Process Parameters Temperature, Pressure, Throughput

The issue of parallel versus sequential synthesis using multimode or monomode cavities, respectively, deserves special comment. While the parallel set-up allows for a considerably higher throughput achievable in the relatively short timeframe of a microwave-enhanced chemical reaction, the individual control over each reaction vessel in terms of reaction temperature/pressure is limited. In the parallel mode, all reaction vessels are exposed to the same irradiation conditions. In order to ensure similar temperatures in each vessel, the same volume of the identical solvent should be used in each reaction vessel because of the dielectric properties involved [86]. As an alternative to parallel processing, the automated sequential synthesis of libraries can be a viable strategy if small focused libraries (20-200 compounds) need to be prepared. Irradiating each individual reaction vessel separately gives better control over the reaction parameters and allows for the rapid optimization of reaction conditions. For the preparation of relatively small libraries, where delicate chemistries are to be performed, the sequential format may be preferable. This is discussed in more detail in Chapter 5. 

A successful two-stage liquefaction process will need to maintain a relatively consistent H-donor cs ability in its recycle solvent arnl should react positively to rectify variations in the consistency outside acceptable limits. In order to react to these variations, the process will need the ability to adjust reaction parameters (e.g. pressure, temperature, throughput, catalyst activity), probably according to its H-donor ability. Hence there is a need to monitor the H-donor content of the solvent. 

Study determined the compact throughput, compact density, and fines (not compacted during vacuum deaeration) when using a new equipment feed system design. The parameters controlled and monitored during the compaction process were vacuum deaeration pressure, roll pressure, roll and screw speeds, room temperature, and humidity. 

The development of a viable process for the HPB ester took more than a year. Even before the age of high-throughput screening, the obvious strategy was first, to screen for the best catalyst, modifier and solvent, second, to optimize relevant reaction parameters (pressure, temperature, concentrations, etc.) and, finally, to scale-up and solve relevant technical questions. Indeed, during the course of the process development more than 200 hydrogenation reactions were carried out The most important results of this development work may be summarized as follows ... 

When an extruder is working under steady-state conditions several factors can influence the process. The primary parameters that in principle can be controlled externally are the screw speed, the throughput, the barrel temperature, and the die resistance. All other parameters are influenced by the changes in the primary variables, e.g., filled length, heat transfer, and pressure gradient, or are predetermined, e.g., screw geometry or material properties. 

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