52 February / March 2018
Mass Balance Analysis for Batch CO2
(Cannabis Sativa) by Shawn C. Helmueller, Waters Corporation, 34 Maple St, Milford MA, 01757
This article was adapted from a presentation given at Waters Symposium on Extraction and Analytical Testing, 14th November 2017, Las Vegas, NV. The goal is to highlight briefly current CO2
-based extraction technology, and discuss considerations for adopting and implementing this
technology for the cannabis industry. As an example, a processing workflow, method parameters, and routine analytical mass balance data will be presented for CO2
performing targeted extractions and monitoring batch performance. What is Modern SFE?
Historically, supercritical fluid extraction (SFE) refers to a technique for extracting compounds of interest (COI) from solid or semi-solid substances using a supercritical fluid as the primary component of the extraction solvent [1][2]. A supercritical fluid results when a solvent is heated and pressurised above its critical temperature and pressure (Figure 1). Today however, the term SFE is also commonly used to describe the general use of carbon dioxide (CO2
)
as the extracting solvent, regardless of its physical state. The flexibility to operate in significantly diverse temperature and
pressure space is a major advantage of CO2 extraction because the solvating strength of
CO2 changes significantly with temperature
and pressure [1][3]. For this reason, the terms ‘CO2
extraction’ and ‘SFE’ are often used
interchangeably since extraction processes in modern instrumentation take place in both the liquid (subcritical) region and supercritical region.
CO2 A Natural Fit for Cannabis
Carbon dioxide-based extraction is an extremely attractive alternative to traditional liquid and light hydrocarbon extractions for the bulk processing of natural products, and this is especially true for products eventually destined for human consumption [2][4]. As
extraction of Vermont Hemp using Waters Bio-Botanical Extraction System, with the goal being to describe a workflow for
a result, SFE has become widely utilised by manufacturers in the emerging cannabis industry to extract, concentrate, and isolate active ingredients from the cannabis plant [5]. SFE extracts are particularly advantageous compared to liquid solvent extracts in that there is no residual solvent present in the final extract and the use of toxic or potentially dangerous solvents such as butane, hexane, and chlorinated solvents can be avoided [1][2][4]. Therefore, the time-consuming steps required to remove these unwanted solvents are lessened in the extraction workflow. SFE is a versatile technique that is able to accept the wide variability of starting materials inherent in the production of natural products [2][4]. The extracts can then be further refined, purified, analysed, or directly incorporated into final products depending on the goal of the workflow [4]. SFE acts as a hub in the processing workflow (Figure 2); it prepares the sample for multiple paths in a single step [6]. Similarly, the ability to fractionate, or create multiple extract fractions, allows manufacturers to develop multiple processing streams and products from a single CO2
extraction.
Figure 1: Phase diagram for carbon dioxide, generated using NIST RefPROP V.9.1 [3]. The three common phases (solid, liquid, gas) are shown, along with the supercritical region above the critical point. The critical temperature for CO2
is 31ºC, and the critical pressure is 1,070 psi (74 bar). Above this point, the gas and liquid densities converge into a single uniform phase with high diffusivity, low viscosity and negligible surface tension.
In the cannabis industry extraction serves as a process step that adds value to a product. For example industrial hemp (cannabis sativa) has a number of benefits associated with its production from bioremediation [7], use as building materials [8], and isolation of therapeutic constituents such as cannabinoids (primarily cannabidiol, CBD) and a variety of terpenes, flavonoids, and fatty acids [5]. Since solvent strength in CO2
is determined by the operating
Extraction of Hemp
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