Module: 2 Lecture: 6 ACETIC ACID (continued) Module:2

Module:2
Lecture:6 Acetic acid
Dr. N. K. Patel
Module: 2
Lecture: 6
ACETIC ACID (continued)
3. Ethylene oxidation
Raw material
Basis: 1000kg of acetic acid by ethylene oxidation
Ethylene
470kg
Oxygen
530kg
Reaction
Manufacture process
Gas recycle
Separator
Acetaldehyde
recycle to
reactor
Reactor
Ethylene
Distillation
Palladium
catalyst
Steam
Oxygen
Acetic acid
Figure: Manufacture of acetic acid by ethylene oxidation
Block diagram of manufacturing process
Diagram with process equipment
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Module:2
Lecture:6 Acetic acid
Dr. N. K. Patel
Animation
Vapour phase oxidation of ethylene was carried out using palladium
supported on alumina as catalyst. Ethylene and oxygen was charged into a
reactor in vapour phase. The reaction temperature and pressure was
215 – 2500C and 150 -300psi respectively. Unreacted ethylene from product
stream was separated in separator. The crude liquid containing
acetaldehyde and acetic acid was separated in a distillation column.
Acetaldehyde and ethylene obtained from distillation and separation
respectively, where recycled to the process for increasing yield and
conversion.
4. Oxidative fermentation
Raw material
Basis: 1000kg of acetic acid by oxidative fermentation
Ethanol
770kg
Oxygen
530kg
Reaction
Manufacture process
Dilute ethanol
solution
Acetobacter
Nitrogen
Water
vapor
Cooled
water
Air
Acetic acid
still
Water
Water
Fermenter
Autoclave
Steam
Scrubber
Acetic acid
Figure: Manufacture of acetic acid by oxidative fermentation
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Module:2
Lecture:6 Acetic acid
Dr. N. K. Patel
Block diagram of manufacturing process
Diagram with process equipment
Animation
Dilute solution of alcohol was first sterilize in autoclave and then
charged in to fermenter. Oxygen in the form of air was supplied by bubbling
through the solution of alcohol in fermenter. An aerobic bacterium like
acetobacter was added into the fermenter for aerobic fermentation.
Oxidation of ethanol was carried out at 26 – 360C temperature.
Nitrogen was removed from product stream in scrubber, by scrubbing
with cooled water. Liquid mixture coming out from bottom of scrubber
containing acetic acid and water was separated in acetic acid still. Vinegar
of 15% and 20% acetic acid was manufacture in 24hrs and 60hrs process
respectively.
5. Anaerobic fermentation
Raw material
Sugar
Anaerobic bacteria (Genus Clostridium)
Nitrogen
Reaction
Manufacture process
The species of anaerobic bacteria, including members of the genus
clostridium are used which are capable to convert sugars to acetic acid
directly, instead of using ethanol. At an actual 85% yield, the anaerobic
process offers 60% reduction in raw material. The mechanism of anaerobic
fermentation of sugar is quite complex.
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Module:2
Lecture:6 Acetic acid
Dr. N. K. Patel
Anaerobic Fermentation of sugar was carried out in fermenter. An
anaerobic bacterium like clostridium was added to initiate the fermentation
process. Nitrogen is supplied by bubbling during the fermentation process.
Clostridium
Nitrogen
Water
vapor
Sugar
Cooled
water
Nitrogen
Acetic acid
still
Water
Water
Fermenter
Scrubber
Steam
Acetic acid
Figure: Manufacture of acetic acid by anaerobic fermentation
Block diagram of manufacturing process
Diagram with process equipment
Animation
The mixture was then charged in to scrubber where it is scrubbed with
cooled water to remove excess nitrogen present in system. Mixture coming
out from bottom of scrubber contains acetic acid and water which was then
separated in acetic acid still.
The most important method for producing acetic acid in modern
industries is carbonylation of methanol.
Engineering aspects
Acetaldehyde oxidation process
 Reactor design
The reaction vessel consists principally of aluminum-lines steel vessel
fitted with air distributor. Aluminum coils for heating and cooling, inlet and
outlet opening and an air distributor.
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Module:2
Lecture:6 Acetic acid
Dr. N. K. Patel
Alternative purification methods for acetic acid from acetaldehyde
have discovered but it has no industrial application. Nitric acid and sodium
nitrate were used for oxidation of formic acid and acetaldehyde, but they
causes serious corrosion problem.
Water
Water
Air
Figure: Rector used in acetaldehyde oxidation
Impurities are reduced rather than oxidized by oxidizing agent. The
reduction is carried out by passing hydrogen over a metallic catalyst such as
nickel or copper turnings. This method is not used because hydrogen can be
explosive. Acetaldehyde conversion is 90%. Stainless steel must be used in
plant construction.
Methanol carbonylation process
In carbonylation process, methanol is obtained from synthesis gas, so
manufacture of acetic acid without isolating methanol is explored in both
vapour and liquid phase. If halide promoted ruthenium catalyst used
alcohols are generated. Acetic acid is produced by addition of Ru 3(CO)12. A
selective synthesis can be done by using complex metallic catalyst
containing rhodium, manganese, iridium and lithium supported on silica.
Catalyst activity can be improved by running them in by stages to the
optimum operating temperature over prolonged time periods.
Ethylene oxidation process
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Module:2
Lecture:6 Acetic acid
Dr. N. K. Patel
 Ethylene concentration
Ethylene concentration was kept below 3%. If it above 3% then there is
always possibilities of formation of by products viz. acetaldehyde, ethanol
etc. There so yield ane acetic acid was lowered.
 Amount of air
The oxygen supply should be kept optimum. If oxygen supply in lesser
amount will kill the bacteria.If over-oxidation takes place, acetic acid will
convert in to CO2 and H2O; which leads to decrease in acetic acid
production. To overcome the problem efficient aeration are used by
compressed air and proper mechanical device.
PROPERTIES
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Molecular formula
Molecular weight
Appearance
Odour
Boiling point
Melting point
Density
Solubility
: C2H4O2
: 60.05gm/mole
: Colourless liquid
: Pungent
: 118-1190C
: 16-170C
: 1.049gm/cm3
: Miscible with water
USES
 As monomer in the production of vinyl acetate
 Used in synthesis of wood glue, synthetic fibres, fabrics and cellulose
acetate
 Esters of acetic acid used as solvent in coatings, inks and paints industry
 20% of acetic acid is used as solvent in terephthalic acid production
 As a stop bath in development of photographic films
 As a household vinegar to clean indoor climbing holds of chalk
 As solvent for recrystallization to purifyorganic compounds
 As wart and verruca remover
 As a food additives
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