SUSTAINABLE FUELS LIKE BIOFUELS
University of Toronto – Institute of Aerospace Studies, Toronto, Ontario
 How to produce Biofuel from Biomass?
Biomass as Feedstock: Biomass has been derived from grasses, plants, trees, and crops are versatile and important feedstock which are renewable for the chemical industry as shown in Fig. 1 . The two metabolic biochemical i.e. primary and secondary can be derived from plants through photosynthesis process which converts them into carbon dioxide and water . Primary metabolic biochemical are carbohydrates and lignocellulose biomass which can be converted into Biofuels . The secondary metabolic chemicals contain rubber, steroids, plant acids, etc. can be utilized to produce pharmaceuticals, cosmeceuticals etc. 
Fig. 1 Biomass as renewable feedstock to biorefineries
Biorefinery system: The Biomass conversion and integrated systems to produce chemicals, power, and fuels from Biomass are called Biorefinery system. The typical conversion process flow chart has been shown in Fig. 2. 
Fig. 2 Biomass conversion process
Classification of Biofuels: Biofuels can be classified into two as primary and secondary . The primary Biofuels mainly used for cooking, heating example: fuelwood which harms the environment by toxic emissions and not efficient . The secondary Biofuels have processed Biomass, for example, ethanol biodiesel, etc. for industrial processes . It is further classified as First, Second and Third generation biofuels . The first generation biofuels which are produced from grains, seeds, and sugar through Transesterification and Ethanol conversion process . It basically produces biodiesel and ethanol for commercial use . The second generation biofuels which are produced from nonfood biomass such as non-edible oils, lignocellulosic feedstock, etc. through Thermochemical and Biochemical processing. It basically produces biofuel, bio-oil, and biodiesel . The Third generation biofuels which are produced from microscopic organisms like microalgae and microbes through thermochemical and biochemical conversion . It can produce methanol, hydrogen, ethanol, and biodiesel from microalgae on which many researchers are working .
Sustainability issues for biofuel: First, the production of fuel crops at large amount is not feasible in developing countries where food cultivation is not available . Second, the production of biofuels requires water for various activities like washing, etc. which may generate the problem of irrigation . Third, some biofuels may create more greenhouse gas rather than reducing it which has created environmental issues .
 How to develop aviation biofuels for Tropical countries?
Oil prices are increasing drastically in aviation industry which affects the operating cost for air transportation throughout the world . Due to which it makes difficult for airlines operators to plan and budget for long-term operating expenses . For reducing the cost of fuel using sustainable biofuels, the production process of aviation fuel was proposed for tropical countries which consist of production technology, socioeconomic conditions, and feedstock sources .
Currently, the different research strategies for alternative aviation fuels are hydroprocessed renewable jet – synthesis paraffin kerosene (HRJ - SPK), Fischer- Tropsch jet – synthesis paraffin kerosene (FTJ – SPK), and fatty acid esters (FAEs) . HRJ – SPK will be produced by the hydrogenative refining of the fatty acids and triglycerides in the vegetable, animal, or waste oils . FTJ – SPK is produced through gasification followed by Fischer-Tropsch synthesis process of biomass, coal, or natural gas feedstock . FAEs are generally known as biodiesel which is derived from transesterification of fatty acids and triglycerides in the vegetable, animal, or waste oils .
For tropics, the production process of aviation biofuel has been shown in Fig. 3 which is based on hydrotreating process with the adjustment of conditions required for the country .
Fig. 3 Production process of aviation biofuel for tropical countries
In this process, the feedstocks should be selected from dominant lauric fatty acid and medium chain . Also, this is a simple production technology because of no cracking step which reduces the investment and production costs for aviation biofuels . Furthermore, it takes full advantage of the current production line of biodiesel . To satisfy aviation standards, bio-jet paraffin is blended with aromatics to form bio-jet fuel which helps in satisfying freezing pint and density requirements . Later, the bio-jet fuel blended with kerosene to form bio-kerosene which can work in existing engines .
The experiments were conducted by considering two aviation biofuels which are bio-paraffin 1 (Bio-P1) and bio-jet paraffin 2 (Bio-JP2) produced by using above process . The results of the experimental and theoretical investigation show that the “drop in” bio-kerosene by directly blending bio-paraffin 1 and bio-jet paraffin 2 with commercial A-1 Jet fuel by 5% and 10% by volume, respectively . By using these two fuels, it can decrease up to 0.8 % of overall aviation CO2 emission for every 1% blending . With preliminary achievements of this study shows that this process is feasible of developing aviation alternative biofuels in tropical countries .
 What are the opportunities and challenges for the development of Aviation Biofuels from renewable resources?
Renewable feedstocks have been used to produce bio jet fuels because of certain advantages like sustainability, renewability, less dependence on petroleum supplying countries, eco-friendly technology, and carbon dioxide recycling . Most the feedstocks come from algae, waste wood, halophytes, non-food energy crops, forest residues, municipal and sewage wastes . The characteristics of some renewable feedstocks are Camelina which has high oil content and comes under the category of non-food energy crop, Algae have high rate of carbon dioxide absorption, faster rate of growth, low land use and high lipid content which is effective solution for the fuel scarcity issues, Jatropha can grow on marginal land and non-edible energy crop, therefore, doesn’t compete with food crops .
Above renewable bio-resources help to produce alternative aviation fuels which have properties like compatibility with conventional fuel, renewable resources, reduced greenhouse gas emission, sustainability, and clean burning . Currently, alternative fuels include Hydroprocessed renewable jet fuels (HRJs) are paraffinic liquids which are produced by hydrodeoxygenation of animal fats, waste grease, bio oil, vegetable oil, algal oil and can be used in present aircraft engines without modification and fuel quality issues . Fischer-Tropsch fuels (FT fuels) can be produced by catalytic conversion of CO and H2 which are hydrocarbon fuels . Biodiesel is an alkyl ester of fatty acid which can be produced by the process of transesterification .
The fuel characters can be determined by fuel production routes which will influence the fuel cost, availability, product composition, fuel properties and environmental impact . The methods used to produce fuels are the Thermochemical process which includes Biomass to liquid process & Fischer-Tropsch process, Hydroprocessing, a Biochemical process which includes Direct sugar to hydrocarbon process and alcohol to jet process & Bio-alcohol production, Liquid hydrogen and liquid methane, Transesterification of oils/fats .
Table 1 Overview of Biojet fuel production routes, renewable sources and various alternative aviation fuels
Renewable sources Routes Alternative aviation fuels
Halophytes Biomass to liquid process
Alcohol to jet process
Direct sugar to Hydrocarbon process Hydroprocessed Renewable Jet fuels
There are many challenges to overcome even using alternative aviation biofuels . One of the major issues that should be faced is environmental challenges like fuel production and management . Production issues are also involved the cost effectiveness and feedstock availability . For effective functioning, the quality of the product and suitable blending is required in supply process . Another challenge can be feedstock availability and sustainability which should be cost effective . Bio aviation fuels must be compatible with conventional fuel like does not contain aromatics and Sulphur with high ignition temperature and low freezing point .
The use of renewable bio-resources to produce alternative aviation fuels shows highly promising results which can be a substitute for petroleum based fuels . The goal can be achieved by the government interest and international organization which will help for commercialization, scaling up and supply chain infrastructure to large extent . The feedstock cost can be reduced using waste materials from various sources which are available in abundant quantity .
 What are the drivers and constraints for the market development of aviation biofuel?
Drivers: There are six main key drivers for the uptake of aviation biofuels and its development . These drivers were either potential benefits associated with the aviation biofuel or external economic factors . Although these factors have no dependence on each other but the main factor was the need to reduce carbon emissions .
Carbon reduction: Most of the airlines recommended that the aviation industry should focus on the reduction of carbon emission which is a significant driver . But U.S & EU respondents have different views . The environment legislation and voluntary industry targets played an important role in the reduction of emissions in EU respondents . On the other hand, U.S respondents were worried about the extra cost associated with biofuels production rather than the reduction in emission .
Energy security: The U.S respondents will be most benefited from energy security which would benefit for the fuel and will provide an opportunity to avoid oil imports . It is the major driver within U.S for military perspective . Outside U.S respondents would like to secure energy supply ultimately help the government to grow economic and commercial perspective .
Volatile oil prices: The long-term drivers by most of the respondents are oil price rise and oil price volatility . It was suggested that oil price volatility will play a major role than oil price in short-term as well as long-term .
Legislation: The legislation is also an important driver like EU Emissions Trading System (EU ETS) and ICAO resolution . The EU ETS states two possibilities: either reduce the profit in the aviation industry or opportunity to reduce emission . EU respondents would like to reduce emission whereas U.S respondents worried about the financial burden it will impose .
Lack of alternative technology: Most of the respondents were worried about the aviation industry has a long-term issue that is they don’t have alternative technologies that offer better performance for jet-airlines . Other technologies like hydrogen and electric are feasible and cost effective but won’t be available soon whereas Aviation Biofuels are an essential intervention .
New Business opportunities: The respondents were confident about the Aviation biofuel technology, which is an economic advantage in long-run and helpful to create new business opportunities among aviation industry .
Constraints: Respondents were worried about the constraints which are interlinked with each other for the market development of aviation biofuels .
High Production Cost: High cost possesses a significant constraint for the development and uptake of aviation biofuel . Currently, Aviation biofuel by current technology costs much more than a standard jet fuel .
Lack of investment: The aviation biofuel receives insufficient investment because of the uncertainty about the technology, legislative support, and an inability for the economic downturn . Further factors are the lack of government investment and de-risk investment .
Sustainable feedstock supply: It is an important constraint to produce aviation biofuel because of less feedstock which impacts the existing technology to develop economically sustainable and viable .
Inadequate legislation: Lack of legislation was a constraint which issues for applying too strict environment criteria and infrastructure certification issue . Another issue is the lack of interlink between aviation biofuel and road-based biofuels .
Some of the other constrain can be Strict environmental controls for biofuels and Lack of supply chain certification .
 What are the pathways for the conversion of algae to alternative aviation fuels?
The most viable feedstock for alternative aviation fuel can be derived from Algae which has the potential to meet the current aims for sustainable energy source and climate change mitigation . Algae usually comprise carbohydrates, lipid with smaller quantities of nucleic acids and proteins . The main factor for the conversion of algae to jet fuels because it contains lipid composition and concertation . The general pathways for the conversion of algae into alternative aviation fuels have been showing in Fig. 4 .
Fig. 4 Pathways for the conversion of Algae into alternative aviation jet fuel
Fischer-Tropsch pathway: The gasification pathway for the conversion of algae which contain less amount of lipid and high carbohydrates is a better choice for bio-kerosene .
Hydrotreated pathway: When the content of lipid is high this pathway should be followed .
Pyrolysis-hydrotreated pathway: When the oxygen-free thermal treatment of algae pyrolysis was conducted, which converts dry algae into charcoal and bio-crude at high temperature and atmospheric pressure .
Hydrothermal liquefaction-hydrotreated pathway: It is a promising pathway because of no dewatering is required for algae-based biofuel production .
In FT selectivity, kerosene work as optimizer which is influenced by feed gas composition, pressure, temperature, catalyst type and carbon distribution product . Algae gasification shows the result of high efficiency and use of wet algae but it is still in the early stage .
Due to hydrotreatment reactions which include hydrocarbonylation, decarboxylation, and hydrodeoxygenation, HRJ fuel contains complex carbon distribution . The process can be economical using high lipid content .
The hydrothermal liquefaction process has similar steps like pyrolysis for bio-crude oil and leads to higher bio-kerosene product .
 How to develop blended aviation biofuel from Jatropha and vegetable oil?
Currently, vegetable oil shows the promising source of energy as well as environment-friendly to replace petroleum-based fuel . Some of the examples of vegetable oils include virgin vegetable oils and waste vegetable oils . When we consider alternative aviation fuel it must have similar properties to petroleum-based aviation fuels so that there won’t be any difficult for aircraft engine start up and during flight .
The easy way to collect waste vegetable oil (WVO) from local restaurants and Jatropha curcas oil as a feedstock . By following the steps in Fig. 5, we can produce jet biofuel .
Fig. 5 Flow chart diagram of jet biofuel production
The collected and treated J. curcas oil and waste vegetable oil were firstly converted into methyl ester which was later blended with Jet A-1 aviation fuel separately . When the comparison was conducted, it shows similar characteristics as Jet A-1 fuel when blended at 10 and 20 % ester . For jet biofuel is blended with 10 % ester it shows around 83 % of similarity in properties of the fuel derived from WVO and jatropha oil .
These much similarity shows that these two renewable resources have a positive influence on climate, reduce the amount of waste oil disposal and food self-sufficiency to produce environmental-friendly fuel .
 What is the prospect of biofuels in Australia as an alternative transport fuel?
Australia is the 2nd largest country which consumes 24% of total energy consumption . The classification of energy resources which contribute to global energy consumption has been shown in Fig. 6 .
Fig. 6 Classification of Energy Resources
Australia’s highest energy consumption sector is electricity generation (36%) and transportation sector (24%) as per 2013 Australian Energy statistics . Biofuels favored to be the alternative source of energy which are further divided into 4 types: First, Second, third generation has been discussed in  and Fourth generation (4G) biofuel are those fuels which are produced from captured carbon from the environment using process like advanced bio-chemistry, geosynthesis or low pressure, petroleum-hydro-processing, and low-temperature electrochemical processes .
Biofuel demand for energy production in Australia market increased drastically since 2006 and reached 20 million litres in 2012 . Biofuel production facilities are increasing in number on the day-by-day basis . This increase in companies helps the investors to invest either in feedstock production or harvesting and processing of biofuel . On the other hand, job opportunities in sector increases which play an important role in economic and social development in Australia . But still the technology is not fully developed, though, biofuel is one of the efficient ways to meet the energy demand in transport sector .
Some of the challenges are relative pricing with respect to fossil fuels, lack of awareness to use biofuel, lack of constant supply of raw materials, etc. .
As per BREE estimation, energy consumption is increasing at the rate of 2.4% per year in the transport sector which can be meet by biofuel .
 How Biofuels in aviation helpful to meet fuel demand and CO2 emissions reduction in Europe by 2030?
The air transport sector is rapidly increasing World air traffic which demands in energy consumption and environment impacts throughout the world . This traffic growth in not increasing steady but accelerating in emerging countries like China, India, Brazil, and Russia . The aviation industry is looking for alternative fuels which can help to reduce oil dependence and lower greenhouse gas emissions which can be meet by using Biofuels . Biofuels has been tested in around 1500 passenger flights which reduce the lifecycle carbon saving by 80% over traditional jet fuel in 2014 .
Data for fuel demand in aviation growth has been projected on a yearly basis from 2010 to 2030 as shown in Fig. 7.
Fig. 7 Fuel projections to 2030, as per optimistic scenario 
 By using Biofuels there will be some uncertainties which will arise in near future includes: (a) Cost of travel will directly influence immediately by changes in oil prices, which will attract the investors in alternative fuel. (b) The EU ETS participation in aviation help to combat climate change by the European Union which will reduce industrial greenhouse gas emission cost effectively. (c) There has been a target by EU which recommend for getting 27% of energy from renewable resources by 2030.
CO2 emission projections to 2030 for different scenarios has been shown in Fig. 8 .
Fig. 8 CO2 emission projection to 2030 for different scenarios
 What are the conversion pathways to Bio-jet fuel?
Alcohol-to-jet (ATJ) fuel: It is also known as alcohol oligomerization, is a fuel converted from alcohols such as ethanol, butanol, methanol, and long-chain fatty alcohols .
Oil-to-jet (OTJ) fuel: There are 3 processes which come under OJT conversion pathway: catalytic hydrothermolysis (CH) basically know as hydrothermal liquefication, HRJ which is known as HEFA, and hydro-treated depolymerized cellulosic jet (HDCJ) known as fast pyrolysis with upgrading to jet fuel. Currently, the product from HRJ has been approved for bleeding which comes under ASTM specification .
Gas-to-jet (GTJ) fuel: It is a pathway for the conversion of natural gas, biogas, and syngas into bio-jet fuel .
Sugar-to-jet (STJ) fuel: The catalytic and biological conversion of sugars to hydrocarbons which provide a biochemical route to produce liquid chemicals and transportation fuels . STJ fuel has two pathways for processing which are: Catalytic upgrading of sugar intermediates or sugar to hydrocarbons, Fermentation of sugars to hydrocarbons .
The Greenhouse Gas emission of jet fuel for various pathways has been shown in Fig. 9 . For ATJ the upgrading process depends on the use of n-butanol or ethanol for GHG emission .
Fig. 9 Greenhouse gas emission of jet fuel from different pathways
 How food waste results in Liquid biofuels?
Food waste disposal has a problem throughout the world, out of which at some place it is directly dumped into land daily . If these waste foods can be used as feedstock for Biogas production and help to clean the environment from these waste . These waste products can be helpful to produce fuels like Biodiesel, Bioethanol and Biooil . A schematic representation of various routes to produce Biofuels from various food wastes have been shown in Fig. 10 .
Fig. 10 A schematic representation of various routes to produce Biofuels from various food wastes
Biofuel from waste food will help to increase the economy of the country since there will be less dependency on fossil fuel rich nations which ultimately reduces the cost of fossil fuels .
There are various challenges for the production of biofuels from food waste: Unorganized sector which is people should be aware of food waste and proper collection of waste food should be done regularly, Separation of food waste generally mix with other waste which should have method for the separation of food waste from non-biological wastes for further processing and utilization, Non-renewable means if the better management will control the food production and its utilization will minimize the production of food waste, etc. 
Since food waste is a non-edible and no-value resource, therefore, can be used as cost-effective in the production of biofuels .
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