August 2005 – Due to the azeotrope, an ethanol-water mixture cannot be concentrated into pure ethanol by simple distillation. Various processes exist for the production of dehydrated ethanol including entrainer distillation, pervaporation and dehydration by adsorption of water molecules.
Molecular sieve technology is particularly suited for the dehydration of ethanol and is therefore being more frequently applied in recent times. GEA Wiegand has improved this process, offering significant possibilities for energy integration and heat recovery.
The figure depicts a model showing the load of a molecular sieve in relation to flow (z axis) and over time. The foreground shows the active zone (blue) which has the greatest potential to adsorb water. The water content in the adsorbent then rapidly rises in the mass transfer zone (green) before passing into the equilibrium (saturation) zone, shown in red. In this region, no more water molecules can be adsorbed.
If concentrated ethanol is to be processed, it is sensible to use the plant configuration shown in the process flow diagram opposite. The latent heat of the dehydrated alcohol vapours flowing from the molecular sieve (S 01) is used to generate flash steam (W 01). The flash vapour produced is recompressed to a higher pressure by means of a jet pump (V 01). This steam is then used for heating the column (K 01) and rectifying the raw ethanol. Depending on the boundary conditions, energy savings of up to 40 % are achieved in this way.
Other concepts can be combined where the dehydration system is to be integrated within an overall process. GEA Wiegand therefore specializes in achieving optimum energy consumption levels, significantly reducing operating costs for the benefit of plant operators at a time of rising energy prices.
