Novasep Technologies: Ion Exchange

Ion Exchange Technologies

Novasep Process, through its processes based on ion exchange and adsorption resins, is a world leader in the food, bio and chemical industries. The Applexion® ion exchange applications in the non-water treatment market are constantly growing, since ion exchange is a very versatile tool to solve a large number of problems for these markets. Novasep Process actively participates in the development of new processes combining ion exchange technology with other technologies, such as membrane filtration, in order to offer optimized answers to market needs.

Basic Ion Exchange Techniques

Decalcification Salt conversion Decationation Deacification Demineralization

Selective Decolorization Separation Catalysis Enzymes mobilization

Definition of ion exchange in the glossary

Ion Exchange Resins

Ion exchange resins consist in a polymeric matrix and a functional group with a mobile ion which can be exchanged with other ions present in the solution to be treated. The most common synthetic structures are:

• Cross-linked polystyrene
• Cross-linked polymethacrylate
• Phenol-formaldehyde

Strong acid cationic resin polystyrenic type	Strong base anionic resin polyacrylic type

The polystyrene type is the most commonly used. The functional groups characterize the ion exchange resin into cationic or anionic types, although an infinite quantity of functional groups can be attached to the polymeric matrix, the most currently used industrially are:

Active groups	Structure	Type of resins
Sulfonic	R-SO3 H	Strong acid cation (SAC)
Carboxylic	R-COOH	Weak acid cation (WAC)
Ammonium	R-N + (CH 3 )3 Cl - R-N + (CH 3 )2 (CH 2 )2 OH Cl- R-N + (CH 3 )2	Strong base anion (SBA) type I Strong base anion (SBA) type II Weak base anion (WBA)
Chelating	R-SH R-CH2 N(CH2 COOH)2 R-CH2 NHCH2 CH2 PO3 H	Chelating resins

Ion exchange resins are mostly available in a moist beads form (granular or powdered forms are sometimes used and dry form is also available for applications in solvent media) with a particle size distribution typically ranging from 0.3 – 1.2 mm (16 – 50 mesh) with a gel or macroporous structure. Nowadays ion exchange resins with a uniform particle size distribution are available resulting in optimum industrial operation.

Ion Exchange Reactions

Salt conversion: The most typical application is softening or decalcification

2R-Na + Ca²⁺ -> 2R-Ca + 2 Na+

Organic acids can be also converted into their salts on passing them through a cationic resin in the appropriate form. We can also mention the Quentin process where potassium and sodium ions are exchanged against magnesium in order to minimize sugar losses in the final molasses.

Demineralization
The use in series of a cationic exchanger in hydrogen form and an anionic exchanger in hydroxyl form allow eliminating all ionic species present in a feed solution. The following figure illustrates a simple pass deashing process.

The mechanism can be illustrated as follows

• Production cycle:
  - On the cationic side
  R-SO₃ H + NaCl  ->  RSO₃Na + HCl
  2 R-SO₃H + CaCl2  -> (R-SO₃)₂Ca + 2 HCl
  - On the anionic side
  SBA type R-N(CH₃)₃OH + HCl  ->  R-N(CH₃)₃Cl + H₂O
  WBA type R-N(CH₃)₂ + HCl  ->  R-N+H(CH₃)₂ Cl^-
   
• Regeneration cycle: The reverse reaction takes place by passing an acid (HCl or H₂SO₄ ) on the cationic resin and an alkaline solution (NaOH, NH₄OH) on the anionic resin.

Deacidification:
An acidic feed solution can be passed through a weak or strong base resin in OH- form, all or only strong acids will be removed. Fruit juices can debiterred on a weak base resin. 

Catalysis:
Ion exchange resins can be used for acid or alkaline catalysis, a sucrose solution can be hydrolized into glucose and fructose by passing them through a cationic resin in hydrogen form. An other application consists in the possibility to immobilize some enzymes (glucoisomerase, lipase, lactas, amylase,...) on resins matrix in order to carry on a batch enzymatic conversion.

Recovery and concentration:
Valuable or toxic substances can be recovered from various solutions, i.e. the nickel used for the hydrogenation of polyols can be recovered on a WAC resin. Metals from the plating or mining industries can be removed with ion exchange or chelating resins.

Example of the removal of a metal with a chelating resin

The availability of numerous types of ion exchange resins allows their combination in various designs and applications.
Novasep Process / Applexion has developed a unique expertise in designing ion exchange systems with co- or counter-current operation, upflow process, simple or double pass, continuous operation...

Continuous Processes

A typical ion exchange resin process includes several steps such as:

• production,
• backwashing,
• regenerant injection,
• regenerant displacement,
• fast rinse,
• eventually sweetening off and sweetening on,
• stand-by.

Each of these sequences - except production - are time consuming and affect the plant productivity. Therefore the food and pharmaceutical industries have been looking for better cost performing designs.

Continuous processes have always been a request from the industry anticipating smooth operations, intermediate storage reduction and constant quality of the product and effluents.

An ion exchange resin process will be qualified as continuous when all individual steps are carried on at the same time.

In batch operation, while one column is in production the second one is in regeneration. This implies that the production time has to be equal to the time spent for all the regeneration sequences.

According to the inlet feed salinity, we will end up with several options:

• when inlet salinity is on the low side, the production time is longer than the regeneration time. This results eventually in stand-by periods
• in contrast, when the inlet salinity is on the high side, the regeneration time is much longer. Therefore, in order to ensure a smooth operation, the flow is slowed down during production to equilize both durations

In order to achieve a continuous production, the first attempts consisted in a large intermediate storage tank (the tank capacity representing the regeneration sequences) or in two lines operating in parallel.

Later on, a "true" continuous system was developed through an arrangement consisting in several small discrete rotating columns. Another approach consisted in moving the resin beds in a loop design divided in 4 zones (production, rinsing, regeneration, rinsing).

Most of these early systems, although providing some real advantages, did not have a great industrial success. Physically moving the resin beds resulted in attrition losses. The operation mode was quite complicated.

In order to achieve a continuous process we can either move the columns or the resins. However both technologies present some drawbacks (either mechanical concerns or resin lifetime issues). In the Applexion® process - derived from the SMB (Simulated Moving Bed) technology - only the inlet and outlet are changing.

Benefits & Advantages of Novasep Continuous Processes

The main advantages of such a design are:

• continuous flow (feed, water, effluents),
• savings on equipments,
• lower resin inventory,
• savings on regenerant and water consumption,
• flexibility (adding cells or on line maintenance).

Applexion® process offers to the industry a truly continuous ion exchange or adsorption system by using multi-cells columns equipped with multi-port valves.

Discontinuous process

 

Continuous process diagram (cationic columns)

Novasep Ion Exchange Equipments & Products

Novasep Process has developed numerous ion exchange equipment and processes for the life science industries.

We continuously test, pilot and develop new grades of resins in order to propose state-of-the -art technologies.

We have gained an outstanding expertise in selecting the most appropriate and best performing resin types available from the market.

Discover our list of ion exchange resins, available for numerous applications and designs.