A discussion of extraction column design would not be complete without first discussing subzero extraction. As the LPG cannabis extraction process has evolved, we’ve learned that extracting cannabis at subzero temperatures in the range of -30/-70C or lower, we can minimize the pickup of molecules larger than our C-10 through C-22 targeted elements. Namely things like beige C-30 plant waxes, yellow to red C-40 Carotene, and olive brown C-55 Pheophytin.
The C-22 and under terpenenes and terpenoids that we covet, with the exception of the C-15 anthocyanins are colorless to light yellow. When extracted at these subzero temperatures, extracts are light in color and do not require subsequent winterizing, so are rife with mono and sesqi-terpenes, giving it a strong aroma and flavor.
Before we move this discussion to how we achieve those subzero temperatures and what equipment is required to operate at those temperatures, lets discuss what products the market covets.
Since 2010 the market has expanded from simple shatter, waxes, and budder concentrates, to include distillates like Clear, and isolates like THC-A and CBD.
There is also more than one way to make shatters, waxes and budders, as well as crude for fractional distillation into clear, plus we also have the attendant issue of plant waste material from the spent columns that is high in residual hydrocarbons, unless we take steps to remediate it.
Given those parameters, let’s start with a discussion of common column design features which has evolved since even the Terpenator Mk II design using sanitary spools for the purpose, mostly by jacketing it for the purpose of temperature control.
A Jacketed column allowing heating/insulating/cooling is the direction the industry has taken, though some jackets are open at the top and others are fully enclosed and plumbed to allow cold vapors and tempering fluids to be circulated through them from remote locations outside a NEMA 7, C1 D1 extraction booth.
Starting in order, why would we want to heat a column? Processes differ, but after recovering to -15” Hg following extraction, I isolate the column from the balance of the system and introduce 150F hot water into the jackets, while recovering the balance of the LPG, as well as during the subsequent full vacuum to -29.9”, before back filling with N2 prior to opening to atmosphere.
The result was the column was below 10% of LEL when opened, something that makes Fire Marshall's smile and subsequent spent material disposal easier.
Why would we want to insulate a column? Most current processes either heat or chill the column and contents prior to or during extraction/recovery, so simply insulating the column reduces heat gain/loss, as well as the worker from contact burns or frostbite.
Lets look at insulation on three levels, starting with the fact that the column is processing food/pharmaceutical products, so must break down into easily cleaned components or be cleanable in place. That means any insulation must be either easily cleaned or easily removed for cleaning.
At the next level, if our process requires pumping chilled liquid through the column jackets during extraction, and heating it with hot water afterwards, the issue of how to not cross contaminate the hot water source with the chiller antifreeze solution.
One solution is an insulated surge tank to blow the chilled solution into using compressed air, before isolating the chiller from the column and flooding it with hot water.
Hot water and Chiller Supply System
As the extraction portion of the process goes relatively fast, another solution is to chill the columns and their contents, wrap them with an insulation blanket, and pull a vacuum on the jacket. That eliminates any need for a column chiller and eliminates any cross-contamination problem.
Column Heat with Vacuum Jacket Insulation
Pulling a vacuum on the column jacket does have its issues without ribs between the inner and outer wall, to prevent the outer jacket from collapsing under vacuum. Properly designed ribs can also direct the heating or cooling liquid over the full surface of the inner tube, as opposed to just finding the most direct way out.
One simple design that accomplishes that end is to simply wrap the rib around the inner tube in a spiral. That would not only support the outer tube under vacuum but would direct the cooling or heating flow of liquid around the inner tube in a spiral, so that there were no dead spots.
The coil can be wrapped/rolled out of several plastic materials besides stainless steel, which would reduce thermal transmission via conduction at contact points.
Spiral ribbed and jacketed column