9 replies to this topic

[rid1kabir]

Hi , 

 

I have thermally cracked Fuel oil and the yield was light distillates and diesel grade fuel. But it turned dark and had a very bad odor after few hours.

 

After searching internet and publications , I learned that it could be due to high boiling range mercaptans. 

 

Is Copper sweetening process suitable for diesel ?

 

Could anyone name a process which I can conduct on a lab scale ?

 

regards,

Ridwan

[PingPong]

The gasoil product from thermal cracking (Visbreaking, Delayed Coking) of fuel oil is not diesel grade.

 

It contains unsaturates which react with oxygen from the air resulting in a very dark colour. Moreover reaction of the unsaturates with oxygen forms polymers that cause fouling and plugging.

 

It needs to be hydrotrated in an HDS unit to make it diesel grade.

 

Without hydrotreating it is only suitable for fuel oil blending.

Edited by PingPong, 14 June 2016 - 02:31 AM.

[rid1kabir]

Thank you for the reply Ping, I understand that HDS is widely accepted method of treating the unsaturated oil. It is too difficult and expensive to perform on small scale.

 

alternately Is there any other process by which the odor can be removed ?

 

earlier i have seen that clay treatment improves the color. But I am not able to remove the odor.

 

sulfur level are not an issue. We dont need ultra low sulfur diesel.

Edited by rid1kabir, 14 June 2016 - 11:32 AM.

[PingPong]

Mercaptans in LPG, gasoline or kerosene (jet fuel) are usually oxidised using UOP Merox process, or Merichem process. But applying Merox on gasoil stream I have never seen, although it may be possible if tat gasoil is straight run (without olefins). Your cracked gasoil however contains unsaturates (olefins) that react with the oxygen that is used in the Merox process resulting in gum (polymer) formation that gradually plugs the catalyst bed. You can contact UOP or Merichem whether they have experience with processing VBU or DCU gasoil containing unsaturates.

 

I am not familiar with the Copper sweetening process, other than what I read in the literature.

I have never seen a refinery scheme that used it. As far as I know it is a very old process used for sweetening naphtha and lighter (not kero or gasoil) but that does not necessarily mean that it could not be made suitable for your unsaturated gasoil. But again I fear that gum formation will be a problem.

[rid1kabir]

ping , thanks so much for your insight.

 

if we go back to the earliest processes. when cracking was developed by Burton , how did they treat the distillates ? every literature says they changed the shutoff valve from "between tank and condenser" to "the end of the condenser".  This resulted in reduction of odor. Moreover they used wet treating processes.  but no where can i find details . Any clue where I can find these resources ?

[PingPong]

Burton thermal cracking process is a hundred years old.

I can't imagine that anybody uses that primitive process anymore.

Moreover that process was designed to produce gasoline, not gasoil (diesel) as far as I know.

 

The gasoline from the Burton process was treated with sulfuric acid to remove bad smelling sulfur compounds and unstable gum forming compounds.

I don't know what they did with the contaminated sulfuric acid after that.

Maybe just neutralize with caustic and simply dump it in the nearest water stream.

In those days hardly anybody cared about the environment.

However the world has moved on since then.

[rid1kabir]

Dear Ping ,

 

Thank you for the insight. All the processes mentioned are on large scale. If i were to proceed on a labscale how would I sweeten cracked gas oil .

 

sincerely

Ridwan

[PingPong]

No refinery sweetens cracked gasoil. It is always hydrotreated if it is to be used as diesel.

I don't think that they did it even in Burton's days.

 

I don't understand why you would want to try this on a lab scale. What is the purpose of that?

What is the origin of the cracked gasoil?

[rid1kabir]

The cracked gas oil is from thermal cracking of furnacr oil 380 cst 3% sulfur.

My aim to use less expensive processes to reduce odor since I do not need ultra low sulfur diesel. Regulators allow sulfur level of 2500ppm marine grade.

[PingPong]

I think it is an illusion that you can come up with a simple and cheap process to eliminate mercaptans from cracked gasoil.

If it were simple it would already have been invented and in use.

 

Maybe it was invented but not used. You can do a patent search on this subject. You will, amongst others, find old patents that use sulfuric acid, as I already mentioned before.

 

But apart from mercaptans, you also have the problem of unsaturates that can cause storage instability and plug filters et cetera with gums.

 

In any cause I can't help you any further as this subject is not really my experience.