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Author Topic: Isolating fine particles via filtration  (Read 633 times)

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AllylicAzideUMN

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Isolating fine particles via filtration
« on: January 11, 2019, 05:36:06 PM »

My research involves isolating many low-solubility solid organic compounds. Filtration is my most common isolation technique, but occasionally I will run into a compound that is so finely dispersed in a solvent (usually hexanes, acetone, or methanol) that it passes almost unchanged through filter paper. I have found that allowing the fine particles to settle can sometimes improve their ability to be filtered out, but I'm wondering if anyone has other techniques to encourage particle aggregation to make filtration more feasible.

Thanks in advance for the suggestions!
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wildfyr

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Re: Isolating fine particles via filtration
« Reply #1 on: January 12, 2019, 03:36:00 AM »

Centrifugation
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pgk

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Re: Isolating fine particles via filtration
« Reply #2 on: January 14, 2019, 06:06:43 AM »

Another technique is recrystallization, followed by slow cooling at room temperature (just, allow to stand at room temperature). Larger crystals tend to form that way.
This doesn’t always works but in many cases, it does.

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phth

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Re: Isolating fine particles via filtration
« Reply #3 on: January 14, 2019, 07:22:10 PM »

sub µm PTFE syringe filters are nice for small samples and fine particles
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zarhym

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Re: Isolating fine particles via filtration
« Reply #4 on: January 16, 2019, 03:05:07 PM »

This is a common problem in process chemistry. The fine particle means poor seperation between soild and mother liquor. This will lower the purity of your filtrate cake since the impurities remains in the mother liquor after drying. Also, it will increase the cost of filtration operation (time and labor).

One solution to this problem is to get better crystalline formation during recrystaliztion by holding the temperature for couple hours at where the crystalline starts to form. This will allow slow growth of the crystalline. In industry, stirring is maintained all the way during this process to provent clogging.

If you are doing small scale (grams to 100 grams) and there are impurities identified in your mixture, you can run a silica column chromatography before recrystalization. Higher purity will help the  crystalline formation.
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jeffmoonchop

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Re: Isolating fine particles via filtration
« Reply #5 on: January 17, 2019, 12:13:24 PM »

yes fine particles result from high supersaturation, more nucleation sites. Hold the solution at a higher temperature instead of cooling it rapidly, less nuclei will form and existing solute will grow on the lower number of nuclei to form larger particles (Ostwalds ripening). Or use a solvent where the solute is more soluble, then you can control the supersaturation more easily
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