Bioethanol is used increasingly as replacement for petrol (gasoline) in petrol engines. At present up to 5 percent of bioethanol may be added by the mineral oil manufacturers to the petrol, without any changes in the engines are necessary. At present, also a direct employment of bioethanol with smaller petrol addition (E-100, E-85, E-50 fuel) in special engines called "flexible fuel vehicles" (FFV) is in test stage. However, these fuels are not suitable for normal petrol engines. Furthermore, bioethanol is used as fuel in stoves.
Bioethanol is normal agrarian alcohol manufactured from crops such as sugar beets, potatoes and in particular grain as well as of their wastes (biomass). Recently for production also wastes from the wood working are used.
With Isobutene bioethanol can be converted to ethyl-tert.-butylether (ETBE), which may be added into conventional petrol with up to 15%.
The advantage of the use of bioethanol opposite conventional gasoline is in the fact that it is produced from renewable, regenerating raw material resources. The CO2 set free by later burning is again needed for the growth of the producing plants. Therefor the greenhouse effect caused by CO2 is not continued to intensify.
The oldest and at present most effective method exists in the hydrolysis of the biomass with diluted sulfuric acid at temperatures of approx. 200 degrees, whereby in the first step first the hemicellulose is converted to sucrose and afterwards in the second step the more resistant cellulose.
Alternatively the dried up to 10% residual moisture biomass can be unlocked in the Arkanol process with concentrated sulfuric acid (70%), where temperatures of 50 degrees are already sufficient.
As a new development the enzymatic splitting is to be seen, which is at present, however, still too expensive.
The sucrose is split afterwards by means of the enzyme invertase contained in yeasts into fructose and glucose, which are subjected by the enzyme zymase also contained in yeasts to an alcoholic fermentation to ethanol. The ethanol is separated afterwards by fractionated distillation from the aqueous solution.