Oxidation of Ethylene(Production)

PRODUCTION FROM ETHYLENE

Ethylene is now the most important starting material for the production of acetaldehyde. Most of the present capacity works by the direct oxidation of ethylene. Direct Oxidation of Ethylene

This process was developed between 195 and 1959 by !acker"#hemie and $oechst %&'(. )ormally* the the reaction proceeds as follows+ 1

C 2 H 4 + O2 → CH 3 CHO −244 kj / mol 2

 ,n a-ueous solution of  PdCI   and CuCI   is used as catalyst. ,cetaldehyde ,cetaldehyde 2

2

formation had already been observed in the reaction between ethylene and a-ueous palladium chloride. This reaction is almost -uantitative+ C 2 H 4 + PdCI 2 + H 2 O→CH 3 CHO + Pd + 2 HCI 

n the !acker"$oechst process* metallic palladium is reoxidi/ed b y CuCI  * 2

which is then regenerated with oxygen+  Pd + 2 CuCI 2 → 2 PdCI 2 + 2 CuCI 

2 CuCI +

1 2

O 2 + 2 HCI → 2 CuCI 2 + H 2 O

Therefore only a very small amount of  PdCI   is re-uired for the conversion of 2

ethylene. The reaction of ethylene with palladium chloride ch loride is the rate"determining step. 0ne" and two"stage versions of the process are on stream. One-Stage Method: n the one"stage method* an ethylene oxygen mixture reacts with the catalyst solution. 2uring the reaction a stationary state is established in which 33reaction44 formation of acetaldehyde and reduction of CuCI  6 and 33oxidation44 2

reoxidation of CuCI  6 proceed at the same rate. 7eaction conditions are about 18 :# and & k;a.

Two-Stage Method: n the two  stage process ethylene and oxygen air6 react in the

li-uid phase in two stages. n the first stage ethylene is almost completely converted to acetaldehyde in one pass in a tubular plug"flow reactor made of titanium. The reaction is conducted at 1'5"18 o# and 1.18 M;a palladium and cupric chloride catalysts.  ,cetaldehyde produced in the first reactor is removed from the reaction loop by adiabatic flashing in a tower. The flash step also removes the heat of reaction. The catalyst solution is recycled from the flash tower base to the second stage or oxidation6 reactor where the cuprous salt is oxidi/ed to the cupric state with air. , schematic diagram is given as follows.  ;2) <=TE6

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Acetaldehyde

Chlorinated aldehydes

Unconverted ethylene

Carbon dioxide

Acetic acid

Chloromethane

Ethyl chloride

Minor side products

The yield in both type of process is nearly the same. The balance of the two stage process is as follows+ Ethylene gives+ >95 acetaldehyde >1.9 chlorinated aldehydes >1.1 unconverted ethylene >.? carbon dioxide >. acetic acid >.1 chloromethane >.1 ethyl chloride >.8 ethane* methane* crotonaldehyde and other minor side products • • • • • • • •

n both one and two"stage processes the acetaldehyde yield is about 95> and the production costs are virtually the same. The advantage of using dilute gases in the two"stage method is balanced by higher investment costs.