Top Flood or Bottom Flood Extraction? Bi-Directional. June 05 2017, 1 Comment
There is a lot of debate on the decision to perform a top flood or bottom flood extraction method. Some might say bottom flood is "too complicated" or "unnecessary". Maybe even that it does not work as well. If the bottom flood method was performed properly they would not be saying anything of the sort.
However, there has always been a correct assumption that the oils and solvent should be washed down the column assisted by gravity. Nonetheless a bottom flood should be used to fill the column with solvent and saturate the material properly for a reliable, high yield extraction. This is where the two methods (top flood and bottom flood) can join forces to use the same force, gravity, to evenly saturate the material and wash the oil and solvent down to the collection chamber afterward.
In order for oils to be dissolved from plant material, the material must be saturated. With dry plant material packed in the column tightly and/or unevenly liquid solvent does not penetrate the plant material evenly when gravity's effects come into play. The liquid will move through the path of least resistance, meaning if there is no opposing force the liquid will move down towards the collection pot without trying to spread out and permeate the material. The oils will only get picked up if they come into contact with the liquid solvent and a wider diameter column can make this problem worse.
This can be easily demonstrated with a pot of dry soil and some liquid water ("the universal solvent"). The dry soil is somewhat "hydrophobic" and repels the liquid water. When quickly washing water over the top of the pot, the water gets pulled down by gravity and flows down the path of least resistance. This washes down any loose particles in the path, opening it up, lessening the resistance of that path. You could imagine how a lot of water could go through the container onto the ground without really achieving it's purpose (wetting down the soil). If the container of dry soil was pushed down into a bucket of water, the water would quickly saturate it because of the force of gravity keeping it in contact with the soil even though it would try to repel the water. This would ensure an even and full saturation of the soil in a quick period of time with very little or no water wasted.
Filling liquid solvent into the plant material column from the bottom to the top ensures a full and even saturation of the product in a quick manner with an easily measurable amount. This enables the extraction operator to determine a more precise amount of solvent to be used, allowing recovery times to be reduced while yield is maximized. Washing too much solvent through the column can lead to longer recovery times and possibly more undesirable compounds being picked up by the solvent.
A benefit of having the "liquid" line, which is overlooked in some cases, is the ability to drain the column with the line at the top open to the collection pot. This allows for almost all of the solvent in the column to drain down to the collection pot. When the top of the column is sealed off, the liquid draining down is not going to make it very far. For example: when a finger is placed on top of a straw full of liquid and the straw is lifted out of the liquid, it may be noticed that the liquid stays in the straw until the finger is removed from the top.
When allowing the solvent to drain from the material column, all of the oil-laden solvent does not drain down to the collection pot. With a Bi-Directional Modification, a top rinse can be performed to wash this oil left behind down the column by top flooding the column through the bi-directional valve up the "liquid" line with the "liquid" valve closed and the "dump" valve open. This also has the benefit of washing free any oil that could have possibly made its way into the "liquid" line.
A method implementing a bottom flood followed by a top flood is the most efficient method of extraction that can be performed on dry plant material to ensure the fastest, most precise, and highest yielding extraction possible.