Plastic-to-hydrogen conversion in island contexts: A socio-technical assessment of microwave pyrolysis in Okinawa

This study evaluates the viability of plastic-to-hydrogen conversion via microwave-assisted pyrolysis within the waste management constraints of Okinawa, Japan. Using a mixed-methods approach, we combine a resident survey (n=91) with laboratory experiments on the catalytic pyrolysis of polypropylene. Exploratory social analysis suggests significant barriers to implementation: limited recycling infrastructure, high system costs, and low public tolerance for effort-intensive sorting and cleaning. While residents support improved recycling and express conditional willingness to pay, their preferences emphasize convenience and tangible value-generating outcomes. Experimentally, microwave-assisted pyrolysis using activated carbon and Fe-based catalysts successfully produced hydrogen-rich gas streams; however, these results utilize virgin plastics and do not yet reflect heterogeneous municipal waste. Comparison of social constraints and technical performance reveals a critical misalignment: the requirement for clean feedstock conflicts with user behavior, and hydrogen production aligns more closely with utility-scale energy needs than household recycling expectations. Because carbon is ultimately released during end-use, this pathway constitutes energy recovery rather than closed-loop circularity. We conclude that plastic-to-hydrogen conversion is not a standalone circular solution but may serve as a niche energy recovery strategy when integrated with industrial feedstock streams and regional decarbonization goals.