scrubber or bed? Need to remove methyl Cl from ethylene

Question

scrubber or bed? Need to remove methyl Cl from ethylene

TPrice (Chemical)

(OP)

11 Jan 03 12:46

I need to find a unit op to remove methyl and ethyl chlorides from an ethylene vent gas being sent back to a cracker charge gas machine.

Any ideas? We are looking at packed beds from UOP and someone suggested caustic bead beds, but i can find no info or vendors. Most stuff I find relates to cleanup of air streams (enviro).

My ethylene stream is about 6 Mg/h and contains 1200 ppmw combined methyl and ethyl chlorides.

Suggestions of technology or vendors?

Terri

rbcoulter (Chemical) · Answer 1 · 2003-01-11 23:11:51

My reference book shows methyl chloride soluble in alcohol - ethylene slightly soluble. Maybe scrub with alcohol and separate the methyl chloride/alcohol mixture by distillation? My reference doesn't say which alcohol but my first guess is ethanol.

gregq8 (Chemical) · Answer 2 · 2003-01-12 01:47:53

Assuming that the impurities you have mentioned are methyl-chloride (BP=-24.22 C) and vinyl-chloride (BP=-13.9 C),there should be NO need to use a solvent such as a caustic solution or amine solution to "scrub" these components from ethylene (BP = -103.7 C). This separation is relatively easy amd therefore does not require a solvent.

Caustic or amine solutions are commonly used to remove acid gas impurities (e.g. CO2/H2S) by absorbtion then chemical reaction. Your problem is therefore different.

From a quick look, this separation should be possible using a conventional distillation column, with ethylene recovered overhead and the impurities removed as bottoms.
The overhead condenser will most likely require a refrigerant cooling medium such as propylene. The column could be equipped with trays or use packing.

The distillation column for this separation could be designed by one of many engineering companies or process engineering consultants who have experience with chemical systems.

Greg

TPrice (Chemical) · Answer 3 · 2003-01-12 20:07:10

Greg,

Thanks for the distillation suggestion.  We were wondering about a bed because we have some existing vessels that currently have alumina (to remove H2O and MeOH) and have found a media from UOP that can remove the methyl- and ethyl-chloride, but not very well.
The caustic bead was suggested because apparently the caustic wash in the ethylene unit (where we are accidentally sending the chlorides now) seems to be removing some of the chlorides.  I have never heard of caustic beads, just the usual caustic wash tower.  Not my specialty (i was put on the project 2 days ago and I have 'til end of March to do the front-end engineering before giving over for detailed eng. What a rush!
Anyway, have you ever heard of caustic beads?

Thanks for your kind input.  Regards, Terri

gregq8 (Chemical) · Answer 4 · 2003-01-13 02:54:53

Terri,

Sorry, I have not heard of a caustic bead before.

It sounds as though you might have two different options to consider (i.e. distillation and adsorption) and that you will need to perform preliminary sizing then costing to decide which route is the best.

Regards
Greg

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scrubber or bed? Need to remove methyl Cl from ethylene