusion resistances which in turn were estimated horn the formula of Fuller et al. The calculation of the Knudsen diffusivities requires information about the pore size. The catalyst had a bimodal pore distribution. Furthermore, via electron microscopy, it was found that the catalyst consisted of crystallites of about 5 p, separated by voids of about 1 ft. Consequently, the maximum length of the micro-... 

To develop a highly efficient AFC, an electrode stracture with more than one pore system or with a bimodal pore distribution is required. The liquid and gaseous reactants must reach the electrolyte that has direct contact with the anode and cathode catalysts. For AFCs, different electrode types have been used. The main types of electrodes are the PTFE-bonded GDE and the DSK. 

For a given membrane the following bimodal pore distribution has been determined experimentally. 

By changing the preparation conditions, (77) can be formed into nanospheres that can be further manipulated into heteroatom containing porous carbon nanospheres. This transformation was accomplished by soaking nanospheres of (77) in aqueous NaOH for 2 hours to allow the base to inpregnate into the stmctures, diying at 110 °C, and then heating at a 5 °C/ min ramp rate to 750 °C in a nitrogen atmosphere. BET analysis revealed a surface area of 1140 m /g and a total pore volume of of 0.9 m /g. Also, a bimodal pore distribution was observed (3-5 nm and 0.6-0.8 nm diameters). 

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