Exploring the potential of hybrid green and blue methanol in achieving negative CO₂ emissions: A carbon techno-economic perspective

Owing to the versatile applications of methanol and its ability to utilize external CO₂, numerous studies on e-methanol and bio-methanol are actively being conducted. However, these methanol processes face economic limitations due to the high levelized cost of methanol (LCOM). This study presents the design of a thermally integrated process that combines oxy-fuel combustion-based steam methane reforming (SMR) with high-temperature electrolysis technologies, specifically solid oxide electrolysis cell (SOEC) or H₂O/CO₂ co-electrolysis cell (HCCEC). The thermal and energy efficiencies, as well as the LCOM of the SMR-SOEC and SMR-HCCEC processes, are compared to those of previously studied SMR-PEMEC (proton exchange membrane electrolysis cell) process. Among the three types of electrolyzers, the HCCEC demonstrated the highest values, achieving 70.1 % thermal efficiency and 65.1 % energy efficiency. High-temperature electrolysis processes yielded negative CO₂ emission values of −0.173 t_CO2 (SMR-SOEC) and −0.185 t_CO2 (SMR-HCCEC) when synthesizing 1 ton of methanol. The LCOMs of the SMR-SOEC and SMR-HCCEC processes were $415.1/t_MeOH and $391.8/t_MeOH, respectively, both of which were lower than that of the SMR-PEMEC process ($437.3/t_MeOH). Notably, the LCOM of the SMR-HCCEC process is comparable to that of the conventional SMR-based methanol process ($380/t_MeOH). Considering the potential cost fluctuations of the HCCEC stack, the SMR-HCCEC process has significant potential for achieving a lower LCOM than the SMR-SOEC and SMR-PEMEC processes. This study is expected to play a significant role as an intermediate stage toward a transition from blue to green.