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    Catalytic activities of non-noble metal catalysts (Cu-B, Fe-B, and Ni-B) with C.Vulgaris microalgal strain support modified by using phosphoric acid for hydrogen generation from sodium borohydride methanolysis
    (Pergamon-Elsevier Science Ltd, 2019) Bekirogullari, Mesut
    In this study, a novel microalgae based support material was developed and applied. The Chlorella Vulgaris microalgal strain was modified by treating the algal biomass with phosphoric acid for proton binding process (CVMS-H3PO4). Ultimately, the CVMS-H3PO4-metal (Cu-B, Ni-B, or Fe-B) catalysts were used as highly efficient solid catalysts to produce hydrogen from the methanolysis of NaBH4. Once the superior metal was identified, the NaBH4 concentration, metal percentage in the supported-catalyst, catalyst amount, and temperature effect on the methanolysis reaction was thoroughly investigated. The maximum hydrogen production rate for the CVMS-H3PO4 supported-catalyst was obtained with the use of 20% Cu metal at 30 degrees C and it was found to be 6500 mL/min/g(cat). In addition, the maximum hydrogen production rate for the CVMS-H3PO4 supported-catalyst was attained with the use of 20% Cu metal at 60 degrees C and it was found to be 21176 mL/min/g(cat). Also, the activation energy was determined as 23.79 kJ/mol. The re-usability studies of the microalgal strain supported-Cu-B catalyst were performed and it was found that there was no decrease in % conversion for this catalyst. XRD, FTIR, SEM, and ICP-MS analysis were carried out to characterize CVMS-H3PO4-CuB catalyst thoroughly. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Chlorella vulgaris microalgae strain modified with zinc chloride as a new support material for hydrogen production from NaBH4 methanolysis using CuB, NiB, and FeB metal catalysts
    (Pergamon-Elsevier Science Ltd, 2020) Saka, Cafer; Kaya, Mustafa; Bekirogullari, Mesut
    This study aims to produce hydrogen (HG) from sodium borohydride (NaBH4) methanolysis using CuB, NiB or FeB catalysts prepared with a different support material including C. vulgaris microalgae strain modified using zinc chloride (CMS-ZnCl2). The NaBH4 concentration, metal percentage in the supported-catalyst, the optimal ZnCl2 percentage, and temperature effect on the NaBH4 methanolysis were investigated. X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Scanning electron microscopy (SEM) analysis were performed for the CMS-ZnCl2-CuB characterization. Also, the low activation energy (Ea) of 22.71 kJ mol(-1) was found with the supported catalyst obtained. Under the same conditions, nearly 100% conversion was achieved in the reusability experiments repeated five times, but a gradual decrease in catalytic activity was observed after each use. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Dual-function macroalgae biochar: Catalyst for hydrogen production and electrocatalyst
    (Elsevier Sci Ltd, 2024) Bekirogullari, Mesut; Abut, Serdar; Duman, Fatih; Hansu, Tulin Avci
    In the current study, Enteromorpha intestinalis, a green macroalgae, has been utilized as a substrate to synthesise a new environmentally friendly and cheap dual -functional (catalyst and electrocatalyst) material. The catalyst was used for efficient hydrogen production from alcoholises sodium borohydride and as an anode catalyst for direct methanol fuel cell applications. At the catalyst synthesis stage, orthogonal arrays of Taguchi is used to find the optimum levels of independent variables for the superior catalyst performance that bears the modest kinetics. The experiments performed in accordance with the L16(45) type orthogonal array. The samples treated at relatively moderate acid, impregnation temperature, impregnation time, burning temperature and burning time showed higher catalytic activities with Exp(5) presenting the optimal catalytic activity followed by Exp(1), Exp (15), Exp(8) and Exp(12), respectively. The experimental levels of coded variables (acid molarity, impregnation temperature and time, burning temperature and time) for Exp(5) were 3 M, 50 C-degrees, 24 h, 500 C-degrees and 2 h., respectively. These finding suggest that providing maximum levels of each of independent variable will not provide high catalytic activity. Taking into account the binary and ternary interactions is an efficient way to determine optimal level of each parameter with regards to maximum hydrogen production rate. The morphological and structural characterization of the optimal catalyst was finally carried out with SEM- EDS, XRD and FT-IR. CV and EIS measurements were taken to determine the electrocatalytic activity of final biochar. Experimental studies revealed that the utilization of E. intestinalis-based electrocatalyst as an anode catalyst for direct fuel cell applications is promising. By employing advanced Taguchi -based experimentation, this research establishes the optimum levels of independent variables, enhancing the catalyst's performance, and highlighting a novel approach to modest kinetics improvement.
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    Effect of stirring speeds on biodiesel yield using an innovative oscillatory reactor and conventional STR (A comparative study)
    (Elsevier Sci Ltd, 2022) Khelafi, Mostefa; Djaafri, Mohammed; Kalloum, Slimane; Atelge, M. R.; Abut, Serdar; Dahbi, Abdeldjalil; Bekirogullari, Mesut
    This paper aims to study the effect of stirring speed on biodiesel yield using an innovative oscillating reactor compared to the conventional stirring tank reactor. The efficiency of the invented reactor was compared with the conventional system, employing two catalysts (a homogeneous catalyst and a heterogeneous bio-catalyst). The obtained results showed that under low agitation speed of 50 rpm, the invented oscillating reactor is more efficient than the conventional system with a biodiesel yield of 93% compared to 90.13% using the heterogeneous catalyst and 93.53% compared to 92.7% using the homogeneous catalyst respectively. As for the higher stirring speeds, the conventional system was found to be slightly more efficient than the oscillating reactor when using the heterogeneous biocatalyst (96.03% against 94.42%) while the contrary was observed when using the homogeneous catalyst (94.43% against 95%). However, this slight increase in the biodiesel yield at higher speeds results in increasing production costs. This indicates that biodiesel production using the innovative oscillating reactor at low speeds is more economically viable. The characteristics of the produced biodiesel using the invented reactor were in agreement with the ASTM D6751 biodiesel standards. Moreover, a two-way ANOVA analysis was conducted to compare between groups that have been split on two independent variables as reactor type and stirring speed. The statistical analysis proved that the invented oscillating reactor performs better when using heterogeneous catalysts at low stirring speed levels. This study suggests that the biodiesel yield of the innovative reactor can be further enhanced by introducing a baffle system which provides a relatively larger contact surface area. Similarly, synthesis of other heterogeneous bio-catalysts derived from the date seed of another date palm cultivar can be tested to further improve the biodiesel yield.
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    Highly efficient Co-B catalysts with Chlorella Vulgaris microalgal strain modified using hydrochloric acid as a new support material for hydrogen production from methanolysis of sodium borohydride
    (Pergamon-Elsevier Science Ltd, 2019) Bekirogullari, Mesut; Kaya, Mustafa; Saka, Cafer
    In this study, we report for the first time the use of C. Vulgaris microalgal strain containing cellulose in the modified form to be used as a catalyst support material for the production of hydrogen from the methanolysis reaction of sodium borohydride (NaBH4). Acetic acid, phosphoric acid, and hydrochloric acid (HCI) at different concentrations and impregnation times were used for the protonation of cellulose in the microalgal strain. The cobalt ions were added to this modified support material and, C.Vulgaris microalgal strain-supported Co-B catalyst was obtained. XRD, BET, FTIR, XPS, ICP-MS, TEM, and SEM-EDX analysis were carried out for characterization of the sample. The maximum hydrogen production rate from the methanolysis reaction of NaBH(4 )with this catalyst was 13215 ml min( )(-1)g(cat)(-1) In addition, the activation energy was determined as 25.22 kJ/mol. At the same time, reusability studies of the microalgal strain-supported Co-B catalyst were performed and it was found that there was no decrease in the % conversion for this catalyst, while the activity decreased. XRD, BET, FTIR, XPS, ICP-MS, TEM, and SEM-EDX. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Highly efficient CoB catalyst using a support material based on Spirulina microalgal strain treated with ZnCl2 for hydrogen generation via sodium borohydride methanolysis
    (Wiley-Hindawi, 2019) Kaya, Mustafa; Bekirogullari, Mesut; Saka, Cafer
    In the study, a different support material based on ZnCl2-treated Spirulina microalgal strain (SSMS-ZnCl2) was prepared. Then, the SSMS-ZnCl2-CoB catalysts were used as a very efficient catalyst to produce hydrogen via the SB methanolysis. The SB concentration, Co metal percentage in the supported-catalyst, ZnCl2 concentration, ZnCl2 impregnation time, temperature, and reusability experiments were performed. The maximum hydrogen generation rates (HGR) for the SSMS-ZnCl2-CoB at 30 degrees C and 60 degrees C were found to be 9266 and 36 366 mL min(-1) g(cat)(-1), respectively. In addition, TOF values for 30 degrees C and 60 degrees C were calculated 33 and 110 L center dot mol(H2)center dot mol(Co)(-1)center dot min(-1) for the methanolysis of SB with SSMS-ZnCl2-CoB catalyst. The activation energy was 31.13 kJ mol(-1). The reusability experiments were repeated five times under the same conditions. The almost 100% conversion was obtained at each use. XRD, FTIR, TEM, SEM-EDX, and ICP-MS analysis were performed for SSMS-ZnCl2-CoB characterization.
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    Hydrogen production from sodium borohydride by ZnCl2 treated defatted spent coffee ground catalyst
    (Pergamon-Elsevier Science Ltd, 2020) Bekirogullari, Mesut
    In the current study, a novel Zinc (Zn) treated defatted spent coffee ground catalyst (DSCG) was developed and applied successfully for hydrogen production from sodium borohydride (NaBH4). In order to synthesise the Zn treated DSCG catalyst, different Zn metal concentrations (10-50%), impregnation temperatures (50-90 degrees C) and burning temperatures (400 -1000 degrees C) were tested. It was found that 40 wt % ZnCl2, 75 degrees C impregnation temperature and 1000 degrees C burning temperature provide the superior catalyst performance. Once the optimal catalyst preparation conditions were determined, the effect of NaBH4 concentration (1-7.5% NaBH4), catalyst amount (0.05-0.2 g catalyst) and temperature (30 degrees C-60 degrees C) on alcoholises reaction of sodium borohydride was comprehensively examined. The maximum hydrogen production rates (HPRs) for the Zn treated DSCG (40 wt % Zn) catalyst at 30 degrees C and 60 degrees C were found to be 8510.1 and 12,364 ml min(-1)g(cat)(-1), respectively. A detailed characterization of the catalyst was performed through use of Brunauer-Emmett-Teller analyser (BET), Fourier Transform-Infrared Spectrometer (FTIR), Thermogravimetric Analyser (TG), Scanning Electron Microscope combined with Energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The activation energy was determined to be 7.87 kJ mol(-1) . Additionally, the reusability of Zn treated DSCG catalyst was examined five times under same operating conditions. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Investigation of Hydrogen Production from Bio-Oil Substances Using Aspen Plus
    (Gazi Univ, 2020) Bekirogullari, Mesut; Kaya, Mustafa
    In this study, a base-case process diagram was established and simulated in Aspen Plus to explore effect of temperature on hydrogen production. The evaluated compounds were acetic acid, ethylene glycol, acetone, ethyl acetate and m-xylene, which are representative of the main bio-oil derived components. UNIQUAC was used as property model to simulate the process in Aspen Plus. Bio-oil components conversions, mass and molar fractions, and the molar flow rates of hydrogen were studied over a range of temperature starting from 30 degrees C to 1100 degrees C. The results obtained from the simulation suggest that all of the five components reach approximately 100% conversion with acetic acid to be the first to reach 100% conversion. The reactor temperature for 100% conversion of the components increases in the following orders: acetic acid > ethylene glycol > ethyl acetate > acetone > m-xylene. It was found that at high temperatures m-xylene was able to produce highest mass fraction of hydrogen and the order was the following: m-xylene> ethyl acetate > acetone > ethylene glycol > acetic acid. Such simulation approaches can be exploited for robust design and optimization of hydrogen production reducing operating cost and taking this process one step closer to industrialization.
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    Lake sediment based catalyst for hydrogen generation via methanolysis of sodium borohydride: an optimization study with artificial neural network modelling
    (Springer, 2021) Bekirogullari, Mesut; Abut, Serdar; Duman, Fatih; Hansu, Tulin Avci
    In the current study, lake sediment, a heterogeneous and complex organic matter, utilized as a catalyst upon acid treatment for efficient hydrogen generation from sodium borohydride. In order to synthesise the catalyst that bears the best catalytic activity, ANOVA, cubic stepwise linear regression and artificial neural network optimization techniques were applied to determine the optimal level of treatment parameters. The results suggest that only Taguchi orthogonal arrays method was able to accurately reflect the overall surface of objective variable. Among the 16 catalyst samples Exp(15) showed the superior catalytic activity followed by Exp(13), Exp(12), Exp(14) and Exp(7). The minimum reaction completion time for Exp(15) corresponding to maximum hydrogen production rate of 3247.15 mL/min/gcat was 2.25 min. A detailed characterization of the final product was carried out by using a Fourier transform infrared spectra (FTIR-Perkin Elmer), an X-ray diffractometer (Bruker D8 Advance XRD), a scanning electron microscopy and energy dispersive X-ray spectroscopy. [GRAPHICS] .
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    Models of microalgal cultivation for added-value products - A review
    (Pergamon-Elsevier Science Ltd, 2020) Bekirogullari, Mesut; Figueroa-Torres, Gonzalo M.; Pittman, Jon K.; Theodoropoulos, Constantinos
    Microalgae are considered a promising feedstock for biorefineries given that their chemical composition - rich in carbohydrate and lipid can be directed towards the co-production of various value-added fuels and chemicals. Production of microalgal biomass for biorefinery purposes requires the identification and establishment of op-timal cultivation systems, a crucial yet complicated task due to the numerous factors (e.g. media composition, light, temperature) that simultaneously regulate biomass growth and intracellular composition. Modelling these biological processes, taking into account a single or multiple growth-limiting factors, offers a valuable tool to simulate, design and optimise the dynamics of microalgae cultivation. This review provides an overview of existing models developed to describe microalgal growth processes at the macroscopic scale (also termed black box models) and discusses their formulation in detail. The black-box kinetic modelling frameworks are compiled into single-factor (6 formulations) and multiple-factor (32 formulations further divided into non-interactive, additive, and interactive) growth kinetic models, as reported in more than 80 studies, for the prediction of biomass growth as a function of major operational factors such as media composition (e.g. nutrient concentration) and environmental factors (e.g. transient light and temperature). In addition, the review focuses on those models that further account for the production dynamics of two microalgal intracellular products with renowned potential as biorefinery substrates: carbohydrate and lipid molecules. Models of microalgal cultivation dynamics offer a robust engineering tool to understand the natural yet complex responses of microalgae to their growing environment and can help if used appropriately to optimise microalgae cultivation and increase the economic viability and sustainability of microalgal systems.
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    Spirulina microalgal strain as efficient a metal-free catalyst to generate hydrogen via methanolysis of sodium borohydride
    (Wiley-Hindawi, 2020) Saka, Cafer; Kaya, Mustafa; Bekirogullari, Mesut
    Metal-free catalyst based on Spirulina platensis microalgae (SPM) is protonated by phosphoric acid (H3PO4) treatment (SPM-H3PO4). The microalgae sample is then exposed to heating with different temperatures including 200, 300, and 400 degrees C (SPM-H3PO4-H). The modified microalgae sample based on Spirulina platensis as a catalyst is directly used to generate hydrogen via the methanolysis of sodium borohydride (MSB). The activation temperature, activation time, NaBH4 concentration, catalyst amounts, temperature and reusability tests were carried out. The maximum hydrogen production rates (HGR) obtained for SPM-H3PO4-H at temperatures of 30 degrees C and 60 degrees C were 3975 and 9600 mLmin(-1)gcat(-1), respectively. At the same time, the activation energy(Ea) of 17.78 kJ mol(-1) was obtained. Reusability experiments were performed for this microalgae-based metal-free catalyst. XRD, SEM, FTIR, BET, and TEM analyzes were performed for characterization of these metal-free catalyst samples.
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    Spirulina Platensis microalgae strain modified with phosphoric acid as a novel support material for Co-B catalysts: Its application to hydrogen production
    (Pergamon-Elsevier Science Ltd, 2020) Saka, Cafer; Kaya, Mustafa; Bekirogullari, Mesut
    Spirulina platensis is defined as the dried biomass of cyanobacteria in commercial use and is biomass with high carbon content. Spirulina platensis microalgae strain supported-CoB catalysts to produce hydrogen from sodium borohydride (NaBH4) were prepared for the first time. The Spirulina platensis microalgae strain was modified with phosphoric acid (H3PO4) to proton. Then, the supported catalyst was performed to produce hydrogen from NaBH4 hydrolysis. The optimum H3PO4 concentration, optimum Co amount, and optimum impregnation time of the H3PO4 with the microalgae strain were investigated. The maximum hydrogen production rate for the 30% CoB catalyst supported on microalgae strain treated with H3PO4 was found to be 3940 mL min-lecatalyst. X-ray powder diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and scanning electron microscope (SEM) analysis were performed for characterization of CoB catalyst supported on Spirulina microalgae strain. After four consecutive uses, the performance and conversion values of this catalyst were investigated. At the same time, the effect of temperature on the hydrogen production from this hydrolysis reaction was examined. The activation energy with the CoB catalyst supported on Spirulina microalgae strain was calculated as 35.25 kJ mol(-1). According to the kinetic model of a power law, n value was found as 0.25 for kinetic studies. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Synthesis of waste eggshell-derived Au/Co/Zn/ eggshell nanocomposites for efficient hydrogen production from NaBH4 methanolysis
    (Pergamon-Elsevier Science Ltd, 2024) Bekirogullari, Mesut
    Developing new pathways to transform biological wastes into value-added products is inevitable in order to mitigate environmental pollution and providing sustainability. Utilisation of eggshell as a substrate, a naturally abandoned organic-inorganic waste, was explored in this study. Herein, Au/Co/Zn/eggshell nanocomposites were synthesised by utilizing waste eggshell as substrate. At the experimental stage, different metal combinations namely unary, binary and ternary combination of Co, Zn and Au and different ratios ranges from %10 to %50 were tested. The catalytic activity of the synthesised materials were investigated in terms of hydrogen production from NaBH4 methanolysis. The catalyst fabricated with the addition of %40 Co + %40 Zn + 3 ppm Au showed the best catalytic activity and the reaction completion time was as low as 2.4 min. The results revealed that the fabricated catalyst showed a superior catalytic activity with the maximum hydrogen production rate of 4394.6 mL/min/gcat. The obtained maximum hydrogen production rate is highly compatible with the existing literature. Different NaBH4 concentrations and catalyst concentrations were also tested to investigate the fabricated catalyst behaviour. The fabricated catalyst was also experimented in different temperatures range from 30 degrees C to 60 degrees C to determine the Arrhenius kinetics and subsequently activation energy. The activation energy was calculated to be 13.25 kJ/mol. SEM-EDX, BET, XRD and FT-IR analysis were finally performed to determine morphological and structural characterization of the superior catalyst. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.