Negative CO2 emissions from flexible biofuel synthesis: Concepts, potentials, technologies

This review reports the available technologies for the flexible utilization of biomass towards negative CO2 emissions and addresses the possibility of coupling bioenergy production plants with the electrical grid converting excess electrical energy into storable chemical molecules. This changed mind-set towards biomass utilization can lead readily to the implementation of negative CO2 emission along the entire bioenergy supply chain without limiting the potential for Power-to-X applications. First, the technologies for direct conversion of waste and wood into gaseous energy carriers are screened, to highlight the current potential for the production of renewable fuels. Second, the processes for the removal of CO2 from biogenic gas streams are analysed in terms of technological performance, cost and further potential for the CO2 recovered. These technologies are the key to pre-combustion CO2 capture and negative emissions. Third, the possibility of coupling biomass conversion and synthetic fuels production is explored, providing an overview on the technical maturity of the various energy storage processes. The flexible use of biomass can be an essential part of the future CO2-free energy systems, as it can directly provide energy carriers all around the year and also large quantities of climate-neutral carbon for the production of synthetic fuels with renewable energy. In turn, when no additional renewable electricity is available, the CO2 by-product from biofuel synthesis can be captured to achieve negative emissions. This opens the way to an efficient strategy for the seasonal storage of electrical energy, realizing a carbon-neutral energy system coupled with the development of carbon-negative energy strategy.