Silica as a filter media

Yesterday I took a batch of winterized crude, scrubbed it with some powdered carbon at a 5% ratio for an hour at about 60C and filtered it thru a funnel with a silica gel slurry on top of a 2.5 micron filter paper. The scrubbed and filtered solution came out dark so I figured I didn’t use enough carbon.
When I took apart the filter for cleaning I noticed that most of the carbon stayed on top of the silica gel, however a small amount of carbon coated the filter paper/parts of the edge of the funnel which made me think that the filtered crude is still dark due to little carbon particles in it. I used the microscope to confirm this.

To load the silica into the filter I:

  1. Measured out 2cm of silica in a separate container the same diameter of my filter
  2. Added ~3" ethanol to the silica.
  3. Stirred silica around so that it was suspended in the ethanol
  4. Dumped solution over the 2.5 micron filter paper
  5. Pulled a small vacuum until some ethanol came thru but leaving most of it over the silica
  6. Added diluted crude to the funnel by slowly pouring down the wall of the filter, making sure not to disturb the bed.
  7. Pressurized filter vessel with 15 PSI to move solution thru the filter.

What should I have done differently to prevent the carbon from getting into the silica?

Check out DCVC video. They spend a lot of time packing the column with silica.

Where can I find that video?

Make sure your paper is seated before adding the slurry, or dry pack. Reguardless, the paper has to be 100% sealed with no debris underneath it.

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I recommend a exploration of

although I suspect @eliotoroboto may have been referring to the top hit with this query dcvc video - Google Search

Here is a column of silica gel, celite 545, and a sand layer. Each layer has a slow flow paper filter on top. The column has been used once and is being prepped to use again.

Each layer is packed beautifully and in simple fashion dry loaded. It nails it every time IF the goal is a properly packed silica gel column. I can see no benefit to using silica gel unless used in a packed fashion. They just do not do their thing until they are made almost as one homogenous column instead of a billion tiny gel beads. The way you pack is to scoop the material in until you get the depth you are after and add about a quarter inch. Then use a hand held massage wand against the lab stand or the glass and vibrate the powder flat. Then when the powder is flat on top turn on your vacuum with the vibration from the wand still churning the fine silica powder. You will see an insta-settling action that really packs it in tight.

Then with vacuum on you are done with vibration but use a large dowel to pack then straight down on the silica with a bit of grunt to the effort. Make it tight and keep the vacuum on. Then once packed with a dowel use a small spatula bent up at the tip to go around the inside edges of the column packing the edges down. The dowel cannot get all the way to the edge and the edges are the problem area if not packed.

Then top it with a paper filter just to protect the column from churning or being disturbed by more layers. I then run clean solvent through until dryish while vacuum is still on. The solvent should descend as a flat line. Then you can choose which layers to add and where to add them. A filter use of the gel would not require more than a few inches of gel and if you are using carbon you can certainly pack it also into its own layer sandwiched between sand then the process would not be a heated process at all but would be pulled through the carbon as it is through silica. Silica gel does work as a filter media because frankly DCVC is as close to being a hybrid method between flash chromatography and simple filtration as it gets.

In essences a chromatography column like the example shown is just a big tall filter. Some things go through the filter faster than others is all but some things will not go through at all if the correct solvent system is used and you can exclude a great deal while keeping what you want this way.

Here is the wand I use but here it is being used during a liquid to liquid extraction to solve a minor problem inherent with the use of glass in this case but that is another topic. I wanted to show the unit.


Nice wand LOL


Here are the three types of silica gel.
TypeA▪︎is a clear pellet.
Approximate pore diameter: 2.5 nm
Drying and moistureproof properties, can be used as catalyst carriers, adsorbents, separators and variable-pressure adsorbent.

TypeB▪︎is a translucent white pellet.
pore diameter: 4.5-7.0 nm
Liquid adsorbent, drier and perfume carriers, also is used as catalyst carriers.

TypeC▪︎is a translucent, micro-pored structure.Raw material for preparation of silica gel. Additionally dried & screened; it will form macro-pored silica gel which is used as drier, adsorbent & catalyst carrier.


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