TABLE OF CONTENTS This chapter examines some areas in which vacuum technology is applied to the chemical sciences. Firstly, unit operations such as drying and distillation, of importance in chemical technology, are discussed. The use of condensers in association with vacuum pumps is introduced and typical calculations demonstrated.
Secondly, the use of UHV/EHV systems is obviously desirable because of the extreme sensitivity of many materials and processes to residual gas. Work in this pressure range has allowed significant advances to be made in, for example, surface science and the exploitation in many areas of research of synchrotron radiation sources based on electron or positron storage rings. Relevant factors in the operation of these systems, such as adsorption and desorption (including diffusive outgassing), are examined in detail.
Thirdly, the use of differential pumping, as a general technique, is examined. It is widely applied in systems where regions having large pressure differentials are interfaced. Specific systems are discussed to indicate the usefulness of the technique.
The application of vacuum conditions in chemical technology lies not in the performance of chemical reactions but in the treatment and purification of reactants and products. This may often involve thermal processing such as distillation and drying.
The advantage of carrying out thermal processes under vacuum pressures can be seen if the liquid-gas boundary is considered.
The Clapeyron equation states the relationship between a phase change for a pure material and changes in pressure and temperature. For vaporisation:
| (6.1) |
