7. SULP

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PROPERTIES OF SULPHURIC ACID

Sulphuric acid is a strong dibasic acid It is oxidizing and dehydrating agent toward organic compounds.

Boiling Point: 335 °C.

Melting Point: 10 °C

MANUFACTURE OF SULPHURIC ACID BY THE CONTACT PROCESS

Sulphuric Acid is commonly prepared by the Contact process.

The raw materials needed are a source of sulphur dioxide; air, water and a catalyst.

MANUFACTURE OF SULPHURIC ACID BY THE CONTACT PROCESS

The main stages in the process are: Production of sulphur dioxide Oxidation of sulphur dioxide to sulphur trioxide Hydration of sulphur trioxide to sulphuric acid

MANUFACTURE OF SULPHURIC ACID BY THE CONTACT PROCESS

Production of Sulphur Dioxide Burning sulphur in an excess of air S(s) + O2(g) SO2(g)

…or by heating sulphide ores like pyrite in an excess of air

4FeS2(s) + 11O2(g) 2Fe2O3(s) + 8SO2(g)

…or by decomposing calcium sulphate in the presence of coke

2CaSO4(s) + C(s) 2CaO(s) + CO2(g) + 2SO2(g)

In either case, an excess of air is used so that the sulphur dioxide produced is already mixed with oxygen for the next stage.

MANUFACTURE OF SULPHURIC ACID BY THE CONTACT PROCESS

Oxidation of sulphur dioxide to sulphur trioxideThis is a reversible reaction, and the formation of the sulphur

trioxide is exothermic.2SO2(g) + O2(g) 2SO3(g) H=-196kJmol-1

Sulphur dioxide +

oxygen (from air)1:1 volume ratio

400-450 degrees1-2 atm

V2O5 catalyst

{vanadium oxide}

Sulphur trioxide

MANUFACTURE OF SULPHURIC ACID BY THE CONTACT PROCESS

Hydration of sulphur trioxide to sulphuric acid This cant be done by simply adding water to the sulphur trioxide- the

reaction is so

uncontrollable that it creates a fog of sulphuric acid. Instead, the sulphur trioxide is

first dissolved in conc. sulphuric acid:

H2SO4(l) + SO3(g) H2S2O7(l)

Oleum

This can then be diluted with water to produce concentrated sulphuric acid.

H2S2O7(l) + H2O(l) 2H2SO4(l)

N.B. Video link http://www.youtube.com/watch?v=Bu3ns9Ii80M

USES OF SULPHURIC ACID Use in fertilizer manufacturing.

Sulfuric acid is the electrolyte used in lead-acid batteries (accumulators).

Sulfuric acid is used to remove oxides from iron and steel before galvanizing or electroplating.

It is widely used in the manufacture of chemicals, e.g., in making hydrochloric acid, nitric acid, sulfate salts, synthetic detergents, dyes and pigments, explosives, and drugs.

Sulfuric acid is used in processing metals, e.g., in pickling (cleaning) iron and steel before plating them with tin or zinc.

Rayon is made with sulfuric acid. It serves as the electrolyte in the lead-acid storage battery commonly used in motor vehicles (acid for this use, containing about 33% H2SO4 and with specific gravity about 1.25, is often called battery acid).

It is used in petroleum refining to wash impurities out of gasoline and other refinery products.

DETAILS OF USES

Sulphuric acid is a very important commodity chemical, and indeed, a nation's sulphuric acid production is a good indicator of its industrial strength. Most of sulphuric acid production (~60%) is consumed for fertilizers, particularly superphosphates, ammonium phosphate and ammonium sulphates. About 20% is used in chemical industry for production of detergents, synthetic resins, dyestuffs, pharmaceuticals, petroleum catalysts, insecticides and antifreeze, as well as in various processes such as oil well acidizing, aluminium reduction, paper sizing, water treatment. About 6% of uses are related to pigments and include paints, enamels, printing inks, coated fabrics and paper, and the rest is dispersed into a multitude of applications such as production of explosives, cellophane, acetate and viscose textiles, lubricants, non-ferrous metals and batteries.

INDUSTRIAL PRODUCTION OF CHEMICALS

The major use for sulphuric acid is in the "wet method" for the production of phosphoric acid, used for manufacture of phosphate fertilizers. In this method, phosphate rock is used, and more than 100 million tonnes are processed annually. This raw material is shown below as fluorapatite, though the exact composition may vary. This is treated with 93% sulphuric acid to produce calcium sulphate, hydrogen fluoride (HF) and phosphoric acid. The HF is removed as hydrofluoric acid. The overall process can be represented as:

Ca5F(PO4)3 + 5 H2SO4 + 10 H2O → 5 CaSO4·2 H2O + HF + 3 H3PO4 Ammonium sulphate, an important nitrogen fertilizer, is most commonly produced as a by product from coking plants supplying the iron and steel making plants. Reacting the ammonia produced in the thermal decomposition of coal with waste sulphuric acid allows the ammonia to be crystallized out as a salt (often brown because of iron contamination) and sold into the agro-chemicals industry.

Another important use for sulphuric acid is for the manufacture of aluminium sulphate, also known as paper maker's alum. This can react with small amounts of soap on paper pulp fibres to give gelatinous aluminium carboxylates, which help to coagulate the pulp fibres into a hard paper surface. It is also used for making aluminium hydroxide, which is used at water treatment plants to filter out impurities, as well as to improve the taste of the water. Aluminium sulphate is made by reacting bauxite with sulphuric acid:

Al2O3 + 3 H2SO4 → Al2(SO4)3 + 3 H2O Sulphuric acid is also important in the manufacture of dyestuffs solutions.

SULPHUR-IODINE CYCLE

The sulphur-iodine cycle is a series of thermo-chemical processes used to obtain hydrogen. It consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen.

2 H2SO4 → 2 SO2 + 2 H2O + O2     (830 °C) I2 + SO2 + 2 H2O → 2 HI + H2SO4     (120 °C) 2 HI → I2 + H2     (320 °C) The sulphur and iodine compounds are recovered and reused, hence the consideration of the process as a cycle. This process is endothermic and must occur at high temperatures, so energy in the form of heat has to be supplied.

The sulphur-iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-based economy. It does not require hydrocarbons like current methods of steam reforming. But note that all of the available energy in the hydrogen so produced is supplied by the heat used to make it.

The sulphur-iodine cycle is currently being researched as a feasible method of obtaining hydrogen, but the concentrated, corrosive acid at high temperatures poses currently insurmountable safety hazards if the process were built on a large scale.

CLEANING AGENTS

Sulphuric acid is used in large quantities by the iron and steel making industry to remove oxidation, rust and scaling from rolled sheet and billets prior to sale to the automobile and major appliances industry. Used acid is often recycled using a spent acid regeneration (SAR) plant. These plants combust spent acid with natural gas, refinery gas, fuel oil or other fuel sources. This combustion process produces gaseous sulphur dioxide (SO2) and sulphur trioxide (SO3) which are then used to manufacture "new" sulphuric acid. SAR plants are common additions to metal smelting plants, oil refineries, and other industries where sulphuric acid is consumed in bulk, as operating a SAR plant is much cheaper than the recurring costs of spent acid disposal and new acid purchases.

IMPACT OF SULPHURIC ACID INDUSTRY

Waste products from production of bauxite {which consists of mainly sulphuric acid} creates a toxic pond

Sulphuric acid will exist as small particles or droplets in air if released in the atmosphere. It dissolves when mixed with water present in clouds, fog and snow and will result in acid rain or acid fog .

Exposure to aerosols at high concentrations leads to immediate and severe irritation of the eyes, respiratory tract and mucous membranes: this ceases rapidly after exposure

Sulfur dioxide is sometimes used as a preservative for dried apricots and other dried fruits owing to its antimicrobial properties, and it is sometimes called E220 when used in this way. As a preservative, it maintains the appearance of the fruit and prevents rotting.

Sulfur dioxide is a major air pollutant and has significant impacts upon human health. In addition the concentration of sulfur dioxide in the atmosphere can influence the habitat suitability for plant communities as well as animal life.