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Biofuels facts and figures

What are biofuels?

Biofuels are alternative fuels produced from a renewable source. The main types of biofuel for transport include biodiesel and bioethanol. 

Biodiesel is a renewable alternative to conventional (or mineral) derived diesel.  It is mainly produced from vegetable oils, with agricultural crops such as oilseed rape and soya being used.  Waste materials such as Used Cooking Oil (UCO) and tallow may also be used in production. Several processes exist to transform vegetable oils, UCO and tallow into biodiesel. The most common of these processes used in the UK is esterification where oils are esterified to produce Fatty Acid Methyl Esters (FAME). Co-products of this process include glycerol (which can be used in animal feed or in solid fuel pellets) and potassium sulphate. A less common process for biodiesel production is hydrogenation of oils to produce Hydrogenated Vegetable Oil (HVO).

Bioethanol is an alcohol-based alternative to petrol and is derived from starch or sugar based crops such as wheat, maize, sugar cane and sugar beet. The production process (see figure below) involves yeast fermentation of sugars followed by distillation of the alcohol. 

Bioethanol process: Grain is delivered, tested for quality, stored and then hammer milled. The milled grain is then mixed with water and enzymes (e.g. alpha amylases), cooked at 100 degrees celsius to enable starch liquefaction (destruction of starch 3D structure) and treated with enzymes (e.g. glucoamylases) to continue breakdown of starch to its constituent glucose sugars. The liquefied mixture is then cooled to about 30 degrees celsius using heat exchangers (the heat being recycled) and applied to tanks where yeast turns the sugars into ethanol and carbon dioxide (for food and drink use) during a 50 h fermentation. The resultant low percentage alcohol brew is then concentrated to around 90% ethanol (by volume) by distillation. During distillation, stillage is removed and processed further to produce Dried Distillers Grains and Solubles (DDGS) for animal feed. The 90% ethanol solution is then concentrated further using molecular sieves that capture the remaining water in the mixture (note water is a smaller molecule that ethanol making molecular sieves a viable option to remove water). The resultant 100% (by volume) ethanol produced can then be used for transport fuel blending.

Biogas is a gas fuel (predominantly methane) derived from the Anaerobic Digestion (AD) of biomass, energy crops, manure, sewage and biodegradable municipal waste. Biogas is a gas mix containing methane, carbon dioxide and small amounts of other gases such as hydrogen sulphide. Biogas can be upgraded to biomethane (by removing the carbon dioxide and other contaminant gases) and injected into the gas grid. For more information on gas grid injection, tariffs that can be earnt and the Renewable Heat Incentive (RHI) please click here. For more information on electricity grid Feed In Tariffs (FITs; for renewables) and the income they can generate please click here.

Advanced biofuel technologies (also known as 'second generation' technologies) are under development to produce bioethanol, other bioalcohols and biodiesel from non-starch biomass materials such as wood, other lignocellulosic materials, grasses, algae and biodegradable municipal waste. For a link to IEAs biofuels from biomass demonstration plant world map click here.

Lignocellulosic bioethanol is produced by breaking down cellulose (a plant cell wall component, see figure below) to sugars which can then be used as feedstock in a fermentation process to generate bioethanol.

Schematic of the lignocellulose fraction of plant cell walls

Cellulose is a polymer of glucose, hemicellulose is a complex polymer of various five carbon sugars such as xylose and arabinose (arabinoxylans) and lignin is a complex polymer of 'lignol' ring structured alcohol compounds. Note that cellulose is hard to break down to its constituent sugars. Due to its complexity, lignin is also very hard to break down to its constituent alcohol compounds. 

Bioethanol can also be produced from municipal waste. The process involves converting the biodegradable fraction of municipal waste into pyrolysis oil (the waste is heated in the absence of air to decompose to hydrocarbons). This oil is then fed to carefully selected bacteria that produce the ethanol.

Biobutanol is a bioalcohol compatible with petrol engines and can be produced from sugars derived from starch or lignocellulosic material. The process involves fermentation of sugars by carefully selected bacteria which produce a mixture of products including butanol.

Biodiesel can be made from upgraded pyrolysis oil by fractionating the oil in a similar way to fossil-derived crude oil. Biodiesel can also be made from algae by extracting the oil, purifying it and processing it by methods such as hydrogenation or esterification in a similar way to the production of plant oil-derived biodiesel (see above).

Biofuels may be used in ordinary vehicle engines, unmodified for low blends (up to 5% for bioethanol and 7% for biodiesel), or with modifications for higher blends. The Renewable Transport Fuel Obligation (RTFO) is the instrument that the UK government has implemented to reduce greenhouse gas emissions from the transport sector and requires the inclusion of biofuels in the road transport fuel mix (for more information please see our UK biofuel policy page here). The general biofuel inclusion target for the RTFO year 2010/11 is 3.5% by volume. Approximately 1.3 billion litres of biofuel was used in the UK between April 2008 and April 2009, this amounted to 2.7% (by volume) of all UK road transport fuel (see figure below).

Biofuels supplied under the RTFO (verified data from 2008/9 RTFO year)

How much road transport fuel does the UK use?

According to figures released by HM Revenue and Customs (HMRC), the UK consumed approximately 22.7 billion litres of petrol (including bioethanol) and 25.7 billion litres of diesel (including biodiesel) in 2008. There is a clear trend towards dieselisation with a percentage split of 47% petrol to 53% diesel in 2008. Biofuels accounted for 2.7% of total road transport fuel used between April 2008 and April 2009.

Road transport fuel supplied in the UK (1970-2008)

Source: HMRC

Biofuel inclusion in the transport fuel mix is set to increase to 5% (by volume) by 2013/14 under the RTFO. However, in 2011 the Renewable Energy Directive (RED; see our EU biofuels policy page here) comes into force and will require inclusion of biofuels in the transport fuel mix in terms of energy. The target is 10% renewable energy in the transport fuel mix by 2020. The RTFO will need to be adapted to take into account the GHG savings, inclusion targets and sustainability criteria set out in the RED.