Manufacturing of Ethylene Oxide by Chlorohydrin Process

Manufacturing of Ethylene Oxide by Chlorohydrin Process

Ethylene Oxide also called as epoxyethane, oxirane. It is cyclic ether, simplest epoxide with faintly sweet odor and colorless flammable gas at room temperature. Ethylene oxide is important to the production of detergents, thickeners, solvents, plastics, and various organic chemicals such as ethylene glycol, ethanolamines, simple and complex glycols, polyglycol ethers and other compounds. It is extremely flammable and explosive and is used as a main ingredient in the manufacturing of thermobaric weapons.

Ethylene oxide was first reported in 1859 by the French chemist Charles-Adolphe Wurtz, who prepared it by treating 2-chloroethanol with potassium hydroxide.

Cl–CH₂CH₂–OH + KOH → (CH₂CH₂)O + KCl + H₂O

Ethylene oxide can readily reacts with divergent compounds with opening of the ring. It’s typical reactions are with nucleophiles which proceed via the SN2 mechanism both in acidic and alkaline media.

Laboratory Synthesis of Ethylene oxide

1] Dehydrochlorination of Ethylene

Dehydrochlorination of 2-chloroethanol, developed by Wurtz in 1859, and it remains a common laboratory route to ethylene oxide:

Cl–CH₂CH₂–OH + NaOH → (CH₂CH₂)O + NaCl + H₂O

This reaction is carried out at elevated temperature, and beside sodium hydroxide or potassium hydroxide, calcium hydroxide, barium hydroxide, magnesium hydroxide or carbonates of alkali or alkaline earth metals can be used.

2] Direct oxidation of Ethylene by Peroxy Acids

Ethylene can be directly oxidized into ethylene oxide using peroxy acids like peroxybenzoic or meta-chloro-peroxybenzoic acid.

Industrial synthesis of Ethylene oxide

In the year 1914, BASF first started the synthesis of ethylene oxide by chlorohydrin process. Later an efficient direct oxidation of ethylene by air was invented by Lefort in 1931 and in 1937 Union Carbide opened the first plant using this process. It was further improved in 1958 by Shell Oil Co. by replacing air with oxygen and using elevated temperature of 200°C-300°C and pressure (1-3 MPa).

Chlorohydrin Process

Chlorohydrin process is comprises of three major steps

• Synthesis of ethylene chlorohydrins
• Dehydrochlorination of ethylene chlorohydrin to ethylene oxide
• Purification of ethylene oxide

Ethylene oxide Commercial Scale Production

The production of ethylene oxide on a commercial scale is attained with the combination of the following unit processes:

Main reactor – The main reactor consists of thousands of catalyst tubes in bundles. The catalyst packed in these tubes is in the form of spheres or rings of diameter 3 to 10 mm. The operating conditions of 200°C to 300°C with a pressure of 1 to 3 MPa prevail in the reactor. The cooling system of the reactor can be used to maintain this temperature. With the aging of the catalyst, its selectivity decreases and it produces more exothermic side products of CO₂.

Ethylene oxide scrubber – After the gaseous stream from the main reactor, containing ethylene oxide (1-2%) and CO₂(5%), is cooled, it is then passed to the ethylene oxide scrubber. Here, water is used as the scrubbing media which wash away majority of ethylene oxide along with some amounts of CO₂, N₂, CH₂CH₂, CH₄ and aldehydes. A small proportion of the gas leaving the ethylene oxide scrubber (0.1-0.2%) is removed continuously to prevent the buildup of inert compounds, which are introduced as impurities with the reactants.

Ethylene oxide de-sorber – The aqueous stream resulting from the above scrubbing process is then sent to the ethylene oxide de-sorber. Here, ethylene oxide is obtained as the overhead product, where as the bottom product obtained is known as the ‘glycol bleed’.

Stripping and distillation column – Ethylene oxide stream is stripped off its low boiling components and then distilled in-order to separate it into water and ethylene oxide.

CO₂ scrubber – The recycle stream obtained from the ethylene oxide scrubber is compressed and a side-stream is fed to the CO₂ scrubber. Here, CO₂ gets dissolved into the hot aqueous solution of potassium carbonate. The dissolution of CO₂ is not only a physical phenomenon, but a chemical phenomenon as well, for, the CO₂ reacts with potassium carbonate to produce potassium hydrogen carbonate.

K2CO₃ + CO₂ + H₂O → 2 KHCO₃

CO₂ de-scrubber – The above potassium carbonate solution is then sent to the CO₂ de-scrubber where CO₂ is de-scrubbed by stepwise (usually two steps) flashing. The first step is done to remove the hydrocarbon gases, and the second step is employed to strip off CO₂.

Applications

Ethylene oxide is one of the most commonly used sterilization methods in the healthcare industry because of its non-damaging effects for delicate instruments and devices that require sterilization, and for its wide range of material compatibility. Ethylene oxide is used as an accelerator of maturation of tobacco leaves and fungicide. Ethylene is used in the synthesis in 2-butoxyethanol, which is a solvent used in many products.

To contact the author mail: articles@worldofchemicals.com