Adsorbents particle size distribution

Moharir, A.S. Kunzru, D., and Saraf, D.N., Effect of adsorbent particle size distribution on breakthrough curves for molecular sieve columns, Chem. Eng. Sci., 35(8), 1795-1802 (1980). 

For large amounts of fillers, the maximum theoretical loading with known filler particle size distributions can be estimated. This method (8) assumes efficient packing, ie, the voids between particles are occupied by smaller particles and the voids between the smaller particles are occupied by stiH smaller particles. Thus a very wide filler psd results in a minimum void volume or maximum packing. To get from maximum packing to maximum loading, it is only necessary to express the maximum loading in terms of the minimum amount of binder that fills the interstitial voids and becomes adsorbed on the surface of the filler. 

Quality of the adsorbent layer. Layers for HPTLC are prepared using specially purified silica gel with average particle diameter of 5-15 /mi and a narrow particle size distribution. The silica gel may be modified if necessary, e.g. chemically bonded layers are available commercially as reverse-phase plates. Layers prepared using these improved adsorbents give up to about 5000 theoretical plates and so provide a much improved performance over conventional TLC this enables more difficult separations to be effected using HPTLC, and also enables separations to be achieved in much shorter times. 

A dispersion of the sample is placed on top of a liq of greater density. The rate of sedimentation is detd by measuring the sediment vol at fixed time intervals. The results are converted to a size distribution by Stoke s Law Nitrogen Adsorption. The amt of N adsorbed on a sample is detd by carefully measuring the press change of a known vol of N exposed to a known wt of dry mat at constant temp. The info is used to detn the surface area which is converted to a particle size distribution Turbidometric Methods. The absorption of a beam of light passing thru a suspended sample in a suitable liq is measured as a function of time. 

If the secondary stream contains emulsifier it can function in three ways. When the emulsion feed is started quickly the added emulsifier can serve to lengthen the particle formation period and hence to broaden the particle size distribution. When the emulsion feed is started later and added in such a manner that the emulsifier is promptly adsorbed on existing particles, one can obtain quite narrow size distributions. If the emulsion feed is started later but added rapidly enough to generate free emulsifier in the reaction mixture a second population of particles can be formed, again yielding a broad size distribution. 

The Pd-Sn/C catalysts (1 to 7.5% Pd containing 0 to 1% Sn) were heated under vacuum at 150°C and then exposed to hydrogen. These preactivated samples were then titrated with carbon monoxide, a veiy specific ligand for Pd, up to 800 Torr at 30°C. A general linear trend of carbon monoxide concentration with % Pd in Figure 15.3 indicates that the carbon monoxide adsorption is directly correlated to Pd concentration, as expected. The trend is independent of Sn content. This linear Pd-CO trend indicates that the particle size distribution is similar for the different catalysts. However, Figure 15.3 also indicates no relationship between % H2S irreversibly adsorbed and % Pd. 

In these cases, the values of w are used as a probing measure, and vsR2 for the spherical molecules radius of R. As a result, nm -R D2. The second method by Pfeifer and Anvir is symmetric to the first one in the sense that instead of adsorbing a set of molecules on samples with a constant particle size distribution, one adsorbs a single adsorbate (e g., N2) on a set of samples with variable particles sizes, Ra. The corresponding equations for this method are... 

These routes involve the formation of (usually) prereduced metal particles that are then adsorbed or deposited onto the support. They have the advantage that the particle size of the particles is predetermined by the chemistry of the colloids and that resulting catalysts have narrow particle size distributions. However, the colloidal particles often are surface stabilized by surfactant molecules, which can be difficult to remove once the particles are adsorbed onto the support. One further disadvantage is that the colloidal particles are prepared at high dilution (typically millimolar concentrations— for example, 0.2 g Ft 1 ), which is a disadvantage in terms of scale-up. 

EM techniques provide important information in the characterization of the dispersion of metallic catalysts. Surface areas of catalysts are measured by the standard BET method described previously. An isotherm is produced using nitrogen as the adsorbate chemisorption of certain gases (e.g. H2 or CO) is also used, including for particle size distributions. We give some examples in chapter 5. 

Decontamination of soils using supercritical fluids is an attractive process compared to extraction with liquid solvents because no toxic residue is left in the remediated soil and, in contrast to thermal desorption, the soils are not burned. In particular, typical industrial wastes such as PAHs, PCBs, and fuels can be removed easily [7 to 21]. The main applications are in preparation for analytical purposes, where supercritical fluid extraction acts as a concentration step which is much faster and cheaper than solvent-extraction. The main parameters for successful extraction are the water content of the soil, the type of soil, and the contaminating substances, the available particle-size distribution, and the content of plant material, which can act as adsorbent material and therefore prolong the extraction time. For industrial regeneration, further the amount of soil to be treated has to taken into account, because there exists, so far, no possibility of continuous input and output of solid material for high pressure extraction plants, so that the process has to be run discontinuously. 

Sodium / -naphthalenesulfonate was chosen as the surface-active electrolyte because its structure is simple and rigid. It does not form micelles, so there is no question as to the species adsorbed on the surface. It is a strong electrolyte and is expected to be essentially completely ionized at saturation coverage. SNS stabilized dispersions flocculate over periods of minutes to months depending on the concentration of SNS. Sterling FTG has a non-polar, non-ionic, hydrophobic surface. The ultimate particles have large, flat, polyhedral surfaces. The particle size distribution of the dry carbon is narrower than that of most colloidal carbons (2). 

Concerning aggregation kinetics and stabilization it was found in case of barium sulfate that barium ions adsorb more readily than sulfate ions [11], Thus, increasing the ratio R of barium to sulfate ions in the educt composition and thereby increasing the excess of barium ions after precipitation leads to high surface potentials and stabilization. Fig. 5 shows measured particle size distributions of continuously precipitated barium sulfate, measured based on quasi-elastic fight scattering (UPA 150 by Microtrac) within 3 min after pie-... 

The presence of high levels of suspended solids in stream surface water during storm episodes resulted in higher concentrations of adsorbed aluminum than in the absence of suspended solids (Goenaga and Williams 1988). The increased adsorption was not strictly linear, with higher concentrations of suspended solids due to variations in the particle size distribution and the nature of the particles. 

Figure 8. Particle size distributions with respect to particle volume in the aqueous suspension of A-300, (a) PEG/A-300, BSA(II)/PEG(I)/A-300 and (h) PVA/A-300, BSA(II)/PVA(I)/A-300 I and II is the first and second adsorbates respectively.

An important feature of the expanded bed compared with a conventional fluidized bed is its low backmixing, achieved by the proper design of the adsorbent and the column. The particle size distribution of the adsorbent gives a segregated or stratified bed in expanded-bed mode. This means that the larger adsorbent particles are found in the lower part of the bed and the smaller adsorbent particles are in the upper part. 

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