Power-to-liquid via synthesis of methanol, DME or Fischer–Tropsch-fuels: a review

The conversion of H2 and CO2 to liquid fuels via Power-to-Liquid (PtL) processes is gaining attention. With their higher energy densities compared to gases, the use of synthetic liquid fuels is particularly interesting in hard-to-abate sectors for which decarbonisation is difficult. However, PtL poses new challenges for the synthesis: away from syngas-based, continuously run, large-scale plants towards more flexible, small-scale concepts with direct CO2-utilisation. This review provides an overview of state of the art synthesis technologies as well as current developments and pilot plants for the most prominent PtL routes for methanol, DME and Fischer-Tropsch-fuels. It should serve as a benchmark for future concepts, guide researchers in their process development and allow a technological evaluation of alternative reactor designs. In the case of power-to-methanol and power-to-FT-fuels, several pilot plants have been realised and the first commercial scale plants are planned or already in operation. In comparison power-to-DME is much less investigated and in an earlier stage of development. For methanol the direct CO2 hydrogenation offers advantages through less by-product formation and lower heat development. However, increased water formation and lower equilibrium conversion necessitate new catalysts and reactor designs. While DME synthesis offers benefits with regards to energy efficiency, operational experience from laboratory tests and pilot plants is still missing. Furthermore, four major process routes for power-to-DME are possible, requiring additional research to determine the optimal concept. In the case of Fischer-Tropsch synthesis, catalysts for direct CO2 utilisation are still in an early stage. Consequently, today's Fischer-Tropsch-based PtL requires a shift to syngas, benefiting from advances in co-electrolysis and reverse water-gas shift reactor design.