Dehydration of Ethanol Using Molecular Sieves

For the catalytic reaction crystalline aluminosilicate salts of the molecular sieve family is used. Now let’s we look how molecular sieve will help in the dehydration of the ethanol.

The rectified spirit which is produced in the rectifier is superheated with steam in feed super- heater. After following this stage the super heated rectified spirit from the feed super heater is passes to one of the pair of molecular sieve bed for many times. Later by time the superheated rectified spirit vapor is poured or moved to another pair of bed. The loaded bed is regenerated by using a small portion of the anhydrous ethanol vapor leaving the fresh adsorption bed. Following this process a moderate vacuum pump operating after the condensation of the regenerated ethanol water mixture. The condensate is then transferred from recycle drum to the rectified column in the hydrous distillation plant by recycle pump. The remaining anhydrous absolute alcohol draw is again condensed in product condenser and passed to product storage.one of the main advantage of using this process is it cost less and also normally the molecular sieve has a life span of around five to seven years. While comparing azeotropic distillation this process cost very low.

Molecular Sieve for Ethanol Dehydration Explored

Now a days  most of the countries are facing a great problem in the production of anhydrous ethanol due to the great efforts directed to use biofuels and diminishment in pollution and environmental problems of fossil fuels, So because of this many countries arising this issue as their main problems. Usually the extraction of anhydrous alcohol production comprises three main steps: fermentation distillation and dehydration. The ethanol quantity will be determined purely based on the last step that is the final dehydration step which depends on the operating conditions and the technology used.

 

It was found to be more time consuming and costly, because of this a new catalyst called molecular sieve beads is introduced for the production of anhydrous ethanol. Absolute alcohol is an important product required by industry. Many countries depends the production of high standard alcohol for their economic uplifting.

As per IS specification alcohol should be nearly 100% pure or water free alcohol. Rectified spirit, which is 94.68% alcohol, and the rest contained with water is currently available in market. Practically it is not possible to remain the water content from the rectified spirit by straight distillation as the compound; ethyl alcohol forms a constant boiling mixture with water at this stage to form a product known as azeotrope. Therefore special extraction process is needed for the removal of water for the manufacture of absolute alcohol. So the manufactures of absolute alcohol or for the dehydration of the alcohol we use molecular sieve process.

Molecular Sieves are used in Desiccant Packets

Another important desiccant is molecular sieves. These are also available in form of granules but are assumed to be little less effective than silica gel. It is used to absorb moisture. Next is activated carbon. These are the odor absorbing specialist. The last one is clay. It is also used for absorbing odor as well as some amount of moisture. Although, clay is not used widely! Reason is that once a bag of clay has fully absorbed moisture it has to be changed immediately as it starts to leak water droplets. And absolutely fails to trap moisture inside. Still it is considered as the cheapest way for absorbing moisture.

Many people use a single desiccant at a time but as per the requirement a combination of more than one desiccant can also be used. Suppose, using silica gel and activated carbon in a same packet can help you to get rid of moisture and odor at the same time. As the product does not release any toxins it is safe to use with eatable items. These desiccants are mostly used at the time of packaging of dry food items, shoe boxes, vitamins medicines and many more.

Molecular Sieves have different properties compare to silica gel!

The properties of molecular sieves are very different with that of silica gel in a number of ways. Molecular gel has the capacity to absorb moisture from the environment more quickly that silica gel. It can reduce the moisture to much lower level than that of silica gel because silica gel only works in an extremely dry environment. One more feature which only molecular sieves possess is that it has the ability to separate gasses or liquids based on it molecular size. These crystalline, metal alumina silicates have 3 dimensional network of interconnected silica. Hydrated water can also be easily separated from the network by heating which produces equal cavities which help in absorbing molecules of specific size. Specifically we can use a 4 to 8 mesh size sieve for gaseous applications as it has very small molecular size.

Different properties of Molecular Sieves!

People usually confuse silica gel beads with molecular sieves. Molecular sieves have absolutely different properties as that of silica gel. These small opaque pinkish colored beads are synthetically produced. They are highly porous crystalline beads which are made up of metal alumina silicate. Depending on the name of the variant, they have internal cavities of different size. The cavities are linked by window openings of different diameters. The diameters are measured in Angstroms or A. Absorption occurs only to those substances which have molecular size smaller than the window openings of these desiccants. Substances with larger molecular sizes will be excluded from absorption. This makes molecular sieves ideal for absorption of water and gaseous particles this is because molecules of both water and gas are very small. Molecular sieves helps to absorb contaminants from water as well as gas and reduce the contamination to very low level.

Molecular Sieves are effective to remove moisture from Liquid!

Molecular sieves are excellent desiccants and are very effective in removing moisture from liquid, semi-liquid or gaseous substances. They are said to be even more effective than silica gel or activated alumina. The reason for their popularity is their crystalline composition which helps to create more moisture free products. Molecular sieves prove to be very useful in many cryogenic operations because this process requires gases to be converted into liquid form and in the process even a minute amount of water has to be extracted out in order to avoid freezing. According to the requirement you have different variants bases on its molecular size. As the molecular size increases it gets more surface area to absorb humidity. The variants available are 3A, 4A, 4A indicating molecular sieves, 5A and 13X.

Benefits of using Molecular sieves

The advantage of using molecular sieves with higher pore size is that it will have higher absorption capacity and is also more resistant against contamination, and thus all these factors increases the cyclic life and increases the regeneration process, increasing the life of the product. So, starting from the protection of historical artwork to the purification of water, molecular sieves are an important desiccant which is widely used. These desiccants are the best to be used even at high temperature as its melting point is slightly less than 2900oF.