Production of anhydrous alcohol from rectified spirit (Industrial Ethanol) with molecular sieve dehydration utilizing pre concentration column:
The rectified spirit before sending in for dehydration process, it is heated and portion of water is stripped in the pre concentration column through a pre-heater. The mixture of alcohol and the remaining portion of water are sent to molecular sieve in the form of vapour.
The molecular sieves are hard granular substances, cylindrical extrudates manufactured from clay like silica gel material such as potassium alumino silicates. They are grated according to the nominal diameter of the myriad of internal pores, which make up the interstitial free volume found within their structure. A typical sieve used in ethanol dehydration is Type 3A. This designation means that the average diameter of the interstitial passageways is 3 Angstroms (One Angstroms: 1A is unit of measures equivalent to 10-8 centi meters). Thus the passageways in the structure have a diameter that is molecular scale. The water molecule has a mean diameter less than 3A, while the ethanol molecule has a mean diameter greater than 3A.
In addition, the water molecules can be absorbed on the internal surface offered by the passageways within the molecular sieve structure. It is the physical property of the sieves, which make them useful for the separation of mixture of ethanol and water.
Water molecules can invade the inner structure of the molecular sieve beeds and be absorbed thereon, while the ethanol molecules are too large and pass out of the vessel leaving the water behind, Thus, dehydration of ethanol takes placer in the molecular sieve technology.
In this technology, the re-generation of beads is done by one bed under vacuum; while the other bed is producing anhydrous ethanol under pressure with an automated operation, the feed of vapour to the molecular sieve system can be taken directly from the pre concentration column passing through a super heater. The condensed anhydrous alcohol vapour are then cooled and passed to storage through product cooler. The recovered ethanol and water from the regeneration phase is fed back to the pre-concentration column for recovery. Thus, there is no generation of effluent except the condensate water from steam is cooled and taken back process.