Through distillation alone, ethanol can only to dehydrated to around 95% purity, with the remaining water unable to be removed due to the formation of an azeotrope, leaving the ethanol unsuitable as fuel.
Dehydration with azeotropic distillation
Most of the ethanol dehydration plants for production of anhydrous ethanol are based on Azeotropic distillation. It is a mature and reliable technology capable of producing a very dry product. However, its high capital cost, energy consumption, reliance on toxic chemicals like benzene and sensitivity to feedstock impurities, has virtually eliminated the use of azeotropic distillation in modern ethanol plants. Benzene has been used as entrainer of choice of ethanol dehydration but it is now known to be a powerful carcinogen.
Dehydration with Molecular Sieve Process
Ethanol can be applied in PSA or VSA dehydration units and is used to remove water in ethanol streams after distillation. This molecular sieve has been specifically designed for Ethanol Dehydration Units and differs from standard molecular sieves. With a high crush strength to withstand the heat and pressure of the dehydration unit, the design of Ethanol dehydration beads maintains a low bulk density, while offering a high working capacity.3A Zeolite, has a superior selectivity between water and ethanol molecules, which increases both efficiency and dehydration capacity each cycle. Once ethanol has been dehydrated, it is about 99.99% pure and can then be applied in biofuels for direct blending and ETBE production, or for other uses such as in chemicals, food industry, pharmaceuticals, and more industries.