[curiouscat]

Consider the following case of a Reactive System where two immiscible reagents  S(organic) & R(aq.) are reacted to give a product P(organic) in a large reactor (20,000 Litre at 90 C) with imperfect mixing in fed-batch mode:

S + R(aq.)    P   

R is present in excess inside the reactor whereas S is the more expensive, limiting reagent that is slowly dosed over a period of time (say 6 hrs). The contents of the reactor are kept isothermal at 90 C by using a heat transfer jacket with cooling water.

Now, S itself is liable to self polymerize to an undesired product U & this reaction increases rapidly with Temperature.

S + S  U

S, P & U form a single organic phase whereas R is an immiscible aqueous reagent.

Question: Does it make sense as a strategy to supress U to prechill the dosed reagent S to a low temperature (say 5 C or even -15 C)  Currently it is dosed at room temp.

I think it does but I wanted to get some opinions & brainstorming.

[DrCMS]

My guess is that no it will not make a big difference but improving other things for the same investment might give a better results my guess is that better mixing will make a bigger difference. I might be wrong, I think it depends on at room temperature how fast is the reaction to give U is.

S + S  U

If you are forming significant amounts of U before it gets feed into the reactor then chilling might make a difference but you need to chill it from delivery until use. If as I expect you only really form U in the reactor from S sitting on top of R then I would look at the feed and mixing arrangement to maximise the

S + R(aq.)    P   

reaction while minimising the side reaction.  That might need modifying the stirrer speed or design, or where the feed enters the reactor, or the feed time or the reaction temperature all of which you could run in the lab to get some ideas before doing plant trials.

[curiouscat]

Thanks!

The U formation by S sitting at room temp. is negligible.

The part I worry about is a mass of S sitting inside the reactor but without intimate contact with R. My hunch was, by precooling one could align the mixing & heating processes. i.e. If it does sit inside the reactor waiting to get mixed I'd rather have it sit cold than hot.

Of course, the key point would be the relative rates of heat transfer to a S parcel by conduction vs. mass transfer.

Modifying stirrer design etc. are definitely under consideration.

[Enthalpy]

Brainstorming, you said? OK then, you filter out the bad suggestions...

• Have micro-reactors instead, where the reactants are mixed very intimately and reside shortly.
• Have a good heat exchanger that pre-heats S only as it enters the reactor, using the output's heat.
• Get inspired by rocket engine injectors to mix the reactants. Each RD-170 chamber burns 165kg/s kerosene and 433kg/s oxygen in D=H=380mm.
• If polymerization is triggered by an impurity, remove it from both reactants.
• Add a poison against polymerization to limit it.
• Search other means than temperature that provoque S+R->P. Light, sonication and so on.
• Use small variants of the reactants that don't polymerize or that give the desired reaction at a lower temperature. Like, acid chloride instead of acid.

[curiouscat]

Brainstorming, you said? OK then, you filter out the bad suggestions...

• Have micro-reactors instead, where the reactants are mixed very intimately and reside shortly.
• Have a good heat exchanger that pre-heats S only as it enters the reactor, using the output's heat.
• Get inspired by rocket engine injectors to mix the reactants. Each RD-170 chamber burns 165kg/s kerosene and 433kg/s oxygen in D=H=380mm.
• If polymerization is triggered by an impurity, remove it from both reactants.
• Add a poison against polymerization to limit it.
• Search other means than temperature that provoque S+R->P. Light, sonication and so on.
• Use small variants of the reactants that don't polymerize or that give the desired reaction at a lower temperature. Like, acid chloride instead of acid.

Great suggestions. Some comments:

A poison is already being added (an inhibitor) but that isn't perfect.  Microreactors have been explored but the capex economics don't work out.

Polymerization is not triggered by any impurity so removing any is moot.

Other options I will explore.

[DrCMS]

Which polymerisation inhibitor do you use?  A lot of them need the presence of oxygen to work.  Is blowing air through the reaction mass possible/safe; it can improve the mixing and inhibit some polymerisations.

[curiouscat]

Which polymerisation inhibitor do you use?  A lot of them need the presence of oxygen to work.  Is blowing air through the reaction mass possible/safe; it can improve the mixing and inhibit some polymerisations.

That's a good idea but I'm not sure of the feasability. The reaction temp. of 90 C is already above the flash point.

I could blow it through the S pre-dosing at room temperature though if pre-saturation with oxygen would help.

We use this inhibitor, does it need Oxygen to function, do you know?