Yıldız, Güray
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Yıldız, G
Yildiz, G
Yildiz, G.
Yildiz, Guray
Yıldız, G.
Yildiz, G
Yildiz, G.
Yildiz, Guray
Yıldız, G.
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gurayyildiz@iyte.edu.tr
guryildiz@gmail.com
guryildiz@gmail.com
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03.06. Department of Energy Systems Engineering
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14
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8DECENT WORK AND ECONOMIC GROWTH
2
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9INDUSTRY, INNOVATION AND INFRASTRUCTURE
7
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26
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1615
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16
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26
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1466
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16
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15
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9953/2899
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1
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WoS Citation Count
323
Scopus Citation Count
378
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20.19
Scopus Citations per Publication
23.63
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8
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1
| Journal | Count |
|---|---|
| Journal of Analytical and Applied Pyrolysis | 5 |
| Energy and Fuels | 2 |
| Biomass Conversion and Biorefinery | 2 |
| Journal Of Cleaner Production | 1 |
| Materials | 1 |
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16 results
Scholarly Output Search Results
Now showing 1 - 10 of 16
Article Citation - WoS: 3Citation - Scopus: 3Continuous Flow Pyrolysis of Virgin and Waste Polyolefins: a Comparative Study, Process Optimization and Product Characterization(Springer, 2024) Ekici, Ecrin; Yildiz, Guray; Yildiz, Magdalena Joka; Kalinowska, Monika; Seker, Erol; Wang, JiaweiUnder optimal process conditions, pyrolysis of polyolefins can yield ca. 90 wt % of liquid product, i.e., combination of light oil fraction and heavier wax. In this work, the experimental findings reported in a selected group of publications concerning the non-catalytic pyrolysis of polyolefins were collected, reviewed, and compared with the ones obtained in a continuously operated bench-scale pyrolysis reactor. Optimized process parameters were used for the pyrolysis of waste and virgin counterparts of high-density polyethylene, low-density polyethylene, polypropylene and a defined mixture of those (i.e., 25:25:50 wt %, respectively). To mitigate temperature drops and enhance heat transfer, an increased feed intake is employed to create a hot melt plastic pool. With 1.5 g<middle dot>min-1 feed intake, 1.1 L<middle dot>min-1 nitrogen flow rate, and a moderate pyrolysis temperature of 450 degrees C, the formation of light hydrocarbons was favored, while wax formation was limited for polypropylene-rich mixtures. Pyrolysis of virgin plastics yielded more liquid (maximum 73.3 wt %) than that of waste plastics (maximum 66 wt %). Blending polyethylenes with polypropylene favored the production of liquids and increased the formation of gasoline-range hydrocarbons. Gas products were mainly composed of C3 hydrocarbons, and no hydrogen production was detected due to moderate pyrolysis temperature.Master Thesis Experimental Spray Investigation of Methyl Ester and Ethyl Ester Type Biodiesel Fuels in a Constant Volume Combustion Chamber(Izmir Institute of Technology, 2020) Ulu, Anılcan; Özkol, Ünver; Yıldız, GürayBiodiesel fuels are promising fuels that can reduce pollutant emissions from diesel engines. Therefore, they are still being investigated in every aspect. In this study, it was aimed at comparing the spray characteristics of methyl ester and ethyl ester type biodiesel fuels with those of fossil diesel fuel. Besides, this study aimed to investigate the spray characteristics of ethyl esters on which few studies have been done, and to help eliminate this gap in the literature. For these purposes, 4 different methyl esters from corn, sunflower, canola and cotton oils, and 2 different ethyl esters from corn and sunflower oils were produced. Commercial diesel fuel was used to compare the characteristics of these fuels. Firstly, physical properties of the fuels produced were investigated to better understand the spray investigation, and it was observed that biodiesel fuels had bigger density and viscosity values than fossil diesel fuel. Additionally, it was found that methyl esters had larger density and smaller viscosity values than ethyl esters. After that, spray characteristics of all fuels were investigated in a constant volume combustion chamber under ambient pressures of 0, 5 and 10 bar, and injection pressures of 600 and 800 bar. Then, these fuels were cnompared to each other. After the experiments, biodiesel fuels were found to have longer spray penetration lengths and narrower spray angles than diesel fuel, although there were no significant differences between them. This may be due to higher density and viscosity values of biodiesel fuels. Furthermore, no significant distinctions were found between the spray characteristics of ethyl esters and methyl esters. In addition, it was observed that ambient and injection pressures were important parameters affecting the spray pattern. As a result, it was obtained that biodiesel-air mixing was slightly worse than diesel-air mixing. However, their potential to reduce pollutant emissions may cause this difference to be ignored. Moreover, it was found that ethyl esters had similar spray characteristics as methyl esters. Hence, ethyl esters are promising to replace methyl esters.Article Citation - WoS: 13Citation - Scopus: 14Perspectives of Biomass Catalytic Fast Pyrolysis for Co-Refining: Review and Correlation of Literature Data From Continuously Operated Setups(American Chemical Society, 2022) Prins, Wolter; Yıldız, GürayFor the co-processing of pyrolysis-based biocrudes within petroleum refineries, a degree of conditioning/upgrading involving the cracking of the oligomers and (partial) removal of oxygen could be operationally beneficial. By inducing a complex set of reactions in biomass-derived fast pyrolysis vapors, catalytic fast pyrolysis (CFP) ensures significant changes in oxygen functionalities and alleviates oxygen concentration in the resulting liquid intermediate (CFP-oil). Due to its reduced oxygen content and acidity, CFP-oil could be considered suitable for co-feeding in FCC units and/or for co-hydrotreatment (co-HT) with gas oils within the existing crude oil processing infrastructure. On the operational side, however, research concerning CFP of biomass has shown poor results: deoxygenation of pyrolysis vapors goes along with a progressive reduction in CFP-oil yield. Apart from any control over catalyst activity, selectivity, and lifetime, the other critical issue is in the process design, which is complicated by rapid catalyst deactivation through coke formation and catalyst poisoning by biomass-originated minerals. This review analyzes the outcome of research efforts concerning in- and ex situ CFP of biomass based on carefully selected literature studies reporting the results obtained from meso- and macrolevel laboratory-scale setups, pilot, process development units (PDU), and (semi-) commercial process units, wherein the biomass feedstock and catalyst is fed continuously. Key operational aspects such as the reactor technology, reactive medium, processing mode, and optimization of process parameters are addressed. The performances of continuously operated CFP units were benchmarked through a comparison of yields and elemental compositions of (by-)products. Despite the considerable research efforts related to CFP technology development, the co-processing of CFP-oil is still in its infancy. However, in close collaboration with refinery professionals, it could be made a serious candidate for biobased co-feeding. For refinery integration, quality parameters of CFP-oil, e.g., acidity, stability, and miscibility, should be considered as crucial as its oxygen content.Article Citation - WoS: 9Citation - Scopus: 11Experimental Investigation of Spray Characteristics of Ethyl Esters in a Constant Volume Chamber(Springer, 2024) Ulu, A.; Yildiz, G.; Özkol, Ü.; Rodriguez, A.D.Abstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Article Citation - WoS: 1Citation - Scopus: 2Effect of Preparation Method on the Activity of Red Mud Based Catalysts in Hydrogen Production From Biomass(Elsevier Ltd, 2025) Cay, Hakan; Akbas, Nazire Merve; Duman, Gozde; Simsek, Osman; Yildiz, Guray; Wang, Weitao; Yanik, JaleBiomass gasification is a promising technology for hydrogen production. This study presents H2 production from olive tree pruning (OTP), employing a fixed dual-bed reactor that combines OPT gasification and volatile reforming. The thermal steam gasification of OTP was performed at 850 degrees C, followed by the catalytic gasification of volatiles at different temperatures. Red mud (RM) and nickel loaded red mud (Ni-RM) catalysts were used as catalytic bed material. The effects of different operating parameters, i.e. catalytic bed temperature, catalyst preparation method (thermal reduction & plasma reduction), and nickel ratios in catalyst on the yield and composition of produced gases were investigated. The catalyst prepared by reduction under non-thermal plasma showed no effect on the gasification due to the insufficient temperature for the reduction of Fe2O3 and NiO. The results indicated that the bottom bed temperature had a significant effect on the H2 yield, especially in the catalytic experiments. The RM alone shows almost the same activity with Ni-RM on the H2 yield; 1076 mL gas/g OTP and 1128 mL gas/g OTP, respectively. The results of present study showed that reduced RM had as much catalytic activity as Ni loaded reduced RM in hydrogen production.Article Citation - WoS: 1Citation - Scopus: 1Co-Pyrolysis of Waste Wind Turbine Blades in a Molten Polyolefin Medium(Elsevier, 2025) Ekici, Ecrin; Yildiz, Magdalena Joka; Kalinowska, Monika; Wang, Jiawei; Yildiz, GurayThis study investigates the pyrolysis and co-pyrolysis processes of waste wind turbine blades (WWTB) and polyolefins (POs) at 450 degrees C in a round bottom tank reactor. The study contains three experimental sets: 1) batch pyrolysis of POs; 2) continuous pyrolysis of WWTB; 3) continuous feeding of WWTB into a molten PO medium, which was previously fed to the round bottom tank reactor batch-wise. Individual WWTB pyrolysis yields a modest 18.7 wt% of liquid, predominantly influenced by elevated ash and fixed carbon content. Conversely, copyrolysis demonstrates positive synergies, with escalating polyolefin content boosting liquid yields, reaching a peak at 61.5 wt% with a WWTB:POs mixture (25:75, wt%), while concurrently suppressing gas production to 21.6 wt%. The primary chemical groups found in the liquid obtained from WWTB are phenol and phenolic compounds, with their abundance diminishing as the POs ratio in feedstocks increases. Analysis of noncondensable gases from WWTB reveals that approximately 57.7 wt% are oxygen-containing, predominantly CO and CO2. Co-pyrolysis with POs at a 25:75 (wt%) ratio yields 47.1 wt% C3H6, resembling POs pyrolysis. The resulting solid products are rich in carbon and contains high ash. This research not only offers a detailed product analysis of WWTB but also sheds light on the dynamics of its co-pyrolysis with POs. Doing so contributes crucial insights into the transformative potential of pyrolysis and co-pyrolysis processes, covering the way for sustainable waste-to-resource solutions.Article Citation - WoS: 15Citation - Scopus: 19Ex Situ Catalytic Fast Pyrolysis of Lignin-Rich Digested Stillage Over Na/Zsm-5, H/Zsm-5, and Fe/Zsm-5(American Chemical Society, 2020) Priharto, Neil; Ghysels, Stef; Opsomer, Wim; Ronsse, Frederik; Prins, Wolter; Pala, Mehmet; Yıldız, GürayThe global increase in lignocellulosic ethanol production goes in tandem with an increase in lignin-rich stillage that remains underutilized to date. Anaerobic digestion could valorize residual (biodegradable) organic fractions into biogas, leaving a lignin-rich digested stillage (LRDS). This LRDS from the lignocellulosic ethanol production has been assessed as a feedstock for slow and fast pyrolysis in earlier studies, with the intention to increase the overall output of useful products or energy carriers from the starting material. While using this lignin-rich feedstock, ex situ catalytic vapor-phase upgrading (VPU) of fast pyrolysis vapors with fractional condensation was conducted over Na/ZSM-5, H/ZSM-5, and Fe/ZSM-5 catalysts. Semicontinuous fast pyrolysis experiments have been carried out at a reaction temperature of 480 degrees C in a mechanically stirred sand bed, which was connected directly to a fixed bed of catalyst particles for ex situ upgrading of the fast pyrolysis vapors. The carbon and mass yields in heavy phase liquids decreased after catalytic VPU (mass: ca. 8-11 wt %; carbon: ca. 11-15 wt %), compared to noncatalytic pyrolysis (mass: ca. 18 wt %; carbon: ca. 23 wt %). However, the yield in specific compounds, that is, alkylphenols and aromatics such as BTX, increased much upon catalytic VPU (especially for Fe/ZSM-5). For Fe/ZSM-5, the concentration in alkylphenols and aromatics was 20.8 wt % on liquid basis and the yield was 1.7 wt % on as-received (a.r.) feedstock basis. For noncatalytic pyrolysis, the concentration in alkylphenols and aromatics was 2.1 wt % (liquid basis) with a yield of 0.4 wt % (a.r. feedstock basis). This study thus demonstrates the potential of (modified) catalysts to upgrade lignin pyrolysis vapors.Article Citation - WoS: 8Citation - Scopus: 10Spray Analysis of Biodiesels Derived From Various Biomass Resources in a Constant Volume Spray Chamber(American Chemical Society, 2022) Ulu, Anılcan; Yıldız, Güray; Rodriguez, Alvaro Diez; Özkol, ÜnverThis research aimed to analyze the spray characteristics of various biodiesels, which have rarely been investigated in terms of spray analysis in the literature compared to fossil diesel. For this purpose, four different methyl ester-type biodiesels were produced from canola, corn, cottonseed, and sunflower oils. These feedstocks were selected due to their wide availability in Turkey and being among the significant resources for biodiesel production. Measured physical properties of biodiesel samples showed that biodiesel fuels had, on average, 1.7 to 1.9 times higher viscosities, 5.3 to 6.6% larger densities, and 37 to 39.1% higher contact angle values than the reference diesel fuel. Spray characteristics of all fuels were experimentally examined in a constant volume spray chamber under chamber pressures of 0, 5, 10, and 15 bar and injection pressures of 600, 800, and 1000 bar. All tested biodiesels performed, on average, 3 to 20% longer spray penetration lengths, 5 to 30% narrower spray cone angles, and 5-18% lesser spray areas than the reference diesel fuel under chamber pressures of 5 and 10 bar. No significant differences occurred at 15 bar ambient pressure between biodiesels and diesel. In addition, analytical and empirical predictions showed that biodiesels had around 21.2-35.1% larger SMD values and approximately 7% lower air entrainment.Article Citation - WoS: 52Citation - Scopus: 60Applied Machine Learning for Prediction of Waste Plastic Pyrolysis Towards Valuable Fuel and Chemicals Production(Elsevier, 2023) Cheng, Yi; Yang, Yang; Coward, Brad; Wang, Jiawei; Yıldız, Güray; Ekici, Ecrin; Yıldız, GürayPyrolysis is a suitable conversion technology to address the severe ecological and environmental hurdles caused by waste plastics' ineffective pre- and/or post-user management and massive landfilling. By using machine learning (ML) algorithms, the present study developed models for predicting the products of continuous and non-catalytically processes for the pyrolysis of waste plastics. Along with different input datasets, four algorithms, including decision tree (DT), artificial neuron network (ANN), support vector machine (SVM), and Gaussian process (GP), were compared to select input variables for the most accurate models. Among these algorithms, the DT model exhibited generalisable and satisfactory accuracy (R2 > 0.99) with training data. The dataset with the elemental composition of waste plastics achieved better accuracy than that with the plastic-type for predicting liquid yields. These observations allow the predictions by the data from ultimate analysis when inaccessible to the plastic-type data in unknown plastic wastes. Besides, the combination of ultimate analysis input and the DT model also achieved excellent accuracy in liquid and gas composition predictions. © 2023 The AuthorsArticle Citation - WoS: 30Citation - Scopus: 35Fast Pyrolysis With Fractional Condensation of Lignin-Rich Digested Stillage From Second-Generation Bioethanol Production(Elsevier Ltd., 2020) Priharto, Neil; Ronsse, Frederik; Yıldız, Güray; Heeres, Hero Jan; Deuss, Peter J.; Prins, WolterPoplar-derived lignin-rich feedstock (i.e. stillage) obtained from bioethanol production was subjected to fast pyrolysis in a modified fluidised bed reactor at 430 degrees C, 480 degrees C, and 530 degrees C. The stillage was pretreated by enzymatic digestion prior to fast pyrolysis. Pyrolysis vapors were collected by fractional condensation to separate the heavy organic and aqueous phase liquids. The intention of this study was to assess the potential utilization of lignin-rich digested stillage as a fast pyrolysis feedstock. Heavy organic and aqueous phase pyrolysis liquids were obtained in yields ranging from 15.1-18.1 wt.% and 9.7-13.4 wt.% respectively. The rest of the feedstock material was converted to char (37.1-44.7 wt.%) and non-condensable gases (27.1-31.5 wt.%). Detailed liquid analysis indicated that the heavy organic phase fractions contain compounds arising from the degradation of lignin, residual microbial biomass and remaining polysaccharides. Fast pyrolysis adds 26.8 wt.% to the conversion of this otherwise recalcitrant feedstock material, thereby reducing waste generation and enhancing the value of second-generation bioethanol production.