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Molecular Sieve Dehydration Technology for Ethanol Production |
To bring down energy consumption and to ensure high level of dryness in final ethanol product, Molecular Sieve (MolSieve) has proved to be ideal. Molecular Sieve is a synthetic adsorbent. It was introduced more than a decade ago to dehydrate ethanol. Earlier systems operated in liquid phase and used thermal swing regeneration process, which did not make them very energy efficient. Further development on the adsorbent saw introduction of vapor phase operation with pressure swing regeneration system. This proved to be highly energy-efficient.
The vapor phase pressure swing regeneration system employs Molecular Sieve beds which act as adsorbent. These beds are made of zeolite with an effective pore size opening of about 3 Angstrom.
In order to understand the process of dehydration of ethanol, consider a column packed with freshly activated Molecular Sieve. As rectified spirit (hydrated ethanol) vapor first enters the bed, water is diffused and adsorbed within the pores of the adsorbent structure in a thin layer. As more alcohol enters the column, it passes through this layer to slightly lower level where another incremental amount of water is adsorbed. This continues until a point is reached where all possible water adsorption from this slug of alcohol is accomplished.
Transfer of water from the vapor of rectified spirit to the Molecular Sieve occurs through a zone where water (adsorbate) content is reduced from its inlet to its outlet concentration. This finite length of bed, where the adsorbate transfer occurs, is known as the mass transfer zone. Two beds are provided in order to make the process continuous. Whilst the active bed is under pressure carrying our dehydration, the regeneration bed is under vacuum. The shift of operation (swing) from one bed to another is controlled with help of control valves and automation.
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