Characterization of a New Flat Sheet Membrane Module Type for Gas Permeation

Modern high‐performance flat sheet gas separation membranes exhibit high permeances as well as high selectivities, e.g., for CO₂ separation. Novel membrane modules are desirable to transfer the intrinsic membrane performance to the process. The introduced module implements countercurrent flow, which allows for the best utilization of the required driving force, provided concentration polarization and pressure drops can be kept at bay. As such, it is different from established flat sheet modules for gas separation. The design features allow for straightforward scaling and easy adjustment to other operating conditions. During module development equation‐oriented modeling, computer‐aided engineering design and application of computational fluid dynamics for flow optimization were integrated. The prototype was investigated in a pilot plant. The experimental results reflected the simulation predictions and proved the validity of the module concept.     

Development and field trial evaluation of a new reverse osmosis module system

A 23 m³/day reverse osmosis pilot plant was installed at Appleby Parva in May 1969 and has been operated on two borehole waters. Initially, this plant contained prototype modules with membranes cast on the outside of tubes, the design of which is described in the paper. Over 3 million module hours of operation have been achieved and the satisfactory performance of both membranes and membrane supports has confirmed that the principle of a membrane cast on the outside of a suitable tubular support is sound.This led to the design of the “spaghetti” module system which is described and which is available commercially. Operating experience with these modules has nearly reached 2 million module hours on a number of brackish waters and on secondary sewage effluent. These field trials are summarised and the current performance of modules is indicated.     

Experimental investigation of cell design for the electrolysis of iron oxide suspensions in alkaline electrolyte

Following feasibility studies of iron production by electrolytic reduction of hematite particles suspended in a strong alkaline medium, this article concerns the use of engineering methods to investigate the performance of various cell configurations, in view to designing larger processes: a horizontal flow cell with parallel electrodes and two rotating cylindrical electrodes were used for this purpose. The performance was analyzed in terms of current efficiency at 0.1 A cm⁻² and deposit morphology. The results reveal a negligible role of the mass transfer of Fe (+III) ions from the bulk electrolyte on the process efficiency, as formerly suggested in reaction mechanism studies. Conventional ion-mass transfer theory is therefore not applicable and another approach is proposed. Dispersed phase transport processes, more precisely the mechanical forces acting on both the 10 μm ore particles and the evolved oxygen bubbles, can quantitatively and qualitatively explain the cells performance. The configuration with the external rotating cathode allows both efficient contacts of the particles with the cathode and rapid removal of the produced gas phase; however the two rotating electrode devices are subject to appreciable ohmic losses due to the current lead system. The parallel plate configuration, with the cathode at the bottom appears as the best configuration for the deposition which can be achieved with low energy consumption.     

The distribution of voltage losses among components of a battery

An approach to identify the contribution of each individual component to the total voltage loss of a battery is presented. This approach combines experimental measurements with a mathematical model of the grid geometry to assess voltage losses due to: (a) terminal post; (b) intercell connector; (c) separator; (d) positive and negative electrodes; (e) positive and negative grids. A circuit model is used to relate the component resistances to the resistance of the battery. The versatile grid geometry model also allows one to predict the effect of a grid design change to the overall performance of a battery.     

Experimental Study and Design of a Submerged Membrane Distillation Bioreactor

A hybrid process incorporating membrane distillation in a submerged membrane bioreactor operated at elevated temperature is developed and experimentally demonstrated in this article. Since organic particles are rejected by an ‘evaporation’ mechanism, the retention time of non‐volatile soluble and small organics in the submerged membrane distillation bioreactor (MDBR) is independent of the hydraulic retention time (mainly water and volatiles). A high permeate quality can be obtained in the one‐step compact process. The submerged MD modules were designed for both flat‐sheet membranes and tubular membrane configurations. The process performance was preliminarily evaluated by the permeate flux stabilities. The module configuration design and air sparging used in the MDBR process were tested. Flux declines were observed for the thin flat‐sheet hydrophobic membranes. Tubular membrane modules provided more stable permeate fluxes probably due to the turbulent condition generated from air sparging injected inside the tubular membrane bundles. The experiments with the submerged tubular MD module gave stable fluxes of approximately 5 L/m² h over 2 weeks at a bioreactor temperature of 56 °C. The total organic carbon in the permeate was consistently lower than 0.7 mg/L for all experiments.     

Combined electrochemical and surface analysis investigation of degradation processes in polymer electrolyte membrane fuel cells

Fuel cells allow an environmentally friendly and highly efficiently conversion of chemical energy to electricity and heat. Therefore, they have a high potential to become important components of an energy-efficient and sustainable economy. The main challenges in the development of fuel cells are cost reduction and long-term durability. Whereas the cost can be significantly reduced by innovative mass production, the knowledge to enhance the lifetime sufficiently is not available.Surface science analysis methods used for the characterization of the new and used electrodes can be use to determine the alterations in the fuel cell components and in this way to identify the degradation processes, but they do not allow to quantify the influence of the alterations in the electrodes on the electrochemical performance. For this purpose electrochemical methods are necessary; especially the electrochemical impedance spectroscopy (EIS) allows to separate the performance losses individually and to assign them to different components and processes of the cell via a model, whereas the choice of the right model can be problematic.Two important and distinct structural degradation processes were identified by surface analysis of the electrodes before and after fuel cell operation: first, the decomposition of poly tetra-fluoro-ethylene (PTFE) which is used as an organic binder and as a hydrophobic agent in the electrodes and second, a change of the structure of the catalysts. The observed decomposition of the PTFE is associated with a decrease of the hydrophobicity of the electrode. A loss of hydrophobicity influences drastically the required operation conditions and leads to a more critical water management of the fuel cell. In contrast, the alteration of the catalysts structure in the electrodes causes an irreversible decrease of the electrochemical performance. In polymer electrolyte fuel cells (PEFCs) a particle agglomeration of the platinum catalysts at the cathodes is detected.With EIS the effect of two different degradation processes in the membrane-electrode-assembly was quantified. During continuous operation the degradation of the PTFE induces an approximately two times higher performance loss compared with the performance loss related to the agglomeration of the platinum catalyst.     

Mathematical model for a direct propane phosphoric acid fuel cell

A mathematical model was developed and used to predict the performance of direct propane phosphoric acid (PPAFC) fuel cells, utilizing both Pt/C state-of the-art electrodes and older Pt black electrodes. It was found that the overpotential caused by surface processes on the platinum catalyst in the anode is much greater than the potential losses caused by either ohmic resistance or propane diffusion in gas-filled and liquid-filled pores. In one comparison, the anode overpotential (0.5 V) was larger than the cathode overpotential (0.3 V) at a current density of 0.4 A cm⁻² for Pt loadings 4 mg Pt cm⁻². The need for sufficient water concentration at the anode, where water is a reactant, was indicated by the large effect of H₃PO₄ concentration. In another comparison, the model predicted that at 0.2 A cm⁻², modern carbon supported Pt catalysts would produce 0.35 V compared to 0.1 V for unsupported Pt black catalysts that were used several decades ago, when the majority of the research on direct hydrocarbon fuel cells was performed. The propane anode and oxygen cathode catalyst layers were modeled as agglomerates of spherical catalyst particles having their interior spaces filled with liquid electrolyte and being surrounded by gas-filled pores. The Tafel equation was used to describe the electrochemical reactions. The model incorporated gas and liquid-phase diffusion equations for the reactants in the anode and cathode and ionic transport in the electrolyte. Experimental data were used for propane and oxygen diffusivities, and for their solubilities in the electrolyte. The accuracy of the predicted electrical potentials and polarization curves were normally within ±0.02 V of values reported in experimental investigations of temperature and electrolyte concentration. Polarization curves were predicted as a function of temperature, pressure, electrolyte concentration, and Pt loading. A performance of 0.45 V at 0.5 A cm⁻² was predicted at some conditions.     

The effect of hydrophobicity in alkaline electrodes for passive DMFC

The effect of hydrophobicity in alkaline electrodes has been investigated in an effort to improve their performance in passive direct methanol fuel cells. Two approaches have been used to increase the hydrophobicity within the electrodes. One is using a more hydrophobic ionomer, and the other is introducing polytetrafluoroethylene (PTFE) into the catalyst layer. Two types of anion exchange ionomers with different hydrophobicity have been synthesized for this study. The effect of ion exchange capacity, ionic conductivity, and water uptake of the ionomers on the electrode performance has been studied using a half-cell test. The use of a hydrophobic ionomer resulted in enhanced cathode performance even though the ionic conductivity was lower than the more hydrophilic ionomer. Also, the addition of PTFE improved both the cathode and anode performance. The improved alkaline electrode performance was compared to a traditional acid electrode using Nafion as the ionomer. The performance increased threefold as a result of higher hydrophobicity in alkaline electrode.     

A complete testing environment for the automated parallel performance characterization of biofuel cells: design,validation, and application

We present a complete testing environment for the parallel performance characterization of biofuel cells. Besides rapid-assembly electrode fixtures and an aseptic electrochemical reactor, it comprises a 24-channel electrical testing system that bridges the gap between simple load resistors and costly multi-channel potentiostats. The computer-controlled testing system features active current control to enable the forced operation of half-cell electrodes, whereas galvanic isolation between individual channels ensures interference-free operation of multiple fuel cells immersed in a common testing solution. Implemented into the control software is an automated procedure for the step-wise recording of polarization curves. This way, performance overestimation due to a too fast increase in load current can be circumvented. As an applicational example, three abiotically catalyzed glucose fuel cells are characterized simultaneously in a common testing solution. Complete disclosure of the electrical system (incl. printed circuit board layout, control software, and circuit diagrams) in the online supplementary material accompanying this paper allows researchers to replicate our setup in their lab and can serve as inspiration for the design of similar systems adapted to specific requirements. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of Geometry Structures on the Transfer and Flow Characteristics of Membrane Modules

The effects of different inlet/outlet features and helical structures on the flow pattern and transfer performance of membrane modules were investigated with both three‐dimensional computational fluid dynamics and experimental methods. In a circular flat membrane module, two types of inlet/outlet with single‐port or three‐port configuration were used to evaluate the influence of small differences in the opening area structure of the inlet/outlet on the flow patterns. Although the transfer regions differ, large flow swirls appear in both systems, leading to stagnation regions and causing significant back‐mixing. To alleviate the swirls and improve the flow pattern, a helix clapboard was used to separate the membrane feed channel as spiral channel. Both the numerical and experimental results indicate that the helical structure can greatly enhance the transfer performance and increase the permeation rate while the increment in energy consumption is very small.     

Toward a low cost and high performance MPC: The role of system identification

The high cost of model predictive control (MPC) technology has hampered its wide application in process industries beyond the refining/petrochemical industry. This work strives to increase the efficiency of MPC deployment. First, a semi-automatic MPC system is introduced. It consists of three modules: an MPC module, an online identification module and a control monitor module. The goal of the MPC technology is twofold: (1) to considerably reduce the cost of MPC commissioning and maintenance and (2) to increase control performance. System identification plays important roles in all the three parts of the MPC system. In the identification module, the so-called ASYM method of identification is used. It is demonstrated with an industrial application. In the control module, adaptive disturbance model identification is developed for improving control performance; in the monitor module, a method of model error detection method is developed. Industrial applications and simulations are used to demonstrate the ideas. Finally, we comment on some industrial needs on MPC research and development.     

Prospects of conducting polymer and graphene as counter electrodes in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) garner considerable research interest because of high photo-to-electric conversion efficiencies at low production cost. Platinum has been reported as an efficient metal as a counter electrode (CE) in DSSCs for its outstanding electro catalytic performance. However, the high cost and susceptibility to corrosion of Pt are paving the way for exploring new materials to replace Pt as a counter electrode in DSSCs. Various conducting polymers, graphene and conducting polymer-graphene nanocomposites have been found as counter electrodes in DSSCs with remarkable photovoltaic performances. The urge to produce composites or hybrids with nanomaterials is derived from the improvement of photovoltaic performances. This review will focus on the unique physical and chemical properties of conducting polymers and graphene, their individual photovoltaic performances as counter electrodes in DSSCs, followed by the synergistic effect of conducting polymers and graphene in conducting polymer-graphene nanocomposites as counter electrodes in DSSCs. Finally a brief outlook is provided to improve the photovoltaic performance of DSSCs using conducting polymers and graphene-based counter electrodes.     

Carbon supported and unsupported Pt–Ru anodes for liquid feed direct methanol fuel cells

A comparative study of the use of supported and unsupported catalysts for direct methanol fuel cells has been performed. The effect of catalyst loading, fuel concentration and temperature dependence on the anode, cathode and full fuel cell performance was determined in a fuel cell equipped with a reversible hydrogen reference electrode. Although the measured specific activities of supported catalysts were as much as 3-fold greater than the unsupported catalysts, membrane electrode assemblies prepared with supported catalysts showed no improvement with loadings above 0.5 mg/cm². Fuel cells utilizing 0.46 mg/cm² supported catalyst electrodes performed as well as unsupported catalyst electrodes with 2 mg/cm². The temperature dependence and methanol concentration dependence studies both suggest increased methanol permeation through the thinner supported catalyst layers relative to the unsupported catalyst layers.     

Modularisierung von Gaswäschern für die CO2‐Entfernung aus Biogas

Modularization has been identified as one of the research fields of the ?50 % idea”?. A development methodology for modules must consider both the economies of scale for investment costs and costs of operation and maintenance. In this paper, the impact of an absorber module, which is offered as discretized diameter scaling, on the total process is investigated at the example of the CO₂ separation from biogas. The simulation shows the effect of this approach to the stripper diameter and the energy demand of the process. The calculations form the basis for applying cost models.     

卷式反渗透膜器浓水侧流道缺陷诊断

引言 反渗透(RO)脱盐是目前最经济的苦咸水和海水淡化技术.卷式反渗透膜器由于各项性能指标较好,膜堆积密度大、脱盐率高、寿命长,而成为被选用最多的膜器.大多数脱盐工厂的设计都基于卷式膜器.     

Co-catalytic effect of Ni in the methanol electro-oxidation on Pt-Ru/C catalyst for direct methanol fuel cell

This research is aimed to improve the utilization and activity of anodic catalysts, thus to lower the contents of noble metals loading in anodes for methanol electro-oxidation. The direct methanol fuel cell anodic catalysts, Pt-Ru-Ni/C and Pt-Ru/C, were prepared by chemical reduction method. Their performances were tested by using a glassy carbon working electrode through cyclic voltammetric curves, chronoamperometric curves and half-cell measurement in a solution of 0.5 mol/L CH₃OH and 0.5 mol/L H₂SO₄. The composition of the Pt-Ru-Ni and Pt-Ru surface particles were determined by EDAX analysis. The particle size and lattice parameter of the catalysts were determined by means of X-ray diffraction (XRD). XRD analysis showed that both of the catalysts exhibited face-centered cubic structures and had smaller lattice parameters than Pt-alone catalyst. Their sizes are small, about 4.5 nm. No significant differences in the methanol electro-oxidation on both electrodes were found by using cyclic voltammetry, especially regarding the onset potential for methanol electro-oxidation. The electrochemically active-specific areas of the Pt-Ru-Ni/C and Pt-Ru/C catalysts are almost the same. But, the catalytic activity of the Pt-Ru-Ni/C catalyst is higher for methanol electro-oxidation than that of the Pt-Ru/C catalyst. Its tolerance performance to CO formed as one of the intermediates of methanol electro-oxidation is better than that of the Pt-Ru/C catalyst.     

Preparation and characterization of core-shell electrodes for application in gel electrolyte-based dye-sensitized solar cells

Core-shell electrodes based on TiO₂ covered with different oxides were prepared and characterized. These electrodes were applied in gel electrolyte-based dye-sensitized solar cells (DSSC). The TiO₂ electrodes were prepared from TiO₂ powder (P25 Degussa) and coated with thin layers of Al₂O₃, MgO, Nb₂O₅, and SrTiO₃ prepared by the sol-gel method. The core-shell electrodes were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy measurements. J-V curves in the dark and under standard AM 1.5 conditions and photovoltage decay measurements under open-circuit conditions were carried out in order to evaluate the influence of the oxide layer on the charge recombination dynamics and on the device's performance. The results indicated an improvement in the conversion efficiency as a result of an increase in the open circuit voltage. The photovoltage decay curves under open-circuit conditions showed that the core-shell electrodes provide longer electron lifetime values compared to uncoated TiO₂ electrodes, corroborating with a minimization in the recombination losses at the nanoparticle surface/electrolyte interface. This is the first time that a study has been applied to DSSC based on gel polymer electrolyte. The optimum performance was achieved by solar cells based on TiO₂/MgO core-shell electrodes: fill factor of ∼0.60, short-circuit current density J_sc of 12 mA cm⁻², open-circuit voltage V_oc of 0.78 V and overall energy conversion efficiency of ∼5% (under illumination of 100 mW cm⁻²).     

Effect of operational parameters of mini-direct methanol fuel cells operating at ambient temperature

There is currently increased interest in small-size direct methanol fuel cells for portable applications. This work presents results of the influence of operational parameters on the performance of a mini-direct methanol fuel cell. The effects of methanol concentration, Pt load, membrane thickness and PTFE content in the cathode diffusion layer on the performance were studied. Two anodic materials were prepared, PtRu 75:25 at.% and PtRu 90:10 at.%, as nanoparticles supported on Vulcan XC-72 carbon, while for the cathodes Pt/C E-TEK catalysts were used. The materials were characterized physically by EDX and DRX and electrochemically in a half-cell. The results with single cells showed better performances with cells operating with 3 mg Pt cm^?2, 5 mol l^?1 methanol solution, Nafion^® 112 membrane and with 30 wt.% PTFE in the cathode diffusion layer deposited on only one face of the electrode support.     

Review in Applied Electrochemistry. Number 54 Recent Developments in Polymer Electrolyte Fuel Cell Electrodes

Since the 1980s there has been a significant lowering of the platinum loading of polymer electrolyte fuel cell electrodes from about 4–10 mg cm^–2(platinum black) to about 0.4 mg cm^–2 or even less (carbon supported platinum), by the introduction of ionomer (liquid Nafion^®) impregnated gas diffusion electrodes, extending the three-dimensional reaction zone. From the 1990s to the present studies have been carried out to decrease the loss of performance during cell operation due both to the presence of liquid water causing flooding of the catalyst layer and mass transport limitations and to the poisoning of platinum by the use of reformed fuels. This review deals with the developments in electrode configuration going from dual layer to three layer electrodes. The preparation methods, the characteristics and the optimal composition of both diffusion and reactive layers of these electrodes are described. The improvement in the performance of both CO tolerant anodes and cathodes with enhanced oxygen reduction by Pt alloying is also discussed.     

Single-pass desalination of high salinity sea water with reverse osmosis

Two types of new “HOLLOSEP” have been developed for single-pass desalination of high salinity seawater. One is a high pressure and high temperature module, type “HPT”. The performance of this new type HOLLOSEP is analyzed in the case of desalination of high salinity seawater under a high pressure Of 75Kg/cm² G at high temperature of 40°C. It has been found that the operation costs can be reduced by this high pressure and high temperature operation system.The other is a large size module containing five elements of 12 inches diameter, type “JM-12”. This module has been developed to reduce the water cost by enlarging the diameter and the length of a vessel coupled with the improvement in water flux rate of the hollow fiber membranes. The fresh water productivity of this module is 150m³/day under the conditions of 3.5% NaCl feed water, 30% product water recovery at 55kg/cm²G.