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    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.
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    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.
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    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.
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    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.
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    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.
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    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.