Help with Anhydrous HF Process Design

[JoeChem]

Greetings

I have been given the responsibility to begin conceptual design work on a batch chemical synthesis process that employs anhydrous HF as a solvent. Essentially, the process involves feeding solid staring materials to a batch reactor system followed by a crystallization and isolation of a solid final product by filtration. In addition, the starting materials and final products are very air and moisture sensitive.

I have no experience at all working with HF solvent or with air/moisture sensitive solids at a large scale. I was hoping to talk with someone that has had experience with this kind of system.

Some immediate questions come to mind:

Are there any published guidelines out there on how to handle anhydrous HF safely?

It is my understanding that anhydrous HF is not corrosive to stainless steel. Will nitrogen purging procedures be adequate to lower the moisture level within a batch tank system to acceptable levels to maintain an "anhydrous" environment?

I am unsure how to handle large amounts of air/moisture sensitive solids. The problem is how to open a bulk container (drum?) and feed the material to a batch tank without damaging due to exposure to the environment? Does anyone have experience dealing with this kind of problem?

Any help/tips/guidance will be greatly appreciated.

JoeChem

 

[25362]

You may find some useful information by Googleing around for alkylation with HF.

One of the sites would be:

http://www.osha.gov/dts/hib/hib_data/hib19931119.html

 

[mbeychok]

JoeChem:

HF is very dangerous, as you no doubt know. You must provide piping, pumps, vessels, sample connections, etc. designed to properly handle it. You must also design a medical examination program for the regular, periodic checking of the workers who will be working in your plant.

I very strongly suggest one or both of the following:

-- Contact Phillips Oil (the licensor of the HF Alkylation process used in many petroleum refineries) and see if they will help you.

-- Visit the nearest petroleum refinery you can find that is using HF alkylation and see if they will help you with some guidelines.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[JLSeagull]

Obtain a throw-down MSDS. You may need to use a nickel alloys such as Monel. Don't even think about anything with glass. Neutralize everything going out of the unit by dunking in a neutralizing bath. Any service requires closed slicker suit with breathing air. It eats through the bone, ...

 

[25362]

If it were a lab bench reaction such as when producing Grignard reagents:

[•] equipment must be dried possibly by using a flame under supervision.
[•] the reagents are kept under a blanket of refluxing solvent vapors that exclude air and moisture.

I don't know whether these procedures are applicable to your case.

Good luck.

 

[mbeychok]

As JLSeagull said "it eats through the bone". In small amounts, the worker does not feel what is happening to his bones. That is why, when I worked in an HF alkylation unit over 50 years ago, we had to have a medical exam at least once a month ... and why I said you must develop a regular medical check-up system.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[StoneCold]

If you really are going to use HF as the solvent you might want to look at a small continuous reaction train. That could reduce your HF volume from thousands of gallons to five or ten. Then if you can recycle it back to the beginning of the train then that would be better still.

As you might have guessed from the last couple of posts, nobody wants to have to deal with HF, and for good reason.

Goodluck

StoneCold

 

[25362]

Except probably the starwar antimissile laser technology.

 

[engrx]

As mentioned above, only special alloys should be used with HF. If you have questions about how to handle HF, don't do it. Somebody will get very hurt. Find an expert and listen to them. Harmful liquid, deadly vapor, don't mess around.

 

[sshep]

Normally I wouldn't reply to an old thread like this but: It is most certainly not true that special alloys are always required for anhydrous HF. Carbon steel is possible for dry HF below 200F (beware iron floride scale), monel is required only when water is present.

HF can (and is) handled safely in many processes. The American Chemistry Council has an HF panel. Manufacturers can provide good advice. Process licensors using HF will devote considerable attention to the safety systems, training, and materials aspects of handling. This forum can supplement but not replace these sources. Don't let fear be the overriding concern about HF- get the facts from reliable sources.

best wishes,
Sean

 

[mbeychok]

Sshep:

Your statement "HF can (and is) handled safely in many processes" is indeed true.

As this thread has emphasized, the statement "HF is extremely dangerous" is also true and it is not spreading "fear" to say that.

I think both of the above statements are "reliable".


Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[sshep]

Thanks Milton,

I guess the fear thing was a bit harsh (for me), but the statement that only special alloys should be used with anhydrous HF seems like such a wrong steer that I couldn't help myself.

My point is that not only is carbon steel used in many parts of HF alkylation processes, but some small levels (i.e. fractional %) of water are also used successfully for emulsion control. It is only in the regenerator tower and other severe service points of the process where monel is needed. HF and water forms a maximum boiling azeotrope- the residue you are left with is some of the most corrosive stuff in the industry and practically there is no MOC that can stand up to that type of punishment without a regular inspection, repair, and replacement program.

best wishes always,
sshep

 

[engrx]

I hate to start this thing going again, but if anybody is still out there- here I go. There has been lots of talk about residual elements in carbon steel used in HF service in the refining industry. Even when using carbon steel care should be taken to make sure you are using the right stuff. I believe that API RP 751 has guidelines for appropriate materials of construction and residual elements concerns.

My point is not to spread fear, however the safety record of people who handle HF is largely based on a healthy respect of the evil HF is capable of.

 

[0707]

In HF service carbon steel should respect the following requirements:

Carbon should be equal or less than 0.20%, Carbon Equivalent should be equal or less than 0.40%, and (Cr+Ni+Cu) should be equal or less than 2%.

 

[25362]

The Hyd Proc. issue of September 2004 has an article on Preferential corrosion of welds in HF service by Munsterman and Mayorga that may be of interest.

 

[m777182]

Contact

http://www.ijs.si.

They have been working with HF for decades. I think they will gladly give you some hints.
m777182