Normal alkane evaporation under vacuum: chain-length dependency and distillation from binary systems

Abstract

Normal alkanes are among the simplest molecules that can be studied in physical chemistry. However, there is still more to learn about their liquid-to-gas phase transition characteristics, especially in vacuo. Here, we investigated the evaporation behavior of 12 different normal alkanes using thermogravimetry, both in air and under reduced pressures (5000 to 10−2 Pa). The reduced pressures lowered the evaporation-onset temperatures of the normal alkanes. The evaporation-onset temperatures at ∼1 Pa were linearly correlated with the chain lengths (molecular weights). Furthermore, we found that the reduced pressures enabled the effective distillation of binary mixtures of normal alkanes because of the differences in the evaporation-onset temperatures. It was empirically determined that distillation (isolated evaporation of one of the binary mixture components) was achieved at ∼1 Pa when the chain of one of the alkanes was 30% longer than that of the other.