Precipitate sizing

Another example of vims clearance is for IgM human antibodies derived from human B lymphocyte cell lines where the steps are precipitation, size exclusion using nucleases, and anion-exchange chromatography (24). A second sequence consists of cation-exchange, hydroxylapatite, and immunoaffinity chromatographies. Each three-step sequence utilizes steps based on different properties. The first sequence employs solubiUty, size, and anion selectivity the second sequence is based on cation selectivity, adsorption, and selective recognition based on an anti-u chain IgG (24). 

This equation shows that for a given collection efficiency, the precipitator size is inversely proportional to particle drift velocity and directly proportional to gas flow rate. Increasing the gas density (migration velocity is a function of gas viscosity) by reducing its temperature or increasing the pressure will reduce the precipitator size. However, theory does not account for gas velocity. This is a variable that influences particle re-entrainment and the drift velocity. This typically requires an ESP design at lower velocities than predicted in theory. 

In the plant used for academic purposes [4], both the solvent and exhausted CO2 are wasted. In an industrial plant both streams should be recycled after purification, for obvious economic reasons. The precipitator size and plant-flow-rates are obtained by increasing 80-fold the relative quantities used in the pilot plant [4]. This scale factor was suggested by the company that supplied the drug. Two vessels, P, in parallel are needed while the former is running, the latter can be cleaned and the solid product can be recovered. Cleaning and product-recovery expenses are not directly evaluated in this example. In the pilot plant, the flow of THF-polymer-drug solution was 0.072 kg/h, and the CO2 flowed in the quantity of 1.08 kg/h (the ratio CO2 to solution equals 15). The precipitator was a 0.4-liter vessel. The actual precipitator scale-up is not considered here. The main factor to consider in scaling-up the precipitator is the nozzle scale-up. The nozzle-size, nozzle-shape, and number of nozzles per reactor volume, determine the precipitate size in a complex and still incompletely understood way [5-8], It is assumed that issues related to the injectors are already solved. 

Once the particle grows to a size that exceeds R, morphological instabilities will set in. The minimum size for instabilities is found from the n = 2 spherical harmonic, giving R (n = 2) = 7Rc.5 Thus the theory predicts instabilities at very small precipitate sizes. 

The conclusions drawn from the different experiments with respect to the effect of RESS process parameters on precipitate size and morphology reflect the importance of specific solute/solvent properties on the process path. This probably results in the apparent contradictions found in experimental results. To date, the theoretical work aimed at gaining a fundamental understanding of the RESS expansion phenomenon and physical processes relevant to droplet, particle or film formation has been quite limited (Debenedetti, 1990 Debenedetti et al., 1993 Kwauk and Debenedetti, 1993 Lele and Shine, 1994). 

Figure 14 Potential distribution at the surface of the A1 matrix near a theta phase precipitate assuming a nonpolarizable cathode site (Al2Cu precipitate), polarizable passive A1 matrix, and a dilute acidic solution. The effect of precipitate size is shown. (From Ref. 26.)...

The morphology of nuclei can be characterized in terms of deposit size and density. Figure 6.14 shows copper precipitate size distribution ofn- and/ -Si materials in 0.5% HF solution." ° The density is higher on n- than on p-type silicon whereas the size is larger on p-Si than on n-Si indicating that the rate of nucleation is higher on... 

FIGURE 6.14. Precipitate size distribution of the wafers immersed for 5min, in 1 100HF containing 400ppb (light on). After Norga et a/. (Reproduced by permission of The Electrochemical Society,... 

This list does not cover all possible applications but relates to many common industrial processes. As each application produces different waste gas flows, temperatures, particulate inlet loading, etc., the precipitator size and its design tend to be site specific for a given duty. 

Petersen, H.H. A precipitator sizing formula. Proceedings of the Fourth ICESP Conference, Beijing. China, September 1990 Int. Academic Pub. Beijing, 1993 330-338. 

Earlier work (9) has shown that the size of the precipitate, but not the protein recovery, depends on the method of addition of the polymer to the protein solution. Mixing conditions in the precipitation vessel also affect the precipitate size (lOh The solubility of the protein-polyelectrolyte complex depends strongly on the solution conditions—pH, ionic strength, polymer dosage level, and the nature of the protein and polyelectrolyte. These factors are discussed below ... 

Fig. 10.15. Series of equilibrium shapes as observed in y Cu-Zn (solid hues) and estimated values of the interfacial energy vs orientation (dashed lines) (adapted from Stephens and Purdy (1975)). The precipitate sizes are roughly 60 (im for all but the 500 °C case, in which the precipitates have a size on the order of 500 (im.

For a cloud to generate precipitation, some drops need to grow to precipitable size around 1mm. Growth of droplets can proceed via a series of mechanisms (1) water vapor condensation, (2) droplet coalescence, and (3) ice processes. 

Table A3.3 lists the characteristics of the different hematite sizes and compares selected characteristics. Specific surface area decreases with particle size and the ferric chloride floes have a much higher surface area, most likely due to a smaller precipitate size or amorphous nature. Zeta potential decreases with particle size (see Chapter 4 for method description and charge characterisation as a function of solution chemistry).

The method of microwave plasma-assisted deposition allows to form nickel/hydrogenated amorphous carbon (Ni/a-C H) nanocomposite films. As the C2H2 concentration in Ar-C2H2 gas mixtures increased from 0 to 100 % the phase composition and precipitates size of Ni/a-C H films varies in the consequence Ni (15 nm)—>Ni + Ni3C (5-17 nm) Ni3C (17 nm)—> Ni + a-C H (1 nm) nc-G H (4 nm). The lowest friction coefficient and wear rate were obtained for Ni/a-C H amorphous nanocomposite films containing 20 % of sp3 bonds and deposited from the gas mixture with a C2H2 concentration of 60 %. 

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