DSpace Coleção: PPGQ

Valorização da silverskin do café por pirólise lenta: modelagem cinética multicomponente e potencial do biocarvão para captura de carbono

2026-10-01T06:10:28Z

Título: Valorização da silverskin do café por pirólise lenta: modelagem cinética multicomponente e potencial do biocarvão para captura de carbono Autor(es): Gouveia, Jhonatas Wagner Barbosa da Costa Orientador: Santos, Nataly Albuquerque dos Abstract: Slow pyrolysis applied to coffee silverskin, an abundant and underutilized agroindustrial residue, represents a strategic alternative for waste valorization and sustainability promotion. However, the literature still lacks investigations that integrate multicomponent kinetic modeling, the evaluation of thermodynamic activation parameters, and the study of the potential of the biochar generated for carbon capture, especially under experimental conditions that represent scenarios close to large-scale production processes. This study proposes, in an unprecedented way, the application of an integrated and rigorous protocol encompassing the detailed physicochemical characterization of silverskin, including proximate and ultimate analyses, higher heating value, density, Fourier transform infrared spectroscopy, X-ray fluorescence, and thermogravimetric analysis, up to the controlled production of biochars at 450 °C and 550 °C in a fixed-bed reactor, with evaluation of yield, composition, and structure of the obtained products. For an in-depth understanding of the thermal decomposition mechanism, isoconversional methods (Friedman, Flynn-Wall-Ozawa, Kissinger- Akahira-Sunose, and Starink) were employed in conjunction with DTG curve deconvolution using the asymmetric sigmoidal function (Asym2Sig), allowing the determination of the kinetic triplet (activation energy, pre-exponential factor, and reaction model) for each pseudocomponent of the biomass (extractives, hemicellulose, cellulose, and lignin). Prior to kinetic modeling, the physicochemical characterization of the biomass revealed that silverskin presents a high volatile content (73.63%), low ash content (6.64%), and a heating value of 21.03 MJ kg⁻¹. The biochars obtained at 450 °C (B45) and 550 °C (B55) exhibited fixed carbon contents of 50.53% and 52.15%, respectively, accompanied by a marked reduction in the atomic ratios H/C and O/C, indicating a higher degree of aromaticity and thermal stability. Elemental analysis placed the materials in the biochar region with greater thermal and structural stability, indicative of high carbon persistence in the material, a feature favorable for environmental applications such as CO₂ adsorption, contaminant retention, and soil quality improvement. In turn, DTG curve deconvolution performed using the Asym2Sig model allowed the discrimination of pseudocomponents and the application of multicomponent kinetic modeling. The activation energies ranged from 101 to 236 kJ mol⁻¹, following the order P-EX < P-HC < P-CL < P-LG. The isoconversional methods of Friedman, Flynn- Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink showed correlation coefficients higher than 0.98, confirming the robustness of the applied model. The thermodynamic parameters indicated that pyrolysis is an endothermic process (ΔH# > 0) and nonspontaneous (ΔG# > 0), with predominantly negative entropy variations associated with the formation of organized products. The kinetic study of CO₂ adsorption, conducted in TGA, fitted well to the pseudo-second-order model (R² > 0.99), indicating that the process is controlled by the interaction between CO₂ and the active sites of the material. The intraparticle diffusion model suggested three distinct stages (film diffusion, internal diffusion, and equilibrium approach), while the activation energies of 28.02 kJ mol⁻¹ (B45) and 37.04 kJ mol⁻¹ (B55) were consistent with reversible physisorption processes. B55 showed higher adsorptive capacity (44.29 mg g⁻¹ at 30 °C), larger surface area (388.36 m² g⁻¹), and good stability in successive adsorption–desorption cycles, suggesting potential for application in cyclic CO₂ capture processes. Overall, the results demonstrate that slow pyrolysis of silverskin generates biochars with high structural stability and potential for carbon capture, in addition to providing relevant kinetic and thermodynamic insights for a detailed understanding of the process. Thus, the results reinforce the potential of silverskin in biochar production, comprising a low-carbon and promising strategy for mitigating environmental impacts. Editor: Universidade Federal da Paraíba Tipo: Dissertação

Análise voltamétrica de diuron em águas usando eletrodo de carbono vítreo

2026-09-30T06:11:35Z

Título: Análise voltamétrica de diuron em águas usando eletrodo de carbono vítreo Autor(es): Soares, Fernanda Silva Orientador: Araújo, Mário César Ugulino de Abstract: The diuron herbicide is one of the most used pesticides in Brazil for weed control and has caused great environmental and public health concerns, due to its toxicity and carcinogenic potential. The use of pesticides on a large scale can contaminate water, which can cause acute problems and effects for the human body, through its exposure. Thus, the development of methods to determine substances in water (or different methods) quickly, effectively and at low cost have been used. As electroanalytical techniques, they can be presented as alternatives of chromatographic practicality, due to their low acquisition cost, high sensitivity, speed, and practical miniaturization capacity for chromatographic analysis. Therefore, in this work, the glassy carbon electrode (GCE) was subjected to electrochemical studies using the techniques of cyclic voltammetry (CV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV). With the voltammetric studies carried out, a peak of diuron oxidation was observed at approximately +1.15 V, through an irreversible process, with pH 2.2 in the Britton-Robson buffer being the most sensitive means of analysis, with a transport of mass governed by diffusion. Among the techniques for quantitative studies, SWV was more sensitive when compared to DPV, so the experimental parameters chosen were frequency 25 s-1, pulse amplitude 70 mV and potential increment of 10 mV. The analytical curve was constructed in a linear range of 38,46 – 115,04 nmol L-1, obtaining a detection and quantification limit of 0.200 nmol L-1 and 0.606 nmol L-1, respectively. The proposed method was successfully applied to the waters of João Pessoa and the metropolitan region, and an amount of diuron (44.02 nmol L-1) was detected in one of them (sample P6). The recovery test applied to all eight analyzed water samples showed good recovery values ranging from 87.99% and 108.02%, which demonstrates the efficiency of the method developed and provides greater reliability in the results achieved. Thus, studies to determine diuron in tap and river water have shown to be promising, enabling the use of the developed method. Editor: Universidade Federal da Paraíba Tipo: Dissertação

Uso de solventes eutéticos profundos ternários na extração de cafeína a partir da borra do café

2026-09-05T06:12:46Z

Título: Uso de solventes eutéticos profundos ternários na extração de cafeína a partir da borra do café Autor(es): Santos, Aline Mendes Gomes dos Orientador: Pontes, Liliana de Fátima Bezerra Lira de Abstract: The growing global demand for coffee results in massive production of coffee waste, primarily in the form of used coffee grounds. This residue, despite being a potentially rich source of bioactive compounds, is often discarded without efficient utilization. Among the bioactive compounds present in used coffee grounds, caffeine stands out due to its stimulating properties and its various applications in the food, pharmaceutical, and cosmetic industries. This study aimed to investigate the use of ternary deep eutectic solvents in the extraction of caffeine from coffee grounds. For this purpose, two eutectic solvents were synthesized using choline chloride as a hydrogen bond acceptor and citric acid, lactic acid, and glucose as hydrogen bond donors. A 22 experimental design was applied to evaluate the influence of temperature and time variables on the caffeine extraction process. Caffeine extraction from used coffee grounds (Coffea arabica) was performed using 0,1 g of grounds and 3 mL of solvent with 10% water addition. All extractions were conducted in a heated bath with vortex assistance. The experimental design showed that temperature had the greatest influence on caffeine extraction, resulting in higher caffeine concentrations (42,90 mg g⁻¹) in the experiment conducted at 85°C for 45 minutes. Overall, caffeine extraction with ternary Deep Eutectic Solvents proved to be an efficient alternative with good recovery rates. The deep eutectic solvent composed of choline chloride, citric acid, and lactic acid demonstrated the highest extraction capacity due to the larger number of hydroxyl sites in its chemical structure, making it an excellent caffeine extraction solvent. However, further research is needed to investigate caffeine degradation processes at higher temperatures. Editor: Universidade Federal da Paraíba Tipo: Dissertação

Determinação de HPAS em cachaça e açúcar utilizando membranas de náilon, espectroscopia de fluorescência e PARAFAC

2026-09-04T06:12:10Z

Título: Determinação de HPAS em cachaça e açúcar utilizando membranas de náilon, espectroscopia de fluorescência e PARAFAC Autor(es): Sousa, Larissa Ferreira de Orientador: Fragoso, Wallace Duarte Abstract: Polycyclic aromatic hydrocarbons (PAHs) are formed from the incomplete combustion of organic matter, being classified as persistent organic pollutants, with some recognized as carcinogenic. In the context of sugarcane, the practice of burning for agricultural management or energy production can generate PAHs, which contaminate derived products such as cachaça and sugar. These products are widely consumed in Brazil, highlighting the importance of monitoring PAHs in these matrices. Chromatography is the reference technique for determining these contaminants; however, it is costly and requires a significant amount of analysis time. In this study, alternative approaches based on fluorescence spectroscopy using nylon membranes combined with second-order calibration (PARAFAC) were evaluated for the determination of PAHs. Two preconcentration systems were employed: (i) positive-pressure filtration using a filter holder, applied to cachaça samples, and (ii) rotating-disk sorptive extraction (RDSE), applied to sugar samples. The PAHs studied were benzo[a]pyrene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[g,h,i]perylene, and dibenzo[a,h]anthracene. For sugar samples, the RDSE system exhibited problems caused by the presence of sucrose, which hindered the achievement of satisfactory results. In addition to the high viscosity of sugar solutions, sucrose impregnated the membrane, leading to fluorescence suppression, thereby evidencing a strong matrix effect. Reflectance and fluorescence spectra of sugar samples were presented in this study to demonstrate this effect. The filtration system for cachaça proved quantitative and effective for detecting PAHs in the range of 24 to 225 ng L⁻¹. The method yielded apparent recoveries between 91% and 105%. RMSEP values ranged from 11 to 17 ng L⁻¹, while limits of detection were between 16 and 27 ng L⁻¹, demonstrating good sensitivity associated with low method errors. Editor: Universidade Federal da Paraíba Tipo: Dissertação