Oxalic acid can be manufactured through three main processes: from sodium formate, from propylene, or through a dimethyl oxalate process. The sodium formate process involves reacting sodium hydroxide and carbon monoxide to produce sodium formate, which is then treated to produce calcium oxalate and ultimately oxalic acid. The propylene process is a two-step oxidation of propylene to a-nitratolactic acid and then to oxalic acid. The dimethyl oxalate process produces dimethyl oxalate and then hydrolyzes it to generate oxalic acid crystals.

1. MANUFACTURING OF
OXALIC ACID
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2. Introduction
• Oxalic acid, H2C204 is a colorless crystalline dicarboxylic acid.
It produces a colorless solution on dissolving in water.
• If we consider the acid strength, it is a much stronger acid than
acetic acid. Oxalic acid is a reducing agent and its conjugate
base is called as oxalate.
• Oxalate acts as a chelating agent for metal cations. Typically,
oxalic acid also exists in the form of dihydrate.
• Ingestion of oxalic acid through skin contact or orally proves to
be fatal.
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3. Cont.
• Scheele in 1776 discovered the oxalic acid.
• Scheele produced oxalic acid by the oxidation
of sugar using nitric acid and it was called
saccharic acid.
• It is odorless with molecular formula
126.07gram per mole.
• It is orthorhombic colorless crystal
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4. Manufacturing of Oxalic acid
• There are three methods for manufacturing of
oxalic acid:
• Oxalic acid from sodium formate
• Oxalic acid from propylene
• Oxalic acid dimethyl oxalate process
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5. Oxalic acid from sodium formate
Raw material
• Solid sodium hydroxide (97-98%)
• carbon monoxide
Working
• Solid sodium hydroxide (97-98%) and carbon monoxide react at
a 2000C temperature and 150psi pressure in an autoclave to
produce sodium formate.
• On completion of this reaction, the pressure in the autoclave is
gradually reduced and the temperature is increased to 4000C.
The ceasing of the evolution of hydrogen results in the
completion of the reaction.
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6. Cont.
• The reaction mixture was collected in a precipitator and calcium
hydroxide was added to it with stirring.
• This was followed by the filtration of the calcium oxalate and then
sodium hydroxide was concentrated that could be reused.
• The filter cake of crude calcium oxalate is taken to an acidifier with a
small amount of calcium carbonate and then treated with dilute
sulfuric acid.
• The precipitation of calcium results in the formation of calcium
sulphate dihydrate (CaSO4.2H20).
• The mother liquor was then taken to a crystallizer and concentrated to
the specific gravity of 300 Be.
• Finally, Crystals of oxalic acid in the form of dehydrating was
obtained which was then washed and dried.
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7. Cont.
• The yield of oxalic acid dehydrate was nearly 80% by
weight depending on sodium formate.
• It is generally sold and used in the form of dihydrate.
• But anhydrous oxalic acid can also be obtained by
heating the dihydrate to 1000C by the loss of two
molecules of water.
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8. Cont.
• The direct acidification of sodium oxalate with methanol in the
ratio of 1:3 and in the presence of 0.8 parts of concentrated
sulfuric acid also produces oxalic acid.
• Then the insoluble sodium sulfate can be separated, from the
methyloxallatemethanol sulfuric acid solution. The sodium
sulfate is then filtered and the mother alcohol is hydrolyzed by
the addition of 3.5 parts water. This yields oxalic acid and
methanol. The methanol obtained is then distilled and recycled.
• The crude oxalic acid solution is then concentrated and
crystallized producing the oxalic acid. Molasses can be oxidized
with nitric acid to also produce oxalic acid. Similarly, oxidation
of organic compounds like glycol, alcohol, fats, and other
cellulosic materials in the presence of nitric acid also produces
oxalic acid.
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9. Oxalic acid from propylene
• This method involves the oxidation of propylene with nitric acid
to produce oxalic acid.
• It involves a two-step process, wherein the first step propylene
gets converted into a-nitratolactic acid and the second step
allows the oxidation of a-nitratolactic acid to oxalic acid.
• In the first reactor, propylene was introduced where it reacts
with nitric acid. The molar ratio of propylene and nitric acid is
kept at 0.01 -0.5. The mixture from the first reactor was taken
into the second reactor where it reacts with oxygen
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10. Cont.
• In this step, the vapor of nitric acid continuously evolves from
the top of the vessel.
• The stream from the vessel has intermediate and a trace amount
of nitric acid.
• It was then taken into the reservoir tank where acid was
evolved. a-nitratolactic acid from the reservoir was then
collected into an autoclave where it oxidization occurs at 45 -
1000C in the presence of mixed acid as catalyst. In this step, a-
nitratolactic acid gets converted into oxalic acid dihydrate. The
crude product was then taken into a crystallizer where oxalic
acid crystals are obtained. The slurry obtained from crystallizer
is filtered and sent for drying operation to generate dried oxalic
acid.
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11. Cont.
11

12. Oxalic acid dimethyl oxalate process
• In this process, methyl nitrite is regenerated from circulating gas
containing CO and from regeneration column it was pressurized
and then fed to the reactor.
• In this vessel, dimethyl oxalate was produced but the
consumption of methyl nitrite takes place.
• Freshly brewed dimethyl oxalate and unconverted mixture were
then taken into the condenser where methanol was added.
• Uncondensed vapour containing methyl nitrite, water and
methanol were drawn to regeneration column accompanied by
the addition of NOx and oxygen to regenerate the methyl nitrite
which is to be recycled.
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13. Cont.
• Condensed dimethyl oxalate from the condenser, when
taken into the distillation column, removes water
vapours while dimethyl oxalate was hydrolysed.
• After the completion of hydrolysis of oxalate, the
slurry was sent to the crystallizer to generate a crystal
of oxalic acid.
• The slurry is then filtered and passed from the dryer to
store dried oxalic acid.
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14. Cont.
• In propylene process, the usage of sulfuric acid results into corrosion
problem at the oxidation step. The oxidation reaction can be enhanced by a
large reactor. There is a possibility of unstable by-product formation along
with a-nitratolactic acid and it may even lead to explosion or decomposition.
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15. uses
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• Oxalic acid can be used as a mordant in dyeing processes
• Oxalic acid can remove rust and thus can be used for cleaning
or bleaching
• Beekeepers use 3.2% solution of oxalic acid or its vaporized
form
• Helps in the removal of mustard, ink, different food stains as
well as other types of stains.