This study presents the development and optimisation of a co-production process for methanol and carbon monoxide via methane decomposition using Aspen Plus. The process model was designed to evaluate the system's energy efficiency, economic viability, and environmental impact. The overall energy efficiency of the process was calculated to be 89.4%, demonstrating its high performance in energy utilisation. The levelised cost of methanol production was determined to be 17.5 € per GJ, indicating competitive economic feasibility. Furthermore, a total life cycle CO₂ emission of 0.5 kg_CO2 kg_product⁻¹ was achieved, highlighting the process's potential for reduced environmental impact compared to conventional methods. The results suggest that methane decomposition for the co-production of methanol and carbon monoxide offers a promising pathway for sustainable chemical production, combining high energy efficiency with low carbon emissions.