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Offline WiXoo

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Drying problem
« on: June 20, 2013, 01:55:40 AM »
Hello,

I'm currently working at company which produces pigments and dyes. One product is getting in the trouble. It is dryed via spray drying and its particles forming hollow balls, and decresiang colour strenght. I need to separate them. Maybe with adding something into mixture, or something else. Please see the attachments. Can someone help me with this problem, how to separate these aglomerates into smaller ones? thank you

Offline Enthalpy

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Re: Drying problem
« Reply #1 on: June 20, 2013, 09:04:05 AM »
Fun!

You are unhappy with your pigment as spheres, but for other materials it may be useful, especially if the production is as easy as spray drying. For pressure swing adsorption maybe?
http://en.wikipedia.org/wiki/Pressure_swing_adsorption
the inner volume would let the gas pass near the solid during each swing.

Or make microballoons that way?

A material that releases a liquid only when crushed?

A super-hydrophobic lacquer, based on the lotus effect?
http://en.wikipedia.org/wiki/Lotus_effect

------------------

One formation mechanism I imagine is that, as the solvent evaporates at the surface of the droplet, the pigment forms a crust there, before the inner volume dries more slowly through this crust.

What about crushing the spheres with a (industrial version of) mortar and pestle?

If you pigment is later incorporated in a liquid matrix, could you mix with the matrix first, and dry the initial solvent later?

Or as only the bigger spheres seem to be hollow, just make smaller droplets? At rocket coaxial injectors this means a stronger shear obtained by a higher gas speed or by a less viscous liquid. Increase the proportion of solvent?

Offline curiouscat

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Re: Drying problem
« Reply #2 on: June 20, 2013, 10:01:45 AM »
Do you want to separate the sphere sizes? Or split large spheres into small ones?

Or something else?

I haven't exactly understood the problem.

Offline WiXoo

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Re: Drying problem
« Reply #3 on: June 20, 2013, 11:30:29 PM »
Do you want to separate the sphere sizes? Or split large spheres into small ones?

Or something else?

I haven't exactly understood the problem.

If you look on the picture closely, the sphere is made of thousounds (milions) of particles (oblong segments ''sticks''). So in ideal I want them to be separated to these ''sticks''

Offline WiXoo

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Re: Drying problem
« Reply #4 on: June 20, 2013, 11:38:23 PM »
Fun!

You are unhappy with your pigment as spheres, but for other materials it may be useful, especially if the production is as easy as spray drying. For pressure swing adsorption maybe?
http://en.wikipedia.org/wiki/Pressure_swing_adsorption
the inner volume would let the gas pass near the solid during each swing.

Or make microballoons that way?

A material that releases a liquid only when crushed?

A super-hydrophobic lacquer, based on the lotus effect?
http://en.wikipedia.org/wiki/Lotus_effect

------------------

One formation mechanism I imagine is that, as the solvent evaporates at the surface of the droplet, the pigment forms a crust there, before the inner volume dries more slowly through this crust.

What about crushing the spheres with a (industrial version of) mortar and pestle?

If you pigment is later incorporated in a liquid matrix, could you mix with the matrix first, and dry the initial solvent later?

Or as only the bigger spheres seem to be hollow, just make smaller droplets? At rocket coaxial injectors this means a stronger shear obtained by a higher gas speed or by a less viscous liquid. Increase the proportion of solvent?

Thank you, the last one is a good idea. I'll try to increase a portion of solvent.

Offline Enthalpy

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Re: Drying problem
« Reply #5 on: June 22, 2013, 06:32:42 AM »
What kind of spray injectors does the chemical industry use presently? On rocket engines, coaxial injectors have brought big improvements by making a finer mist. Drawings there for instance:
https://www.jstage.jst.go.jp/article/tjsass/50/169/50_169_201/_pdf
with one injector element on page 204 and the injection head on page 206 (pages 4 and 6 of the pdf).
They often inject the swirling liquid at the center and shear it by the outer gas, but some excellent engines (RD-170) do the opposite.

The industrial version of a mortar and pestle is for instance a ball mill, to crunch the spheres:
http://en.wikipedia.org/wiki/Ball_mill
you could experiment with bearing balls in a concrete mixer. With a pigment, it would be dirty for real. ;D

Though I wonder if one can get a powder of 500nm size without chunks. Graphite, which is little sticky (I suppose a pigment sticks much more), always makes chunks. That's why I suggested - if possible - to mix the pigment with the binder first, and only later evaporate the solvent; so to say, the pigments would stick to the binder rather than with another.

You might also take the hollow pigment spheres, mix them with the binder - if your product alllows this - and then break the spheres, say by a strong shear in the binder, as some miniature chemical reactors do to mix the reactants.

Offline WiXoo

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Re: Drying problem
« Reply #6 on: June 23, 2013, 11:38:31 PM »
What kind of spray injectors does the chemical industry use presently? On rocket engines, coaxial injectors have brought big improvements by making a finer mist. Drawings there for instance:
https://www.jstage.jst.go.jp/article/tjsass/50/169/50_169_201/_pdf
with one injector element on page 204 and the injection head on page 206 (pages 4 and 6 of the pdf).
They often inject the swirling liquid at the center and shear it by the outer gas, but some excellent engines (RD-170) do the opposite.

The industrial version of a mortar and pestle is for instance a ball mill, to crunch the spheres:
http://en.wikipedia.org/wiki/Ball_mill
you could experiment with bearing balls in a concrete mixer. With a pigment, it would be dirty for real. ;D

Though I wonder if one can get a powder of 500nm size without chunks. Graphite, which is little sticky (I suppose a pigment sticks much more), always makes chunks. That's why I suggested - if possible - to mix the pigment with the binder first, and only later evaporate the solvent; so to say, the pigments would stick to the binder rather than with another.

You might also take the hollow pigment spheres, mix them with the binder - if your product alllows this - and then break the spheres, say by a strong shear in the binder, as some miniature chemical reactors do to mix the reactants.

Thank you for your reply.

So one by one. I have tried e.g. jet milling. It worked really fine. But after two months pigment stick together again.
Mortar and pestle are not suitable for industry (because of price)
And by the binder you mean what? Or what solvent you have on your mind?

Offline curiouscat

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Re: Drying problem
« Reply #7 on: June 24, 2013, 12:01:05 AM »
So one by one. I have tried e.g. jet milling. It worked really fine. But after two months pigment stick together again.

Try an anti-caking agent? Some sort of filler that inhibits sticking. Magnisium Carbonate? Zinc Oxide? Talc? etc.

Offline Enthalpy

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Re: Drying problem
« Reply #8 on: July 24, 2013, 02:19:22 PM »
Hollow balls of pigment may result in a superior black paint, because the small refractive index of light materials reflects less incoming light - just like an anechoic chamber is made.

50µm diameter are too much for visible light, though. This would better have 0.5µm. If the simple process can produce them after some tuning, black paint can be an application.

Marc Schaefer, aka Enthalpy

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