化学工学の研究者がポリスチレンのリサイクル技術を分析(Chemical Engineering Researchers Analyze Technology for Polystyrene Recycling)

2024-05-23

2024-05-22 ウースター工科大学(WPI)

WPIの化学工学部と英国のバース大学の研究チームは、現在の技術では5%以下しかリサイクルできないポリスチレンを最大60%リサイクル可能にする技術を分析しました。ポリスチレンは低コストで耐衝撃性が高く、食品包装や壊れやすい部品の配送に適していますが、その構造がリサイクルを困難にしています。
◆研究チームは、ピロリシスという加熱分解法を用いてモノマー級のスチレンを回収し、蒸留で純度を高める多段階プロセスを分析しました。このプロセスは信頼性が高く、エネルギー効率も良いため、経済的に実現可能であり、温室効果ガス排出量も削減できます。研究は、ポリスチレンを環境から効果的に除去するための現実的な方法として評価されています。

＜関連情報＞

廃ポリスチレンからモノマーグレードのスチレンを回収する展開可能でスケーラブルなプロセスの熱力学的・経済学的分析 Thermodynamic and economic analysis of a deployable and scalable process to recover Monomer-Grade styrene from waste polystyrene

Madison R. Reed, Elizabeth R. Belden, Nikolaos K. Kazantzis, Michael T. Timko, Bernardo Castro-Dominguez
Chemical Engineering Journal Available online: 9 May 2024
DOI:https://doi.org/10.1016/j.cej.2024.152079

Highlights

Chemical recycling of polystyrene using technology ready yields > 99 % pure styrene.
The process is thermodynamically (<10 MJ/kg) and economically competitive.
60% of virgin polystyrene can be replaced by chemical recycling.

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 CO₂ abatement cost is roughly $1.5 per ton of averted CO₂, 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.