(37b) Flash Extractive Pyrolysis of Industrial Hemp Biomass to Produce Cannabidiol (CBD)

Cannabidiol (CBD) and cannabinol (CBN) are phytocannabinoid extractives found in significant quantities in industrial hemp biomass. These extractives have important pharmacological properties and therefore they are attracting great attention for development by the pharmaceutical and neutraceutical industries for various medicinal applications. CBD is currently produced by solvent extraction of the whole aerial industrial hemp plants (leafs, stems, and flowers). Typical solvents include ethanol, pentane, supercritical CO₂, water, olive oil, and others. These solvents extract in addition to CBD, chlorophyll, terpenes, lipids and other compounds in the leafs and flowers. The crude extract is purified by first winterizing the mixture, which causes the lipids to crystallize and is then removed from the mixture. The next step involves vacuum distillation of the winterized product to generate the CBD that boils at 179-180 ^oC. This approach results in the production of excessive amounts of biomass residue that must be dispose and also risks explosion because of excessive amounts of flammable extraction solvents that must be stored during the off-season.

In the new approach, the industrial hemp biomass was subjected to flash extractive pyrolysis (FEP) in a catalytic fluidized bed reactor at relatively low temperatures (200-300 ^oC), and atmospheric pressure. The CBD was vaporized and condensed in a train of condensers. The most effective way of condensing the material was to use Venturi expansion chamber at room temperature. Under Venturi expansion condensation, the CBD crystallized as a creamy-colored solid. After collection, the CBD crystals melted at room temperature and changed from creamy-color to dark brown color apparently due to oxidation of the sample on exposure to air. The yield of liquids ranged from 20-25 wt% depending on the flash pyrolysis temperature. Biochar production was very high and ranged from 40-60 wt% and gas yields ranged from 10-40 wt%. The liquid product samples were characterized using FTIR and TGA analysis. The reaction temperature, moisture content, hemp biomass particle size, and pyrolysis medium (catalyst) strongly influenced the flash pyrolysis reactions. The reaction temperature also played a key role in the flash extractive pyrolysis process. When temperature was lowered to 200 ^oC, although there was CBD production, the reactor pipelines were quickly clogged because of rapid crystallization of the CBD on the biochar resulting in the complete blockage of the reactor pipelines especially at pipeline junctions. When reaction temperature was 230 ^oC or higher, there was no blockage of the reactor pipelines. The pyrolysis medium was also critical for effective production of CBD. When reformulated red mud catalyst was used for the pyrolysis, the yield of CBD was high and there was less gas produced and condensation and crystallization were very effective. When the reaction medium was replaced with silica sand, there was excessive cracking of the CBD and production of extraneous biomass pyrolysis products because of the excessive heat transfer from the silica sand to the hemp biomass. The reformulated red mud catalyst moderated the heat transfer, prevented the formation excess gas, and cracking of the CBD. The reformulated red mud catalyst was also effective in producing other cannabinoids such as CBN, CBC in small qualities which complemented the CBD.

The cannabinoid potency analysis of the liquid product showed that the total cannabinoid content ranged from 19 to 24% and total CBD content ranged from 17 to 22%. The potential delta THC content was below 1% and CBN contents was also less than 1%. The highest terpene content of the liquid was 1.09%. The original raw material (whole hemp biomass) used for these studies contained 5.96% total cannabinoids and therefore the FEP process was able to concentrate the cannabinoid content fourfold in the liquid products. Thus, for hemp flower feedstock which could contain as much as 19% total cannabinoid, we expect the total cannabinoid content of the liquid product to be as high as 76% which could be used for various applications.

The cannabinoid content of the FEP products at 200 ^oC and 250 ^oC showed only minor differences in the cannabinoid content of the liquid product, but the biochar and gas contents were significantly affected. Thus, it is recommended to carry out FEP process at 220-230 ^oC to produce high concentrations of total cannabinoids in the liquid FEP products.

The results of these studies demonstrated that CBD and total cannabinoids can be effectively produced from the flash extractive pyrolysis (FEP) of either whole hemp biomass or fractions of the biomass containing sufficient content of CBD or any biomass feedstock with high essential oil content without using solvent.