Due to the increasing popularity of cannabis derivatives, particularly concentrates, scientists and researchers have worked relentlessly to discover novel methods of extracting these extracts, breaking new ground in their endeavor. Despite the fact that some sophisticated techniques have demonstrated significant efficacy and have received FDA approval, the majority of them are not environmentally friendly due to the usage of chemical solvents. Although many of these extraction techniques are effective and environmentally friendly, a few stand out due to their environmental and health safety as well as their high efficiency. These extraction procedures include Ultrasonic Extraction, Microwave Extraction, and Pressurized Hot Water Extraction.
EXTRACTION OF HOT WATER UNDER PRESSURE (PHWE)
This process, which was discovered by Hawthorne and his team in 1994, uses superheated water as the extractant. The water is heated to a temperature over its atmospheric boiling point of 100°c/273k, 0.1MPa, but below its supercritical threshold of 374°c/647k, 22.1MPa. One of the most distinguishing characteristics of water as an extractant in this technique is that it is environmentally benign, has a high appropriateness for extracting thermally labile chemicals, and is readily available.
Water as a Universal Solvent: Is it a Myth or a Reality? Water’s universal solvent status has been a hotly debated topic for a long time, and this is most likely related to the fact that water exhibits different properties at different temperatures. Although analytical investigations have demonstrated that water transmutes into its non-polar form above a specified temperature and pressure, this is not the case for all water. Water transmutes into its non-polar form when exposed to a specific temperature and pressure. As a result, this idea is now established as reality, with the added benefit of being effective in both polar and nonpolar states.
BEING AWARE OF THE METHOD OF EXTRACTION IN CANNABIS
Throughout the years, Hawthorne’s invention has progressed from its original, exclusive application in environmental analysis to being employed in a wide variety of applications, including the manufacture of consumables.
Numerous studies to determine the efficiency of PHWE in extracting cannabinoids under varying conditions have revealed that at optimal settings of 50°C extraction temperature, 160°C collection vessel, and 45 minutes extraction length time, there is a resultant high yield of the non-psychoactive compounds (CBC, CBG, CBD), collectively referred to as CBDT, to the psychoactive compounds (THC and CBN), collectively referred to as THCT, when compared to when using other extraction methods
Degassing of the extractant (water) is required before using the PHWE process for cannabis extraction in order to avoid oxidation of the analytes in the extract. The process of degassing, which in this context refers to the removal of oxygen molecules, can be accomplished by the use of sonication or helium purging, with the latter requiring a minimum of 60 minutes of exposure time. Chromatographic methods such as high-performance liquid chromatography (HPLC) and a UV-detector or a gas chromatography-mass spectrometer are excellent channels for monitoring the quality of the extracts obtained and the effectiveness of the process.
The PHWE technique offers two approaches to cannabis extraction: the dynamic or continuous flow approach and the static or bath system approach. The dynamic or continuous flow approach is the more common option. Despite the fact that both methods are autonomous, synergy is conceivable for increased efficiency.
Extraction of Hot Water under Dynamic and Static Pressure
When it comes to dynamic PHWE, there are five essential components that must be present: the pump, the extraction vessel, the heating device, the pressurization restrictor, and the collection vial. It is possible that the pump will be an HPLC pump, and it will transport the activated extractant into the extraction vessel containing the sample biomass, through the pressure restrictor, and finally into the collection vessel, where vaporization will take place in order to separate the extractant from the extract.
The Static PHWE approach does not require the use of a pump, and extraction occurs at the saturated vapor pressure of the vessel, which is a conventional inessential feature. If a pump is used, it must be accompanied by two pressure valves, which are responsible for regulating and maintaining the fluid’s pressure when in operation.
In general, a setup must include a pressure restrictor that is effective enough to maintain the liquid state of the extractant, a heating device that is capable of raising the temperature of the fluid to a high enough level, and a corrosion-resistant extraction vessel that is capable of withstanding the corrosive ability of water that has reached or exceeded the critical point. While the process of dynamic PHWE does not necessitate the use of a specific extraction vessel, the process of static PHWE, which is highly dependent on pressure, is most effective when carried out in an autoclave with a diameter large enough to accommodate the stirrer, which facilitates mass transfer in the medium.
BENEFITS IN GENERAL
The green extraction method is a breath of fresh air for industries seeking to transition to more environmentally friendly and non-toxic operations, particularly the pharmaceutical industry, which frequently requires guaranteed high-purity, low-toxicity, psychoactive-free raw materials, among other things.
By using vaporization and a trapping system, this method also has the advantage of preserving the final analyte’s properties, resulting in a lower risk of toxicity by eliminating up to 99.9 percent of the extractant and other undesired compounds present. It also has the advantage of higher efficiency due to its high selectivity, low surface tension, high kinetics, and ease of use.
Although the cost-effectiveness of this process has not yet been determined, when compared to other methods such as supercritical CO2 extraction, this technology is more widely applicable and, as a result, reduces the cost of manufacturing.
THE BENEFITS AND DISADVANTAGES
When comparing the two systems in terms of simplicity and ease of use, the static PHWE comes out on top because it does not require the usage of a pump or a pressure restrictor to function. While both systems have high levels of efficiency and output quality, the long residence time of extracts in the static PHWE raises the risk of phytochemical degradation, particularly when dealing with heat-labile compounds; as a result, this system is less favoured.
Taking into consideration both the start-up and operating costs, the dynamic PHWE is significantly more expensive than the static, owing to additional implements that must be purchased and the increased risk of accumulating precipitates in the system’s pipes. It is possible to regulate precipitates by adding an additional pump between the extraction vessel and the pressure restrictor for back-flushing, but this would increase the cost of the system. Alternatively, heating tape can be wrapped around the tube.
Although the following parameters should be considered when deciding which system to use: the system’s maximum operating temperature and pressure, the material used to construct its extraction vessel, and general safety precautions.