Transition to low-carbon ammonia and methanol through hybrid energy systems and direct air capture: A 4E assessment

Decarbonizing methanol and ammonia production has become increasingly important for reducing greenhouse gas emissions; however, balancing environmental benefits with economic feasibility remains a major challenge. This study addresses this challenge by providing a unified comparative assessment of four production pathways integrating advanced carbon capture technologies and hybrid energy systems. Four scenarios, including blue methanol, green methanol, gray ammonia, and green ammonia, are evaluated in terms of their technical, economic, exergy, and environmental performance. The process units, including steam methane reforming (SMR) and water electrolysis for hydrogen production, post-combustion carbon capture (PCC) and direct air capture (DAC), and methanol and ammonia synthesis, were simulated using Aspen HYSYS and Aspen Plus. The parabolic trough collector (PTC)-based solar plant was modeled using Thermoflex and System Advisor Model (SAM) software to meet the thermal demands of the production chain. A sensitivity analysis on the solar fraction was conducted to determine the economically optimal point. Economic analysis indicates that blue methanol and gray ammonia exhibit significant profitability, with net present values (NPV) of 285 and 207 M$, respectively. In contrast, green methanol and green ammonia have high levelized costs (LCOM = 856 $/t; LCOA = 837 $/t), rendering them economically unviable at a 10% discount rate. At a reduced discount rate of 4%, green methanol and green ammonia achieve NPVs of 123 and 135 M$, respectively, indicating improved economic viability. Exergy analysis shows that green methanol and green ammonia attain the highest overall exergy efficiencies of 41.9% and 43.5%, respectively. Environmental analysis using Global Warming Potential (GWP) metric shows that green methanol and green ammonia reduce greenhouse gas emissions by 57% and 90%, respectively. The findings of this study demonstrate that low-carbon and green pathways can reduce emissions while remaining economically viable under hybrid energy systems, with supportive policies and financial incentives.