Solvent-assisted recrystallisation for the recovery of cannabinoids from Cannabis extraction by-products

Abstract

A wax by-product removed from the initial stages of commercial Cannabis processing, which contains significant amounts (39–51% (w/w)) of cannabinoids, is currently underutilised due to a lack of information on wax composition and further processing options. Significant value might be generated from further recovery of the cannabinoids entrapped within the wax fraction, and from further processing of the wax into useable products. This study aimed to develop a method to recover the cannabinoids contained in the wax and to prepare the wax for further refinement into a valuable product. A method where the wax by-product was dissolved in ethyl acetate and then recrystalized was developed, which consisted of a heating and mixing stage followed by filtering and washing with additional solvent. The main variables for the experiments were the ratio of solvent to wax for dilution, and the ratio of solvent to wax for post-crystallisation washing. The recrystallisation method was successful in recovering the cannabinoids from the wax and the effectiveness of the recovery was significantly impacted by the solvent addition. The method was validated on two samples of industrial by-products sourced from the cannabinoid extraction industry, and the highest recovery over two consecutive dissolution-recrystallisation cycles was 68.3% and 96.3%, for wax A and B respectively. In both cases, maximum recoveries were achieved with the experiments corresponding with the highest solvent addition. It was therefore concluded that the use of more solvent during recrystallisation, especially for the washing step during filtering, was favourable as it resulted in a higher recovery of cannabinoids from the wax by-product. Furthermore, wax carry-over to the recovered filtrate was sufficiently low (< 3% (w/w)), and was easily removed by centrifugation. The majority of the carried-over lipophilic components were fatty acids, with a maximum concentration of 17.39 mg/g in the filtrate removed after the first stage of recrystallisation with wax A. The other components (n-alkanes, fatty alcohols) were in significantly lower abundance compared to the fatty acid fraction. The recovery when the wax was filtered without undergoing recrystallisation was 33.5%, significantly less than the recovery of the recrystallisation method. This work successfully demonstrated a methodology for simple cannabinoid recovery from Cannabis processing by-products, with the potential to create significant additional value from what is currently regarded as a waste in this industry.