Abstract
Experiments on molecular distillation of a multicomponent system-polyethylene glycol (average molecular weight=0.3 kg/mol) -were performed by use of a pot still under a residual air pressure less than 0.13 Pa. The following results were obtained : (1) In the domain of evaporation without molecular-burst (M-B) evaporation, polymerization grade (mob) of distillate observed at each fraction is equal to the value (mcal) calculated under the condition of ideal solution and constant liquid surface temperature (140°C). This result indicates that a multicomponent solution can be regarded as an ideal solution in this domain. (2) In the domain of evaporation with M-B evaporation, mob does not agree with mcal. The cause of this disagreement is that relative volatility becomes smaller than the theoretical value by M-B evaporation. In this domain, a multicomponent solution cannot be regarded as an ideal solution. (3) An equation which represents the relationship between liquid weight and its composition in the pot still can be derived from the evaporation rate equation (Langmuir's equation). In the domain of evaporation without M-B evaporation, the relationship obtained experimentally is accurately estimated by using this equation and theoretical relative volatility.
