9 replies to this topic

[Vegeta]

Dears,

I need your help in understanding the basic chemistry & the reaction kinetiic of liquid polymerization of a stream that contains the following:

Propylene
1-butene
Trans-2-butene
Cis-2-butene
Isobutylene
1,3-butadiene
Acetone & methanthiol in very low concentration

The liquid is in contact with carbon steel only.

I need very basic information such as at what temperature the reaction happens, the activation energy, what concentration enhances the reaction... etc.

Regards,

[Pilesar]

I suggest you research "green oil" oligomer formation in olefins plants. Green oil is a common contaminant and has been studied extensively due to its economic impact.

[Vegeta]

I tried that but most of the articles talks about catalytic processes while my problem is not.
In my case the stream is a mixed C4 stream that forms polymers when it passes through a heat exchanger.

One more question: which one of the above chemical is the most readily polymerized? And at what temperature ?

[abhi_agrawa]

Vegeta,

 

Inyour list, I believe Butadiene would be the easies one to form polymers. I butadiene polymer is know as "popcorn" and is a well studied issue for Butadiene plant. Suggest reading about the same.

 

Can you provide some background of the problem. Also the temperature, pressure and composition of the problematic stream would be helpful in advising the potential issue.

 

abhishek

[Vegeta]

The problem is a polymerization in a heated vessel to vaporize its content of olefins. The operating temperature is between 80 and 95 deg C.
The composition is like this (in liquid volume percentage):

Propylene 4%
1-butene 12%
Trans-2-butene 18%
Cis-2-butene 12%
Isobutylene 25%
1,3-butadiene
Acetone & thiols 5%
the rest is parrafinic C3, C4 & C5

[Vegeta]

I missed the composition of the butadien: it is 2%.

[Vegeta]

Any idea ?

what could be employed to avoid the polymerization.

By the way, the polymeric material is dark & gummy.

[abhi_agrawa]

Vegeta,

My understanding of your problem is as follows:

 

a. You have a continuous stream, with the composition as indicated in your earlier posts. This stream is in liquid phase. 

b. This stream comes to a vessel and is vaporized completely in this vessel.

c. You see dark and gummy polymeric material.

 

In order to better define the problem, I have the following questions:

 

1. What is the temperature and pressure of the liquid stream?

2. How is the stream vaporized - do you have a jacketed vessel or a coil in vessel or and external heat exchanger? A PFD of the system would be helpful.

3. What is the heating media?

4. Where do you see the polymeric material?

5. Did you get the polymeric material analyzed to understand what polymer is it? If yes, can you share the results?

6. Can you also please provide the source of your stream.

 

Having said the above, there are several polymerization inhibitors available. The most optimum choice depends on the several factors, including the usage of the vaporized stream. Depending on how the vaporized stream is being further processed, you may or may not be able to use an inhibitor.

 

abhishek

[Vegeta]

Your understanding is right. 

 

Here are the answers to some of your questions:

 

1. The liquid is pumped and it reaches the vessel at 8 to 15 barg. Its temperature is ambient in the range of 30 C. 

2. There is a coil.

3. Low pressure steam. 

4. Covering the coils and on the shell's wall of the vessel.

5. Not detailed analysis. The analysis says it is 100% organic.

6. The source is from variuos places including untreated field sources. 

[abhi_agrawa]

Vegeta,

 

Are you using desuperheated steam? As the polymerization is seen on the coils, a possible reason would be a high temperature gradient at the coil. To overcome this, the options would be to either lower the temperature of the heating medium or using a suitable polymerization inhibitor.

 

To reduce the steam temperature, the only option is to desuperheat. This may give you some relief, but I am not sure if it would mitigate your problem. I would also recommend that you should look at the possibility of passivating the vessel. Since the polymerization is also seen at the walls, a possible cause could also be metal - butadiene interaction. To overcome the same, people producing butadiene passivate the unit before start-up.

 

The other possibility is using inhibitors. For that you should get in touch with the experts - NALCO is one of them. Depending on your stream they would be able to devise an inhibitor injection plan for you.

 

Another thing that I have seen sometimes is that people install a reboiler for vaporizing the stream. In such a situation, using atleast two reboilers is recommended - one operating and one spare. This way you can maintain production when you are cleaning the spare. Since you use a coil, it looks like the required duty is not very large and I am not sure if installing a reboiler would be economical or not.

 

Hope this helps,

Abhishek