WHat is ETBE ?
ETBE stands for "Ethyl tertio-butyl ether".
Chemically, this has the following format :
and is produced out of Ethanol (CH3-CH2OH) and iso-butylene. The iso-butylene is coming from a fossil-fuel source.
This is only a biofuel if the ethanol used to produce it did come from a bio-ethanol source.
Why using ETBE ?
Both ethanol and ETBE are primarly used as fuels through blending into (fossil-fuel) gasoline. Even though it seems more logical to use ethanol in its neat form, ethanol has an important draw-back : ethanol and gasoline do not form a stable solution. In the presence of water, it tends to separate into 2 phases, like vinaigrette... The oil-phase with the gasoline on top, the water-phase including the gasoline in the bottom. Additionally, ethanol is aggressive to some motor-engine components and cannot be used in all engines without modifications.
ETBE does not pose this difficulty. It however poses another problem : ETBE, like its older fossil-fuel brother MTBE (methanol-based) is not biodegradable. It has a very low odour and taste threshold when present in underground or ground-water.
Bio-content of ETBE
ETBE is only "bio" for its ethanol-part. According to the European Biofuels Directive, this means 47% of ETBE by volume and by energy. These numbers are disputed, 43% being more in line with the chemical composition.