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Silva V.,Institute for Sustainable Process Technology | Poiesz E.,Cosun Food Technology Center | Van Der Heijden P.,Paques BV
Journal of Applied Electrochemistry | Year: 2013

Industrial processes usually generate streams enriched with high organic and inorganic components. Due to the complexity of these streams sometimes it is not quite straightforward to predict the performance of desalination technologies. Some technologies are available for the selective removal of salts from aqueous stream, but in general these technologies are applied in high value applications where salts are either the product or limit further purification of the final product is required. These technologies are, however, not widely used in low value applications like wastewater treatment. The aim of this article is to review, improve and perform the design of electrodialysis processes for relevant industrial wastewater applications. It is focused on the determination of the critical design parameters like membrane resistance, current efficiency and limiting current density through lab scale experiments and its further use for industrial scale first approximation design. In this article, the basic equations for design are reviewed and a practical approach to obtain the number of stacks required for a certain separation is introduced. An industrial wastewater stream has been used for lab batch experiment and its following continuous plant design. The results show that it is possible to separate monovalent ions in a high rate (more than 70 %) and divalent ions were less separated (less than 50 %). The energy required for the particular case was evaluated in a range from 6 to 11 kWh/m3 of feed stream depending on the water reclamation rate. © 2013 Springer Science+Business Media Dordrecht.


Milosevic M.,TU Eindhoven | Staal K.J.J.,Institute for Sustainable Process Technology | Schuur B.,University of Twente | de Haan A.B.,TU Eindhoven
Desalination | Year: 2013

Concentration of aqueous salt solutions is among the most energy intensive processes in the chemical industry. We here report on extractive concentration as an alternative for the traditional technologies based on water evaporation or reverse osmosis. Extractive technologies are potentially energy-efficient, key is avoiding evaporation of (co-)extracted water during the recovery of the solvent. Polymers have been applied as solvents, because recovery may be done through mild temperature swing. For in total 53 commercially available polymers, the phase behavior of ternary systems containing water, salt (NaCl, Na2SO4, and FeCl3) and polymer was studied at room temperature (294K) and atmospheric pressure. Formation of aqueous two phase systems (ATPS) was studied for various solvent/feed ratios (mass) of (0.25


Krebs T.,Institute for Sustainable Process Technology | Krebs T.,Wageningen University | Schroen C.G.P.H.,Wageningen University | Boom R.M.,Wageningen University
Chemical Engineering Science | Year: 2012

The breakup of crude oil emulsions to produce clean oil and water phases is an important task in crude oil processing. We have investigated the demulsification kinetics of a model oil-in-water emulsion in a centrifugal field to mimic the forces acting on emulsion droplets in oil/water separators such as hydrocyclones. The rate of growth of separated oil phase and the change in mean droplet diameter of the emulsion layer was measured as a function of surfactant concentration, centrifugal acceleration and time. Demulsification is enhanced with increasing centrifugal acceleration and time and decreasing surfactant concentration. A kinetic analysis was performed that allows to estimate the characteristic coalescence times between droplets in the emulsion and between a droplet and the separated oil interface. The experimental procedure presented in this work can serve as a simple, but useful test to predict the separation efficiency of emulsions in separators with swirling flow fields. © 2011 Elsevier Ltd.


Patil N.V.,Institute for Sustainable Process Technology | Patil N.V.,Wageningen University | Janssen A.E.M.,Wageningen University | Boom R.M.,Wageningen University
Chemical Engineering Science | Year: 2014

To assess the potential use of ideal nanofiltration cascades for the industrial fractionation of oligosaccharides, simulations of single, three and five stage NF cascades were carried out. Three and five stage ideal cascades show significant improvement in separation with diafiltration compared to single stage systems. The calculations do imply different membrane areas in each stage of the cascade. The ratio of the sieving coefficients of a binary mixture over the membrane plays an important role in determining the relation between yield and purity in a cascade system. At high sieving coefficient ratios, both yield and purity increase concurrently in a three stage system, whereas at a low ratio of the sieving coefficients, the yield and purity become inversely proportional on the retentate side. In a five stage systems, both yield and purity become inversely proportional at high and low sieving coefficient ratios. A five stage cascade system installation would be optimal for most applications since at very low local separation factors sufficient separation and yield could be achieved. © 2013 Elsevier Ltd.


Patil N.V.,Institute for Sustainable Process Technology | Patil N.V.,Wageningen University | Janssen A.E.M.,Wageningen University | Boom R.M.,Wageningen University
Separation Science and Technology (Philadelphia) | Year: 2014

Whey protein isolate, containing α-Lactalbumin and β-Lactoglobulin, was separated by using a continuous three-stage ultrafiltration cascade system. Single-stage experiments were optimized to enable good and stable cascade operation. Three different cascade configurations, a non-constrained ideal system (Configuration A), and adapted version (Configuration B), and a countercurrent cascade (Configuration C) were experimentally tested and compared. The countercurrent cascade system showed the traditional trade-off between yield and purity. Both the adapted cascade system and the non-constrained ideal cascade gave better performance in terms of recovery and purity and show potential for application, albeit for different purposes. © Taylor & Francis Group, LLC.


Krebs T.,Institute for Sustainable Process Technology | Krebs T.,Wageningen University | Schroen C.G.P.H.,Wageningen University | Boom R.M.,Wageningen University
Fuel | Year: 2013

We report the results of experiments on the coalescence dynamics in flowing oil-in-water emulsions using an integrated microfluidic device. The microfluidic circuit permits direct observation of shear-induced collisions and coalescence events between emulsion droplets. Three mineral oils with a range of viscosities 8-70 mPa s and five silicone oils with a range of viscosities 6-100 mPa s were chosen as dispersed phase. Pure water was used as continuous phase. Trajectory analysis of colliding droplet pairs allows evaluation of the film drainage profile and coalescence time. From the coalescence times obtained for ten thousands of droplet pairs we calculate coalescence time distributions for the different emulsions. For all systems, the coalescence time decreases with increasing capillary number and increases with increasing dispersed phase viscosity. Scaling relations for the coalescence time are derived and compared with theoretical predictions. The potential of the procedure as a diagnostic tool for the prediction of emulsion stability in oil/water separation is discussed, as well as alternative applications of the microfluidic circuits. © 2012 Elsevier Ltd. All rights reserved.


Krebs T.,Institute for Sustainable Process Technology | Krebs T.,Wageningen University | Schroen K.,Wageningen University | Boom R.,Wageningen University
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2012

We present the results of experiments studying droplet coalescence in a dense layer of emulsion droplets using microfluidic circuits. The microfluidic structure allows direct observation of collisions and coalescence events between oil droplets dispersed in water. The coalescence rate of a flowing hexadecane-in-water emulsion was measured as a function of the droplet velocity and droplet concentration from image sequences measured with a high-speed camera. A trajectory analysis of colliding droplet pairs allows evaluation of the film drainage profile and coalescence time t c. The coalescence times obtained for thousands of droplet pairs enable us to calculate coalescence time distributions for each set of experimental parameters, which are the mean droplet approach velocity 〈v 0〉, the mean dispersed phase fraction 〈〉 and the mean hydraulic diameter of a droplet pair 〈d p〉. The expected value Et c of the coalescence time distributions scales as Et c ∝ 〈v 0〉 -0.105±0.043〈d p〉 0.562±0.287, but is independent of . We discuss the potential of the procedure for the prediction of emulsion stability in industrial applications. © 2012 The Royal Society of Chemistry.


Krebs T.,Institute for Sustainable Process Technology | Krebs T.,Wageningen University | Krebs T.,Delta Systems | Ershov D.,Wageningen University | And 2 more authors.
Soft Matter | Year: 2013

We report an experimental method to investigate droplet dynamics in centrifuged emulsions and its application to study droplet compression and coalescence. The experimental setup permits in situ monitoring of an ensemble of droplets in a centrifuged monolayer of monodisperse emulsion droplets using optical microscopy. We studied a hexadecane-in-water emulsion stabilized by the ionic surfactant sodium-n-dodecyl sulfate as a model system. With a microfluidic T-junction emulsion droplets of 97 μm diameter are produced which are subsequently inserted into a rectangular glass chamber of 100 μm height. Using an emulsion which is stable against coalescence, we measured the steady-state oil volume fraction in the compressed layer as a function of the compressive force induced by centrifugation, and quantified the deformation of droplets upon compression. To induce coalescence, we decreased the SDS bulk concentration by dilution of the continuous phase with water before the start of centrifugation. The growth rate of the separated oil phase, which forms on top of the emulsion, and the extent of drop-drop coalescence in the droplet layer upon centrifugation were evaluated as a function of the radial acceleration. The potential of the method for studies in emulsion science and possible improvements of the experimental setup are discussed. This journal is © The Royal Society of Chemistry 2013.


Krebs T.,Institute for Sustainable Process Technology | Krebs T.,Wageningen University | Schroen K.,Wageningen University | Boom R.,Wageningen University
Soft Matter | Year: 2012

We report the results of a study on emulsion stability in a microfluidic channel flow using an integrated microfluidic device. The microfluidic circuit enables production of a monodisperse oil-in-water emulsion and monitoring of emulsion stability upon shear-induced collisions. Sodium-n-dodecyl sulfate was used as emulsifier, and hexadecane as dispersed phase. We measure the mean drop size at the end of the collision channel as a function of the surfactant and sodium chloride bulk concentration, and as a function of the total flow rate. We find that emulsions are stable against coalescence for SDS bulk concentrations down to 10 -6 M within the residence time of the droplets in the channel in the absence of added NaCl. The stability of the emulsion at these low SDS bulk concentrations is interpreted in terms of a reduced mobility of the droplet interfaces, which slows down drainage of the film of the continuous phase between the droplets. Emulsions stabilized by SDS with added NaCl in the continuous phase display a transition from a stable to unstable regime when increasing the NaCl bulk concentration from 0.1 M to 0.3 M, which is in agreement with predictions using simple DLVO force calculations for colloidal stability. We also estimate the characteristic coalescence time between droplets using a simple coalescence theory and compare the results with values obtained by us previously from trajectory analysis of colliding droplet pairs. © 2012 The Royal Society of Chemistry.


News Article | March 9, 2016
Site: phys.org

Scientists at the University of Twente research institute MESA+ have developed an electrode in the form of a hollow porous copper fibre which is able to convert carbon dioxide (CO2) into carbon monoxide (CO) extremely efficiently. In principle the invention enables a wide variety of industrial processes, for example in the steel industry, to be made more sustainable. The researchers have applied for a patent on their invention, and their research results have been published in the scientific journal Nature Communications. Researchers at the University of Twente have developed a hollow copper fibre which can be used to convert CO2 into CO with a very high efficiency. The fibre, which serves as an electrode, is provided with countless minute pores. If the fibre is placed in a bath of water, a voltage potential applied, and CO2 pumped in, the CO2 is converted into CO as it passes out through these pores. The principle is straightforward but the efficiency and selectivity of the reaction are surprisingly high, in part because the electrode provides a huge surface area on which the reaction can take place. An important innovation is the optimized interface between gas, fluid and copper particles, allowing the very efficient supply of CO2 and removal of the product, CO. Conversion takes place at about ten times the rate when using the most advanced copper electrodes currently available, while the selectivity (expressed as the percentage of electrons that actually convert CO2 into CO) is 85%, compared to 35% in current copper electrodes. The newly developed electrode also performs better than electrodes made of expensive precious metals such as gold or silver. The fibres are manufactured in the following way. Small copper particles are added to a polymer solution. This solution is guided through a small, ring-shaped slit in a water bath, in which the polymer solution solidifies into the form of a thin hollow fibre. A thermal treatment is then employed to remove the polymer and partially fuse the copper particles. The result is a copper oxide fibre. Reacting this with hydrogen at a high temperature yields the final product: a hollow, porous copper fibre with a diameter of 1.5mm and a wall thickness of 0.1mm. Because this manufacturing technique is based on the way polymeric hollow-fibre membranes are currently constructed on a very large scale, e.g. for kidney dialysis equipment, the researchers involved believe it will be relatively easy to produce the new electrode on a commercial scale. The method can be used for a wide variety of chemical processes requiring gas conversion, in particular because the method used to manufacture the fibres is also suited to materials other than copper; it could apply, for instance, to oxygen conversion in a fuel cell, or hydrogen conversion in the electrochemical production of ammonia. The researchers particularly envisage an important area of application for these copper electrodes to be in the steel industry, where large volumes of CO2 are produced and CO is needed to convert iron ore into iron. The application of these fibres could lead to a step increase in sustainability in this area. The operation of the fibre has been demonstrated in the laboratory; working together with the Institute for Sustainable Process Technology the researchers now plan to optimize the design and develop the methods to suit industrial applications. More information: Recep Kas et al. Three-dimensional porous hollow fibre copper electrodes for efficient and high-rate electrochemical carbon dioxide reduction, Nature Communications (2016). DOI: 10.1038/ncomms10748

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