Pure bioethanol

Pure bioethanol (ElOO-fuel) is the most produced biofuel, mainly in Brazil and the USA. More widespread practice has been to add up to 20% to gasoline by volume (E20-fuel or gasohol) to avoid the need of engine modifications. Nearly pure bioethanol is used for new "versatile fuel vehicles." (E80-fuel only has 20% gasoline, mainly as a denaturaliser.) Anhydrous ethanol (<0.6% water) is required for gasoline mixtures, whereas for use-alone up to 10% water can be accepted. 

The partial oxidation of ethanol was investigated, but with less intensity than in the case of steam reforming. The reason is that the use of the pure partial oxidation process is not advised for bioethanol reforming because bioethanol is an ethanol-water mixture in which removal of all the water entails a significant cost. Therefore, for bioethanol partial oxidation, the process is combined with steam reforming in autothermal schemes with the stoichiometry shown in Equation 6.18. 

Bioethanol is also a very attractive compound for increasing gasoline octane quality and it can be added up to 10% to gasoline (E5 is the preferred European solution while ElO is used in USA) without engine modification or also used practically pure, as E85 or ElOO, in the Flexible Fuels Vehicles. 

The transformation of ethanol into hydrocarbons on acid catalysts is an interesting approach to upgrading renewable resources, such as biomass, via fermentation [1]. There is currently a great interest in the catalytic transformation of aqueous ethanol, as it avoids the costly operations involved in the total elimination of water for obtaining pure ethanol [2]. The aim of the catalytic transformation is to obtain ethene, which is the objective of the BETE process (bioethanol to ethene) [3] or obtain C5+ hydrocarbons (BTG process) (bioethanol to gasoline) [1]. The latter process requires a reaction temperature above 350 C, when deactivation by coke is significant. 

Table 2.8 Ethanol conversion and pure hydrogen recovery data for bioethanol steam reforming reaction...

Bioethanol that is obtained by enzymatic decomposition of biomasses such as com or wheat waste comes as an aqueous solution that contains about 12 vol% of ethanol (H20/EtOH >= 2 1). Pure ethanol can be obtained from this solution by distillation. 

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