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Renewable Jet fuels: The Current State of Affairs

JFK in his 1960 speech in Raleigh, NC, Coliseum said, “…Efforts and courage are not enough without purpose and direction…” He was perhaps also indirectly addressing to the state of mind of an investor, entrepreneur, policy maker or a venture capitalist in the bio-renewables sector today.

While the purpose is clear – to create disruptive technology to sustain life on earth while creating a commercial success, the lack of direction is clear, which usually stems from the plethora of technologies available at our disposal given the staggering pace of R&D across the board. The initial direction chosen was to generate transportation fuel from renewables. The industry soon realized it was time to pivot towards more profitable renewable chemicals sector. With a further pivot now the direction is towards Renewable Jet Fuels. The idea here is to prioritize for biofuel applications in industries – which do not have feasible alternatives to liquid fuels, such as Aviation and Shipping. Road transport, for example, has the possibility of electric power, whereas jet aircraft do not have an alternative to liquid fuels in the near- to medium future. With substantial improvements from the much-discussed Elon Musk’s – Tesla focused on road transport with electric cars. In addition, Toyota Motor Corp., for example has recently announced that by 2050, it aims to reduce global average new-vehicle CO2 emissions by 90% – by switching to alternatives such as gas-electric hybrids, fuel cell and electric vehicles. With more in the automobile industry joining the bandwagon across the globe.

Jet fuel conventionally is produced from petroleum crude refining. Its composition depends on the raw crude oil, but the composition is typically around 20% paraffins, 40% isoparaffins, 20% naphthenes and 20% aromatics. Each of these components has a very specific role towards critical fuel requirements of the Aviation sector. For example, the high hydrogen-to-carbon ratio of paraffins and isoparaffins enhance the heat density per unit mass of fuel; naphthenes help to reduce the freeze point, which is critical at high altitudes; while the aromatics contribute to material compatibility and prevent leaks in the seals of some aircraft models.

Jet fuel specifications are defined in the US and Europe by two alternative standards: ASTM D1655 of the American Society for Testing and Materials (ASTM) and Def Stan 91-91 of the UK Ministry of Defense. Other commonly used specifications are the Joint Check List (AFQRJOS) and GOST 10227 TS-1. These are broadly equivalent and focus primarily on performance properties rather than chemical composition, due to the complexity and variability of the latter. Several fuel requirements have been identified as being particularly key to the development of aviation biofuels, namely: energy content, freeze point, thermal stability, viscosity, combustion characteristics, lubricity, material compatibility and safety properties. Table 1 below provides an overview of these in terms of their operational purpose/properties and associated specifications.

Table 1: Key jet fuel properties, and specifications

Requirement

Purpose

Specification

Energy Content

Affects aircraft range

Minimum energy density by mass

Thermal stability

Coke and gum deposits can clog or foul fuel system and nozzles

Maximum allowance deposits in standardized heating test

Freeze point

Impacts upon ability to pump fuel at low temperature

Maximum allowable freeze point temperature

Viscosity

Viscosity impacts ability of fuel nozzles to spray fuel and of engine to relight at altitude

Maximum allowable viscosity

Combustion characteristics

Creation of particulates in combustor and in exhaust

Maximum allowable sulfur and aromatics content

Lubricity

Impacts upon ability of fuel to lubricate fuel system and engine controls

Maximum allowable amount of wear in standardized test

Material compatibility

Fuel comes in to contact with large range of metals, polymers and elastomers

Maximum acidity, maximum mercaptan concentration, minimum aromatics concentration

Safety

To avoid explosions in fuel handling and tanks

Minimum fuel electrical conductivity and minimum allowable flash point.

Numerous stringent fuel specifications apply to the aviation fuel infrastructure due to obvious reasons. To deploy the use of any new alternative aviation fuel in this infrastructure, a new specification needs to be developed or an existing specification needs to be revised. If the alternative fuel is found to have essentially the same performance properties as conventional jet fuel then there is no need to change ground and supply infrastructure, airframe or engines (i.e. a “drop-in fuel”). The specifications of the new fuel may be incorporated into the existing jet fuel specifications, and will therefore meet the established operating limitations for the existing fleet of turbine engine powered aircraft.

As of today, there are essentially five primary conversion pathways that have the potential to produce a drop in alternative for fossil kerosene; Fischer-Tropsch (FT) process – also known as Biomass-to-Liquid (BtL), Hydro-processed Esters and Fatty Acids (HEFA) process, Direct Sugar to Hydrocarbon Conversion (DSHC), Direct Liquefaction, and Alcohol-to-Jet (AtJ). (Table 2) Next to these, there are several other secondary production pathways that yield liquid fuels, although it is uncertain to which extent these fuels can be used as drop in alternative to fossil jet fuel. These are:

  • Fatty Acid Esters
  • Furan derivatives 

  • Succinic acids derivatives
  • Cryogenic fuels (LNG & liquid Hydrogen)
  • CO2 remediation

Table 2: Key jet fuel technologies, their feedstock, products and certification

Technology

Feedstock

Products

Certification

FT (also known as CtL, GtL, BtL, WtL etc.)

Any material containing carbon (coal, gas, biomass, waste)

Straight alkanes – Biomass to syngas to jet

ASTM (2009)

DEFSTAN (2009)

HEFA (also known as HRJ, HVO)

Vegetable oils and animal fats

Straight alkanes – Biomass deoxygenation with H2 and cracking to jet

ASTM (2011)

DEFSTAN (2011)

Direct Sugar to Hydrocarbon Conversion

C6 sugars (from starch or cellulose)

Alcohols, alkanes, and other hydrocarbons – Sugar to hydrocarbon to jet

None

Direct Liquefaction (e.g. pyrolysis, hydrothermal upgrading)

Any material containing carbon (coal, biomass, plastic waste)

Mainly naphtenic compounds – Biomass to depolymerization to jet

None

Alcohol to Jet (AtJ)

Any alcohol

Straight alkanes – Biomass to alcohol dehydration & oligomerization to jet

None

Synthetic jet fuels (including biofuels) and synthetic/petroleum fuel blends are specified by standards ASTM D7566, established in 2009. Specific fuel blends certified for commercial use are added to the standard as an annex. These ‘drop in’ fuels are considered to be equivalent to conventional jet fuel (ASTM D1655) and can be mixed in aircraft and supply infrastructure without the need for separate tracking or approval. Some organizations are investigating the potential for non-drop-in fuels that could be used instead of (but not mixed with) petroleum-based fuels, for example butanol. A further standard, ASTM D4054, provides guidance on the testing and property targets necessary to evaluate a candidate alternative fuel. Biofuel producers wishing to certify their product must collate the data required by D4054 in a research report and submit this to engine and airframe manufacturers (original equipment manufacturers, OEMS) for review. If the fuel is approved by the OEMs it is balloted to the ASTM’s membership for approval to develop an annex to D7566. Exhibit 1 illustrates the detailed process.

replacement

Exhibit 1: ASTM D4054 Process for aviation biofuel certification

Renewable Jet Fuels have been used in both commercial and military aviation on a small scale. As of today Feb 2016, more than 50 routes of commercial flights have used or tested bio-based fuels as a portion of their fuel source, and the number of flights that have used biofuels or are contemplating its use in near future continues to increase. One of the largest hurdles within the industry is a purchase contract. Purchase contracts to date have generally only been for 1-year terms with the idea to move to 5 years for alternative fuels. Industry experts have realized that 5-year contracts are – not sufficient to stimulate the private capital market or potential alternative fuels suppliers to construct or expand production facilities. Purchase contracts of at least 10 years in duration could potentially stimulate additional capital investment in alternative fuels production beyond the small volumes currently planned in response to commercial demand. The length of the contract term is only one of many factors that prospective investors would assess in their evaluation of financial risk and return.

These parameters and initiatives are not an end stadium; they are constantly evolving due to increased insights on both production & demand side and improvements in technology. The development and deployment of comprehensive sustainability frameworks, certification and verification will thus take more time. What is also important in the coming years is a gradual harmonization of standards and frameworks and incorporation of indicators that cover sustainable land-use, food security and other main themes that relate to land use in general.

Dr Kapil Shyam Lokare's picture

Thank Dr Kapil Shyam for the Post!

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Robert Hargraves's picture
Robert Hargraves on Feb 12, 2016 4:11 pm GMT

Biofuels usurp agricultural land used for growing food. A crime agains humanity, says the UN.

A proven alternative is the US Navy Research Labs’ process for extracting CO2 from seawater, elecrolizing water to get H2, then synthesizing JP-6 jet fuel at about $5/gallon. Known since 2012, here http://www.nrl.navy.mil/media/news-releases/2012/fueling-the-fleet-navy-....

The nuclear power plants abord Nave ship have the power to refuel the fleet. The process is CO2 neutral because CO2 released into the air dissolves in the ocean from which the Navy extracts it. Check THORIUM: energy cheaper than coal for other ideas.

Dr Kapil Shyam Lokare's picture
Dr Kapil Shyam Lokare on Feb 14, 2016 10:51 am GMT

Dear Robert,

Good points but inaccurate conclusions. You make my argument much clear – you cite $5/gallon in your argument.

An average – a B-747 will consume about 18 million gallons per year so a price increase of 1 cent per gallon would add $180,000 per year to your bill if you were flying a B-747. You mention a price of $5 per gallon – I recommend you do the math as to what your bill would be to fly one aircraft.

In addition, the goal of using biomass is to use what is usually classified as waste and hence does not interfere with food – further, the idea is to supplement the petroleum sector NOT replace it.

Hope this helps – I will be glad to have more elaborate conversation to help clarify things further.

Regards,

Kapil

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