By Filip Rochette, PuriTech

Belgian separations technology company PuriTech (www.PuriTech.be) has taken a fresh look at ion exchange system design. By effectively reversing a commonly used approach to distributing fluids to ion-exchange cells, it has developed IONEX. Based on an innovative valve design, this liquid adsorption separation technology, which is now being targeted at a broad range of industries, improves liquid–resin contact efficiency while reducing plant operating costs and capital expenditure, as PuriTech’s Filip Rochette explains.

The applications for ion exchange have many forms, and these will undoubtedly increase as awareness of the technology continues to grow.

In addition, as scientists and engineers create an ever-increasing variety of polymers and other materials, the potential for producing new, useful ion exchange resins will also expand.

Growing Markets [top]

A major application for ion exchange is the treatment of water for drinking, for commercial and industrial use, and wastewater treatment. Ion exchangers can soften water, deionize it and even be used in desalination. In industrial sectors — for example, the manufacture of semiconductors — pure water is crucial to both product development and yield.

The growing developmental accent on clean water is also creating enormous opportunities for the water treatment business worldwide, particularly in regions such as Asia and Africa. The order flow for ion exchange systems and resins has been growing steadily and long-term growth prospects appear to be bright. Recent developments and refinements in resin technologies make ion exchange one of the best and most complete forms of wastewater treatment available today.

The preparation of various acids, bases, salts and solutions is aided by ion exchange, and the recovery of valuable metals is also possible using resins.

The use of ion exchange and adsorbent technology for the processing of food streams within the nutrition market place is well established, with a history stretching back decades. The food industry uses the process in a variety of ways, ranging from wine-making to sugar manufacture.

Technology Development

Against this backdrop of strengthening markets and the growing potential of ion exchange, PuriTech developed IONEX, its liquid adsorption separation technology. Its aim was to build on and dramatically improve existing systems, particularly the continuous countercurrent process, and broaden the technology’s application base.

Standard, existing technologies include fixed-bed, and both continuous and continuous countercurrent ion exchange systems. Based on a batch-style operation, fixed-bed units are used in around 90% of the projects, but compared with continuous countercurrent systems their performance is relatively weak. Furthermore, they waste 2–4% of the treated fluid-flow in water treatment applications.

Continuous ion exchange, which makes use of an array of automated valves for each resin cell, offers an improved approach and some advantages, but relies on a lot of piping and complex controls. Two major companies have developed continuous countercurrent ion exchange units that use a turntable, or carousel, to rotate the resin cells around a central valve. This also requires complex controllers, and the use of flexible hoses between the valve and resin chambers.

Fresh approach [top]

PuriTech has taken a fresh look at continuous countercurrent ion exchange system design.

The company has effectively reversed a tried and tested approach to distributing fluids to ion exchange cells, or chambers, used by competitor companies, to create a ingenious system that not only improves liquid–resin contact efficiency, but also leads to a reduction in plant operating costs and capital expenditure.

Design features

IONEX uses a single, multi-port distribution valve (see Figure 1), creating a process system for continuous, countercurrent ion exchange. The patented valve distributes different flow streams to several resin cells and determines whether the resin is in an adsorption, a regeneration or a rinsing cycle.

The technology is markedly different from other continuous, countercurrent ion exchange systems that are available in the market place. Instead of using a turntable, or carousel, to move the cells around a central valve manifold, the process disc within the IONEX valve rotates around a central axis (see Figure 1) and distributes the different flow streams to the cells containing ion exchange resin or other adsorption materials (see Figure 2). During a full rotation each cell is subjected to an entire sorption cycle.

Adsorptive and ion exchange separation generally comprises a two- phase mass-transfer — an adsorption cycle and a desorption cycle — separated by washing or rinsing of the solid phase between these mass transfer steps. The use of shorter and smaller resin beds allow for maximum resin usage.

The mass-transfer zone in a standard ion exchange plant is typically a small section of the actual operating bed length. This small production section, where mass transfer takes place, passes as a transfer zone throughout the bed — from a saturated resin to an unsaturated resin.

To avoid frequent bed regeneration, the content of a vessel is saturated before regeneration takes place. Each regeneration follows a batch sequence. Countercurrent contacting on a continuous basis does not suffer these limitations, because it is not a batch process.

Advantages [top]

PuriTech’s design offers a number of advantages. For instance, rigid pipes can be used between the valve and ion exchange vessels, and sealing is greatly simplified, which means only O-rings and gaskets are required. In addition, a simple control unit can be employed because the system does not use a carousel.

IONEX is also designed to be adaptable and versatile. A number of user functions can be carried out simultaneously under continuous operating conditions. Easy access to the valve — the system's only moving part — and the ion exchange vessels, simplifies maintenance procedures. (see figures 3 and 4).

It is possible to build compact systems based on the technology. The ion exchange cells can be positioned in any desired pattern, providing maximum installation flexibility. IONEX also can be retrofitted to an existing ion exchange system, regardless of where the ion exchange cells are located.

Compared with traditional fixed-bed systems, and depending on the application, IONEX can consume up to 75% less water, while the volume of ion exchange resin required can be reduced by up to 50%, offering significant savings. Actual savings would be calculated on a project by project basis using PuriTech’s bespoke system design capability.

A further comparison with alternative systems shows that a higher separation efficiency and product concentration can be achieved by using IONEX technology. Countercurrent fluid flow and recycling, together with uninterrupted process streams, guarantee high levels of recovery.

Market opportunities and applications

Plants based on IONEX technology are set to displace some fixed-bed units, and even other countercurrent systems which are now in use, because they are more cost-effective and require a smaller investment.

In some applications the capital investment on specific projects can be reduced by 20–40%, which illustrates a like-for-like comparison of a typical carousel system and an IONEX unit — both rated at 40 m3/h.

Further market opportunities for IONEX include replacing ‘old’ generation multi-port valves.

Various valve configurations and materials are available for specific applications. For instance, for a non-corrosive processing environment it is possible to use a standard stainless steel valve head with a polytetrafluoroethylene (PTFE) process disc, while one that is corrosive would require the system to be configured with a polyvinyl chloride (PVC) or polyvinylidenefluoride (PVDF) valve head and an adapted process disc. Hasteloy and Inconel are available for specialist applications.

IONEX is targeted at a diverse range of industries. In the wastewater sector it can effectively treat industrial effluents, removing small traces of toxic substances such as heavy metals and solvents. It also can be used to produce potable and ultrapure water. Other common uses are nitrate, arsenic and perchlorate removal. Other areas in which it may be applied include the electroplating, food processing, pharmaceutical and biotechnology, and petrochemical and chemical industries.

Factory acceptance testing [top]

Each ion exchange system that is manufactured undergoes factory acceptance testing (FAT) before it is delivered to a customer's site.

FAT includes static pressure testing procedures and hydraulic tests. The software that is used to control the IONEX system is also trailed and assessed at this stage to ensure that it operates correctly and meets all necessary requirements.

Clients are invited to attend the FAT, which gives them an opportunity to see directly what is involved.

Conclusions

PuriTech has assessed and analyzed the operational characteristics, performance and the way in which ion exchange systems are used, and has applied its findings to rethink ion exchange system design.

Realizing the growing market potential of ion exchange the company has created an ingenious mechanical device that not only improves liquid–resin contact efficiency, but also leads to a reduction in plant operating costs and capital expenditure.

IONEX is versatile, cost-effective and broadly applicable in a range of industrial settings either as a bespoke system or retrofitted unit.

Author [top]

Filip Rochette, PuriTech, Brasel 143, B-2480 Dessel, Belgium.

Tel: +32-495-574719, Fax: +32-14-371513

Email: sales@PuriTech.be
Web: www.PuriTech.be