Single phase processes

Many organic syntheses can be carried out in single liquid phase systems. The choice of a reactor type is then only determined by two factors  

An important decision that has to be made at an early stage, is whether to carry the reaction to virtually complete conversion, which is common practice in the laboratory, or to opt for an intermediate degree of conversion for obtaining a higher selectivity. The choice will be determined by the nature of the selectivity-conversion relation, see section 3.4. These two cases will be dealt with separately in the next two sections. 

---

Favoring multi-phase processing, including powder making Favoring single-phase processing... 

Tubular reactors are widely used in studying single-phase processes and gas-solid catalytic... 

How the number of process variables, design relationships, and design variables defines a system can be best illustrated by considering the simplest system a single-phase, process stream. 

To attain conversions higher than attainable fi om equilibrium constraints in a single-phase process and... 

D.G.V. Boocock, in Single-phase process for production offatty acid methyl esters from mixtures of triglycerides and fatty acids , USA, 2003. 

Thus, when the substrate can be dissolved in a suitable solvent at reasonable concentrations, pressures, and temperatures, the excellent reaction properties of the supercritical single-phase process can be utilized also for large molecules. 

In this chapter we have presented an overview of scale-up considerations involved as one moves from bench-scale reaction calorimetry to larger scale pilot plant and production reactors. Our focus has been on heat transfer and single-phase processes, addressing primarily the problem that the heat transfer area per unit reactor volume decreases with scale. Clearly, there are many challenging problems associated with multiphase vessels, with evaporation/distillation and crystallization as obvious examples, but these topics are beyond the scope of this chapter. 

Some important aspects of topochemical polymerizations can be understood by inspection of Eq. (1), All reactivity comes about by very specific rotations of the monomers and by 1,4-addition of adjacent units and an extended, fully conjugated polymer chain is formed. The unique feature of the topochemical polymerization of diacetylenes is the fact that in many cases the reaction can be carried out as a single phase process. This leads to macroscopic, defect-free polymer single crystals which cannot be obtained, in principle, by crystallization of ready-made polymers by conventional methods. Thus, polydiacetylenes are ideal models for the investigation of the behaviour of macromolecules in their perfect three dimensional crystal lattice. 

In some special cases, however, both the polymerization and the side group reorientation are single phase processes. They are of special interest for understanding the dynamics and side group mobility in the solid-state polymerization of diacetylenes. 

On the other hand, an asymmetric version of the epoxidation can be achieved using Salen-manganese complexes (2) instead of porphyrins (eq 29). Nevertheless, modest yields and selectiv-ities are obtained when NaI04 is used, whereas the previously described single phase process with M-BU4NIO4 leads to higher asymmetric inductions. 

In the case of slow reactions, the transformation rate is limited by intrinsic kinetics. A drastic increase of the temperature allows exponential acceleration of the reaction rate in agreement with the Arrhenius Law. Moreover, the pressure can be advantageous to accelerate reactions, to shift equilibrium, to increase gas solubility, to enhance conversion and selectivity, to avoid solvent evaporation, and to obtain single-phase processes [8, 13]. The overall transformation rate of such reactions could be significantly increased in these wove/ operating windows. 

Only single-phase processes were considered. 

Of course, the selection of a phase for a single-phase process cannot be made independently from the choice of reaction temperature and pressure. 

However, some products have unfavourable filtration characteristics. In that case it may be prefarable to find conditions where the product remains dissolved, and separate it from the reaction mixture in other ways, e.g., by evaporation or extraction. This is practised in some polymerization processes. One disadvantage of single phase processes is obvious the viscosity of the mixture is increased considerably, particularly in the case of dissolved polymers. 

---