Upstream Process

EMi Group 's commitment on the construction of Bioethanol plants is based on a very specialized technical knowledge of the Ethanol production processes; in this article you will find a more detailed understanding about the Upstream process.

In Europe and the US, the existing traditional 1" generation bioethanol plants typically process cereals (maize/corn, wheat, rye, ...) and other starch or sugar containing raw materials (e.g. sugar beet). The raw material initially undergoes crushing (milling for cereals) to reduce the particle size distribution to such a degree that the enzymes enter in contact with the starch molecules in the subsequent steps. During liquefaction with alpha-amylase, starch is dismantled into low molecular sugar units, the so-called dextrines. In the next process step, saccharification, these dextrines are further dismantled into fermentable sugars by means of gluco-amylase. In the fermentation process, these fermentable sugars are partly aerobically transformed, but mainly anaerobically by Saccharomyces cerevisiae (yeast) into biomass and ethanol; sugar containing raw material as e.g. sugar cane can be directly fed into fermentation after crushing.

Upstream process groups:

• Storage
• Cleaning
• Milling / Crushing
• Mashing
• Liquefaction
• Saccharification
• Fermentation (batch or continuous)

Because cellulosic feedstock are more difficult to break down into fermentable sugars than starch and sugar based feedstock, the cellulosic biochemical conversion (2nd generation bioethanol technology) process requires additional steps- the two key steps are biomass pre-treatment and cellulose hydrolysis. To break down cellulose- the primary source of sugar in fibrous biomass-you have to first get past hemicelluloses and lignin, which surround the cellulose in a protective sheath. Overall approach converting cellulosic ethanol is pre-treatment to open up biomass to enzymes- biological steps to produce enzymes, hydrolyze biomass and ferment sugars- ethanol recovery and purificationboiler and power generation- and residue processing. Acids can break down the long chains in hemicelluloses and cellulose to release sugars comprising these materials through hydrolysis reactions, but because of their high specifity, enzymes known as cellulase can achieve higher yields of glucose from cellulose and are often favored. However, to survive in nature, cellulosic biomass has evolved a structure that resists enzymatic attack, and it must first be pretreated to better expose the cellulose to enzymes. Over the years, biological, chemical, mechanical, physical, and thermal pre-treatments have been tried, but currently, only methods that treat biomass at temperatures of about 80- 200 "C with one or more chemicals have been able to realize the high sugar yields vital to economic success. Leading thermo chemical pretreatment options include dilute sulfuric acid, ammonia fiber expansion (AFEX), neutral pH, and lime, although the choice depends on many factors including the nature of the substrate, enzymes and organisms and other process details.