Extraction - Ice extraction

[kant]

Is anyone familiar with the chemical theory behind separating the alkaloids from water by freezing? Could they please explain how it works?

SWIM wants to know how effective this method actually is before discarding the ice he has removed from the freezed PPT. What SWIM is concerned about is that the ice is not clear and has a bitter taste, though not nearly as bitter as the remaining liquid. Perhaps it is due to improper freezing and a lot of alkaloids are frozen in the ice? Or maybe the ice is supposed to have a certain colour and taste because of other molecules?

SWIM also wonders why he can find very little information on this here. The freezing method sounds far more convenient than the risky evaporation.

[jon-q]

Yes - Ice filtration is possible because of a phenomenon called “Freezing Point Depression”.
Pure water freezes at 0c, however if you add another compound to water it will depress (lower) its freezing point.
Ice filtration takes advantage of this phenomenon.
When impure water begins to freeze, the impurities get pushed aside by the growing ice crystals allowing the now pure water to freeze.
This method isn’t all that efficient because some impurities can get trapped in tiny pockets of air, or they get stuck to the sides of the forming ice.

It’s best to try and freeze the liquid slowly around –5c, this helps encourage long crystal growth and will limit the amount of air and impurities that get trapped in the ice. Its mainly trapped air that gives ice its cloudy look.
Here’s a more detailed explanation taken from a PPT Extraction TEK, the guy who posted it was called shangoz.

The crystallization of water in the solution forces other molecules than water out of the matrix.
Small molecules, like morphine maleate move easily to stay in the liquid phase.
Large molecules, like (poly) saccharides and (poly) peptides cannot move easily enough, and are included in the ice.
An additional effect may be that plant saccharides have a high affinity to water.
So, may be, small saccharides are included in the ice as well.

The freezing therefore accomplishes a separation between alkaloids and "nutritional" materials.

It is important not to break the ice crystals during formation, because cavities will form, enclosing active ingredients.



Don’t throw the ice away, save it and re-filter again.
Q

[kant]

Thank you very much!

SWIM supposes another filtration should be enough, as long as its done carefully, by removing ice every hour or so.

What's long crystal growth? I've noticed that the ice looks fibrous, are the fibers "long crystals"?

[jon-q]

Ice is made up of tiny crystals; each crystal tends to have a hexagonal shape, the length and density of these crystals change at differing temperatures.
When the temperature is around –5c the hexagonal blocks are much longer and dense than they are at say –15c, at this temperature a thinner, flat plate is formed, at temperatures –6c to –10c long needles and long hollow blocks form.
The crystals then join or rather clump together this process is called accretion, this basically describes many small items adding to one another to form one bigger item, in this case the bigger item is ice.

The fibrous strands are likely to be clumped crystals with impurities or air trapped inside and around them. This happens when impure water freezes to quickly, Cooling at lower temperatures will reduce the amount of trapped impunities.
If you can't turn the freezer temp down? try leaving the freezer door a jar, but be careful, you don't want to defrost the sunday roast.
Q

[samuraigecko]

The Ice-O-Lation technique can be found as a part of the CFO technique and in a fair number of tea recipes already here.

Peace