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Supercritical extraction of plant material with carbon dioxide. Scaling up from laboratory to quarter technical scale
zygmunt BUJNOWSKI, Robert BRzOzOWSKI, Stefan SzARLIK, Jacek CyBULSKI, Magdalena JEzIERSKA-zIĘBA, Barbara KąKOL, zbigniew DąBROWSKI, Andrzej GOŚ – Prof. Ignacy Mościcki Industrial Chemistry Research Institute, Warsaw
Please cite as: CHEMIK 2011, 65, 9, 849-858
Extraction is a diffusive process of exchanging mass, used for the separation of elements from mixtures of solids and liquids. An element from the extracted phase moves to the solvent as a result of concentration differences until it reaches a state of equilibrium.
Supercritical extraction is a special type of solvent extraction in which the role of the solvent is played by the liquid which is above critical temperature and pressure. Under supercritical conditions, the physical and chemical parameters of the liquid reach intermediate values between the gaseous and liquid state and are characterized by low viscosity at a relatively large density and high values of the diffusion coef cient. Because of this, supercritical liquids have good penetration and transport properties and are suitable for use as solvents in extraction processes. Changes in pressure and temperature with regard to supercritical parameters considerably change their solvency and selectivity [1, 2].
In certain cases, a continuous stream of liquid solvent, referred to as entrainer, is added to the gas stream. A proper selection of the entrainer may considerably increase the rate and selectivity of extraction. Evaporation of the entrainer may be obtained through determining the proper working temperature of the separator receiving the extract.
Carbon dioxide is very often used for separating elements from permanent plant materials. Carbon dioxide is physiologically inert and does not react with the majority of natural substances and is easily separated from the extracted product. Moreover, it has bacteriostatic properties; it is incombustible, cheap and easily accessible. Industrial scale processes are conducted with its full recirculation.
Another important reason for using supercritical extraction for isolating substances from plant materials is that extracts obtained via co2 extraction do not contain solvent residues, which is often the case with classic solvent extractions. Furthermore, organic solvents and the temperature used in classic solvent extraction may cause the decrease or even loss of the extracted elements’ active properties.
The mentioned advantages of carbon dioxide as a solvent in supercritical extraction contribute to its application in extractions whose products are intended for use in the pharmaceutical, cosmetic and food industry.
The application of extraction via supercritical and liquid CO2 for secreting oil from linseed has been presented in numerous publications. Some of them tested the in uence of pressure, material break-up and co2 ow on the rate and capacity of the process, while in certain cases experimental results were compared with the results obtained by means of calculations using mathematical models of the process [3÷5]. Other publications presented tests which compared the capacity of linseed oil extraction using supercritical CO2, conducted under different temperature and pressure conditions, with classic solvent extractions using petroleum ether  and hexane .
Supercritical extraction of dried tea leaves using CO2 was discussed in a patent which described a multi-variant extraction process in which, depending on the extraction parameters and the used entrainer, different end products were obtained . These products were de- caffeined tea leaves, caffeine, tea aroma and poliphenols.
The variety of plant materials and the changing physical and chemical parameters of obtained extracts require a separate determination of extraction conditions for each case. Besides extraction parameters such as the process’s pressure and temperature, the manner of receiving the extract itself may also prove to be a signi cant factor. When conducting the batch extraction to the end in order to eliminate all the elements from the material, the obtained extract changes its composition, density and viscosity. In certain cases, at the end of the extraction process and in conditions of extraction reception it may be a semi-solid or solid body.
The available literature does not provide examples of CO2 supercritical extraction of linseed cake which constitutes the residue of pressing oil from linseed, nor does it contain descriptions of green tea leaves’ extraction which leads to a complete isolation of all elements. For this reason, the process parameters for both these cases had to be determined via experiments.
This work presents the results of linseed cake and dried green tea leaves extraction using CO2, on a lab scale and 1⁄4 technical scale.
The extraction trials performed on a laboratory scale contributed to determining the optimum temperature of the process and showed the in uence of using ethanol and methanol as entrainers. The results obtained on a laboratory scale were then used to increase the process scale and to perform extraction via CO2 on a 1⁄4 technical scale.
Materials and reagents
In the experiments, extraction was performed on plant materials, i.e. linseed cakes and dried green tea leaves.
The linseed cakes came from oil manufacturing plants and they constituted typical production waste from lines for pressing oil from linseed, used as an additive to fodder.
The amount of oil substances in the cakes has been determined during extraction using toluene at boiling point and equaled approx. 10÷12% by weight.
The dried green tea leaves of a commercial name “Gun Powder” were obtained from the Natur-Vit herbal Industry Plants in Pińczów. This tea belongs to a type of green tea imported in wholesale packs and batched at the plant.
Prior to the extraction, both plant materials were grinded using a percussive mill, thus obtaining a grain break-up below 0.75 mm.
The extraction used carbon dioxide from the Messer Polska company in Chorzów, as well as entrainers in the form of 95% recti ed spirit from the lubelskie Spirit Plants and analytically pure methanol from the Chempur company.
Apparatus for supercritical extraction and conducting experiments
Figure 1 presents a simpli ed installation diagram for testing supercritical extraction processes. The process line of the laboratory
nr 9/2011 • tom 65
M03 - Supercritical extraction products and their applications
Image | Supercritical extraction of plant material with carbon dioxide. Scaling up from laboratory to quarter technical scale
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