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Anticancer activities of bioactive peptides derived from rice husk both in free and encapsulated form in chitosan
(Elsevier Science Inc, 2021) Ilhan-Ayisigi, Esra; Budak, Gozde; Celiktas, Melih Soner; Sevimli-Gur, Canan; Yesil-Celiktas, Ozlem
Cereal grain-derived protein hydrolysates exert beneficial effects for human health, thus utilization of by-products with high protein content has drawn attention. In this study, hot water extraction of rice husk has been optimized to obtain protein hydrolysate with the highest anticancer activity. The optimum protein value was obtained as 2.40 g/L corresponding to 43.2 g protein/kg dried rice husk under the conditions of 60 degrees C, 2.0 mL/min flow rate and pH 10.0. The protein hydrolysate was encapsulated with chitosan, where the mean particle size of protein hydrolysate (0.3 %) loaded chitosan nanoparticles was 256.4 +/- 33. 4 nm with 89 % encapsulation efficiency and a 65% release at the end of 6 days. Cytotoxicity assays showed that the lowest cell viabilities have been achieved with A549 and MCF7 cells with IC50 values of 1.98 and 3.58 mu g/mL, respectively, whereas nuclear fragmentation and apoptotic bodies were observed through Hoechst 33342 staining. The cytotoxic effect might be associated with the wide variety of peptide/protein subunits ranging from 10 kDa to more than 180 kDa in the protein hydrolysate of rice husk. (C) 2021 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Bioconversion of hazelnut shell using near critical water pretreatment for second generation biofuel production
(Elsevier Sci Ltd, 2020) Uyan, Merve; Alptekin, Fikret Muge; Cebi, Dilvin; Celiktas, Melih Soner
The global energy deficiency and depletion of fossil fuels have raised concerns leading to a wide scale examination of alternative and renewable energy sources. Lignocellulosic biomass that is one of the renewable energy sources has major potential in the world and it has a wide variety of sources including agricultural residues such as cotton stalk, corn stover, wheat straw, etc. Including over 65% cellulose and hemicelluloses content, these materials can be hydrolyzed into monomeric sugars and then can be converted into biofuels and other industrial products. the main objective of this study is bioethanol production with bioconversion of lignocellulosic biomass, namely hazelnut shell. in order to efficiently utilize this raw material for ethanol production by degrading the lignocellulosic structure, an effective pretreatment is required. LHW, a near critical water pretreatment method, is chosen for this particular research due to its unique environmental and economic properties. the experiment design was prepared with Response Surface Estimation Method (RSM) by Design Expert software. the experiment parameters were selected as temperature (100-200 degrees C), pressure (80-200 bar) and flow rate (2-8 ml/min). the optimum condition (OC) for the process was determined as 138 degrees C, 2 ml/min and 200 bar according to the Dinitrosaliclic acid (DNS) method. Additionally, in order to achieve maximum ethanol concentration, the condition producing maximum reducing sugar content is determined. Separated hydrolysis and fermentation (SHF) process was used for bioethanol production. Enzymatic hydrolysis was conducted with a part of solid residue obtained from the maximum ethanol condition (MEC) for bioethanol production. MEC is 200 degrees C, 2 ml/min and 200 bar. Under MEC, at the end of the fermentation process maximum ethanol yield was 44.89% with 0.5 g of solid loading. the main purpose of the study is to determine the effects of different solid loading rates in the enzymatic hydrolysis stage of SHF process to ethanol production as a result of fermentation. There are several pretreatment methods for this process. It is concluded that the superior qualifies of LHW pretreatment in means of environmental friendliness, non-toxic and non-corrosive byproducts, water usage instead of other chemical additives, degradation of lignocellulosic structure and low cost were suitable for the intended purpose of bioethanol production using hazelnut shell.
Cascade processing of wheat bran through a biorefinery approach
(Pergamon-Elsevier Science Ltd, 2014) Celiktas, Melih Soner; Kirsch, Christian; Smirnova, Irina
Structural characteristics of wheat bran such as surface area, crystallinity, cellulose, hemicellulose, and lignin content significantly affect the yield of biorefinery products such as protein, fermentable sugar and lignin. The aim of the study was to use a sequence of high pressure extraction and hydrolysis processes in a cascade to create high potential value added products, namely, proteins, fermentable sugars and lignin. In the present study, four different sets of experiments were carried out step by step in a cascade sequence. The main experiments were the sequential extraction and hydrolysis which were optimized using design of experiments. Protein extraction from wheat bran was performed in a fixed bed reactor and was maximized to 1.976 g/L at the elicited optimum conditions which were 80 degrees C, pH 9.3 for a duration of 30 min. In the sequential experiment, process parameters such as temperature, flow rate and duration were optimized for liquid hot water (LHW) hydrolysis. The maximum reducing sugar concentration was 200 g/kg which corresponded to 34% per dry biomass obtained at a flow rate of 5 ml/min, temperature of 210 degrees C during a 45 mm treatment. The following step was enzymatic hydrolysis to saccharify the cellulose under high pressure, where the independent variables were pressure, temperature and process time in order to ascertain the process conditions maximizing the reducing sugar content, where a positive correlation was observed between the solid-liquid loading ratio and reducing sugar yield. In the final step, the lignin content of all analyzed lignin fraction was found 70% (w/w). (C) 2014 Elsevier Ltd. All rights reserved.
Combined biofuel production from cotton stalk and seed with a biorefinery approach
(Springer Heidelberg, 2020) Uyan, Merve; Alptekin, Fikret Muge; Bastabak, Benginur; Ozgul, Sevim; Erdogan, Baris; Ogut, Tuba Ceren; Celiktas, Melih Soner
Due to usage of fossil fuels, the depletion of world crude oil reserves and increased deteriorating climate conditions have reached a high level. These circumstances have led researches to search for alternative and efficient fuels. the main biofuels considered are bioethanol and biodiesel. in this study, ethanol and biodiesel production from cotton stalk and seed were aimed using liquid hot water (LHW) along with consecutive processes, where separate saccharification and fermentation (SHF) process was carried out. the maximum ethanol concentrations of 0.348 g/L and 0.721 g/L were achieved at 24 h and 72 h, respectively. For biodiesel conversion, cottonseed oil was subjected to transesterification, where the main interest was to utilize the by-product, glycerol. Three different glycerol concentrations were investigated in terms of ethanol fermentation using Escherichia coli K1 active culture. the maximum ethanol concentration of 0.415 g/L was achieved at 20 mL glycerol concentration for 48 h. Overall, cotton stalk and seed have the potential to be utilized on an industrial scale.
Conversion of model biomass to carbon-based material with high conductivity by using carbonization
(Pergamon-Elsevier Science Ltd, 2019) Celiktas, Melih Soner; Alptekin, Fikret Muge
Biomass materials are renewable sources that abundant worldwide due to natural plants and living organisms. Lignocellulosic biomass can be categorized as hardwood, softwood, agricultural wastes, and grasses. Agricultural residues those which of them have importance due to being produced in huge amounts in the worldwide annually. Food wastes and agricultural wastes are utilized either alternative use such as generating energy, fuels or disposal. However, disposal of these residues is follow out either scraping or burning way. This study aims to convert industrial agricultural origin biomass by using hydrothermal carbonization method to carbon-based material having high conductivity for use in supercapacitor production by using different activating chemicals. Hydrothermal carbonization was applied to different biomass samples such as nutshell, hazelnut shell, and corn cob. the elemental analysis of the obtained biochar was carried out and it was determined that the highest source of biomass was corn cob. the selected biochar has been chemically activated with different chemicals such as KOH, NaOH, H3PO4 and, ZnCl2. Advanced carbonization of activated biochar was carried out at 500, 600, 700 and 800 degrees C with 1, 1.5 and 2-h retention times. the resulting carbon-based products were mixed with KBr and identical pellets were prepared and their electrical conductivity values were measured. Electrical conductivity results, NaOH-800 degrees C-2h and ZnCl2-700 degrees C-1.5 h obtained from the process prepared from the biocidal pellets were determined to have the highest conductivity value. Brunauer Emmett Teller (BET) and Scanning Electron Microscope (SEM) analyses of the samples with the highest conductivity values were performed and surface morphologies were examined. (C) 2019 Elsevier Ltd. All rights reserved.
From potential forecast to foresight of Turkey's renewable energy with Delphi approach
(Pergamon-Elsevier Science Ltd, 2010) Celiktas, Melih Soner; Kocar, Gunnur
A Delphi Survey is a series of questionnaires that allow experts or people with specific knowledge to develop ideas about potential future developments around an issue. The Delphi questionnaires were developed throughout the foresight process in relation to the responses given by participants in bibliometric and SWOT analysis conducted prior to the Delphi survey. In this paper, Turkey's renewable energy future is evaluated using the Delphi method. A two-round Delphi research study was undertaken to determine and measure the expectations of the sector representatives regarding the foresight of renewable energies. First and second round of Delphi study were carried out by using online surveys. About 382 participants responded in the first round of the Delphi questionnaire yielding a respond rate of 20.1%, whereas 325 participants responded at the second round yielding a respond rate of 84.9%. About 50% of Turkey's energy demand was foresighted to be met by renewable energies around 2030. The results showed that all types of renewable energies would not only provide economic and environmental benefits but also improve living standards. (C) 2010 Elsevier Ltd. All rights reserved.
A holistic engineering approach for utilization of olive pomace
(Elsevier Science Bv, 2015) Akay, Fazilet; Kazan, Aslihan; Celiktas, Melih Soner; Yesil-Celiktas, Ozlem
Olive pomace is a by-product of olive oil production and an important biomass for the Mediterranean countries. The aim of this study was to optimize the oil extraction from olive pomace by supercritical CO2 and utilize the remaining biomass by hydrolysis. A Box-Behnken statistical design was used to evaluate the effect of temperature (30-80 degrees C), pressure (120-300 bar) and CO2 flow rate (10-20 g/min) for 60 min. The most effective variable was pressure (p < 0.005) and optimum extraction conditions were elicited as 68 degrees C, 280 bar and 20 g/min flow rate yielding 4.8% of oil. Additionally, the effect of particle size was investigated on extraction efficiency. Indeed, the oil yield was increased to 13.8% by decreasing the particle size from 2000 to 850-500 mu m. For utilization of remaining biomass, both supercritical CO2 (SC-CO2) and hexane de-oiled pomaces were subjected to acid and enzymatic hydrolyses. Hydrolyses with 2% of sulfuric acid for 90 min yielded 12.30 and 12.65 g/l reducing sugar from SC-CO2 and hexane treated biomasses, whereas the highest reducing sugar concentrations achieved with enzymatic hydrolysis with a substrate amount of 6g, 20-27% Cellic CTec2/Novozyme 188 for 24h were 12.72 g/l and 10.13 g/l, respectively. A holistic engineering approach is proposed where supercritical CO2 can be used as a main process to extract remaining oil in olive pomace and as a pretreatment loosen the structure in order to obtain liquor which can be converted to a biofuel. (C) 2015 Elsevier B.V. All rights reserved.
A holistic engineering approach for utilization of olive pomace
(Elsevier Science Bv, 2015) Akay, Fazilet; Kazan, Aslihan; Celiktas, Melih Soner; Yesil-Celiktas, Ozlem
Olive pomace is a by-product of olive oil production and an important biomass for the Mediterranean countries. The aim of this study was to optimize the oil extraction from olive pomace by supercritical CO2 and utilize the remaining biomass by hydrolysis. A Box-Behnken statistical design was used to evaluate the effect of temperature (30-80 degrees C), pressure (120-300 bar) and CO2 flow rate (10-20 g/min) for 60 min. The most effective variable was pressure (p < 0.005) and optimum extraction conditions were elicited as 68 degrees C, 280 bar and 20 g/min flow rate yielding 4.8% of oil. Additionally, the effect of particle size was investigated on extraction efficiency. Indeed, the oil yield was increased to 13.8% by decreasing the particle size from 2000 to 850-500 mu m. For utilization of remaining biomass, both supercritical CO2 (SC-CO2) and hexane de-oiled pomaces were subjected to acid and enzymatic hydrolyses. Hydrolyses with 2% of sulfuric acid for 90 min yielded 12.30 and 12.65 g/l reducing sugar from SC-CO2 and hexane treated biomasses, whereas the highest reducing sugar concentrations achieved with enzymatic hydrolysis with a substrate amount of 6g, 20-27% Cellic CTec2/Novozyme 188 for 24h were 12.72 g/l and 10.13 g/l, respectively. A holistic engineering approach is proposed where supercritical CO2 can be used as a main process to extract remaining oil in olive pomace and as a pretreatment loosen the structure in order to obtain liquor which can be converted to a biofuel. (C) 2015 Elsevier B.V. All rights reserved.
A holistic engineering approach for utilization of olive pomace
(Elsevier Science Bv, 2015) Akay, Fazilet; Kazan, Aslihan; Celiktas, Melih Soner; Yesil-Celiktas, Ozlem
Olive pomace is a by-product of olive oil production and an important biomass for the Mediterranean countries. The aim of this study was to optimize the oil extraction from olive pomace by supercritical CO2 and utilize the remaining biomass by hydrolysis. A Box-Behnken statistical design was used to evaluate the effect of temperature (30-80 degrees C), pressure (120-300 bar) and CO2 flow rate (10-20 g/min) for 60 min. The most effective variable was pressure (p < 0.005) and optimum extraction conditions were elicited as 68 degrees C, 280 bar and 20 g/min flow rate yielding 4.8% of oil. Additionally, the effect of particle size was investigated on extraction efficiency. Indeed, the oil yield was increased to 13.8% by decreasing the particle size from 2000 to 850-500 mu m. For utilization of remaining biomass, both supercritical CO2 (SC-CO2) and hexane de-oiled pomaces were subjected to acid and enzymatic hydrolyses. Hydrolyses with 2% of sulfuric acid for 90 min yielded 12.30 and 12.65 g/l reducing sugar from SC-CO2 and hexane treated biomasses, whereas the highest reducing sugar concentrations achieved with enzymatic hydrolysis with a substrate amount of 6g, 20-27% Cellic CTec2/Novozyme 188 for 24h were 12.72 g/l and 10.13 g/l, respectively. A holistic engineering approach is proposed where supercritical CO2 can be used as a main process to extract remaining oil in olive pomace and as a pretreatment loosen the structure in order to obtain liquor which can be converted to a biofuel. (C) 2015 Elsevier B.V. All rights reserved.
Investigation of lactic acid production by pressurized liquid hot water from cultivated Miscanthus x giganteus
(Taylor & Francis Inc, 2022) Gunes, Kaniye; Sargin, Sait; Celiktas, Melih Soner
The production of lactic acid, a polylactic acid monomer from energy crop Miscanthus x giganteus lignocellulosic biomass cultivated in Izmir was investigated. Liquid hot water (LHW) pretreatment was carried out at a temperature range of 140-200 degrees C, pressure 100 to 200 bar and reaction time of 15-45 min at a fixed flow rate of 2 mL/min using D-optimal experimental plan. The optimum conditions were elicited as 140 degrees C, 100 bar and 45 minutes, yielding the highest reducing sugar content of 77.32 mg/g, whereas 1.25 mg/mL arabinose and 1.35 mg/mL xylose as monomeric sugars. Subsequently, the enzymatic hydrolysis was applied to the solid fraction. The optimum conditions for enzymatic hydrolysis were determined as 5% (w/v) solid/liquid ratio, 20 FPU/mL enzyme loading and 72 hours, revealing the highest amount of reducing sugar as 200 mg/mL. LHW hydrolysate was used as a production medium for lactic acid manufacturing in submerged fermentation by Rhizopus oryzae. The maximum lactic acid content was found to be 6.8 g/L at 24 hours, whereas the lactic acid yield was 0.28 g/L.h. The sequential design of LHW, followed by enzymatic hydrolysis and submerged lactic acid fermentation can be utilized in industry, contributing to the bioeconomy.
Miscanthus-Derived Energy Storage System Material Production
(Amer Chemical Soc, 2023) Alptekin, Fikret Muge; Dunford, Nurhan Turgut; Celiktas, Melih Soner
Carbon derived from various biomass sources has been evaluated as support material for thermal energy storage systems. However, process optimization of Miscanthus-derived carbon to be used for encapsulating phase change materials has not been reported to date. In this study, process optimization to evaluate the effects of selected operation parameters of pyrolysis time, temperature, and biomass:catalyst mass ratio on the surface area and pore volume of produced carbon is conducted using response surface methodology. In the process, ZnCl2 is used as a catalyst to promote high pore volume and area formation. Two sets of optimum conditions with different pyrolysis operation parameters in order to produce carbons with the highest pore area and volume are determined as 614 degrees C, 53 min, and 1:2 biomass to catalyst ratio and 722 degrees C, 77 min, and 1:4 biomass to catalyst ratio with 1415.4 m2/g and 0.748 cm3/g and 1499.8 m2/g and 1.443 cm3/g total pore volume, respectively. Carbon material produced at 614 degrees C exhibits mostly micro-and mesosized pores, while carbon obtained at 722 degrees C comprises mostly of meso-and macroporous structures. Findings of this study demonstrate the significance of process optimization for designing porous carbon material to be used in thermal and electrochemical energy storage systems.
Novel constitutive models, challenges and opportunities of shape memory polymer composites
(Emerald Group Publishing Ltd, 2024) Uyan, Merve; Celiktas, Melih Soner
Shape memory polymers (SMPs) are smart materials that have been widely accepted in potential applications ranging from biomedical devices to aerospace. Despite their limitations in engineering applications, SMPs have been utilized for strengthening, innovation and improvement of driving methods, leading to an increase in research on SMP composites (SMPCs). In this review, SMPs used in the production, actuation mechanisms, fabrication and testing methods of SMPCs are presented. Current and potential applications and novel constitutive models that have a very important place in elucidating the interface of SMPCs are introduced. Finally, challenges and opportunities are presented to provide future prospects for SMPCs.
Optimization of Green Extraction Techniques for Polyphenolics in Pinus brutia Bark Extract and Steam Gasification of the Remaining Fraction to Obtain Hydrogen-Rich Syngas and Activated Carbon
(American Chemical Society, 2024) Yildiz Ozturk, Ece; Secim Karakaya, Pelin; Alptekin, Fikret Muge; Celiktas, Melih Soner
Utilization of renewable resources has become imperative, and considerable efforts have been devoted to tackling diverse global sustainability challenges, which contribute to the circular economy. The focus of this work was to optimize the extraction of polyphenolic compounds in Pinus brutia bark using microwave-assisted (MAE) and ultrasonically assisted (UAE) extractions and evaluate the biological efficacies of the extracts. Additionally, the residue of the extracted pine bark was subjected to steam gasification to produce hydrogen-rich syngas and activated carbon. The optimum process parameters for MAE were determined as 70 degrees C, 10 min, and 900 W, and 987.32 mg gallic acid equivalent (GAE), 23.7 mg quercetin/g extract, and 86.2% antioxidant activity were obtained. The optimum process parameters for UAE were determined as 70 degrees C, 20 min, and 50% power, and 811.84 mg gallic acid equivalent (GAE), 30.1 mg quercetin/g extract, and 90.8% antioxidant efficiency were obtained. The extracts obtained under optimized conditions were assessed for the bioactive phenolic compounds taxifolin, (-)-catechin, (-)-epicatechin, and (-)-epicatechin gallate by ultra performance liquid chromatography (UPLC). Especially in MAE (ethanol), taxifolin content was notable (34.0 mg/g extract), followed by UAE (ethanol) (23.5 mg/g extract). Compared to MAE (ethanol) and UAE (ethanol) with regards to catechin content, 1.05 mg/g extract and 0.81 mg/g extract were obtained, respectively. Catalytic and noncatalytic steam gasification of pine bark residue yielded 57.3 and 60.8 mol % H2, respectively. In addition, excellent tar reduction was achieved through utilizing a 10% boron-modified CaO alkali catalyst, and the obtained activated carbon exhibited 1358.32 m2/g Brunauer-Emmett-Teller (BET) surface area and 1.05 cm3/g total pore volume, which has potential use as an adsorbent for removing heavy metals and electrode material for supercapacitor application.
Performance evaluation and thermal stabilization of photovoltaic panels using phase-change materials
(Pergamon-Elsevier Science Ltd, 2024) Sen, Ecem; Celiktas, Melih Soner
Photovoltaic (PV) is a widely used technology that generates power from solar energy. The solar radiations reaching PV panels are converted into electrical energy and heat, however the panel temperature increases, leading to a decrease in performance. This issue can be resolved using cooling methods. Phase -change materials (PCMs) are utilized in passive cooling methods, which do not consume energy, store the heat from the panel and cool them. In this study, sodium acetate trihydrate (PCM-1), palmitic acid (PCM-2), and a eutectic mixture of stearic acid and palmitic acid (PCM-3) were placed in a container and integrated into monocrystalline and polycrystalline PV panels to examine the impact of PCM on various performance metrics including power output, energy efficiency, and PV panel surface temperature. The experiments are carried out in Izmir, which has a hot climate condition in summer months. The solar irradiance of Izmir city and standard test condition of 1000 W/ m 2 were applied to the panels in the experiments. Results showed that the maximum temperature decreased, compared to the reference panel (without PCM), by 22.84 % and 14.4 %, respectively, when using PCM-1 and eutectic mixture in the monocrystal panel at 1000 W/m 2 in August. The power and efficiency increased by 24.97 % and 24.95 %, respectively, for the polycrystalline panel in July. These results indicate that PCMs enhanced the cooling and increased the performance of the PV panels with high surface temperatures due to intense solar irradiation.
Pressurized liquid hot water pretreatment and enzymatic hydrolysis of switchgrass aiming at the enhancement of fermentable sugars
(Taylor & Francis Ltd, 2019) Gunes, Kaniye; Yaglikci, Mine; Celiktas, Melih Soner
Pressurized Liquid Hot Water (PLHW) process is an essential and new method to remove lignin from biomass for biorefinery applications. in this study, a cascade method was investigated to obtain reducing sugars of switchgrass using optimization of PLHW and enzymatic hydrolysis. Optimization of pressurized liquid hot water and enzymatic hydrolyses were achieved by Box-Behnken design. First, pretreatments including PLHW were carried out step by step, with respect to the independent variables such as temperature (100, 140, 180 degrees C), pressure (100, 150, 200 bar) and time (20, 40, 60 min) at fixed flow rate (2 ml/min). the conditions which give the most optimized reducing sugar were 122.12 degrees C, 100 bar and 50.08 min and optimized fermentable sugar content was measured 107.49 g/l. Then, enzymatic hydrolysis was applied to solid phase with 4.8 pH citrate buffer at 50 degrees C during 24, 48 and 72 h with the help of Novozyme 188 and Celluclast enzymes. the reducing sugar amount obtained from switchgrass with enzymatic hydrolysis was measured 248.23 g/L, which means totally 355.72 g/L.
Pressurized liquid hot water pretreatment and enzymatic hydrolysis of switchgrass aiming at the enhancement of fermentable sugars
(Taylor & Francis Ltd, 2022) Gunes, Kaniye; Yaglikci, Mine; Celiktas, Melih Soner
Pressurized Liquid Hot Water (PLHW) process is an essential and new method to remove lignin from biomass for biorefinery applications. In this study, a cascade method was investigated to obtain reducing sugars of switchgrass using optimization of PLHW and enzymatic hydrolysis. Optimization of pressurized liquid hot water and enzymatic hydrolyses were achieved by Box-Behnken design. First, pretreatments including PLHW were carried out step by step, with respect to the independent variables such as temperature (100, 140, 180 degrees C), pressure (100, 150, 200 bar) and time (20, 40, 60 min) at fixed flow rate (2 ml/min). The conditions which give the most optimized reducing sugar were 122.12 degrees C, 100 bar and 50.08 min and optimized fermentable sugar content was measured 107.49 g/l. Then, enzymatic hydrolysis was applied to solid phase with 4.8 pH citrate buffer at 50 degrees C during 24, 48 and 72 h with the help of Novozyme 188 and Celluclast enzymes. The reducing sugar amount obtained from switchgrass with enzymatic hydrolysis was measured 248.23 g/L, which means totally 355.72 g/L.
A quadratic helix approach to evaluate the Turkish renewable energies
(Elsevier Sci Ltd, 2009) Celiktas, Melih Soner; Kocar, Gunnur
The first renewable energy law concerning the 'Use of Renewable Energy Resources for the Generation of Electrical Energy' was adopted from European Union regulations on 18 May 2005 in Turkey. The purpose of the Law is to expand the utilization of renewable energy resources for generating electricity. Renewables are defined in the Law as generation facilities based on wind, solar, geothermal, biomass, biogas, wave, current and tidal energy resources, hydrogen energy and hydroelectric generation facilities. The aim of the study was to use strengths, weaknesses, opportunities and threats (SWOT) analysis to identify Turkish renewable energy market strategy and perspective by focusing on four different concepts: policy, market, technology and the social dimension. Different information gathering strategies have been applied such as monitoring of all statements and press releases published in the newspapers by all Turkish renewable energy parties starting from the launch of the law, articles presented in the events between 2000 and 2008 and face-to-face interviews. Our results demonstrated the importance of technology development and knowledge creation for gaining competitiveness on the global arena and the need for a systematic approach for transforming the created know-how into economic and social benefits. (C) 2009 Elsevier Ltd. All rights reserved.
A quadratic helix approach to evaluate the Turkish renewable energies
(Elsevier Sci Ltd, 2009) Celiktas, Melih Soner; Kocar, Gunnur
The first renewable energy law concerning the 'Use of Renewable Energy Resources for the Generation of Electrical Energy' was adopted from European Union regulations on 18 May 2005 in Turkey. The purpose of the Law is to expand the utilization of renewable energy resources for generating electricity. Renewables are defined in the Law as generation facilities based on wind, solar, geothermal, biomass, biogas, wave, current and tidal energy resources, hydrogen energy and hydroelectric generation facilities. The aim of the study was to use strengths, weaknesses, opportunities and threats (SWOT) analysis to identify Turkish renewable energy market strategy and perspective by focusing on four different concepts: policy, market, technology and the social dimension. Different information gathering strategies have been applied such as monitoring of all statements and press releases published in the newspapers by all Turkish renewable energy parties starting from the launch of the law, articles presented in the events between 2000 and 2008 and face-to-face interviews. Our results demonstrated the importance of technology development and knowledge creation for gaining competitiveness on the global arena and the need for a systematic approach for transforming the created know-how into economic and social benefits. (C) 2009 Elsevier Ltd. All rights reserved.
Reply to the comments of Kucukali on "A quadratic helix approach to evaluate the Turkish renewable energies"
(Elsevier Sci Ltd, 2010) Celiktas, Melih Soner; Kocar, Gunnur
Review on Catalytic Biomass Gasification for Hydrogen Production as a Sustainable Energy Form and Social, Technological, Economic, Environmental, and Political Analysis of Catalysts
(Amer Chemical Soc, 2022) Alptekin, Fikret Muge; Celiktas, Melih Soner
Sustainable energy production is a worldwide concern due to the adverse effects and limited availability of fossil fuels, requiring the development of suitable environmentally friendly alternatives. Hydrogen is considered a sustainable future energy source owing to its unique properties as a clean and nontoxic fuel with high energy yield and abundance. Hydrogen can be produced through renewable and nonrenewable sources where the production method and feedstock used are indicators of whether they are carbon-neutral or not. Biomass is one of the renewable hydrogen sources that is also available in large quantities and can be used in different conversion methods to produce fuel, heat, chemicals, etc. Biomass gasification is a promising technology to generate carbon-neutral hydrogen. However, tar production during this process is the biggest obstacle limiting hydrogen production and commercialization of biomass gasification technology. This review focuses on hydrogen production through catalytic biomass gasification. The effect of different catalysts to enhance hydrogen production is reviewed, and social, technological, economic, environmental, and political (STEEP) analysis of catalysts is carried out to demonstrate challenges in the field and the development of catalysts.

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