Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Membrane reactor is a device that simultaneously carrying out reaction and membrane-based separation. The advantageous transport properties of the membranes can be employed to selectively remove undesired products or by-products from the reaction mixture, to break the thermodynamic barrier, and to selectively supply the reactant. In this work, membrane reactor technology has been exploited with robust H₂ selective polymeric membranes in the process of hydrogenation and dehydrogenation. A state-of-the-art 3-phase catalytic membrane contactor is utilized in the processes of soybean hydrogenation and bio-oil hydro-deoxygenation, where the membrane functions as phase contactor, H₂supplier, and catalytic support. Intrinsically skinned asymmetric Polyetherimide (PEI) membranes demonstrated predominant H₂permeance and selectivity. By using the PEI membrane in the membrane contactor, soybean oil is partially hydrogenated efficiently at relatively mild reaction conditions compared with a conventional slurry reactor. In the hydroprocessing of bio-oil using the same system, the membrane successfully removed water, an undesired component from bio-oil by pervaporation. The more industrially feasible membrane-assisted reactor is studied in the alkane dehydrogenation process. Viable polymeric materials and their stability in elevated temperatures and organic environment are examined. The blend polymeric material of Matrimid® 5218 and Polybenzimidazole (PBI) remained H₂permeable and stable with the presence of hydrocarbons, and displayed consistent selectivity of H2/hydrocarbon, which indicated the feasibility of using the material to fabricate thermally stable membrane for separation. The impact of membrane-assisted reactor is evaluated using finite parameter process simulation in the model reaction of the dehydrogenation of methylcyclohexane (MCH). By combining tested catalyst performance, measured transport properties of the material and hypothetical membrane configuration, by using a membrane assisted packed-bed reactor, the thermodynamic barrier of the reaction is predicted to be broken by the removal of H₂. The overall dehydrogenation conversion can be increased by up to 20% beyond equilibrium. The predicted results are justified by preliminary experimental validation using intrinsically skinned asymmetric Matrimid/PBI blend membrane. The conversions at varied temperatures partially exceeded equilibrium, indicating successful removal of H₂by the blend membrane as well as decent thermal stability of the membrane at elevated temperatures with the presence of hydrocarbons. The successful outcome of membrane contactor and membrane-assisted reactor using robust polymeric membranes shows the effectiveness and efficiency of membrane reactors in varied application. The future work should be focusing on two direction, to further develop durable and efficient membranes with desired properties; and to improve the reactor system with better catalytic performance, more precise control in order to harvest preferable product and greater yield.

Maintenance of membrane performance requires inevitable cleaning or defouling of fouled membranes. Membrane cleaning using enzymes such as proteases, lipases, α-glucosidases from a sulphidogenic bioreactor was investigated. At first, dilute and concentrated enzyme extract were prepared form the sulphidogenic pellet. Enzyme assays on 0.5 % azocaisen, 1 % triacetin and 1 mg/ml ρ-nitrophenyl-α-D-glucopyranoside were performed using the concentrated enzyme extract (0 – 200 mg/ml). For membrane fouling, an abattoir effluent was obtained from Ostritech Pty (Ltd), Grahamstown, South Africa. The effluent was characterised for presence of potential foulants such as lipids, proteins, amino acids and carbohydrates. Static fouling of polysulphone membranes (0.22 μm, 47 mm) was then performed using the abattoir effluent. Cleaning of the fouled membranes was also performed using at first the dilute and then the concentrated form (200 mg/ml) of enzyme extracts. Qualitative and quantitative biochemical analysis for proteins, lipids and carbohydrates was performed to ascertain the presence of foulants on polysulphone membranes and their removal by dilute or concentrated enzyme extracts. The ability of dilute enzyme extracts to remove proteins lipids, and carbohydrates fouling capillary UF membrane module; their ability to restore permeate fluxes and transmembrane pressure after cleaning/defouling was also investigated. Permeate volumes from this UF membrane module were analysed for protein, amino acids, lipids, and carbohydrates concentrations after fouling and defouling. Fouling was further characterized by standard blocking, cake filtration and pore blocking models using stirred UF cell and polyethersulphone membranes with MWCO of 30 000, 100 000 and 300 000. After characterization of fouling, polyethersulphone membranes with MWCO of 30 000 and 300 000 were defouled using the concentrated enzyme extract (100 mg ml). Enzyme activities at 200 mg/ml of enzyme concentration were 8.071 IU, 86.71 IU and 789.02 IU for proteases, lipases and α-glucosidases. The abattoir effluent contained 553 μg/ml of lipid, 301 μg/ml of protein, 141 μg/ml of total carbohydrate, and 0.63 μg/ml of total reducing sugars. Proteins, lipids and carbohydrates fouling polysulphone membranes after a day were removed by 23.4 %, when a dilute enzyme was used. A concentrated enzyme extract of 200 mg/ml was able to remove proteins, lipids and carbohydrates up to 5 days of fouling by 100 %, 82 %, 71 %, 68 % and 76 % respectively. Defouling of dynamically fouled capillary ultrafiltration membranes using sulphidogenic proteases was successful at pH 10, 37°C, within 1 hour. Sulphidogenic proteases activity was 2.1 U/ml and flux Recovery (FR %) was 64. Characterization of fouling revealed that proteins and lipids were major foulants while low concentration of carbohydrates fouled polyethersulphone membranes. Fouling followed standard blocking for 10 minutes in all the membranes; afterwards fouling adopted cake filtration model for membranes with 30 000 MWCO and pore blocking model for membranes with 300 000 MWCO. A concentration of 100 mg/ml of enzyme extract was able to remove fouling from membranes with MWCO of 30 000. Defouling membranes that followed pore blocking model i.e. 300 000 MWCO was not successful due to a mass transfer problem. From the results of defouling of 30 000 and 300 000 MWCO it was concluded that defouling of cake layer fouling (30 000 MWCO) was successful while defouling of pore blocking fouling was unsuccessful due to a mass transfer problem. The ratio of enzymes present in the enzyme extract when calculated based on enzymatic activity for proteases, lipases and α-glucosidases was 1.1 %, 11 % and 87.9 %. It was hypothesized that apart from proteases, lipases, α and β-glucosidases; phosphatases, sulphatases, amonipeptidases etc. from a sulphidogenic bioreactor clean or defoul cake layer fouling by organic foulants and pore blocking fouling provided the mass transfer problem is solved. However, concentration of enzymes from a sulphidogenic bioreactor has not been optimized yet. Other methods of concentrating the enzyme extract can be investigated for example use of organic solvents.

Lack of clean fresh water is one of the most pervasive problems afflicting people throughout the world. Efficient desalination of sea and brackish water and safe reuse of wastewater become an insistent need. However, such techniques are energy intensive, and thus, a good control design is needed to increase the process efficiency and maintain water production costs at an acceptable level. This thesis proposes solutions to the above challenges and in particular will be focused on two membranebased water systems: Membrane Distillation (MD) and Membrane Bioreactor (MBR) for wastewater treatment plant (WWPT). The first part of this thesis, Direct Contact Membrane Distillation (DCMD) will study as an example an MD process. MD is an emerging sustainable desalination technique which can be powered by renewable energy. Its main drawback is the low water production rate. However, it can be improved by utilizing advanced control strategies. DCMD is modeled by a set of Differential Algebraic Equations (DAEs). In order to improve its water production, an optimization-based control scheme termed Model Predictive Control (MPC) provides a natural framework to optimally operate DCMD processes due to its unique control advantages. Among these advantages are the flexibility provided in formulating the objective function, the capability to directly handle process constraints, and the ability to work with various classes of nonlinear systems. Motivated by the above considerations, two MPC schemes that can maximize the water production rate of DCMD systems have been developed. The first MPC scheme is formulated to track an optimal set-point while taking input and stability constraints into account. The second MPC scheme, Economic MPC (EMPC), is formulated to maximize the distilled water flux while meeting input, stability and other process operational constraints. The total water production under both control designs is compared to illustrate the effectiveness of the two proposed control paradigms. Simulation results show that the DCMD process produces more distilled water when it is operated by EMPC than when it is operated by MPC. The above control techniques assume the full access to the system states. However, this is not the case for the DCMD plant. To effectively control the closed-loop system, an observer design that can estimate the values of the unmeasurable states is required. Motivated by that, a nonlinear observer design for DCMD is proposed. In addition, the effect of the estimation gain matrix on the differentiation index of the DAE system is investigated. Numerical simulations are presented to illustrate the effectiveness of the proposed observer design. The observer-based MPC and EMPC are also studied in this work. Mathematical modeling of a wastewater treatment system is critical because it enhances the process understanding and can be used for process design and process optimization. Motivated by the above considerations, modeling and optimal control strategies have been developed and applied to the MBR-based wastewater treatment process. The model is an extension of the well-known Benchmark simulation models for wastewater treatment. In addition, model predictive control has been applied to maintain the dissolved oxygen concentration level at the desired value. In addition, a conventional PID controller has also been developed. The simulation results show that the both of controllers can be used for dissolved oxygen concentration control. However, MPC has better performance compared to PID scenario.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22895号 / 工博第4792号 / 新制||工||1749(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 SIVANIAH Easan, 教授 田中 庸裕, 教授 今堀 博 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Membrane distillation (MD) is an emerging technology capable of treating high-saline feeds and operating with low-grade heat energy. However, commercial implementation of MD is limited by so-called temperature polarization, which is the deviation in the temperature at the feed-membrane interface with respect to the bulk fluid. This work presents solutions to alleviate temperature polarization in MD by employing a localized heating concept to deliver heat at the vicinity of the feed-membrane interface. This can be realized in multiple ways, including Joule heating, photothermal heating, electromagnetic induction heating, and nanofluid heating. In the first experiment, a Joule heating concept was implemented and tested, and the results showed a 45% increase in permeate flux and a 57% decrease in specific energy consumption. This concept was further improved by implementing a new dead-end MD configuration, which led to a 132% increase in the gained output ratio. In addition, the accumulation of foulants on the membrane surface could be successfully controlled by intermittent flushing of feedwater. Three-dimensional CFD calculations of conjugate heat transfer revealed a more uniform heat transfer and temperature gradient across the membrane due to the increased feedwater temperature over a larger membrane area. In another approach, a photothermal MD concept was used to heat the feed water locally. A 2-D photothermal material, MXene, recently known for its photothermal property, was used to coat commercial MD membranes. The coated membranes were evaluated under one-sun illumination to yield a permeate flux of 0.77 kg.m$^{−2}$h$^{−1}$ with a photothermal efficiency of 65.3% for a feed concentration of 0.36 g.L$^{−1}$. The system can produce around 6 liters of water per day per square meter of membrane. An energy analysis was also performed to compare the efficiency of various energy sources. Considering the sun as a primary energy source, the performance of different heating modes was compared in terms of performance and scale-up opportunities. Overall this work demonstrates that the application of localized heating will enable the scale-up and the use of renewable energy sources to make the MD process more efficient and sustainable. / The illustrative figure was produced by Ana Bigio, scientific illustrator, KAUST.

Since the discovery of size-selective metal-organic frameworks (MOF) researchers have tried to manufacture them into gas separation membranes. ZIF-8 became the most studied MOF for membrane applications mainly because of its simple synthesis, good chemical and thermal stability, recent commercial availability and attractive pore size. The aim of this work is to develop convenient methods for growing ZIF thin layers on polymer supports to obtain defect-free ZIF membranes with good gas separation properties. We present new approaches for ZIF membranes preparation on polymers. We introduce zinc oxide nanoparticles in the support as a secondary metal source for ZIF-8 growth. Initially the ZnO particles were incorporated into the polymer matrix and later on the surface of the polymer by magnetron sputtering. In both cases, the ZnO facilitated to create more nucleation opportunities and improved the ZIF-8 growth compared to the synthesis without using ZnO. By employing the secondary seeded growth method, we were able to obtain thin (900 nm) ZIF-8 layer with good gas separation performance. Next, we propose a metal-chelating polymer as a suitable support for growing ZIF layers. Defect-free ZIF-8 films with a thickness of 600 nm could be obtained by a contra-diffusion method. ZIF-8 membranes were tested for permeation of hydrogen and hydrocarbons, and one of the highest selectivities reported so far for hydrogen/propane, and propylene/propane was obtained. Another promising method to facilitate the growth of MOFs on polymeric supports is the chemical functionalization of the support surface with functional groups, which can complex metal ions and which can covalently bond the MOF crystals. We functionalized the surface of a common porous polymeric membrane with amine groups, which took part in the reaction to form ZIF-8 nanocrystals. We observed an enhancement in adhesion between the ZIF layer and the support. The effect of parameters of the contra-diffusion experiment (such as temperature lower than room temperature and synthesis times shorter than 1 hour) on ZIF-8 membrane properties was evaluated. We could prepare one of the thinnest (around 200 nm) yet selective ZIF-8 films reported.

No description available.

Climate change, water stress, and rapid population growth have increased the need to manage water resources through innovative sustainable technologies. Decentralized systems such as membrane treatment trains have become increasingly important to provide high volumes of potable water to millions of people. Pressure-driven membrane systems have dominated separation processes due to their low cost, small footprint, ease of operation, and high permeate quality. Conventionally, pressure-driven membranes are classified into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). MF and UF membranes operate under low pressure (< 7 bar, <~100 psi). They can separate a variety of large particles such as bacteria, natural organic matter, suspended solids, and colloids. In contrast, NF and RO membranes are more energy-intense due to operating at high pressures (7 – 80 bar, ~100 – 1200 psi) and can remove small molecules such as ions, pharmaceuticals, and heavy metals. Fouling is a primary challenge with membranes that compromises the membrane performance, increases energy consumption, and reduces the membrane lifetime. Many strategies are used to address fouling, such as pre-treatment (pH adjustment, screening, coagulation), membrane modification (chemical and morphological properties), and membrane cleaning (physical, chemical). However, such strategies increase operational expenditures, produce waste products that can impact the environment, and negatively impact membrane lifetimes. Recently, electrically conductive membranes (ECMs) have been introduced to address the challenges with traditional membranes. They contain conductive surfaces that offer self-cleaning and antifouling properties across the surface in response to electrical potential externally applied to them. ECMs are advantageous as compared to traditional membranes because (a) they are more effective in treating foulants as they target foulants at the membrane/solvent interface, (b) they are more economical and environmentally friendly as they reduce the need for chemical consumption, and (c) they can be responsive to fouling conditions as their antifouling mechanisms can be easily manipulated by changing the applied current type (positive, negative, direct current, alternating current) to match the foulant. ECMs have been formed from all categories of membranes (MF, UF, NF, MD, FO, and RO) with a range of applications. Despite the remarkable progress in demonstrating their excellent antifouling performance, there are many hurdles to overcome before they can be commercialized. Two of these are (a) a fundamental understanding of their underlying mechanisms, (b) surface materials that can withstand extreme chemical and electrical conditions. In this work, we have comprehensively discussed antifouling mechanisms with respect to surface polarization and elaborated on the impact of electrically-induced mechanisms on four major fouling categories. i.e., biofouling, organic fouling, mineral scaling, and oil wetting. In addition, we characterized surface properties of a common electrically conductive composite membrane composed of carbon nanotubes (CNTs) and polyvinyl alcohol (PVA). We then investigated the impact of cross-linkers in CNT/PVA network on transmembrane flux, electrical conductivity, hydrophilicity, and surface roughness. In addition, we proposed standard, practical, and straightforward methodologies to detect and quantify the electrochemical, physical, and mechanical stability of ECMs, using chronoamperometry and cyclic voltammetry, an evaluation of polymer leaching from membranes, and micro mechanical scratch testing, respectively. Our methods can readily be extended to all membrane-based separation processes and different membrane materials (carbonaceous materials, ceramics, metal-based, and polymers). To demonstrate the antifouling properties of ECMs, we challenged ECMs with mixed-bacterial cultures in a flow-through system. Although ECMs showed high rejection, comparable flux, and excellent self-cleaning performance under application of electrical potential, understanding the relationship between applied electrical currents and antifouling mechanisms demands a well-controlled investigation. To this end, we quantified the impact of electrochemically-induced acidic conditions, alkaline conditions, and H2O2 concentration on model bacteria, Escherichia Coli. We first quantified the electrochemical potential of CNT-based ECMs in generating stressors such as protons, hydroxyl ions, and H2O2, under a range of applied electrical currents (± 0-150 mA). Next, these individual stressors with identical magnitude were imposed on E. Coli cells and biofilms in batch and flow-through systems, respectively. This thesis guides researchers to understand the underlying antifouling mechanisms associated with ECMs, how to match the mechanisms to the application of ECMs, and offers benchmarks for making practical ECMs. / Thesis / Doctor of Philosophy (PhD)

One of the important factors determining the lifetime of polymer electrolyte membrane fuel cells (PEMFCs) is membrane degradation and failure. The lack of effective mitigation methods is largely due to the currently very limited understanding of the underlying mechanisms for mechanical and chemical degradations of fuel cell membranes. In order to understand degradation of membranes in fuel cells, two different experimental approaches were developed; one is fuel cell testing under open circuit voltage (OCV) with bi-layer configuration of the membrane electrode assemblies (MEAs) and the other is a modified gas phase Fenton's test. Accelerated degradation tests for polymer electrolyte membrane (PEM) fuel cells are frequently conducted under open circuit voltage (OCV) conditions at low relative humidity (RH) and high temperature. With the bi-layer MEA technique, it was found that membrane degradation is highly localized across thickness direction of the membrane and qualitatively correlated with location of platinum (Pt) band through mechanical testing, Infrared (IR) spectroscopy, fluoride emission, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) measurement. One of the critical experimental observations is that mechanical behavior of membranes subjected to degradation via Fenton's reaction exhibit completely different behavior with that of membranes from the OCV testing. This result led us to believe that other critical factors such as mechanical stress may affect on membrane degradation and therefore, a modified gas phase Fenton's test setup was developed to test the hypothesis. Interestingly, the results showed that mechanical stress directly accelerates the degradation rate of ionomer membranes, implying that the rate constant for the degradation reaction is a function of mechanical stress in addition to commonly known factors such as temperature and humidity. Membrane degradation induced by mechanical stress necessitates the prediction of the stress distribution in the membrane under various conditions. One of research focuses was on the developing micromechanism-inspired continuum model for ionomer membranes. The model is the basis for stress analysis, and is based on a hyperelastic model with reptation-inspired viscous flow rule and multiplicative decomposition of viscoelastic and plastic deformation gradient. Finally, evaluation of the membrane degradation requires a fuel cell model since the degradation occurs under fuel cell operating conditions. The fuel cell model included structural mechanics models and multiphysics models which represents other phenomena such as gas and water transport, charge conservation, electrochemical reactions, and energy conservation. The combined model was developed to investigate the compression effect on fuel cell performance and membrane stress distribution.

Yes / To solve the multi-objective mobile robot path planning in a dangerous environment with dynamic obstacles, this paper proposes a modified membraneinspired algorithm based on particle swarm optimization (mMPSO), which combines membrane systems with particle swarm optimization. In mMPSO, a dynamic double one-level membrane structure is introduced to arrange the particles with various dimensions and perform the communications between particles in different membranes; a point repair algorithm is presented to change an infeasible path into a feasible path; a smoothness algorithm is proposed to remove the redundant information of a feasible path; inspired by the idea of tightening the fishing line, a moving direction adjustment for each node of a path is introduced to enhance the algorithm performance. Extensive experiments conducted in different environments with three kinds of grid models and five kinds of obstacles show the effectiveness and practicality of mMPSO. / National Natural Science Foundation of China (61170016, 61373047), the Program for New Century Excellent Talents in University (NCET-11-0715) and SWJTU supported project (SWJTU12CX008); grant of the Romanian National Authority for Scientific Research, CNCSUEFISCDI, project number PN-II-ID-PCE- 2011-3-0688.