Process integration by application of an extractive dividing-wall column: An industrial case study

Extractive distillation for the separation of azeotropic or narrow-boiling mixtures has been known for a long time and is well established in the chemical industry. For the separation of zeotropic ternary mixtures, however, dividing wall columns have gained importance for two decades. Both processes incorporate a high degree of intensification, which yields in a considerable reduction of both, capital and operational costs. The trend towards intensified processes is unbroken in the chemical industry, particularly in the industrial nations, since it facilitates the struggle with high energy prices and helps to withstand the increasing competition from low-cost countries. The combination of extractive distillation and dividing wall column allows the separation of narrow-boiling or azeotropic components in one single column tube, using a suitable entrainer. Recently, the Lonza AG has successfully developed and implemented an extractive dividing wall column. The entire equipment design was exclusively carried out based on simulations without carrying out time-consuming pilot or mini plant experiments. This approach considerably shortens the time-to-market cycle and reduces the development costs to a large extent. Despite their great potential to notably reduce costs, only a very limited number of extractive dividing wall columns are being operated in the chemical industry and published data is scarce. This paper aims to close this gap.