Thermodynamic and economic analysis of a deployable and scalable process to recover Monomer-Grade styrene from waste polystyrene

Madison R. Reed, Elizabeth R. Beldon, Nikolaos K. Kazantzis, Michael T. Timko, Bernardo Castro Dominguez

Research output: Contribution to journalArticlepeer-review

Abstract

Less than 5% of polystyrene is recycled, motivating a search for energy efficient and economical methods for polystyrene recycling that can be deployed at scale. One option is chemical recycling, consisting of thermal depolymerization and purification to produce monomer-grade styrene (>99%) and other co-products. Thermal depolymerization and distillation are readily scalable, well-established technologies; however, to be considered practical, they must be thermodynamically efficient, economically feasible, and environmentally responsible. Accordingly, mass and energy balances of a pyrolysis reactor for thermal depolymerization and two distillation columns to separate styrene from α-methyl styrene, styrene dimer, toluene, and ethyl benzene co-products, were simulated using ASPEN to evaluate thermodynamic and economic feasibility. These simulations indicate that monomer-grade styrene can be recovered with energy inputs <10MJ/kg, comparable to the energy content of pyrolysis co-products. Thermodynamic sensitivity analysis indicates the scope to reduce these values and enhance the robustness of the predictions. A probabilistic economic analysis of multiple scenarios combined with detailed sensitivity analysis indicates that the cost for recycled styrene is approximately twice the historical market value of fossil-derived styrene when styrene costs are fixed at 15% of the total product cost or less than the historical value when feedstock costs are assumed to be zero. A Monte Carlo and Net Present Value-based economic performance analysis indicates that chemical recycling is economically viable for scenarios assuming realistic feedstock costs. Furthermore, the CO 2 abatement cost is roughly $1.5 per ton of averted CO 2, relative to a pyrolysis process system to produce fuels. As much as 60% of all polystyrene used today could be replaced by chemically recycled styrene, thus quantifying the potential benefits of this readily scalable approach.

Original languageEnglish
Article number152079
Number of pages14
JournalChemical Engineering Journal
Volume492
Early online date9 May 2024
DOIs
Publication statusE-pub ahead of print - 9 May 2024

Data Availability Statement

No data was used for the research described in the article.

Keywords

  • Chemical recycling
  • Polystyrene
  • Process design
  • Pyrolysis
  • Thermodynamic analysis

ASJC Scopus subject areas

  • General Chemical Engineering
  • General Chemistry
  • Industrial and Manufacturing Engineering
  • Environmental Chemistry

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