High-Efficient Blue and White Organic Light-Emitting Diodes Showing Color Stability

서지훈 홍익대학교 대학원 2011 국내박사

고효율, 색 안정성을 갖는 청색 및 백색 유기 발광 다이오드 21세기에 들어서서 정보통신과 컴퓨터의 급격한 발달로 인해 고도의 정보화 사회로 급속히 진행됨에 따라 고성능 평판디스플레이 (flat panel display)의 중요성이 갈수록 커지고 있다. 이에 따라 CRT (cathode ray tube)가 주도하여 온 디스플레이 산업은 CRT보다 얇고 가벼우며 대면적, 고휘도, 고해상도, 낮은 소비전력, 저 생산비용의 평판 디스플레이로의 급격한 시장변환을 꾀하고 있으며, 그 중에서 LCD(liquid crystal display) 및 PDP (plasma display panel) 는 모니터 및 TV 분야에서 가장 큰 시장을 형성하고 있다. 디스플레이 시장에서 LCD와 PDP의 시장 점유율은 우리나라가 전 세계에서 가장 선두에 있으며, 반도체 산업과 더불어 우리나라 경제를 지탱하고 있다기 발광 다이오드(Organic Light-Emitting Diodes; OLEDs)는 시장 및 기술이 급속이 성장하고 있으며 현재 삼성 모바일 디스플레이의 AM-OLED제품은 전세계 98%이상의 시장 점유율을 나타내고 있는 차세대 디스플레이 산업이다. 많은 연구자들은 현재까지 형광 및 인광 녹, 적색 유기 발광 다이오드를 연구했고, 그 결과 풀컬러 유기 발광 다이오드를 구현하기 위한 필요조건을 만족시키는 결과를 나타내었다. 그러나 아직 인광 및 형광 청색 유기 발광 다이오드는 낮은 효율과 만족할 만한 색좌표는 실현되고 있지 않다.

Lignocellulosic biomass pyrolysis and hydrodeoxygenation of bio-oil using transition metals (Ni, Co, Fe) based catalysts

Quoc Khanh Tran 강원대학교 대학원 2022 국내박사

Biomass is a promising renewable resource to generate energy owing to its abundance and low cost. Lignocellulosic biomass is known as a strong candidate due to their advantages compare to other biomass, e.g. high energy, but low costs, low ash content, and very low nitrogen and sulfur contents. Lignocellulosic biomass is consisted of hemicellulose, cellulose, and lignin. Among several thermal conversion technologies, pyrolysis is a feasible approach to convert biomass into energy and chemicals due to reasonable coast and simple operation. To understand the pyrolysis kinetic of lignocellulosic biomass, the main components of lignocellulosic biomass such as cellulose and lignin were used to investigate systematically using thermal gravimetric analysis (TGA) and micro-tubing reactor. The simulated data of α-cellulose is in good agreement with the experimental data in the aspects of the conversion and the conversion rate versus temperature. The decomposition of α-cellulose, mainly occurring at 270–420℃, induced an apparent activation energy ranging from 175.42 kJ/mol to 197.73 kJ/mol at a conversion of 10–90%. With 0.1–0.2 wt% K or Ca impregnation into the α-cellulose, the mean activation energy for pyrolysis was lowered (from 181.47 kJ/mol (for α-cellulose) to 141.11 kJ/mol (for 0.2 wt% K/α-cellulose) and 159.46 kJ/mol (for 0.1 wt% Ca/α-cellulose)) and higher amounts of liquid and gas products were produced. Furthermore, the addition of potassium and calcium increased the production of lower molecular weight components, such as furfural and its derivatives. The kinetic rate constants indicate that the predominant reaction pathway is from α-cellulose into a liquid product, rather than from α-cellulose into a gas product. The pyrolysis characteristics and kinetics of Organosolv lignin from pine trees were also investigated. Through these approaches, the activation energy of Organosolv lignin pyrolysis was calculated. The activation energy by the Friedman method ranged from 70.11–355.92 kJ/mol, while relatively lower values (48.51–302.47 kJ/mol) were calculated by the peak separation method. Thermodynamic parameters such as entropy (ΔSo), Gibbs free energy (ΔGo), and enthalpy (ΔHo) were also calculated to understand the reaction pathways from a thermodynamic perspective. Based on the pyrolysis mechanisms proposed in this study, the reaction rate constants of different steps were determined. The primary reaction route was identified to be the pyrolysis of Organosolv lignin to liquid products such as bio-oils. Finally, the compositions of gaseous and liquid products formed by pyrolysis were analyzed using the micro-tubing reactor. The Organosolv lignin was polymerized into lower molecular weight structures by the pyrolysis process. CO, CO2, and CH4 were mainly produced as gaseous products, while Organosolv lignin was primarily decomposed into guaiacol, 3-methoxy-1,2-benzendiol, vanillin, vanillic acid, acetovanillate, and syringaldehyde. Pine trees is considered as promising candidate biomass sources compare to other lignocellulosic biomasses for the production of high liquid yield bio-oil. Pyrolysis of pitch pine has been investigated in a bubbling fluidized bed reactor. In this system, silica sand and nitrogen were used as the fluidizing bed material and fluidizing medium, respectively. The experimental was systemically perform on different temperature, fluidized velocity, and particle size of biomass. The optimum temperature condition at which the bio-oil yields reached the highest value (65.5%) was 500 ℃. In addition, the higher heating values of bio-oils from pitch pine biomass were reached in the range 22 MJ/kg to 24 MJ/kg. Moreover, this bio-oil had high content of useful chemicals including such as levoglucosan, furfural, and guaiacol. The large amount of C5–C11 (gasoline fraction) produced make the pyrolyzed oil originating from pitch pine trees a promising biofuel candidate. Since guaiacol is a key compound obtained from lignocellulosic biomass pyrolysis bio-oil, it is often utilized as a model compound in most studies. Additionally, it contains methoxy (-OCH3) and hydroxy (-OH) groups, which are important in ascertaining its value as a fuel source. Spherical -Al2O3-SiO2 catalysts with varying Al/Si ratios were prepared by combining the sol-gel and spray pyrolysis (SP) methods to examine in hydrodeoxygenation process. The effectiveness of the product catalysts was then tested via the hydrodeoxygenation (HDO) of guaiacol, a model compound of bio-oil obtained from the pyrolysis of lignocellulosic biomass. Our results showed that the -Al2O3-SiO2 catalyst with a 50:50 Al/Si ratio after calcination at 450 C exhibited the highest guaiacol conversion (81.79%) at a reaction temperature of 300 C, atmospheric pressure, and a weight hourly space velocity (WHSV) of 6.5 h-1. During guaiacol HDO, the carbon–oxygen cleavage and methyl group transfer reactions occurred on the -Al2O3-SiO2 catalyst, which converted the guaiacol into the respective deoxygenated products, including 2,6-xylenol, 2,3,5,6-tetramethyl phenol, pentamethyl benzene, and hexamethyl benzene. In addition, Ni/γ-Al2O3 and Fe/activated carbon (AC) catalysts were prepared by an incipient impregnation method and then also utilized for hydrodeoxygenation (HDO) of guaiacol (GUA). The AC used in the process was derived from bamboo through steam activation. At 300 °C and atmospheric pressure, 91.52% of GUA was successfully transformed into cresol and 1,2-dimethoxybenzene in liquid phase using 10 wt% of the Fe/AC catalyst, which was calcined at 550 ℃. Under the same reaction conditions, utilizing 10 wt% of the Ni/γ-Al2O3 catalyst, which was calcined at 450 ℃, resulted in 96.88% GUA conversion, producing 13.03% of cresol, 58.98% of 1,2-dimethoxybenzene, and 27.99% of 3-methyl guaiacol. The reaction pathways for the conversion of guaiacol HDO were also proposed in this study. The catalytic hydrodeoxygenation (HDO) processes for upgrading pyrolysis bio-oils from wood pallet sawdust (WPS) were studied using activated carbon (AC) as a support of mono- (Co/AC and Fe/AC) and bi-metallic (Co-Fe/AC) catalysts. At 350 ℃ and 60 bar, 20 wt% Co/AC showed the highest liquid yield (70.46 wt%) along with HHV of 34.22 MJ/Kg. Among the tested bimetallic catalysts, comparable liquid yield (68.85 wt%) and HHV (34.16 MJ/kg) were achieved with 20 wt% 4Co-1Fe/AC catalyst. Methyl phenol derivatives were found to be the main component in upgraded bio-oil. The carbon number of upgraded bio-oil was mainly distributed in C5–C11 fraction, especially with the C8 component (20.40 wt%). The catalysts were deactivated by the formation of carbonaceous compounds on the external surface, oxidation of metal species, and blocking of active sites on catalysts.

Hydrodeoxygenation of BHET/DMT on Bimetal catalysts as the Model Compounds of Polyester Waste and Fast Pyrolysis of Polyethylene Terephthalate

이데이야 앳 시아리프 강원대학교 대학원(삼척캠퍼스) 2026 국내박사

The worldwide increase of plastic trash, especially polyethylene terephthalate (PET), has raised significant environmental and economic issues. Among emerging strategies, catalytic pyrolysis and hydrodeoxygenation has shown great promise for the direct conversion of PET into valuable aromatic hydrocarbons under thermal conditions. This study investigates the hydrodeoxygenation (HDO) of bis(2-hydroxyethyl) terephthalate (BHET), a model compound representing polyethylene terephthalate (PET) waste, using Ni–Fe bimetallic catalysts supported on γ-Al2O3 synthesized via spray pyrolysis. The objective was to enhance deoxygenation efficiency and aromatic hydrocarbon selectivity under atmospheric pressure conditions. Catalysts with different Ni/Fe ratios were analyzed using XRD, XPS, BET, TPR, and NH₃-TPD to investigate the structural, electrical, and acidic aspects affecting catalytic performance. Among all tested catalysts, Ni5-Fe15 exhibited the highest performance, achieving 99.79% BHET conversion and a 76.57% degree of deoxygenation at 500 °C. GC–MS analysis revealed dominant formation of benzene (37.21 area%), naphthalene (30.21 area%), and biphenyl (13.21 area%), confirming efficient C–O bond cleavage through synergistic Ni–Fe alloy interactions. Gas analysis indicated balanced H2 (47.49 mol%), CO (24.85 mol%), and CO2 (21.60 mol%) selectivity, suggesting concurrent decarbonylation and decarboxylation pathways. The spray pyrolysis synthesis provided uniform metal dispersion and enhanced acidity, resulting in superior catalytic stability and minimized coke formation. Overall, this work establishes Ni–Fe/γ-Al2O3 as a cost-effective and sustainable catalyst for converting PET-derived oxygenated intermediates into valuable aromatic hydrocarbons, contributing to the advancement of green catalysis and circular economy-based plastic recycling technologies. The selective HDO of BHET, a model compound had been tested using bimetallic Pt-Sn/γ- Al2O3 catalysts. The objective was to enhance deoxygenation efficiency and aromatic selectivity under mild, atmospheric conditions. Catalysts with different Pt/Sn ratios (Pt7Sn3, Pt7.5Sn2.5, Pt8Sn2, and Pt8.5Sn1.5) were synthesized using incipient wetness impregnation and studied using XRD, BET, H₂-TPR, NH₃-TPD, SEM-EDX, and XPS to clarify structure–function correlations. The Pt7.5Sn2.5 catalyst exhibited best performance, achieving 100% BHET conversion and a 94.24% degree of deoxygenation at 400 °C, with high selectivity toward benzene (45.42%), ethylbenzene (40.56%), and toluene (7.59%). This optimal behavior results from the synergistic electronic and structural interactions between Pt and Sn, which facilitate C–O bond cleavage while suppressing excessive hydrogenation and cracking. Reaction pathway analysis revealed that BHET transformation proceeds via benzoic acid and benzaldehyde intermediates, leading to fully deoxygenated aromatics. These findings highlight the potential of Pt–Sn/γ-Al₂O₃ catalysts for efficient, low-pressure chemical upcycling of PET-derived compounds. The proposed catalytic strategy provides a sustainable and scalable pathway for transforming polyester waste into valuable aromatic hydrocarbons, contributing to the advancement of circular economy and green chemical recycling technologies. The investigates the selective hydrodeoxygenation (HDO) of dimethyl terephthalate (DMT) a primary PET depolymerization intermediate into benzene, toluene, and xylene (BTX) over Co– Fe/SiO2 catalysts using tetralin as an in situ hydrogen donor. Bimetallic catalysts with varying Co/Fe ratios were synthesized via wet impregnation and characterized by BET, XRD, SEM-EDX, NH₃-TPD, H2-TPR, and XPS to correlate physicochemical properties with catalytic performance. The 5 wt% Co–15 wt% Fe/SiO2 catalyst exhibited the highest efficiency, achieving 99% DMT conversion, 28.9% benzene yield, and 95.1% deoxygenation degree at 450 °C after 1 h. The enhanced activity was attributed to strong Co–Fe alloy interactions that improved reducibility, dispersion, and acid–metal balance, facilitating selective C–O bond cleavage while preserving aromatic rings. Methyl benzoate was identified as a key intermediate, transforming via decarbonylation, decarboxylation, and methylation pathways. Reaction temperature and time significantly influenced selectivity, while tetralin effectively provided hydrogen without external supply. These findings highlight the potential of Co–Fe alloy catalysts and hydrogen-donor solvents to convert PET-derived intermediates into sustainable aromatic chemicals, offering a promising and scalable route for circular carbon utilization and reduced dependence on fossil-based aromatics. The study investigates of catalytic fast pyrolysis of waste polyethylene terephthalate (PET) conducted in a bubbling fluidized-bed reactor, emphasizing the effect of natural dolomite (CaMg(CO3)2) on product distribution and deoxygenation behavior. Calcined dolomite was characterized by XRD, BET, SEM-EDX, ICP-OES, and TGA, confirming its crystalline CaO–MgO phases, mesoporous texture (13.23 m²/g), and bifunctional basic–acidic surface active for C–O bond cleavage. Fast pyrolysis experiments were performed between 475–550 °C and at different fluidization velocities (2.0–3.0×Umf) to evaluate product yields of major products . At optimal conditions (500 °C, 2.5×Umf), catalytic pyrolysis produced a liquid yield of 35.66 wt%, biphenyl yield of 5.53 wt%, and decreased gas yield (37.87 wt%), outperforming non-catalytic reactions. The presence of dolomite increased the aromatic hydrocarbon peak area from 12.89% to 20.15%, enhanced H2 evolution (up to 9.65 mol%), and reduced CO2 selectivity from 51.94 mol% to 41.60 mol%, confirming its role in deoxygenation and CO2 sorption. Elemental analysis and FTIR/UV–Vis spectra of recovered terephthalic acid (rTPA) showed high structural similarity to pure TPA, indicating effective depolymerization and reformation. The study demonstrates that dolomite catalysis promotes deoxygenation and aromatic formation during PET pyrolysis, establishing a sustainable and cost-effective route for plastic waste valorization and green aromatic chemical production.