Saturday, 28 January 2017

Experimenting with ion exchange resins requires a simple setup and a few basic precautions.

Laboratory trials and setup

Introduction

Experimenting with ion exchange resins requires a simple setup and a few basic precautions.
Resin volume
For most applications, resins are used and measured by volume, not by weight. A quantity of 50 to 250 ml of resin is usually sufficient to perform efficiency and capacity tests.
Basic setup
The laboratory setup shown here can be used as an example. More sophisticated arrangements including pumps and regeneration equipment are also used. The basic setup includes:
  1. A tank containing the solution to be treated.
  2. A small tap or a rubber tube with a screw clamp to control the flow rate.
  3. A column fitted with a rubber stopper.
  4. The ion exchange resin to be tested.
  5. The bottom of the column must be fitted with fritted glass. Another option is a second rubber stopper covered with a nylon cloth and a small layer of glass beads.
  6. Another small tap.
  7. The bottom tank collects the treated solution.
The column diameter should be selected so as to have a resin bed depth of 300 to 800 mm. In most cases, this means a diameter of 20 to 25 mm. Glass or plexiglas columns are usually suitable. Glass columns should be avoided when resins are regenerated with caustic soda. The volume of resin should be measured with sufficient precision. As in small columns, a wall effect may affect the results, you can weigh a resin quantity, transfer it to a graduated cylinder, tap it gently on a rubber mat and measure the volume.
The operating capacity of the resin can be calculated using the information in the capacity page.

The picture shows a quantity of solution above the resin bed. It is most important never to let the column run dry, otherwise the hydraulic distribution may be disturbed and the resin may be damaged. Regeneration of the resin can be carried out in the same equipment. Regeneration steps include:
  • Backwash (optional)
  • Regenerant injection
  • Regenerant displacement
  • Rinse
  Recommended operating conditions
Resin volume50 to 250 ml
Column diameter20 to 30 mm
Resin bed depth150 to 800 mm
Loading flow rate2 to 40 BV/h
Regenerant flow rate2 to 5 BV/h
Regenerant contact time20 to 60 minutes
Regenerant displacement2 to 4 BV of water
Final rinse2 to 10 BV at service flow rate
The flow rate is expressed in bedvolumes per hour (BV/h), i.e. in litres of solution per litre of resin per hour. In general, the highest the concentration of contaminants to remove, the lowest the flow rate to use. When filling the column with resin, a short backwash with deionised water is recommended to ensure proper packing and classification of the bed.

More than one cycle may be required

To determine the operating capacity and the leakage, it is often necessary to perform several cycles of exhaustion and regeneration. The first run made with a new, totally regenerated resin, produces generally a higher capacity and a lower leakage. After two or three cycle, an equilibrium is obtained, and the subsequent cycles should be more or less identical.
 
Lab columnsGlass columns in the Lanxess laboratory

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