Study of membrane - based solvent extraction

The present thesis aims at studying the liquid - liquid membrane - based solvent extraction and consists of the understanding of the mass transfer mechanism, the process design and the development of criteria for the performance optimization upon the selection of the operating conditions. In order to study mass transfer in membrane modules, the following case is considered: parallel flow through a bundle of hollow fibers with simultaneous solute diffusion from an aqueous feed phase (flowing in the shell side) to an organic solvent (flowing in the fiber lumen). The study is focused on the shell side mass transfer and in particular on the effect of the fiber packing fraction, φ. For the class of problems considered here, i.e. liquid systems characterized by sufficiently large Schmidt numbers, Sc, a laminar flow boundary layer solution is obtained for the mass transfer rate to the outer fiber surface. To assess the aforementioned closed - form equation, two model flow fields are considered: flow along a single fiber, placed symmetrically in a tube (Model I) and flow along hypothetical annular elements or cells (each one surrounding a fiber) (Model II). According to this analysis (for the shell side), the Sherwood number, Shw, dependence on Reynolds number, Rew, and on fiber packing fraction, φ, is derived. By combining the closed - form equation for the shell side mass transfer with known expressions for the diffusion through the membrane pores as well as for the lumen side mass transfer, a predictive model is obtained for the solute concentrations at both exit streams (aqueous and organic phases), depending on several physico - chemical parameters.The experimental part consists of the mass transfer study of a solute (benzaldehyde or hexanal) from a diluted aqueous feed phase (solute concentration 100 μl lt -1) to the organic solvent n-hexane. These physico - chemical systems are described by relatively large partition coefficients. For experimentation, four membrane modules are constructed comprised of a bundle of hydrophobic polypropylene hollow fibers with packing densities ranging from 0.093 to 0.402. Data are collected in a great range of Reynolds number in the shell side, Rew, and in fiber lumen, Reo, by feeding the fluids in a co - current or counter - current mode. To further assess, two criteria are used to retain experimental data for the determination of mass transfer coefficient, kw,exp. The experimental data are in good agreement with theoretical predictions with no recourse to adjustable parameters or empirical coefficients. According to this comparison, the Sherwood number, Shw, dependence on the Reynolds number, Rew, to the 1/3 power is confirmed, for the range of the packing density, φ, tested. The effect of φ on shell side mass transfer (if any) is considered to be very weak and in all probability it is well within the narrow range of uncertainty due to experimental inaccuracies. Hence, a shell side mass transfer correlation is recommended, covering the range of packing density with practical interest 0.05 < φ < 0.45. Moreover, the analytical expressions developed in this thesis for the prediction of exit solute concentrations in membrane - based solvent extraction are in very good agreement with the experimental data. Taking advantage of the ability of mass transfer prediction in membrane modules, basic issues involved in designing membrane - based extraction process are evaluated in the present thesis. The main objectives of liquid - liquid extraction operations (i.e. maximization of solute recovery and of solvent saturation of the solute) serve as the basis of this analysis. Firstly, the operating characteristics of a single membrane module (comprised of a bundle of parallel fibers) are analyzed and two parameters are shown to determine process performance: the extraction factor E (reflecting thermodynamic limitations) and a lumped parameter A which takes into account the geometrical features of the module as well as kinetic and thermodynamic limitations. According to the present analysis, a narrow range of E and A seems to lead to near optimum module performance and thus, a procedure for preliminary design and module selection are recommended. The relative significance and inter - relation of geometric and operating variables are also appraised and, in the form of dimensionless quantities, closed - form expressions of general validity are developed for a variety of continuous process options (single module, counter - current and “cross - flow” arrays).Η παρούσα εργασία έχει ως στόχο την μελέτη της διεργασίας εκχύλισης υγρού - υγρού με μεμβράνες και συνίσταται στην κατανόηση του μηχανισμού μεταφοράς μάζας, την κατάστρωση πορείας σχεδιασμού και τον καθορισμό κριτηρίων για την επιλογή των βέλτιστων συνθηκών λειτουργίας της διεργασίας. Για την μελέτη μεταφοράς μάζας σε στοιχεία μεμβρανών θεωρείται η περίπτωση της παράλληλης ροής διαμέσου δέσμης κοίλων ινών με ταυτόχρονη διάχυση ενός συστατικού από μία υδατική φάση (που ρέει στην πλευρά του κελύφους) προς έναν οργανικό διαλύτη (που ρέει στο εσωτερικό των ινών). Η μελέτη εστιάζεται στο φαινόμενο μεταφοράς μάζας στην πλευρά του κελύφους και ιδιαίτερα στην επίδραση της πυκνότητας των ινών, φ. Για την κατηγορία προβλημάτων που μελετάται, δηλαδή για συστήματα υγρών που χαρακτηρίζονται από επαρκώς μεγάλους αριθμούς Schmidt, Sc, εξάγεται μία γενική αναλυτική έκφραση, με βάση την θεωρία οριακού στρώματος στρωτής ροής, για τον ρυθμό μεταφοράς μάζας στην εξωτερική επιφάνεια της ίνας. Για την εφαρμογή της σχέσης αυτής, θεωρούνται δύο μοντέλα που περιγράφουν το πεδίο ροής, δηλαδή μία ίνα τοποθετημένη ομοαξονικά σε σωλήνα (Μοντέλο Ι) και δακτυλιοειδή στοιχεία ροής γύρω από κάθε ίνα (Μοντέλο ΙΙ). Από την ανάλυση αυτή προκύπτει (για την πλευρά του κελύφους) η εξάρτηση του αριθμού Sherwood, Shw, από τον αριθμό Reynolds, Rew, και από την πυκνότητα των ινών, φ. Συνδυάζοντας την αναλυτική λύση για την πλευρά του κελύφους με γνωστές εκφράσεις για την μεταφορά μάζας στο εσωτερικό των ινών και στους πόρους της μεμβράνης και επιλύοντας κατάλληλα ισοζύγια μάζας του μεταφερόμενου συστατικού, εξάγονται εξισώσεις που προβλέπουν τις συγκεντρώσεις του συστατικού στα ρεύματα εξόδου του στοιχείου, ως συνάρτηση διαφόρων φυσικο - χημικών παραμέτρων. Το πειραματικό μέρος συνίσταται στην μελέτη μεταφοράς μάζας ενός συστατικού (βενζαλδεΰδης ή εξανάλης) από αραιό υδατικό διάλυμα τροφοδοσίας (συγκέντρωση συστατικού 100 μl lt-1) προς τον οργανικό διαλύτη κ-εξάνιο. Τα φυσικο - χημικά αυτά συστήματα χαρακτηρίζονται από σχετικά μεγάλους συντελεστές κατανομής. Για πειραματισμό κατασκευάστηκαν τέσσερα στοιχεία με υδρόφοβες πολυπροπυλενικές ίνες με κατάλληλο πλήθος ώστε να καλύπτεται η περιοχή πυκνότητας ινών, φ, 0.093 < φ < 0.402. Συλλέχθησαν επαρκή δεδομένα για ικανοποιητικό εύρος τιμών των αριθμών Reynolds στην πλευρά του κελύφους (Rew) και στο εσωτερικό των ινών (Reo), εφαρμόζοντας τροφοδοσία των ρευστών με ομορροή και αντιρροή. Για την αξιοποίηση των δεδομένων αυτών στον πειραματικό προσδιορισμό του συντελεστή μεταφοράς μάζας kw χρησιμοποιήθηκαν κατάλληλα κριτήρια αξιολόγησης των δεδομένων. Η σύγκριση των πειραματικών δεδομένων με τις θεωρητικές προβλέψεις δίνει καλή συμφωνία χωρίς εφαρμογή οποιουδήποτε διορθωτικού παράγοντα ή εμπειρικού συντελεστή. Από την σύγκριση αυτή επιβεβαιώνεται ότι η θεωρητική πρόβλεψη της εξάρτησης του αριθμού Sherwood, Shw, από τον αριθμό Reynolds, Rew, στην δύναμη 1/3 περιγράφει ικανοποιητικά τα πειραματικά δεδομένα, για το εύρος τιμών της πυκνότητας των ινών, φ, που ελέγχθηκε. Η επίδραση του φ στην μεταφορά μάζας από την πλευρά του κελύφους (αν υπάρχει) φαίνεται ότι είναι πολύ μικρή, και πιθανώς κυμαίνεται μέσα στα σχετικά στενά όρια του πειραματικού σφάλματος. Έτσι, προτείνεται ένας κατάλληλος συσχετισμός για τον αριθμό Shw, που καλύπτει την περιοχή τιμών της πυκνότητας των ινών με πρακτικό ενδιαφέρον 0.05 < φ < 0.45. Επιπλέον, οι σχέσεις που αναπτύχθηκαν στα πλαίσια της παρούσας εργασίας για την πρόβλεψη των συγκεντρώσεων εξόδου για μία διεργασία εκχύλισης με μεμβράνες δίνουν πολύ καλή συμφωνία με όλα τα πειραματικά δεδομένα. Αξιοποιώντας την ικανότητα πρόβλεψης της μεταφοράς μάζας στα στοιχεία μεμβρανών, αξιολογούνται στην εργασία οι διάφοροι παράγοντες που διαδραματίζουν βασικό ρόλο στον σχεδιασμό της διεργασίας εκχύλισης με μεμβράνες. Η προσέγγιση του θέματος γίνεται από την σκοπιά των κύριων στόχων της διεργασίας εκχύλισης υγρού - υγρού, που είναι η μεγιστοποίηση της ανάκτησης του συστατικού από το διάλυμα τροφοδοσίας και του κορεσμού του διαλύτη από το συστατικό. Αρχικά, αναλύονται τα χαρακτηριστικά λειτουργίας ενός μεμονωμένου στοιχείου μεμβρανών που αποτελείται από δέσμη παραλλήλων ινών από όπου προκύπτει ότι δύο παράμετροι καθορίζουν την απόδοση της διεργασίας: ο συντελεστής εκχύλισης Ε, ο οποίος εκφράζει τους θερμοδυναμικούς περιορισμούς της διεργασίας και μία παράμετρος Α, η οποία περιλαμβάνει τα γεωμετρικά χαρακτηριστικά του στοιχείου μεμβρανών καθώς επίσης κινητικούς και θερμοδυναμικούς περιορισμούς

Innovative Gas-Liquid Membrane Contactor Systems for Carbon Capture and Mineralization in Energy Intensive Industries

CO2 mineralization is an alternative to conventional geological storage and results in permanent carbon storage as a solid, with no need for long-term monitoring and no requirements for significant energy input. Novel technologies for carbon dioxide capture and mineralization involve the use of gas-liquid membrane contactors for post-combustion capture. The scope of the present study is to investigate the application of hollow fiber membrane contactor technology for combined CO2 capture from energy-intensive industry flue gases and CO2 mineralization, in a single-step multiphase process. The process is also a key enabler of the circular economy for the cement industry, a major contributor in global industrial CO2 emissions, as CaCO3 particles, obtained through the mineralization process, can be directed back into the cement production as fillers for partially substituting cement in high-performance concrete. High CO2 capture efficiency is achieved, as well as CaCO3 particles of controlled size and crystallinity are synthesized, in every set of operating parameters employed. The intensified gas-liquid membrane process is assessed by calculating an overall process mass transfer coefficient accounting for all relevant mass transfer resistances and the enhanced mass transfer due to reactive conditions on the shell side. The obtained nanocomposite particles have been extensively characterized by DLS, XRD, TGA, SEM, TEM, and FTIR studies, revealing structured aggregates (1–2 μm average aggregate size) consisting of cubic calcite when the contactor mode is employed

Fabrication and Optimization of 3D-Printed Silica Scaffolds for Neural Precursor Cell Cultivation

The latest developments in tissue engineering scaffolds have sparked a growing interest in the creation of controlled 3D cellular structures that emulate the intricate biophysical and biochemical elements found within versatile in vivo microenvironments. The objective of this study was to 3D-print a monolithic silica scaffold specifically designed for the cultivation of neural precursor cells. Initially, a preliminary investigation was conducted to identify the critical parameters pertaining to calcination. This investigation aimed to produce sturdy and uniform scaffolds with a minimal wall-thickness of 0.5 mm in order to mitigate the formation of cracks. Four cubic specimens, with different wall-thicknesses of 0.5, 1, 2, and 4 mm, were 3D-printed and subjected to two distinct calcination profiles. Thermogravimetric analysis was employed to examine the freshly printed material, revealing critical temperatures associated with increased mass loss. Isothermal steps were subsequently introduced to facilitate controlled phase transitions and reduce crack formation even at the minimum wall thickness of 0.5 mm. The optimized structure stability was obtained for the slow calcination profile (160 min) then the fast calcination profile (60 min) for temperatures up to 900 °C. In situ X-ray diffraction analysis was also employed to assess the crystal phases of the silicate based material throughout various temperature profiles up to 1200 °C, while scanning electron microscopy was utilized to observe micro-scale crack formation. Then, ceramic scaffolds were 3D-printed, adopting a hexagonal and spherical channel structures with channel opening of 2 mm, and subsequently calcined using the optimized slow profile. Finally, the scaffolds were evaluated in terms of biocompatibility, cell proliferation, and differentiation using neural precursor cells (NPCs). These experiments indicated proliferation of NPCs (for 13 days) and differentiation into neurons which remained viable (up to 50 days in culture). In parallel, functionality was verified by expression of pre- (SYN1) and post-synaptic (GRIP1) markers, suggesting that 3D-printed scaffolds are a promising system for biotechnological applications using NPCs

Development of a dose-controlled multiculture cell exposure chamber for efficient delivery of airborne and engineered nanoparticles

In order to study the various health influencing parameters related to engineered nanoparticles as well as to soot emitted b diesel engines, there is an urgent need for appropriate sampling devices and methods for cell exposure studies that simulate the respiratory system and facilitate associated biological and toxicological tests. The objective of the present work was the further advancement of a Multiculture Exposure Chamber (MEC) into a dose-controlled system for efficient delivery of nanoparticles to cells. It was validated with various types of nanoparticles (diesel engine soot aggregates, engineered nanoparticles for various applications) and with state-of-the-art nanoparticle measurement instrumentation to assess the local deposition of nanoparticles on the cell cultures. The dose of nanoparticles to which cell cultures are being exposed was evaluated in the normal operation of the in vitro cell culture exposure chamber based on measurements of the size specific nanoparticle collection efficiency of a cell free device. The average efficiency in delivering nanoparticles in the MEC was approximately 82%. The nanoparticle deposition was demonstrated by Transmission Electron Microscopy (TEM). Analysis and design of the MEC employs Computational Fluid Dynamics (CFD) and true to geometry representations of nanoparticles with the aim to assess the uniformity of nanoparticle deposition among the culture wells. Final testing of the dose-controlled cell exposure system was performed by exposing A549 lung cell cultures to fluorescently labeled nanoparticles. Delivery of aerosolized nanoparticles was demonstrated by visualization of the nanoparticle fluorescence in the cell cultures following exposure. Also monitored was the potential of the aerosolized nanoparticles to generate reactive oxygen species (ROS) (e.g. free radicals and peroxides generation), thus expressing the oxidative stress of the cells which can cause extensive cellular damage or damage on DNA

Solvents for Membrane-Based Post-Combustion CO2 Capture for Potential Application in the Marine Environment

Carbon capture on-board ships represents a powerful technological measure in order for the shipping industry to meet the very stringent GHG emission reduction requirements. Operation within the ship environment introduces a number of constraints associated mainly with space, energy supply, and safety which have to be addressed using compact yet efficient solutions. To this end, solvent-based membrane CO2 capture offers several advantages and has the necessary technological maturity for on-board installation. Solvent choice remains a critical issue both for reasons associated with process efficiency as well as on-board safety. In this paper, we present an up-to-date comprehensive review of the different solvents that can be used for post-combustion CO2 capture. Furthermore, we investigated the solvents&rsquo; performance as determined by their inherent characteristics, properties, and behavior for a range of operating conditions against the strict shipping requirements. A preliminary qualitative comparative assessment was carried out based on appropriately selected key performance indicators (KPIs) pertinent to the requirements of the shipping industry. The identified solvent classes were compared using the most critical KPIs for system integration with the ship. It was concluded that at present, no solvent category can efficiently address all the requirements of the ship. However, widely used solvents such as secondary amines showed relatively good compatibility with the majority of the introduced KPIs. On the other hand, more recently developed molecules, such as phase change solvents and ionic liquids, can easily prevail over the vast majority of the identified solvents as long as they are brought to the same level of technological maturity with benchmark solvents. Such a conclusion points toward the need for accelerating research on more tailor-made and performance-targeted solvents

Solvents for Membrane-Based Post-Combustion CO₂ Capture for Potential Application in the Marine Environment

Carbon capture on-board ships represents a powerful technological measure in order for the shipping industry to meet the very stringent GHG emission reduction requirements. Operation within the ship environment introduces a number of constraints associated mainly with space, energy supply, and safety which have to be addressed using compact yet efficient solutions. To this end, solvent-based membrane CO2 capture offers several advantages and has the necessary technological maturity for on-board installation. Solvent choice remains a critical issue both for reasons associated with process efficiency as well as on-board safety. In this paper, we present an up-to-date comprehensive review of the different solvents that can be used for post-combustion CO2 capture. Furthermore, we investigated the solvents’ performance as determined by their inherent characteristics, properties, and behavior for a range of operating conditions against the strict shipping requirements. A preliminary qualitative comparative assessment was carried out based on appropriately selected key performance indicators (KPIs) pertinent to the requirements of the shipping industry. The identified solvent classes were compared using the most critical KPIs for system integration with the ship. It was concluded that at present, no solvent category can efficiently address all the requirements of the ship. However, widely used solvents such as secondary amines showed relatively good compatibility with the majority of the introduced KPIs. On the other hand, more recently developed molecules, such as phase change solvents and ionic liquids, can easily prevail over the vast majority of the identified solvents as long as they are brought to the same level of technological maturity with benchmark solvents. Such a conclusion points toward the need for accelerating research on more tailor-made and performance-targeted solvents