Types of Biofuels used on Jets
Plant oils such as jatropha oil, coconut oil, palm oil & camelina oil are hydro-treated to convert them into aviation fuel, a type of fuel known as the Hydro-treated renewable jet (HRJ) fuel. Biofuel made from palm oil is twice as expensive as regular aviation fuel; the reason being, massive deforestation is necessary to obtain palm oil. However, the actual amount of biofuel required for flights remains unknown; the only estimate being Virgin’s test flight in the year 2008 that used five percent of biofuels (which required 1, 50,000 coconuts as well babassu nuts) for just one flight.
Sugar based biofuels can also be converted into aviation fuels after some processes. Various techniques are under development to utilize this fuel. Biobutanol and isobutanol process involves fermentation by bacteria such as E.coli. Although this faces some technical difficulty, it could be overcome using synthetic biology. Another fuel, Biogasoline undergoes thermal conversion so that it can be suitable for aircraft. Bio-Forming engages a series of treatments on biomass which is followed by an aqueous re-forming process that breaks down organic hydrocarbons into hydrogen, carbon dioxide, alcohols and other components. After this, the fuel is abstracted from water. A small pilot-plant making such bio-fuel is being operated in the United States, with plans to switch to a full-fledged one in near future. Lastly, biocrude can also be made suitable for aviation. The process involves exposing of biomass to high temperature using a catalyst in the absence of oxygen. This type of biofuel has already been refined by four test flights.
Another process known as Fischer-Tropsch gasification is also utilized to make biofuels suitable for aircrafts. It exposes biomass or fossil fuels to high-temperatures which turns them into synthetic-gases, followed by conversion into liquid hydrocarbons and then liquid fuel that can be used in airplanes. This technology is being used in South Africa to produce road-transport fuel from coal, which received certification in 2008. This synthetic fuel can be obtained from natural gas, a coal-biomass mixture, or biomass alone.
The production of synthetic fuel from biomass requires a huge cost, ample amount of energy for conversion, cost of feedstock and most importantly, large reserves of biomass which currently is practically impossible. However, there is another option for this known as the pyrolysis process. Here the capital cost is low and the size of the plants required also is comparatively smaller. But again, this option comes with its disadvantages, mainly environmental pollution.