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Ethylene oxide and Ethanolamines

Introduction

• Ethylene oxide is produced by the oxidation of ethylene using air.
• Ethanolamines are produced using the series reaction scheme of ethylene oxide with ammonia.
• Ethanolamines are significantly used as absorbents to remove CO2 and H2S from process gas streams.

Reactions

• C2 H4 + 0.5 O2→ CH2 O.CH2O
• Ethylene to air ratio: 3 – 10 %
• Side reaction products: CO2 , H2O
• Catalyst: Silver oxide on alumina
• Operating temperature and pressure: 250 – 300°C and 120 – 300 psi
• Supressing agent for side reactions: Ethylene dichloride
• Reaction is exothermic
• Air and ethylene are separate compressed and along with recycle stream are sent to the shell and tube reactor.
• The reactor is fed on the shell side with Dowtherm fluid that serves to maintain the reaction temperature. A dowtherm fluid is a heat transfer fluid , which is a mixture of two very stable compounds, biphenyl and diphenyl oxide. The fluid is dyed clear to light yellow to aid in leak detection.
• The hot dowtherm fluid from the reactor is sent to a waste heat recovery boiler to generate steam.
• The vapour stream is cooled using a integrated heat exchanger using the unreacted vapour stream generated from an absorber.
• The vapour stream is then sent to the heat integrated exchanger and is then sent back to the reactor and a fraction of that is purged to eliminate the accumulation of inerts such as Nitrogen and Argon.
• The product vapors are compressed and sent to a water absorber which absorbs ethylene oxide from the feed vapors. Eventually, the ethylene oxide rich water stream is sent to a stripper which desorbs the ethylene oxide + water as vapour and generates the regenerated water as bottom product. The regenerated water reaches the absorber through a heat integrated exchanger.
• The ethylene oxide + water vapour mixture is compressed (to about 4 - 5 atms) and then sent to a stripper to generate light ends + H2O as a top product and the bottom product is then sent to another fractionators to produce ethylene oxide as top product. The heavy ends are obtained as bottom product.


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