In 2018, the EU's revised Renewable Energy Directive came into force, increasing renewable energy targets for all energy sectors while limiting the use of first-generation biomass as feedstock. Fuel components like methanol, ethanol, propanols, and butanols represent promising candidates to enable the targets for transportation to be achieved because they can be used with existing infrastructure and can be further processed to give additives and substitutes. A wide variety of feedstocks and processes are available for this purpose. In this review, the thermocatalytic and biological synthesis routes for C1–C4 alcohol fuels are summarized to illustrate the many alternatives. They include biomass and waste gasification and carbon capture and utilization to obtain syngas for catalytic conversion, fermentation of sugars from lignocellulosic feedstock, and novel, less developed pathways like syngas fermentation, glycerol conversion, and biogas reforming. The current state of technology is presented by discussing the advantages and technical hurdles, and by introducing recent scaled-up approaches. This demonstrates the need for further research and development. The assessment of techno-economic analyses in the literature illustrates the dominant factors affecting production costs and reveals the broad range of feasibility of the various production routes. The review shows that the routes most similar to conventional, well-established syntheses bear the highest potential to be implemented in the short and medium term. The availability of cheap and abundant feedstock also plays a crucial role. Methanol synthesis from biomass gasification and ethanol, and acetone-butanol-ethanol fermentation from lignocellulosic biomass, are therefore considered to be very promising.
- advanced biofuels