28
2 The Contested Sustainability of Biofuels …
wastewater, and they would not directly compete with food production (Gouveia
and Oliveira 2009; Wu et al. 2012). However, high production, harvesting and oilextraction costs currently have limited the economic competitiveness of this pathway
(Baicha et al. 2016), and doubts concerning the engine performance of fuels from
microalgae remain (Piloto-Rodríguez et al. 2017).
2.2.6 Liquid Biofuels: Aviation Fuels
Although nearly all biofuels have been used for road transportation, aviation also
has received increasing attention. The European Commission, the International Air
Transport Association, as well as public and private actors in the US and Brazil have
all launched initiatives for R&D and adoption of aviation biofuels (Rosillo-Calle
et al. 2012; Boeing et al. 2013).
Aviation contributes to 2% of all anthropogenic GHG emissions, and these emissions are forecast to triple by 2050, reaching 3% in relative terms, despite expected
fuel efficiency improvements (Boeing et al. 2013). Among various aviation fuels,
the focus has been replacing jet fuels, which are oil-based hydrocarbon combinations akin to diesel and used in the combustion-turbine engines of most commercial
aircraft. As in the biodiesel case, research and development efforts have focused
on “drop-in” replacements, i.e., biofuels that can be used by conventional engines
without modifications (Boeing et al. 2013). Such aviation biofuels are important
because hydrogen-, solar-powered, and other more advanced aircraft types are not
expected to become commercially viable until “well after 2050” (IRENA 2017, p. 2).
Several production pathways exist, but only a few have been approved by the
ASTM International
2 (a US-based organization that sets technical standards for
commercial jet fuels) and commercially tested. One is a thermo-chemical pathway
that converts syngas (from biomass gasification) through a Fischer-Tropsch and
fractioning process. Yet most aviation fuels used to date follow a hydroprocessing
pathway akin to biodiesel (IRENA 2017). This lipid conversion, breaking large
hydrocarbon molecules of vegetable oils or animal fats into smaller ones that can
replace conventional jet fuels, is cheaper and considered technically simpler than
existing alternatives (Rosillo-Calle et al. 2012; Boeing et al. 2013). Generally,
however, feedstock costs still are comparably high (vis-à-vis fossil fuels); there is
uncertainty in the industry regarding upcoming sustainability requirements on aviation fuels, and limited availability of suitable feedstocks (Pearlson et al. 2013; Gegg
et al. 2014). Despite long-standing aims of producing jet biofuels from advanced
feedstocks such as algae or cellulosic biomass, their fledgling production has utilized
mainly the same feedstocks as biodiesel (e.g., palm oil, jatropha, soy oil) (Bailis and
Baka 2010; IRENA 2017). The technology and the technical potential are generally
2 Originally the American Society for Testing and Materials, but its spelled-out name has been
dropped in favor of ASTM International.
2 The Contested Sustainability of Biofuels …
wastewater, and they would not directly compete with food production (Gouveia
and Oliveira 2009; Wu et al. 2012). However, high production, harvesting and oilextraction costs currently have limited the economic competitiveness of this pathway
(Baicha et al. 2016), and doubts concerning the engine performance of fuels from
microalgae remain (Piloto-Rodríguez et al. 2017).
2.2.6 Liquid Biofuels: Aviation Fuels
Although nearly all biofuels have been used for road transportation, aviation also
has received increasing attention. The European Commission, the International Air
Transport Association, as well as public and private actors in the US and Brazil have
all launched initiatives for R&D and adoption of aviation biofuels (Rosillo-Calle
et al. 2012; Boeing et al. 2013).
Aviation contributes to 2% of all anthropogenic GHG emissions, and these emissions are forecast to triple by 2050, reaching 3% in relative terms, despite expected
fuel efficiency improvements (Boeing et al. 2013). Among various aviation fuels,
the focus has been replacing jet fuels, which are oil-based hydrocarbon combinations akin to diesel and used in the combustion-turbine engines of most commercial
aircraft. As in the biodiesel case, research and development efforts have focused
on “drop-in” replacements, i.e., biofuels that can be used by conventional engines
without modifications (Boeing et al. 2013). Such aviation biofuels are important
because hydrogen-, solar-powered, and other more advanced aircraft types are not
expected to become commercially viable until “well after 2050” (IRENA 2017, p. 2).
Several production pathways exist, but only a few have been approved by the
ASTM International
2 (a US-based organization that sets technical standards for
commercial jet fuels) and commercially tested. One is a thermo-chemical pathway
that converts syngas (from biomass gasification) through a Fischer-Tropsch and
fractioning process. Yet most aviation fuels used to date follow a hydroprocessing
pathway akin to biodiesel (IRENA 2017). This lipid conversion, breaking large
hydrocarbon molecules of vegetable oils or animal fats into smaller ones that can
replace conventional jet fuels, is cheaper and considered technically simpler than
existing alternatives (Rosillo-Calle et al. 2012; Boeing et al. 2013). Generally,
however, feedstock costs still are comparably high (vis-à-vis fossil fuels); there is
uncertainty in the industry regarding upcoming sustainability requirements on aviation fuels, and limited availability of suitable feedstocks (Pearlson et al. 2013; Gegg
et al. 2014). Despite long-standing aims of producing jet biofuels from advanced
feedstocks such as algae or cellulosic biomass, their fledgling production has utilized
mainly the same feedstocks as biodiesel (e.g., palm oil, jatropha, soy oil) (Bailis and
Baka 2010; IRENA 2017). The technology and the technical potential are generally
2 Originally the American Society for Testing and Materials, but its spelled-out name has been
dropped in favor of ASTM International.