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Theoretical Study for Optimizing Methane Conversion Bioprocess to Biodegradable Plastics in Bubble Column Reactors using Flux Balance Analysis

Nasershariat, Mohadeseh | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58451 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Pishvaie, Mahmoud Reza; Bozorgmehry Boozarjomehry, Ramin; Waldherr, Stephane
  7. Abstract:
  8. In recent years, the production of biodegradable plastics from renewable resources has been proposed as an effective solution to address the issue of fossil fuel-based plastic accumulation. Recently, the technology of converting methane into biodegradable plastics has emerged as an effective process in this field. The advantages of this process include reducing the accumulation of fossil fuel-based plastics in the environment, lower production costs due to the use of inexpensive raw materials, and decreasing greenhouse gas emissions. In this process, methanotrophic microorganisms convert methane into biodegradable plastics in two stages: biomass growth and plastic production under nutrientlimited conditions. This research focuses on converting methane into biodegradable plastics using the microorganism Methylocystis hirta. The objectives of this study include examining the metabolic pathways and fluxes in both stages of the microbial process using flux balance analysis, modeling and analyzing the performance of bubble column reactors for this process through dynamic flux balance analysis. Estimating the volumetric mass transfer coefficients of the reactors by fitting existing experimental data with the results of the implemented model and refining the Monod kinetic model used to determine constraints in flux balance analysis during growth and plastic production phases are also among the goals of this research. Additionally, the study investigates two gas feeding approaches— serial and parallel—in the growth and plastic production reactors, modeling the methane conversion reactor while considering the reactor's geography, and analyzing the production of side products during the growth phase of this process. By studying the impact of gas recirculation into the reactor and the gas residence time on the growth reactor’s performance through the implemented dynamic model, it was observed that methane removal efficiency increased by 38% when the recirculation ratio was changed from 0 to 30 at a residence time of 60 minutes. Additionally, the results indicated that the method of gas feeding influences the process performance. Switching the feeding mode from parallel to serial resulted in a 67% reduction in the gas recirculation rate in the growth reactor. Modeling results considering reactor geography showed that, given the small size of the reactor, there was no significant change compared to the lumped model. Ultimately, considering the discrepancies between the kinetic Monod model and the flux balance analysis model for the laboratory-scale reactor during the growth phase, evidence was found for the formation of a side product. This discrepancy was further investigated by examining riboflavin production as a side product and applying a multi-objective optimization approach. The results suggested the potential production of riboflavin as a side product in the reactor
  9. Keywords:
  10. Flux Balance Analysis Method ; Polyhydroxybutyrate ; Methane ; Methylocystis Hirsuta ; Genome Scale Metabolic Model ; Methane Conversion

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