If you use centrifuge technology to extract cannabinoids from biomass, we strongly recommend Lenticular based filtration methods. For this reason, we created a multistage filtration skid that addresses the filtration needs of this extraction method and also addresses most pros and cons of lenticular systems.
Most centrifuges use 74-micron bags to house biomass to be washed in centrifuges. This makes loading and unloading the centrifuge fast and efficient. This, however, allows the introduction of sub 74-micron biomass particles into the miscella stream. We address this issue using a bag filter, where most of these biomass particles are captured. Typically, we use 25-10 micron bags to capture these particles (pre-filtration). We do this because the bags are cheap and disposable. Lenticular modules are not. When appropriate, the stream can be recirculated to eliminate biomass through the bag filter only, so that the solution can be reused in the centrifuge without accumulation of solids in the stream. This “rough” pass filtration quickly removes large particles when necessary. Once bags fill, the process is stopped, and bags quickly changed out.
We typically have duplex bag housings that can be run continuously. Bags seem to fill up rather quickly, especially when running the centrifuge continually. Some customers swap bags 4-8 times per day. Our duplex bags reduce the frequency of bag changes since we use 2 bags. A duplex housing also allows you to use only 1 bag at a time or both simultaneously. This allows us to "hot swap" a bag while continuing to run, a huge improvement on operational efficiency.
The second issue with centrifuges comes with temperature. Waxes and other fats typically will not heavily dissolve at temperatures below -60C. Many centrifuges operate at -20F or even -40F so some fasts, waxes, and lipids dissolve into the solution. As the solution accumulates more and more fats and lipids, the solution is no longer able to hold as many fats and they drop out of suspension. The removal of fats is usually done in a separate process, but since most labs reuse their solution, a concentration of 20% cannabinoids is common. Those fats become problematic when the saturated solution is recirculated through a chiller to be reused to extract more biomass. The cold walls of the chiller cause fats and lipids to coagulate in the chiller and either decrease efficiency or clogging the system altogether. Dissolved fats that coagulate in a concentrated solution are a headache and must be removed.
To alleviate this issue, a lenticular module is used. Filtration paper impregnated with filter media such as diatomaceous earth is used to capture small particles and fats. By removing these solids, we help alleviate further problems downstream. Lenticular filters do a great job of removing fats, though they are not cost-effective when the amounts of fats are great. For this reason, you would not use a lenticular for CO2 based crude.
Chlorophyll typically dissolves in ethanol at temperatures above -67F or so. Since most centrifuges operate at warmer temperatures, some level of chlorophyll and carotenoids inevitably makes it into the solution. A third stage lenticular with carbon impregnated modules is used to remove these molecules in a process called carbon adsorption. Carbon improves color and also helps adsorb heavy metals, some molds, and pesticides.
Unfortunately, the carbon modules do create problems since some carbon particles make it through the modules. A fourth stage filter with a rating as low as 0.2 microns (typically 1 micron) is used to remove any loose carbon particles that may make it through. The resulting stream is free from biomass, solid fats and lipids, and carbon scrubbed. It can also be sterilized free of mold and bacteria. It now can proceed to other downstream processes that will work more efficiently and trouble-free.
Holding tanks are used before and after the skid. These tanks allow you to accumulate solution to act as a buffer between processes. It eliminates concerns when cleaning the skid is necessary during production. It also allows downstream processes to catch up.
Each stage of filtration can be fully drained and dried using compressed air or nitrogen. This reduces potential losses of solvent or oil.
The main drawback of this technology is cleaning and cost. Though one can process hundreds of gallons per batch, eventually modules get clogged and must be replaced. There is “differential pressure” that is visible through pressure gauges, which indicates to the user when each stage of the process needs to be serviced. Swapping a lenticular module need not be a lengthy process, but it can be quite messy. The real issue is the cost associated with replacing modules since an entire cartridge swap can cost close to a thousand dollars.