Non porous particles

Kohne, A.P., Welsch, T. (1999). Coupling of a microbore column with a column packed with non-porous particles for fast comprehensive two-dimensional high-performance liquid chromatography. J. Chromatogr. A 845, 463-469. 

In an early attempt to remove mists from a gas stream, by using a fluidized bed as a kind of filfer (Meissner and Mickley, 1949), if was found that the operation worked well if the bed particles had a porous structure, and that when non-porous particles were used fluidization ceased (i.e. the bed quenched) at very low moisture contents. This view is supported in work on the effect of bed moisture on the fluidization characteristics of fine powders (D Amore et al., 1979) in which if was shown that porous materials can tolerate considerably more liquid than non-porous particles (such as glass ballotini, sand and limestone) before what these workers call bed compaction occurs. Smith and... 

Nienow (1983a) observed a delay in the start of particle growth when binder was added to a bed of porous particles and stable fluidization under conditions which produced quenching with non-porous particles. Nitrogen adsorption measurements showed that the pore surface area of alumina decreased as spraying proceeded, indicafing that an effective reduction in pore volume was taking place. 

When the fluidized bed consists of non-porous particles, solvent in the feed liquid is evaporated in a well-defined zone close to the spray nozzle and from fhe surface of the bed particles with which it inevitably comes into contact. No permanent gas jet or void exists in this region particle motion is not well ordered and no regular coating of parficles wifh feed solution takes place. The random and intense contact between particles and liquid results in agglomeration. Even if the mass and heat balances for the bed as a whole have been satisfied, both... 

Since is proportional to VF we may conclude that for competing simultaneous reactions strongly influenced by diffusion effects (where is large and tanh — 1) the selectivity depends on Vs (where S = kjk2), the square root of the ratio of the respective rate constants. The corollary is that, for such reactions, maximum selectivity is displayed by small sized particles and, in the limit, if the particle size is sufficiently small (small so that tanh - )the selectivity is the same as for a non-porous particle, i.e. S itself. 

If the bed is made of non porous particles and if axial dispersion in the bed is negligible, the mass balance for the oil in solvent phase is given by ... 

The elimination or estimation of the axial dispersion contribution presents a more difficult problem. Established correlations for the axial dispersion coefficient are notoriously unreliable for small particles at low Reynolds number(17,18) and it has recently been shown that dispersion in a column packed with porous particles may be much greater than for inert non-porous particles under similar hydrodynamic conditions(19>20). one method which has proved useful is to make measurements over a range of velocities and plot (cj2/2y ) (L/v) vs l/v2. It follows from eqn. 6 that in the low Reynolds number region where Dj. is essentially constant, such a plot should be linear with slope Dj, and intercept equal to the mass transfer resistance term. Representative data for several systems are shown plotted in this way in figure 2(21). CF4 and iC io molecules are too large to penetrate the 4A zeolite and the intercepts correspond only to the external film and macropore diffusion resistance which varies little with temperature. 

Hochleitner, E.O. et al. Analysis of isolectins on non-porous particles and monolithic polystyrene divinylbenzene-based stationary phases and electrospray ionization mass spectrometry. Int. J. Mass Spectmm. 2003, 223-224,519-526. 

The other overloading effect that is rarely observed in HPLC separations is on the columns with very low surface area, like columns packed with non-porous particles. In figure 3-29 the retention of 0.1% solution of benzene is shown. When only 1 pL is injected, the resulting peak shows only slight tailing however, when the injection volume is increased to 5 pL, a severe shoulder in... 

The above result is correct as far as slurries of non-porous particles are concerned. If particles of small size and high porosity are suspended a significant increase in k] a over that for the gas-liquid system can be observed (68,73,74). Kars et al. (74) and Alper et al ( ) studied physical absorption in the presence of suspended activated carbon and found increased k values. Alper et al. (68) explained their findings with the absorption capacity of charcoal which leads to in-... 

The drying of wet granular beds containing non-porous particles, which are insoluble in the wetting liquid, has been extensively studied. The operation is presented as the relation of moisture content and time of drying in Fig. 5A. It should be noted that the equilibrium moisture content is approached slowly. A protracted period may be required for the removal of water just above the equilibrium value. This is not justified if a small amount of water can be tolerated in further procession establishing realistic drying requirements. 

Assumptions on particles or pores shape for raw data acquisition non porous particles of any shape none no assumption on shape of particles, cylindrical pores Non porous spherical particles... 

Figure 3.1 shows a scheme of an HPLC plant. The column contains a packing that is a dense array of porous or non-porous particles. Alternatively, the column is composed of a continuous bed, i.e. a porous piece called a monolith. 

The size of the colloidal non-porous particles determines the specific surface area of an adsorbent (Eq. 3.12) and the porosity of particles is controlled by the average contact number of non-porous primary particles. 

Axial dispersion, D When a band migrates along a column packed with non-porous particles, it spreads axially because of the combination effects of axial diffusion and the inhomogeneity of the pattern of flow velocity in a packed bed. This combination of effects is accounted for by a single term, proportional to the axial dispersion coefficient. It is independent of the mass transfer resistance and of the other contributions of kinetic origin to band broadening. 

From this short analysis, it is evident that specific surface area comprises the total surface of particles including its pores and includes at least part of the free volume in aggregates. For non-porous particles it is useful for calculation of the average particle size. It is also used to calculate the average particle size of materials (such as for example carbon black) which are porous but for which particle size cannot be more precisely determined because of the effect of its structure. 

It is often necessary to treat a porous particle or an aggregate of non-porous particles as the medium in which the diffusion takes place instead of considering the pores themselves. Equations similar to the above can be developed for the porous medium using an effective diffusion coefficient. 

Studies to reduce the time of analysis while maintaining the quality of resolution. To achieve this, short columns are used with stationary phases formed either from non-porous particles of small diameter (3pm or less), or of porous networks of silica gel (monolithic column). This allows faster flow rates, then more rapid separations (Figure 3.24). This technique is most frequently used in chemical industries, and areas as food processing, environment, pharmacy and biochemistry. 

A spherical non-porous particle of radius R is considered, on the external surface of which a unimolecular first order irreversible chemical reaction is taking place catalyzed by the surface of the pellet. The solid particle has a finite thermal conductivity and is immersed in an infinite medium. 

In heterogeneous catalytic reactions, the problem is even more subtle what exactly is the reaction volume If the catalyst has a porous structure accessible to the reactants, is it the bulk volume of the porous catalyst particles Or perhaps the volume of the pores themselves What if the catalyst is non-porous and reaction takes place only on the external surfaces of the non-porous particles Should we then use the void volume or the catalyst volume as the reaction volume Or perhaps all catalytic reaction rates should be expressed per unit of time per unit of available surface area. 

Begin by considering a catalyst whose active surface is all on the exterior of non-porous particles. Reaction therefore takes place only on surfaces exposed in the interstices of the packing. What volume should we use for calculating the pertinent time for the measuring the rate of the reaction Neither the volume of the interstices nor that of the solid packing correctly represents the active volume in the reactor. It is the area of the active surface exposed to the reactants that is the best representation of this volume. We are forced to consider a very different measure of space time ... 

Comprehensive multidimensional liquid chromatography is a relatively new development and has yet to develop a diverse application base. For the time being applications are dominated by the separation of proteins and synthetic polymers. For proteins the first dimension separations are usually based on ion exchange and the second dimension separations on reversed-phase liquid chromatography. Gradient elution was often used for both separation modes with a separation time less than 2 minutes for the second dimension separation and from 30 minutes to several hours for the first dimension separation. Current trends include the use of non-porous particles and perfusive stationary phases for the second dimension separation to reduce the total separation time and wider internal diameter columns in place of packed capillary columns to simplify interface construction and instrument operation and to allow the loading of larger sample sizes. 

Non porous particles (NPS) Not only the theoretical plate numbers changes but also tbe selectivity, because the stationary phase is different. 

Non-porous particles. Problem expensive, high back pressure, low loadability, high requirements of the equipment... 

---