Dear Loutfy,
1- The Contact Process:
makes sulphur dioxide;
convers the sulphur dioxide into sulphur trioxide (the reversible reaction at the heart of the process);
converts the sulphur trioxide into concentrated sulphuric acid.
2- Sulfuric acid is made from dry SO2, O2, N2 gas. The gas comes from combusting elemental sulfur, smelting and roasting sulfide minerals, and decomposing contaminated sulfuric acid catalyst. Sulfur burning is far and away the largest source.
The SO2 in the gas is made into sulfuric acid by (i) catalytically oxidizing it to SO3 then (ii) reacting this SO3 with the H2O(ℓ) component of strong sulfuric acid.
Sulfuric acid is used for making fertilizer, leaching metal ores, refining petroleum, and manufacturing a myriad of products. About 200 million tonnes of sulfuric acid are produced/consumed per year.
3-Burning elemental sulfur
Sixty percent of the world's sulfuric acid is made from elemental sulfur. Virtually, all of this sulfur is the by-product of natural gas and petroleum refining. The first step in making sulfuric acid from elemental sulfur is burning the sulfur with dried air. It entails.
(a) atomizing molten sulfur in a hot furnace and oxidizing the resulting fine droplets with excess dried air
(b) cooling the product SO2, O2, N2 gas in a heat recovery boiler.
The product is ~12 volume% SO2, 9 volume% O2, and 79 volume% N2 gas (420 °C), perfect for subsequent catalytic SO2 oxidation and H2SO4(ℓ) manufacture.
4- About 30% of the world's sulfuric acid is made from the SO2 in smelter and roaster offgases. These gases contain 10-75 volume% SO2. Their SO2 is suitable for making sulfuric acid, but the gases must be cooled, cleaned, diluted, and dried before being sent to acidmaking.
Cooling is usually done in a heat recovery boiler—which cools the gas and recovers its heat as steam. Considerable dust is removed in this heat recovery boiler. Additional dust and unwanted vapors are removed from the gas by subsequent electrostatic precipitation and aqueous scrubbing.
Finally, H2O(g) is removed by (i) condensation and (ii) dehydration with strong sulfuric acid. The gas is then ready for catalytic SO2 oxidation and H2SO4 making
5- Sulfuric acid is used as a catalyst in gasoline, jet fuel, and polymer manufacture. The sulfuric acid catalyst is not consumed, but it becomes ineffective as it absorbs water, hydrocarbons, and other chemicals over time. Its catalytic properties are maintained by bleeding off some of the contaminated “spent” acid and regenerating it to high purity 98% H2SO4() sulfuric acid.
The spent acid bleed is recycled and made into new acid by
(a) decomposing its H2SO4() to SO2, O2, and H2O(g) in a hot (1000 °C), mildly oxidizing furnace
(b) removing dust and condensing water from the decomposition furnace’s offgas
(c) adding air
(d) dehydrating the gas with strong sulfuric acid
(e) catalytically oxidizing the gas’s SO2 to SO3
(f) making new, strong sulfuric acid from (e)’s SO3.
6- SO2-bearing gas must be dry before it goes to catalytic SO2 oxidation. Otherwise, the SO3 made by catalytic oxidation will react with the gas's H2O(g) to form corrosive liquid sulfuric acid in cool flues and heat exchangers, especially during shutdowns.H2Og+H2SO4linstrongacid→H2SO4·H2Olinslightlyweakenedacid
Industrially, the process is carried out in brick-lined stainless steel towers packed with ceramic saddles. Acid descends around the saddles where it meets and reacts with ascending H2O(g)-laden gas.
7- Catalytic oxidation of SO2 to SO3 is a key step in sulfuric acid production. It produces the SO3 required for subsequent H2SO4(ℓ) making. oxidation is always done by passing warm SO2-bearing gas through horizontal beds of V, K, Na, Cs, S, O, SiO2 catalyst. The catalyst promotes rapid SO2 oxidation at temperatures (400-600 °C) where SO2 oxidation is thermodynamically efficient.
Industrially, the oxidation is carried out in a sequence of three to five catalyst beds with gas cooling between beds. Removal of heat from the gas between catalyst beds allows it to leave the last bed at a low temperature (~ 450 °C)—where equilibrium oxidation efficiency is high (98+%).
8- SO3 is a key ingredient in making H2SO4(ℓ). It is produced rapidly and efficiently by oxidizing SO2 to SO3 in a molten V, K, Na, Cs, S, O catalyst film, 400-600 °C. The molten film is supported on a solid, porous silica substrate.
SO2 and O2 dissolve in the molten catalyst. They then react with V, S, O cations to form and release SO3 into the gas. The reactions are rapid at temperatures (400-600 °C) where oxidation is thermodynamically efficient.
The process is carried out industrially in three to five 0.5- to 1-m thick beds of 10- to 25-mm diameter catalyst rings or “star” rings. Gas residence times in each bed are 1.5-2 s.
9- The final step in sulfuric acid manufacture is the production of H2SO4(ℓ) from SO3-bearing gas.
The H2SO4 is made by sending strong sulfuric acid down around ceramic saddles in a packed bed while blowing SO3 gas up through the bed.SO3ginSO3,O2,N2gas+H2Olin98.5mass%H2SO4,1.5mass%H2Osulfuricacid→80-110°CH2SO4linstrengthenedsulfuricacid~99mass%H2SO4
The strengthened acid is mostly diluted and sold. Some is recycled to the dehydration and absorption towers.
Most sulfuric acid plants are double contact plants. They efficiently oxidize their feed SO2 to SO3 and efficiently make the resulting SO3 into H2SO4(ℓ). Single contact plants are simpler and cheaper, but their exit gases contain more SO2.
http://www.sciencedirect.com/science/book/9780080982205
https://www.google.ps/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjXgobP6PfKAhUGvRoKHTkFBjwQIAgcMAA&url=http%3A%2F%2Fwebcache.googleusercontent.com%2Fsearch%3Fq%3Dcache%3A478VLixWh3sJ%3Awww.chemguide.co.uk%2Fphysical%2Fequilibria%2Fcontact.html%2B%26cd%3D1%26hl%3Den%26ct%3Dclnk%26gl%3Dps&usg=AFQjCNHgdIhodwehyZw9CYc-z5g9v7FH3w&sig2=qLzBujTkGdlDAFibeGentg
Hoping this will be helpful,
Rafik
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