Search the digital library catalog

Abstract: The discharge of synthetic dyes into aquatic environments poses a significant environmental threat. Waste from the vegetable oil industry, such as hemp oil cake, offers a low-cost feedstock for the production of carbonaceous adsorbents for water purification due to its high carbon content and availability. In this study, hydrochars produced from hemp oil cake and cheese whey were thermo-chemically modified using natural vinegars and compared with conventional modifiers, then tested for adsorption of bromocresol green (BCG) and methylene blue (MB) dyes. According to FTIR, BET and SEM-EDS analyses, modifications with alcoholic and wine vinegar, acetic acid and KOH significantly altered the structural properties of the hydrochars, increasing the specific surface area from 1.60 to 234.35, 260.73, 71.32 and 582.84 m²/g, respectively. Among the acid-modified hydrochars, the hydrochar modified with alcoholic vinegar was the most effective, with an adsorption capacity of 15.45 mg/g for BCG and 62.16 mg/g for MB, as determined by Langmuir kinetic model, while the unmodified hydrochar had lower capacities. In comparison, the highest adsorption capacities for KOH-modified hydrochar were 640.15 mg/g for MB and 38.17 mg/g for BCG. Adsorption kinetics mostly followed a pseudo-second order model, indicating a combination of chemical and physical adsorption mechanisms driven byelectrostatic interactions, hydrogen bonding and π–π interactions. Isothermal kinetic modelling revealed heterogeneous adsorption behaviour, with the Redlich-Peterson and Freundlich models providing the best fit to the experimental data. The results emphasise the enhanced effectiveness of thermo-chemically modified hemp oil cake hydrochars for sustainable dye removal and water purification applications.
Keywords: hydrothermal carbonization, hydrochar modification, lignocellulosic biomass, adsorption, kinetics, dyes
Published in DKUM: 21.01.2026; Views: 0; Downloads: 1
Full text (4,26 MB)

Abstract: Heterogeneous photocatalysis is an advanced oxidation technique widely explored for the selective conversion of benzyl alcohol (C₇H₈O) into benzaldehyde, an important intermediate in organic synthesis. This review critically examines the influence of key operational and morphological factors—including solvent choice, temperature, and light intensity—on photocatalytic performance. The synthesis method notably affects catalyst activity, with solvothermal preparation of TiO₂ significantly enhancing the reaction rate constant. Photo-deposition emerges as an effective alternative when both catalyst and support materials are available. Among various TiO₂ nanostructures (nanowires, nanotubes, nanofibers, nanosheets, and hollow nanospheres), hollow nanospheres exhibit superior photocatalytic activity due to improved light absorption and charge separation. Elevated light intensity and temperature further accelerate the reaction rate, resulting in higher rate constants. A range of catalysts—including C-ZnInS₄, ZnInS₄, Pt-TiO₂, RuO₂/TiO₂ nanobelts, 0.95Ru/3DOM BiVO₄-Ar-300, Pt/Bi₂MoO₆-glycerol, Ni-OTiO₂, W₁₀O₃₂⁴⁻, WO₃(7.6)/TiO₂, TiO₁.₉₆₆N₀.₀₃₄, and Bi₂WO₆—demonstrate promising rate constants of 75.0, 53.75, 57, 46.0, 38.0, 34.0, 33.25, 29.6, 28.0, 27.0 and 22.25 gcat−1 h−1 for alcohol oxidation. Notably, TiO₁.₉₆₆N₀.₀₃₄ and ZnIn₂S₄ achieve 100% conversion with>99% selectivity within 4 and 2 h, respectively, underscoring their excellent photocatalytic potential.
Keywords: alcohol, aldehyde, oxidation, photo-oxidation, semiconductor, TiO2
Published in DKUM: 19.12.2025; Views: 0; Downloads: 0
Full text (1,33 MB)

Abstract: Waste heat recovery technologies play an important role in enhancing energy efficiency and supporting sustainable energy production. This study investigates the utilization of waste heat from aluminium production through an Organic Rankine Cycle (ORC) system to generate electricity and heat simultaneously. Based on operational data from an aluminium plant, the system is firstly optimized from both the thermodynamic and economic perspectives. To maximize performance and to identify optimal configurations, a mathematical model is developed and solved using GAMS, capturing the complex interdependencies between the operational, economic and thermodynamic parameters. The environmental impact of the optimized scenarios is subsequently evaluated using a Life Cycle Assessment (LCA), considering a broad range of impact categories. The results indicate a maximum power output of 830.9 kW and a maximum net present value (NPV) of 51.71 M€, confirming the system’s technical and economic viability. The environmental assessment demonstrates the potential of ORC systems as sustainable energy solutions, with significant environmental unburdening under optimized operating conditions (up to -606.0 kg CO2 eq./h). A sensitivity analysis indicates that the greatest environmental benefits occur under the optimal thermodynamic scenario, achieved through the utilization of higher-energy flue gas streams (up to -515.0 kg CO2 eq./h), and under the optimal economic scenario by balancing the electricity and heat prices optimally for simultaneous heat and power production (up to -696.7 kg CO2 eq./h). These findings highlight the importance of the thermal input quality and availability in maximizing ORC performance. With the ability to prioritize electricity, heat, or both, the optimized ORC systems support flexible energy solutions tailored to specific applications and environmental conditions, offering a promising pathway for unburdening the environment through the efficient utilization of industrial waste heat.
Keywords: waste heat recovery, aluminium production, organic rankine cycle, environmental impact, life cycle assessment, sustainable energy solutions
Published in DKUM: 13.06.2025; Views: 0; Downloads: 21
Full text (1,30 MB)

Abstract: This study presents an integrated design and optimization of an Organic Rankine Cycle (ORC) for the recovery of waste heat from aluminium production. Non-Linear Programming (NLP) models were developed, with the objectives of maximizing electricity production and the Net Present Value (NPV) of the system. The models account for optimizing the operating conditions and changes in thermodynamic features of the system. The developed models are applied to a case study of Slovenian aluminium company where the performance of three different working fluids (R245fa, R1234yf and R1234ze) are compared. The optimization is performed considering different temperatures and prices of produced hot water and electricity, minimum approach temperature (DTmin), concentration of CO2 in flue gas and temperature and flowrate of flue gas. Results show that the selected working fluids for the proposed waste heat-based ORC system have the potential to substitute up to about 830 kW of electricity in a sustainable and economic manner. Out of the three working fluids considered, R245fa showed up to 7.9% efficiency of the ORC cycle and was identified as the best performing working fluid considering both economic viability and the amount of electricity produced by the system, however the refrigerant inherently has higher GHG footprint.
Keywords: waste heat, waste heat utilization, aluminium industry, organic rankine cycle, power generation, optimization
Published in DKUM: 10.04.2025; Views: 0; Downloads: 9
Full text (2,73 MB)
This document has many files! More...

Keywords: multiple heat sources, Organic Rankine cycle, separate and cascade designs, Steam Rankine cycle, thermodynamic optimisation
Published in DKUM: 28.02.2025; Views: 0; Downloads: 4
Full text (5,16 MB)