Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 6Citation - Scopus: 4Regenerable Nickel Catalysts Strengthened Against H2s Poisoning in Dry Reforming of Methane(Elsevier, 2025) Kesan Celik, Nazli; Yasyerli, Sena; Arbag, Huseyin; Tasdemir, H. Mehmet; Yasyerli, NailIn this study, alumina-supported bimetallic Ni-Cu and trimetallic Ni-Cu-Ce catalysts were synthesized to improve catalysts resistant to coke formation and sulfur poisoning for dry reforming of methane (DRM). The effects of parameters such as feed composition, synthesis method, and H2S concentration using the catalyst with the best activity were also investigated. To determine the physical and chemical properties of the synthesized catalysts, XRD, N2 adsorption-desorption, TGA-DTA, ICP-OES, SEM-EDX, XPS, and DRIFTS analyses were performed. XRD analysis showed that the fresh Ni-Cu catalysts have elemental nickel and gamma- alumina phases in their structures. In addition to these structures, the CeO2 crystal structure was determined for the Ni-Cu-Ce catalyst. Type IV isotherm with H1 hysteresis indicating uniform mesoporous structure was obtained with all the catalysts. The activities of the synthesized catalysts in DRM were performed in the presence of different concentrations of H2S (2 ppm, 50 ppm, and 500 ppm) in a fixed bed reactor at 750 degrees C using a gas chromatography-equipped system. The alumina-supported 8Ni-3Cu-8Ce catalyst prepared by the impregnation method exhibited a higher and more stable activity comparing the bimetallic Ni-Cu catalyst in the presence of H2S. Adding copper and cerium to the nickel catalyst has a curative effect on resistance to coke formation and sulfur poisoning. Excess CO2 in the feed stream increased the H2S poisoning resistance of the catalyst. To analyze the reactor exit stream in catalytic activity using different feed stream compositions such as H2S+He, H2S+CO2+He, and H2S+CO2+CH4+He, FTIR with a gas cell was used. The formation of carbonyl sulfide (COS) and H2O, which occurs due to the possible reaction between CO2 and H2S, was observed. Regeneration studies showed that the catalyst could undergo regeneration with a low oxygen concentration (0.3 % O2 in He). 8Ni-3Cu-8Ce@SGA, which gave 71 % CH4 conversion in the first minute of the reaction test in the presence of 50 ppm H2S, was regenerated after completely losing its activity at the end of 5 h. 66 % CH4 conversion was achieved when tested again in the absence of H2S (CH4/CO2/Ar:1/1/1). The 8Ni-3Cu-8Ce@SGA catalyst was deemed worthy of investigation for industrial applications.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: 2Citation - Scopus: 3A Phenomenological Kinetic Flotation Model: Distinct Time-Variant Floatability Distributions for the Pulp and Froth Materials(Elsevier, 2023) Polat, Mehmet; Polat, HürriyetA simple and easy-to-use phenomenological kinetic flotation model, strongly connected with the physics of the process, is proposed in this paper. The model explicitly contains the cell volume, aeration rate, volumetric holdup, mean bubble size, and particle density as input variables. It can be employed to characterize the floatability distributions of the particles in the pulp and the froth separately any time during the flotation process. Two new time-dependent kinetic parameters, the bubble loading factor & phi;(t) and the maximum cell mass transfer capacity Mmax(t) also appear in the model expression. & phi;(t) is a measure of the degree of crowding of the bubble surfaces and accounts for the deviations from the first-order rate equation. Mmax(t) describes the maximum amount of mass that can be transported to the froth phase by the bubble population in the cell. Screen fractionation of each froth product collected at different time intervals during a single kinetic flotation test is sufficient to generate the data required by the model for analysis. Application of the model to this data yields directly time-dependent functions for the floatability of the particles reporting to froth Kf(t) or remaining in the cell Kp(t) for each size fraction separately, without the need for any empirical parameters. The test of the model was carried out using published kinetic flotation data from the literature.Article Citation - WoS: 6Citation - Scopus: 9The Effect of Military Conflict Zone in the Middle East on Atmospheric Persistent Organic Pollutant Contamination in Its North(Elsevier, 2023) Ayrı, İlknur; Genişoğlu, Mesut; Sofuoğlu, Aysun; Kurt Karakuş, Perihan B.; Birgül, Askın; Sofuoğlu, Sait CemilThis study aimed to investigate long-range atmospheric transport of selected POPs released due to the effects of mili-tary conflicts in regions to the south of Turkey's borders. Ten locations were selected to deploy passive air samplers at varying distances to the border on a southeast-west transect of the country, proximity-grouped as close, middle, and far. Sampling campaign included winter and transition months when desert dust transport events occur. Hypothesis of the study was that a decreasing trend would be observed with increasing distance to the border. Group comparisons based on statistical testing showed that PBDE-183, E45PCB, and dieldrin in winter; PBDE-28, PBDE-99, PBDE-154, p,p '-DDE, E14PBDE, and E25OCP in the transition period; and PBDE-28, PBDE-85, PBDE-99, PBDE-154, PBDE-190, PCB-52, E45PCB, p,p '-DDE, and E25OCP over the whole campaign had a decreasing trend on the transect. An analysis of concen-tration ratio to the background showed that long-range atmospheric transport impacted the study sites, especially those of close group in comparison to the local sources. Back-trajectory analyses indicated that there was transport from the conflict areas to sites in the close-proximity group, while farther sampling locations mostly received air masses from Europe, Russia, and former Soviet Union countries, followed by North Africa, rather than the military con-flict areas. In consequence, decrease in concentrations with distance and its relation to molecular weight through pro-portions, diagnostic ratios, analysis of concentration ratio to the background, and back-trajectory analyses support the effect of transport from the military-conflict area to its north.Article Citation - WoS: 17Citation - Scopus: 20Polyoxometalate-Based Hybrid Composites in Multi-Functional Wastewater Treatment Applications(Elsevier, 2023) Recepoğlu, Yaşar Kemal; Gören, Ayşegül Yağmur; Orooji, Yasin; Vatanpour, Vahid; Kudaibergenov, Nurbolat; Khataee, AlirezaThe inorganic polyanionic clusters known as polyoxometalates (POMs) have several structural variations at the nanoscale scale. They have many uses in chemistry, materials science, medicine, and other fields. This review considers the developments in treating hazardous contaminants from wastewater using POMs-based compounds. Four main treatment methods using POM-based compounds to remove water pollutants have been developed: adsorption, photocatalytic treatment, Fenton-like treatment, and membrane separation. Moreover, we report the types of POMs, synthesis procedures, strategies performed to modify POM-based compounds, and their appli-cations in wastewater treatment. To promote the development of these compounds for large-scale production and real-scale applications, gaps in knowledge and recent research obstacles are also pointed out. Most research on metal organic complexes (MOCs) based on POM has focused on using these compounds as catalysts, with little focus on their additional uses. The adsorption and photocatalytic efficiency of modified POM-based compounds are attributed to their enhanced contaminant removal efficiency, and recovery of certain POM-based compounds by magnetic separation is presented as a promising option for their recyclability. Among the reviewed studies, the highest adsorption capacity was 1108.9 mg/g, with a removal efficiency of 100 % for acid red dye using poly-[N,N-dimethyl-dodecyl-(4-vinylbenzyl)ammonium chloride] (PIL)-POM. The studies also indicate that the POM-based adsorbents could be effectively reused to remove pollutants and sustain their activity in 3-10 cycles. This review is believed to provide an overview of recent advancements in POM-based compounds for water and wastewater treatment, offers thorough research to anyone interested in learning more about this topic, and acts as a manual for researchers working in this area.Article Citation - WoS: 15Citation - Scopus: 19Immobilization of Esterase From Bacillus Subtilis on Halloysite Nanotubes and Applications on Dibutyl Phthalate Degradation(Elsevier, 2023) Rosales, Emilio; Pazos, Marta; Sanroman, Maria Angeles; Balcı, Esin; Sofuoğlu, AysunDibutyl phthalate (DBP) is one of the listed phthalic acid esters (PAEs) known as the priority toxicants which exhibit carcinogenic and teratogenic properties and is responsible for endocrine disruption. Therefore, its removal has become a matter to tackle with. In this work, the feasibility of DBP degradation by esterase and lipase enzymes obtained from various microorganisms and the immobilization of the most effective in a clayey material were investigated. Esterase from Bacillus subtilis exhibited the highest degradation efficiency reaching a complete degradation. Its immobilization onto halloysite nanotubes (HNTs) by adsorption method was studied by response surface methodology using a central composite design face-centered. The four selected factors that affect the HNT-enzyme composite generation were: pH, adsorption time, enzyme/HNT (E/H) ratio, and adsorption temperature, and the optimal conditions were determined (pH 7, time 360 min, E/H ratio 0.2, temperature 30oC). Consequently, the activity did not significantly decrease by immobilization, and the adsorption efficiency and relative activity were determined to be 73.15% and 82.7%, respectively. Besides, the immobilization enhanced thermal and storage stability. As for enzyme reusability, after 7 continuous cycles, the composite maintained almost 75% of its initial activity. Both the free enzyme (1 mg/mL) and the composite degraded 100 mg/L DBP with 100% efficiency and several byproducts were detected. Moreover, the composite could be reused for 7 cycles keeping a remarkable catalytic activity. Overall, this study indicated that the HNT-enzyme composite may be used as an effective candidate for remediation of the environmental media contaminated with DBP and other PAEs.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Article Citation - WoS: 4Citation - Scopus: 5Antifouling Polydopamine-Modified Poly (ether Sulfone) Membrane Immobilized With Alumina-Calcium Oxide Catalyst for Continuous Biodiesel Production(Elsevier, 2023) Güngörmüş, Elif; Şeker, Erol; Alsoy Altınkaya, SacideBiodiesel is an alternative biofuel that can be blended with conventional petroleum-derived diesel fuel to partly reduce the dependence on the imported oil. Catalytic membrane reactors are promising candidates for sustainable biodiesel production. Herein, we report a novel catalytically active polydopamine-modified poly (ether sulfone) (PES) membrane immobilized with an alumina-calcium oxide catalyst. The reaction temperature, butanol to canola oil ratio, and transmembrane pressure applied through the membrane were optimized with response surface methodology and Box-Behnken design. In contrast to all previous catalytic membrane studies for biodiesel production, we used butanol as a co-reactant to improve the winter problems of biodiesel made with methanol. FTIR and SEM-EDX analysis confirmed the successful immobilization of the catalyst. At the end of 30 days of storage in the reactant mixture, 95% of the catalyst loaded to the membrane was still on the surface, and biodiesel yield values and butanol flux of the membrane did not change. We compared the batch and flowthrough operation modes by measuring the catalytic activity of membranes under static and dynamic conditions within 24 h (8-cycle). The biodiesel yield under dynamic condition decreased in the first three cycles from 54.54 +/- 0.65% to 47.31 +/- 0.70% and then stayed constant, whereas a continuous decrease from 25.42 +/- 0.57% to 17.19 +/- 0.58% was observed under static condition. In each cycle, the equilibrium limitation for the yield was overcome only when the membrane was operated under pressure. The main reason for the decrease in catalytic activities was the fouling on the catalyst surface which was quickly removed by backwashing with butanol. It is concluded that catalytic membranes with antifouling properties and alcohol stability can make biodiesel production more cost-effective and environmentally friendly.Article Citation - WoS: 7Citation - Scopus: 7Insights Into Sustainability of Engineered Carbonaceous Material-Based Technologies for Advanced Cyanide Removal From Wastewater(Elsevier, 2023) Yoon, Yeojoon; Khataee, Alireza; Gören, Ayşegül Yağmur; Recepoğlu, Yaşar KemalCyanide (CN) is a serious concern in industrial and goldmine wastewater. Strict regula-tory standards have been established by various agencies due to the detrimental effects that CN has on human health. Therefore, before discharge to water bodies or land, it is essential to create a sus-tainable model for the safe removal of CN. Carbon-based materials are well known for their adsorption and oxidation features, which can be conducive to CN removal. This paper reviews the relevant literature on the application of modified and unmodified carbon-based materials to CN removal in water; these materials include activated carbon (AC), graphene, graphene oxide (GO), and carbon nanotubes (CNTs). Moreover, CN removal mechanisms and photocatalytic removal of CN are comprehensively discussed, with a particular emphasis on modifying carbon-based materials. It has been observed that adding various elements to carbon-based materials improves their surface area, functional groups, CN adsorption capacity, and pore volume. Impacts of operational parameters, isotherm models, kinetics, and types of carbon-based materials are also outlined. This study provides insight into the real-scale applicability of carbon-based materials for CN removal from waters. Moreover, this review indicates that essential work on CN removal using carbon-based materials is still needed. Future research should focus on developing modified carbon-based materials to encourage multidisciplinary research. The most crucial gap in the literature is that the studies have been performed on a lab scale. Therefore, further pilot and real-scale applica-tions should be conducted. Overall, the cost assessment, environmental effects, and human health risks of carbon-based materials should be studied in future research to achieve a realistic perspective on applicability on an industrial scale.(c) 2023 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).Article Citation - WoS: 31Citation - Scopus: 34Insights Into Engineered Graphitic Carbon Nitride Quantum Dots for Hazardous Contaminants Degradation in Wastewater(Elsevier, 2023) Gören, Ayşegül Yağmur; Recepoğlu, Yaşar Kemal; Vatanpour, Vahid; Yoon, Yeojoon; Khataee, AlirezaIncreased environmental pollution is a critical issue that must be addressed. Photocatalytic, adsorption, and membrane filtration methods are suitable in environmental governance because of their high selectivity, low cost, environment-friendly nature, and excellent treatment efficiency. Graphitic carbon nitride (g-C3N4) quantum dots (QDs) have been considered as photocatalysts, adsorbents, and membrane materials for wastewater treatments, owing to their stability, adsorption capacity, photochemical properties, and low toxicity and cost. This review summarizes g-C3N4 QD synthesis techniques, operating parameters affecting the removal performance in the treatment process, modification effects with other semiconductors, and benefits and drawbacks of g-C3N4 QD-based materials. Furthermore, this review discusses the practical applications of g-C3N4 QDs as adsorbents, photocatalysts, and membrane materials for organic and inorganic contaminant treatments and their value-added product formation potential. Modified g-C3N4 QD-based material adsorbents, photocatalysts, and membranes present potentially applicable effects, such as removal of most waterborne contaminants. Excellent results were obtained for the reduction of methyl orange, bisphenol A, tetracycline, ciprofloxacin, phenol, rhodamine B, E. coli, and Hg. Overall, this paper provides comprehensive background on g-C3N4 QD-based materials and their diverse applications in wastewater treatment, and it presents a foundation for the enhancement of similar unique materials in the future.Article Citation - WoS: 6Citation - Scopus: 7Designing Robust Xylan/Chitosan Composite Shells Around Drug-Loaded Msns: Stability in Upper Git and Degradation in the Colon Microbiota(Elsevier, 2023) Zeybek, Nüket; Büyükkileci, Ali Oğuz; Güleç, Şükrü; Polat, Mehmet; Polat, Hürriyetong residence times, near-neutral pH values, and release triggered by the enzymatic action of the resident microbiota offer unique opportunities for improved drug delivery in the colon. The fact that a delivery agent must also pass through the complete GI tract without degradation presents a challenge due to widely changing pH conditions. In this study, a promising colon-targeted drug delivery system was composed of a xylan/chitosan composite shell formed on curcumin-loaded mesoporous silica nanoparticles (MSNs). A novel synthesis approach was employed to facilitate precipitation of negatively charged xylan on negatively charged MSNs by concurrent chitosan polymerization. Curcumin-loaded xylan/chitosan-coated MSNs (C-MSNs) were determined to contain nearly 42% xylan by the inclusion of chitosan in a one-to-one ratio with xylan. The xylan/chitosan composite shell demonstrated excellent stability in the acidic upper GI tract. The hydrolysis of glycosidic bonds by resident microbiota was the triggering mechanism for xylan degradation and curcumin release in the colon. The presence of xylan has the further benefit of increasing the number of beneficial bacteria and improving short-chain fatty acid production for improved colon health.