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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Large-scale computational screening of MOF membranes and MOF-based polymer membranes for H2/N2 separations(American Chemical Society (ACS), 2019) Department of Chemical and Biological Engineering; Azar, Ayda Nemati Vesali; Velioğlu, Sadiye; Keskin, Seda; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; N/A; 200650; 40548Several thousands of metal organic frameworks (MOFs) have been reported to date, but the information on H-2/N-2 separation performances of MOF membranes is currently very limited in the literature. We report the first large-scale computational screening study that combines state-of-the-art molecular simulations, grand canonical Monte Carlo (GCMC) and molecular dynamics (MD), to predict H-2 permeability and H-2/N-2 selectivity of 3765 different types of MOF membranes. Results showed that MOF membranes offer very high H-2 permeabilities, 2.5 x 10(3) to 1.7 x 10(6) Barrer, and moderate H-2/N-2 membrane selectivities up to 7. The top 20 MOF membranes that exceed the polymeric membranes' upper bound for H-2/N-2 separation were identified based on the results of initial screening performed at infinite dilution condition. Molecular simulations were then carried out considering binary H-2/N-2 and quaternary H-2/N-2/CO2/CO mixtures to evaluate the separation performance of MOF membranes under industrial operating conditions. Lower H-2 permeabilities and higher N-2 permeabilities were obtained at binary mixture conditions compared to the ones obtained at infinite dilution due to the absence of multicomponent mixture effects in the latter. Structure performance relations of MOFs were also explored to provide molecular-level insights into the development of new MOF membranes that can offer both high H-2 permeability and high H-2/N-2 selectivity. Results showed that the most promising MOF membranes generally have large pore sizes (>6 A) as well as high surface areas (>3500 m(2)/g) and high pore volumes (>1 cm(3)/g). We finally examined H-2/N-2 separation potentials of the mixed matrix membranes (MMMs) in which the best MOF materials identified from our high-throughput screening were used as fillers in various polymers. Results showed that incorporation of MOFs into polymers almost doubles H-2 permeabilities and slightly enhances H-2/N-2 selectivities of polymer membranes, which can advance the current membrane technology for efficient H-2 purification.Publication Open Access Effects of force field selection on the computational ranking of MOFs for CO2 separations(American Chemical Society (ACS), 2018) Department of Chemical and Biological Engineering; Keskin, Seda; Dokur, Derya; Master Student; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; 40548; N/AMetal-organic frameworks (MOFs) have been considered as highly promising materials for adsorption-based CO2 separations. The number of synthesized MOFs has been increasing very rapidly. High-throughput molecular simulations are very useful to screen large numbers of MOFs in order to identify the most promising adsorbents prior to extensive experimental studies. Results of molecular simulations depend on the force field used to define the interactions between gas molecules and MOFs. Choosing the appropriate force field for MOFs is essential to make reliable predictions about the materials' performance. In this work, we performed two sets of molecular simulations using the two widely used generic force fields, Dreiding and UFF, and obtained adsorption data of CO2/H-2, CO2/N-2, and CO2/CH4 mixtures in 100 different MOF structures. Using this adsorption data, several adsorbent evaluation metrics including selectivity, working capacity, sorbent selection parameter, and percent regenerability were computed for each MOF. MOFs were then ranked based on these evaluation metrics, and top performing materials were identified. We then examined the sensitivity of the MOF rankings to the force field type. Our results showed that although there are significant quantitative differences between some adsorbent evaluation metrics computed using different force fields, rankings of the top MOF adsorbents for CO2 separations are generally similar: 8, 8, and 9 out of the top 10 most selective MOFs were found to be identical in the ranking for CO2/H-2, CO2/N-2, and CO2/CH4 separations using Dreiding and UFF. We finally suggested a force field factor depending on the energy parameters of atoms present in the MOFs to quantify the robustness of the simulation results to the force field selection. This easily computable factor will be highly useful to determine whether the results are sensitive to the force field type or not prior to performing computationally demanding molecular simulations.Publication Open Access Exploring the performance limits of MOF/polymer MMMs for O-2/N-2 separation using computational screening(Elsevier, 2021) Eruçar, İlknur; Department of Chemical and Biological Engineering; Harman, Hilal Dağlar; Keskin, Seda; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of EngineeringAir separation is one of the most challenging separations because of the very similar molecular dimensions of gas molecules. We used a high-throughput computational screening approach to identify the upper performance limits of metal organic framework (MOF) membranes and MOF/polymer mixed matrix membranes (MMMs) for O-2/N-2 separation. Gas permeabilities and selectivities were calculated for 5629 MOF membranes and 78,806 different types of MOF/polymer MMMs, which represent the largest number of MOF-based membranes studied to date for air separation. Our results showed that many MOF membranes exceed the upper bound established for polymer membranes due to their high permeabilities and/or selectivities. The maximum achievable O-2 permeability and O-2/N-2 selectivity of MOF/polymer MMMs were computed as 2710.8 Barrer and 19.8, respectively. Results revealed that MOF/polymer MMMs can outperform MMMs composed of traditional fillers, such as zeolites, in terms of O-2 permeability and O-2/N-2 selectivity. The impacts of purity of air mixture and the structural flexibility of MOFs on the gas separation performances of MMMs were also discussed. These results provide molecular-level insights into adsorption and diffusion behaviors of O-2 and N-2 in MOF membranes in addition to presenting structure-performance relations of MOFs that can lead to high-performance membranes and fillers for MMMs.Publication Open Access Neovascularization of engineered tissues for clinical translation: where we are, where we should be?(American Institute of Physics (AIP) Publishing, 2021) Department of Chemical and Biological Engineering; N/A; Nazeer, Muhammad Anwaar; Karaoğlu, İsmail Can; Albayrak, Cem; Kızılel, Seda; Özer, Onur; PhD Student; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; 28376; N/AOne of the key challenges in engineering three-dimensional tissue constructs is the development of a mature microvascular network capable of supplying sufficient oxygen and nutrients to the tissue. Recent angiogenic therapeutic strategies have focused on vascularization of the constructed tissue, and its integration in vitro; these strategies typically combine regenerative cells, growth factors (GFs) with custom-designed biomaterials. However, the field needs to progress in the clinical translation of tissue engineering strategies. The article first presents a detailed description of the steps in neovascularization and the roles of extracellular matrix elements such as GFs in angiogenesis. It then delves into decellularization, cell, and GF-based strategies employed thus far for therapeutic angiogenesis, with a particularly detailed examination of different methods by which GFs are delivered in biomaterial scaffolds. Finally, interdisciplinary approaches involving advancement in biomaterials science and current state of technological development in fabrication techniques are critically evaluated, and a list of remaining challenges is presented that need to be solved for successful translation to the clinics.Publication Open Access Assessing CH4/N2 separation potential of MOFs, COFs, IL/MOF, MOF/Polymer, and COF/Polymer composites(Elsevier, 2022) Department of Chemical and Biological Engineering; Keskin, Seda; Uzun, Alper; Altıntaş, Çiğdem; Haşlak, Zeynep Pınar; Faculty Member; Researcher; 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); College of Engineering; Graduate School of Sciences and Engineering; 40548; 59917; N/A; N/ASeparating CH4/N2 mixture is challenging, and performance of the existing materials is still open to improvement. In this study, we examined both the adsorption- and membrane-based CH4/N2 separation performances of 5034 different materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), ionic liquid (IL)/MOF composites, MOF/polymer composites, and COF/polymer composites by performing high-throughput computational screening and molecular simulations. The top performing adsorbents and membranes were identified by computing several performance evaluation metrics. Investigation of the interactions between the gas molecules, the IL, and the top MOF was performed by density functional theory (DFT) calculations. Results pointed out that the interactions between the gas molecules and the linker fragments of the MOF are stronger than their interactions with the IL. Thus, as the IL molecules are loaded into the selected top MOF, they occupy the adsorption sites of the gases, decreasing CH4 and N2 uptakes and increasing the CH4/N2 selectivity. Our results revealed that MOFs offer great potential for adsorption-based CH4/N2 separation, and IL incorporation into MOFs remarkably increases their CH4/N2 selectivities. More than 25% of MOF and 70% of the COF membranes surpassed Robeson's upper bound because of high N2 permeabilities and outperformed conventional polymeric membranes. N2 permeabilities and selectivities of MOF/polymer and COF/polymer composites were found to be significantly higher than those of pure polymers. Our results emphasize the promises of the design and development of new MOF and COF adsorbents, membranes, and their composites with ILs and polymers for efficient CH4/N2 separation.Publication Open Access Computational insights into efficient CO2 and H2S capture through zirconium MOFs(Elsevier, 2022) Department of Chemical and Biological Engineering; Keskin, Seda; Demir, Hakan; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 40548; N/ASeparation of CO2 involving mixtures is relevant to the various industrial settings and preserving environment for which different classes of materials including metal-organic frameworks (MOFs) have been researched. Herein, CO2/CO, CO2/H-2, CO2/N-2, and H2S/CO2 separation properties of the zirconium MOFs are computationally investigated mimicking vacuum swing adsorption (VSA) process. Structure-performance relationships are established and the best performing adsorbent materials are determined considering three performance metrics: adsorption selectivity, working capacity, and regenerability. For CO2/CO separation in dry conditions, PCN-59, BUT-10, and PCN-58 are identified to be the top three materials with CO2/CO selectivities of 219.8, 47.2, and 28.6, CO2 working capacities of 6.9, 5.3, and 4.0 mol/kg, CO2 regenerabilities of 63.3, 82.1, and 87.2 %, successively. In humid conditions, UiO-66-OH and MOF-805 appear promising for CO2/CO separation. Regarding CO2/H-2 separation in dry conditions, PCN-59, BUT-10, and LIFM-94 are ranked as the top three MOFs exhibiting CO2/H-2 selectivities of 1445.6, 378.1, and 411.3, CO2 working capacities of 3.6, 2.4, and 2.2 mol/kg, and CO2 regenerabilities of 56.6, 84.9, and 83.9 %, successively. These three materials are also found to be the top three materials for CO2/N-2 separation in dry conditions with CO2/N-2 selectivities of 346.0, 53.3, and 54.9, CO2 working capacities of 3.6, 2.3, and 2.2 mol/kg, and CO2 regenerabilities of 56.3, 84.1, and 83.9 %, successively. For CO2/H-2 and CO2/N-2 separation in humid conditions, UiO-66-NH2 is potentially useful. Considering H2S/CO2 separation in dry conditions, NU-1101, PCN-58, and LMOF-1 are identified to be the best three MOFs attaining H2S/CO2 selectivities of 109.7, 30.9, and 90.7, H2S working capacities of 1.6, 2.3, and 1.2 mol/kg, and H2S regenerabilities of 43.0, 56.4, and 43.7 %, respectively. All top materials for H2S/CO2 separation show relatively large water affinities (PCN-57 having the smallest affinity) which might render them inefficient for H2S/CO2 separation in humid conditions. Adsorbate density profiles are generated for the top 3 materials to elucidate the adsorption mechanisms for each gas separation. A comparison of predictions based on PACMOF and EQeq charges demonstrates drastic differences in material rankings, and separation performance metrics.Publication Open Access Uncertainty propagation based MINLP approach for artificial neural network structure reduction(Multidisciplinary Digital Publishing Institute (MDPI), 2022) Şıldır, Hasan; Sarrafi, Şahin; Department of Chemical and Biological Engineering; Aydın, Erdal; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of EngineeringThe performance of artificial neural networks (ANNs) is highly influenced by the selection of input variables and the architecture defined by hyper parameters such as the number of neurons in the hidden layer and connections between network variables. Although there are some black-box and trial and error based studies in the literature to deal with these issues, it is fair to state that a rigorous and systematic method providing global and unique solution is still missing. Accordingly, in this study, a mixed integer nonlinear programming (MINLP) formulation is proposed to detect the best features and connections among the neural network elements while propagating parameter and output uncertainties for regression problems. The objective of the formulation is to minimize the covariance of the estimated parameters while by (i) detecting the ideal number of neurons, (ii) synthesizing the connection configuration between those neurons, inputs and outputs, and (iii) selecting optimum input variables in a multi variable data set to design and ensure identifiable ANN architectures. As a result, suggested approach provides a robust and optimal ANN architecture with tighter prediction bounds obtained from propagation of parameter uncertainty, and higher prediction accuracy compared to the traditional fully connected approach and other benchmarks. Furthermore, such a performance is obtained after elimination of approximately 85% and 90% of the connections, for two case studies respectively, compared to traditional ANN in addition to significant reduction in the input subset.Publication Open Access Coordinate interleaved orthogonal design with media-based modulation(Institute of Electrical and Electronics Engineers (IEEE), 2021) Yldırım, İbrahim; Altunbaş, İbrahim; Department of Chemical and Biological Engineering; Başar, Ertuğrul; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 149116In this work, we propose a new multiple-input multiple-output (MIMO) concept, which is called coordinate interleaved orthogonal design with media-based modulation (CIOD-MBM). The proposed two novel CIOD-MBM schemes provide improved data rates as well as diversity gain while enabling hardware simplicity using a single radio frequency (RF) chain. Moreover, using the equivalent channel model, a reduced complexity can be obtained for maximum likelihood (ML) detection of the proposed system. Using computer simulations, it is shown that CIOD-MBM schemes provide remarkably better performance against the conventional MBM and CIOD systems.Publication Open Access CO2 absorption into primary and secondary amine aqueous solutions with and without copper ions in a bubble column(TÜBİTAK, 2022) Güler, Cansu; Uzunlar, Erdal; Department of Chemical and Biological Engineering; Erkey, Can; Yousefzadeh, Hamed; Faculty Member; Researcher; Department of Chemical and Biological Engineering; College of Engineering; 29633; N/AChemical absorption of CO2 into aqueous amine solutions using a nonstirred bubble column was experimentally investigated. The performance of CO2 absorption of four different primary and secondary amines including monoethanolamine (MEA), piperazine (PZ), 2-piperidineethanol (2PE), and homopiperazine (HPZ) were compared. The effects of initial concentration of amine, the inlet mole fraction of CO2, and solution temperature on the rate of CO2 absorption and CO2 loading (mol CO2/mol amine) were studied in the range of 0.02–1 M, 0.10–0.15, and 25–40 °C, respectively. The effect of the presence of copper ions in the amine solution on CO2 loading was also studied. By comparison of the breakthrough curves of the amines at different operational conditions, it was revealed that the shortest and longest time for the appearance of the breakthrough point was observed for MEA and HPZ solutions, respectively. CO2 loading of MEA, 2PE, PZ, and HPZ aqueous solutions at 25 °C, 0.2 M of initial concentration of amine, and 0.15 of inlet mole fraction of CO2 were 1.06, 1.14, 1.13, and 1.18 mol CO2/mol amine, respectively. By decreasing the inlet mole fraction of CO2 from 0.15 to 0.10, CO2 loading slightly decreased. As the initial concentration of amine and temperature decreased, CO2 loading increased. Also, the presence of copper ions in the absorbent solution resulted in a decrease in the CO2 loading of MEA and HPZ aqueous solutions. In case of PZ and 2PE amines, adding copper ions led to precipitation even at low copper ion concentrations.Publication Open Access Combined GCMC, MD, and DFT approach for unlocking the performances of COFs for methane purification(American Chemical Society (ACS), 2021) Department of Chemical and Biological Engineering; Keskin, Seda; Haşlak, Zeynep Pınar; Altundal, Ömer Faruk; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; Graduate School of Sciences and Engineering; 40548; N/A; N/ACovalent organic frameworks (COFs) are promising materials for gas storage and separation; however, the potential of COFs for separation of CH4 from industrially relevant gases such as H-2, N-2, and C2H6 is yet to be investigated. In this work, we followed a multiscale computational approach to unlock both the adsorption- and membrane-based CH4/H-2, CH4/N-2, and C2H6/CH4 separation potentials of 572 COFs by combining grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Adsorbent performance evaluation metrics of COFs, adsorption selectivity, working capacity, regenerability, and adsorbent performance score were calculated for separation of equimolar CH4/H-2, CH4/N-2, and C2H6/CH4 mixtures at vacuum swing adsorption (VSA) and pressure swing adsorption (PSA) conditions to identify the best-performing COFs for each mixture. Results showed that COFs could achieve selectivities of 2-85, 1-7, and 2-23 for PSA-based CH4/H-2, CH4/N-2, and C2H6/CH4 separations, respectively, outperforming conventional adsorbents such as zeolites and activated carbons for each mixture. Structure-performance relations revealed that COFs with pore sizes <10 angstrom are promising adsorbents for all mixtures. We identified the gas adsorption sites in the three top-performing COFs commonly identified for each mixture by DFT calculations and computed the binding strength of gases, which were found to be on the order of C2H6 > CH4 > N-2 > H-2, supporting the GCMC results. Nucleus-independent chemical shift (NICS) indexes of aromaticity for adsorption sites were calculated, and the results revealed that the degree of linker aromaticity could be a measure for the selection or design of highly alkane-selective COF adsorbents over N-2 and H-2. Finally, COF membranes were shown to achieve high H-2 permeabilities, 4.57 x 10(3)-1.25 x 10(6) Barrer, and decent membrane selectivities, as high as 4.3, outperforming polymeric and MOF-based membranes for separation of H-2 from CH4.