Nitric Acid (Hydric Nitrate) (HNO 3 ) Dr. Muhammad Aslam Assistant Professor-Chemistry Division of Science and Technology University of Education, Township Campus, Lahore. (HNO 3 ) Basic and Heavy Chemical Industries • Raw materials and chemicals • Flow sheet diagrams and commercial production of – Sulphuric acid – Nitric acid – Hydrochloric acid – Hydrochloric acid – Oxalic acid – Formic acid – Caustic soda – Washing soda • Applications of these chemicals in chemical industries Books Recommended • Advanced Inorganic Chemistry (Volume 1) – S. Parakash • Inorganic Chemistry – Haq Nawaz Bhatti • Handbook of Industrial Chemistry (Volume 1) – KH Davis, FS Berner Nitric Acid, HNO 3 • The most important and useful oxoacid of nitrogen is nitric acid. • Its molecular formula is HNO 3 and molar mass 63 01 g mol -1 63.01 g mol -1 . • Nitric acid is a chemical of great commercial importance because of its use in the manufacture of explosives like nitroglycerine, trinitrotoluene, gun cotton, picric acid etc., in the manufacture of nitrates which are used as fertilizers and in the manufacture of dyes, drugs and artificial silk. Structure of HNO 3 • HNO 3 is a monobasic acid and is supposed to exist in the following two resonating forms: • As indicated by electron diffraction studies, the molecule of nitric acid, in vapour state, possesses a planar structure as shown below: Properties • Pure 100% nitric acid is a colourless, highly corrosive liquid with powerful oxidizing properties. • The commercial acid varies from colourless to a yellowish red colour, owing to the presence of dissolved nitrogen oxides. • Soluble in all proportions in water and forms a constant-boiling mixture at 760 mm. pressure of 68% acid and 32% water with a boiling point of 110°C. • Solutions containing more than 86% HNO 3 are known as fuming nitric acids.
Transcript
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Nitric Acid (Hydric Nitrate)
(HNO3)
Dr. Muhammad AslamAssistant Professor-Chemistry
Division of Science and TechnologyUniversity of Education, Township Campus, Lahore.
(HNO3)
Basic and Heavy Chemical Industries
• Raw materials and chemicals• Flow sheet diagrams and commercial production of– Sulphuric acid– Nitric acid– Hydrochloric acid– Hydrochloric acid– Oxalic acid– Formic acid– Caustic soda–Washing soda
• Applications of these chemicals in chemicalindustries
Books Recommended
• Advanced Inorganic Chemistry (Volume 1)– S. Parakash
• The most important and useful oxoacid ofnitrogen is nitric acid.
• Its molecular formula is HNO3 and molar mass63 01 g mol-163.01 g mol-1.
• Nitric acid is a chemical of great commercialimportance because of its use in the manufactureof explosives like nitroglycerine, trinitrotoluene,gun cotton, picric acid etc., in the manufacture ofnitrates which are used as fertilizers and in themanufacture of dyes, drugs and artificial silk.
Structure of HNO3• HNO3 is a monobasic acid and is supposed to exist in
the following two resonating forms:
• As indicated by electron diffraction studies, they ,molecule of nitric acid, in vapour state, possesses aplanar structure as shown below:
Properties• Pure 100% nitric acid is a colourless, highly corrosive
liquid with powerful oxidizing properties.• The commercial acid varies from colourless to a
yellowish red colour, owing to the presence ofdissolved nitrogen oxides.
• Soluble in all proportions in water and forms aconstant-boiling mixture at 760 mm. pressure of 68%acid and 32% water with a boiling point of 110°C.
• Solutions containing more than 86% HNO3 are knownas fuming nitric acids.
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Manufacture of Nitric Acid
• The following methods are used to manufacture nitricacid:
(i) From Nitrates• Nitric acid is prepared on large scale by heating Chile
saltpetre (NaNO3) with concentrated sulphuric acid.
• The mixture is placed in a cast iron retort and subjectedto distillation at a temperature of about 200°C.
• Potassium nitrate has also been employed.• The yellow colour of HNO3 is due to the presence of
NO2 in it which can be removed by distillation invacuum.
(ii) From Air by Birkland Eyde Process• Nitrogen and oxygen of the atmosphere can be made to
combine by passing an electric discharge through air orthe air may be passed through an electric arc (temp.3500°C).
• This process at first gives nitric oxide, which is thenquickly cooled to 500°C, when it further combines withoxygen to give about 2% nitrogen peroxide.yg g g p
• The vapours are then washed down by water trickling inabsorption towers filled with quartz stones when nitricacid is produced:
• Before the gases escape in air, they are led throughtowers containing lime or caustic alkali which recover allthe oxides of nitrogen.
(iii) From Ammonia (Ostwald's Process)(Industrial Preparation)
• On a commercial scale, nitric acid is manufactured through theO t ld' th f t l ti id ti f iOstwald's process - the process of catalytic oxidation of ammonia.
• The conversion of ammonia into nitric acid in this process is donethrough the following steps:
Oxidation of ammonia to nitric oxide• In this method a mixture of ammonia gas with air in the ratio 1:8
is passed through a catalyst chamber packed with platinum gauzemaintained at temperature of 800°C.
• The ammonia is oxidized to nitric oxide.
• The exothermic reaction proceeds without supply of heatexcept the initial heating.
• About 90% NH3 is converted to NO under theseconditions.
Oxidation of NO to NO2 and Formation of nitric acid• NO is converted to NO2 in the presence of air or oxygen
and passed through the absorption tower as mentionedabove in arc process.p
• The acid so obtained is dilute which can be concentratedto 68% by distillation, when constant boiling mixture isformed.
• This constant boiling mixture of HNO3 has a specificgravity of 1.42 and is the commercial concentratedHNO3.
• More concentrated acid needed for certain uses isproduced by distillation with conc. H2SO4 which holdsback the water.
• The distillate is 98% HNO3 having density 1.5.Parts of Plant• The manufacturing plant for the production of nitric acid
by the Ostwald's process, has the following componentsand processes.and processes.
Converter• The converter is made of aluminium and fitted with
platinum - rhodium gauze cylinder (23 cm x 34 cm).• The cylinder is closed at the bottom with a silica lid.• The gauze is initially heated to 800°C electrically.• Thereafter no external heating is required as oxidation
of ammonia is an exothermic reaction.
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• A mixture of ammonia and clear air (volume ratio =(1:8) is then passed through the gauze from the top, andthe products leave from the bottom.
• Every 1000 cm2 area of the gauze produces about 500kg of nitric oxide, every 24 hours.
Converter for the Ostwald's process
Ostwald's process for the manufacture of nitric acid.
Ostwald's process for manufacture of HNO3.
Oxidation tower• When nitric oxide, containing nitrogen and some water
vapors, come out of the converter, they are cooled toabout 100°C by passing them through coolers.
• In the oxidation tower, nitric oxide is mixed with moreair and it gets converted to NO2.
Absorption tower• NO2 is allowed to enter the absorption tower from the
lower end.• The tower is packed with quartz pieces and water is
sprinkled from the top.• Here, NO2 is absorbed into water in the presence of air to
yield nitric acid.
• Commercial nitric acid has a brown color due todissolved NO2.
• The procedure of bubbling dry air through warmcommercial nitric acid, is to drive away the dissolvednitrogen dioxide so that the acid becomes colorless.
Concentrating nitric acid• Aqueous nitric acid obtained by this method can be
concentrated by distillation to 68 5% by massconcentrated by distillation to 68.5% by mass.• Further concentration to 98% acid can be achieved by
dehydration with concentrated sulphuric acid.Anhydrous nitric acid• Anhydrous nitric acid can be obtained by distillation of
concentrated aqueous nitric acid with phosphoruspentoxide (P2O5 or P4O10).
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Fuming Nitric Acid
• Fuming nitric acid is made by distilling conc. HNO3with a little starch.
• The starch reduces some acid to NO2 which dissolves inthe remaining acid to form fuming nitric acid.g g
• It is yellow in colour due to NO2.• It is a much more powerful oxidizing agent and
nitrating agent than conc. HNO3.
Laboratory Preparation• Nitric acid is usually prepared by heating potassium
nitrate with concentrated sulphuric acid.• This heating is done in a glass retort and vapors of nitric
acid are condensed in a receiver, which is cooled bywater.
• The reaction is:
Laboratory preparation of nitric acid
Production Unit of Nitric Acid and Nitric Fertilizers
• The section of nitric products practically consists of twoseparate unitsseparate units.
• The first one produces Nitric Acid and the second oneproduces Nitric Ammonia and Nitric Fertilizers.
• The production procedure is briefly shown in thefollowing graph:
• The unit of nitric acid uses ammonia as raw materialwhich is oxidized in the presence of a catalyst initiallyto nitrogen monoxide and then to nitrogen dioxide.
• The produced nitrogen oxides after giving their energyindirectly (steam turbine) or directly (gas turbine), theyare converted into nitric acid by absorbing water.
• In the ammonium nitrate production unit, the nitricid t ith i d dacid reacts with gaseous ammonia and produces a
solution of ammonium nitrate.• A part of the produced solution of ammonium nitrate is
led via a pipe to the production unit of compoundfertilizers.
• The remaining quantity after first being condensed isused for the production of nitric fertilizers.
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Grades• In addition to the various grades of nitric acid, a
nitrating or mixed acid (nitric acid, sulphuric acid andwater) is produced by nitric acid manufacturers in thefollowing standard promotions:
Containers
• Technical grades of weak acids (50 to 70%) in glasscarboys and bottles.
• Concentrated acid (95%) in aluminium or stainlesssteel drums and tank cars.steel drums and tank cars.
• Mixed acid (nitric and sulphuric) in iron drums ortank cars.
Economic Aspects• Nearly all nitric acid manufactured today comes from
the catalytic oxidation of ammonia.• Further most of it is converted to ammonium nitrate at
the same site.• Thus nitric acid manufacture is tied very closely to the
fertilizer industry, and only secondarily to the explosiveindustryindustry.
• The most promising new uses of nitric acid are as anacidulant for superphosphate manufacture and as acomponent of the oxidant for missiles and rockets.
• Both uses are still only problematical.• Efforts to develop processes for making nitric acid
directly from the nitrogen of the air have not beensuccessful.
• Neither the Wisconsin "pebble bed" process nor nuclearnitrogen fixation using uranium 235 have provedeconomically competitive with ammonia oxidation.
• A small amount of acid may still be made from sodiumnitrate, but the process is practically extinct.
• Most current nitric acid plants are built in batteries of55 tons per day.
• Recently the size of individual units has been increasingand one plant produces 250 tons per day in a singleabsorber and a single cooler.
• The single burner also has the same capacity.
UsesIt is used:– in the manufacture of nitrates which are important
chemicals of commerce.Basic calcium nitrate is used as fertilizer.Silver nitrate is used in photography and sodiumnitrate is used in the manufacture of gun powder.
– in the manufacture of explosives like nitroglycerine,p g y ,dynamite, trinitrotoluene, picric acid etc.
– in the manufacture of artificial silk, dyes, medicines,and perfumes.
– in the purification of gold and silver.– as a important reagent in the laboratory.– in the manufacture of H2SO4.– in the preparation of aqua regia.
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Safety• Nitric acid is a corrosive acid and a powerful oxidizing
agent.• The major hazard posed by it is chemical burns as it
carries out acid hydrolysis with proteins (amide) andfats (ester) which consequently decomposes living tissue(e.g. skin and flesh).
• Concentrated nitric acid stains human skin yellow due toConcentrated nitric acid stains human skin yellow due toits reaction with the keratin.
• These yellow stains turn orange when neutralized.Systemic effects are unlikely, however, and thesubstance is not considered a carcinogen or mutagen.
• The standard first aid treatment for acid spills on theskin is, as for other corrosive agents, irrigation withlarge quantities of water.
• Washing is continued for at least ten to fifteen minutesto cool the tissue surrounding the acid burn and toprevent secondary damage.
• Contaminated clothing is removed immediately and theunderlying skin washed thoroughly.
• Being a strong oxidizing agent, reactions of nitric acidwith compounds such as cyanides, carbides, metallicpowders can be explosive and those with many organiccompounds, such as turpentine, are violent andhypergolic (i.e. self-igniting).
• Hence, it should be stored away from bases andorganics.
