Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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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: 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: 12Citation - Scopus: 13Development of Agcl-Tio2 Xerogels Entrapped Antibacterial Polyacrylonitrile Membranes: the Effect of High Salinity Water on Silver Release, Antibiofouling and Antibacterial Efficacies(Elsevier Ltd., 2020) Uz, Metin; Yaşar Mahlıçlı, Filiz; Şeker, Erol; Alsoy Altınkaya, SacideSilver-containing antibacterial membranes are commonly used to control biofouling during bacteria filtration. Unfortunately, fast and uncontrolled release of silver to water is a challenge since this causes mass accumulation of silver in water resources and insufficient long-term antimicrobial effect. To overcome these disadvantages, we propose to add AgCl-TiO2 xerogels (0–0.8 wt%) in the polyacrylonitrile membranes. The long-term silver retaining of the membranes was evaluated by measuring the silver release under filtration of deionized water in the absence and the presence of 1 M NaCl up to 5 days. The antibiofouling and the antibacterial efficacies were determined by measuring the changes in antibacterial activity and DI water flux of the membranes at the end of 5 days of E. coli filtration. The 0.2 wt% AgCl-TiO2 xerogel incorporated polyacrylonitrile membrane demonstrated a constant ~1 ?g of silver release/cm2 per filtration cycle after a total filtration of 0.05 L/cm2 with 1 M NaCl solution. Additionally, it showed antibacterial efficacy and ~100% recovery of deionized water flux by simple backwashing with water after having been used in many E. coli filtration cycles. Thus, this membrane could potentially be used up to ~5.8 years for 8000 h a year for the filtration of high salinity water. Statement of novelty: Silver-containing antibacterial membranes are commonly used to control biofouling during bacteria filtration. Uncontrolled release of silver from the membrane causes massive silver accumulation in water which in turn leads to contamination of water resources and threat to aquatic organisms. Although silver release is strongly influenced by the salinity of water, the release data was collected through filtration of pure DI water or tap water in literature. To overcome the shortcomings of the published studies, we propose to use AgCl-TiO2 xerogels in membranes due to low solubility of AgCl in water and measure the release by filtering high-salinity water. © 2020 Elsevier B.V.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: 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.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.