Particles pellets

Wash the activated particles 3 times with anhydrous THF to remove excess CDI and reaction by-products. After the final wash, remove the solvent and perform a quick wash with ice-cold water to remove most traces of solvent in the particle pellet. Finally, resuspend the particles at 10 mg/ml in cold 0.1 M sodium phosphate, pH 8.2, or 0.1 M sodium carbonate, pH 9.5 (coupling buffer). The higher pH coupling buffer will result in greater reactivity of the imidazole carbamate and greater coupling yields for proteins. 

Wash the activated particles 3 times with anhydrous solvent to remove excess DSC and reaction by-products. After the final wash, remove the solvent and perform a quick wash with ice-cold water to remove most traces of solvent in the particle pellet. 

Microencapsulation - The deposition of a coating material onto a particle, pellet, granule, or bead core. The substrate in this application ranges in size from submicron to several millimeters, tt is this size range that differentiates it from the standard coating described in 1 and 2 above. 

These information from the pore structure data show that a simple two-stage zone reaction model can be successfully used to describe the mechanism of the calcination of this particular limestone and it is not necessary to consider much more complex models such as three-zone and particle-pellet models. 

Figure 13.7. Comparison between (a) rate-zonal and (b) isopycnic centrifugation. Note that the gradient used in rate-zonal techniques is shallow, and if the centrifugation continues, the particles pellet. The diffusion process causes band broadening in rate-zonal centrifugation, but this is not evident when the particles are focused using isopycnic centrifugation.

The maximum density of the gradient usually does not exceed the density of the particles. Because of this, if the centrifugation continues indefinitely, the particles pellet at the tube bottom. The gradient is chosen to have the minimal density and viscosity possible to allow rapid separation and minimize diffusional band broadening. 

Example 2.12 In order to reduce the CO content in the waste gas from a furnace, the exhaust gas is passed over the porous CuO particles (pellets) of a catalytic reactor in the exhaust pipe. The CO (substance A) is oxidised with O2 to CO2 inside and at the surface of the pellets, according to the reaction... 

Particle Pellet Micro Macro Total Macro Micro... 

FIGURE 11.11 The particle-pellet model for gas-sold noncatalytic reactions. 

Some basic macroscopic models were described in the previons sections, including the slightly more rigorous particle-pellet model. These models ignored several complexities, mainly the effects of bnUc flow, nonisothermicity, and variations in structure due to reaction. The first two can be inclnded in the basic models and become extensions of them. The effects of structural changes can, however, be better defined in newer models that incorporate them at a more basic level. 

One way to account for structural changes is to allow for changes in the grain size in the particle-pellet model (Garza-Garza and Dudukovic, 1982a, b). A more useful way is to incorporate... 

Derivation of the model equation is reported by Evans and Song (1974). The following equations are written material and energy balances for the gas phase and the rate equations for the pellet assuming any one of the models described in Section 11.3.4. As mentioned earlier, we use the particle-pellet model. Appropriate initial and boundary conditions are also written. Assuming isothermal behavior, the material balance equation is... 

The particle-pellet equation is written in terms of a generalized effectiveness factors defined as... 

Heesink and van Swaaij (1995) proposed a particle-pellet model for reaction between calcined limestone and H2S at temperatures ranging from 500 to 700°C using a pellet of conventional... 

An important feature of packed DCRs is the need to pack the catalyst in a special way to ensure good flow, mass transfer, and contact characteristics. An example of this is the use of an ion-exchange resin catalyst (Amberlyst 15) in methyl tertiary butyl ether (MTBE) manufacture. The bed consists of bags made in the form of a cloth belt with narrow pockets sewn across it (Figure 25.7). The pockets are filled with catalyst granules, and the belt is twisted into a helical form, referred to as a bale (see Smith, 1980, for details). Clearly, each pocket represents a closely packed bed of unconsolidated particles, and the pocket and the individual particles exhibit, respectively, their own distinctive macro- and microdiflfusional features. This is broadly similar to the particle-pellet model of a catalyst pellet (see Chapter 7) but with distinctly different pellet behavior. Therefore, it is necessary to define an overall effectiveness factor which takes this unique feature into account. An attempt to do this was recently reported (Xu... 

PANl nanoparticles were doped with DBSA and electrospun with nylon-6 by Hong et al. Conductivities of different forms were compared. The electrical conductivity of PANl (DBSA) particle pellets was about 4.27 x 10 S/cm, the conductivity of the PANl (DBSA)-nylon-6 film was about 1.68 x 10 S/cm, and the conductivity of the PANl (DBSA)-nylon 6 electrospun fiber web was about 6.19 x 10" S/ cm. It was concluded that when the PANl (DBSA-nylon 6) composite solution was electrospun by electric power, the overall crystallinity of the composite polymer decreased so the conductivity decreased. This was explained with the rapid evaporation of the solvent during the electrospinning process. 

Figure 18.1 shows a particle (pellet) with a pore through which the reactant A diffuses, reaches the active site, and reacts to form the product R, which follows the reverse path until it reaches the external film. Therefore, the observed rate should take into account the reaction and intraparticle diffusion, i.e. ... 

E21.1 Hydrogenation of particular oil is performed in a liquid phase catalytic reactor (plug flow reactor (PFR)) containing catalytic particles (pellets—spherical diameters) of 1 cm. The external concentration is 1 kmol/L and on the particle surface is 0.1 kmol/L at a superficial velocity of 0.1 m/s. Verify if there are mass effects. There will be a change if the particle diameter is equal to 0.5 cm Neglect the effects in diffusive pores (Fogler, 2000). Additional data ... 

When k is known (normally provided by manufacturer), the minimum run time required for particle pelleting may be calculated from the relation... 

Miscellaneous effects A number of factors can influence the effectiveness factor, some of which are particle size distribution in a mixture of particles/pellets, change in volume upon reaction, pore shape and constriction (such as ink-bottle-type pores), radial and length dispersion of pores, micro-macro pore structure, flow regime (such as bulk or Knudsen), surface diffusion, nonuniform environment around a pellet, dilution of catalyst bed or pellet, distribution of catalyst... 

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