Navegando por Assunto "Pyrolysis"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Análise do processo de despolimerização de resíduos de resinas dentárias à base de pmma em diferentes escalas de produção
(Universidade Federal do Pará, 2024-06-26) RIBEIRO, Haroldo Jorge da Silva; MACHADO, Nélio Teixeira; http://lattes.cnpq.br/5698208558551065; BORGES, Luiz Eduardo Pizarro; http://lattes.cnpq.br/8756886156388456; https://orcid.org/0000-0002-2337-4238
In recent years, the increasing use of plastics has brought economic and industrial benefits but has also led to a significant rise in waste, representing a global environmental challenge. In this context, pyrolysis emerges as a promising technology, offering potential solutions to address the growing problem of plastic waste and promote a more sustainable circular economy. This study investigated the thermal decomposition of dental waste based on poly(methyl methacrylate) (PMMA), focusing on the thermodynamic characterization and optimization of pyrolysis processes at different production scales. Thermogravimetric analysis (TG) showed that PMMA waste remains stable up to 200 ºC, with degradation starting as mass loss occurs beyond this temperature. Thermal decomposition was observed to occur in a single stage, with a decomposition peak at 366 ºC, within the range of 327 ºC to 405 ºC, primarily due to radical depolymerization under inert nitrogen and argon atmospheres. Differential Scanning Calorimetry (DSC) analysis revealed an endothermic peak between 370 ºC and 433 ºC, highlighting the complexity of the pyrolysis processes. The energy characterization showed specific values of 423 J/g for total heat, 1748 J/g for gasification heat, and approximately 820 J/g for decomposition heat, indicating discrepancies that require further investigation for a more complete understanding. In studies using semi-batch fixed-bed reactors, a temperature gradient along the bed was observed to have an adverse impact on the liquid yield and MMA concentration, especially in technical and pilot scales, where the gradient was more pronounced due to the thicker bed. Two critical variables were identified: reactor load and power load, both of which decreased as the process scale increased, leading to lower pyrolysis temperatures and negatively affecting MMA production. Additionally, higher temperatures were found at the edges of the fixed bed, which increased gas production and reduced liquid yield. The liquid fraction analysis revealed a predominance of MMA at the beginning of the reaction, with a gradual transition to aromatic hydrocarbons in the final stages, associated with the pyrolysis of residual char, which increased with the scale of production. The results highlight the effectiveness of temperatures below 450 ºC in producing MMA-rich liquid fractions, even under temperature gradient conditions, emphasizing the importance of moderate heating rates for efficient PMMA depolymerization in semi-batch systems. These findings provide valuable insights for reactor design and are essential for the economic evaluation and optimization of PMMA recycling processes through pyrolysis at various production scales.
Acesso aberto (Open Access)
Estudo do processo de depolimerização de resíduos de resinas dentárias de polimetilmetacrilato (PMMA) via pirólise
(Universidade Federal do Pará, 2022-01-05) SANTOS JUNIOR, Paulo Bisi dos; MACHADO, Nélio Teixeira; http://lattes.cnpq.br/5698208558551065
Polymer materials, due to the diversity of their properties, ease of processing and ability to replace traditional materials, have become indispensable in modern society, although the growing accumulation of plastic waste has become a relevant problem that is difficult to manage. Given this situation, sustainability research has invested in new strategies focused on the processing and transformation of plastic waste where the pyrolysis process presents itself as a promising technology. In this work, the cross-linked PMMA-based dental resins scraps submitted to pyrolysis to recover MMA (Methylmethacrylate). The thermal degradation of cross-linked PMMA-based dental resins scraps analyzed by TG/DTG to guide the operating conditions. The pyrolysis carried out in a reactor of 143L, at 345, 405, and 420 °C, 1.0 atm. The reaction liquid products obtained at 345 °C, 30, 40, 50, 60, 70, 80, and 110 minutes, physicochemical characterized for density, kinematic viscosity, and refractive index. The chemical composition of reaction liquid products obtained at 354 °C, 30, 40, 50, 60, 70, 80, and 110 minutes, at 405 °C, 50, 70, and 130 minutes, and at 420°C, 40, 60, 80, 100, 110, and 130 minutes determined by GC-MS. The experiments show that liquid phase yields were 55.50%, 48.73%, and 48.20% (wt.), at 345, 405, and 420 °C, respectively, showing a smooth sigmoid behavior, decreasing with increasing process temperature, while that of gas phase were 31.69%, 36.60%, and 40.13% (wt.), respectively, increasing with temperature. The reaction liquid products density, kinematic viscosity, and refractive index obtained at 30, 40, 50, 60, 70, 80, and 110 minutes, varied between 0.9227 and 0.9380 g/mL, 0.566 and 0.588 mm2/s, and 1.401 and 1.414, respectively, showing percentage errors between 0.74 and 2.36%, 7.40 and 10.86%, and 0.00 and 0.92%, respectively, compared to standard values for density, kinematic viscosity, and refractive index of pure MMA (Methylmetaclylate) at 20 °C. The GC-MS identified in the reaction liquid products during pyrolysis at 345, 405, and 420 °C, 1.0 atm, esters of carboxylic acids, alcohols, ketones, and aromatics, showing concentrations of MMA (Methylmetaclylate) between 83.454 and 98.975% (area.). For all the depolymerization kinetic experiments at 345, 405, and 420 °C, 1.0 atm, the concentrations of MMA (Methylmetaclylate) in the liquid phase, between 30 and 80 minutes, reach purities above 98% (area.), decreasing drastically with increasing reaction time after 100 minutes, thus making it possible to depolymerize the cross-linked PMMA-based dental resins scraps by pyrolysis to recover MMA (Methylmethaclylate).
Acesso aberto (Open Access)
Estudo dos constituintes dos produtos de pirólise visando a produção de biocombustíveis e químicos
(Universidade Federal do Pará, 2020-09-21) FERREIRA, Márcia de Fátima Pantoja; RIBEIRO, Nielson Fernando da Paixão; http://lattes.cnpq.br/0755443458423442; https://orcid.org/0000-0001-6145-7993; FRANÇA, Luiz Ferreira de; http://lattes.cnpq.br/6545345391702172
This work aims to use slow pyrolysis in biomass residues (EFB) as an energy potential in the production of biofuels. The raw material was obtained from agribusiness and subjected to washing, drying and crushing. The experiments were carried out in a fixed bed reactor and the central rotational composite design was used to optimize the variables temperature (459, 500, 600, 700, 741 °C) and carrier gas flow (0.259; 0.3; 0.4; 0.5 and 0.541 L/min), in order to identify the ideal conditions for obtaining bio-oil (BO). From the optimized result, the products were characterized using various techniques (FTIR, CG / MS, HPTLC, NMR, MEV, humidity, CHNO). Temperature was the most influential parameter in relation to liquid and solid yields, and the combination of variables influenced the yield in gas. There was a higher yield in BO (45.29%) whose composition showed a large amount of fatty acids, alkanes, alkenes and phenolic compounds, the latter with high antioxidant capacity. Biochar showed low yield (27.52%), but good energy capacity, the gas yield was 27.89%. The calorific value of the BO was 24.48 MJ/kg and the biochar was 19.27 MJ/kg. The results of the techniques used, prove the use of EFB as a renewable source in obtaining biofuels.