Hi! I want to have an explanation 1

[GasOilEng]

Hi!
I want to have an explanation for this phenomenon happened recently in our LPG dehydration section;

We are using UOP94 and UOP945 Mol Sieve A4. While trying to empty dryer vessel for changing a new UOP Mol sieve we had checked the the gases outlet from the dryer with Gas Tester before getting in to remove the screens, we found that there is >400ppm H2S and >500ppm CO. And the temperature have passed from 50C to 180C while using air extraction to remove Hydrocarbon before entering the vessel.

Tanks

 

[don1980]

GasOilEng - This bed is not sufficiently prepared for air/O2 exposure.

Stop immediately.

Read the UOP instructions for deactivating the bed in preparation for a change-out.

Otherwise, you are risking fire and a severe exothermic reaction in this vessel.

 

[GasOilEng]

Hi don1980, thanks for your replying

We have followed UOP instructions for change out, but what I want , is possible scientific explanation of what happened.

Thanks

 

[don1980]

You're seeing the effects of an oxidation reaction, a reaction between oxygen and materials that are adsorbed onto the molsiv. H2S is produced by a reaction between O2 and sulfides. CO is produced by partial (incomplete) oxidation of combustible materials. The high temperature is due to the fact that oxidation is an exothermic reaction. All of these are signs that the molsiv isn't adequately prepared to be exposed to air (unloaded, or even opening a manway flange).

This is explained in the supplier's instructions for safe handling. Molsiv is a great material - very useful in industry - but it's also a material that's frequently involved in accidents/incidents. With some activities, one can get away with taking shortcuts, but that's not true when the handling of spent molsiv. If you take a shortcut, and don't prepare the molsiv adequately, you'll pay a price for that shortcut.

Since you obviously have questions and concerns, call the supplier and let them help you do this safely. The suppliers are very knowledgeable of the hazards associated with spent molsiv. That's why they prominently publish their phone number in the molsiv instructions documents.

 

[GasOilEng]

Hi Don1980

Many thanks for your brief explanation ,sounds that's H2S doesn't previously exist in the process gas, it is the product of chemical reaction of O2 with sulfides adsorbed on Mosiev.

 

[GasOilEng]

Hi Don1980,
(sufide an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions)

Is is possible that O2 reacts w/ sufides in normal conditions 1atm. and 30 - 35°C to produce H2S. If it is possible, I think it would be the SO2 as product not H2S.

 

[don1980]

The materials (reactants) adsorbed on the molsiv do not undergoing a complete oxidation reaction when there's an insufficient amount of O2 for that to occur. That's why you see significant amounts of CO. If it was a complete reaction you'd see CO2 and no CO.

 

[GasOilEng]

Hi

I entirely agree with you about CO (incomplete reaction of oxidation, but what about H2S.Is is possible that O2 reacts w/ sufides in normal conditions 1atm. and 30 - 35°C to produce H2S. If it is possible, I think it would be the SO2 as product not H2S.

 

[don1980]

GasOil - This is getting unnecessarily tedious and academic.

Will atmospheric O2 react with a sulfur containing compound and produce H2S at 1 atm and 35C? No. Can hazardous amounts of H2S be released when used molsiv is exposed to air? Yes. When used and inadequately prepared molsiv, at 35C, is exposed to air, will the molsiv temperature remain at 35C? Hell NO.

If you want to see a real show and learn a hard lesson, then ignore the vendor's safe handling guide, and go with your intuition instead. It'll be a memorable experience!

 

[georgeverghese]

Suspect H2S is formed by decomposition of organic sulfides ( co adsorbed on mole sieves ) on contact with water vapor at elevated temperatures during regeneration with hot air?