3 replies to this topic

What are the impurities in Ethylene produced by Ethanol dehydration over alumina catalyst.
Which of these impurities can affect catalyst selectivity in ethylene oxide production on silver catalyst.

[Padmakar Katre]

Dear Ashok
In ethylene produced by ethanol dehydration, there are no as such impurities provided that there is no cracking of alcohol over alumina catalyst and your ethanol has no any other impurities like bittrex and acetone (0.5 % v/v) which is added in ethanol in order to prevent its misuse. Normally reaction is carried out over alumina catalyst and and the energy required or to attain the reaction temperature for dehydration is supplied by superheated steam (5kg/cm2g and 580 C) along with your ethanol inthe alumina catalyst bed reactor. So there is very less chance of cracking of ethanol in reactor provided your reactor inlet temperature doesn't exceed 490 C at 3.5 kg/cm2g pressure.Now ppm level you will find acetaldehyde which is product of dehydrogenation of the ethanol but you can remove it by quenching the reactor effluent in a wash tower and subseqent washing with the 10% caustic so you will get 99.8 % v/v purity of ethylene and the balance will be ethane,methane,propane as cracking products because of presence of higher alcohols in your feed which will crack into the impurities stated above.
Ethanol conversion is 99.99% provided your reactor outlet temperature is 375 C(minimum temperature required to maitain in reactor outlet otherwise you will find alcohol sleepage i.e. unreacted alcohol in reactor effluent) and the specifications of the ethanol you are feeding in the reactor should have less than 10 ppm of acetone and bittrex each , these are the components which affects the selectivity and your reactor inlet temperature which cause the cracking products to lower the selctivity of the catalyst mainly if carbon forms as cracking a product.......
Now regarding the Etlylene oxidation reaction over Silver oxide catalyst - if methane is higher in conc. among thesse impurities it will help you to remove the exothermic heat of reaction simply it works as ballast gas but if you have higher ethane conc. then you will find constraint on your EO reactor outlet Oxygen conc. as it lower the flemmability limit.And the aldehydes come with the ethylene around 800 ppm which may lowers the selectivity exact mechanism I don't know but it makes acids when reacts with water which may lead to corrosion problems.Apart from that the actual conc of aldehydes in your EO reactor is very less around 12 ppm cause the volume handled by the EO reactor very large as compraed to the conc of aldehydes coming with ethylene feed.

Apart from this still have any doubts please let me know
or you can mail me at
padmakar.katre@eil.co.in

cheers........Njoy

[pawan]

Dear Ashok

What Mr Katre has written is 100% right but practical situation is different in general.
Impurities start from fermentation broth ( Bcoz Only U & I are producing it through Green route all over the world) Acetaldehyde, Acetone, S containing compounds consuming lot of energy for repeated purification of Ethanol.

Further the condition of Ethanol dehydration generates few other organic impurities which are complex in nature & are not known to enable us to analyse them properly.

However, the most important Impurity for Oxidation is S.

It will be better for improving the discussion if U can focus on specific problem as such not the derived Questions based on problem.

[Padmakar Katre]

Dear Ashok,
As per Mr. Pawan organic sulpher for oxidation is important.I am 100 % agree with his statement.I am not aware about any removal techniques about this sulpher .I think zinc oxide bed is used for the removal of the inorganic sulpher but there is less quantity of it as you get ethylene from alcohol and not from Cracker.
AS Mr. Pawan said come with the specific problem so that we can discuss enough in this forum.