Ethanol can be produced chemically starting from a fossil source or by fermenta­tion starting from biomasses. This second method leads to the so-called bio-ethanol production.

Bio-ethanol is a vegetable origin fuel which is obtained by the fermentation of alcohol from sugars and complex carbohydrates, such as starch, cellulose and hemi — cellulose. However, the raw materials for ethanol production can be derived from alcohol-producing dedicated cultures if they are sacchariferous (sugar beet, sugar

cane, sugar sorghum) or starchy (soft wheat and corn) as well as from lignocellulosic residuals obtained from the forest and agricultural workings. The last materials mentioned do not require specific workings, as in the case of dedicated cultures, which reduces the cost for the retrieval of the raw material; therefore, they represent the most interesting option from the economical point of view.

The bio-ethanol production spinneret comprises three sections (analysed in detail in par. 2.3, Chapter 4): sacchariferous, starchy and lignocellulose.

In addition to the biomasses described above, as raw materials for bio-ethanol, agricultural and food industries residuals and urban wastes can also be used, and based on their nature they can be included in one of the three categories of the bio-combustible production spinneret.

Bio-ethanol can be mixed with gasoline or, in some cases using appropriate expedients, it can be substituted as the feed in vehicles; this bio-combustible, in fact, shows chemical-physical characteristics that are similar to gasoline. Table 14 lists the main energy characteristics of bio-ethanol compared with those of gasoline [1, 2, 24, 29].

The country that stands out for the use of bio-ethanol is Brazil where, even in the 1970s, the engines were modified for the use of anhydrous bio-ethanol (with 5% of water residuals as a substitute for gasoline. This practice is today a reality in the South American country. The interventions needed to adapt engines for the use of anhydrous bio-ethanol as a substitute for gasoline include valves regulation and replacement of the components that can corrode. In USA and Canada, on the contrary, anhydrous bio-ethanol is used in mixtures with gasoline up to 10% in non-modified engines and up to 85% in modified engines. The feeding of these latter engines, called flexible fuel vehicles (FVV), can be realized either with gasoline and bio-ethanol mixtures or with gasoline only; in fact, they are equipped with the automatic regulation of the injection times and the ratio of air-fuel mixing. In European and American studies, the possibility of using bio-ethanol in mixtures up to 23.5% without changes to the motor has been emphasized.

At present, in Europe, the presence of anhydrous bio-ethanol in gasoline in concentrations up to 5% is allowed. It is also important to underline that the properties of bio-ethanol increases the engine efficiency and reduces the fuel combustion [1, 2, 24].

Instead of bio-ethanol it is possible to use ethyl tert-butly ether (ETBE), obtained by the reaction between ethanol and isobutylene in the presence of appropriate catalysts, which finds use as an antiknock with a high octane number. ETBE can be used in place of benzene (carcinogen) and methyl tert-butyl ether (MTBE; highly polluting, especially in subterranean waters) compared to which it has a lower environmental and human health impact. Furthermore, ETBE, if it is used in mixtures with gasoline at 15% gives an octane number equal to 110, which is higher than the octane number of 95-98 that is typical of traditional antiknocks [2, 30]. Some stud­ies have also demonstrated the possibility of using bio-ethanol in mixtures with diesel: up to mixtures of 15%, without any modification to the diesel engine.