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.
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