Engineering Papers

Textile wastewater is characterized by strong color, large amount of suspended and dissolved solids, broadly fluctuating pH, high chemical oxygen demand (COD) and bio-toxicity. Physico-chemical treatments such as coagulation, adsorption, and other processes generate secondary pollutants. Advanced oxidation processes are efficient in decolorizing dye containing effluents but often they are preferred due to their high investment and operational cost. Therefore such processes can be used as pretreatment before biological treatment to make the pollutants bio-amenable. Electrochemical methods are used successfully for the degradation of dyes and treatment of textile industry wastewater. This study presents the electrochemical degradation of dye containing effluents by airlift type electrochemical. Granulated activated carbon and stainless steel was used as an anode and cathode, respectively. Chemical oxygen demand (COD), color and toxicity reduction during electrochemical degradation was monitored. The experimental results showed that the removal efficiency was as much higher as 94% in the investigated time of 30 min to 1 h, which is normally efficient for industrial level processing. Further, influence of initial concentration of dye and pH on degradation of dye was studied.

Key words: COD removal, Dye wastewater, Airlift type electrochemical bipolar reactor

Evaluation of electrochemical and mechanical properties of composite bipolar plate for acid and alkaline fuel cells

Proton exchange membrane fuel cell (PEMFC) is one of the most promising clean energy sources for residential and automotive applications due to its attractive features such as high power density, relatively low operating temperature, convenient fuel supply, longer lifetime, modular in shape etc. [1,2]. Bipolar plate is one of the most important components of low temperature fuel cell, which contributes to about 80% of the total weight of the PEMFC stack [3,4]. Recent cost analysis shows that 38% of the total cost of the PEMFC stack is incurred by the bipolar plate followed by the cost of electrodes, membrane, and catalyst as 32, 12 and 11%, respectively [4]. Different type of materials like metal sheet, polymer coated metal sheet, graphite, flexible graphite, C-C composite, advanced composites etc. are under investigation for the development of low cost and low weight bipolar plates [3-5].

Composite bipolar plates for proton exchange membrane fuel cell were prepared by compression molding technique using novolac type phenol formaldehyde resin as a binder and natural graphite, carbon black and carbon fiber as reinforcements. The effects of different reinforcements on the properties of composite bipolar plate were studied. The bipolar plates were characterized for electrical conductivity, mechanical strength and corrosion resistance. The optimum flexural strength of the composite bipolar plate was 55.28 MPa, with a deflection of 5.2% at mid-span, while the in-plane and through-plane electrical conductivities were 285.54 and 91.79 S·cm^-1, respectively. Corrosion analysis of the bipolar plates conducted in simulated fuel cell environment showed significantly high corrosion resistance or low current density, which made it suitable for proton exchange membrane fuel cell. The corrosion current density of the bipolar plate for the optimum composition was 0.245µA∙cm^-2 at 0.004V corrosion potential with respect to standard hydrogen electrode. Moreover, corrosion analysis in alkaline solution also showed that the developed bipolar plate had a potential scope for use in alkaline fuel cell.

Keywords: Bipolar plate; Corrosion; Fuel Cell; Phenolic Resin; Reinforcement

Experimental studies of sugar effluent by electrochemical – oxidation in batch reactor using artificial neural network and response surface methods

The Experimental studies of sugar effluent by electrochemical – oxidation in Batch reactor using Artificial Neural Network and Response Surface Methods” elucidates the reduction of organics in sugar effluents through electrochemical oxidation technique. Effect of parameters such as current density and mediator concentration on % COD reduction and power consumption for batch reactor without recirculation and the influence of current density, volume and flow rate on % COD reduction, power consumption, mass flux and rate constant for batch reactor with recirculation has been studied and analyzed.

It was found out that, the % COD removal efficiency can be improved by the addition of mediator (NaCl). The maximum % COD reduction of 80.74 % was achieved at current density of 5 A/dm²and 5 gpl of mediator concentration for Batch reactor. A maximum % COD reduction of 64.28 was achieved at flow rate 20 lph, current density 3 A/dm^2, Volume 5 litre for batch reactor with recirculation. Artificial neural network has been used to simulate the batch reactor without recirculation results and the predicted values are then compared with the experimental values. Response surface methodology has been used to study the effects of various parameters on % COD reduction, power consumption and mass flux for batch reactor with recirculation and quadratic models have been generated.

Ethanol & fuel cell – converging paths of opportunity

The energy challenges facing our Nation offer tremendous opportunities for agriculture and technology. For example, by combining fuels such a ethanol with fuel cells, farmers can be energy producers as well a consumers. Meanwhile, the US is under increasing pressure to reduce greenhouse gas emissions. Recent energy supply crunches and price spikes have once again focused attention on the need to improve energy security, increase and diversify domestic energy supplies, ensure environmental quality, and modernize the nation’s energy infrastructure. Ultimately, America’s economic prosperity and national security depend on the availability of reliable, affordable energy. This paper presents a vision of how ethanol and fuel cells can be combined to create significant synergy, reaching markets and bringing benefits that are not achievable with any other fuel or with any other power technology. In the pages ahead, we will describe these benefits and present a roadmap for how these synergies can be developed in an effective and stepwise fashion through contributions from the ethanol, fuel cell, automotive, and utility industries along with support from state and federal governments. The basis or platform for this vision is the existing, ongoing investment in ethanol and fuel cell markets, which has already been committed by government and industry.

Parametric studies of a polymer electrolyte membrane fuel cell (PEMFC) cathode

A two-dimensional two-phase steady state model of a Polymer Electrolyte Membrane Fuel Cell (PEMFC) cathode is developed to study the effects of various operating, design, and model parameters on the cell performance. The model domain consists of the cathode flow field, two layers of diffusion medium, catalyst layer, and the polymer membrane. In this work, the catalyst layer is modeled using flooded spherical agglomerate characterization. An expression is developed for the void fraction of the catalyst layer in terms of its design parameters. The developed model is validated with experimental data available in open literature. The effects of various operational parameters such as cell temperature, pressure, and the cathode air flow rate are studied in detail. The effects of the design parameters of the parallel flow field geometry and that of the diffusion medium are observed. In addition, the role of electric conductivity of the gas diffusion layer (GDL) on the cell current density is studied. Many limiting mechanisms take place in the cathode catalyst layer. Therefore, special emphasis is given on the parametric study of the catalyst layer. The effects of the catalyst layer design parameters such as the thickness, and the loadings of platinum and ionomer are studied. Finally, the issues related to water management are studied.

The effects of liquid water are considered in all the porous layers. Both electro-osmotic drag and back diffusion are considered for transport of liquid water in the membrane. The importance of modeling the membrane for capturing the cell performance is shown by simulating the effects of low concentration gradient of water in the membrane. The study on operating conditions showed that the optimum operating temperature of the cell is 80°C - 85°C and the performance of the cell is better at high pressures and flow rates. The study on design parameters suggests that the optimum porosity of the GDL for this cell is in the range of 0.7 to 0.8 and a thinner catalyst layer with high platinum and membrane content performs better than other combinations considered in this study. The detailed parametric study considering the effects of liquid water provides a pathway for different optimization studies in various layers.

Influence of Ca3(PO4)2 on the electrochemical properties of Poly (ethylene oxide)/LiN(CF3SO¬)2 - based nanocomposite electrolytes for lithium batteries

The development of polymer electrolytes has long been the subject of research interest due to their potential applications not only in the area of rechargeable lithium batteries but also in other electrochemical devices. In the present study nanocomposite polymer electrolytes (NCPE’s) comprising poly(ethylene oxide), Ca₃(PO₄)₂ and LiClO₄/LiN(CF₃SO₂)₂ in varying proportions are prepared by a hot press method. The nanosized calcium phosphate filler particles were synthesized using in situ deposition technique in the presence of poly ethylene oxide (PEO) as follows: Firstly, a complex of calcium chloride with PEO was prepared in desired proportions in methanol. An appropriate stoichiometric amount of trisodium phosphate, Na₃(PO₄) in distilled water was added to the above complex slowly without stirring. The whole mixture was allowed to digest at room temperature for 24h when both the chloride and phosphate ions diffused through the PEO and formed a white gel like precipitate, which was filtered, washed and dried.

The membranes were characterized by SEM, DSC, TG-DTA, ionic conductivity and transference number studies. The evolution of interfacial resistance as a function of time is followed with Li/NCPE/Li symmetric cells at 80°C under open- circuit conditions. This paper also describes FTIR spectroscopic studies of the interface between lithium metal and NCPE, which suggests that the surface chemistry of lithium electrodes in contact with NCPE is dominated by compounds with Li₃PO₄ bonding. The free volume (V_f) of the membranes is probed by positron annihilation lifetime spectroscopy at 30°C and the results support ionic conductivity data. The NCPE’s with LiClO₄ exhibits higher ionic conductivity than that of NCPE with LiN(CF₃SO₂)₂ (LiTFSI) as salt.

References

[1] A. Manuel Stephan, T. Prem Kumar, M.Anbu Kulandainathan, N. Angulakshmi

J. Phys. Chem. B 113 (2009)

[2] A. Manuel Stephan, Eur. Polym. J. 41 (2006) 21-42

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