Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Molecular Modelling of the Effect of Alkali Promoters on Co Adsorption and Dissociation on the Co(111) Surface(2023) Özbek, Özüm; Kızılkaya, Ali CanFischer-Tropsch Synthesis (FTS) is a surface polymerization process that has been industrially used to convert non-petroleum feedstocks to synthetic transportation fuels. Modification with an alkali promoter of the Co-based catalysts provided promising results to obtain hydrocarbons with enhanced olefin content in FTS. Activation of CO is the key factor to achieve desired end products in FTS, yet the mechanism related to the CO dissociation behavior on alkali promoted cobalt surfaces remains unknown. This study aims to examine the impact of alkali promoters (Li, Na, K) on the adsorption and dissociation characteristics of CO on the Co(111) surface using Density Functional Theory (DFT). Our results revealed that CO adsorption energy increased by 32-37% with alkali addition, yet H adsorption energy remained relatively unchanged. The effect of alkali addition on CO dissociation routes were also examined. The high activation barrier (>200 kJ/mol) makes it improbable for direct CO dissociation to occur on alkali promoted Co(111) surfaces under FTS conditions. For H-assisted pathways, alkali addition increased the activation barrier for HCO and H2CO dissociation, overall reducing the H-assisted CO dissociation rate. It was found that alkali addition makes the surface more carbophilic since the C adsorption energy increased by 7-11% upon alkali addition. Also, with increasing C concentration on the Co(111) surface, subsurface carbon geometries became more stable. Ultimately, it is concluded that alkali promoters of Li, Na and K have similar effects on CO adsorption and dissociation on the Co(111) surface.Master Thesis Recovery of Lithium From Aqueous System Using Manganese Oxide Adsorbent With Developed Electrospun Mat Substrate(01. Izmir Institute of Technology, 2023) Akgün, Berk; Ebil, Özgenç; Demir, Mustafa MuammerLithium is used in many fields due to its high energy density and unique electrochemical properties. Recently, there has been a strong increase in demand for lithium, so the extraction of lithium from natural water resources has become a remarkable research topic. One of the most effective methods of separating lithium from natural water sources is adsorption using lithium ion-sieve adsorbents. However, the powdered nature of the adsorbents makes them challenging to process and less recyclable. Recent studies have focused on developing adsorbents using different polymeric materials as substrates or binders. In the thesis, as a new approach, flexible and free-standing polyurethane electrospun mat substrates were produced and combined with λ-MnO2 to extract lithium from aqueous systems, and their lithium removal performance was investigated. After the fabricated mats and λ-MnO2 powder were characterized, the deposition process was performed, and filtration studies were carried out in synthetic lithium solution. Optimum conditions for lithium removal were found as an adsorbent amount of 200 mg, and 200 ppm initial [Li+], and pH 12. In addition, lithium removal performances have been improved by stacking mats and multi-stage filtration processes. Lithium removal reached 76.6% when a 400 ppm lithium solution and an 8-step filtration were used. Lithium removal experiments were performed with salt-lake brine containing high concentrations of various ions and showed that these ions reduced the lithium removal. In the study, PU electrospun mats for λ-MnO2 powder were found to be a promising substrate for lithium removal from aqueous systems.Master Thesis Adsorbent Synthesis for the Recovery of Lithium Water Resources(01. Izmir Institute of Technology, 2022) Kahvecioğlu, Anıl; Yüksel Özşen, Aslı; Yüksel Özşen, AslıLithium is a crucial mineral for the 21st century due to its utilization in a wide range of industries. Lithium demand will increase because of car battery developments and the necessity for power storage. Investigating alternative strategies for resource recovery is the only way to fulfill this unexpected rise properly and sustainably in demand. Adsorption has been discovered to have some technological advantages over other methods. It is considerably less expensive, lacks the chemical resistance present in membranes, lacks the significant electrical demand of electrochemical approaches, as well as the restricted selectivity and challenges in integration into commercial processes. Lithium manganese oxides, also known as lithium ion-sieves, are adsorbents for lithium extraction that have remarkably high selectivity, high adsorption capacity, minimal toxicity, good chemical stability and cheap cost. They are one of the most promising inorganic adsorbents. This research emphasized on the recovery of lithium from water resources through the use of lithium manganese oxide, which were synthesized in laboratory. They were transformed into spherical beads by adding chitosan, followed by crosslinking these beads with epichlorohydrin to increase their adsorption yield, stability, and reusability. Characterization techniques such as SEM, XRD and BET were applied on the adsorbents. Results shows that the adsorbents distributed uniformly, the adsorbent powder was mesoporous, and from the adsorption studies it was found that the adsorbent worked much better in alkaline conditions such as pH 12, optimum adsorbent dosage estimated as 4 g/L and the equilibrium time measured as 10 hours. From the desorption study approximately 95% of Li desorbed for the first cycle, after the second cycle the adsorbent efficiency started to decrease.Master Thesis Lithium Extraction From Geothermal Brine by Adsorption Method With Electrolytic Y-Mno2 Sorbent(Izmir Institute of Technology, 2022) Toprak, Seyra; Demir, Mustafa Muammer; Baba, AlperIn recent years, studies on the recovery of lithium metal have attracted great attention due to its wide application areas, especially in lithium-ion batteries. Recovery of lithium from brines is preferred considering the environmental impacts in mining. The application of manganese oxide sorbents to recover lithium from geothermal brines has been extensively studied as it is a potential source of lithium. In this thesis, adsorption was performed in Tuzla Geothermal Power Plant (TGPP) at 87 °C and 2 bar using a mini-pilot system in the reactor near the reinjection well of the plant to investigate the adsorption performance in field conditions. As a new approach, electrolytic manganese dioxide (γ-MnO2), which is widely used as cathode material in batteries, was used as the sorbent material for lithium and its adsorption/desorption performance was investigated. Batch adsorption experiments were performed in synthetic lithium solution and the optimum working conditions were determined as pH 12, adsorbent concentration of 3 g/L, and initial lithium-ion concentration of 200 mg/L. The highest adsorption capacity of the sorbent in the Langmuir model was found as 9.74 mg/g. The maximum adsorption performance was obtained at 1h adsorption in Tuzla GPP. In the continuation of the study, desorption was carried out in acidic medium with the brine-treated sorbent. Lithium concentration was enriched to around 250 ppm with repetitive desorption studies. Reusability of the sorbent was investigated and the reused sorbent showed almost 40% performance compared to virgin powder. γ-MnO2 was found as a promising sorbent for the separation of lithium from geothermal brines.Master Thesis The Effect of Atmospheric Gases on the Electrical Stability of Graphene(Izmir Institute of Technology, 2017) Kalkan, Sırrı Batuhan; Çelebi, CemIn this thesis, adsorbate induced variations in the electrical conductivity of graphene layers with two different types of charge carriers are investigated experimentally by using Transient Photocurrent Spectroscopy (TPS) method. In-vacuum TPS measurements taken for a duration of 5 ks, revealed that the adsorption/desorption of atmospheric adsorbates leads to a 45 % incerment and 110 % decrement in the conductivity of CVD graphene (p--type) and epitaxial graphene (n-type) layers on semi-insulation (SI) Silicon Carbide (SiC) substrates, respectively. The graphene layers on SI-SiC substrates are encapsulated and passivated with thin SiO2 film grown by Thermal Evaporation and Pulsed Electron Deposition (PED) techniques. The mesurements conducted for short periods and a few cycles showed that the thermal passivation of graphene layers is insufficient. However, the PED encapsulation process completely suppresses the time-dependent conductivity instability of graphene independent of its charge carrier type. The obtained results are used the construct an experimental model for identifying adsorbate related conductivity variations in graphene and also in other 2D materials with inherently high surface-to-volume ratio.Master Thesis Adsorption of Methane Reformer Off-Gas Components in a Column Packed With Cu, Al,ti and Zn Based Organic Frameworks(Izmir Institute of Technology, 2016) Kanaltı, Gaye; Çakıcıoğlu Özkan, Seher FehimeWithin the past decade, CO2 emissions from fossil fueled power plants has accelerated rapidly as a result of the increase in energy consumption associated with industrial development all over the world. Beyond the necessity of reduction in CO2 emissions, concerning on the crude oil reserves depletion induced the urgent need of transition to more efficient, renewable, cleaner and cheaper fuel, hydrogen. In the world, most of the hydrogen is produced by hydrogen-rich stream methane reformer (SMR) off gas streams composed of 80-60% H2, 15-25% CO2, 3-6% CH4 and 1-3% CO, thereby separation of SMR components became more of an issue. In this study, adsorption based separation of SMR components were investigated in a column packed with copper (CuTPA, (SLang: 776 m2g-1)), aluminum (AlTPA, (SLang: 1330 m2g-1)), titanium (TiTPA, (SLang: 1835 m2g-1)) and zinc (ZnTPA, (SLang: 1023 m2g-1)) based organic frameworks (MOFs). The pure gas adsorption studies on equimolar CO2/H2, CH4/H2 and CO/H2 systems and the equimolar mixture of CO2/CH4 system were carried out and the experimental breakthrough curves were obtained at three different feed flow rates (10, 20 and 30 mL/min) at three column pressure (1, 5 and 10 bar) at 303 K. The highest adsorption capacities of all MOFs were achieved at 30 mL/min of feed rate and 10 bar operating pressure, at these conditions the non-adsorptive behavior of hydrogen on the aforementioned MOFs was ensured. The amounts of CO2 adsorbed were calculated as 1.61, 5.54, 5.20 and 2.11 mmolCO2/g, while adsorbed CH4 amounts were 1.50, 3.16, 3.25 and 1.90 mmol CH4/g and the adsorbed CO amounts were 1.47, 2.59, 1.91 and 1.83 mmol CO/g on CuTPA, AlTPA, TiTPA and ZnTPA, respectively. The highest selectivity for CO2 over CH4 was attained on TiTPA as 8.0 at 10 mL/min feed rate of CO2/CH4 mixture at atmospheric column pressure and 303 K. The experimental adsorption isotherms of SMR components were fitted well with Langmuir and virial models and the best fitted model parameters were evaluated for each MOF.Master Thesis A Study on Cop Improvement of a Household Refrigerator by Using an Adsorption Heat Pump(Izmir Institute of Technology, 2015) Arslan, Gizem; Barışık, Murat; Mobedi, MoghtadaThe thesis aims to increase the coefficient of performance of a domestic type household refrigerator. A household refrigerator is a kind of mechanical heat pump which works based on the vapor compression cycle. On the other hand, adsorption heat pump is a thermal heat pump and it can directly operate with any kind of third energy source such as solar, waste heat. The heat released from the condenser of a mechanical heat pump provides the desorption of the adsorbate in the adsorbent bed and helps the transfer of the adsorbate to the condenser of the adsorption heat pump. Then, the adsorbent bed which has low level adsorbate concentration provides the evaporation of the adsorbate in the evaporator and generates a cooling effect. By this way, an additional cooling effect can be generated without the increase of energy consumption of refrigerator. In this thesis, a detailed literature survey on the combination of hybrid cooling systems is done. The suggested hybrid cooling systems are classified, and their advantages and disadvantages are discussed. In order to analyze heat and mass transfer of an adsorption heat pump, different conditions for adsorbent bed design are studied, theoretically. To design an adsorption heat pump the effects on the heat and mass transfer should be well known. Theoretical studies on heat and mass transfer in a rectangular adsorbent bed is performed to understand what can be effected on the heat and mass transfer in an adsorbent bed. Heat and mass transfer equations for a rectangular adsorbent bed are derived for non-uniform pressure approaches and numerically solved to determine temperature and concentration profiles in the bed with using Comsol Software. Furthermore, our CFD program coded in FORTRAN language. The code is used to validate the obtained results from Comsol. An experimental setup was designed and constructed in the light of these numerical studies. The enhancement of performance of a household refrigerator is calculated by using an adsorption heat pump.Master Thesis Comparative Adsorption Studies of Heavy Metal Ions on Chitin and Chitosan Biopolymers(İzmir Institute of Technology, 2007) Keleşoğlu, Serkan; Polat, Hürriyet; Polat, HürriyetIn this study comparative adsorption studies of heavy metal ions (Cu2+, Pb2+,Cd2+, Ni2+) on chitin and chitosan biopolymers were performed to investigate the uptake performances. For this purpose chitosan was prepared from chitin in controlled experimental conditions and then these biopolymers were characterized with Elemental Analysis, Viscosity, FT-IR, Potentiometric Titration, XRD, SEM, Zeta Potential,Particle Size Distribution and TGA/DTA measurements. Batch adsorption experiments were performed at eight different initial heavy metal ion concentrations (10, 25, 50, 100, 250, 500, 750, 1000 m/L), two different temperatures (298.15 K and 328.15 K), time period ranging from 5 minutes to 1 day and pH of solutions ranging from 1 to 7. The results indicated that the uptake performence of chitin and chitosan biopolymer significantly changed with pH, adsorbent dosage,concentration and temperature. In general, chitosan biopolymer demonstrated greater fixation abbility for heavy metal ions than chitin. However the fixation trend of heavy metal ions on chitin and chitosan biopolymers was the same (Cu2+ > Pb2+ > Cd2+ > Ni2+). Moreover Irwing-Williams Series support the dominancy of the binding mechanism for Cu2+, Cd2+ and Ni2+ ions on both biopolymers. Adsorption of heavy metal ions on both chitin and chitosan biopolymers followed pseudo second order kinetics with the rate constant indicating faster adsorption on chitin for Cu2+ and Pb2+ ions and faster adsorption on chitosan for Cd2+ and Ni2+ ions.Both of the Freundlich and Langmuir adsorption isotherms seem to adequately represent the adsorption data obtained in this study. The positive value of enthalpy change (Ho) and negative value of free energy change (Go) shows the adsorption process is endothermic and spontaneous. Moreover obtained positive entropy changes (So) show that an increase in randomness, is associating the adsorption of metal ions onto chitin and chitosan biopolymers.Master Thesis A Study on Isotherm Characteristics of Adsorbent-Adsorbate Pairs Used in Adsorption Heat Pumps(Izmir Institute of Technology, 2011) Yıldırım, Zeynep Elvan; Mobedi, Moghtada; Ülkü, SemraAdsorption heat pumps are promising systems due to their ability to recover heat at low temperature levels and to provide cooling and/or heating effects. It has advantages such as using renewable energy sources, being environmental friendly, having no vibration and lower operation costs. In this study, the most common pairs used in adsorption heat pumps were reviewed and their thermophysical and adsorption behaviors were discussed. The adsorption equilibrium phenomena were explained in details. The different experimental methods for determination of adsorption equilibrium for pairs were explained and compared. The change of heat of adsorption according to the varying adsorbed amount was studied numerically for two different equilibrium equations. It is found that, the heat of adsorption for pairs fitting Dubinin-Astakhov equation has a decrease with increasing adsorbed amount, while the heat of adsorption for pairs fitting Freundlich equation does not depend on adsorbed amount. A numerical study was performed to investigate the performances and cooling capacities of three different adsorption chillers for six different pairs. The results showed that when S40 silica gels - water pair is used, the chiller cooled with low temperature source gives the highest performances.In the experimental section of the present study, a volumetric setup was designed and constructed. Experiments were performed for a conventional pair of silica gel - water. It was observed that the maximum adsorption capacity of the experimented silica gel -water pair was 21% (kg water vapor /kg silica gel) at 35 °C, 19% (kg water vapor/kg silica gel) at 45 °C and 11% (kg water vapor /kg silica gel) at 60 °C.Master Thesis Purification of Polyphenolic Compounds From Crude Olive Leaf Extract(Izmir Institute of Technology, 2011) Karakaya, Alihan; Bayraktar, OğuzStudy was carried out to investigate the adsorption characteristics of olive leaf extract on the macroporous adsorption resins and the efficiency of the adsorption column for the separation and purification of oleuropein and rutin from the crude plant extract. Both static and dynamic experiments were performed. In static studies, the performances of three macroporous Amberlite resins namely XAD4, XAD 16 and XAD7HP for the adsorption of polyphenols were evaluated. XAD7HP was chosen as an adsorbent for further adsorption study. XAD7HP was selected for the studies of isotherms, kinetics of adsorption. In conventional alcohol extraction, crude feedstock is mixed with solvent which is alcohol for most cases, and then extract is distilled to remove ethanol. This process ends with a certain amount of residual ethanol because of complication in separation process for ethanol and water makes an azeotropic binary system. The results showed that adsorption capacity of an alcoholic solution with 10 % ethanol content is better than aqueous solution which contained no ethanol. In dynamic studies, the adsorption and desorption experiments were carried out on a glass column packed with XAD7HP resin. The flow velocity 122 cm/h operated as a fixed bed while operation was in an expanded bed mode at 367 cm/h and 611 cm/h, respectively. The effectiveness of the packed bed adsorption and the fluidized bed adsorption were compared. The results show the breakthrough occurred earlier when the feed flow velocity increased. In the elution step, elution program with 2,000 ml for 0 %, 4,000 ml for 40 % and 3,000 ml for 90 % aqueous ethanol was used to achieve an efficient separation. Total phenol content and antioxidant capacity of olive leaf crude extract and effluent fractions were analyzed in order to find the difference between before and after separation. Consequently, fluidized bed adsorption is a promising alternative for the packed bed adsorption in order to isolate oleuropein and rutin from the olive leaf extract.