Optimization of particle size

As mentioned above, among many possible process variables, industrial crystallization frequently focuses on the optimization of particle size. In many cases this may be fixed by market demands, in others it may be a variable e.g. during the processing of intermediates. 

The activity in terms of 1st order rate constant khcalc was calculated in Table 2 from (8) and (9) with effective diffusivity Dejf=5.3-10 6 m2/s and intrinsic rate constant =33000 Nm3/h/m3 = 23 s"1 fitted to the measurements. This simple and useful method models the measured influence of particle size satisfactorily for a first optimization of particle size and shape. The 35% higher activity measured for the 9-mm Daisy compared to the 12-mm Daisy, however, exceeds the 25% expected from (8), and this illustrates the importance of measuring the activity of the actual shape. 

For a more detailed analysis of measured transport restrictions and reaction kinetics, a more complex reactor simulation tool developed at Haldor Topsoe was used. The model used for sulphuric acid catalyst assumes plug flow and integrates differential mass and heat balances through the reactor length [16], The bulk effectiveness factor for the catalyst pellets is determined by solution of differential equations for catalytic reaction coupled with mass and heat transport through the porous catalyst pellet and with a film model for external transport restrictions. The model was used both for optimization of particle size and development of intrinsic rate expressions. Even more complex models including radial profiles or dynamic terms may also be used when appropriate. 

Worlitschek, J. Mazzotti, M., Model-based optimization of particle size distribution in batchcooling crystallization of paracetamol Cryst. Growth Des. 2004 ASAP Web Release Date 17.2.2004 http //dx.doi.org DOI 10.1021/cg034179b. 

M. N. Trainer. Optimization of particle size measurement from 40 nanometers to millimeters using high-angle light scattering. In T. Provder, ed., Particle Size Distribution III Assessment and Characterization, ACS Symp. Ser. 693, 1998, pp. 130-147. 

Ellis, I.O., Bell, J., and Bancroft, J.D. (1988) An investigation of optimal gold particle size for immuno-histological immunogold and immunogold-silver staining to be viewed by polarized incident light (EPI polarization) microscopy./. Histochem. Cytochem. 36, 121-124. 

High crystallization rates and the possibility to stabilize X-ray amorphous phases, which exhibit ZSM-5 like properties, were among the reasons why we decided to investigate the procedure B in more detail. In order to optimize the particle size, homogeneity, morphology and composition, we have questioned more systematically the influence of secondary synthesis variables such as the pH, solvent viscosity or the nature of the alkali cation, added as chloride. 

Reduction of PdO particles to metallic Pd° does not significantly modify the size of theparticle to the extent shown by the BIOS YM calculation (Fig. 13.26). This important result means that the optimization of the size of the PdO particle, carried out during the preparation of the suspension, should remain even after activation, i.e. reduction under hydrogen, necessary for catalytic purposes to produce metallic active sites. 

Since the Sorbex process is a liquid-phase fixed-bed process, the selection of particle size is an important consideration for pressure drop and process hydraulics. The exact particle size is optimized for each particular Molex process to balance the liquid phase diffusion rates and adsorbent bed frictional pressure drop. The Sorbex process consists of a finite number of interconnected adsorbent beds. These beds are allocated between the following four Sorbex zones zone 1 is identified as the adsorption zone, zone 2 is identified as the purification zone, zone 3 is identified as the desorption and zone 4 is identified as the buffer zone. The total number of beds and their allocation between the different Sorbex zones is dependent on the desired performance of the particular Molex process. Molex process performance is defined by two parameters extract normal paraffin purity and degree of normal paraffin recovery from the corresponding feedstock. Details about the zone and the bed allocations for each Molex process are covered in subsequent discussions about each process. 

The paper addresses the problem of optimising design of a grinding mill-classifier system in order to satisfy the product requirements expressed as a combination of the mean and variance of particle size. A discrete model is used for describing the material transport in the mill, and the optimal conditions are chosen by numerical experiments and nonlinear optimisation. 

In the case where stability issues prevent the pursuit of the preferred formulation, then it becomes more important to optimize the dry granulation process to achieve an improved uniformity of drug as a function of particle size. For these cases, it is important to consider the impact of the optimized granulation on tableting performance. Although it is important to consider the commercial manufacturing efficiency, the process challenges that impact quality are of primary importance. 

They found that optimal conditions of the position of the stirrer exist in the range of 0.25 < HJd < 0.75 for both turbine and propeller stirrers. Their work suggests that beyond a Reynolds number of 20,000, the power number becomes constant. An increase in solid content increases the power consumption, while an increase in gas velocity reduces the power consumption. Kurten and Zehner (1979) examined the effect of gas velocity on the power consumption for suspension of solids and found that because of simultaneous aeration, a higher power input is required for suspension in the presence of gas. This is mainly due to the reduced liquid circulation velocity in the presence of gas bubbles. Most recently, Albal et al. (1983) evaluated the effect of liquid properties on power consumption for both two- and three-phase systems. They found that power consumption per unit volume increases with solid concentration. The influence of particle size on power consumption increases with the solids concentration. For an unconventional arrangement of a stirrer, they also found different Ne-Re curves for glycerine and CMC solutions. 

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