Oxalic acid industrial preparation

This presentation will support you in the understanding of commercial preparation of Oxalic acid.

1. Commercial Production of Oxalic Acid By Mr. Muhammad Ullah Afridi Institute of Chemical Sciences, University of Peshawar.

2. MANUFACTURING OF OXALIC ACID 1

3. Introduction Oxalic acid, H 2 C 2 4 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. 2

4. C o nt inue.. . 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 3

5. 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 4

6. 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 2000 C 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. 5

7. C o nt inue… . 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 ( CaSO 4 .2H 2 O ). 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. 6

8. C o nt inue.. . 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. 7

9. C o nt inue… . 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. 8

10. 2. 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 9

11. Continue … . 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. 10

12. C o nt inue... . 11

13. 3. 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 NO x and oxygen to regenerate the methyl nitrite which is to be recycled. 12

14. C o nt inue.. . 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. 13

15. C o nt inue.. . 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. 14

16. Applications 15 Oxalic acid can be used as a mordant (substance used to treat leather before dyeing aids) in dying processes Oxalic acid can remove rust and thus can be used for cleaning or bleaching Bee keepers 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.

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