Reactor for liquid and gas

[Enthalpy]

Hello nice people!

 

Here a bizarre idea to let liquids and gas react together:

 

 

It's essentially the same hardware used to humidify air: many disks soaked partially in a liquid are rotated; they shall be wetted at each turn to expose a big area of liquid to the gas and promote the reaction.

 

The (better detachable) disks surface is close to the liquid-gas interface and can also be a catalyst, or be itself a reagent, for instance copper-activated zinc. This must be an advantage over other processes, like a mist or bubbles.

 

The gas could also be an other liquid if it's hard to mix - in case no better method exists. One could even superimpose several liquids and a gas, for instance to expose a single-molecular layer of liquid to the gas.

 

It resembles also the heart-lung machine, where rotating disks put blood in contact with air to remove carbon dioxide and bring oxygen:

www.ncbi.nlm.nih.gov/pmc/articles/PMC2028454

http://www.ncbi.nlm....j03398-0009.pdf

 

Sub-sub-details:

 

The vessel would better withstand pressure and vacuum. You can fit pumps compressors heater coolers exchangers separators and all that stuff.

 

Screws around the shaft between the disks and the bearings can prevent liquid wetting the shaft from seeping into the bearings - but they won't stop the gas... You can try to inject grease at high pressure in the bearing to prevent leaks there, as usual. At least no chemical has to be pumped to mix in this reactor.

 

You can vary the rotation speed to adjust the thickness of the liquid film. If the disk surface must be exposed to the gas close to the liquid, it could be made hydrophobic from place to place. Corrugations at the disk could even, as the disk rotates, pour the liquid at places that were in contact with the gas.

 

Marc Schaefer, aka Enthalpy

 

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The liquid has its biggest contact area with the rotating disks. This will drag the liquid to make a loop, along the disks at the upper part of the bath, and returning at the lower part. This mixes the liquid in the rotation plane, and as the disks can be thin, diffusion across a few mm can be efficient enough in many cases.

 

The axial direction is less favourable to mixing, with no natural flow there. I imagine the tank's inner face can have fins that take advantage of the loop to create some axial movement as well.

 

A different approach would replace the many disks by a helix, which achieves an additional global axial flow. Or, as disks are simpler to produce and fit, especially if they're consumed by the reaction, a durable helix could occupy the smaller radii near the shaft, and the consumed disks the bigger radii. Or keep individual disks, but cut and warp some fins in them to get an axial flow component.

 

Marc Schaefer, aka Enthalpy

[John Cuthber]

The shaft seal problem is easy.

You use a magnetic coupling (like a magnetic stirrer on a grand scale.

 

But I don't see why this system is better than the usual trickle tower type (which has no moving parts).

This sort of thing.

 

http://www.airpoll.co.in/packed-tower-gas-scrubber.html

[Enthalpy]

In fact, both operate much alike.

Thinner and uniform liquid film? Even smoother operation? Horizontal?

 

Ah, yes: if the solid surface is coated with an expensive material like a precious metal catalyst, disks are easier to coat and make better use of the area.

 

If the solid area is a catalyst or one reactant more, the better controlled thin liquid film provides a shorter and better reproducible path to the gas.

Edited November 14, 2012 by Enthalpy

[John Cuthber]

Do you know the typical specific area of modern precious metal catalysts catalysts?

"BASF offers Porous Activated Aluminas, Catalyst Substrate Spheres (CSS), High Surface Area (>300 m2/gram) to maximize surface area..."

from

http://www.basf.com/group/corporate/en/brand/CATALYST_SUBSTRATE_SPHERES

 

Other catalyst supports are available.

[Enthalpy]

Fun, that's less than 10 atoms. Thanks for the link!

 

I believe to remember that catalyst cost, or simple availability, can still be a limit. Not for iron, but things like rhenium. Wetting nicely the whole catalyst area would be an advantage in such cases.

 

What remains is the uniform thin liquid film. If the disks are catalysts or reactants, the intermediate compounds (carbenes?) in the liquid are produced near to the gas. A stack of spheres would do it less uniformly, say where the drop leaves the sphere. The adjustable rotation speed of the disks gives also more control than a seeping liquid.

 

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Wipers, standing brushes or mobile brushes, liquid jets... can wipe away from the disks reaction products or poisons that would slow down the reaction or bring other unwanted effects, maybe undesired further reaction steps. This can be done for instance where the disks enter the liquid bath.

 

One thing a stack of pebbles can't do. Ah!

Marc Schaefer, aka Enthalpy

Edited November 16, 2012 by Enthalpy

[Enthalpy]

Here's an other reactor that brings a liquid and a gas in large contact.

 

The paddles can have many pourer spouts to create more droplets in a better controlled way and let the droplets fall well within the rotating drum. Bubbles created in the liquid enhance the reaction area too.

This apparatus can also react immiscible liquids, for instance molten sodium and dioxane containing a reactant. The liquids can fill the vessel completely.

The paddle wheel shall cope with dirty, hot, corrosive compounds more easily than other dousing and bubbling reactors that use pumps - for liquid metals loaded with salt for instance. While the previously described rotating disks run more smoothly and create possibly a bigger contact area, the paddle wheel doesn't need the liquid to wet any surface, hence it can accept more dirty and corrosive environments that stain the surfaces.

The paddle wheel can remove solid products or by-products if they settle under the liquid and keep mobile, as the mud will fall from the paddles after the liquid.

Some materials were developed for fast neutron reactors to resist liquid sodium and metals. If I remember properly, the base alloy gets protected from dissolution by adding a layer of metal like molybdenum, which is refractory and builds no oxide layer.

Marc Schaefer, aka Enthalpy

[Sensei]

The paddles can have many pourer spouts to create more droplets in a better controlled way and let the droplets fall well within the rotating drum.

If paddles would have tiny holes, like strainer, it would work even better to create droplets.

 

Bubbles created in the liquid enhance the reaction area too.

That's job for what we call 'pearls'.

Tiny 2mm, 1mm or less size spherical pieces of glass.

I have 250 pieces in my distillation flask.

But for high temperature one can imagine using other material than glass for producing them.

Edited October 4, 2015 by Sensei