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CO (Carbon Monoxide): Pollutant Profile

Direct answer: Carbon monoxide is a toxic, flammable combustion intermediate formed wherever carbon burns with insufficient oxygen or mixing. It is removed by catalytic oxidation to CO₂ — a strongly exothermic reaction whose practical design is dominated by light-off temperature, oxygen availability and exotherm control.

Definition

CO is a colorless, odorless gas; molar mass 28.01 g/mol; boiling point −191.5 °C (Literature Value). It binds hemoglobin far more strongly than oxygen, which is why emission and workplace limits treat it as a primary toxic hazard. In flue gas it indicates incomplete combustion — either oxygen starvation, poor mixing or quenched combustion.

Industrial sources

  • Sintering machines and pellet plants (iron & steel)
  • Waste incineration and medical waste incineration
  • Coke ovens and gas flares
  • Catalyst regeneration vents and FCC units
  • Incomplete combustion in boilers under load swings
  • Charcoal/activated carbon kilns and pyrolysis off-gas

Treatment challenges

  1. Light-off temperature — catalysts only work above their light-off point (T50/T90); cold starts and low-load operation may fall below it.
  2. Exotherm — CO oxidation releases heat; concentrated CO streams can raise bed temperature hundreds of degrees and must be managed by staging, dilution or heat recovery.
  3. Poisoning — sulfur, halogens, moisture and metal fumes degrade oxidation catalysts; upstream gas cleaning defines catalyst life.
  4. Peak vs average — compliance tests can occur at peak CO; sizing to average fails.

Suitable materials

  • Precious-metal catalysts (Pt, Pd) — lowest light-off, highest activity; see CO Catalyst Selection.
  • Base-metal catalysts (hopcalite-type, transition metal oxides) — lower cost, higher light-off, poison-sensitive.
  • Activated carbon does not oxidize CO at industrial scale; it is not a CO treatment material.

Suitable technologies

  • Catalytic oxidation — the default route for ppm-to-low-percent CO; see the CO Oxidation Complete Guide.
  • Thermal oxidation — for concentrated streams where the heat is usable.
  • Process integration — sintering machine flue gas recirculation combined with catalytic oxidation.

Operating conditions that matter

  • Inlet CO concentration and its peak/transient behavior
  • Gas temperature vs catalyst light-off (T50/T90)
  • Oxygen content — stoichiometric requirement is 0.5 mol O₂ per mol CO, with excess for kinetics
  • Space velocity and bed residence time
  • Dust, SO₂, HCl, moisture load

Data type: ranges quoted in the linked pages are Typical Value engineering references unless a specific field test is cited. See Data Classification.

Testing

Limitations

  • Below light-off temperature the catalyst does nothing; supplemental heating or bypass strategy required.
  • High-dust gas fouls the bed; dedusting is normally mandatory.
  • Very concentrated CO requires staged oxidation or thermal route; a single catalyst bed cannot absorb unlimited exotherm.
  • Halogen-containing streams need halogen-tolerant formulations or pre-scrubbing.