Synthetic fuels made from biomass are a recent development. At present, there are only research and pilot systems. Nonetheless, hopes are high for biomass-to – liquid (BTL, also known as synfuel and sunfuel) fuels. A wide range of biomass – from wood to straw and other energy crops – is converted into a synthetic gas, from which methanol or a fuel similar to diesel is made.34 The process is similar to Fischer – Tropsch synthesis. Such procedures are well known in the chemical industry. What is new about BTL production is the use of biomass as the precursor; a number of problems therefore still have to be solved. On the one hand, vegetable material is more heterogenous than oil and natural gas; on the other, the low energy density and distributed production of biomass mean that storage and transport have to be optimized (see 5.6).
The largest pilot unit for BTL fuel (Sundiesel) was inaugurated in 2008 in Freiberg, Germany. The plant, owned by Choren, which is partnered with car companies VW and Daimler and the Shell oil company, produces BTL fuel from any kind of biomass, such as wood chips, straw, weeds or leftover milk rejected by the agrofood industry. The plan is to have the plant produce 18 million litres of Choren’s Carbo-V (a type of biodiesel).
Two specific benefits are expected from BTL fuel:35
1 Cars are increasingly expected to have lower emissions and better gas mileage. Such engines need fuels with properties that fall into an increasingly narrow window. The properties of rapeseed oil fluctuate slightly depending on the quality of the material used, so it seems clear that rapeseed oil will not be able to comply with the Euro 5 standard. But the hope is that synthetic fuels will be tailored to the requirements of specific engines in order to reduce emissions and make engines more efficient.
2 A wider range of plants can be used to make BTL fuels than to make other biofuels (see 5.7 and 5.8),36 and the entire plant can be used, not only the fruit. The energy yield is thus higher. Nearly 4000 litres of fuel can be produced from a hectare, roughly twice as much as with biodiesel (see Figure 5.9).
On the other hand, the use of the entire plant also has a drawback; because no nutrients are returned to the soil, fertilizer has to be used, which raises the energy input. The humic content and overall productivity of the soil can be drastically altered. Here, sustainable agriculture is a must, and we must be careful not to quickly assume that BTL will be the biofuel of the future.
Figure 5.9 How much a hectare can produce
Source: Spiegel Special 5/2006, authors’ depiction