Polymer adsorption

Synonyms, abbreviations and/or process names

n/a

Removed components

—  VOC

Diagram

Process description

During polymer adsorption, a polymer is used as absorbent. Essentially, they are small plastic balls.  The polymer costs approximately 20 times the price of activated carbon. As a result, polymers are only used for regenerative purposes.

Pores of varying sizes are created during the production of polymers. However, the smallest pores in a polymer are still larger than the micro-pores of activated carbon.

Polymers have low selectivity to VOC adsorption. Though every polymer is better at adsorbing a particular VOC. Polymers also have a high adsorption capacity.

The polymer is used in a fixed-bed to collect VOC. The saturation and evolution of the adsorption zone is the same as with activated carbon.

Polymers have a linear adsorption isotherm. In other words, their adsorption capacity rises in proportion to the partial pressure of the VOC in flue gases. The higher the pressure in flue gases and the higher the concentration in the flue gases, the higher the VOC per kg that can be adsorbed.

Variants 

Polymers can be used in combination with activated carbon and zeolites. This is possible in series, whereby polymers collect high concentrations in the first phase and zeolites collect low concentrations in the second phase – as in a mixed bed.

Efficiency

A well-designed adsorption process has an efficiency of 95 – 98 % for inlet concentrations of 500 – 2000 ppm [2].

The following concentrations are stated for formaldehyde [4]:

—  In-going: 16.6 – 20.5 ppmv
—  Out-going: 0.5 -0.7 ppmv

Boundary conditions

—  Low flue gas temperature
—  Dust content must be low to prevent the bed from blocking
—  Maximum 25 % of lowest explosion limit
—  For regeneration, the temperature must lie above the boiling point of the VOC, but below the melting point of the
      polymer.
—  Moisture content is less critical than for activated carbon

Auxiliary materials

Periodic replacement is rare because polymers are used for regenerative purposes.

Environmental aspects

When the polymer is replaced, the plastic must be destroyed.

Energy use

No specific usage. See regenerative adsorption.

Cost aspects

  • Investment
    —  No info

Advantages and disadvantages

  • Advantages
    —  Simple and robust technology
    —  Simple desorption of the VOC
    —  High adsorption capacity
    —  No chance of catalytic reactions that cause spontaneous combustion
    —  Long life-span
    —  Low moisture-sensitivity
    —  Suitable for discontinuous processes
    —  Easy to maintain
    —  Easy to place
  • Disadvantages
    — 
    Dust can lead to blockages
    —  Component mixes may lead to early malfunction
    —  High initial costs

Applications

The technology is used in regenerative adsorption.

Outlined areas for implementation are:

—  OSB industry for formaldehyde and VOC removal
—  Removal of styrene

References

  1. “Solvent capture for recovery and re-use from solvent laden gas streams”, Environmental Technology Best Practice programme, guide GG 12
  2. EPA technical bulletin: “Choosing an adsorption system for VOC: carbon, zeolite, or polymers?” May 1999
  3. BREF: "Common waste water and waste gas treatment /management systems in the chemical sector" EIPPC, February 2002
  4. Supplier information
  5. J. Van Deynze, P. Vercaemst, P. Van den Steen and R. Dijkmans., “Best Available Techniques for paint, varnish and printing ink”, 1998