Mass Exchangers

1
Mass Exchangers

• Direct-contact mass-transfer unit
• Utilizes a Mass Separating Agent (MSA) to
  selectively remove pollutants from rich streams
  (waste streams).
• The MSA should be partially or completely
  immiscible in the rich phase.

2
Mass Exchangers

• Absorption, liquid solvent removes certain
  components from a gas.
• Examples
• Desulfurization of flue gas using alkaline
  solutions.
• VOCs recovery using light oils
• NH3 removal from air using water.

3
Mass Exchangers

• Adsorption, a solid adsorbs specific components
  from a gaseous or liquid solution.
• Examples The use of granular activated carbon
• For the removal of benzene/toluene/xylene
  mixture from underground water.
• Separation of ketones from aqueous wastes of
  an oil refinery.
• Recovery of organic solvents from the exhaust
  of polymer manufacturing facilities.

4
Mass Exchangers

• Extraction, employs a liquid solvent to remove
  components from other liquid.
• Examples Wash oils are used
• To remove phenol and polychlorinated biphenyls
  from aqueous wastes of synthetic-fuel plants.
• To remove Chlorinated hydrocarbons for organic
  wastewater.

5
Mass Exchangers

• Ion Exchange, cation and/or anion resins are
  used to replace undesirable anionic species in
  liquid solution with non-hazardous ions.
• Examples Removal of dissolved metals, cyanides,
  phenols, and halides from wastewater.
• Cation-exchange resins may contain mobile,
  positive ions such as, Na or H which are
  attached to immobile acid groups, such as
  sulfonic or carboxylic. Anion-exchange, OH- or
  Cl- attached to amine.

6
Mass Exchangers

• Leaching, selective solution of specific
  components of a solid mixture when brought in
  contact with a liquid solvent.
• Examples Removal of metals from solids or sludge.

7
Mass Exchangers

• Stripping, desorption of relatively volatile
  components from liquid or solid streams using a
  gaseous MSA.
• Examples
• Recovery of VOCs from wastewater using air.
• Removal of NH3 from wastewater using steam.
• Regeneration of spent activated carbon using
  steam or N2.

8
Mass-Exchange Network Synthesis

• Given a number NR of waste (rich) streams
  (sources) and a number NS of MSAs (lean streams),
  it is desired to synthesize undesirable species
  from the rich streams to the MSAs.