[curiouscat]

In order to speed up a Liquid 2-phase reaction I am doing experiments by adding in some phase transfer catalysts. Are there any heuristics or other calculations to decide how much to add? The area looks like black magic to me. Even the selection of which quat. salt to use as a PTC.

I was planning on using ~1% w/w PTC based on a survey of not-so-related literature but anyone know any better?

This is a Liq-Liq 2 phase reaction of a higher alkene and H2SO4 (~65%). The phase transfer catalysts I was planning on using are quat. ammonium compounds like   Cetyl Tri-Et. amm. bromide,  Tetra n-octyl ammonium bromide etc.

Is there a thing as having too much of a PTC? Would the rate go down eventually or does it simply level off?

[discodermolide]

It's usually a catalytic amount one uses. If you start adding too much you may well get separation problems and a real messy work-up. I would not go above 10 mol%.
As the name suggests, phase transfer catalysts.

[curiouscat]

Thanks! Which are the ones you've used, may I ask? There seems to be an awfully large choice (even among the quat. ammonium compounds) and I've scarce idea of how to get my Reaction Chemistry to guide my choice.

[discodermolide]

There are lots to choose from. I've usually gone for the tetra-n-Butyl ammonium salts. Maybe it was just lucky but they always worked. The longer chain ones always gave me separation problems due to the lipophillic chain(s) emulsions and the like.

[Enthalpy]

To improve the contact between two liquids, you might consider this
http://www.chemicalforums.com/index.php?topic=56452.0
but it would probably need you to build one first. Sorry for the interruption.

[curiouscat]

To improve the contact between two liquids, you might consider this
http://www.chemicalforums.com/index.php?topic=56452.0
but it would probably need you to build one first. Sorry for the interruption.

Glad you "interrupted"!

I've the possibility of building a rig; and your idea does look interesting.

But why do you think this'll work better than, say, a conventional mechanical stirrer? What's your underlying rationale?

[Enthalpy]

Until someone tries, I can only imagine how the thingy performs...

As compared with a phase transfer catalyst, the disks avoid one added compound which I suppose sticks at the interface of the reactants to stabilize an emulsion, hence resides where the reaction takes place.

Compared with a stirrer, the disks work by letting one reactant (or both) adhere on them to form a film, so they don't need a stable emulsion. They also avoid long and brutal stirring of two badly miscible reactants, which would heat the mix.

The disks can also be a catalyst or a reactant, like Zn, Zn-Cu...

[curiouscat]

This one  sounds similar: "Spinning Disk Reactor"

http://www.chemicalprocessing.com/articles/2011/spinning-disk-reactor-reveals-potential/

[Enthalpy]

Very interesting!

The spinning disk reactor suggests similarity by its name, and also has disks, but the aim and construction differ. It wants to create a huge shear in a small volume by spinning (=fast) a disk very close to a wall; the turbulence supposed to result from it is to mix finely the reactants.

My (?) reactor doesn't rely on turbulence. It exposes two reactants only at a surface equal to all the disks - which are preferably many. It can expose immiscible phases without the aid of tensides, very near to a catalyst if desired.

[curiouscat]

Your idea sounds more promising for G-L reactions. Not so sure if the L-L contact's going to happen the way we want it to.

[Enthalpy]

If you fear that both liquids stay where they are because both wet the disks immediately, just choose a disk material or coating that only one liquid wets, or one liquid wets far better than the other does, and then the rotation will expose one liquid to the other.

With liquids as different as a mineral acid and an alkene, the selective material should be easy to find. Maybe polyethylene, or conversely PVC.

Corrugations at the disk's surface will help them hold the preferred liquid.