The sacchariferous section of the bio-ethanol production spinneret

The sacchariferous section is aimed at the energy conversion of the sugars that are obtained from sugarcane, sugar sorghum and sugar beet. From a technological point of view, the energy spinneret is articulated in the following phases: extraction of the sugars from the vegetable textiles, their fermentation and ethanol distillation. Generally, the fermentation is induced by the yeast Saccharomyces cerevisiae. It is used in bioreactors that reproduce the ideal conditions which favour its anaero­bic metabolism (i. e. in presence of low oxygen concentrations), at a temperature between 5°C and 25°C and with a variable pH between 4.8 and 5.


Figure 12: Sugar beet and sorghum.

The separation of ethanol from the mixture that is obtained at the end of the fermentation phase (whose duration is around 72 hours) is achieved by distillation, exploiting the components present in the mixture. From the distillation, ethanol is obtained in concentrations equal to 95% of weight and with a residual water content of 5% [2, 30].

To obtain ethanol concentrations close to 100%, it is possible to resort, but with an increase of the process costs, to fractional distillation (concentration of ethanol equal to 99% of weight) or to the separation by pervapouration (concentration of ethanol equal to the 97% of weight). Fractional distillation involves the addition of benzene in the starting mixture.

The separation by pervapouration involves transporting the mixture that is obtained downstream of the fermentation in the vapour phase to filter it with appropriate selective hydrophile membranes.

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