Sugar Beet as a Raw Material for Bioethanol Production

Many papers have been focused on the total energy effectiveness of bioethanol production from sugar beet. Itis considered that energy needed for sugar beet processing to obtain ethanol is equal to 25–50% of the energy cost of produced ethanol. The costs depend on the technique of treatment and that is why it is possible to find variant numbers qualifying the total efficiency in a widerange from 67% (loss) to 300% (very optimistic estimation) .

From an economic point of view and in comparison with cereals, sugar beet and intermediates from beet processing are very good raw materials for alcohol productiondue to their content of fermentable sugars which can be directly used for fermentation without any modification. Molasses is a traditional raw material for distilleries inthe Czech Republic and about 90% of ethanol production comes from this raw material now a days. Molasses production has decreased every year since 1997 and the estimated last year’s production of 118 thousand tons is not sufficient for domestic alcohol production. This insufficiency was partly covered by an increased import.  Disadvantage of direct beet and beet pulp fermentation is a slow release of sugars from pulp into the fermented solution. The second aspect is a sort of problematic storability of beet that brings about sugar loss due to enzyme action.

Raw juice contains about 15–20% of dry solids. Raw juice purity ranges between 85 and 90% that means there are about 85–90% of sugars and 10–15% of nonsugars in dry matter. Considering these facts, raw juice can be used straight away after pH adjustment for fermentation. All these properties together with a relatively low price incomparison with other intermediates from beet processing make the raw juice a very profitable material for alco-hol production. Its only disadvantage is low storability and easy decomposition by the action of micro organisms. Contrary to molasses, raw juice contains all non sugarsthat are usually removed by purification process in further steps of sugar beet processing. Hence, these nonsug-ars remain in a broth and after the fermentative processpass to stillage making its composition very suitable for addition into fodder. Additional advantage is a low content of inorganic salts (especially potassium). Another suggestion how to decrease the volume of stillage from juice fermentation is based on a recycling of the part of distillation residue for sugarextraction from the raw material. Thin juice is very suitable for ethanol production butthe biggest disadvantage is a very small or hardly any possibility of its storage because the concentration of sugars is almost ideal for microorganism growth. For thesereasons it is necessary to supply the distillery very fluently with this material, which requires a contact between the distillery and the sugar plant. Thick juice is a relatively pure and highly concentrated sugar solution (RDS content 60–65%, polarization 55–65%,purity 90–95%) that is obtained by the concentration and thickening of thin juice on evaporators. This eliminates problems with storability that is comparable with molasses. On the other hand, the production of thick juice is very complicated and expensive, and it consequently influences the ethanol price, too.  (Source : Czech J. Food Sci., Vol. 19, No. 6: 224–234)