Particle size quality aspects

Tailoring of the particle size of the crystals from industrial crystallizers is of significant importance for both product quality and downstream processing performance. The scientific design and operation of industrial crystallizers depends on a combination of thermodynamics - which determines whether crystals will form, particle formation kinetics - which determines how fast particle size distributions develop, and residence time distribution, which determines the capacity of the equipment used. Each of these aspects has been presented in Chapters 2, 3, 5 and 6. This chapter will show how they can be combined for application to the design and performance prediction of both batch and continuous crystallization. 

Each of the PLgel individual pore sizes is produced hy suspension polymerization, which yields a fairly diverse range of particle sizes. For optimum performance in a chromatographic column the particle size distribution of the beads should be narrow this is achieved by air classification after the cross-linked beads have been washed and dried thoroughly. Similarly, for consistent column performance, the particle size distribution is critical and is another quality control aspect where both the median particle size and the width of the distribution are specified. The efficiency of the packed column is extremely sensitive to the median particle size, as predicted by the van Deemter equation (4), whereas the width of the particle size distribution can affect column operating pressure and packed bed stability. 

Process validation should be extended to those steps determined to be critical to the quality and purity of the enantiopure drug. Establishing impurity profiles is an important aspect of process validation. One should consider chemical purity, enantiomeric excess by quantitative assays for impurity profiles, physical characteristics such as particle size, polymorphic forms, moisture and solvent content, and homogeneity. In principle, the SMB process validation should provide conclusive evidence that the levels of contaminants (chemical impurities, enantioenrichment of unwanted enantiomer) is reduced as processing proceeds during the purification process. 

Multiple phases. Natural or artificial (manufactured) solids can be composed in several phases. The quality of the dispersion of these phases one in the other will allow the analyst to benefit from similar test samples within the entire batch of material. Material sciences teach us that the degree of homogeneity of the mixture will depend on the nature of the mixed phases and, in particular, the size of the solid particles, the particle size distribution and the respective density. The more similar the density and the particle size, the better is the achieved homogeneity. To achieve similar test samples, even for very small particle sizes, requires a narrow particle size distribution. Muntau et al. [29-30], Griepink et al. [31] and Pauwels et al. [32] have studied the relation between particle size and minimum sample intake. They have demonstrated that a major factor for homogeneity of small sample intakes is the low particle size of the solid material and their size distribution. This aspect will be discussed in more details in the section on homogeneity testing. 

Besides the LHV a lot of additional quality aspects are relevant concerning biomass provision, storage, transportation and efficient conversion processes. Density and heat capacity, for example, are important parameters for unconditioned and for conditioned biomass. Particle density and particle-size distribution are of importance for chips and pellets, viscosity for liquid biomass. 

Control of the average particle size, the particle size distribution, the purity and the aspect ratio of the filler is necessary to achieve consistent product quality in talc filled PP. In some grades of talc filled PP, water absorption may be an important factor. This will affect the surface appearance of the moulded product and the adhesion of the resin to the filler. 

Part A gives general guidelines for the design of large commercial fluidized bed reactors with respect to the following aspects (1) solids properties and their effect on the quality of fluidization (2) bubble size control through small solid particle size or baffles (3) particle recovery by means of cyclones (4) heat transfer tubes (5) solids circulation systems (6) instrumentation, corrosion and erosion, mathematical models, pilot plants and scale-up techniques. 

The performance of concrete depends on the quality of the ingredients, their proportions, placement, and exposure conditions. For example, the quality of the raw materials used for the manufacture of clinker, the calcining conditions, the fineness and particle size of the cement, the relative proportions of the cement phases, and the amount of mixing water influence the physico-chemical behavior of the hardened cement paste in concrete. In addition, the cementtype, nature of fine and coarse aggregates, water, temperature of mixing, admixture, and the environment will determine the physical, chemical, and durability aspects of concrete. Thermal analysis techniques are widely applied to investigate the physico-chemical behaviors of cement compounds, cement, and concrete subjected to various conditions. 

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