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HALOGENATED HYDRO-CARBONS

BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS. DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING. FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING. HALOGENATED HYDRO-CARBONS. Authors: Dr. Bajnóczy Gábor Kiss Bernadett Tonkó Csilla.

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HALOGENATED HYDRO-CARBONS

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  1. BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS • DEPARTMENT OF CHEMICAL AND • ENVIRONMENTAL PROCESS ENGINEERING • FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING HALOGENATED HYDRO-CARBONS Authors: Dr. Bajnóczy Gábor Kiss Bernadett Tonkó Csilla

  2. The pictures and drawings of this presentation can be used only for education !Any commercial use is prohibited !

  3. 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: • Degradable in troposphere (e.g. methyl-chloride, methyl-bromide etc.) • 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.

  4. 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 andflame 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.

  5. 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)

  6. 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

  7. Formation of halogenatedhydrocarbons • 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: chlorine content of some combustible material 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 containsmostly hydrochloric acid, elemental chlorine and alkali-chlorides

  8. 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

  9. Formation of chlorine from HCl in the flue gas I. Deacon reaction 2 HCl + ½O2<=> Cl2 + H2O (slow) Metal oxid catalyst: Hydrochloric acid + metal → metal chloride Metal chlorine + O2→ metal-oxid + chlorine II. Another possible way: HCl + OH• <=> H2O + Cl HCl + O <=> OH• + Cl

  10. 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 Source: Desroches-Ducarne 1997

  11. 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.

  12. 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)

  13. DIOXINS • Chlorinated aromatic hydrocarbons • Polychlorinated dibenzodioxin (PCDD) • Polychlorinated dibenzofuran (PCDF) 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 75 pieces 135 pieces

  14. 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 • Number of chlorine substituents > 4: growing number of chlorine substituents makes the PCDD/PCDF less toxic. 2,3,7,8- tetrachlorodibenzodioxin

  15. DIOXINS Expression of toxicity : toxic equivalent factor (TEF): Proved to be toxic: 7 pieces PCDD and 10 pieces PCDF 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

  16. Dioxin concentration The concentration is given in Toxic Equivalent (TEQ) 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.

  17. 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

  18. 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

  19. 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

  20. 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 → halogenatedhydrocarbon 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 Cl

  21. 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

  22. 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.

  23. Effect of halogenated hydrocarbons on plants • Atmospheric concentration is not dangerous. • Halogenated hydrocarbons → hydrochloric acid (not significant) – environmental acidification

  24. 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

  25. 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

  26. Hydrochloric acid reducing technologies SORBENT INJECTION IN FLUE GAS calcium-carbonate, calcium-oxide, calcium-hydroxide, sodium-carbonate, 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

  27. 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

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