[ejnov]

Hi Organic Chemistry Forums,

I'm searching for a very polar, reasonably safe (max. Health Code of 2) organic solvent. I've read through polarity indexes, such as this one: http://macro.lsu.edu/howto/solvents/Polarity%20index.htm, although the organic solvents listedseem to be pretty limited. I'm currently using Glycerol and PEG 200 in my system. Please let me know of any organic solvents you recommend.

Thank You,

Ethan

[Babcock_Hall]

What is your application?

[ejnov]

I'm trying to separate Sulfur Dioxide gas and Carbon Dioxide gas. I'm looking for a high polarity organic solvent that will dissolve the Sulfur Dioxide at high concentrations and the Carbon Dioxide at very low concentrations.

[Enthalpy]

Apologies for the vague answer, but...

One solvent would be SO₂. That is, if you accept to compress or cool the mixture.

Both molecules have a strong quadripolar field that overshadows the small (for SO₂) or approximately zero (CO₂) dipolar field. If the solvent has a brutal +- transition between two neighbour atoms, these will interact with C-O as well as S-O. It could be more efficient if the solvent's +- transition takes three atoms distance, so its electric field interacts weakly with OCO.

Please take with caution.

[ejnov]

Hi Enthalpy,

I will not be able to compress and cool the system so that SO2 would work. I'm searching for a solvent that has a higher boiling point (at least 80C) and dissolves NH3 at high concentrations and CO2 at very low concentrations.

[Enthalpy]

What compound do you want to dissolve? Previously it was SO₂, now it's NH₃. I have some doubts that NH₃ dissolved in high concentration anywhere would let CO₂ pass by without reacting.

Can "dissolving" involve some reaction? Water would dissolve SO₂ but little CO₂, and I expect water to dissolve very little CO₂ once it is saturated with SO₂; you could have several dissolution steps, where water and the gas take the steps in opposite directions, so the gas is very clean at the end while the solvent is saturated. This saves solvent and minimizes the amount of dissolved CO₂.

[Enthalpy]

DMSO, dimethyl sulfoxide, is more selective than water in favouring SO₂ over CO₂. A free Pdf called "Dimethyl Sulfoxide (DMSO) Solubility Data" tells 574g/kg and 0.5g/kg at RT. It's also less volatile than water, with bp=+189°C.

Though, it dissolves SO₂ by a reaction, as water does. Health code is 1, flammability 2, and it lets perceive a bad odour.
http://en.wikipedia.org/wiki/Dimethyl_sulfoxide

Did you check sulfuric acid to dissolve SO₂? Provided it's acceptable for your use.

With some solvents, you won't desire a fog to exit your machine. You might consider rotating disks to put the gas and the solvent in contact, a usual construction resembling the sketch there
http://www.chemicalforums.com/index.php?topic=56452.0
despite it is to serve different purposes in that other discussion.

The multistep dissolution suggested on Nov 17 applies to any solvent.