Suspension Process Concepts

In the group of suspension processes, there are the jacket cooled and the directly (e.g., by inert gases) cooled processes. The Amoco process, on the one hand, and the Maruzen or Chevron process, on the other hand, are, according to Ransley (1984), representatives for such processes. Other developments are scrapes crystallizers according to the Humble-Oil, the Krupp-Harpen (see Ritzer 1973), or the Hoechst AG (DE-PS 1969) process which are used for the production of p-nitrochlorobenzene. These scraped surface crystallizers are in fact solid layer processes, but in the handling of the products—crystals in suspension—they have to be treated like suspension processes. A number of processes that feature a combination of a scraped crystallizer and suspension techniques will be discussed. 

The pumping helps to wash away the highly contaminated liquid sticking to the crystals. The contaminated reflux melt, which worked 

The TNO crystal purifier (Arkenbout et al. 1976) is a column with a number of sieve trays fixed to a central shaft that oscillates vertically. The trays have bouncing balls caused by the oscillation. The balls break up some of the crystals through collisions. Small crystals melt quickly because they have greater solubility than larger ones, thereby enriching the melt with pure product. The large crystals in the slurry feed, which are introduced in the middle of the column, move down and become remolten. Some of the remolten liquid is removed as product, some is used as reflux. The small crystals move up with the reflux and will be molten. The highly contaminated reflux is removed from the column at the top. A pilot plant column with 19 trays has been built and is expected to have a capacity of 300 tons per year. 

According to Arkenbout (1978), the first compound to be purified was naphthalene. This was achieved after successful results with laboratory scale in the purification of p-xylene from an eutectic system and benzene-based system as a solid solution system. There is no published data on industrial experience for this process. 

A third process, the Kureha Double Screw Purifier (Yamada et al. 1982), also called the KCP column, works with a crystal slurry introduced at the bottom of a column. The crystal is transported to the top by a double screw conveyer. There is a melter at the top of the column. The molten crystals are the product and some part is used as reflux. The reflux washes the crystals while moving in a counter current direction. Some residue is taken out at the bottom. 

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These qualitative differences in suspension properties based on the attractive or repulsive nature of the interparticle forces have been utilized in the optimization of colloidal processing concepts and have led to the development of the direct casting techniques which will be described in more detail below. 

Suspension crystallization is capable of producing very pure crystals mostly in a continuous operating mode, which is an advantage compared to the most batch solid layer crystallization processes. Another positive feature compared to solid layer crystallization is the better purification per process step and hence a less number of process steps usually with respect to crystallization. Therefore, suspension crystallization plants need in principle less energy compared to solid layer processes. Whether the investment costs of such plants are smaller as well depends on the complexity of the moving parts in suspension plant concepts compared to solid layer concepts (no moving parts, except pumps). 

There are numerous examples of purified materials by the above-mentioned two types of suspension crystallization process designs some of them are acetic acid, caprolactam, methacrylic acid, and phenol. The two discussed suspension crystallization concepts, shown in the Figures 17.9 and 17.10, count to the continuous packed column with mechanical forced transport. 

This chapter deals with the microbial transformations of wastewater under aerobic conditions in a sewer network. It emphasizes the transformations of the organic matter and includes processes in both the water phase and the biofilm. Furthermore, transformations of particles in suspension originating from sewer sediments are included. A concept and a corresponding model for the integration of the major microbial processes, i.e., growth of the heterotrophic biomass, the respiration and the hydrolysis, are also dealt with. The basic chemical and biological aspects of sewer processes are focused on in Chapters 2 and 3. The reaeration process is dealt with in Chapter 4. 

The general concept of the synthesis of sandwich materials is illustrated in Figure 1.15. In our first report on this [22], we first inserted a neutral dyel from the gas phase, filling the channels to the desired degree. It was possible to find conditions to insert a cationic dye2 from an aqueous suspension, despite the fact that neutral dyes are usually displaced by water molecules. This process can be well controlled so that a specific desired space is left for the third dye3 to be inserted. It is also possible to insert first a cationic dye and then a neutral one or to use other combinations. The principle can be extended to more than three different dyes. 

A pigment-binder dispersion is a suspension before it is dried after drying it is a solid sol. In pigment-binder systems, the concepts and laws of colloid chemistry therefore apply. The dispersing of pigments and extenders in binders is an extremely complex process of a series of steps that can be interlinked [1.63]. Dispersing involves the following steps ... 

The model based on the concept of pure limiting film resistance involves the steady-state concept of the heat transfer process and omits the essential unsteady nature of the heat transfer phenomena observed in many gas-solid suspension systems. To take into account the unsteady heat transfer behavior and particle convection in fluidized beds, a surface renewal model can be used. The model accounts for the film resistance adjacent to the heat transfer... 

This book provides an introduction to the colloid and interface science of three of the most common types of colloidal dispersion emulsions, foams, and suspensions. The initial emphasis covers basic concepts important to the understanding of most kinds of colloidal dispersions, not just emulsions, foams, and suspensions, and is aimed at providing the necessary framework for understanding the applications. The treatment is integrated for each major physical property class the principles of colloid and interface science common to each dispersion type are presented first, followed as needed by separate treatments of features unique to emulsions, foams, or suspensions. The second half of the book provides examples of the applications of colloid science, again in the context of emulsions, foams, and suspensions, and includes attention to practical processes and problems in various industrial settings. 

Light-scattering experiments on flocculating suspensions of silica colloids provided the data in the following table. (R is the average cluster radius.) Estimate the fractal dimension of the clusters formed and indicate whether the flocculation process is transport or reaction controlled. Hint Apply Eq. 6.1 and the concepts in Section 6.1.)... 

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