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Molecular Sieve Adsorption

New Multifab Engineers Pvt Ltd offers adsorptive and catalytic drying systems based on molecular sieves.

Adsorptive Drying systems can be designed and manufactured in different configurations as: Single Column (Bed) Adsorption or Multiple Column Adsorption.

Depending on the type of regeneration, Multiple Column Adsorption systems are further classified as:

  • Temperature Swing Adsorption (TSA).
  • Pressure Swing Adsorption (PSA).
  • Vacuum Swing Adsorption (VSA).

We have vast experience in drying of liquids, solvents, and other media and we have designed, manufactured, and supplied PSA & TSAMolecular Sieve based Adsorption systems to various Clients in India and abroad.

Molecular Sieve Drying Technical Paper International
Reference List of Molecular Sieve

There is increased demand for drying and purification of liquids in the Chemical, Pharmaceutical, Petrochemical, and allied industries over the last two decades. There are various reasons, prominent of which are listed here:

  • Physical effects.
  • Chemical effects.
  • Corrosion effects.
  • Stringent specifications (Client/Statutory/etc).

Physical effects: Solubility of water in organics decreases with reduction in temperature and there is physical separation of water from organic layer. This can lead to problems in material flowability at reduced temperatures.

Chemical effects: Water can poison catalysts and reduce their efficacy. In certain reactions, such as some esterification reactions, presence of water can result in promotion of reverse reaction, which is detrimental to yield. Many Acylation and Alkylation Reactions use Metallic Halides such as AlCl¬3 or BF3 as catalyst. These catalysts react with water and form acidic impurities. Other examples include: Toluene drying for isobutyl benzene synthesis, Ethanol drying for glycol ether manufacture, Ether drying for Grignard reactions, N-hexane drying for butene-1 manufacture (Friedel Crafts reaction), Drying of solvents like ethylene chloride, tetra hydro furan, acetone, MEK etc. for recycle in pharma/ dyes/ rubber and intermediates plants, Drying of methanol for formic acid manufacture and Drying of feeds for polymerization processes for EPDM, isoprene, polypropylene and polyethylene.

Corrosion effects: Presence of water can cause corrosion. Sometimes, presence of water can lead to two-fold corrosion. For example, in the situations where HCl or HF are formed as by-products and the acid in presence of water is highly corrosive. Examples include: Adsorptive Drying of Benzene for Chlorination Reactions, Adsorptive Drying of Ethyl Acetate for use as solvent.

Stringent Specifications: In the increasingly competitive global market, Client and Statutory specifications are becoming more & more stringent. The fraction of so-called allowable impurities such as moisture has to be reduced to match international standards at competitive prices.

The most common application of Molecular Sieves Drying Systems is removal of water/moisture from liquids, vapours, solvents, and other materials. Adsorption is a physical phenomenon and Molecular Sieve based Dryers work by physical or chemical bonding of the water molecule on to the Adsorbent surface. The molecular sieves provide sieving action depending on the size of pore opening of the adsorbent material. For example, molecular sieve 3A has pore opening of 3.2 Å i.e. it will allow molecules with size smaller than 3.2 Å to enter the pore and diffuse to the adsorption site. Larger sized molecules will simply pass over the molecular sieve. The strong adsorptive forces in zeolite molecular sieves are primarily due to the cations that are exposed within the crystal lattice. They act as sites of strong localized positivecharges that electrostatically attract the negative end of polar molecules. The greater thepolarity of the molecule, the more strongly it will be attracted and adsorbed. In this way, molecular sieves work by separating and removing the water from the mixture.

These operate with a single column filled with molecular sieves. The liquid/vapour to be dried is passed over the molecular sieves and dried liquid/vapour is achieved at the other end. The drying continues till the capacity of the molecular sieves is exhausted. The column is then regenerated by heating to desorb the adsorbed water. Due to the break in process required to regenerate the adsorption sites, this form of Dryers are non-continuous in operation.

Depending on the method used for regeneration of adsorbent, the Drying Systems can be classified as:

  • Thermal Swing Adsorption (TSA).
  • Pressure Swing Adsorption (PSA).
  • Vacuum Swing Adsorption (VSA).

Often, pressure and vacuum are used simultaneously to improve the efficiency and product purity in molecular sieve dryers.

Thermal Swing Adsorption Drying Systems: In this process, there are multiple columns, the least being two columns to convert the process into a continuous process. One of the columns is used for carrying out drying and simultaneously, the other column molecular sieves are being regenerated. When the 1st column adsorption capacity is exhausted, the product to be dried is switched over to the 2nd column and the 1st column is taken up for regeneration. By controlling the cycle time, the process can be made continuous. We have designed, manufactured, and supplied various capacities of TSA Drying Systems with capacities as high as 14500 Kg/h flow.

Pressure Swing Adsorption Drying Systems: In this process, there are multiple columns, the least being two columns, just as in TSA to convert process into continuous process. This process operates in almost isothermal conditions. Adsorption is carried out under pressure. Lower pressure or vacuum or a combination of both is used to desorb the water. The advantage of this method is possibility of lower cycle times, therefore reducing the size of Adsorption Column and Adsorbent inventory requirement. Another advantage is that the compressed fluid is used as the main source of energy and separate utilities are not required.