ethylene santosh

8/7/2019 Ethylene santosh

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Ethylene (H 2C=CH 2 )

History and introduction

Ethylene discovered by Johann Joachim Becher , who obtained it by heatingethanol with sulfuric acid . Ethylene ( IUPAC name: ethene ) is a gaseousorganic compound with the formula C 2H4. It is the simplest alkenes (older name: olefin from its oil-forming property). Because it contains a carbon-carbondouble bond, ethylene is classified as an unsaturated hydrocarbon. Largest volume hydrocarbon used in the petrochemical industry and is also a planthormone .[2] Ethylene is the most produced organic compound in the world;global production of ethylene exceeded 107 million tonnes in 2005. Ethyleneis a plant hormone that differs from other plant hormones in being a g as . Ethylene

promotes the ripenin g of the fruit. Ethylene, also known as the 'death' or 'ripeninghormone' plays a regulatory role in many processes of plant growth, developmentand eventually death.

Processing methods

Ethylene produced mainly by thermal cracking of hydrocarbons in thepresence of steam, and by recovery from rtefinery cracked gas.

1.from hydrocarbons by steam cracking

*The hydrocarbon stream is heated and then diluted by mixing with steam,before entering a tubular reactor.

*Depending on the feed stock used cracking takes place at atemperature of 750-870 c under partial pressure with a residence time of up to 1seconds.Reaction is endothermic.

*The exit gases are rapidly quenched to 550-600 c to prevent secondary

reactions the heat is used to generate high-pressure steam.*After each stage liquid is removed and the remaining gases are treated withan aqueous caustic alcohol-amine mixture to remove any sulphurous gasesand carbon dioxide.


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*Hydrogen and methane are removed in demethanizer .Bottoms from thedemethanizer, containing c 2 and heavier products, are fed to the deethanizer,where acetylene, ethylene and ethane are separated overhead.

*Effluent from the base of the deethanizer passes to the depropanizer and c 3 fractions are separated overhead from c 4 and higher carbon fractions.Propylene is separated from propane by fractionation.

Reaction

C2H6 C 2H4 + H 2

2. From propylene by disproportionation

*A demethanized propylene-propane stream is fed into a reactor operating at7 bar and a temperature of 366-450 c and containing a catalyst.

*Catalyst used :-oxides of molybdenum, cobalt , tungsten or rhenium on analumina or silica support.

*The effluent gases are fractioned and ethylene is recovered overhead.Anyunconverted propane is recycled to the reactor.

*Bottoms from the fractionator pass into a butene purifier where high purity

butenes are collected overhead. Propylene conversion per pass is around 40%.

Reaction

2 C 3H6 C 2H4 + C 4H8

3.From ethyl alcohol by dehydrogenation

*Ethyl alcohol is vaporized by preheating with high-pressure steam beforepassing over a fixed bed of activated alumina and phosphoric acid .

*The reactors can be either isothermal or adiabatic.The temperature ismaintained at 296-315 C

*Accurate temperature control is required to minimize the formation of by-product acetaldehyde or ether. The catalyst is regenerated by passing air andsteam over it to ramove carbon deposits .


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* Gases from the top of the reactor are quenched and water washed toremove any unreacted ethyl alcohol and acetaldehydes. This is followed byscrubbing with dilute caustic soda which absorbs any carbon dioxide.

*A fluid bed process has been developed which provides a more efficientmeans of temperature control and conversion rates of up to 99 %.

Reactions

2 C 2H5OH (C 2H5)2O +H 2O

(C2H5)2O 2 C 2H4 + H 2O

Other processes:-

1.from crude or residual oil

2.from coal

Properties

Molar mass 28.05 g/mol

Density 1.178 kg/m 3 at 15 C, gas [1]

Melting point

169.2 C (104.0 K, -272.6 F)

Boiling point

103.7 C (169.5 K, -154.7 F)

Solubility in water 3.5 mg/100 ml (17 C)

Acidity (pK a) 44

*Colourless gas with faintly pleasant odour

*Highly flammable and forms explosive mixtures with air.

*Slightly soluble in water. Soluble in liquid hydrocarbons.

y Major hazard : Fire and High Pressurey Toxicity : Simple Asphyxiant


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y Flammability limits in air (STP conditions) : 2.7-34 vol%y Odour : Sweet

Applicationsy Chemicals

In term of quantity produced, ethylene is the most important organic chemical. Ethylene is thefeedstock in the manufacture of the most important polymer: polyethylene.

y F ood and Beverage

Ethylene is used to ripen various fruits (largely bananas).

Reference

y http://en.wikipedia.org/wiki/Ethylene y http://www.catalyticgenerators.com/whatisethylene.html y http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=29#MajorAppl

ications y Handbook of petrochemicals and processes,G Margaret wells.

ethylene santosh

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