Routine Ion Exchange Testing
Membrane Works now offer extensive Ion exchange (IX) resin testing services in our Sydney laboratory.
What are ion exchange resins?
Synthetic ion exchange resins are a copolymer of divinylbenzene (DVB) and either styrene or acrylic polymers. These are reacted chemically during manufacture to create anion or cation anion exchange sites by functionalizing the polymer skeleton. The active exchange sites are located not just on the surface of the resin but also on the inside. The result is small, insoluble and permeable beads of varying particle sizes. Each bead contains water that makes up approximately 50% of its weight. The polymer structure of the resin bead is wraparound, much like a ball of twine. Thus, water flows not just over the surface but also through the permeable bead.
Ion exchange resins are commonly used to demineralise make-up water in power stations,
to remove contaminants from drinking water and increasingly in process and mine water
Ion exchange resins are broken down into four broad categories:
- Strong Acid Cation Resins (SAC): strongly acidic, typically featuring sulfonic acid groups, e.g. sodium polystyrene sulfonate or polyAMPS,
- Strong Base Anion (SBA): strongly basic, typically featuring quaternary amino groups, for example, trimethylammonium groups, e.g. polyAPTAC),
- Weak Acid Cation (WAC): weakly acidic, typically featuring carboxylic acid groups,
- Weak Base Anion (WBA): weakly basic, typically featuring primary, secondary, and/or tertiary amino groups, e.g. polyethylene amine.
Who should be doing routine testing?
Ion exchange resins degrade over time and lose effectiveness. This is usually designed into a system and for smaller de-mineralising systems, for example a small industrial boiler, it often makes sense to simply replace the resin rather than spend money on assessing its performance.
However for a number of applications, having a system performing at its best is key to avoiding costly problems downstream. This is particularly of true in the power industry where silica must be removed to prevent deposition on turbine blades. Regular testing of ion exchange resin is recommended to ensure optimum performance of softeners, dealkalisers, condensate polishers, deionisers, ultrapure water systems and/or demineraliser systems. For critical systems an annual resin check is recommended by manufacturers. In other instances, an analysis may be done every few years, or when resin performance decline has been noticed.
Benefits to regular testing
The benefits to regular testing are:
- Understanding of remaining resin life, and replacement planning. This is especially important when resin lead times are long
- Ability to rotate resins to maximise life and use deteriorated resins in higher fouling areas
- Manage resin regeneration cycles to minimise waste water and costs
- Have a clear understanding of exchange capacity to avoid ion breakthrough when this cannot be tolerated
Routine Testing Suite
Our resin testing suite will help you both evaluate resin life for retirement planning, and solve performance issues such as poor regeneration or decreased adsorption capacity. Organic fouling is commonly encountered in many resins as is inorganic scaling or physical damage caused by mechanical or chemical shocks. We can help you identify these problems ensuring smooth operation in the years to come.
Routine ion exchange test list
The table below outlines our standard tests that are included in our routine testing suite.
|Resin beads can crack and degrade due to high pressure, osmotic shock or chemical damage. Broken beads fill voids to impede flow and increase bed pressure. Resin integrity uses microscopy to measure the percentage of broken and cracked beads as well as any fouling on the resin surface.
|Total Exchange Capacity (TEC)
|Over time, ion-exchange resins can lose functionality due to degradation or fouling. Total exchange capacity (TEC) first regenerates the resin to a known ionic form and then elutes these from the resin using an excess of a different reagent. Total Exchange Capacity is used to measure a resin's deterioration and determine if replacement is required.
|Measuring the exchange capacity of a resin directly after a plant regeneration allows us to determine regeneration efficiency. Comparing with the Total Exchange Capacity indicates whether regeneration can be improved or if a resin needs to be replaced. Field regenerated samples are expected to be in the range of 65-80% percent regeneration.
|Water Retention Capacity
|Measures the inherent water content of a fully hydrated resin by drying it in an oven. Elevated water content indicates degradation of the polymer chains and loss of cross-linking, while depressed water content typically results from accumulation of foulants on the beads.
An increase in Water Retention Capacity is a key indicator of oxidative damage.
|Measures the degree of extractable organic fouling accumulated on the resin. High levels of organics will inhibit exchange, leading to long rinse times. The expected fouling limits are:
< 5 mg/kg resin for resin less than 3 years operation
< 10 mg/kg resin for resins less than 5 years operation
> 10 mg/kg resin indicates replacement is required
|Measures the degree of extractable inorganic fouling on the resin. The results can help identify fouling or regeneration issues. High-impact foulants such as aluminium, iron and silica are also detected. As a general guide
< 400 ppm is considered low
> 400 to 3500 ppm is considered moderate
> 3500 ppm is considered heavy
|Measures the strong base (quaternary amine) sites on an anion resin. Salt-splitting sites are necessary to remove weak acid species such as bicarbonate and silica. A reduction in SSC typically indicates an increase in weak base capacity. Most significant loss of % strong base is traceable to organic fouling and leads to poor demineraliser performance