Oxides of Sulfur SOx

SO2: largest amount

SO3 very small amount 2SO2 + O2 SO3

Sulfuric acid

H2SO4 : Acid rain

Sulfuric acid : uses Batteries in cars drain cleaners Synthesize more than 100 million tons of sulfuric acid each year!

SOx SO 2 : produced in largest amount Slowly oxidized to SO 3 Reaction is catalyzed by : – heavy metal pollutants/finely divided particles – hydroxyl free radical /OH –Ozone, and sunlight 2SO 2 (g) + O 2 (g) 2 SO 3 (g)

Principal Sources: Anthropogenic : man made: 150 million tons –Coal, low grade, 7% S ( 1-5 % S) –As iron pyrite FeS 2 and –Organic sulfur / proteins –Combustion of sulfur to sulfur dioxide –4FeS O 2 2 Fe 2 O SO 2 –Petroleum refining removes sulfur impurities by bubbling Hydrogen gas in presence of a catalyst –Heavy fuel used by ships/ high sulfur content

SO 2 Smelting Plants –Oxidize sulfide ore to metal oxide –Cu 2 S(s) +2 O 2 2CuO(s) + SO 2 (g) –Sulfuric acid plants: acid is produced by the oxidation of SO 2 Reacts with water to form sulfuric acid O 2 + SO 2 (g) SO 3 (g) H 2 O(l) + SO 3 H 2 SO 4 (l)

SO 2 Natural Sources Volcanic and bacterial activities Atmospheric oxidation of Hydrogen sulfide gas ( SO 2 as secondary pollutant) H2S is produced by the decay of organic matter ( swamps, ocean) 2H 2 S(g) + 3O 2 (g) 2 SO H 2 O(l)

Effect of SO2 on Health Acidic oxide Breathing aerosol irritates respiratory tract Greatest effect on elderly and young and those suffering from asthma

Methods of controlling Sox pollution Converting high sulfur coal to Synthetic natural gas Requires 30 % of energy for the conversion P 608 Sulfur is converted to H2S gas S + H 2 H 2 S

4 steps 1.Hydrogasification: synthesis gas C(s) + H2O(g) CO(g) + H2(g) + impurities Ho = kJ/mol endothermic Synthesis gas is used as a fuel 2.catalytic increase of hydrogen gas CO(g) + H2O(g) CO 2 (g) + H2(g) more steammore H2 heat

SNG 3.Removal of impurities: CO2, water, and hydrogen sulfide gas –H 2 S sulfur and sold as by-product 4. Catalytic Methanation: water gas with more H2 is passed over heated catalyst 3H2 + CO CH4 + H2O water vapor is removed This reaction is similar but opposite for synthesis of ammonia oxidized catalyst

SNG Summary 1. Hydrogasification: high temp/pressure C(s) + H2O(g) CO(g) + H2(g) + impurities 2.Catalytic increase of H2 CO + H2O (g) CO2 + H2 3.Removal of CO2 and H2O, and H2S 4. Catalytic Methanation 3H2 + CO CH4 + H2O water vapor is removed More H2 gas

Methods of controlling Sox pollution Using cleaner burning coal Controlling before burning fossil fuel a. removing S before burning using H2/catalyst b. coal washing/finely ground coal and wash with water/iron pyrites removed Post combustion method a. limestone fluidized beds or injection method b. Wet scrubber method

3.Pre- Combustion Method Controlling before burning fossil fuel : 2 ways A. bubble H2 gas in presence of catalyst – remove sulfur as H2S during refining process –B: desulfurize / finely ground the coal and wash with water –FeS2/ iron pyrite is dense; –settles down –Remove it. Organic sulfur can not be removed

4. Post Combustion Method Removal of S from exhaust gases after burning the coal but before releasing to the atmosphere a) Limestone fluidized beds or injection systems –Add powdered limestone, CaCO3 with coal in the combustion process –CaCO3 CaO + CO2 heat

Sulfur SO 2 can be removed by injecting powdered limestone which is converted to calcium oxide. The CaO reacts with SO 2 to form a precipitate of calcium sulfite.

a) Limestone fluidized beds or injection systems CaO + SO2 CaSO3 2CaO + 2SO 2 + O2 2 CaSO 4 Calcium sulfate, un-reacted CaO, SO2 and particulates are absorbed into water in a wet-scrubber.

b. Wet scrubber Usually water based Removes particulates/ contaminants Alkaline liquid is sprayed downward while the gas stream moves upward Effectiveness depends upon the contact between the alkaline liquid and SO2 CaO + SO 2 CaSO 3 Slurry goes to ponds

b. Wet scrubber Drawbacks: Deposition of CaSO 3 on the scrubber surface Need extremely large amounts of calcium carbonate SO 2 is replaced by greenhouse gas

b. Wet scrubber with Mg(OH) 2 Mg(OH) 2 + SO 2 MgSO 3 + H2O MgSO 3 MgO + SO 2 SO2 is used in the manufacturing of sulfuric acid MgO is recycled as Mg(OH) 2 MgO + H 2 O Mg(OH) 2 Drawback: heating requires lot of energy / expensive heat

2. Using low sulfur, cleaner burning coal Hard coal / anthraciteanthracite

CO(g) + H2O(g) CO2(g) + H2(g) Ho = kJ/molrxn

C(s) + CO2(g) 2 CO(g) –Ho = kJ/molrxn

N2(g) + 3 H2(g) 2 NH3(g) It can also be used to make methyl alcohol, or methanol. CO(g) + 2 H2(g) CH3OH(l)

Methanol can then be used as a starting material for the synthesis of alkenes, aromatic compounds, acetic acid, formaldehyde, and ethyl alcohol (ethanol). Synthesis gas can also be used to produce methane, or synthetic natural gas (SNG). CO(g) + 3 H2(g) CH4(g) + H2O(g) 2 CO(g) + 2 H2(g) CH4(g) + CO2(g)