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Item type:Publication, Access status: without files , Aqueous food-grade and cosmetic-grade surfactant systems for the continuous countercurrent cloud point extractionNonionic surfactant aqueous two-phase systems represent an alternative extracting media to conventional organic solvents by ensuring a mild process temperature in an aqueous environment. However, their large-scale implementation is limited due to the challenging stripping of the target substances from the surfactant. In this study, we demonstrate the application of aqueous food-grade and cosmetic-grade surfactant systems as extraction media for solutes of natural origin. We suggest that no separation of surfactant and target product (or only rough separation is sufficient) is needed in this case due to the application of both substances in the final food or cosmetic formulation. To this purpose, sixteen potential commercial surfactants applied in food or in the personal care industry were investigated for their cloud point temperature and their phase separation kinetics. Among those, the aqueous surfactant systems containing Silwet L-7230 (poly[dimethylsiloxane-co-methyl(3-hydroxypropyl)siloxane]-graft-poly(ethylene/propylene glycol) and ROKAnol NL5 (C9–11, branched and linear, ethoxylated alcohol) separated in two phases rapidly at temperatures below 50 °C. Therefore, the liquid-liquid equilibria of the mixtures Silwet L-7230/water and ROKAnol NL5/water were determined, exhibiting lower critical solution temperatures (LCSTs) of 37.3 °C and 33.5 °C, respectively. Additionally, the mixtures were investigated for their capacity to extract the model solute cinnamic acid ((2E)-3-phenylprop-2-enoic acid, CA). Batch separations with 10logPCA=0.9 for ROKAnol NL5 and 10logPCA=1.6 for Silwet L-7230 were achieved, proving the potential of these surfactants for the extraction of hydrophobic compounds. To further design a stable liquid-liquid extraction process, the density and viscosity of the surfactant-water mixtures were measured. The density differences between the micellar and aqueous phases was found to be sufficient for continuous extraction, whereby the system with ROKAnol NL5 consisted of an upper surfactant-rich phase and a lower surfactant-lean phase, and vice versa for the Silwet L-7230 system. The formation of a liquid crystalline structure with high viscosity was observed in the Silwet L-7230 micellar phase. Based on these investigations, the corresponding processes were designed and finally, for the first time, the food-grade Silwet L-7230 and the cosmetic-grade ROKAnol NL5 surfactant systems could be successfully implemented in the batch (yield = 77% and 80%) and in the continuous (yield = 96% and 100%) cloud point extraction of cinnamic acid.Publicationtype: Journal Article196 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , In situ continuous countercurrent cloud point extraction of microalgae culturesGreen microalgae are gaining increased interest due to their ability to accumulate high-value compounds such as pigments, oils, antioxidants, and aromatics. These hydrophobic compounds can be extracted from the culture by the means of the biocompatible surfactant-based in situ cloud point extraction. In this study, we developed a continuous cloud point extraction using the nonionic surfactant Triton X-114, in order to extract the lipophilic substances from a green microalgae culture and accumulate these in the surfactant-rich phase. Cinnamic acid was applied as tracer in order to determine the optimal operating conditions for the extraction in a stirred extraction column. This model substance shows satisfying partitioning in the micellar phase (10logPCA = 1.2 ± 0.2) and the maximal yield of 79.1 ± 0.2% in a corresponding batch experiment. The process window for the continuous extraction was developed based on three parameter ranges: feed-to-solvent ratio of 6–10, a total column capacity of 1–2 l·h−1, and a stirring speed of 20–60 rpm. Statistical experimental design utilizing a response surface method was applied to investigate the influence of the three process parameters mentioned above on the yield and productivity of cinnamic acid. The optimal conditions for the in situ extraction of the microalgae were validated with an Acutodesmus obliquus culture (cell dry weight = 1g·l−1). A total amount of 0.2 ± 0.1 gAlgae product/kgCulture (0.2 ± 0.1 gAlgae product/gcell dry weight) accumulated in the extract phase. A good biocompatibility of the surfactant with the microalgae cells in raffinate was demonstrated by measuring the photosynthetic activity with a pulse amplitude measurement. This study demonstrated for the first time a successful application of a surfactant-based cloud point extraction of microalgae in a continuous mode. The presented results proved the potential of the in situ surfactant-based extraction of microalgae products as an alternative to conventional extraction techniques.Publicationtype: Journal Article137 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Micelle mediated extraction of fatty acids from microalgae cultures: Implementation for outdoor cultivation(2014-10-15); ; ; In this work micelle-mediated extraction was investigated in order to develop an alternative process for the in situ extraction of hydrophobic substances from microalgae cultures. The main requirements for an in situ extraction process such as biocompatibility, phase separation behavior and partitioning of the hydrophobic target substance between micellar- and aqueous phases were studied for a number of surfactants. The cloud point temperatures (CPT) as well as the biocompatibility of seven nonionic surfactants with the microalgae Scenedesmus obliquus were determined as a function of time. For the most biocompatible surfactant, Triton X-114 with a biocompatibility of 98%, the kinetics of phase separation in the temperature range between 30 and 40 °C have been investigated. The fastest phase separation (12 min) took place at a Triton X-114 concentration of 3 wt% at 40 °C, in contrast to the slowest (55 min) at a Triton X-114 concentration of 5 wt% at 30 °C. The partitioning of representative hydrophobic substances between the both phases was predicted using the model COSMO-RS, the results were compared to experimental data with satisfying accordance (LogPcalc. palmitic acid: 0.82; LogP exp. palmitic acid: 0.75). Based on these results the extraction of valuable compounds from the microalgae S. obliquus was realized on a pilot plant and compared to the lab scale experiments.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Cloud point extraction of microalgae culturesThe micellar in situ extraction of hydrophobic compounds from microalgae cultures (Chlamydomonas reinhardtii, Chlorella vulgaris, Scenedesmus obliquus) using nonionic surfactants (Triton X-114, Tergitol TMN 6, Tergitol 15-s-7) was studied in lab- and pilot scale. Therefore, phase separation behavior of the cloud point systems as well as the biocompatibility of the surfactants was investigated. It was shown that algae cells are concentrated in the aqueous phase, whereas the hydrophobic compounds (fatty acids) are enriched in the micellar phase. The thermodynamic model COSMO-RS was used to calculate partitioning coefficients of fatty acids between the phases. The biocompatibility of the surfactants applied was studied by monitoring the photosynthetic activity of algae upon contact with surfactants using puls amplitude modulation. Significant differences in growth and the photosynthetic activity of different algae strains after exposure to surfactants were determined. Whereas the photosynthetic activity of C. reinhardtii decreased rapidly upon contact with surfactants, the photosynthetic activity of S. obliquus, was 90% in comparison to a control after exposure for 240 min to all tested surfactants. C. vulgaris showed an intermediate decrease. Thus, besides extraction, surfactants might be applied to control the growth of certain algae enabling the monoalgal culturing in outdoor cultivation of microalgae since the growth of the less surfactant-tolerant microalgae could be suppressed. Overall, the results indicate that a micellar extraction with nonionic surfactants offers the opportunity for an in situ extraction of hydrophobic substances directly from the culture medium and might be a promising alternative to a classic solvent extraction of dried algal biomass.Publicationtype: Journal Article36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of mixing and shear stress on Chlorella vulgaris, Scenedesmus obliquus, and Chlamydomonas reinhardtii(Springer, 2012-08-04); ; ; ; Photosynthetic activity (PA) and growth of different microalgae species (Chlorella vulgaris, Scenedesmus obliquus, and Chlamydomonas reinhardtii) depends in addition to other factors on mixing (tip speed) and shear stress (friction velocity) and was studied in a stirring tank (microcosm). In order to detect cause-effect relationships for an increase in photosynthetic activity, experiments were conducted under different pH values (6. 0-8. 5) and CO2 concentrations (0. 038 and 4 % (v/v)). The PA was determined as the effective quantum yield by pulse amplitude modulation during a stepwise increase of the tip speed from 0 to 589 cm s-1 (friction velocity: 0-6. 05 cm s-1) in short-term experiments. The increase caused a distinctive pattern of PA of each species. Compared to 0 cm s-1, C. vulgaris and S. obliquus showed a 4. 0 and 4. 8 % higher PA at the optimum tip speed of 126 cm s-1 (friction velocity of 2. 09 cm s-1) and a 48 and 71 % higher growth, respectively. At 203 cm s-1, the PA dropped to the value of the unstirred control, while at 589 cm s-1, the PA decreased of up to 7 and 8 %. In contrast, C. reinhardtii showed 7 % stronger growth at 126 cm s-1, while the PA decreased about 15 % at an increase of tip speed to 589 cm s-1. For all investigated microalgae, the pattern of PA and higher growth was not only explained by the main contributing factors like light supply, nutrient supply, and overcoming diffusion gradients. The results indicate that hydrodynamic forces have a stimulating effect on the physiological processes within the cells.Publicationtype: Journal Article53