Carbon monoxideCarbon monoxide

Authors: Dr. Bajnóczy Gábor

Kiss Bernadett

BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS

DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING

FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING

The pictures and drawings The pictures and drawings of this presentation can be of this presentation can be used only for education !used only for education !

Any commercial use is Any commercial use is prohibited !prohibited !

Carbon monoxideCarbon monoxide

Some physical properties of COMoolecular mass 28.01

Melting point -199 oC

Boiling point -191.5 oC

density0 0C, 101.3 kPa

25 0C, 101.3 kPa1.250 g/dm3

1.145 g/dm3

Solubility in water*

0 0C20 0C

25 0C

3.54 cm3/100 cm3 (44.3 ppmm)**

2.32 cm3/100 cm3 (29.0 ppmm)**

2.14 cm3/100 cm3 (26.8 ppmm)**

Low and high flamabilitylimits

12,5 – 74,2 tf %

Conversion factors0 0C, 101.3 kPa

25 0C, 101.3 kPa

1 mg/m3 = 0.800 ppmv***

1 ppm = 1.250 mg/m3

1 mg/m3 = 0.800 ppmv***

1 ppm = 1.250 mg/m3

* volume of CO in STP ** mass/mass*** volume/volume

•colorless

•odorless

•tasteless

•Burns with blue flame

Most abundant and widely distributed pollutant in the lower atmosphere

It has a density 96.5% that of air

low

Wide range

Reversible effect in small concentration

Sources of carbon monoxideSources of carbon monoxide

Natural <=> Antropogenic ( 10-50% of the total)

Differences: Distribution:

1. Natural sources: distributed throughout the world

2. Anthropogenic sources: concentrated in small area

Rates of formation:

1. Natural conditions:rate of formation ≈ rate of elimination

1. In the vicinity of antropogenic sources (towns, industrial areas):rate of formation > rate of elimination (accumulation)

Natural sources of carbon Natural sources of carbon monoxidemonoxide

Indirect sources: mud, bogs ►anaerob conditions ►methane formation from the decay of organic materials

The surface of oceans is supersaturated in carbon monoxide:

Algae and other biological sources.

Decay of chlorophyll in the soil

Mud, oceans, chlorophyll… The majority of CO is indirect origin:

oxidation of methan ► CO!

organic materials methane

Sources of natural carbon Sources of natural carbon monoxidemonoxide

Anaerob conditionsBiological decay

CO

OH *

Formation CO from methaneFormation CO from methane

1. CH4 + •OH = •CH3 + H2O

2. •CH3 + O2 + M = •CH3O2 + M *

3. •CH3O2 + NO = •CH3O + NO2

4. •CH3O + O2 = HCHO + •HO2

5. HCHO •H + •HCO6. •HCO + O2 = CO + •HO2

HCHO + •OH = CO + •HO2 + H2O

λ<338nm

Strong oxidation character

Lifetime: some hours 4-6 ppbv

•H + O2 + M = •HO2 + M *•HO2 + NO = •OH + NO2

Reactions of the other formed radicals

CO from anthropogenic sourcesCO from anthropogenic sources

1. Transportation: Internal combustion engines (~75%)

2. Agricultural burning: (~ 10%)3. Industrial process losses: Steal

industry, carbon black production, petroleum refineries (~ 10%)

4. Fuel combustion – stationary sources: coal, fuel oil, natural gas, wood(~ 1%) Low CO → greater efficiency

Chemistry of the CO formationChemistry of the CO formation

The formation of anthropogenic CO is generally the result of the following chemical processes:

1. Incomplete combustion of carbon or carbon containing compounds

2. High temperature reaction of glowing carbon and carbon dioxide

3. Dissociation of carbon dioxide at high temperature

Incomplete combustion of carbon or Incomplete combustion of carbon or carbon containing compoundscarbon containing compounds

ORIGIN OF THE RADICALS IN THE FLAME H2O → H + OH* thermal decay O2 → 2 O thermal decay CxHy → CxHy-1 + H thermal destruction O + H2O → 2 OH*

650ºC alatt leáll

Stops under 650 °C

Incomplete combustion of carbon Incomplete combustion of carbon or carbon containing compoundsor carbon containing compounds

Fuel and air are poorly mixed

Localized areas of oxygen deficiency

Accumulation of CO

Optimized combustion conditions:

air excess ratio (n) = ▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬Actual input of air

Theoretical need of air input for the perfect combustion

Incomplete combustion of carbon or Incomplete combustion of carbon or carbon containing compoundscarbon containing compounds

• n = 1 : In case of perfect mixing the available lowest CO content

• n < 1 : the amount of oxygen is not enough for the CO → CO2 transformation

• n > 1 : too much air cools down the combustion chamber and residence time is decreasing. There is not enough time for the slow CO → CO2 reaction.

CO2 + C = 2 CO Reduction of iron ore: CO + iron oxide iron

a part of it escapes into the atmosphere

Coal in the fire box:Air input is limited suddenly

CO accumulation

CO concentration is above the low flamability limit

CO & air is exploded from the glowing carbon

Reaction of glowing carbon with carbon Reaction of glowing carbon with carbon dioxidedioxide

reduction

Dissociation of carbon dioxideDissociation of carbon dioxide

In spite of the perfect burning conditions carbon monoxide is present because of the dissociation of carbon dioxide:

CO2 <=> CO + O

The temperature increase shifts the equilibrium towards the CO

Eg. 1745 ºC 1% , 1940 ºC 5 %

The quick cooling of the hot gases results in untransformed CO. (There is no time to be transformed. At low temperature the rate of the reaction is very slow, can be neglected.)

The fate of atmospheric COThe fate of atmospheric CO

The CO concentration should be doubled within 4-5 years

The CO concentration is nearly constant in the troposphere ► effective elimination reaction must exist.

A hydroxyl radicals ~ 40% CO is oxidized

CO + OH• → CO2 + H•

The fate of atmospheric COThe fate of atmospheric CO

Condition:

CO uptake by the soil Different microscopic fungi CO → CO2 CO uptake 0 – 100 mg CO/(hour m2 ) The rate of uptake depends on the organic

content of the soil.

O3 nm310 O*+ O2

*

O* + H2O = 2 ∙OH

CO + • OH = CO2 + H

The CO uptake by the soil types I.The CO uptake by the soil types I.

~ 0 mg CO/m2hour

~ 100mg CO/m2hour

The CO uptake by the soil types The CO uptake by the soil types II.II.

significant CO uptake

CO uptake is low

The CO uptake is restricted in the town. The soil is covered or severely polluted

Effects of CO on plantsEffects of CO on plants

No detrimental effects have been detected. Urban air : 50-60 ppm → no problem

Effects of CO on HumansEffects of CO on Humans

The oxygen uptake is restricted

Hemoglobin (Hb): O2 and CO2 transport.

CO2Hb in the lung, CO2 is exchanged to O2,

O2Hb in the tissue, O2 is exchanged to CO2

CO2Hb + O2 O2Hb + CO2

In COHb the bond is 250 times stronger

Effects of CO on HumansEffects of CO on Humans

The COHb content of the blood depends on the CO concentration of the air, the physical activity and the residence time in the polluted area.

Control of CO pollutionControl of CO pollution Transportation is mainly responsible

Solutions: Perfect mixing of air and fuel. The maximum has been reached. Slow cooling of the exhaust gases. It is not possible Quick oxidation to CO2: catalytic transformation of carbon

monoxide to carbon dioxide

Combustion of coal, oil, gas and biomass: The emission is restricted officially.

Emission limits for different fuels in Hungary [mg/Nm3]Output range 140 kW-50 MW regulation number: 23/2001 KöM

Solid fuel Liquid fuel Gas fuel

Carbon monoxide 250 175 100

Control of CO emissionControl of CO emission

Combustion devices, the CO depends on:

Particle size of the fuel (greater the size, higher the CO emission)

Structure of the solid fuel (airy, loose structure eg. straw, local oxygen deficiency in the bulk)

Mixing of air and fuel (perfect mixing results in low CO emission)

Air excess ratio (lack of oxygen or low temperature and residence time)

Residence time at high temperature (longer residence time at high temperature decreases the CO emission)

Control of CO emission: boilersControl of CO emission: boilers

Thermal afterburner

Min. temp: 850 °C

Min. residence time: 2 sec

heat exchanger

flue gas with high CO content

preheatedflue gas

afterburner

gas burner

Control of CO pollution: Control of CO pollution: transportationtransportation

Will be discussed later. ( See: hydrocarbons)