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