Past, Present and Future: A Role for Liquid Biofuels in Transitioning to Net Zero?

Over the last decade, the uptake rate of first-generation biofuels (ethanol and biodiesel) has decelerated as low blend limits have increased only slowly and extreme volatility in oil prices has limited investment in biofuels production infrastructure. Concerns over the environmental impacts of large-scale biofuels production combined with tariff barriers have greatly restricted the global trade in biofuels. First-generation biofuels produced either by fermentation of sugars from maize or sugarcane (ethanol) or transesterification of triglycerides (biodiesel) presently contribute less than 4% of terrestrial transportation fuel demand and techno-economic modelling foresees this only slowly increasing by 2035. With internal combustion and diesel engines widely anticipated as being phased out in favour of electric power for motor vehicles, a much-reduced market demand for biofuels is likely if global demand for all liquid fuels declines by 2050. However, second-generation, thermochemically produced and biomass-derived fuels (renewable diesel, marine oils and sustainable aviation fuel) have much higher blend limits;combined with policies to decarbonise the aviation and marine industries, major new markets for these products in terrestrial, marine and aviation sectors may emerge in the second half of the 21st century.

Chemical Properties,Low-Temperature Performance,and Burning Performance of Bio-Jet Fuel

The effects of composition of bio-jet fuels on freezing point,smoke point,distillation range,and flash point are investigated.Performance tests using petroleum-based jet fuel with different compositions are conducted in line with standard test specifications.The results show that alkylbenzenes reduce the freezing point,with the amount of reduction becoming greater with increasing alkylbenzene content.For a 25%content of the C_8 aromatic xylene,the freezing point is in the range from-55.5℃to-60.1℃.The presence of monocyclic aromatic hydrocarbons leads to an increase in carbon deposition performance,especially when alkyl side chains are present.With cycloalkanes,carbon deposition is reduced,although alkyl side chains weaken this beneficial effect.Isomeric hydrocarbons are beneficial in reducing carbon deposition.The ASTM D7566 specifications for the distillation range are based on the average properties of petroleum-based aviation fuel,and if all the parameters governing the distillation range of an alternative jet fuel are at their lower limits,it is necessary to check whether other performance standards are met.Light components affect the flash point greatly,with 5%of benzene reducing the flash point by 17℃,whereas intermediate components(e.g.,xylene and ethylbenzene)and heavier components have less impact.Although alcohols provide better combustion performance,their content must be strictly limited owing to their effects in reducing the flash point.