Life cycle assessment of clean ammonia synthesis from thermo-catalytic solar cracking of liquefied natural gas

Ammonia is considered a sustainable energy storage medium with zero carbon content. In this work, thermal catalytic cracking of liquefied natural gas (LNG) at elevated temperatures employing concentrated solar tower is considered to produce clean hydrogen (CO₂-free) and studied in terms of life cycle emissions. The generated hydrogen is utilized for clean ammonia synthesis in a Haber-Bosch reactor. The proposed system is initially assessed from a thermodynamic perspective, considering energy and exergy analyses emphasizing optimization of operating conditions. Then, the proposed system's life cycle assessment (LCA) is performed to analyze ammonia synthesis's environmental impacts. The aggregate environmental impact of the proposed system is quantified and compared with conventional production processes. Through the utilization of solar energy resources, ammonia production can be attained, avoiding high harmful emissions. The LCA study is carried out in GaBi software, and the selected impact assessment methodology is ReCiPe. The impact categories studied in this work are global warming potential (GWP), terrestrial acidification, human toxicity, and particulate matter formation potential. Considering 30 years of use phase and allocation, the predicted GWP is approximately 0.616 kg CO₂ (eq.)/kg NH₃, showing the potential to reduce up to 69.2% of the GWP compared to the global average value. Concerning human toxicity and fine particulate matter formation impact categories, the system produces about 3.32E-2 kg 1,4-DB (eq.) and 5.96E-4 kg PM2.5 (eq.), respectively, per kg NH₃. The results are further analyzed by dominance, break-even, and variation analyses in detail.