HALOGENATED HYDRO-CARBONS Authors: Dr. Bajnóczy Gábor Kiss Bernadett Tonkó 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 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, 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 (CFCl 3 ) and CFC-12 (CF 2 Cl 2 ), 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 = 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 CF 3 Br, H-1211 CF 2 BrCl ). 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 methyl chloride 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 methyl chloride 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 decabromo- diphenylether /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. Burning: Néhány éghető anyag klórtartalma FuelChlorine %Flammable materialChlorine % Lignite, coal0.01– 0,2Communal waste0,05 – 0,25 Fuel oil0,001Hospital waste1 – 4 Biogas0,005Electronic waste0,1 – 3.5 Cortex, bark0,02 – 0,4PVC (Polyvinylchloride)50 Paper, textile0,1 – 0,25Communal waste water sludge0,03 – 1 Tree0,001 Herbaceous plants0,5 – 1,5 Natural gasNot 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 + H 2 O HCl + KOH KCl + CO 2 + H 2 O K 2 CO 3 + 2HCl Hydroxide, carbonate and chlorides : condenses in the heat exchanger chimneyatmosphere hydrochloric acid

Formation of chlorine from HCl in the flue gas I. Deacon reaction 2 HCl + ½ O 2 Cl 2 + H 2 O (slow) Metal oxid catalyst: 1. Hydrochloric acid + metal → metal chloride 2. Metal chlorine + O 2 → metal-oxid + chlorine II. Another possible way: HCl + OH H 2 O + 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 CO 2 + H HCl + OH H 2 O + 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 ▼ ▲ Effect of dry chlorine and HCl on carbon steel alloy Source: 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 hydrocarbons Deacon reaction in firebox → formation of elemental chlorine creates a possibility to form chlorinated hydrocarbons C x H y + Cl 2 = C x H y-1 Cl + HCl Most dangerous species: Polychlorinated dibenzodioxin (PCDD) Polychlorinated dibenzofuran (PCDF)

DIOXINS Chlorinated aromatic hydrocarbons Polychlorinated dibenzodioxin (PCDD) Polychlorinated dibenzofuran (PCDF) 75 pieces135 pieces Natural resources - forest fires - bacterial activity Anthropogenic sources - chemical - waste burning - fossil and biomass power plant 2,3,7,8- tetrachlorodibenzodioxin2,3,7,8- tetrachlorodibenzofurane

DIOXINS 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

DIOXINS TEF of PCDD and PCDF PCDDTEFPCDFTEF 2,3,7,8-TCDD12,3,7,8-TCDF0,1 1,2,3,7,8-PCDD0,51,2,3,7,8-PCDF0,05 1,2,3,4,7,8-HxCDD0,12,3,4,7,8-PCDF0,5 1,2,3,6,7,8-HxCDD0,11,2,3,4,7,8-HxCDF0,1 1,2,3,7,8,9-HxCDD0,11,2,3,6,7,8-HxCDF0,1 1,2,3,4,7,8,9-HpCDD0,012,3,4,6,7,8-HxCDF0,1 1,2,3,4,6,7,8,9-OCDD0,0011,2,3,7,8,9-HxCDF0,1 1,2,3,4,6,7,8-HpCDD0,01 1,2,3,4,7,8,9-HpCDF0,01 1,2,3,4,6,7,8,9-OCDF0,001 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 concentration PCDD/PCDF (TEQ) = ∑ (PCDD/PCDF concentration) k x (TEF) k Limit value of dioxin concentration in flue gas: 0,1 ng TEQ/Nm 3, (O 2 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 dioxin conc. ng/Nm 3 TEF product arithmetical TEQ 2,3,7,8-TCDD212 x 12 1,2,3,6,7,8-HxCDD100,110 x 0,11 2,3,4,7,8-PCDF120,512 x 0,56 1,2,3,4,6,7,8,9-OCDD1000, x 0,0010,1 Unit: ng TEQ/Nm 3 9,1 The concentration is given in Toxic Equivalent (TEQ)

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 - 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, de novo synthesis - 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. 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 CF 2 Cl 2 CF 2 Cl* + Cl Chlorine atom speed up ozone decomposition Cl + O 3 = ClO + O 2 ClO + O = Cl + O 2 O 3 + O 2 O nm Halogenated hydrocarbons in atmosphere Cl

Halogenated hydrocarbons in atmosphere 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 atmosphere Ozone depletion potential (ODP) and global warming potential (GWP) of CFC compounds compoundlife (year)ODPGWP CO 2 01 CFC CFC , CFC ,96030 HCFC-141b9,40,1713 CF 4 > CH 3 Br1,30,6144 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 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, sodium- carbonate, sodium-hydrocarbonate CaCO HCl CaCl 2 + CO 2 + H 2 O CaO + 2 HCl CaCl 2 + H 2 O Ca(OH) HCl CaCl H 2 O Na 2 CO HCl 2 NaCl + CO 2 + H 2 O NaHCO HCl 2 NaCl + 2 CO H 2 O The method is suitable for sulfur-dioxide absorption T > 770 o C (melting point of calcium-chloride): reduction of hydrochloric acid is only % 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