Chemical Engineering / Kimya Mühendisliği
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Article Citation - WoS: 10Citation - Scopus: 12Novel Hybrid Adsorption-Electrodialysis (aded) System for Removal of Boron From Geothermal Brine(American Chemical Society, 2022) Altınbaş, Bekir Fırat; Orak, Ceren; Ökten, Hatice Eser; Yüksel, AslıA novel hybrid adsorption-electrodialysis (AdED) system to remove environmentally harmful boron from geothermal brine was designed and effective operating parameters such as pH, voltage, and flow rate were studied. A cellulose-based adsorbent was synthesized from glycidyl methacrylate (GMA) grafted cellulose and modified with a boron selective n-methyl-d-glucamine (NMDG) group and characterized with SEM-EDX, FT-IR, and TGA analyses. Batch adsorption studies revealed that cellulose-based adsorbent showed a remarkable boron removal capacity (19.29 mg/g), a wide stable operating pH range (2-10), and an adsorption process that followed the Freundlich isotherm (R2= 0.95) and pseudo-second-order kinetics (R2= 0.99). In the hybrid AdED system, the optimum operating parameters for boron removal were found to be a pH of 10, a voltage of 10 V, a flow rate of 100 mL/min, and an adsorbent dosage of 4 g/L. The presence of the adsorbent in the hybrid system increased boron removal from real geothermal brine (containing 199 ppm boron) from 7.2% to 73.3%. The results indicate that the designed AdED system performs better than bare electrodialysis for boron removal from ion-rich real geothermal brine while utilizing environmentally friendly cellulose-based adsorbent.Article Citation - WoS: 1Citation - Scopus: 1Selective Catalytic Hydrogenation of Cellulose Into Sorbitol With Ru-Based Catalysts(TÜBİTAK, 2022) Orak, Ceren; Sapmaz, Aycan; Yüksel, AslıSorbitol is one of the platform chemicals and can be produced from various renewable and sustainable sources via different processes. Hydrothermal liquefaction is an effective and promising approach to produce sorbitol, since the subcritical reaction media and appropriate catalysts provide a selective production of platform chemicals. In this study, sorbitol was produced from different renewable sources (cellulose and glucose) in the presence of Ru-based catalysts (Ru/SiO2, Ru/AC, Ru/SBA-15, and Ru/SBA-15-SO3) under subcritical conditions. The highest cellulose conversion was achieved as 90% in the presence of Ru/SBA-15-SO3 for 1 h of reaction duration. The highest sorbitol yield (%) by hydrothermal liquefaction of cellulose was obtained as 6.2% by using Ru/AC for 1 h of reaction duration. A total of 99.9% of glucose conversion was achieved in the presence of all catalysts. The highest sorbitol yield (%) by hydrothermal liquefaction of glucose was found as 3.8% for 1 h of reaction duration. Owing to the results of GC-MS analysis, the intermediate products were identified, and, thus, a reaction pathway was proposed.Article Citation - WoS: 31Citation - Scopus: 38Liquefaction of Waste Hazelnut Shell by Using Sub- and Supercritical Solvents as a Reaction Medium(Elsevier, 2019) Demirkaya, Emre; Dal, Orkan; Yüksel, AslıDirect thermochemical biomass degradation to obtain bio-oil by using organic solvents is not a new process type, and it has some advantages over hydrothermal liquefaction technique. However, up to our best knowledge, in this study, hazelnut shell decomposition by using ethanol, acetone and their mixtures at sub/supercritical conditions was studied for the first time in literature. Experiments were carried out between 220-300 degrees C, at three different reaction times (30, 60 and 90 min) for five different solvent ratios. Highest solid conversion achieved at 300 degrees C by using pure ethanol was 64.2%, whereas highest bio-oil yield was found as 44.2% at 300 degrees C with 50/50 (EtOH/Ac: v/v). Ethanol and acetone showed different characteristics during the reactions and their effects on the conversion and bio-oil yield were discussed. Statistical analysis showed that time, temperature, ratio and synergy between temperature-time were affecting parameters for the conversion and bio-oil yield. (C) 2019 Elsevier B.V. All rights reserved.Conference Object Electrolysis of Alcohols in High Temperature-High Pressure Water(Materials Research Society, 2013) Yüksel, Aslı; Sasaki, Mitsuru; Goto, MotonobuThe design of clean, efficient and environmentally friendly routes that reduce the waste production and fuel emissions of pollutants into the atmosphere, produce clean, affordable, and renewable energy sources to lessen energy consumption and toxicity on the environment, has become a central issue of chemical research both in industry and academia. One of the approaches being used in green chemistry practices is to use water as a solvent and reaction medium where possible. Much of this work deals with liquid water at temperatures exceeding the normal boiling point which is denoted as sub-critical water. Electrochemical reaction, usually operated at atmospheric condition in water, is generally slow, although it has advantages over chemical reaction such as suppression of side reaction by tuning operating conditions. Since sub-critical water (7 MPa and 250 °C) has remarkable properties such as high ion product and low dielectric constant, it could be a suitable reaction media. We have been studying electrolysis of organic compounds in sub-critical water as waste treatment and molecular degradation technologies. Electrolysis in sub-critical water could degrade harmful and thermally stable organic compounds into innocuous compounds such as hydrogen and water. In this research, we focused on the investigation of the electrochemical reactions of alcohols in sub-critical water to evaluate possibility for the selective production of hydrogen and value-added chemicals. Electrochemical reactions were carried out in sub-critical water using a specially designed autoclave made of SS 316 with a volume of 500 mL. For comparison, thermal degradation experiments of alcohols were also conducted without any direct current loading at identical conditions. Here we employed glycerol and 1-butanol as model compounds of alcohols. As a result of 1-butanol experiments, butanal and butyric acid were produced via partial oxidation at 250 °C and by applying 1-3 A of direct current while no oxidation products were observed at the hydrothermal degradation run. As a gaseous product, hydrogen gas was generated according to the electrochemical reaction mechanism. In the case of glycerol experiments, the main gaseous product was hydrogen gas, whereas glycolaldehyde, lactic acid, and formic acid were generated as the main liquid products at 280 °C. Results indicated that greater than 92% of the glycerol could be decomposed under optimum conditions by hydrothermal electrolysis technique. This presented research will help to degrade stable organic materials in an environmentally friendly way and without need for secondary treatment processes. It will also address the need for novel more efficient techniques for the degradation of stable organic compounds in aqueous conditions and it will advance the use of water as a reaction medium in an efficient way without any organic solvent.Article Citation - WoS: 9Citation - Scopus: 10Novel Hybrid Process for the Conversion of Microcrystalline Cellulose To Value-Added Chemicals: Part 2: Effect of Constant Voltage on Product Selectivity(Springer Verlag, 2017) Akın, Okan; Yüksel, AslıIn this study, electrochemical degradation of microcrystalline cellulose (MCC) under hot-compressed water was investigated via application of constant voltage on reaction medium. Constant voltage ranges from 2.5 to 8.0 V was applied between anode (Titanium) and cathode (reactor wall). As an electrolyte and proton source 5–25 mM of H2SO4 was used. Reactions were carried out in a specially designed batch reactor (450 mL) made of T316 for 240 min at temperature of 200 °C.MCC decomposition products such as glucose, fructose, furfural, 5-HMF and levulinic acid were detected and quantified by High Performance Liquid Chromatography (HPLC). In the absence of electrolyte, applied voltage (2.5 and 4.0 V) decreased the total organic carbon (TOC) yield, in contrast at 8.0 V, TOC yield increased to 13%. Application of 8.0 V in hydrothermal conditions alter MCC decomposition pathway selectively to furfural (15%). Addition of electrolyte (5 mM, H2SO4) and application of 2.5 V potential increased TOC (54%) and changed the decomposition pathway in favor of 5-HMF (30%) and levulinic acid (21%). The structural changes in solid residues of electrochemically reacted MCC was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and found that MCC particles functionalized by carboxylic acid and sulfonated groups by the application of constant voltage to reaction medium. In the presence of electrolyte, under certain voltage (2.5 V), functionalization of solid particles became more obvious in FTIR spectrum results. Therefore, change in the selectivity values of degradation products were conducted with the functionalization of MCC particles due to applied voltage under sub-critical conditions.Article Citation - WoS: 19Citation - Scopus: 23Valorization of Hazelnut Shell Waste in Hot Compressed Water(Elsevier Ltd., 2017) Gözaydın, Gökalp; Yüksel, AslıHydrothermal conversion of waste hazelnut shell in hot compressed water, green and environmentally friendly medium, was investigated under different operating conditions to clarify the effects of reaction temperature, reaction time, acid concentration and acid kind (H2SO4 and H3PO4) on the production of value-added chemicals with high temperature/high pressure autoclave. In literature, to our best knowledge, there is no study about the production of levulinic acid, as a high value chemical, from waste hazelnut shell in hot-compressed water without using any mineral and heterogeneous catalyst. Hydrothermal reactions were conducted at 150–280 °C for reaction times of 15 to 120 min with various H2SO4 and H3PO4 concentrations varying from 0 to 125 mM. The detailed liquid product species were identified with High Performance Liquid Chromatography (HPLC) and gaseous products were analyzed by Gas Chromatography with a Thermal Conductivity Detector (GC-TCD). The main identified liquid compounds were levulinic acid, acetic acid and furfural while carbon dioxide and carbon monoxide were the major gaseous products. Increasing the reaction temperature (280 °C) and reaction time (120 min) resulted in a significant increment on the conversion (65.40%) as well as levulinic acid yield (13.05%). The production of levulinic acid was enhanced with H2SO4 addition; whereas treatments with H3PO4 improved the furfural production.Article Citation - WoS: 11Citation - Scopus: 12Novel Hybrid Process for the Conversion of Microcrystalline Cellulose To Value-Added Chemicals: Part 1: Process Optimization(Springer Verlag, 2016) Akın, Okan; Yüksel, AslıIn this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30–120 min of reaction time at temperature range of 170–230 °C. As a proton donor H2SO4 was used at concentrations of 1–50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC–MS) were used. A ½ fractional factorial design with 2-level of four factors; reaction time, temperature, H2SO4 concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200 °C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230 °C, 120 min., 2 A, 50 mM H2SO4). © 2016, Springer Science+Business Media Dordrecht.