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A process that we carry out is to remove metals from a polymer so that the amounts of 16 metals are all below 1 ppm. The process is carried out at 180C at around 10 bar. The metal ions are soluble in water, but the reason that a high temperature is used is that under theses conditions water is much less polar. It therefore is able to swell and plasticize the polymer so that the metals can more easily diffuse out of it.




A schematic diagram of the plant is shown, with temperatures at each point of the system. Water is supplied at 15C and is first heated by the water coming out of the cell. It then passes to a second heat exchanger where it is heated by oil to 180C before passing through the cell. On leaving the cell, the water is cooled by the incoming water.


Superheated water is not energy intensive. It takes only about one fifth of the energy to heat water from 15C to 180C as it does to convert water at 15C to steam at 100C. Further, heat can be recycled. By using the arrangement shown 82% of the heat is recovered and recycled.


The process is a low volume and high value and only 200 kg are processed in one batch. The cell has a volume of 700 L and the flow rate of water is 16 L per minute. 5 m3 of water are required for each batch of material. The plant is constructed of stainless steel.




A picture of the plant before cladding is shown above with the vessel, hopper, cold-water tank and ion exchange cylinders (for purifying the water) labelled. The heat exchangers are behind the bottom of the vessel and the oil heater is behind the product-collecting bath. A large compressor is required to dry the product after extraction.


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