MANUFACTURE
1. Oxalic acid from sodium formate
RAW MATERIALS
Basis: 1000kg oxalic acid dihydrate from sodium formate
Sodium formate
Calcium hydroxide
Module:2
Sulfuric acid
Lec ture:10 Oxalic ac id
1325kg
650kg
950kg
Dr. N. K. Patel
REACTION:
Reaction
Manufacture
process
MANUFACTURE
PROCESS
Sodium formate was obtained by the reaction of solid sodium hydroxide (97 - 98%)
Sodium
formate
was temperature
obtained by
reac
tion of
solid
sodium
and carbon
monoxide
at 200C
and the
150psi
pressure
in an
autoclave.
hydroxide (97 - 98%) and c arbon monoxide at 2000C temperature and 150psi
pressure
an autoclave.
Sodium in
oxalate
was obtained, at the completion of above reaction by reducing the
pressure in autoclave and increasing the temperature to 400C. Reaction was
Sodium
oxalate
was obtained,
at the
of above reac tion by
completed
after
the evolution
of hydrogen
wascompletion
ceased.
reduc ing the pressure in autoc lave and inc reasing the temperature to 4000C .
Reac
was cmixture
ompleted
the evolution
of hydrogen
was c eased.
The tion
reaction
wasafter
transferred
to precipitator
and calcium
hydroxide was
C a l c iu mThe calcium oxalate
D i lu t e
added under
was filtered and sodium hydroxide was
H y d r o g e n stirring.
h y d r o x id e
s u l fu r i c a c id
concentrated
for reuse. Filter cake of crude calcium oxalate run to an acidifier with
S o d iu m
fo r m a te
C r y s t a l li z e r
small amount of calcium carbonate and treated with dilute sulfuric acid. Calcium
precipitated out as calcium sulphate dihydrate (CaSO4.2H2O). Mother liquor was
run to a crystallizer and concentrated to specific gravity of 300Be. Crystallize oxalic
acid in the form of dehydrate was washed and dried.
The yield of oxalic acid dehydrate was about 80% by weight based on sodium
formate. It is generally sold and used, as the dihydrate, but heating the dihydrate to
100C where it loses 2 molecules of water may form anhydrous oxalic acid.
The sodium oxalate may be acidified directly to oxalic acid by mixing 1 part sodium
oxalate with 3 parts of methanol and 0.8 parts of concentrated sulfuric acid.
Separate insoluble sodium sulfate, from the methyloxallate- methanol-sulfuric acid
solution. Filter sodium sulfate and hydrolyze the mother liquor by the addition of 3.5
parts water to form oxalic acid and methanol. Distilled the methanol and recycled to
the process. Concentrate the crude oxalic acid solution and crystallized the oxalic
acid.
Oxalic acid is also manufactured by the oxidation of molasses with nitric acid.
Similarly, oxalic acid can be obtained from many other organic compounds like
glycol, alcohol, fats, oat hulls saw dust and other cellulosic materials by oxidation
with nitric acid.
BLOCK DIAGRAM:
2
2. Oxalic acid from propylene
RAW MATERIALS
Basis: 1000kg oxalic acid from propylene
Propylene
460kg
Nitric acid
1375kg
Oxygen
870kg
REACTION
3
Dr. N. K. Patel
Lec ture:10 Oxalic acid
Reaction
Manufacture process
MANUFACTURING
PROCESS
In thisoxalic
process
acid wasbyobtained
propylene
withIt
In this process
acidoxalic
was obtained
oxidationby
ofoxidation
propyleneofwith
nitric acid.
nitric acid. It is the two-step process, in first step propylene was converted into
α-nitratolactic acid and sec ond step leads to oxidation of α-nitratolactic acid
acid and second step leads to oxidation of α-nitratolactic acid to oxalic acid.
to oxalic acid.
is the two-step process, in first step propylene was converted into α-nitratolactic
In the first reactor,
N it r ic a c idpropylene was introduced where it was reacted with nitric acid.
N it r ic a c id
re c ove ry
Propylene to nitric acid molar ratio is kept at 0.01 - 0.5. The mixture from first
reactor was run into second reactor where it was reacted with oxygen. In this
reactor vaporF ir of
nitric acid was continuously evolved from the top of the vessel. The
st
r e a c to r
stream from vessel contains intermediate and trace amount of nitric acid was run
P r o p y le n e
into reservoir tank where acid was evolved. α-nitratolactic acid from reservoir was
then run into autoclave where it was oxidized at 45 - 1000C in the presence of
O xyg en
mixed acid as catalyst. In this step α-nitratolactic acid is converted into oxalic acid
dihydrate. The crude product was then transfer into a crystallizer where oxalic acid
I n t e r m e d ia t e
crystals obtained. The slurry from r crystallizer
is filtered and sent for drying
e s e r v o ir
O xyg en
operation where dried oxalic acid is obtained.
N it r ic a c id
BLOCK DIAGRAM
C a t a ly s t
F ilt e r
A u t o c la v e
M o th e r
li q u o r
C o ld
a ir o u t
D rye r
H ot
a ir
O x a lic a c id
F ig u r e : M a n u fa c tu r e o f O x a lic a c id fr o m P r o p y le n e
Block diagram of manufac turing process
4
C a rb o n
m o n o x id e
N it r ic a c id
N it r ic a c id
re c o ve ry
F ir s t
re a c to r
S econd
r e a c to r
O xyg en
C a t a ly s t
I n t e r m e d ia t e
r e s e r v o ir
A u t o c la v e
N it r ic a c id
C r y s t a lliz e r
F ilt e r
D ryer
O x a lic a c id
M o th e r
liq u o r
F ig u r e : M a n u fa c tu r e o f O x a lic a c id fr o m P r o p y le n e
5
3. Oxalic acid dimethyl oxalate process
RAW MATERIALS
Basis: 1000kg oxalic acid from methyl nitrite and carbon monoxide
Carbon monoxide
957kg
Methyl nitrite
1330kg
Water
395kg
REACTION
MANUFACTRING PROCESS
In this process, circulating gas containing CO and regenerated methyl nitrite from
regeneration column was pressurized and fed to the reactor. In this vessel dimethyl
oxalate was produced while methyl nitrite is mostly consumed. The dimethyl
oxalate and unconverted mixture was run into the condenser where methanol was
added. Uncondensed vapor contains methyl nitrite, water and methanol was drawn
to regeneration column where NOx and oxygen are added to regenerate the methyl
nitrite which is to be recycled.
Condensed dimethyl oxalate from condenser was run into the distillation column
where water vapors were removed while dimethyl oxalate was sent for hydrolysis
where water is added. After the hydrolysis of oxalate, slurry was sent to the
crystallizer where a crystal of oxalic acid is obtained. The slurry is then filtered and
passed from dryer and dried oxalic acid stored.
6
BLOCK DIAGRAM
7
4. Oxalic Acid from Molasses using Nitric Acid:
RAW MATERIALS:
1.
2.
3.
4.
5.
Nitric Acid
Sulphuric Acid
Water
Molasses
Vanadium Pentoxide (Catalyst)
REACTION
C6H12O6 + HNO3
3 [COOH]2. 2H2O + 6NO
MANUFACTURING PROCESS:
Molasses is a viscous by-product of the refining of sugarcane, grapes, or sugar beets
into sugar. The word comes from the Portuguese―melaço, ultimately derived from
Mel, the Latin word for "honey”. The quality of molasses depends on the maturity of
the source plant, the amount of sugar extracted, and the method employed.
Molasses are of various type based on plant material from which it is produced. So
different type of molasses produced base upon on various raw material are cane
molasses from sugarcane, beet molasses from sugar beet, grape molasses from
grapes .Its major constituents are- 1) Glucose–35.9% 2) Fructose-5.6% 3) Sucrose–
2.6% 4) Water-23.5%
Initially molasses was preheated & temperature of it was increased from 37oC to 65.5oC. After that it was
fed into a CSTR. Simultaneously Nitric acid was also fed into the CSTR along with Vanadium Pentoxide,
which act as a catalyst. This mixture was mixed thoroughly & was allowed to react for 2-3 hours. After 23 hours, Oxalic acid, un-reacted molasses, un- reacted Nitric acid, Nitrogen Oxide was formed. Oxalic
acid along with un-reacted molasses, unreacted Nitric acid and Vanadium Pentoxide comes out from the
bottom section of CSTR and undergoes further separation process. During this process Vanadium
Pentoxide gets first get separated out with help of a filter. Oxalic acid & mother liquor (unreacted Nitric
acid & molasses) is separated in a 2-stage process. In the first stage, solution that has been filtered is fed
8
into a crystallizer in which oxalic acid crystals along with mother liquor comes out and further these are
separated with help of a centrifuge. After Oxalic acid gets separated, to remove inclusion (process by
which a solvent particles get trapped inside a crystal) ,it is re-crystallized by adding hot water inside a
crystallizer containing these Oxalic acid crystals.
After separating out the mother liquor again, Oxalic acid crystals are sent into drier to remove the
moisture present on the surface of the crystals. Nitrogen Oxide gas which comes out from the top surface
of CSTR cannot be discharged directly to the atmosphere, as it can cause air pollution, so this gas was
sent into a compressor to increase the pressure & to a steam heater to increase the temperature. After that
this gas was sent to fluidized-bed reactor & in presence of Al203catalyst, Nitrogen dioxide gas is formed.
Al203after this get separated by cyclone separator. After this process, in an absorber, Nitrogen dioxide
gas was allowed to react with water sprayed inside the absorber to produce Nitric acid & Nitrogen oxide
gas. Nitric acid (20%)obtained which is less concentrated than the Nitric acid (95%)which was used as a
fed can further be used in other industrial process and Nitrogen oxide gas can be recycled back to stream
leading to fluidized bed reactor.
BLOCK DIAGRAM
V2O5
NO
CS
HNO3
NO
MOLASSES
NO
R1
T
S
F
S
R2
NO+NO2
NO
HNO3 (20%)
FILTER
HOTWATER
N1
C1
N2
C2
TD
OXALICACIDCRYSTALS
9
Figure: Manufacture of oxalic acid using Molasses & Nitric Acid
Equipments:
S – STEAM HEATER
R1 – CSTR
T – COMPRESSOR
F – FLUIDIZED BED REACTOR
R2 – ABSORBER
CS- CYCLONE SEPARATOR
N1 & N2 – CRYSTALLIZERS
C1 & C2 – CENTRIFUGE
TD- TUNNEL DRYER
ENGINEERING ASPECTS & TECHNOLOGY SELECTION

In propylene process, sulfuric acid is used which results into corrosion problem

at the oxidation step.
Oxidation reaction can be made speedy by using large reactor, thus increase

in capital investment.
Possibility of unstable by-product formation along with α-nitratolactic acid

leads to explosion or decomposition.
In dimethyl oxalate process, the manufacturing process is complex, time

consuming and requires highest capital investment.
In the sodium formate process, the temperature pressure conditions are quite

high which might lead to safety issues and high equipment cost.
Thus, considering the above drawbacks of the first three processes used in
manufacturing oxalic acid, we choose the 4 th process i.e., Manufacture of

oxalic acid using molasses & nitric acid.
Reasons for selecting the 4th process are as follows:
1. Abundance of raw materials
2. Good yield of oxalic acid
3. Low cost of operation
4. No pollution caused during the process
5. Simplicity of operation
10