Greenhouse Gas Emission Assessment of PTA Production Systems: Integrating Wastewater-Treatment Methane Emissions

Purified terephthalic acid (PTA) is a key intermediate in the global polyester industrial chain, and its carbon intensity directly governs the sustainability of downstream products. The production of PTA involves high-temperature oxidation and catalytic refining processes, generating large volumes of organic wastewater whose on-site anaerobic treatment converts dissolved organic carbon into methane. This study presents a gate-to-gate process emission assessment methodology for PTA production, coupling energy-based emission factors, process carbon balance, and wastewater methane accounting within the system boundary, thereby extending conventional process-accounting frameworks. Based on a gate-to-gate life-cycle assessment of four representative PTA production systems across three industrial settings, we quantified emissions from energy consumption, process-related carbon losses, and wastewater treatment, with particular emphasis on the methane generated in the anaerobic treatment stage. Results demonstrate that steam constitutes the dominant carbon-emission contributor, accounting for 62–70% of total emissions, indicating that heat structure and recovery optimization are the highest-priority targets for emission reduction. According to carbon-flow analysis, although PX accounts for 97–98% of total carbon input, PTA products retain 95–97% of the carbon. Critically, wastewater treatment emerges as a significant yet overlooked emission pathway of methane generated during anaerobic digestion owing to its high global warming potential (GWP), so omitting methane emissions from wastewater treatment understates the total emission intensity by 7.5% to 10.8%, whereas the wastewater-treatment stage as a whole contributes 10.84% to 16.13% of total emissions. In addition, the results provide local carbon-emission factors for similar technologies, with advanced technology systems achieving 0.214 t CO2/t PTA, while less integrated systems reach 0.395 t CO2/t PTA. Low-carbon steam supply, improved heat integration, oxidation-loop control, solvent-cycle stability, and methane capture or oxidation in wastewater treatment are therefore important measures for reducing emissions, supporting the Sustainable Development Goals of responsible consumption and production and climate action. This integrated approach provides actionable insights for guiding low-carbon process optimization and more accurate carbon-accounting practices in the PTA industry.