One of the most common methods of recovering solvent from hash in the lab is with a rotary evaporator.
This distillation apparatus operates under vacuum to reduce the boiling point of the solvent, allowing us to evaporate off our solvent without damaging the cannabinoids, at much lower temperatures. The boiling flask rotates to create a thin film, which speeds up the evaporation.
After the solvent is evaporated, and is traveling towards the vacuum pump in the vapor stream, it passes over the condenser which forces the solvent back into its liquid phase, allowing gravity to pull the liquid solvent into the receiving flask.
This device, on paper, can be summarized as a simple equation.
Heat (energy) Into the boiling flask = Heat (energy) Out of the condenser
And since deeper vacuum lowers the amount of heat (Energy) needed on the boiling flask, the equation dictates that less heat (energy) is needed on the condenser side. It’s important to note that Heat (energy) is being removed with the condenser via cold fluid, fluid which required (energy) to create.
So how do we apply this knowledge to improve the performance of our roto?
- In order to maximize vacuum performance, it is necessary to condense as many volatile molecules in the vapor stream as possible. This means that a cold trap is in order. A dry ice dewar style, similar to those standard on a SPD setup, will suffice.
- In order to maintain the equilibrium of our still (heat in = heat out) it makes sense to preheat our incoming feed solution. This can be easily achieved by incorporating a heat exchanger into the feed line. Simply, a coil submerged in a bucket of souz vide heated water, will bring the incoming feed up to temp cheaply and easily without significantly increasing hot residence time.
- As we improve the efficiency of our Heat In side, we must balance the equation on our Heat Out side. While buying a larger chiller is the most efficient step, sometimes ingenuity is all we have at our disposal. Another heat exchanger, the coil for example, can be submerged in a cooler full of dry ice, which can be inserted between the output of the chiller, and the input of the roto condenser. It is important to place the exchanger here vs between the chiller and condenser on the fluid input to the chiller so as not to confuse the chillers internal thermostat.
If you find that after these steps you still are at a solvent recovery bottle neck, its time to consider a Falling Film.