Liquid-solid conversion

Here F is the liquid-solid conversion factor F = with porosity and bulk... 

Thermoplastics consist of long chain molecules that are produced from small molecules (called mers) by a polymerization process. An example of the formation of a typical polymer is given in Fig. 9.2 where polyethylene is produced from the monomer ethylene by application of heat, pressure, and a catalyst. When the resulting polymer is cooled, it solidifies. When reheated, a thermoplastic such as this will become liquid again. Due to this reversible liquid-solid conversion, scrap thermoplastic material may be recycled. Other thermoplastics are polypropylene, polyvinylchloride (PVC), polystyrene, polytetrafiuoro-ethylene (PTFE), polyesters, polycarbonates, nylons, cellulosics. 

Shelby A. Miller, Ph.D., P.E., Resident Retired Senior Engineer, Argonne National Laboratory American Association for the Advancement of Science (Fellow), American Chemical Society, American Institute of Chemical Engineers (Fellow), American Institutes of Chemists (Fellow), Filtration Society, New York Academy of Sciences, Society of Chemical Industry (Section 18, Liquid-Solid Operations and Equipment Section 27, Energy Resources, Conversion, and Utilization)... 

Chemical reactions obey the rules of chemical kinetics (see Chapter 2) and chemical thermodynamics, if they occur slowly and do not exhibit a significant heat of reaction in the homogeneous system (microkinetics). Thermodynamics, as reviewed in Chapter 3, has an essential role in the scale-up of reactors. It shows the form that rate equations must take in the limiting case where a reaction has attained equilibrium. Consistency is required thermodynamically before a rate equation achieves success over tlie entire range of conversion. Generally, chemical reactions do not depend on the theory of similarity rules. However, most industrial reactions occur under heterogeneous systems (e.g., liquid/solid, gas/solid, liquid/gas, and liquid/liquid), thereby generating enormous heat of reaction. Therefore, mass and heat transfer processes (macrokinetics) that are scale-dependent often accompany the chemical reaction. The path of such chemical reactions will be... 

The chemical engineer is concerned with the industrial application of processes. This involves the chemical and microbiological conversion of material with the transport of mass, heat and momentum. These processes are scale-dependent (i.e., they may behave differently in small and large-scale systems) and include heterogeneous chemical reactions and most unit operations. Tlie heterogeneous chemical reactions (liquid-liquid, liquid-gas, liquid-solid, gas-solid, solid-solid) generate or consume a considerable amount of heat. However, the course of... 

Example 7.6 Suppose a liquid-solid, heterogeneously catalyzed reaction is conducted in a jacketed, batch vessel. The reaction is A B. The reactants are in the liquid phase, and the catalyst is present as a slurry. The adiabatic temperature rise for complete conversion is 50 K. The reactants are charged to the vessel at 298 K. The jacket temperature is held constant at 343 K throughout the reaction. The following data were measured ... 

This result is very interesting because whilst we have shown that G(0) has been excluded from the relaxation spectrum H at all finite times (Section 4.4.5), it is intrinsically related to the retardation spectrum L through Jc. Thus the retardation spectrum is a convenient description of the temporal processes of a viscoelastic solid. Conversely it has little to say about the viscous processes in a viscoelastic liquid. In the high frequency limit where co->oo the relationship becomes... 

Even a partial conversion of the hydroxyl groups of kraft lignin into a cationic ether derivative containing quaternary ammonium groups imparts water solubility to the derivative which is a promising candidate as a potential flocculant in liquid/solid separations in industrial and municipal water treatment. 

In the case of saturated liquid feed, the conversion achieved is almost identical for both reactors. This is why in the respective reactor model, the gas-phase mass transfer is theoretically infinite and the difference in the liquid-solid mass transfer between the reactors is small, only 1.21 times higher than that in the packed bubble bed reactor. 

FIGURE 17.3 Molecular randomness—and thus entropy—increases when a solid melts and when a liquid vaporizes. Conversely, randomness and entropy decrease when a vapor condenses and when a liquid freezes. Note the sign of AS for each process. 

This reaction is an example of a heterogeneous reaction with a solid catalyst with one reactant principally in solution and another in the gas phase the gas-liquid-solid mixture has to be mixed thoroughly to promote conversion (see Chapter 5 for more detailed consideration of multiphase reactions). Compared with the examples above, the measurement of the hydrogen uptake delivers an additional signal, which can also be used for the determination of reaction parameters. 

---