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Publication Metadata only [BMIM][OAc] coating layer makes activated carbon almost completely selective for CO2(Elsevier Science Sa, 2022) N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Durak, Özce; Zeeshan, Muhammad; Keskin, Seda; Uzun, Alper; Master Student; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 40548; 59917Tuning the molecular affinity of porous materials towards desired gases is important to achieve superior selectivity for a target separation. Herein, we report a novel composite, prepared by coating an ordinary activated carbon (AC) with an ionic liquid (IL) (1-butyl-3-methylimidazolium acetate, [BMIM][OAc]) offering an almost complete CO2 selectivity over N-2 and CH4. Data indicated that pore blockage by the IL accompanied with the enhancement in polarity and reduction in the hydrophobic character of the surface hindered the sorption of N-2 and CH4. For CO2, on the other hand, new chemisorption and physisorption sites became available associated with the IL layer on the surface, making the composite material significantly selective. Newly formed chemisorption sites attributed to the cation's acidic C2H sites, which become available with bi-layer formation. Presence of multiple competitive sorption sites with different energies was further proven with thermal analysis and detailed spectroscopic analysis. Data showed that CO2/CH4 and CO2/N-2 ideal selectivities boosted from 3.3 to 688.3 (2.3 to 54.7) and from 15.6 to 903.7 (7.1 to 74.3) at 0.1 (1) bar and 25 degrees C, respectively, upon the deposition of IL layer. Especially at lower pressures, the IL/AC material became almost fully selective for CO2 offering ideal selectivities in the order of several tens of thousands. To the best of our knowledge, the remarkable enhancement in the ideal CO2 selectivity by a straightforward post-synthesis modification of an ordinary AC, as reported here, sets a new benchmark in high-performance and efficient gas separation for similar porous materials.Publication Metadata only A bi-criteria optimization model to analyze the impacts of electric vehicles on costs and emissions(Elsevier, 2017) N/A; N/A; Department of Industrial Engineering; Kabatepe, Bora; Türkay, Metin; Master Student; Faculty Member; Department of Industrial Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 24956Electric vehicles (EV) are emerging as a mobility solution to reduce emissions in the transportation sector. The studies environmental impact analysis of EVs in the literature are based on the average energy mix or pre-defined generation scenarios and construct policy recommendations with a cost minimization objective. However, the environmental performance of EVs depends on the source of the marginal electricity provided to the grid and single objective models do not provide a thorough analysis on the economic and environmental impacts of EVs. In this paper, these gaps are addressed by a four step methodology that analyzes the effects of EVs under different charging and market penetration scenarios. The methodology includes a bi-criteria optimization model representing the electricity market operations. The results from a real-life case analysis show that EVs decrease costs and emissions significantly compared to conventional vehicles.Publication Metadata only A LES/PDF simulator on block-structured meshes(Taylor & Francis Ltd, 2019) Pope, Stephen B.; N/A; Department of Mechanical Engineering; Türkeri, Hasret; Muradoğlu, Metin; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 46561A block-structured mesh large-eddy simulation (LES)/probability density function (PDF) simulator is developed within the OpenFOAM framework for computational modelling of complex turbulent reacting flows. The LES/PDF solver is a hybrid solution methodology consisting of (i) a finite-volume (FV) method for solving the filtered mass and momentum equations (LES solver), and (ii) a Lagrangian particle-based Monte Carlo algorithm (PDF solver) for solving the modelled transport equation of the filtered joint PDF of compositions. Both the LES and the PDF methods are developed and combined to form a hybrid LES/PDF simulator entirely within the OpenFOAM framework. The in situ adaptive tabulation method [S.B. Pope, Computationally efficient implementation of combustion chemistry using in situ adaptive tabulation, Combust. Theory Model. 1 (1997), pp. 41-63; L. Lu, S.R. Lantz, Z. Ren, and B.S. Pope, Computationally efficient implementation of combustion chemistry in parallel PDF calculations, J. Comput. Phys. 228 (2009), pp. 5490-5525] is incorporated into the new LES/PDF solver for efficient computations of combustion chemistry with detailed reaction kinetics. The method is designed to utilise a block-structured mesh and can readily be extended to unstructured grids. The three-stage velocity interpolation method of Zhang and Haworth [A general mass consistency algorithm for hybrid particle/finite-volume PDF methods, J. Comput. Phys. 194 (2004), pp. 156-193] is adapted to interpolate the LES velocity field onto particle locations accurately and to enforce the consistency between LES and PDF fields at the numerical solution level. The hybrid algorithm is fully parallelised using the conventional domain decomposition approach. A detailed examination of the effects of each stage and the overall performance of the velocity interpolation algorithm is performed. Accurate coupling of the LES and PDF solvers is demonstrated using the one-way coupling methodology. Then the fully two-way coupled LES/PDF solver is successfully applied to simulate the Sandia Flame-D, and a turbulent non-swirling premixed flame and a turbulent swirling stratified flame from the Cambridge turbulent stratified flame series [M.S. Sweeney, S. Hochgreb, M.J. Dunn, and R.S. Barlow, The structure of turbulent stratified and premixed methane/air flames I: Non-swirling flows, Combust. Flame 159 (2012), pp. 2896-2911; M.S. Sweeney, S. Hochgreb, M.J. Dunn, and R.S. Barlow, The structure of turbulent stratified and premixed methane/air flames II: Swirling flows, Combust. Flame 159 (2012), pp. 2912-2929]. It is found that the LES/PDF method is very robust and the results are in good agreement with the experimental data for both flames.Publication Metadata only A new approach for predicting gas separation performances of MOF membranes(Elsevier Science Bv, 2016) N/A; Department of Chemical and Biological Engineering; Gürdal, Yeliz; Keskin, Seda; Master Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 40548Metal organic framework (MOF) membranes are widely used for gas separations. Permeability and selectivity of MOF membranes can be accurately calculated using 'the detailed method' which computes transport diffusivities of gases in MOFs' pores. However, this method is computationally demanding therefore not suitable to screen large numbers of MOFs. Another approach is to use the approximate method' which uses self-diffusivities of gases to predict gas permeabilities of MOF membranes. The approximate method requires fewer amounts of time compared to the detailed method but significantly underestimates gas permeabilities since mixture correlation effects are ignored in this method. In this work, we first used computationally demanding detailed method to calculate permeabilities and selectivities of 8 different MOF membranes for Xe/Kr and Xe/Ar separations. We then compared these results with the predictions of the approximate method. After observing significant underestimation of the gas permeabilities by the approximate method, we proposed a new computational method to accurately predict gas separation properties of MOF membranes. This new method requires the same computational time and resources with the approximate method but makes much more accurate predictions for gas permeabilities. The new method that we proposed in this work will be very useful for large-scale screening of MOFs to identify the most promising membrane materials prior to extensive computational calculations and experimental efforts. (C) 2016 Elsevier B.V. All rights reserved.Publication Metadata only Adsorption of Pt(cod)me(2) onto organic aerogels from supercritical solutions for the synthesis of supported platinum nanoparticles(Elsevier Science Bv, 2011) Yasar, N. S.; Zhang, L. C.; Aindow, M.; N/A; Department of Chemical and Biological Engineering; Bozbağ, Selmi Erim; Erkey, Can; Researcher; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; College of Engineering; N/A; 29633The thermodynamics and kinetics of adsorption of Pt(cod)me(2) onto resorcinol-formaldehyde aerogel (RFA) from supercritical carbon dioxide (scCO(2)) was investigated by using high performance liquid chromatography (HPLC) to measure Pt(cod)me(2) concentrations in the fluid phase. It was found that the adsorption isotherms of Pt(cod)me(2) at 35 degrees C for different CO2 pressures could be represented by modified Langmuir isotherms. The kinetics of adsorption was determined by following the Pt(cod)me(2) uptake of the RFA spheres; these data correspond closely to the behavior from a mass transfer model based on diffusion within the pore volume with the assumption of local equilibrium at the solid-fluid interface. The adsorbed Pt(cod)me(2) molecules were reduced at atmospheric pressure under flowing hydrogen at 200 degrees C. The resultant Pt nanoparticles were distributed uniformly on the surface and had narrow size distributions. The average particle size of the nanoparticles increased with platinum loading from 2.0 nm at 10 wt.% to 3.3 nm at 34 wt.%. The Pt nanoparticles in an RFA pellet had a uniform radial size distribution, even though the pellet was impregnated with Pt(cod)me(2) for too short a short period of time for the system to reach adsorption equilibrium. The high mobility of the atomic Pt evolved during the reduction process is believed to be responsible for this phenomenon. Performing the adsorption of Pt(cod)me(2) onto RFA at 80 degrees C led to concurrent reduction and Pt nanoparticle growth. (C) 2010 Elsevier B.V. All rights reserved.Publication Metadata only Adsorption- and membrane-based CH4/N2 separation performances of MOFs(Amer Chemical Soc, 2017) N/A; Department of Chemical and Biological Engineering; Sümer, Zeynep; Keskin, Seda; Master Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 40548Metal organic frameworks (MOFs) have been widely studied as adsorbents and membranes for gas separation applications. Considering the large number of available MOFs, it is not possible to fabricate and test the gas separation performance of every single MOF using purely experimental methods. In this study, we used molecular simulations to assess both adsorption-based and membrane-based CH4/N-2 separation performances of 102 different MOFs. This is the largest number of MOF adsorbents and membranes studied to date for separation of CH4/N-2 mixtures. Several adsorbent evaluation metrics such as adsorption selectivity, working capacity, and regenerability were predicted, and the top performing adsorbents were identified. Several MOFs were predicted to exhibit higher adsorption selectivities than the traditional adsorbents such as zeolites and activated carbons. Relation between adsorption-based separation performances of MOFs and their structural properties were also investigated. Results showed that MOFs having the largest cavity diameters in the range of 4.6-5.4 angstrom, pore limiting diameters in the range of 2.4-3.7 angstrom, surface areas less than 2000 m(2)/g, and porosities less than 0.5 are promising adsorbents for CH4/N-2 separations. We then combined adsorption and diffusion data obtained from molecular simulations and predicted both membrane selectivities and gas permeabilities of MOFs for separation of CH4/N-2 mixtures. A significant number of MOF membranes were identified to be CH4 selective in contrast to the traditional membrane materials which are generally N-2 selective. Several MOFs exceeded the upper bound established for the polymeric membranes, and many MOFs exhibited higher gas permeabilities than zeolites. The results of this study will be useful to guide the experiments to the most promising MOF adsorbents and membranes for efficient separation of CH4/N-2 mixtures.Publication Metadata only Alternative fuel additives from glycerol by etherification with isobutene: structure-performance relationships in solid catalysts(Elsevier, 2015) Tunç, F. Meliz; Bağlar, Nur; Çelebi, Serdar; Günbaş, I. Doğan; N/A; Department of Chemical and Biological Engineering; Bozkurt, Özge Deniz; Uzun, Alper; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Engineering; N/A; 59917The expansion of biodiesel industry is expected to introduce over three million tons of glycerol into the market in 2020. Various routes have been proposed to produce glycerol-based value-added products to sustain renewable glycerol and biodiesel industries. One of these routes is the catalytic etherification of glycerol with isobutene for producing fuel oxygenate glycerol ethers as an alternative to today's petroleum based oxygenates. The products of the etherification of glycerol with isobutene are mono-, di-, and tri-tertiary butyl ethers of glycerol (MTBG, DTBG, and TTBG) and dimers of isobutene (DIE). Among these, DTBG and TTBG are the desired products for fuel blends because of their better blending properties. Different heterogeneous catalysts including acidic ion exchange resins (e.g. Amberlyst 15 and 36), sulfonated wide pore zeolites (e.g. zeolite Beta and Y), sulfonated mesoporous silica (e.g. MCM-41 and SBA-15) and some functionalized porous materials (e.g. sulfonated peanut shell, sulfonated aerogel, sulfonated graphene, spherical silica supported Hyflon) have been proved to demonstrate superior catalytic activity with complete glycerol conversion and over 90 mol% selectivity to the desired ethers. Here, we review the studies on glycerol etherification with isobutene from 1990s to the first half of 2015 specifically focusing on structure-performance relationships in heterogeneous catalysts. (C) 2015 Elsevier B.V. All rights reserved.Publication Metadata only An advantageous technique to load drugs into aerogels: gas antisolvent crystallization inside the pores(Elsevier Science Bv, 2017) N/A; Department of Chemical and Biological Engineering; Ülker, Zeynep; Erkey, Can; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; 262388; 29633Over the past few years, both organic and inorganic nanoporous aerogels have shown a great promise as drug delivery vehicles. Different methods are utilized to load drugs into aerogels such as the addition of the drug to the reaction mixture in one of the steps before the gel formation or by supercritical deposition to the aerogels. These techniques have disadvantages such as possible reactions of pharmaceutical compounds with reactants used to form gels and low solubility of pharmaceutical compounds in supercritical carbon dioxide (scCO(2)). An alternative technique is to load the drug after gel formation by contacting the gel with a solution of the drug. The drug diffuses into the liquid inside the pores. When this drug-loaded gel is subjected to supercritical drying, scCO(2) not only removes the solvent from the pores but also acts as an antisolvent, which causes the precipitation of the drug in the pores of the aerogel. This is similar to the gas antisolvent crystallization (GAS) process but in this case the process takes place inside the pores. In this study, this technique was used to load paracetamol into silica aerogels. The factors affecting the amount and distribution of the drug inside the aerogel matrix were investigated and a mathematical model to account for the movement of paracetamol inside the pores during supercritical drying leading to a varying drug concentration in the matrix with position was developed. It was concluded that high initial concentrations resulted in more homogeneous drug distributions. Moreover, XRD analysis demonstrated that paracetamol was in crystalline form. The process enables higher amount of loadings than conventional systems and also offers an advantage as it combines two processes such as drying and loading in a single one reducing the time and the operating expenses.Publication Metadata only An aerogel-based photocatalytic microreactor driven by light guiding for degradation of toxic pollutants(Elsevier Science Sa, 2021) Jonas, Alexandr; N/A; Department of Chemical and Biological Engineering; Department of Physics; Özbakır, Yaprak; Erkey, Can; Kiraz, Alper; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Physics; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; 29633; 22542Efficient utilization of light in photocatalytic chemical processes requires careful optimization of the photocatalytic reactor layout to maximize the interaction between the incident light, photocatalyst and reactant molecules. Herein, we report a new type of photocatalytic flow microreactor with an integrated light guide, formed by a channel fabricated inside a hydrophobic composite aerogel monolith made of silica and titania (TiO2). The liquid-filled channel simultaneously acts as a reaction vessel and as a liquid-core optofluidic waveguide, distributing the incident light over the whole reaction volume. Anatase TiO2 nanoparticles embedded in the channel walls then serve as a photocatalyst that can efficiently interact with both the guided light and the reactant solution along the channel length. Composite aerogels were synthesized with TiO2 content between 1 and 50 wt %, retaining their interconnected mesoporous network, low refractive index, and waveguide propagation losses below -3.9 dB/cm over this range of compositions. Using photocatalytic degradation of phenol - an organic compound with harmful environmental effects - as a model chemical reaction, the performance of the microreactor was systematically investigated. Reactant conversion was observed to increase with increasing incident light power, decreasing reactant flow rate and increasing mass fraction of TiO2 in the composite. An analytical model of the reactor/light guide system was developed that predicted successfully the scaling of the reactant conversion with the incident light power and reactant flow rate. The presented concept of aerogel-based optofluidic photocatalytic microreactors is readily scalable and possesses great potential for carrying out other photocatalytic reactions in both polar and non-polar solvents.Publication Metadata only Anisotropy of ultrafine-grained alloys under impact loading: the case of biomedical niobium-zirconium(Pergamon-Elsevier Science Ltd, 2012) Rubitschek, F.; Niendorf, T.; Maier, H. J.; N/A; Department of Mechanical Engineering; Toker, Sıdıka Mine; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; 255504; 23433The anisotropy-impact response relationship of a biocompatible niobium zirconium (NbZr) alloy with an ultrafine-grained microstructure was investigated. The current findings not only shed light on the micromechanisms dictating the impact response in the microstructures studied, but are also encouraging with respect to the use of NbZr in orthopedic and dental implants.