Chemical Engineering / Kimya Mühendisliği
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Article Citation - WoS: 35Citation - Scopus: 38Ethyl Esters Biodiesel Production From Spirulina Sp. and Nannochloropsis Oculata Microalgal Lipids Over Alumina-Calcium Oxide Catalyst(Elsevier, 2020) Türkkul, Berk; Deliismail, Özgün; Şeker, ErolIn this study, we present the ethyl esters biodiesel production from Nannochloropsis oculata and Spirulina sp. microalgal lipids on 60 wt% CaO on Al2O3 catalyst at 50 degrees C and 1.0 atm. The activity of the catalyst was studied as a function of ethanol:lipid molar ratios, catalyst amounts and reaction times. It was found that 6 wt% of the lipids as catalyst amount resulted in 59% biodiesel yield in 30 min at 12 of ethanol:lipid molar ratio whereas 90-99% biodiesel yield was obtained at 24 and 48 of ethanol:lipid molar ratios. In order to achieve 90-99% yields, the basic strength was found to be weak and to be in the form of bi-carbonate, whereas high basicity was not necessary. Besides, pure CaO and Al2O3 were not active under the same reaction conditions. We found that the glycerolysis of triacylglyceride occurred in series with the reverse of the transesterification of the triacylglyceride when the catalyst amount was 6 wt% of the lipids and the ethanol:lipid molar ratio was 24 and 48 and the reaction time was 60 min. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 38Citation - Scopus: 43Characterization and Performance Evaluation of Pt[sbnd]ru/C[sbnd]tio2 Anode Electrocatalyst for Dmfc Applications(Elsevier Ltd., 2017) Erçelik, Mustafa; Özden, Adnan; Şeker, Erol; Çolpan, C. ÖzgürIn this study, the effect of introduction of titania (TiO2) material into Pt[sbnd]Ru/C anode electrocatalyst on the performance of direct methanol fuel cells (DMFCs) was investigated. TiO2 materials were first synthesized applying a sol–gel method and then incorporated directly into commercial Pt[sbnd]Ru/C anode electrocatalyst with different TiO2 weight ratios (5, 15, and 25 wt.%) to improve the performance of the DMFC. For comparison, the anode electrocatalysts with the same TiO2 weight ratios were also prepared using commercial TiO2 materials. The performance tests of the DMFCs based on these composite anode electrocatalysts were conducted and their performances were also compared to that of a DMFC based on a traditional anode electrocatalyst (Pt[sbnd]Ru/C) under various operating conditions. In addition, 4 h short-term stability tests were conducted for all the manufactured DMFCs. The highest power densities were found as 705.12 W/m2 and 709.32 W/m2 at 80 °C and 1 M for the DMFCs based on Pt[sbnd]Ru/C[sbnd]TiO2 anode electrocatalysts containing 5 wt.% of commercial and in-house TiO2, respectively. The results of the short-term stability tests showed that introduction of 5 wt.% of commercial TiO2 into commercial Pt[sbnd]Ru/C anode electrocatalyst improved its stability characteristics significantly.Article Citation - WoS: 39Citation - Scopus: 44Layer-By Surface Modification of Polyethersulfone Membranes Using Polyelectrolytes and Agcl/Tio2 Xerogels(Elsevier Ltd., 2015) Kaner, Papatya; Johnson, Daniel J.; Şeker, Erol; Hilal, Nidal; Alsoy Altınkaya, SacideIn this study, the layer-by-layer (LbL) assembly method was employed to modify a commercial polyethersulfone (PES) membrane by successive adsorption of chitosan and alginate as cationic and anionic polyelectrolytes. To enhance anti-biofouling property, pure, PEG mixed and PEGylated AgCl/TiO2 xerogels were incorporated solely in the top layer of the LbL-modified membranes. Organic and biological foulings were addressed separately using alginate and Escherichia coli bacteria suspensions as the organic and biological model foulants, respectively. LbL-modifying the commercial PES membrane successively with chitosan and alginate polyelectrolyte multilayers prevented organic fouling extensively. In addition, we found that AgCl/TiO2-incorporated membranes show higher water permeability and improved resistance to biological fouling as compared to the PES membrane. Silver amounts in consecutively collected permeate samples were quantified by ICP-MS analysis to assess the stability of AgCl/TiO2-incorporated layers. Silver loss per filtration cycle followed an increasing trend initially, up to a filtration volume totaling 3000L/m2, leading to 4.2% reduction in the immobilized silver amount. After that, silver loss per filtration cycle stabilized at ~7.44μg/L, which extrapolates to ~265 days time-span for the remaining silver to be released at a filtration rate of ~1000L/m2 h. Antibacterial activity tests showed that AgCl/TiO2-incorporated layers do not permit bacterial growth on the membrane surface.Article Citation - WoS: 23Citation - Scopus: 24Epoxidation of Propene by High-Throughput Screening Method Over Combinatorially Prepared Cu Catalysts Supported on High and Low Surface Area Silica(Springer Verlag, 2012) Düzenli, Derya; Şeker, Erol; Senkan, Selim; Önal, IşıkGas phase epoxidation of propene using molecular oxygen was studied by use of a high-throughput testing technique. A large number of catalysts including promoted and un-promoted Cu were synthesized in a much faster combinatorial fashion using a sol-gel method. Metal catalysts supported on high and low surface area silica were tested and ranked in a high-throughput activity and selectivity testing apparatus at different experimental conditions such as reaction temperature and reactant gas ratio. The amount of Cu loading and the addition of alkali promoters such as K and Li resulted in different tendencies in consumption rate for both silica materials. The maximum PO production rate was obtained as 25.82 μmol/g/ cat./min (2.90 % conv. and 20.49 % selectivity) for 3 % Cu-2.25 % K catalyst supported on high surface area silica. There was no noticeable difference in structural and chemical properties of catalysts after modification with K when examined by XRD and TEM; however, the overall activation energy of un-modified catalysts (92 kJ/mol) decreased to 71 kJ/mol for K-modified catalyst. There was negligible difference between the activation energies calculated for PO production (75 vs. 77 kJ/mol).Article Citation - WoS: 12Citation - Scopus: 13Single Step Sol-Gel Made Silver Chloride on Titania Xerogels To Inhibit E. Coli Bacteria Growth: Effect of Preparation and Chloride Ion on Bactericidal Activity(Springer Verlag, 2011) Tuncer, Mert; Şeker, ErolWe report the antibacterial efficacies of silver and/or silver chloride containing titania xerogels synthesized with modified single step sol-gel methods against Escherichia coli bacteria. As the silver loading in TiO 2 increases, the amount of the xerogel required to inhibit the growth of the bacteria decreases and also we found that pure TiO2 was not bactericidal. Among modified single step sol-gel methods used in this study, the additional HCl treatment sol-gel route III was very effective to obtain only AgCl crystallites in TiO2. Based on viable cell count method, 0.125 g/L of 29%Ag/TiO2 (made with HNO3 sol-gel route I) was enough to inhibit the growth of E. coli whereas 0.6 g/L of 29%Ag/TiO2 (made with the additional HCl treatment sol-gel route III) was required. However, antibacterial activity of 29%Ag/TiO2 (made with HNO 3 sol-gel route I) after 6 usages was the same as 29%Ag/TiO 2 (made with the additional HCl treatment sol-gel route III).Article Citation - WoS: 36Citation - Scopus: 39Transesterification of Sunflower Oil on Single Step Sol-Gel Made Al2o3 Supported Cao Catalysts: Effect of Basic Strength and Basicity on Turnover Frequency(Elsevier Ltd., 2012) Umdu, Emin Selahattin; Şeker, ErolThe activities of single step sol-gel made calcium oxide on alumina catalysts were studied as a function of CaO loading, methanol/oil molar ratio and the amount of the catalyst in the transesterification of sunflower oil at 50°C. Also, the turnover frequency (TOF) of the catalysts was calculated to better understand the relationship between the basicity/basic strength and the catalytic activity. From volcano curve (TOF vs. basic strength), it was found that under 50°C and methanol/oil molar ratio of 9, 60% CaO/Al 2O 3 had the highest turnover frequency, 0.028s -1, whereas 85% CaO/Al 2O 3 showed the highest biodiesel yield, ∼96.6%, but TOF obtained on it was 0.012s -1. It seemed that 60% CaO catalyst had the proper basic strength to obtain the highest TOF. © 2011 Elsevier Ltd.Conference Object Citation - WoS: 22Citation - Scopus: 22Propylene Epoxidation: High-Throughput Screening of Supported Metal Catalysts Combinatorially Prepared by Rapid Sol-Gel Method(Springer Verlag, 2010) Önal, Işık; Düzenli, Derya; Seubsai, Anusorn; Kahn, Michael; Şeker, Erol; Senkan, Selim M.The gas phase oxidation of propylene using molecular oxygen was studied on a variety of supported metal catalysts. The most promising PO activity was obtained for Cu supported on high surface area SiO 2 and the multimetallic systems exhibit synergistic effects that increased the desired PO yield by several folds for Ag promoted with Cu on SiO 2 after screening a large number of catalysts by a high throughput testing technique. © 2009 Springer Science+Business Media, LLC.Article Citation - WoS: 273Citation - Scopus: 327Transesterification of Nannochloropsis Oculata Microalga's Lipid To Biodiesel on Al2o3 Supported Cao and Mgo Catalysts(Elsevier Ltd., 2009) Umdu, Emin Selahattin; Tuncer, Mert; Şeker, ErolIn this study, we present the activities of Al2O3 supported CaO and MgO catalysts in the transesterification of lipid of yellow green microalgae, Nannochloropsis oculata, as a function of methanol amount and the CaO and MgO loadings at 50 °C. We found that pure CaO and MgO were not active and CaO/Al2O3 catalyst among all the mixed oxide catalysts showed the highest activity. Not only the basic site density but also the basic strength is important to achieve the high biodiesel yield. Biodiesel yield over 80 wt.% CaO/Al2O3 catalyst increased to 97.5% from 23% when methanol/lipid molar ratio was 30.Article Citation - WoS: 20Citation - Scopus: 19The Catalytic Reforming of Bio-Ethanol Over Sio2 Supported Zno Catalysts: The Role of Zno Loading and the Steam Reforming of Acetaldehyde(Elsevier Ltd., 2008) Şeker, ErolIn this study, the activity and the product distributions of sol-gel made SiO2 supported ZnO catalysts in the steam reforming of ethanol and acetaldehyde is presented as a function of ZnO loading and temperature. We show that although highly dispersed ZnO in SiO2 (upto 50% ZnO loading) can be prepared using a single step sol-gel method, a precise control of crystallite size could not be achieved. From CO2 TPD measurements, we found that the basic site densities of ZnO/SiO2 catalysts stays < 0.05 μ mol / m2 and do not increase linearly with ZnO loading. The highest basic site density among the catalysts occurs on pure ZnO. All ZnO/SiO2 catalysts are active at 350 °C whereas pure ZnO catalyst is active at 450 °C. Iso-conversion activity tests show that ethanol steam reforming activities of the catalysts seem to be dependent on the ZnO crystallite size rather than the basic site density of the catalysts when the surface coverage of the basic site density is < 0.32 % but acetone is not formed only on catalysts with ZnO crystallite size < 5 nm regardless of their basic site densities. Interestingly, we found that ethanol was mostly dehydrogenated to acetaldehyde and hydrogen although H2O/C2H5OH molar ratio in the feed was 12. CO was not also produced in the steam reforming of ethanol over all the catalysts. Acetone and propene are produced from acetaldehyde as observed in the steam reforming of acetaldehyde. The steam reforming of acetaldehyde as compared to its decomposition was found to be more favorable over the catalysts with small ZnO crystals, such as 30% and 50% ZnO catalysts.