Mixed waste organic solvent DCM adsorption/desorption question 1

[silebi66]

Dear Professional members :

The dichloromethane, DCM ( CH2Cl2, Methylene chloride) solvent is widely used in the resin plant, since t has high water solubility than other organic solvent, and low boiling point ( b.p is 39.95C at atm). My research is finding a good molecular sieve or active carbon treat 2000kg/day (99.6% DCM + 0.3%water+ trace oligomers) to finial 30ppm water concentration.

Since active carbon adsorption ability is affected much on water content, and DCM may be decomposed some HCl，the molecular sieve vendor from UOP told me that they don't have such type molecule sieve to treat 1000kg/day.

Could anyone kindly give me any suggestion or hint about the proper DCM adsorption/desorption process, and operation procedure, ex. in desorption process, N2, air to depressurizing procedure ?

Thank you very much.

 

[Compositepro]

In my opinion steam stripping would be a far more practical approach to removing methylene chloride from water. That is what we used at a vinyl chloride plant to remove ethylene dichloride from water.

 

[moltenmetal]

The OP's question was not clear, and the title totally misleading. After re-reading the OP several times, it seems that they are trying to DRY dichloromethane from 0.3% water (30,000 ppm) to 300 ppm.

It does not seem that they are trying to recover a DCM vapour stream which also contains water, by adsorption. Or maybe they've already done so- again, it's not clear.

Activated carbon is not a drying agent. It is USELESS for drying.

Molecular sieves can be used for drying. The OP states that whatever their (unclear) application, is, UOP was concerned about DCM hydrolysis presumably during desorption, forming HCl. That's a risk, but one which varies greatly based on how the desorption is done.

If the OP responds to clarify their application we might be able to help.

 

[silebi66]

Dear Moltenmetal and Compositepro

Thank you very much for your insightful suggestions. I am sorry that the process OP is not provided clearly at first time. The mixed organic liquid process condition s OP is at Atm, and OT is around10C.

I tried to find most cost-effectiveness's drying agent eg. Synthetic zeolite, activated alumina or silica gel used in the dehydration process.

I wonder it is possible to adopt two columns(full of drying agents), which one is used for water absorption, the other is used for water desorption., and it could run as regeneration step by stripping the hot steam vapor into the bottom of the column.

Could you please kindly give any suggestion or hint for this issue ?

Thank you very much.

 

[moltenmetal]

OK: so it IS a liquid phase drying process! Now we can help.

What about a conventional chemical dessicant, rather than a reversible adsorbent like a molecular sieve? You're not talking about much water- 0.3% of 2000 kg/d is 6 kg/d of water. A dessicant that you have to throw away after a basic bake-off to remove the methylene chloride on it would probably be quite economical, rather than heating up a large bed of a reversible sorbent to regenerate it. Something like calcium chloride or calcium sulphate? These materials can be regenerated off-line too.

 

[Compositepro]

Calcium oxide is a powerful desiccant that can reach ppm water levels. I do not think that the chloride or sulfate will get that low. It is cheap but not regenerable though. It would be most effective if you mix it with your solvent and then filter it out. It will also neutralize any acid present.

 

[georgeverghese]

Regenerable mole sieves are used commonly for final drying of liquid phase LPG streams. You could also talk to BASF about silica gel in this application. There are some rough sizing guidelines for these in the GPSA. Another inorganic drying agent to consider would be anhydrous copper sulfate.

 

[silebi66]

Dear Moltenmetal, Compositepro, Georgeverghese

Thank you very much for your highly professional suggestions. I assume that 3A, 4A molecule sieve could be used to in this water removal process. The small water molecule could be adsorbed on pore surface, and the larger molecule, such as DCM and other trace organic solvent will be excluded.
Some detail design issue is what is the proper size of the column (height of the equilibrium zone mass transfer zone) , loading and dumping，and proper operating parameter, such as residence time and velocity for the two bed adsorption process design.

Could you please kindly give me any suggestion or hint on this ?

Thank you very much.

 

[georgeverghese]

Agreed, pore size influences what may be preferentially adsorbed, but so does dipole moment. Water dipole moment is 1.85D ,while that for methylene chloride is not far off at 1.6D. Think it would be better to call UOP, Dow or other mole sieves vendors to discuss selectivity for adsorption in this case and bed sizing details. These high mol wt oligomers may need to be removed upstream if you this mole sieves bed to work well.