HALOGENATED HALOGENATED HYDRO-CARBONSHYDRO-CARBONS
Authors: Dr. Bajnóczy GáborKiss BernadettTonkó Csilla
BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS
DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING
FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING
The pictures and drawings of this presentation can be used only for education !
Any commercial use is prohibited !
Origin of haloOrigin of halogenated genated hydrocarbonshydrocarbons
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, methyl-bromide 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 Nomenclature of compoundscompounds
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 sourcesNatural sources Atmosphere (largest volume): methyl chloridemethyl 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 chloridemethyl 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 sourcesHuman sourcesPrimary 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
decabromo-diphenylether /DBDPE/.
Secondary sources: e.g. biomass firing: source of easily volatile chlorinated
hydrocarbons
Formation of halogenatedFormation of halogenated hydrocarbonshydrocarbons
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.
• Burning:
Néhány éghető anyag klórtartalma
Fuel Chlorine % Flammable material Chlorine %
Lignite, coal 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
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 alkali-chlorides
chlorine content of some combustible material
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 + KOHKCl + CO2 + H2O <=> K2CO3 + 2HCl
Hydroxide, carbonate and chlorides : condenses in the heat exchanger
chimney atmosphere hydrochloric acid
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 + Clcompetitive 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
▼
▲Effect of dry chlorine and HCl on
carbon steel alloySource: Breyers 1996
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 hydrocarbonsChlorinated 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)
DIOXINSDIOXINS Chlorinated aromatic hydrocarbons
Polychlorinated dibenzodioxin (PCDD)
Polychlorinated dibenzofuran (PCDF)
75 pieces 135 pieces
Natural resources- forest fires- bacterial activity
Anthropogenic sources- chemical- waste burning - fossil and biomass power plant
2,3,7,8- tetrachlorodibenzodioxin 2,3,7,8- tetrachlorodibenzofurane
DIOXINSDIOXINS
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
Number of chlorine substituents > 4: growing number of chlorine substituents makes the PCDD/PCDF less toxic.
Toxic effect depends on the chlorine content
2,3,7,8- tetrachlorodibenzodioxin
DIOXINSDIOXINS
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
Expression of toxicity : toxic equivalent factor (TEF):
Proved to be toxic: 7 pieces PCDD and 10 pieces PCDF
Dioxin concentrationDioxin concentration
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.
Measured dioxinconc.
ng/Nm3TEF
product arithmetical
TEQ
2,3,7,8-TCDD 2 1 2 x 1 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
Unit: ng TEQ/Nm3 9,1
The concentration is given in Toxic Equivalent (TEQ)
Formation of dioxFormation of dioxiinsns
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 oFormation of PCDD/PCDFf PCDD/PCDFPreconditions: chlorine source (e.g. PVC, alkali-chloride) and hydrocarbons
- thermal decomposition of dioxins starts T >850°C- thermal decomposition of dioxins starts T >850°C - decays totally over 1200 °C - decays totally over 1200 °C - reformation of dioxins in the slow cooling flue gas, - reformation of dioxins in the slow cooling flue gas, dde novo synthesise novo synthesis
How could almost ruin a famous wine region by a biomass plant
Planned biomass power plantIn 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.
The wine competitor companies would ruin the reputation of the famous vineyard
straw with high chlorine content
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 CF2Cl* + Cl
Chlorine atom speed up ozone decomposition
Cl + O3 = ClO• + O2
ClO• + O = Cl + O2
O3 + O 2 O2
175-185 nm
Halogenated hydrocarbons in Halogenated hydrocarbons in atmosphereatmosphere
Cl
Halogenated hydrocarbons in Halogenated hydrocarbons in atmosphereatmosphere
Ozone layer depletion: bromine more effective (25%)
Reason: 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
carbon compounds containing only fluorine atom (perfluoro compounds) are stable 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 Halogenated hydrocarbons in atmosphereatmosphere
Ozone depletion potential (ODP) and global warming potential (GWP) of CFC compounds
compound life (year) ODP GWP
CO2 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
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.
Effect of halogenated Effect of halogenated hydrocarbons on plantshydrocarbons on plants
Atmospheric concentration is not dangerous. Halogenated hydrocarbons → hydrochloric acid
(not significant) – environmental acidification
Effect of halogenated Effect of halogenated hydrocarbons on peoplehydrocarbons 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 Restriction of halogenated hydrocarbons formationhydrocarbons 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 Hydrochloric acid reducing technologiestechnologies
SORBENT INJECTION IN FLUE GAScalcium-carbonate, calcium-oxide, calcium-hydroxide, sodium-
carbonate, sodium-hydrocarbonate
CaCO3 + 2 HCl <=> CaCl2 + CO2 + H2OCaO + 2 HCl <=> CaCl2 + H2O
Ca(OH)2 + 2 HCl <=> CaCl2 + 3 H2ONa2CO3 + 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 Reduction of halogenated hydrocarbon emissionemission
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