A novel chemical looping route for efficient hydrogen production from polystyrene waste: An energy, exergy, economic, and environmental evaluation

This study evaluates the technical and economic feasibility of converting problematic polystyrene waste into clean hydrogen through two process routes: conventional syngas processing (Case 1) and an innovative chemical looping approach (Case 2). The second case integrates a chemical looping CO₂ removal process where calcium oxide captures CO₂ while a high-temperature water-gas shift (WGS) reaction and subsequent calcination occur within the same reactor, enabling simultaneous syngas cleaning and efficient hydrogen production with CO₂ separation for storage. The technical analysis reveals that the chemical looping case (Case 2) outperforms the base case (Case 1) across several key metrics. In Case 2, the process efficiency is notably higher at 80 %, compared to just 39 % in Case 1. Additionally, the smooth temperature profile in Case 2 leads to lower exergy destruction and higher overall exergy efficiency of 82.5 % compared to 54.7 % in Case 1. The life cycle assessment demonstrates that the chemical looping design (Case 2) reduces cradle-to-gate greenhouse gas emissions to 4.84 kg CO₂-eq per kg H₂, achieving a 64 % lower carbon footprint than the conventional design (Case 1). Economic evaluation further highlights the benefits of the chemical looping method. In Case 2, the levelized cost of hydrogen production decreased by 10 % compared to Case 1, dropping from $1.33/kg to $1.20/kg. The novelty of this work lies in integrating syngas processing and CO₂ capture within a single chemical looping reactor, enabling simultaneous water–gas shift and carbonation–calcination reactions.