Feature 15Technology review 15Filtration+Separation July/August 2007

IONEX Technology

Since 1996, PuriTech has continuously refined its IONEX technology to meet increasing global demand from a range of industries for an enhanced and cost-effective ion-exchange process. PuriTech set out to improve existing ion-exchange technologies including fixed-bed and continuous counter current systems. The process can be applied to various applications in sugar processing as well as a number of other separation requirements in various industries.

Fixed bed resin vessels are used in around 90% of ion-exchange projects. Their design is based on batch operation but compared with continuous countercurrent systems their performance, in terms of treated water quality and cost-effectiveness, is relatively low. The environmental impact is higher as fixed bed units typically waste 2–4% of the treated fluid-flow.

Continuous counter current ion-exchange, which makes use of a turntable, offers an improved approach with some advantages over fixed-bed alternatives. This technology is well established but installation has been relatively expensive, requiring a turntable, or carousel, to rotate the resin vessels around a central valve. This requires complex control sequences to be programmed, controlled and monitored, adding to cost and complexity.

Based on an innovative valve design developed over a number of years, IONEX uses a single, multi-port distribution valve

(see Figure 1) as the key component of the process system. The technology is different from other continuous, counter current ion-exchange systems because instead of using a turntable to move large resin vessels, the process disc within the IONEX valve rotates around a central axis. This means that the vessels and pipework remain stationary whilst the valve distributes the different flow streams to the ion-exchange vessels in the different operational zones (see Figure 2).

Ion-exchange separation generally comprises two-phase mass-transfer. This includes an adsorption cycle and a desorption cycle, separated by washing or rinsing of the solid phase between these mass transfer steps. During a full rotation of the IONEX valve, each resin vessel is subjected to an entire asorption cycle, with part of the ion-exchange resin being continuously removed and regenerated, and then returned to the treatment system. The cycle consists of each vessel passing through the Adsorption Zone and the Regeneration Zone, with rinsing cycles taking place in between (see Figure 3). This approach eliminates long periods of down time for regeneration whilst maintaining consistent product and waste characteristics.

Rigid pipes can be used between the valve and ion-exchange vessels, which greatly simplifies sealing and eliminates the risk of leaks. Also, a simplified control unit can be used because the system does not use a turntable, and the vast array of automated valves seen on traditional fixed bed systems can be eliminated.

It is also possible to build compact systems based on the technology. The ion-exchange vessels can be positioned in any desired pattern, providing maximum installation flexibility. IONEX can be retrofitted to replace an existing ion-exchange system, regardless of where the ion-exchange vessels are placed. Also, easy access to the valve, the system’s only moving part, and the ion-exchange vessels, simplifies maintenance procedures.

Sugar applications

IONEX is well suited for use in the sugar industry as the process can be effectively integrated into the production of sucrose and glucose syrups.

Separation technology:

A solution for the sugar industry

ONEX is a patented continuous ion-exchange process that allows effective purification of cane sugar, sugar beet and corn syrup by using a combination of demineralising, decolourising and softening technology configurations. In this review, Peter Brewer describes how it operates and outline its applications in the food separation sector.

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Figure 1: IONEX multi-port valve following factory acceptance testing.

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Feature16Filtration+Separation July/August 2007

Technology review16

Sucrose (table sugar) is extracted from crops of cane sugar and sugar beet. Cane sugar production is restricted to tropical areas, whereas sugar beet production is common in temperate regions such as the UK. Glucose is extracted from corn starch to produce corn syrup. A series of three enzymatic reactions are used to convert the corn starch to corn syrup. Its major use is in commercially prepared foods as a sweetener and for its moisture-retaining properties which help to maintain freshness.

The major process applications for IONEX in the sugar industry are demineralisation and decolourising. Decolourising is typically used for removing colour in sugar cane and corn syrups. Demineralisation of sugar syrups is required to typically remove anions, cations and some organic components. Here, we concentrate on

demineralisation, which is usually used in the purification of sugar cane and corn syrup. The specific removal of calcium is required in the purification of sugar beet.

Demineralising

Demineralisation of syrup solutions using IONEX technology removes ash (calcium primarily), protein and colour, and contaminants associated with fertilizer such as phosphate, sulphate and potassium. The process also increases the long-term colour stability of the syrup and eliminates the need to add sulphur dioxide, which can cause allergic reactions. Two IONEX systems are typically used simultaneously to achieve demineralisation. One IONEX system contains the cation resin, and the second contains the anion resin.

In the Adsorption Zone, following an initial adsorption rinse, syrup is pumped into the IONEX cation unit first before passing through the IONEX anion unit to leave as a ‘de-ashed’ product. Treated syrup can be further purified using an additional adsorption pass on the cation and the anion units. Following adsorption and prior to regeneration, sweetening-off again takes place, the rinse water passing through the IONEX system in a counter-current flow pattern.

In the Regeneration Zone, dilute acid (for the cation IONEX) and alkali (for the anion IONEX) is used to regenerate the ion exchange resin. The positively charged hydrogen ions in the acid are exchanged for the cations removed from the syrup and adsorbed onto the resin. Negatively charged hydroxyl ions in the alkali regenerant are exchanged for anions and some organic molecules present. The Regeneration Rinse removes any residual chemicals. The rinse effluent is used to dilute the acid and alkali solutions, dilution taking place in line. If required a backwash zone can be employed to remove solid particles and fines that can accumulate in the resin.

Softening

The removal of calcium is required in the purification of sugar beet. The resin is initially loaded with calcium in the Adsorption Zone. As the valve rotates, the resin vessels that have been saturated with calcium move into sweeten-off before entering the Regeneration Zone. Here, resin is contacted with an acid solution and the calcium is replaced by hydrogen ions, thus regenerating the resin. After regeneration the resin enters the Regeneration Rinse zone to rinse out the acid using condensate. Rinse water can be re-used to dilute the acid.

Following the Regeneration Rinse, the resin enters an additional Conditioning Zone. Here resin is contacted with an alkali solution and the hydrogen ions are replaced by sodium ions. After the conditioning step the resin enters the Conditioning Rinse Zone to rinse out the alkali with the use of condensate. Again, rinse water is reused to dilute the alkali.

Conclusion

The IONEX system can easily be tailored to a number of applications in the sugar industry by using different types of resins and flow configurations, and chemicals in the Regeneration Zone including salt, acid and alkali. The continuous ion-exchange process can be applied to a number of other separation needs in various industries. •Contact:Peter Brewer is General Manager at PuriTech Limited. He can be contacted on:Tel: +44 (0) 7850 896 863Fax: +44 (0) 1756 709 560Email via www.puritech.co.uk

Figure 2: Stainless steel IONEX multi-port valve installed on a PuriTech continuous ion-exchange system.

Figure 3: Typical ion exchange vessel configuration.

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