1,721,016 research outputs found
Thermodynamic modeling of the phase behavior of binary systems of ionic liquids and carbon dioxide with the group contribution equation of state
Full text linkThe group contribution equation of state (GC-EOS) was applied to predict the phase behavior of binary systems of ionic liquids of the homologous families 1-alkyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate with CO2. Pure group parameters for the new ionic liquid functional groups [-mim] [PF6] and [-mim] [BF4] and interaction parameters between these groups and the paraffin (CH3, CH2) and CO2 groups were estimated. The GC-EOS extended with the new parameters was applied to predict high-pressure phase equilibria in binary mixtures of the ionic liquids [emim][PF6], [bmim][PF6], [hmim][PF6], [bmim][BF4], [hmim][BF4], and [omim][BF4] with CO2. The agreement between experimental and predicted bubble point data for the ionic liquids was excellent for pressures up to 20 MPa, and even for pressures up to about 100 MPa, the agreement was good. The results show the capability of the GC-EOS to describe phase equilibria of systems consisting of ionic liquids. © 2007 American Chemical Society.Fil: Breure, Bianca. Delft University of Technology; Países BajosFil: Bottini, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Witkamp, Geert-Jan. Delft University of Technology; Países BajosFil: Peters, Cor J.. Delft University of Technology; Países Bajo
Natural deep eutectic solvents as performance additives for biocatalysis
No full textFollowing ionic liquids, (natural) deep eutectic solvents ((NA)DES) are receiving significant attention as performance additives for biocatalytic reactions. (NA)DES are increasingly evaluated as solvents to replace water in hydrolase-catalyzed esterification reactions thereby shifting the reaction equilibrium. They also frequently outperform water in terms of solubility properties of hydrophobic reagents and thereby enable higher space-time yields. Furthermore, (NA)DES frequently exceed stabilizing effects on enzymes and thereby enable more robust (and therefore economically more attractive) biocatalytic syntheses. In this contribution, we will summarize and critically evaluate the recent literature on (NA)DES-supported biocatalysis.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Biocatalysi
Deep eutectic solvents:Teaching nature lessons that it knew already
No full textWhen Brønsted and Lewis acids and bases are mixed strong hydrogen bonds develop and these deviate from ideal mixtures resulting in a significant depression of freezing point. Many of these mixtures are liquid at ambient temperatures. These so-called deep eutectic solvents have become an area of intense study since their discovery. Mixtures of Brønsted and Lewis acids and bases are commonly found in nature and the properties of these mixtures are similar to ionic liquids. This article explains the types of mixtures which form and how bioinspired formulations can be used to form materials which mimic natural structures and can be used for applications such as drug delivery. The ability of sugars to form concentrated complex liquid mixtures is discussed and compared to aqueous solutions. DESs have complex phase behavior when solutes of lower polarity are included and it is shown that microemulsions are formed when water is introduced into DESs. This may explain the behavior of proteins and bio-macromolecules in DES-water mixtures. The thermodynamics of species partitioning into DESs is discussed together with methods to calculate enthalpies of interaction
Sustainable Production of Cannabinoids with Supercritical Carbon Dioxide Technologies
No full textThis thesis concerns the production of natural compounds from plant material for pharmaceutical and food applications. It describes the production (extraction and isolation) of cannabinoids, the active components present in cannabis. Many cannabinoids have medicinal properties but not all cannabinoids are available in the (large) quantities necessary to develop new medicines, because so far, for large scale production, there are no economically and technically viable methods to extract those cannabinoids present in low quantities in the plant. Moreover, the currently used production process for the most important cannabinoid, tetrahydrocannabinol (?9-THC), has many drawbacks, such as the large use of the organic solvents, which is not only a burden to the environment but also to the safety of the operators, the production costs as well as the treatment of the produced waste. In this thesis, an alternative process using supercritical carbon dioxide is presented for the production of cannabinoids, including ?9-THC, cannabinol (CBN), cannabigerol (CBG) and cannabidiol (CBD). One of the steps of ?9-THC production from cannabis plant material, is the decarboxylation reaction, transforming the ?9-THC-acid naturally present in the plant into the psychoactive ?9-THC. Experiments showed a pseudo first order reaction, with an activation barrier of 85 kJ.mol-1 and a pre-exponential factor of 3.7x108 s-1. Using molecular modeling, two options for an acid catalysed ?-keto acid type mechanism were identified. Each of these mechanisms might play a role, depending on the actual process conditions. Formic acid was shown to be a good model for a catalyst of such a reaction. A direct keto-enol mechanism catalyzed by formic acid seems to be the best explanation for the observed activation barrier and the pre-exponential factor of the decarboxylation of ?9-THC-acid. Evidence for this was found by performing an extraction experiment with Cannabis Flos. It revealed the presence of short chain carboxylic acids supporting this hypothesis. Then, in order to develop the supercritical fluid extraction process, the solubility of ?9-THC, CBN, CBG and CBD in supercritical carbon dioxide has been determined using an analytical method with a quasi-flow apparatus. First the solubility of ?9-THC has been determined at 315, 327, 334 and 345 K and in the pressure range from 13.2 to 25.1 MPa. The molar solubility for ?9-THC ranged from 0.20 to 2.95x10-4. Then, the solubility of CBN, CBG and CBD in supercritical carbon dioxide has been determined at 314, 327 and 334 K and in the pressure range from 11.3 to 20.6 MPa. The molar solubility of CBN, CBG and CBD ranged from 1.26 x 10-4 to 4.16 x 10-4, from 1.17 to 1.91 x 10-4 and from 0.88 to 2.69 x 10-4, respectively. These solubility data have been compared to each other. The solubility of the different cannabinoids in supercritical CO2 increases at 326 K in the following order: ?9-THC < CBG < CBD < CBN. The solubility data were correlated using the Peng-Robinson equation of state in combination with Van der Waals mixing rules. To continue, supercritical fluid extraction (SFE) using carbon dioxide was performed with Cannabis Sativa L. in a pilot scale set-up at 313 and 323 K in the pressure range from 18 to 23 MPa. The SFE yield of ?9-THC is at maximum 98 %, which is comparable to classical hexane extraction. CBN and CBG can be extracted in higher amounts with SFE than with hexane extraction. Waxes are co-extracted with the cannabinoids. They can be easily removed via a winterization step. The purity of the final extract after winterization was 85 % ?9-THC at the optimal experimental conditions found in these experiments. With a two-steps extraction, it is possible to selectively extract minor cannabinoids (i.e. CBN, CBD and CBG) in a first step at low pressure (~15 MPa), and ?9-THC in a second step at higher pressure (~20 MPa). The last step of the process is performed using Centrifugal Partition Chromatography. It uses a two-phase liquid system, instead of a solid stationary phase, as it is the case in High Pressure Liquid Chromatography (HPLC). Separation is realized by the partitioning of compounds between the two phases. With this technique, a successful separation of ?9- THC, CBN and CBG is presented using the two-phase system hexane / acetone / acetonitrile. A purity higher than 99% is achieved with ?9- THC. With CBN and CBG the best purity obtained is higher than 90%. To conclude, an economical and ecological evaluation of two production routes to obtain pure ?9-THC is presented: the current process using organic solvents is compared with the alternative process using supercritical carbon dioxide developed in this thesis. The alternative process is significantly cheaper than the current one, although the high price of the starting material cannabis dominates the ultimate cost price. From an ecological point of view, the alternative process is also more sustainable as it consumes less energy and generates less waste. Therefore, this alternative process is preferred from an economical and ecological point of view.Process and EnergyMechanical, Maritime and Materials Engineerin
Interactions of water and amphiphiles with deep eutectic solvent nanostructures
Full text linkDeep eutectic solvents (DES) are extensively hydrogen-bonded eutectic mixtures with low melting points. The presence of H-bonding makes them highly susceptible to interactions with water and also allows them to support amphiphile self-assembly, both for surfactants and biological lipids. Water disrupts the DES nework through intermolecular H-bonding, leading to changes in physicochemical properties: melting point, density and viscosity decrease; whereas electrical conductivity increases as water is added. Trends in these properties and structural studies suggest an upper hydration limit, where a transition is observed, around 60–80 mol% water, from water-in-DES to DES-in-water behavior. Amphiphiles form aggregates in DES depending on solvophobicity, water content and Gordon parameter with structures ranging from globular micelles to highly ordered hexagonal/cubic phases. Lipid vesicle formation is also ob- served in DES with and without water. These interactions find important applications in fields such as biology, nanoparticle synthesis and electrodeposition
Pilot study and modelling of remineralization of low-temperature desalinated water by calcite filtration
No full textTo prepare for future challenges, such as possible upcoming organic micro pollutants in the source water, including traces of medicines, pesticides, and industrial by-products, it is expected that the conventional treatment does not ensure a reliable quality of drinking water. As a result, during the past few years, Oasen started to research a new treatment concept based on 100% reverse osmosis (RO) membrane filtration to provide an excellent barrier for organic micro pollutants. However, the water produced by the RO membranes, called permeate, is corrosive, bitter in taste and does not comply with the drinking water regulation standards in the Netherlands. Therefore, a certain degree of remineralisation is crucial to solve these problems and improve the water quality. A commonly used remineralisation process is to filter the desalinated water through a calcite contactor, providing the appropriate amount of bicarbonate and calcium in the water. In order to properly design and operate the calcite filters as well as to predict the final water quality, it is essential to understand the processes that occur in the filter. The aim of this study was to find the best kinetic calcite dissolution model in order to understand the calcite grains dissolution behavior inside the filter and subsequently to adequately design and operate the calcite filter. Therefore, extensive pilot research was conducted to investigate the effect of various parameters on calcite dissolution such as the calcite grain size, velocity and carbon dioxide concentration. On top of that, the dissolution was modelled based on a successful empirical expression given by Yamauchi et al. (1987). However, it was found that the effect of the flow rate on the diffusion boundary layer around the calcite grains has not been taken into account in the study carried out by Yamauchi et al. (1987). Therefore, the effect of velocity on the calcite dissolution coefficient was investigated at five different velocity ,i.e., 5, 10,15,20,30 m/h. From there, a function was developed to describe the correlation between flow rate and the dissolution rate coefficient. In order to calculate the equilibrium concentration, the chemical reactions were simulated using PhreeqPython (Phreeqc built in Python).The main difference of this study compare to previous investigations was the low temperature of the water (12 oC vs 22-40 oC) and the smaller grain size of the calcite (0.5-1.2 mm vs 1-2 and 2-3mm) which was tested. Besides that a high range of CO2 dosing (1.45- 9.5 mmol/l) was tested. As expected from theory, the dissolution rates was strongly affected by the varied parameters. It is concluded that the smaller grain size of 0.5-1.2 mm reduced the required empty bed contact time (EBCT) to15 min where operating the filter with the larger grain size of 1-2mm needs a minimum EBCT of 25 min to reach calcite equilibrium. The CO2 dosing is recommended to be less than 3 mmol/l, since the CO2 efficiency will drop under the 60% at higher CO2 concentrations. Eventually, the optimal design will be introduced for the remineralisation process at Oasen treatment plant De Hooge Boom located in Kamerik. For this purpose various operational scenarios were compared on capital and operational cost. The overall cost including, both Capital expenses (CAPEX) and Operational expenses OPEX, was estimated between € 0.048 and 0.064 per m3 for different scenario’s where 71% consists of investment cost. The total treatment cost of this design is 0.057 €/m3 and the investment cost was found to be € 1.351.000 which is 32% less than price estimated by previous study done by Oasen. Remineralisatio
Sustainable Ways of Combining Reactions and Separations Using Ionic Liquids and Carbon Dioxide
No full textTraditional chemical processes show shortcomings caused by using volatile organic compounds as solvents during reactions and separations. Therefore, it is necessary to address this issue by moving toward more environmentally friendly processes. This is possible by using less toxic and hazardous solvents, such as ionic liquids and supercritical carbon dioxide (scCO2). Ionic liquids have attracted a lot of attention as potential “green” solvents to replace conventional organic solvents due to their unique properties. Ionic liquids are molten salts, which are liquid below 373 K. They consist of organic cations with organic or inorganic anions. Typically, ionic liquids possess an extremely low vapor pressure, a high thermal stability, and a wide liquid range. Ionic liquids show high solubility for both polar and apolar compounds. As a result of these properties, there are many reports where ionic liquids have been used as solvents for chemical reactions. Moreover, ionic liquids in combination with CO2 show numerous advantages. For instance, ionic liquids do not dissolve in CO2, but CO2 is highly soluble in ionic liquids. Moreover, it is shown before that CO2 is able to force two immiscible liquid phases to form one homogeneous phase as CO2 pressure increases. This interesting behavior, which is known as the miscibility switch phenomenon, is generally applicable for ternary systems containing ionic liquids, CO2 and organics. A new process set-up based on this phase behavior has been proposed, in which the reaction is carried out in a homogenous phase at high rate (no mass transfer limitations) by selection of a suitable pressure, temperature and CO2 concentration. After completion of the reaction, a phase separation is induced by changing the conditions. The product can be recovered with high purity from one of the two phases that is substantially free of ionic liquid. Two model reactions were studied to apply this new process concept. First, the epoxidation reaction of cinnamyl alcohol to 3-phenylglycidol was studied in the presence of ionic liquids as solvents. (2S,3S)-(-)-3-Phenylglycidol is an intermediate for a well-known potent active anti-inflammatory agent, Ibuprofen. In order to scale up the reaction in an ionic liquid/scCO2 miscibility switch system, a study was started to select the optimum ionic liquid in this case. The catalytic epoxidation reaction of cinnamyl alcohol in the presence of ionic liquids was optimized with respect to various parameters: (i) type and amount of oxidizing agent, (ii) type and amount of catalyst, (iii) type of ionic liquids (ranging from hydrophobic to hydrophilic), and (iv) temperature. Optimization of the conditions revealed that product stability is the key factor in determining the reaction conditions. Optimum conditions were obtained using the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) with 3 mol% vanadyl acetylacetonate as a catalyst and 1,5 equiv. of tert-butyl hydroperoxide as oxidant at 25 °C. In order to design the subsequent separation step using CO2 extraction, it is critical to have the knowledge on the phase behavior of the systems involved. Therefore, the high-pressure phase behavior of ternary systems containing epoxidation reaction compounds, ionic liquids and scCO2 were measured. Phase behavior experiments were carried out using a synthetic method in the Cailletet apparatus at five different concentrations of CO2, at temperatures and pressures up to 368 K and 12.1 MPa, respectively. Both ternary systems (cinnamyl alcohol + ionic liquid + CO2 and (2S,3S)-(-)-3-phenylglycidol + ionic liquid + CO2) only show one type of phase transition (liquid-vapor to liquid) at the highest pressures studied. A comparison between the two systems shows that both systems behaved similarly at low concentrations of CO2 (less than 40 mol%). However, by increasing the concentration of CO2 (more than 40 mol%) higher pressures are necessary to completely dissolve CO2 in the system containing cinnamyl alcohol compared to (2S,3S)-(-)-3-phenylglycidol. Moreover, a comparison between the binary system of [bmim][Tf2N] + CO2 and the studied ternary systems indicates that the addition of organic compounds decreases the solubility of CO2 in [bmim][Tf2N]. Finally, using data obtained during this work, the conditions for carrying out the epoxidation reaction in a homogeneous phase and extracting the product with scCO2 in the two-phase region are determined. The second model reaction was Friedel-Crafts acylation reaction of ferrocene to acetylferrocene. Ferrocene, which is solid up to 445 K, is a building block for wide range of applications from homogeneous catalysis and material science to biology and medicine. Acetylferrocene is the product of the acylation reaction of ferrocene and has applications as an intermediate in the production of functional groups, combustion catalysts for propellants, and in medicinal chemistry. Recently, a comprehensive investigation of the acylation of ferrocene into acetylferrocene has been conducted in the presence of ionic liquids as solvents instead of conventional organic solvents. The promising results showed that up to 100% conversion and yield could be reached using imidazolium-based ionic liquids, specially [bmim][Tf2N] as a solvent with scandium triflate (Sc(OTf)3) as a catalyst. In order to investigate the feasibility of the product extraction using scCO2, the solubilities of ferrocene and acetylferrocene in scCO2 were measured using an analytical method in a quasi-flow apparatus. High-performance liquid chromatography was applied through an online sampling procedure to determine the concentration of ferrocene and acetylferrocene in the scCO2 phase. The experiments were performed within a temperature range of 308 to 348 K and at pressures ranging from 7.7 to 24.4 MPa. The molar solubilities at the applied conditions range from 8.9 to 31.2 × 10-4 for ferrocene and 2.5 to 79.2 × 10-4 for acetylferrocene. The existence of a cross-over area for acetylferrocene is detected at a pressure of around 15 MPa and for ferrocene at a pressure of around 10 MPa. The comparison between the experimental solubility data shows that ferrocene is more soluble in scCO2 at lower pressures, while at higher pressures acetylferrocene was more soluble in scCO2. The reason for this behavior is a trade-off between the lower polarity of ferrocene (more dominant at lower pressures) and the molecular structure of acetylferrocene (more dominant at higher pressures). Results obtained in this work show that the solubility of the reaction product acetylferrocene in scCO2 was sufficiently high to use scCO2 extraction at high pressures to separate it from its reactant ferrocene in Friedel-Crafts acylation processes. Furthermore, to investigate the possibility of applying the miscibility switch phenomenon to perform Friedel-Crafts acylation reaction, the high-pressure phase behavior of the ternary system containing ferrocene or acetylferrocene, the ionic liquid [bmim][Tf2N] and CO2 were studied experimentally. The experiments were performed using a synthetic method in the Cailletet apparatus within a pressure range of 0.25 up to 10 MPa and in a temperature range of 278 up to 368 K. Five different concentrations of CO2 (10, 20, 31, 40 and 50 mol% of CO2) were investigated. While for the ternary systems containing ferrocene + ionic liquid + CO2 three phase transitions (SLV ? SL, SL ? L and LV ? L) were experimentally measured, for the ternary systems with acetylferrocene two different regions of liquid-vapor (LV) and liquid (L) were recognized. It is also shown that CO2 acts as a co-solvent in all measurements in the presence of ferrocene, even at high CO2 concentrations (50 mol%). Ferrocene is thus more soluble in the [bmim][Tf2N] + CO2 mixture than in pure [bmim][Tf2N]. Removing CO2 from the system by pressure release results in precipitation of the ferrocene, so that it can be recovered from the ionic liquid phase. This is contrary to many other ionic liquid + organic systems that show anti-solvency behavior in the presence of large amounts of CO2, where it is possible to recover the organic compound as precipitate by the addition of supercritical CO2. The solute effect on the phase behavior was studied by comparing the experimental results of the binary system [bmim][Tf2N] + CO2 with those of the ternary system acetylferrocene/ferrocene + [bmim][Tf2N] + CO2. It is shown that addition of an acetyl group to the ferrocene molecule dramatically changes the phase behavior of the binary system. Finally, the homogeneous liquid phase region was determined experimentally. This study indicates that performing the acylation reaction of ferrocene to acetylferrocene in the presence of [bmim][Tf2N] and CO2 in a homogeneous liquid phase is feasible. Finally, the benefits of applying new process set-up were investigated from economical and ecological point of view. For this purpose, the conventional production process is compared with the alternative process proposed in this study using ionic liquid/CO2 for both model reactions. From an ecological point of view, the ionic liquid/CO2 production process generates much less catalyst and solvent losses and consumes much less energy. From an economical point of view, there are capital expenditures associated with the purchase of new equipment for the ionic liquid/CO2 production process, but the savings in operational costs for both reactions are much higher, making the new process overall more attractive than the conventional one. For the market of 100 ton per year 3-phenylglycidol production, new process saving will be 3.10 million euros per year. For the production of 100 ton per year of acetylferrocene, it is estimated that using ionic liquid/CO2 process will save 0.94 million euros per year regarding variable and fixed costs for the production of acetylferrocene. In conclusion, even though the ionic liquid/CO2 production process needs high start-up investment but the amount of the money saved each year is higher than this investment, and therefore it is economically and ecologically feasible to replace the current production process.Process and EnergyMechanical, Maritime and Materials Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
