In the simplest of terms, and this is not limited to super critical extraction alone, pilot scale systems are smaller than production scale setups. Pilot scale equipment is often used for research and development (R&D). It is also used for initial production runs where the objective is to understand the process completely and get it right before moving on to mass production. Considering the amount of trial and error involved in research and development as well as in the initial runs, it makes sense to experiment at the smaller, laboratory level.
Carbon dioxide (CO2) and water are the most popularly utilized fluids in the supercritical fluid extraction (SCFE) process. What is supercritical extraction? Or using the more technically correct term, what is SCFE? SCFE employs a supercritical fluid (SCF) for separating a specific part (target molecule) from raw material. Any fluid at a pressure and temperature above its respective critical pressure and temperature is a SCF. SCFs exist in a state that is partly gas and partly liquid. What is more interesting for us is their properties.
SCFs have interesting characteristics. They can be liquid-like, gas-like, or somewhere in between. For example, SCFs have:
- Density similar to that of liquids. Such higher density makes it an excellent solvent.
- Surface Tension like that of gases. Low surface tension enables it to better penetrate porous solids.
- Viscosity as that of gases. With smaller values of viscosity, SCFs can seep more inside porous solids.
It is these interesting features as well as the fact that they can be modified for a specific purpose that makes SCFs useful. Rising density improves their solvent power. Density changes with changes in pressure and temperature. Calibrated alterations in pressure and temperature enable SCFs to specifically separate the target molecule.
Take the case of cannabis extraction for example. CO2 SCFE of cannabis looks to extract a product with the maximum concentration of cannabidiol (CBD). CBD has countless medicinal properties and it is this that is making medical cannabis increasingly acceptable to people, doctors, and authorities alike.
A CO2 SCFE pilot plant for cannabis extraction will look to investigate the process parameters that optimize the process i.e. maximize extraction yield and purity at the least possible operational expenditures. Parameters include pressure, temperature, flow rate of CO2, relative flow rate between CO2 and the co-solvent (in case co-solvent is used), time duration of contact between the SCF and the raw material, and the like.
Finalizing the optimal values of parameters takes multiple pilot runs, the number often running into hundreds. And the results of most are stepping stones in the direction of the final values. Therefore, it is worthwhile to use smaller capacity equipment so as to minimize the amount of raw material, utilities, and efforts consumed – something which also minimizes expenses associated with pilot runs and research-development.
Production scale equipment, on the other hand, is of larger capacity. The pilot runs have already finalized the optimal parameter values. Therefore, production equipment can operate at higher capacities without worrying about the end result.
