HF vs. sulfuric for alkylation catalyst.

[kenvlach]

The following thread, in the Chemical plant design & operations Forum, describes corrosion problems using 98% sulfuric acid in an alkylation unit.
Refinery Alkylation Unit - Metallurgy Upgrade
thread124-187428

Recently, the proposed use of hydrofluoric acid (rather than sulfuric acid) as alkylation catalyst in a Bakersfield refinery expansion has become an issue. HF being highly volatile is a far greater threat to neighbors in the event of a leak. The Big West refinery “has already agreed to use a modified form of HF that is less likely to form lethal clouds of gas if it escapes into the atmosphere. The refinery initially planned to use an unmodified form of HF...”

http://www.bakersfield.com/102/story/122840.html

Can a refinery person please explain 1) what concentration of HF is typically used, and 2) what do they mean by a modified form of HF?

 

[mbeychok]

kenvlach:

The Conoco Phillips oil company licenses a new version of the original Phillips HF process. The new process is called the "Reduced Volatility Alkylation Process" (commonly known as the ReVAP process). It was developed because of the very serious safety problems with using HF acid as the catalyst in the original process.

The ReVAP process uses an additive (or suppressant) that reduces the vapor pressure of the HF acid catalyst so as to lessen the hazardous effects of any accidental releases of the HF catalyst.

As one who has designed and worked in both types of alkylation plants (Sulfuric acid and HF acid), it is my subjective opinion that the Sulfuric acid plants are much safer than the HF plants. Sulfuric acid has an extremely low vapor pressure.

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

 

[25362]

I was under the impression that precisely because of the environmental concerns associated with HF releases it is impossible to get approvals to construct new HF alkylation units in the United States. Was my impression wrong ?

 

[unclesyd]

I don't see anywhere that there are permitting problems except So Cal though I suspect one have to work awfully had to get one elsewhere.

http://www.fluoridealert.org/pollution/1173.html

 

[mbeychok]

25362:

There are national (i.e, Federal) governmental regulations that prohibit ReVAP alyklation plants using the modified HF catalyst.

As for the 50 States in USA, some of them may have regulations that prohibit ReVAP plants, but I have not heard of that being the case.


unclesyd:

California's South Coast Air Quality Management District (AQMD) has no regulations that prohibit ReVAP plants ... but you must certainly jump through some stringent hoops to obtain approval.





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

 

[kenvlach]

Thanks for the info.
I'm familar with using fluoride acid salts (ammonium bifluoride, sodium fluoride, etc.) in combination with nitric acid for pickling metals but had never heard of 'modified HF.'
Am dubious about this ReVAP additive that suppresses HF vapor pressure since, from chemical thermodynamics, this will also suppress the chemical activity of the HF.
Ken

 

[mbeychok]

My response of 5 July 07 has a typo in it. The sentence reading "There are national (i.e, Federal) governmental regulations..." should read "There are no national (i.e, Federal) governmental regulations...".



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

 

[25362]

The big engineering companies are now offering solid catalyst HF-based units.