Electrolyser and anaerobic digestion driven CO2 hydrogenation routes towards sustainable dimethyl ether production: A review of carbon capture technologies, advanced reactor technologies, and sustainability assessment

Power-to-X (PtX) technology-based fuels can reduce greenhouse-gas (GHG) emissions by using captured carbon dioxide (CO 2 ) and can therefore support climate-change mitigation goals. PtX products include methane, methanol (MeOH), Fischer-Tropsch fuels, ammonia, and dimethyl ether (DME). DME is a potentially sustainable energy carrier that can substitute for diesel and liquefied petroleum gas (LPG), and it can be blended with LPG as a cleaner alternative fuel. Although previous studies have reported advances in catalyst developments, individual production routes, and PtX products, however, limited attention has been provided to a systems-level comparison of two feasible renewable DME production routes. This review compares water-splitting electrolysis and anaerobic-digestion routes and evaluates carbon-capture technologies, catalysts and reactor performance, process intensification, energy requirements, carbon utilization, and scale-up limitations within a systems framework. Techno-economic analysis (TEA) and life-cycle assessment (LCA) indicates the environmental and economic performance of each route is conditional rather than inherent. The electrolyser-driven route can achieve a low life-cycle carbon footprint when hydrogen is produced using low-carbon based electricity source along with CO 2 capture, followed by compression, are supplied by low-emission energy. The anaerobic-digestion-driven route can provide significant GHG reductions and may achieve a net-negative result under specific waste-management scenarios. However, its performance strongly depends on feedstock source, avoided-emission credits, process-energy demand, biogas purification, reforming, and digestate management. Consequently, neither of the specific routes should be classified as universally net-zero nor carbon-negative without clearly defining their LCA boundaries and assumptions.