MANUFACTURE

1. Oxalic acid from sodium formate

RAW MATERIALS

Basis: 1000kg oxalic acid dihydrate from sodium formate

Sodium formate 1325kg

Calcium hydroxide 650kg

Sulfuric acid 950kg

REACTION:

MANUFACTURE PROCESS

Sodium formate was obtained by the reaction of solid sodium hydroxide (97 - 98%) and carbon

monoxide at 200C temperature and 150psi pressure in an autoclave.

Sodium oxalate was obtained, at the completion of above reaction by reducing the pressure in

autoclave and increasing the temperature to 400C. Reaction was completed after the evolution of

hydrogen was ceased.

The reaction mixture was transferred to precipitator and calcium hydroxide was added under stirring.

The calcium oxalate was filtered and sodium hydroxide was concentrated for reuse. Filter cake of

crude calcium oxalate run to an acidifier with 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:

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2. Oxalic acid from propylene

RAW MATERIALS

Basis: 1000kg oxalic acid from propylene

Propylene 460kg

Nitric acid 1375kg

Oxygen 870kg

REACTION

MANUFACTURING PROCESS

In this process oxalic acid was obtained by oxidation of propylene with nitric acid. It is the two-step

process, in first step propylene was converted into -nitratolactic α acid and second step leads to

oxidation of -nitratolactic α acid to oxalic acid.

In the first reactor, propylene was introduced where it was reacted with nitric acid. 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 vapor of nitric acid was continuously evolved from the top

of the vessel. The stream from vessel contains intermediate and trace amount of nitric acid was run

into reservoir tank where acid was evolved. -nitratolactic α acid from reservoir was then run into

autoclave where it was oxidized at 45 - 1000C in the presence of mixed acid as catalyst. In this step -α

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nitratolactic acid is converted into oxalic acid dihydrate. The crude product was then transfer into a

crystallizer where oxalic acid crystals obtained. The slurry from crystallizer is filtered and sent for

drying operation where dried oxalic acid is obtained.

BLOCK DIAGRAM

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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.

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BLOCK DIAGRAM

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4. Oxalic Acid from Molasses using Nitric Acid:

RAW MATERIALS:

1. Nitric Acid

2. Sulphuric Acid

3. Water

4. Molasses

5. 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 2-3

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 into a crystallizer in

which oxalic acid crystals along with mother liquor comes out and further these are separated with help of a

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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

Figure: Manufacture of oxalic acid using Molasses & Nitric Acid

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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 -nitratolactic α 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 4th 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

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