Regenerate mixed bed resin
Regenerating mixed-bed resin means that if the conductivity in the outlet of the ion exchanger cartridge or demineralization cartridge rises above the normal operating value, the mixed-bed resin (e.g. Lewatit NM60) must be reprocessed for further use. Typically, mixed bed resin provides a conductance of < 1 µS/cm. Even a slight increase to 3-5 µS/cm indicates that the demineralization cartridge in which the mixed bed resin is located is already in the discharge phase, i.e. the demineralization cartridge is exhausted and has therefore already been overrun. At this point, the mixed-bed resin should be regenerated, as undesirable substances, especially the most weakly bound ions such as corrosive chlorides or silicates that form deposits, are already leaving the mixed-bed resin at a disproportionately high rate compared to the inlet.
Mixed bed resin consists of two different fractions, a strongly acidic cation exchanger and a strongly basic anion exchanger. These must be separated for ion exchanger regeneration. It is therefore not possible to regenerate the mixed bed resin within the demineralization cartridge. The mixed bed resin must be removed from the demineralization cartridge for ion exchanger regeneration and separated into its two individual fractions. This is done in batches in large regeneration plants. Due to the density, the two fractions can be separated and then ideally be regenerated individually in two different columns. The strongly acidic cation exchanger is regenerated with hydrochloric acid and converted back to the H+ form, the anion exchanger is regenerated with caustic soda and converted back to the OH- form. However, other forms are also possible for special applications. The amount of chemicals used depends on the application and the condition of the resins. In the OH- form, a new anion exchanger emits an at leastundesirable fishy odour, trimethylamine, which must be removed in a cleaning cycle.
After the subsequent washing out of the regeneration chemicals with demineralized water up to <1 µS/cm or up to < 0.056 µS/cm, depending on the application, the two fractions of the mixed bed resin are mixed together again. Since the process cannot be carried out with a single 10-50L cartridge, as the amount of resin is too small, it is usually an open pool. This means that different demineralization cartridges of the same application are regenerated together, so-called mixing and blending. The individual demineralization cartridge receives back the proportion corresponding to its input volume. Any unavoidable resin losses due to ageing processes (especially in the anion exchanger with a typical service life of 4-7 years) are compensated for by rejuvenating the pool with new mixed bed resin. In rare cases, however, this is not possible due to contamination, impurities or ageing, and the ion exchanger needs to be replaced.
In contrast, there is also a so-called closed-pool regeneration for special applications (such as UPW mixed-bed resins after an electrodeionization system), in which the resins are not mixed with the resins of other customers. However, this must have a critical mass of typically 400 liters and must be agreed separately in advance.
The regular duration for the external regeneration of mixed bed resin in a central regeneration station for ion exchangers is regularly 2 weeks. However, in individual cases announced in advance, this can also be reduced to 1-2 days up to the same day. In principle, it is also possible to regenerate mixed bed resin yourself, but this is not recommended, as the instructions for regenerating ion exchangers show, as there are a number of things to consider with ion exchangers.
Would you like to have your mixed bed resin regenerated? Please ask about our mixed bed resin regeneration prices.
