BUDAPEST
FACULTY
UNIVERSITY OF TECHNOLOGY AND ECONOMICS
OF CHEMICAL AND
BIOCHEMICAL ENGINEERING
DEPARTMENT OF
ENVIRONMENTAL
CHEMICAL AND
PROCESS
ENGINEERING
HALOGENATED
HYDRO-CARBONS
Authors: Dr. Bajnóczy Gábor
Kiss Bernadett
Tonkó Csilla
The pictures and drawings of this
presentation can be used only for
education !
Any commercial use is prohibited !
Origin of halogenated hydrocarbons


Application is banned in the field of industry and agriculture in
developed countries
Effect of previous/earlier emissions are long-term (ozone layer
depletion)
Most toxic:


Polychlorinated dibenzo-dioxin (PCDD)

Polychlorinated dibenzo-furan (PCDF)
Environmental aspect:
1.
Degradable in troposphere (e.g. methyl-chloride, methylbromide etc.)
2.
Only degradable in stratosphere → characteristic property:
there is no hydrogen atom, double bond in the molecule, e.g.
chlorofluorocarbons.

Used in largest volume : CFC-11 (CFCl3) and CFC-12 (CF2Cl2),
and the quantity used more than 80 % is in atmosphere.
Nomenclature of compounds
CFC (chlor, fluor carbon gases)


nineties rule
Number after CFC +90 = the first digit is the carbon atom number, the
second is the hydrogen atom number, the third is fluorine atom number.
Chlorine atom can be calculated, if double or triple bond and aromatic ring
aren’t in the molecule.
E.g. CFC-11 11+90= 101 (1 piece C, 0 piece H, 1 piece F and Cl
piece 3).
Brominated hydrocarbons, halons: fire extinguishing agent and flame

retardant (H-1301 CF3Br , H-1211 CF2BrCl ).
nomenclature of bromine contant halons: H-wxyz, where w: carbon atom
number, x: fluorine atom number, y: chlorine atom number, z: bromine atom
number.
Natural sources


Atmosphere (largest volume): methyl chloride
Above the sea: in lower layer of troposphere there is
much more than in the upper layer. Over land: there is
no atmospheric stratification
Sea is a source of methyl chloride
e.g. biological activity of algae
Air: 0,6ppbv → majority: natural resource
Methyl-bromine and chloroform: much less quantity
Carbon tetrachloride: anaerobic process (e.g. in biogas)
Human sources
Primary sources: significant decrease
application area:
 Chlorinated hydrocarbons:
 Degreasing (methyl-chloroform, carbon tetrachloride,
dichloroethane)
 Dry cleaning (perchloroetylene)
 Chemical industry
 Pharmaceutical industry
 Chlorofluorocarbons (CFC gases)
 Foaming agent
 Propellant gases
 Operating agent in refrigerator
 Brominated hydrocarbons:
 Fire extinguishers
 Fire retardants (tetrabromobisphenol A /TBBA/ és decabromodiphenylether /DBDPE/.
Secondary sources:
e.g. biomass firing: source of easily volatile chlorinated
hydrocarbons
Formation of halogenated hydrocarbons


Significant part: evaporation without control.
Other part: burning of fossil fuels, biomass, household and dangerous
waste. Due to variable chlorine content chlorinated hydrocarbons and
hydrochloric acid are formed.
éghető
anyag
klórtartalma material
chlorineNéhány
content
of some
combustible
Fuel
•
Chlorine %
Flammable material
Chlorine %
0.01– 0,2
Communal waste
0,05 – 0,25
Fuel oil
0,001
Hospital waste
1–4
Biogas
0,005
Electronic waste
0,1 – 3.5
Cortex, bark
0,02 – 0,4
PVC (Polyvinylchloride)
50
Paper, textile
0,1 – 0,25
Communal waste water sludge
0,03 – 1
Tree
0,001
Herbaceous plants
0,5 – 1,5
Natural gas
Not significant
Burning:
Lignite, coal
In fossil fuels: chlorine in form of (K-, Na- and Ca-chloride)
In biogas: in form of carbon tetrachloride
In waste: in form of organic bond (e.g. PVC derivatives).
The flue gas contains mostly hydrochloric acid, elemental chlorine and alkalichlorides
Formation of hydrochloric acid in flue gas

The non-arboreal biomass fuel has high chlorine (organic and inorganic)
content due the application of fertilizer.

Release of HCl happens in two temperature steps: 250 – 400 °C and over
700 °C

Inorganic chlorides form hydrochloric acid at high temperature
KCl + H2O <=> HCl + KOH
KCl + CO2 + H2O <=> K2CO3 + 2HCl

Hydroxide, carbonate and chlorides : condenses in the heat exchanger

hydrochloric acid
chimney
atmosphere
Formation of chlorine from HCl in the flue gas
I. Deacon reaction
2 HCl + ½ O2 <=> Cl2 + H2O (slow)

Metal oxid catalyst:
1.
Hydrochloric acid + metal → metal chloride
2.
Metal chlorine + O2 → metal-oxid + chlorine
II. Another possible way:
HCl + OH• <=> H2O + Cl
HCl + O <=> OH• + Cl
Effect of HCl in the flue gas
The combustion of loose structure fuels results in increased
amount of carbon monoxide in the exhaust gas
The HCl in the exhaust gas
significantly retards the
transformation of carbon
monoxide to carbon dioxide
CO + OH• <=> CO2 + H
HCl + OH• <=> H2O + Cl
competitive reaction
rate of CO oxidation in the presence of HCl
Source: Desroches-Ducarne 1997
Effect of Cl and HCl on the metallic structure
of the boilers
Corrosion rate of austenitic steel alloy
▼
Source: Breyers 1996
▲
Effect of dry chlorine and HCl on
carbon steel alloy
The outer surface temperature of the heat exchanger tubes must be under 450 °C
and must be over 80 °C, because of the danger of HCl condensation.
Chlorinated hydrocarbons

Deacon reaction in firebox
→ formation of elemental chlorine creates a
possibility to form chlorinated hydrocarbons
CxHy + Cl2 = CxHy-1Cl + HCl

Most dangerous species:
 Polychlorinated dibenzodioxin (PCDD)

Polychlorinated dibenzofuran (PCDF)
DIOXINS

Chlorinated aromatic hydrocarbons

Polychlorinated dibenzodioxin (PCDD)

Polychlorinated dibenzofuran (PCDF)
Natural resources
- forest fires
- bacterial activity
2,3,7,8- tetrachlorodibenzodioxin
75 pieces
Anthropogenic sources
- chemical
- waste burning
- fossil and biomass power plant
2,3,7,8- tetrachlorodibenzofurane
135 pieces
DIOXINS
Toxic effect depends on the chlorine content

Number of chlorine substituents < 4 chlorine: PCDD/PCDF aren’t
considered to be toxic

Number of chlorine substituents = 4: symmetrically substituted,
is the most toxic ; 2,3,7,8-tetrachlorodibenzodioxin
2,3,7,8- tetrachlorodibenzodioxin

Number of chlorine substituents > 4: growing number of chlorine
substituents makes the PCDD/PCDF less toxic.
DIOXINS
Expression of toxicity : toxic equivalent factor (TEF):
Proved to be toxic: 7 pieces PCDD and 10 pieces PCDF
TEF of PCDD and PCDF
PCDD
TEF
PCDF
TEF
2,3,7,8-TCDD
1
2,3,7,8-TCDF
0,1
1,2,3,7,8-PCDD
0,5
1,2,3,7,8-PCDF
0,05
1,2,3,4,7,8-HxCDD
0,1
2,3,4,7,8-PCDF
0,5
1,2,3,6,7,8-HxCDD
0,1
1,2,3,4,7,8-HxCDF
0,1
1,2,3,7,8,9-HxCDD
0,1
1,2,3,6,7,8-HxCDF
0,1
1,2,3,4,7,8,9-HpCDD
0,01
2,3,4,6,7,8-HxCDF
0,1
1,2,3,4,6,7,8,9-OCDD
0,001
1,2,3,7,8,9-HxCDF
0,1
1,2,3,4,6,7,8-HpCDD
0,01
1,2,3,4,7,8,9-HpCDF
0,01
1,2,3,4,6,7,8,9-OCDF
0,001
At the begining of PCDD/PCDF : T, P, Hx, Hp, O are the abbreviations of
Greek numbers; tetra, penta, hexa, hepta, okta
Notice,chlorine substituents in 2,3,7,8 proved to be toxic
Dioxin concentration
The concentration is given in Toxic Equivalent (TEQ)
conc.
ng/Nm3
TEF
product
arithmetical
TEQ
2,3,7,8-TCDD
2
1
2x1
2
1,2,3,6,7,8-HxCDD
10
0,1
10 x 0,1
1
2,3,4,7,8-PCDF
12
0,5
12 x 0,5
6
1,2,3,4,6,7,8,9-OCDD
100
0,001
100 x 0,001
0,1
Measured dioxin
Unit: ng TEQ/Nm3
9,1
PCDD/PCDF (TEQ) = ∑ (PCDD/PCDF concentration)k x (TEF)k



Limit value of dioxin concentration in flue gas: 0,1 ng TEQ/Nm3, (O2 11 tf%)
Limit value is valid in case of burning of human products e.g. waste
burning.
The coal and a biomass burning result in order of magnitude more
dioxin emission, but this hasn’t limit value.
Formation of dioxins

manufacturing of chemical products
 Production of chlorinated organic compounds
 Organic compound + chlorine
 paper bleaching
 corkwood bleaching

Thermal resources
 Burning in the presence of chlorine source
 Sintering

Other resources
 municipal waste water sludge
Formation of PCDD/PCDF
Preconditions: chlorine source (e.g. PVC, alkali-chloride) and hydrocarbons
- thermal decomposition of dioxins starts T >850°C
- decays totally over 1200 °C
- reformation of dioxins in the slow cooling flue gas, de novo synthesis
How could almost ruin a famous wine region
by a biomass plant
Planned biomass power plant
In the vicinity of vineyard
Dioxin emission towards the vineyards
Dioxin emission is not restricted
by the EU regulations
if natural products are incinerated.
Nevertheless the dioxin emission exists.
straw with high
chlorine content
The wine competitor companies would ruin
the reputation of the famous vineyard
Halogenated hydrocarbons in atmosphere
Hydrogen-containing halogenated hydrocarbons decay in troposphere
possibility: reaction with hydroxyl radical, chlorine → hydrochloric acid
Hydrogen free halogenated hydrocarbons: excessively stable


Decomposition begins in stratosphere
High energy UV photons → halogenated hydrocarbon radical + chlorine atom
CF2Cl2

175-185 nm
CF2Cl* + Cl
Chlorine atom speed up ozone decomposition
Cl + O3 = ClO• + O2
ClO• + O = Cl + O2
O3 + O
Cl
2 O2
Halogenated hydrocarbons in atmosphere

Ozone layer depletion: bromine more effective (25%)

Reason:



carbon compounds containing only fluorine atom (perfluoro
compounds) are stable



HOCl is a storage of active chlorine atoms, effect of sunshine releases
chlorine
HOBr: not stable in stratospheric conditions, the presence of bromine is
continuous
in stratosphere – no decomposition
in mesosphere – photo decomposition
Halogen-containing compounds:

varying degrees of risk on the ozone layer

„ozone depletion potential” (ODP), reference CFC-11 → ODP = 1
Halogenated hydrocarbons in atmosphere
Hydrogen-containing CFC compounds are short life.
Hydrogen atom free CFC compounds have more ozone depletion
potential and greenhouse effect.
Perfluorinated hydrocarbons don’t decompose the ozone layer, but the
greenhouse effect is significant.
Ozone depletion potential (ODP) and global warming potential (GWP) of CFC compounds
compound
life (year)
CO2
ODP
GWP
0
1
CFC-11
50
1.0
4680
CFC-12
102
0,82
7100
CFC-113
85
0,9
6030
HCFC-141b
9,4
0,1
713
CF4
>50000
0
6500
CH3Br
1,3
0,6
144
Effect of halogenated hydrocarbons on
plants


Atmospheric concentration is not dangerous.
Halogenated hydrocarbons → hydrochloric acid
(not significant) – environmental acidification
Effect of halogenated hydrocarbons on
people

Chlorinated hydrocarbons: used as solvent for a long time:



toxic
carcinogenic effect
limited use → health hazard work exposition decreased or ceased

Toxic of CFC compounds is variable (bromine derivatives are
significant toxic – fire extinguisher.

In spite of the prohibition of halogenated hydrocarbons the most
toxic PCDD and PCDF compounds are existing

acute effect – well-known
atmospheric concentration – chronic effect is being examinated

Restriction of halogenated hydrocarbons
formation


Chemical industry:

Halogenated compounds – substitution on the field of
production and application

Chlorine – substitution with chlorine-dioxide in oxidation
reactions
Combustion technologies:

Restriction of the formation of hydrochloric acid and dioxins,
and/or effective removal from flue gas

adsorption of hydrochloric acid in combustion chamber

PCDD/PCDF compounds – utilization of increased absorption
ability
Hydrochloric acid reducing technologies
SORBENT INJECTION IN FLUE GAS
calcium-carbonate, calcium-oxide, calcium-hydroxide, sodiumcarbonate, sodium-hydrocarbonate
CaCO3 + 2 HCl <=> CaCl2 + CO2 + H2O
CaO + 2 HCl <=> CaCl2 + H2O
Ca(OH)2 + 2 HCl <=> CaCl2 + 3 H2O
Na2CO3 + 2 HCl <=> 2 NaCl + CO2 + H2O
NaHCO3 + 2 HCl <=> 2 NaCl + 2 CO2 + 2 H2O

The method is suitable for sulfur-dioxide absorption

T > 770 oC (melting point of calcium-chloride): reduction of
hydrochloric acid is only 10 - 40 % in flue gas, due to the sorbent
melting

Better results with sodium-based sorbents
Reduction of halogenated hydrocarbon
emission
Any particle separator method is a dioxine emission reducing method
1. Most effective: bag filter t < 180 °C
2. Electrostatic dust separator
3. Fast cooling of flue gas with water (quenching)
effective method but heat energy is lost
4. DENOX method,
The technology is applied for NO reduction, but the ammonia
deactivates the surface of copper (catalyst) decreasing the
formation of dioxins.
5. Direct adsorption

On activated carbon bed at 100 – 150 °C