Systematic Analysis Reveals Thermal Separations Are Not Necessarily Most Energy Intensive

Summary At the industrial level, separation of a variety of mixtures is predominantly carried out by thermally driven processes such as distillation. Nevertheless, the current literature seems to suggest that much is to be gained by replacing these processes with alternative non-thermal methods, which will potentially require a fraction of the energy used by distillation. This is primarily due to the widespread perception that thermal separation processes, particularly those that involve vaporization, are highly energy intensive. However, this belief is not well founded, because it is based on extrapolation from comparisons in the literature, many of which make ad-hoc assumptions and result in incorrect conclusions. Our analysis shows that this confusion arises because the processes utilize different types of energy: heat and electricity. Here, we present a consistent framework that enables a fair comparison between different processes that consume different forms of energies. Using this framework, we refute the general perception that thermal separation processes are inherently the most energy intensive and conclusively show through the examples of two challenging mixtures constituting components with low relative volatilities, that distillation processes, when run properly, can consume remarkably lower fuel than non-thermal membrane alternatives, which have often been touted as more energy efficient.