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Liquid biofuels

Biofuels as liquid bioenergy sources

Liquid bioenergy sources such as vegetable oils, biodiesel and ethanol are now already substituting petroleum and diesel fuels. Yet they are also substituting heating oil in boilers, used in single-family or multi-family residential buildings, or in CHP units that generate electricity and heat in municipalities. Above all, this is due to the high energy density that liquid energy sources offer advantages in transport and storage. A large part of modern infrastructure is set up to suit liquid energy sources; this is done in order to make sure that, when it is distributed, liquid biomass can make use of the available transport and storage systems. While electricity and heat from biomass are primarily generated through solid fuels and biogas, biofuels are the most important renewable alternative with regard to mobility.

Our society is now more mobile than ever. Even if current forecasts predict a downturn in levels of use of personal transportation, primarily due to new traffic concepts, goods traffic on our roads is set to increase significantly. Current status indicates that electromobility does not yet offer any alternative: thus liquid fuels can be expected to continue to dominate our heavy-goods road transport, ship transport and air travel, at least, over the next decades to come. Likewise, for personal vehicles engines fuelled by petrol and diesel will not disappear from one day to the next. These factors make it all the more true that sustainability and avoidance of greenhouse gases are taking centre-stage in the discussion on mobility, as are effciency and the economical use of resources. Biofuels such as biodiesel, ethanol and vegetable oil are making a decisive contribution here.

Of the 53 million tonnes of petroleum and diesel consumed in Germany in 2012, approx. 5.7 percent (in terms of their energy content) were substituted by biofuels – mainly by an admixture. With sales of 3.8 million tonnes, Germany takes the leading position within the EU. The sale of biofuels is more or less constant, after the major downturn in 2008 – in 2007 the share was yet 7.2 percent. To help support the market introduction, pure biofuels were initially largely exempted from taxes (mineral oil tax/energy tax). The step-by-step introduction of taxation, together with increasing raw material prices, caused a collapse in the market for pure biofuels – especially in the commercial vehicles sector. Since January 2013, the tax concession no longer applies to biodiesel and vegetable oil as a pure fuel. Up to the year 2020 – due to the current biofuel objectives – a major increase in the use of biofuel can be expected in Germany.


Biodiesel or also fatty acid methylester (FAME) accounts for the largest market share of biofuels consumed in Germany, at approx. 65 percent. At over 30 production sites, it is produced from vegetable oils and fats – primarily rapeseed oil; so called rapeseed oil methylester (RME). In production, the three fatty acids contained in the oil are separated off from the glycerine in the presence of a catalyst and then esterified with methanol. The requirements applicable to fuel quality are established by the norm DIN EN 14214, which is valid Europe-wide.

Since 2004, oil companies have been admixing up to 5 percent biodiesel to traditional diesel, and from 2010 up to 7 percent – hence the name of the fuel “B7”. While in 2006 only around 40 percent of German biodiesel was sold through the admixture process, it is now over 90 percent.

Vegetable Oil

A further source of pure biofuel is rapeseed oil. Mainly in agriculture and forestry, it is an option in modified engines. While in the case of biodiesel the fuel is adapted to the necessary engine characteristics by means of esterification, with vegetable oil fuel the engine needs to be adapted to suit the fuel. Appropriate distribution outlets offer special equipment for making the conversion. As the oil or fuel quality respectively has a decisive impact on perfect functioning, compliance with the rapeseed oil fuel norm DIN 51605 is highly significant in this.

Like for biodiesel, a reduced energy tax rate applied to rapeseed oil fuel until December 2012. By contrast, in agriculture and forestry, this use of pure fuel is exempt from energy tax. The current limited level of competitiveness compared to conventional diesel fuel has caused sales of vegetable oil fuel to collapse from 840,000 tonnes (2007) to less than 25,000 tonnes (2012).

Vegetable oils are used in Germany not only as fuel, but also for the generation of electricity and heat. In 2010, around 1,400 CHP units fuelled by vegetable oil produced approx. 1.8 TWh electricity (i. e. 1.8 billion kWh). With an average electricity consumption in German of approx. 3,600 kWh per household and year, this corresponds to electricity production for 500,000 households. CHP units fuelled by vegetable oil are usually operated on a highly-effcient heat-led basis – the advantage is high overall efficiency, at over 80 percent. Even if there is remuneration for generating electricity from vegetable oil in existing installations, via the Renewable Energy Sources Act (EEG) high prices for these raw materials in recent years have made it harder for them to be run on a commercially viable basis. For new installations going into service from 2012 onwards, the EEG remuneration no longer applies, so this form of use will not be further expanded in the future.


While vegetable oil and biodiesel provide the fuel for diesel engines, bioethanol can replace “Super”-category petrol. Ethanol emerges in the anaerobic digestion of carbohydrates that are present in crops containing starch (potatoes, maize, grain) or sugar (sugar beet, sugar cane). Using yeast and enzymes, this sugar is converted to ethanol and to CO2 . For the use as fuel, the alcohol content must then be raised, to at least 99.7 percent, via distillation and draining process in several stages.

In Germany, ethanol is primarily produced from grain or sugar beet. Six large installations and several smaller ones, with a total production capacity of more than 1 million tonnes, currently produce approx. 0.6 million tonnes of ethanol per year. In 2012 the industry sold approx. 1.2 million tonnes of bioethanol, almost all of which was used as admixture in the fuel category “Super” (Super E5, Super E10). Only approx. 1 percent or 17,000 tonnes of E85, as a pure fuel, were sold at German service stations.


While up to 2010 a maximum of 5 percent of bioethanol was admixed to petroleum fuels in Germany (in terms of volume), since January 2011 it is possible to double the biogenic share to up to 10 percent. Bioethanol is admixed to basic petroleum in the refineries. From there it is distributed to the service stations. “E10” – the new term used for it at the petrol pumps – is compatible with the engines of more than 90 percent of petrol-fuelled vehicles. The remaining vehicles are essentially not suitable for operation with E10 due to incompatibility of materials. That is why German service stations continue to offer petrol of the category “Super” with an ethanol share of up to 5 percent (E5). There is no indication of negative consequences in terms of how suitable vehicles run when fuelled by E10 (e. g. cold-start problems, output performance). Neither does the 10 percent bioethanol content in the petrol have a significant effect on fuel consumption, compared to conventional petrol. On the one hand, the difference in terms of energy content is only small, especially compared to E5; on the other hand, subject to having the appropriate engine technology any loss can, to a large degree be compensated for by the advantageous characteristics of ethanol fuel (e. g. high level of heat of evaporation, high octane rating). This is confirmed by tests on vehicle fleets, for example tests conducted at Vienna Technical University.

E85 and Flexible Fuel Vehicles (FFV)

So-called Flexible Fuel Vehicles (FFV) have been on the market in Germany since 2005. These vehicles' engines are able to use fuels with a higher ethanol content (E85), as well as conventional petrol. E85 is a fuel mixture consisting of 85 percent ethanol and 15 percent petrol. As ethanol has a lower energy content, when using E85 a 10–30 percent higher rate of consumption must be expected, compared to E10. However, extra consumption is in part balanced out by a lower fuel price. E85 is available at more than 300 service stations in Germany.

The future and BtL-fuels

At present and for the foreseeable future, it is primarily vegetable oil methylesters (from rapeseed, but also from soy oil and palm oil) and bioethanol (from grain, maize, sugar cane and sugar beet) that are and will continue to be used, as a constituent part of fuel mixtures. The prospects are that biomethane and new biofuel options of the future, including ethanol from lignocellulose (straw) or synthetic biofuels (biomass-toliquid fuels), will noticeably broaden and supplement this product range.

The production of synthetic fuels from solid biomass is currently still in the development stage; relevant pilot installations are expected to go into operation in 2014. This gives rise to the hope that the processes for making so-called BTL fuels (biomass-toliquid) will achieve market readiness in the years to come. These fuels promise a range of advantages: the biomass is used in its entirety, not merely individual constituent parts of the plant, such as oil or starch. Accordingly, BTL achieves strong land effciency results; also, a broad base of natural materials is suitable for its production – such as wood chip, straw or municipal organic waste – some of which do not compete with food production.

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