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Sulfur oxides

BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS. DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING. FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING. Sulfur oxides. authors: Dr. Bajnóczy Gábor Kiss Bernadett.

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Sulfur oxides

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  1. BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS • DEPARTMENT OF CHEMICAL AND • ENVIRONMENTAL PROCESS ENGINEERING • FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING Sulfur oxides authors: Dr. Bajnóczy Gábor Kiss Bernadett

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

  3. Physical properties of atmospheric sulfur oxides • Sulfur dioxide: • colorless • irritating odor (odor threshold 0,3-1 ppm) • soluble in water • natural background~1 ppb • Sulfur trioxide: • highly reactive => short lifetime in the atmosphere, sulfuric acid formation with water Direct emission is mainly sulfur dioxide, only some percent of sulfur trioxide

  4. Natural sources of sulfur dioxide • Volcanic action. • A volcanic gases: 90% water and CO2, SO2 content 1-10 % . • Sulfur compounds from biological activity • (CH3SCH3, H2S, CS2, COS) will be oxidized in the atmosphere. • Sulfur emission in highest amount: dimethyl-szulfide from the oceans → biological activity of fitoplankton.

  5. Sulfur dioxide from human activity Atmospheric sulfur content is mainly anthropogenic origin. Main source: combustion of fossile fuels Sulfur content of coal and crude oil differs. Crude oil: mainly organic, (sulfides, mercaptenes, bisulfides, tiofenes) => can be removed by simple technology. • Coal: • pyritic (FeS), removable by physical method , • sulfates (CaSO4, FeSO4) removable by physical method (no decay at combustion temperature to SO2) • matrix sulfur a incorporated in polymer molecule

  6. Sulfur dioxide from human activity Another significant source: smelter operation • Cu, Zn, Cd, Pb occur in the nature mainly in sulfide ore form. Can not be reduced directly. • Roasting of sulfide ores on air produces oxides (ZnO, CdO, CuO….) → the oxides can be reduced • Cu, Ni: • roasting: only the metal content can be concentrated • Final sulfur elimination: air blowing through the melted sulfur contaminated ore • Sulfur content is transformed to sulfur dioxide => the capture of SO2 depends on the level of technology.

  7. Sulfur dioxide from human activity smelter operation : far from built-up area. Not a solution due to the global character of sulfur oxide pollution !

  8. Chemistry of sulfur oxide formation Burning of elemental sulfur: oxygen atom starts the reaction, transition compound: sulfur monoxide. Combustion of sulfur containing materials (fuel-S) : thermal decay → char-S, (shrunken solid fuel)hydrogen sulfide (H2S) and carbonyl sulfide (COS) form. All of the three products is oxidized to sulfur dioxide Fuel-S Heat effect Thermal decay char-S char-S char-S char-S

  9. Chemistry of sulfur oxide formation Further oxidation of sulfur dioxide → sulfur trioxide: O + SO2<=> SO3 • oxygen atoms and hydroxyl radicals play a significant role. • equilibrium shifts left with temperature increase • the reaction rate is slow • only 0.5-2.5% of SO2 is converted to SO3 • the time to reach the equilibrium depends of the catalytic effect of the metal content (W, Mo, V, Cr, Ni, Fe oxides) in ash

  10. Chemistry of sulfur oxide formation • Sulfur trioxide at 482 oC transforms to sulfuric acid. Under the dew point sulfuric acid condensates on the structure materials (heat exchanger, stack wall ). The dew point of sulfuric acid depends on the SO3 and water content of the stack gas. Dew point of sulfuric acid in function of SO3 and water concentration in stack gas ..and the damage stack gas temperature

  11. Dimethyl sulfide, hydrogen sulfide, carbonyl sulfide, carbon disulfide in the atmosphere • Oxidized to sulfur dioxide • Oxidizing agent: hydroxyl radicals • Oxidation of dimethyl-sulfide→ methane sulfonic acid aerosol (CH3SO3H) → serves as nuclei for cloud formation • carbonyl-sulfide: • Slow oxidation by hydroxyl radicals => oxidation in the stratosphere by atomic oxygen • Lifetime in years. • Hydrogen sulfide, carbonyl disulfide quick oxidation to SO2 in the troposphere

  12. Catalytic transformation of sulfur dioxide to sulfuric acid SO2 dissolution catalyst O2 dissolution Ash particles

  13. Photochemical transformation of sulfur dioxide to sulfuric acid • Hydroxyl radicals oxidize the sulfur dioxide to sulfur trioxide. Sulfur trioxide and water → quick reaction → sulfuric acid ▼ Acidic rain

  14. Effects of acidic rain • pH of rain: adjusted by the rate of natural acidic and basic materials • Usually acidic: solution of carbon dioxide (pH=5.56) • Generally accepted: pH under 5 is due to human activity . The acidity surplus : • 60-70% sulfuric acid from sulfur dioxide • The rest comes from nitric acid formed from nitric oxide • Some percent hydrochloric acid • pH of rain > pH of fog particles

  15. Effects of acidic rain on plants Three stages can be distinguished • Mobilization of soluble plant nutrients, e.g. nitrogen compounds • Nutrient wash out by the rain water → nutrient shortage • Al 3+ ion liberation from the clay minerals due to the decreasing pH in the soil. • The free aluminum ion is toxic to the roots, weakens the immunizing system → secondary infections ▐ toxic Non toxic Soil pH

  16. Effect of acidic rain on natural water I. • The excess of H+ ion in rain water shifts the hydro carbonate equilibrium towards the formation of free carbon dioxide. H+ + HCO3─<=>H2O + CO 2 • The physically dissolved CO2 inhibit the O2↔ CO2exchange in living organisms : e.g. fish). • occurs at spring when the melted acidic snow flows suddenly into the rivers of catchments area. • If natural water is in contact with limestone, dolomite, the pH does not change → buffer effect. The living organisms are killed by the increased CO2 content • In case of week buffer effect (small Ca- and Mg-hydro carbonate content) the living organisms are killed by the decreased pH

  17. Effect of acidic rain on natural water II. pH tolerance of waterborne organisms The lack of mussels in natural waters may indicate the change of pH, they can not change theirs position quickly

  18. Effect of acidic rain on calcium carbonate containing materials I. • calcium carbonate containing materials: marble,limestone, plaster, concrete → sensitive to acidic rain • in the last fifty year the weathering of open air ancient monuments speeded up

  19. Effect of acidic rain on calcium carbonate containing materials II. • Effect: The infiltrating acidic rainwater contaminated by sulfuric acid changes the crystals of calcium carbonate to calcium sulfate • The solubility of calcium sulfate > solubility of calcium carbonate. • Crystal volume of CaSO4 > crystal volume of CaCO3 stress in the material structure → crack

  20. Effect of acidic rain on metal constructions I. Preliminary conditions of the electrochemical corrosion: • 1. two metallic material with different electrochemical potential in metallic contact. • 2. electrolyte cover on the metallic contact, (e.g.. water solutions of acids, salts) • 3. presence of electron uptake material (H+ O2 Cl2 ) Electrochemical corrosion of metal: • Oxidation: the metal transform to ion and free electrons release. Fe = Fe 2+ + 2 e- • Reduction: uptake of free electrons by • 2H+ + 2e- = H2 • O2 + 4H+ + 4e- = 2 H2O • H2O + CO2 + e- = H + CO32- • Cl2 + 2e- = 2 Cl-

  21. Effect of acidic rain on metal constructions II. Acid rain: electrolyte and the hydrogen ion serves the reduction (electron uptake) Air pollution induced electrochemical corrosion resulted in the collapse of Silver bridge over Ohio river on 15-th. Dec. 1967.

  22. Effect of atmospheric SO2 on papers The paper gets yellow and brittle. Paper surface The result H2SO4 formation on the surface adsorption Fe catalyst desorption Destroyed surface No damage

  23. Anthropogenic effects of SO2 • Good solubility in water → the effect on the upper part of the respiratory system. • Irritating effect over 10 ppm • Nonstop irritation of mucous lining in urban air results in frequent colds, flu

  24. Control of sulfur dioxide emission • Power plants based on fossil fuels produce sulfur oxide emission • Transportation is based on fossil fuel but the emission is not so serious • The sulfur can be removed easily from liquid material • The anthropogenic emission decreased half of the original one since. • Sulfur dioxide easily can be eliminated from the stack gas • Problems to be solved: fate of the sulfur containing product • SO2 emission controls are divided into two categories: • Reduction of the sulfur content of the fuel, • The sulfur dioxide is removed from the exhaust gas.

  25. Power plants • Simplest way: replacement of high sulfur content fuel with low sulfur content fuel • e.g. coal fired power station → gas fired power plant. Not a final solution: the available gas resources are restricted Coal might be the fuel of future again

  26. Sulfur content reduction of solid fuel • Sulfur content of the coal: <1% . . . 10-12% • Form of sulfur: • pyritic sulfur (FeS2) • sulfate sulfur (e.g.. iron- and calcium sulfate) • matrix sulfur. (sulfur in organic bond ) • Extraction of sulfur: • 1.and 2. by simple technology (e.g.. flotation) , based on density difference of coal and pyrite, sulfate • 3. chemically bonded => physical methods can not be applied. • Direct chemical treatment e.g. NaOH is not economical • Gasification of coal by air and/or water. Removal of the formed hydrogen sulfide H2S from the gas.

  27. Sulfur content reduction of liquid and gas fuel • Desulphurization: • Hydro processing: evaporated fractions of crude oil and hydrogen is in contact with catalyst Co/Mo to transform organic sulfur to hydrogen sulfide at high pressure. • Hydro processing might be • Destructive: carbon chain crack and sulfur transformation • Nondestructive: to improve the quality of oil fractions • Sulfur content → hydrogen sulfide • Nitrogen content → ammonia

  28. Hydrogen sulfide removal • Physical absorption at low temperature minus 30-120 °C (methanol, dimethyl ether) • Chemical adsorption (organic amines, metal oxides) Reversible processes→ the absorbed and adsorbed hydrogen sulfide can be recovered in concentrated form The concentrated hydrogen sulfide → Claus plant

  29. Hidrogen sulfide treatment by Claus process • Concentrated gas (> 50..60 vol % H2S) is partially oxidized to sulfur and water • 2/3 part of the H2Sconcentrated gas is oxidized and combined with the rest → 1000-1400 0C → after cooling the sulfur can be separated After cooling the gas mixture is feed into the Claus reactor at 200-350 0C(catalist: aluminum oxide) to increase the conversion.

  30. Sulfur dioxide removal from the flue gas by wet process reactant: lime CaO / limestone CaCO3 → product: CaSO4 (gypsum) • Cheap raw material → 80 % of SO2 cleaning technologies are based on this one Wet scrubbers, at 70 – 90 0C Flue gas treatment by lime suspension in water Flue gas treatment by limestone suspension in water efficiency 90-95%

  31. Wet scrubber for SO2 removal

  32. Flue gas desulphurization (FGD) regenerable adsorbent • Wellman-Lord technology, advantages: • Not too much byproduct • Extracted sulfur dioxide in concentrated form

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