Beatriz P. Nobre

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.

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.

Effect of light on the production of bioelectricity and added-value microalgae biomass in a Photosynthetic Alga Microbial Fuel Cell

This study demonstrates the simultaneous production of bioelectricity and added-value pigments in a Photosynthetic Alga Microbial Fuel Cell (PAMFC). A PAMFC was operated using Chlorella vulgaris in the cathode compartment and a bacterial consortium in the anode. The system was studied at two different light intensities and the maximum power produced was 62.7 mW/m(2) with a light intensity of 96 μE/(m(2)s). The results showed that increasing light intensity from 26 to 96 μE/(m(2)s) leads to an increase of about 6-folds in the power produced. Additionally, the pigments produced by the microalga were analysed and the results showed that the light intensity and PAMFC operation potentiated the carotenogenesis in the cathode compartment. The demonstrated possibility of producing added-value microalgae biomass in microbial fuel cell cathodes will increase the economic feasibility of these bioelectrochemical systems, allowing the development of energy efficient systems for wastewater treatment and carbon fixation.

A biorefinery from Nannochloropsis sp. microalga – Energy and CO2 emission and economic analyses

Are microalgae a potential energy source for biofuel production? This paper presents the laboratory results from a Nannochloropsis sp. microalga biorefinery for the production of oil, high-value pigments, and biohydrogen (bioH2). The energy consumption and CO2 emissions involved in the whole process (microalgae cultivation, harvest, dewater, mill, extraction and leftover biomass fermentation) were evaluated. An economic evaluation was also performed. Oil was obtained by soxhlet (SE) and supercritical fluid extraction (SFE). The bioH2 was produced by fermentation of the leftover biomass. The oil production pathway by SE shows the lowest value of energy consumption, 177-245 MJ/MJ(prod), and CO2 emissions, 13-15 kgCO(2)/MJ(prod). Despite consuming and emitting c.a. 20% more than the SE pathway, the oil obtained by SFE, proved to be more economically viable, with a cost of 365€/kg(oil) produced and simultaneously extracting high-value pigments. The bioH2 as co-product may be advantageous in terms of product yield or profit.

Nannochloropsis sp. biomass recovery by Electro-Coagulation for biodiesel and pigment production.

Biofuel production from microalgal biomass could be an alternative solution to conventional biofuels typically dependent on food and high land/water demanding crops. However, the economic and energetic viability of microalgal biofuels is limited by their harvesting processes. The finding of innovative, low cost and efficient harvesting method(s) is imperative. In this study, the Electro-Coagulation (EC) was studied as a process to harvest the marine Nannochloropsis sp. microalga. Several EC operational conditions were studied and the best EC recovery efficiency (>97%) was achieved using a current density of 8.3 mA cm(-2) for 10 min. The quality of the recovered microalgal biomass was evaluated in terms of total lipids, fatty acid and pigment profile where no significant differences were observed after EC treatment. The energy requirements of the harvesting process were estimated and the combination of EC and centrifugation processes proved to decrease significantly the energy demand when compared with the individual process.

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.

Modeling of the Kinetics of Supercritical Fluid Extraction of Lipids from Microalgae with Emphasis on Extract Desorption

Microalgae contain valuable biologically active lipophilic substances such as omega-3 fatty acids and carotenoids. In contrast to the recovery of vegetable oils from seeds, where the extraction with supercritical CO2 is used as a mild and selective method, economically viable application of this method on similarly soluble oils from microalgae requires, in most cases, much higher pressure. This paper presents and verifies hypothesis that this difference is caused by high adsorption capacity of microalgae. Under the pressures usually applied in supercritical fluid extraction from plants, microalgae bind a large fraction of the extracted oil, while under extremely high CO2 pressures their adsorption capacity diminishes and the extraction rate depends on oil solubility in supercritical CO2. A mathematical model for the extraction from microalgae was derived and applied to literature data on the extraction kinetics in order to determine model parameters.

Extraction of value-added compounds from microalgae

Microalgae have been proposed as a multiproduct biorefinery feed stock. The algae-based biorefinery concept relies on the complete optimization process from the biomass production to processing and generating different products. Microalgae are composed of a high number of biocompounds with numerous applications. It has been pointed out by several researchers that one of the major process constraints in microalgae biorefineries is an efficient and cost-effective extraction process. Thus the optimization of integrated extraction processes (composed of effective pretreatment techniques followed by various extraction and purification process schemes) of bioproducts from microalgae has been the main goal of several research studies. This chapter will analyze the extraction of polysaccharides, carotenoids, chlorophylls, fatty acids, and proteins with major emphasis on the most used extraction methods, required pretreatment operations, and purification technologies to achieve feasible and sustainable products to be applied in different industrial sectors.