New Phase Equilibrium Device Allows Handling of Vapour-Liquid-Liquid Equilibriums

When Standard Equipment Reaches Its Limits

The standard until now has been a phase equilibrium device capable of determining experimentally the vapour/liquid equilibria of binary or multi-component mixtures if the boiling points of the components are far enough apart. But, in cases involving calculations for mixtures whose components boil in a narrow and simultaneously low temperature range or which form azeotropic mixtures, the standard equipment reaches its limits. “The practical measurement and determination of this data proves difficult because of the phase formation of the liquids,” explains Koenen.

As the vapour concentration vacillates back and fore between the phases, VLE (vapour liquid equilibration) equipment does not distinguish these adjacently boiling components well enough — much like the human eye, which makes one light source out of two flashes happening in quick succession. In order to make the data accessible and reach a stable equilibrium, therefore, the relevant components have to be dissolved in a third phase, resulting in a vapour-liquid-liquid equilibrium.

This is the case in e.g. extractive distillation. The prime example in petrochemicals is the separation of butadienes from a C4 mixture. Although the addition of acetone or furfural makes the butadiene less volatile, the description of the resulting vapour-liquid-liquid equilibrium is a challenge for the process developer.

The solution for this problem was found a few years ago by researchers at Alicante University with whom i-Fischer was collaborating closely under an exclusive licence. “We have now adapted the patented, scientific idea to create a device design suitable for series production and have got it ready for market release,” says Koenen. At this year’s Achema, the distillation experts have showed that the new development not only has a high performance, but also pleases the eye. There is also a metal version for overpressure.

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