Rui L. Mendes

Supercritical carbon dioxide extraction of compounds with pharmaceutical importance from microalgae

Abstract Four microalgae ( Botryococcus braunii , Chlorella vulgaris , Dunaliella salina , Arthrospira maxima ) were object of supercritical CO 2 extraction studies, which were carried out in a flow apparatus at temperatures between 313.1 and 333.1 K and pressures up to 35.0 MPa. The microalga Botryococcus braunii produces extracellular alkadienes. Supercritical extracts obtained at 313.1 K, and pressures of 12.5, 20.0 and 30.0 MPa, were golden and limpid, unlike those obtained with organic solvents. The hydrocarbons of this microalga were selectively extracted and this selectivity increased with pressure. The microalga Chlorella vulgaris is a carotenoid producer of canthaxanthin and astaxanthin. The extraction yields of lipids and carotenoids were compared for whole, crushed and slightly crushed algae at a pressure of 35.0 MPa and a temperature of 328.1 K. The yield of supercritical extraction of carotenoids was also compared at several conditions of pressure and temperature. It increased with pressure at constant temperature, remained practically constant with temperature, at pressures of 27.5 and 35.0 MPa, and decreased with temperature at 20.0 MPa. The third alga studied was the Dunaliella salina , which produces β-carotene in high yield. Natural β-carotene ( cis and trans mixture) from this alga was submitted to supercritical carbon dioxide and it was assessed, at pressures up to 30.0 MPa and temperature of 313.1 K, that both isomers presented higher solubility than the synthetic trans -β-carotene and that the cis isomer was much more soluble in supercritical CO 2 than the trans isomer. Moreover, it was shown that the cis / trans ratio, in the supercritical extracts, increased significantly, relatively to the original one in the microalga, when the Dunaliella was submitted to supercritical CO 2 . The cyanobacteria Arthrospira ( Spirulina ) maxima can produce in large amounts the γ-linolenic acid (GLA), C18:3 ω6. The yield and selectivity of the supercritical extraction, using CO 2 and CO 2 doped with ethanol, of the lipids and GLA were determined and compared with those obtained with organic solvents.

Supercritical CO2 extraction of carotenoids and other lipids from Chlorella vulgaris

Freeze-dried samples of the microalga Chlorella vulgaris were submitted to supercritical CO2 at temperatures of 40 and 55 °C and pressures up to 35.0 MPa. This study was carried out on whole and crushed algae. The extraction yields of carotenoids and other lipids were low in the former case and improved significantly in the latter one. Extraction yields of carotenoids and other lipids increased with pressure. The fraction of carotenoids in the oil was also greater at higher pressures. On the other hand, supercritical CO2 extraction of carotenoids compared favourably with hexane and acetone extractions.

A biorefinery from Nannochloropsis sp. microalga - extraction of oils and pigments. Production of biohydrogen from the leftover biomass.

The microalga Nannochloropsis sp. was used in this study, in a biorefinery context, as biomass feedstock for the production of fatty acids for biodiesel, biohydrogen and high added-value compounds. The microalgal biomass, which has a high lipid and pigment content (mainly carotenoids), was submitted to supercritical CO2 extraction. The temperature, pressure and solvent flow-rate were evaluated to check their effect on the extraction yield. The best operational conditions to extract 33 g lipids/100 g dry biomass were found to be at 40 °C, 300 bar and a CO2 flow-rate of 0.62 g/min. The effect of adding a co-solvent (ethanol) was also studied. When supercritical CO2 doped with 20% (w/w) ethanol was used, it was possible to extract 45 g lipids/100 g dry biomass of lipids and recover 70% of the pigments. Furthermore, the remaining biomass after extraction was effectively used as feedstock to produce biohydrogen through dark fermentation by Enterobacter aerogenes resulting in a hydrogen production yield of 60.6 mL/g dry biomass.

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.

Extraction of Volatile Oil from Aromatic Plants with Supercritical Carbon Dioxide: Experiments and Modeling

An overview of the studies carried out in our laboratories on supercritical fluid extraction (SFE) of volatile oils from seven aromatic plants: pennyroyal (Mentha pulegium L.), fennel seeds (Foeniculum vulgare Mill.), coriander (Coriandrum sativum L.), savory (Satureja fruticosa Béguinot), winter savory (Satureja montana L.), cotton lavender (Santolina chamaecyparisus) and thyme (Thymus vulgaris), is presented. A flow apparatus with a 1 L extractor and two 0.27 L separators was built to perform studies at temperatures ranging from 298 to 353 K and pressures up to 30.0 MPa. The best compromise between yield and composition compared with hydrodistillation (HD) was achieved selecting the optimum experimental conditions of extraction and fractionation. The major differences between HD and SFE oils is the presence of a small percentage of cuticular waxes and the relative amount of thymoquinone, an oxygenated monoterpene with important biological properties, which is present in the oils from thyme and winter savory. On the other hand, the modeling of our data on supercritical extraction of volatile oil from pennyroyal is discussed using Sovová’s models. These models have been applied successfully to the other volatile oil extractions. Furthermore, other experimental studies involving supercritical CO2 carried out in our laboratories are also mentioned.

Supercritical carbon dioxide extraction of pigments from Bixa orellana seeds (experiments and modeling)

Supercritical CO2 extraction of the pigments from Bixa orellana seeds was carried out in a flow apparatus at a pressure of 200 bar and a temperature of 40 oC at two fluid flow rates (0.67g/min and 1.12g/min). The efficiency of the extraction was low (only about 1% of the pigment was extracted). The increase in flow rate led to a decrease in pigment recovery. A large increase in recovery (from 1% to 45%) was achieved using supercritical carbon dioxide with 5 mol % ethanol as extraction fluid at pressures of 200 and 300 bar and temperatures of 40 and 60 oC. Although the increase in temperature and pressure led to an increase in recovery, the changes in flow rate did not seem to affect it. Furthermore, two plug flow models were applied to describe the supercritical extraction of the pigments from annatto seeds. Mass transfer coefficients were determined and compared well with those obtained by other researchers with similar models for the supercritical extraction of solutes from plant materials.

Supercritical extraction of lycopene from tomato industrial wastes with ethane.

Supercritical fluid extraction of all-E-lycopene from tomato industrial wastes (mixture of skins and seeds) was carried out in a semi-continuous flow apparatus using ethane as supercritical solvent. The effect of pressure, temperature, feed particle size, solvent superficial velocity and matrix initial composition was evaluated. Moreover, the yield of the extraction was compared with that obtained with other supercritical solvents (supercritical CO2 and a near critical mixture of ethane and propane). The recovery of all-E-lycopene increased with pressure, decreased with the increase of the particle size in the initial stages of the extraction and was not practically affected by the solvent superficial velocity. The effect of the temperature was more complex. When the temperature increased from 40 to 60 °C the recovery of all-E-lycopene increased from 80 to 90%. However, for a further increase to 80 °C, the recovery remained almost the same, indicating that some E-Z isomerization could have occurred, as well as some degradation of lycopene. The recovery of all-E-lycopene was almost the same for feed samples with different all-E-lycopene content. Furthermore, when a batch with a higher all-E-lycopene content was used, supercritical ethane and a near critical mixture of ethane and propane showed to be better solvents than supercritical CO2 leading to a faster extraction with a higher recovery of the carotenoid.

Effects of hydrocarbon additions on gas-liquid mass transfer coefficients in biphasic bioreactors

The effects of aliphatic hydrocarbons (n-hexadecane andn-dodecane) on the volumetric oxygen mass transfer coefficient (kLa) were studied in flat alveolar airlift reactor and continuous stirred tank reactors (CSTRs). In the flat alveolar airlift reactor, high aeration rates (>2 vvm) were required in order to obtain efficient organic-aqueous phase dispersion and reliablekLa measurements. Addition of 1% (v/v)n-hexadecane orn-dodecane increased thekla 1.55-and 1.33-fold, respectively, compared to the control (superficial velocity: 25.8×10−3 m/s, sparger orifice diameter: 0.5 mm). Analysis of the gas-liquid interfacial areaa and the liquid film mass transfer coefficientkL suggests that the observedkLa increase was a function of the medias liquid film mass transfer. Addition of 1% (v/v)n-hexadecane orn-dodecane to analogous setups using CSTRs led to akLa increase by a factor of 1.68 and 1.36, respectively (superficial velocity: 2.1×10−3 m/s, stirring rate: 250 rpm). These results propose that low-concentration addition of oxygen-vectors to aerobic microbial cultures has additional benefit relative to incubation in purely aqueous media.