Deducing targets of emerging technologies based on ex ante life cycle thinking: Case study on a chlorine recovery process for polyvinyl chloride wastes

A novel chlorine (Cl) recovery process for polyvinyl chloride (PVC) wastes can potentially avoid the formation of undesirable Cl-containing compounds during thermal treatments, improve hydrocarbon usability, and create a Cl circulation system. Here, using a case study in Japan, we applied an approach based on ex ante life cycle thinking to guide the future development of the Cl recovery process in terms of the potential energy efficiency and greenhouse gas (GHG) emission. First, energy consumption and GHG emissions associated with current PVC waste treatments were investigated to benchmark the evaluated process. Next, a life cycle inventory (LCI) model containing two variables, dechlorination degree X and P/K (a variable decided by operating conditions), was developed based on chemical stoichiometry using previous experimental and material flow analysis studies. Using the LCI, the potential net energy consumption and GHG emission of the Cl recovery process based on the investigated variables were obtained. Subsequently, the target thresholds of variable values were deduced by comparing the impacts against the benchmarks. Based on a contribution analysis, although the dechlorination process would be a hotspot for energy consumption, the energy credit could be generated from the reduced Cl treatment for tail gas during thermal processing of PVC wastes and recovered salt. The acceptable variable thresholds can be used to suggest the development target setting for the Cl recovery process at an industrial scale.