Improving Steam Stripping for Monomer Recover from Latex 1

[lcms]

Dear Sirs,

I have to improve my existing process for recovering Acrylonitrile from an emulsion and I am considering to test a Prosonix direct steam injection device in a recirculation pipe to mix better the steam within the latex in order to increase the contact efficiency between steam and latex, very poor so far (I have been using a sparger inside the recovering vessel and a single "T" to mix the steam (1") with the latex (3") in a recirculation pipe that presented better results).

I would like to know if any of you have already been tried this device in such application and what was your results. In my case (with my single "T" as a mixer) the contact efficiency have improved a lot, but the steam pipe from the control valve to the latex inlet clogs very easily between heating/stripping cycles (my process is in batch mode).

My goal is to remove 1.4% (14,000 ppm) of Acrylonitrile from 4,300 pph of recirculating latex using 1,000 pph of 28 psig saturated steam. The concentration in the latex after the removel must reach bellow 500 ppm (0.05%).

Thanks in advance.

 

[ajs1972]

I was working in a plant where the product passed for a vessel with three inlets for steam in the bottom and another pipe for recieve the latex. The residual styrene monomer was reduced from 3500 ppm until 30 ppm. We didn´t have this device, the mix was produced in the vessel, because it had a agitator.

Some improvements in the process helped with residual monomer remotion for example: increse the vacuum due to the use of cold water in the condenser and vacuum pump, or control in a lower temperature.

 

[lcms]

Dear ajs1972,

First, thanks for your fast and valueable answer.

Actually, this is exactly my recovering process for Acrylonitrile recovering (agitated expansion vessels with perforated pipe for stripping steam inlet), and as long as I know (since I also have a Styrene monomer recover system that uses a columm with perforated plates instead of vessels) it should be working well, but it is not.

My main problem with this system is related to foam formation (I am not quite sure if you are removing this residual monomer from latex, that is my case) that could never reach the evacuation system otherwise it will dramatically clogs all the system (believe me: - it is a nightmare). Therefore I am trying to use an alternative that, in fact, I have already tried sucessfully (and I recommende you to try in you plant if you have foam problems) which is the in-line steam injection. My only concern reagarding this approach is the clogging of the latex pipe and within the steam pipe during the cycle, and I am truly believing that this problem comes from the high temperature of the steam (which is still superheated) and the poor mixing condition in the "T" I have been using instead of a mixer device.

Just to sum up, I would like to know your impressions about the following issues:

1)What is your first vacuum pressure? Now I am working at 100 mmHgabs (for styrene and for Acrylonitrile) but, as you cleverly said, I also intend to use a lower pressure (may be 50 mmHgabs @ 60oC).

2) Do you have an intermediate condenser with chilled water? What is the temperature of chilled water? I am thinking about 10 Celsius degree, whta is you impression?

Looking forward to hear from your soon,

LCMS.

 

[ajs1972]

Hello LCMS:

The problem with the foam was solved using a defoamer (for instance, a batch for 16 tons needs something like 50 mililiters).

Operating conditions:

Temperature: 80 celsius degrees
Pressure: 200 mbar abs (150 mmHg abs)
The condenser uses cooling water (28 celsius degrees)
Vacuum pump (liquid ring) uses cold water (6 celsius degrees)

In fact, I have proposed use cold water in condenser in order to avoid monomer condensation in vacuum pump (you can imagine the polymer formed in impeller of the pump!), but the problem is the excessive thermic load for the chiller. There is a project for place two condenser in series (the first condenser with cooling water and the second one, with cold water). With this proposal, I think we can achieve the needed vacuum and we will avoid the polymerization in the impeller of the vacuum pump.

If you want, let me check the product used like antifoam.

For the stripping we use saturated steam, in the arrival of the plant, the steam is 4.5 barg (160 celsius degrees) and before enter to stripping vessel, there is a humidification tank that adds water to steam. The flow of steam to stripping vessel is controlled by three valves in the bottom of the stripping vessel that are regulated by differential pressure.

Regards.

 

[lcms]

Hello, ajs1972.

Thanks for your help. I am also thinking about (actually I am already working on it) including in my styrene recovering system an adittional condenser with chilled water in order to improve the liquid ring vaccum pump efficiency (removing as condensable material as possible and reducing the remaining non-condensables temperature, maximimizing pump efficiency), since I have exactly the same vaccuum system of yours (a condenser with cooling water - 30 Celsius - and a liquid ring vaccuum pump with 8 Celsius chilled water for sealing). Unfortunatelly, though, I have been using much more defoamer than you (probably because some difference in our latex recipes - mine have plenty emulsifier) and I have been using a hidrocarbon emulsion which trade mark is GAPMASTER NXZ (they never reveal details of this recipe. Sorry about that).

I would really apreciate your opinion about this product (if you know it or based upon its nature) or, better than that, telling me what is your defoamer. Unfortunatelly I am not allowed to use silicon based materials because I work at rubber industry and this kind of chemicals impaired our products in a critical way.

Regarding my other monomer recovering process, our discussion about styrene enlighted me already, and I will release the resulsts as soon as I have tried to help other people like us.

Thanks in advance.

Regards,

LCMS

 

[ajs1972]

Hello LCMS:

The defoamer is TMC-1, right now I don´t remember the supplier, but let me check and I will tell you.

Regards.