Techno-environmental assessment of methanol production using chemical looping technologies

In light of the growing energy demand, fossil fuels (e.g., coal, gas or crude oil) continue to play an essential role in meeting the world's energy requirements. Methanol shows great potential both as an energy carrier or as a building block for several products including methyl tert-butyl ether, dimethyl ether, formaldehyde, acetic acid, etc. The current research focuses on methanol production via CO2 hydrogenation since it is the technology with the largest development perspective at commercial scale. The much-needed H2 and CO2 are obtained using chemical looping technologies involving calcium oxide (CaO), iron oxide (Fe2O3), and CaO-CuO as oxygen carriers. The proposed technologies are compared against conventional technology involving the steam methane reforming process for H2 generation, as well against green methanol production (i.e., electrolytic H2 generation using renewable sources). CHEMCAD software is employed to perform the modelling and simulation aspects with all investigated scenarios considering a daily production capacity of 2400 tons of methanol. The environmental analysis is carried out based on Life Cycle Assessment (LCA) methodology using mass and energy balance data retrieved from process modelling and simulation section. One ton of methanol is set as functional unit. Based on the technical evaluation, even though sorption enhanced reforming (SER) configuration provides the highest H2 efficiency (78.62 %), the iron-based chemical looping (CLH) system offers higher carbon capture rate with similar efficiency (76.61 %). Green methanol manufacturing scores best, getting the lowest effect score in eight out of twelve impact categories; yet, its performance is heavily dependent on the availability of renewable power sources. Of the looping technologies, the use of iron-based chemical looping has the least negative effects in eight of them, including global warming potential (GWP), fossil depletion potential (FDP) and freshwater eutrophication potential (FEP). It is found that, in terms of greenhouse gas emissions, direct methanol synthesis using chemical looping technology proves competitive against the traditional natural gas approach.