Pores characteristics

Catalysis. Kistler explored the catalytic appHcations of aerogels ia the 1930s because of the unique pore characteristics of aerogels (24), but this area of research stayed dormant for about three decades until less tedious procedures to produce the materials were introduced (25,26). Three recent review articles summarize the flurry of research activities since then (63—65). Table 3 is a much abbreviated Hst of what has been cited in these three articles to demonstrate simply the wide range of catalytic materials and reactions that have been studied. 

The effectiveness is known from experiment for important industrial catalysts and is correlated, in general, in terms of pore characteristics, concentrations, and specific rate equations. 

Modeling the pore size in terms of a probability distribution function enables a mathematical description of the pore characteristics. The narrower the pore size distribution, the more likely the absoluteness of retention. The particle-size distribution represented by the rectangular block is the more securely retained, by sieve capture, the narrower the pore-size distribution. 

Houghton et al. (HI3) have reported data on the size, number, and size-distribution of bubbles. Distinction is made between bubble beds, in which bubble diameter and gas holdup tend to become constant as the gas velocity is increased (these observations being in agreement with those of other workers previously referred to), and foam beds, in which bubble diameter increases and bubble number per unit volume decreases for increasing gas velocity. Pore characteristics of the gas distributor affect the properties of foam beds, but not of bubble beds. Whether a bubble bed or a foam bed is formed depends on the properties of the liquid, in particular on the stability of bubbles at the liquid surface, foam beds being more likely to form in solutions than in pure liquids. 

Conditions during start-up can have a dramatic impact on time required to reach reasonable performance levels and on the ultimate reactor performance. Dilution rate, loading rate as measured by chemical oxygen demand (COD), carrier choice, inoculum amount, inoculum strategy, and inoculum species distribution are critical parameters (Sreekrishnan et al., 1991 Araki and Harada, 1994 Austermann-Haun et al., 1994 Yongming et al., 1993). Pore characteristics have a strong influence on time required for start-up and on the ultimate biomass density in the... 

The major technical difficulty in gel permeation chromatography involves the careful packing of the column to ensure a uniform structure and it is absolutely essential that the level of the solvent is never allowed to fall below the level of the gel otherwise disruption of the gel bed occurs. Additionally, because most gels are compressible, only an absolute minimum of pressure should be applied to prevent alteration of the pore characteristics. In practice hydrostatic pressures greater that 30-40 cm should not be used and pumps should be used only with non-compressible gels. 

Another method to measure pore size distribution is capillary flow porometry [202,203], in which a sample material is soaked with a low surface tension liquid that fills all its pores. Then, gas pressure is applied on one side of the sample in order to force the liquid out of the pores. At low pressures, the flow rate is close to zero however, as the pressure increases, the flow rate also increases and the amount of liquid inside fhe pores decreases. Thus, the flow rate is determined as a function of pressure and is then used to calculate the desired pore characteristics, such as pore size distribution, largest pore diameter, and mean flow pore diameter. 

The testing of battery separators and control of their pore characteristics are important requirements for proper functioning of batteries. Mercury porosim-etry has been historically used to characterize the separators in terms of percentage porosity, mean pore size and pore size distribution. In this method, the size and volume of pores in a material are measured by determining the quantity of mercury, which can be forced into the pores at increasing pressure. Mercury does not wet most materials, and a force must be applied to overcome the surface tension forces opposing entry into the pores. 

Munkholm, L.J., Schjonning, P. and Kay, B.D. 2002. Tensile strength of soil cores in relation to aggregate strength, soil fragmentation and pore characteristics. Soil and Tillage Research 64 125-135. 

NaA102, Al, (S04)3, Al (N03)3, A1C13 as Al source have been studied, respectively. When pH=10, microwave oven pressure =0.2Mpa, CTAC as a surfactant and Na2Si03 as Si source, the pore characteristic of the synthesis samples listed in table 4. The data in table 4 indicates... 

NaA102 as Al source, the synthesis condition is the same as 2.1, the pore characteristic of the synthesis samples show in table 5. From table 5 we can see that different Si sources also influence on pore characteristic of the synthesis samples drastically. Comparing these 4 kinds of Si sources, TEOS is the optimal Si source. 

Influence of different Al sources on pore characteristic of the synthesis samples ... 

Table 2 shows that SC-155(G40.60) and C-l55(G20.20), which have comparable values of specific surface area, have very different CO conversion values. Both materials were produced under different gelling and drying conditions, and as a consequence the C-155 precursor (SC-I55/G20.20) was different in pore size distribution than the SC-I55(G40.60), but that difference has not sense when silica was eliminated for to produce C-155, having the last one other new characteristics then the observed differences in CO conversion are mainly attributed or to the higher value of specific pore volume of C-155, or because some of the metallic iron were on silica surface of the SC-155 diminishing its catalytic activity, but not attributed to the different gelling and drying conditions. CON material, in spite of its low specific surface area and its low specific pore volume is a fully carbon material like C-155 is, then its lower performance in CO conversion is attributed to the specific surface and pore characteristics. 

Leis, J., Arulepp, M., and Perkson, A. Method to modify the pore characteristics of porous carbon and porous carbon materials produced by this method. European Patent WO/2004/094307, 2004. 

The pore volume and specific surface area of carbosils decrease with Cc values independent of pyrocarbon origin (Table 2, Figure 2).16 However, the precursor type as well as the initial pore structure of silica gels, e.g. Si-40 (Table 1) and Si-60 (Table 2), affect the pore characteristics of carbosils (Figures 1 and 2). The narrower the pores of the pristine silica gel, the larger the specific surface area reduction under the same pyrolysis conditions. 

The performance of a catalyst in industrial usage is likely to be determined by its pore structure, that is to say, by its total pore volume and its pore size distribution. In cases where the active phase is mounted on a porous support, its pore characteristics may affect the accessibility of the active phase to the reactants, as well as other features of the catalyst s performance. For these and other reasons it is important to have agreed and reliable procedures for the measurement of these and related quantities progress in this direction is surveyed in Section 11.1.4.7. 

An industrially spent hydrotreating catalyst from naphtha service was extracted with tetrahydrofuran, carbon dioxide, pyridine and sulfur dioxide under subcritical and supercritical conditions. After extraction, the catalyst activity, coke content, and pore characteristics were measured. Tetrahydrofuran was not effective in the removal of coke from catalyst, but the other three solvents could remove from 18% to 54% of the coke from catalyst. 

In this project, the feasibility of catalyst regeneration by supercritical fluid extraction was studied. A spent catalyst from an industrial naphtha hydrotreater was extracted with tetrahydrofuran, pyridine, carbon dioxide, and sulfur dioxide under subcritical and supercritical conditions. The coke reduction and changes in the catalyst pore characteristics were measured and to a limited extent the catalyst activity was evaluated. It is shown that by supercritical extraction, the coke content of spent hydrotreating catalysts can be reduced and the catalyst pore volume and surface area can be increased. 

The catalyst was removed and analyzed for its coke content, pore size distribution, pore volume, and surface area. All the catalyst samples were analyzed after a Soxhlet extraction with tetrahydrofuran for 24 h and drying in oven at 100 C. The catalyst weight loss due to combustion at 550 C was considered as the coke on catalyst. The catalyst pore characteristics were measured by a Quantachrome Autoscan Porosimeter. 

Suzuki, R., Ohdaira, T., Shioya, Y. and Ishimaru, T. (2001) Pore characteristics of low-dielectric-constant films grown by plasma-enhanced chemical vapor deposition studied by positron annihilation lifetime spectroscopy , Jpn. J. Appl. Phys. 40, L414. 

The synthesis of phenolic-formaldehyde and melamine-formaldehyde resins in the presence of fumed silica allows obtaining porous organic materials with a differentiated porous structure and surface properties. The pore characteristics of the studied resins in dry state were determined from nitrogen adsorption isotherms. The differences in surface character of the synthesized polymers were estimated satisfactorily by XPS spectra showing the presence of various functional groups. The adsorption/desorption mechanism of water and benzene on the investigated porous polymers was different due to differentiated hydrophobicity of the bulk material. 

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