Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Simultaneous Topology Design and Optimization of Pde Constrained Processes Based on Mixed Integer Formulations(Elsevier, 2024) Ertürk, Emrullah; Deliismail, Özgün; Şıldır, HasanSimultaneous topological design and optimization of complex processes that are described by partial differential equations is a challenging but promising research area. Widely adopted nested and sequential approaches are mostly applicable based on heuristic solutions, hindering the theoretical improvement potential due to decentralized decision-making in subsequent stages with a significant number of trial-and-error procedures. This study introduces a mixed integer formulation addressing the governing equations and case-dependent topological constraints at each discretization point, enabling solutions through rigorous solvers under process-related constraints and objectives. Nonlinear expressions in the formulations are further tailored using piecewise linear approximations, still representing the major nonlinear trends through a mixed-integer linear nature to favor global optimality and benefit from computational advancements, when needed. Heat and Stokes flow problems are used as case studies to demonstrate the applicability of the methodology. © 2024 Elsevier B.V.Article Citation - WoS: 6Citation - Scopus: 6Inverse Effects of Lanthanide Co-Doping on the Photocatalytic Hydrogen Production and Dye Degradation Activities of Cu Doped Sol-Gel Tio<sub>2</Sub>(Elsevier, 2023) Yurtsever, Husnu Arda; Erzin, Kubilay; Ciftcioglu, Muhsin; Yurtsever, Hüsnü Arda; Erzin, Kubilay; Çiftçioğlu, MuhsinCopper doped and lanthanide-copper co-doped titania powders were prepared by sol-gel technique and the effects of co-doping on the photocatalytic reduction and oxidation activities of titania were investigated in this work. Characterization studies indicated that a reduced structure was formed due to the presence of Ti3+ species in copper doped titania powder and a more stable structure was formed when lanthanides were used as co-dopants. Copper doped powder had a significantly higher activity in photocatalytic hydrogen production (1037 mu mol/g/h) than the co-doped powders (similar to 400 mu mol/g/h). The oxidation activities of co-doped powders however were determined to be about 2 times higher than that of the copper doped powder. The decrease in the reduction activity was attributed to the decrease in the number of Ti3+ sites, whereas the increase in oxidation activity was probably a result of the increase in the surface area and dye adsorption due to lanthanide co-doping.Article Citation - WoS: 6Citation - Scopus: 8Effect of the Combination of Organic Acid Solutions on Tinplate Corrosion(Elsevier, 2022) Yıldırım, Koray; Kızılkaya, Ali CanTinplate corrosion as a result of canned food is typically tested in industry by tinplate in synthetic media based on single organic acids. However, the combination of organic acids, which is present in applied conditions, is not previously investigated in terms of its effect on tinplate corrosion mechanism. In this manuscript, we combine structural characterization of tinplate surfaces with electrochemical measurements, to investigate the corrosion mechanism of tinplate under acetic acid-NaCl, citric acid-NaCl, and a combined acetic acid, citric acid and NaCl media. The results show that the combined acid media causes does not result in a pronounced formation of a protective passivation layer, in contrast to the single acid based media. Our findings demonstrate the combined effects of the organic acids in corrosive media has to be taken into account for tinplate corrosion, as they can alter the corrosion mechanism. Furthermore, we show that combination of organic acids can accelerate tinplate corrosion testing in packaging industry. Thus, our findings can contribute to the design of new aging media for tinplate corrosion testing.Article Citation - WoS: 12Citation - Scopus: 12Supercritical Fluid Reactive Deposition: a Process Intensification Technique for Synthesis of Nanostructured Materials(Elsevier, 2022) Yousefzadeh, Hamed; Akgün, Işık Sena; Barım, Şansım Bengisu; Sarı, Tarık Bercan; Eriş, Gamze; Uzunlar, Erdal; Bozbağ, Selmi Erim; Erkey, CanSupercritical fluid reactive deposition (SFRD) is a promising process intensification technique for synthesis of a wide variety of nanostructured materials. The enhanced mass transfer characteristics of supercritical fluids (SCFs) coupled with high solubilities of reducing gases in SCFs provide many advantages related to equipment size and time minimization over conventional techniques. Among SCFs, the emphasis has been placed on supercritical CO2 (scCO2) which is non-toxic, cheap and leaves no residue on the treated medium. Moreover, in SFRD, multiple processes such as dissolution, adsorption, reaction, and purification are combined in a single piece of equipment which is an excellent example of process integration for process intensification. In this review, the fundamental thermodynamic and kinetic aspects of the technology are described in detail. The studies in the literature on synthesis of a wide variety of nanostructured materials including supported nanoparticles, films, and ion-exchanged zeolites by SFRD are reviewed and summarized. The applications of these materials as catalysts and sensors are described. The review hopes to lead to further studies on further development of this technology for a wide variety of applications.Article Citation - WoS: 7Citation - Scopus: 8Compositional, Microstructural and Mechanical Effects of Nacl Porogens in Brushite Cement Scaffolds(Elsevier, 2021) Şahin, Erdem; Çiftçioğlu, MuhsinModification of the setting process of brushite cements by varying the concentration of ions that alter calcium phosphate crystallization kinetics, is known to enable control on the monetite conversion extent and the accompanying microporosity. This is useful because monetite serves as a suitable matrix in macroporous scaffolds due to its higher phase stability and finer crystal morphology compared to its hydrous counterpart brushite. In this study the synergistic effect of NaCl and citric acid on the microstructural evolution of brushite cement was demonstrated and microporosity of macroporous monetite-rich cement blocks was minimized by a variable NaCl porogen size distribution approach. Initially, maximum packing ratio of various combinations of NaCl size groups in PEG were determined by their rheological analysis in a range between 57% and 69%. Statistical analysis revealed a positive correlation between the amounts of NaCl particles under 38 mu m and 212 mu m and the maximum packing ratio. Further broadening the size distributions of NaCl porogens with fine cement precursors was effective in increasing the solids packing ratio of cement blocks more than the maximum packing ratio for the porogens. This improvement in packing was accompanied by a reduction in microporosity despite the increase in micropore volume with ion induced monetite formation. The detrimental effect of the microporosity introduced to the structure during monetite formation was balanced for some size distributions and not so much for others, thereby resulting in a wide range of porosities and mechanical properties. Thus, the exponential dependence of mechanical properties on porosity and the mechanical properties of monetite-rich macroporous blocks at the theoretical zero-porosity were determined according to Rice's model. Zero-porosity extrapolations were much higher than those predicted for brushite cement, contrary to the common assumption that brushite is mechanically stronger than monetite.Article Citation - WoS: 8Citation - Scopus: 11The Effect of Protein Bsa on the Stability of Lipophilic Drug (docetaxel)-Loaded Polymeric Micelles(Elsevier, 2021) Polat, Hürriyet; Çevik Eren, Merve; Polat, MehmetPolymeric micelles are promising delivery vehicles for improving the efficacy of anticancer drugs and reducing their side effects. However, considering the binding ability of serum albumin, the possible interaction of micelles with the native plasma components in the bloodstream raises serious questions on micellar stability. The stability of barren or drug-loaded copolymeric micelles was investigated systematically in distilled water (DW) and simulated body fluid (SBF) solutions in the presence of a model protein. The copolymer was a Pluronic® series triblock copolymer (P-123), the drug was strongly lipophilic docetaxel (DOC) and the protein was Bovine Serum Albumin (BSA). The effect of such factors as BSA and DOC concentrations and the aging of the micellar solutions was studied. Both the barren and drug-loaded micelles were quite stable in blank DW and SBF solutions for long times up to 10 days. They lost integrity and showed no inclination to re-assemble when the BSA concentration reached a critical value, which was very close to the plasma Human Serum Albumin (HSA) concentration. The presence of DOC in the micellar cores could not prevent disintegration. The results illustrate clearly that ensuring the stability of polymeric micelles in blood plasma should be an important design factor in their use as drug carriers.Article Citation - WoS: 4Citation - Scopus: 4Optical and Photocatalytic Properties of Zno and Zns Structures Formed as Controlled Calcination Products of L-Cysteine Assisted Aqueous Precipitation(Elsevier, 2020) Şen, Selin; Top, AybenZnO and ZnS structures were obtained by the calcination of the aqueous precipitation products of Zn(NO3)2, NaOH and L-cysteine (Cys). Initial Cys:Zn molar ratios were changed as 0.1:1, 0.5:1, 1:1 and 1.5:1. All the precursors were transformed into ZnO upon calcination at 700 °C. ZnS structures were obtained by calcining the precursors prepared at the Cys:Zn ratios of 1 and 1.5 at 350 °C. In addition to changing chemical composition of the precipitation products, calcination temperature and initial Cys:Zn ratio also affected morphology, surface area, photoluminescence and photocatalytic properties of the final products. Free exciton energy values of the ZnO samples were observed to be between 3.29 eV and 3.35 eV. PL spectra of the ZnO samples indicated blue and green emission centers. Zinc interstitials (Zni), revealed by the blue emissions in the PL spectra were also confirmed by Auger Zn L3M4.5M4.5 spectra. The samples calcined at 350 °C removed rhodamine B mainly by adsorption. All the samples calcined at 700 °C successfully degraded the dye under UV light. Among the samples calcined at 700 °C, ZnO sample prepared at Cys:Zn = 0.5, which has the highest surface area and unique photoluminescence spectrum exhibited the fastest photodegradation rate. © 2020 Elsevier LtdArticle Citation - WoS: 31Citation - Scopus: 38Liquefaction of Waste Hazelnut Shell by Using Sub- and Supercritical Solvents as a Reaction Medium(Elsevier, 2019) Demirkaya, Emre; Dal, Orkan; Yüksel, AslıDirect thermochemical biomass degradation to obtain bio-oil by using organic solvents is not a new process type, and it has some advantages over hydrothermal liquefaction technique. However, up to our best knowledge, in this study, hazelnut shell decomposition by using ethanol, acetone and their mixtures at sub/supercritical conditions was studied for the first time in literature. Experiments were carried out between 220-300 degrees C, at three different reaction times (30, 60 and 90 min) for five different solvent ratios. Highest solid conversion achieved at 300 degrees C by using pure ethanol was 64.2%, whereas highest bio-oil yield was found as 44.2% at 300 degrees C with 50/50 (EtOH/Ac: v/v). Ethanol and acetone showed different characteristics during the reactions and their effects on the conversion and bio-oil yield were discussed. Statistical analysis showed that time, temperature, ratio and synergy between temperature-time were affecting parameters for the conversion and bio-oil yield. (C) 2019 Elsevier B.V. All rights reserved.Article Citation - WoS: 23Citation - Scopus: 27Use of Deep Eutectic Solvents in the Enzyme Catalysed Production of Ethyl Lactate(Elsevier, 2019) Arıkaya, Azime; Ünlü, Ayşe Ezgi; Takaç, SerpilThe use of deep eutectic solvents (DESs) in the lipase-catalysed esterification of lactic acid with ethanol was explored by screening several DESs. Choline chloride:glycerol (1:2) was the most effective DES and provided 28.7% yield of ethyl lactate under the following conditions: 10% (v/v) of water content in DES, 3 M of initial lactic acid concentration, 5 M of initial ethanol concentration, 30 mg/mL of enzyme concentration, 50 degrees C temperature and 200 rpm agitation rate. Individual and combined effects of the reaction medium components on the enzyme activity were investigated and it was discovered that DES stimulated the enzyme activity while reactants inhibited it. A kinetic model that obeys the Ping-Pong Bi-Bi mechanism with ethanol inhibition was suggested. The kinetics parameters were determined as r(max) = 0.401 mol/L h, the Michaelis constants K-A = 1.657 mol/L and K-B = 0.799 mol/L, the inhibition constant K-iB = 0.156 mol/L. The model reasonably predicted the experimental data. The activation energy was found to be 43.28 kJ/mol. Mass transfer limitations in the reaction medium were negligible. The results are promising for further studies that will research on the use of green solvents in enzyme catalysed lactic acid esterification reactions.Article Citation - WoS: 14Citation - Scopus: 15Investigation of the Effect of Gel Properties on Supercritical Drying Kinetics of Ionotropic Alginate Gel Particles(Elsevier, 2019) Şahin, İbrahim; Uzunlar, Erdal; Erkey, CanA series of spherical ionotropic alginate gel particles with different diameters ranging from 2.8mm to 5.0mm and porosities ranging from 0.899 to 0.976 were prepared by dripping a Na-alginate solution into a solution of salts of divalent cations (Ca2+, Mn2+, Ni2+, Co2+, Cu2+ and Zn2+). After solvent exchange with ethanol, kinetics of supercritical drying of these ionotropic alginate gel particles in a packed bed was investigated at 308-338 K and 100-120 bar. Experimental data were compared with predictions of a model which considers diffusive transport inside the pores and convection in the flowing fluid stream. The model predicted drying profiles by taking into account only the changes in porosity and diameter of the gel particles. A convective mass transfer coefficient correlation that was originally developed for supercritical drying of Ca-alginate gel particles was found to be suitable for M-alginate gel particles. (C) 2019 Elsevier B.V. All rights reserved.