/ Production

As a fermentation alcohol, ethanol can be produced from any feedstock containing fermentable sugars. These feedstocks are commonly divided into four categories: sugar-based raw materials, starch, cellulose raw materials, and excess or by-products of wineries.


  • SUGAR: A common sugar-based raw material is molasses, a residue of sugar refining processes of sugar beet or sugar cane. Others include sugar beet or sugar cane, fruits such as apples or grapes, and a wide range of plants (sorghum, agave, Jerusalem artichokes etc.). These are pressed, sieved, soaked or processed in a diffuser to extract a sugary juice.
  • STARCH: Includes cereals like wheat, maize/corn, rye or rice and tubers such as manioc, tapioca and potatoes. As starch cannot ferment directly, a process is required. Corn, for example, is ground into a fine powder and fed into a mashing system, where it is mixed with water and the enzyme alpha-amylase. It then passes through cookers, where the heat liquefies the starch and the enzymes start to break it down into sugars. The mash is then cooled and pumped to a fermenter.
  • CELLULOSE: Wood, woodcuttings, sawdust and residues from paper factories is transformed into sugar through acid hydrolysis. While this is an effective process with considerable potential in its own right, it requires a lot of energy and produces substantial amounts of methanol (wood alcohol) during fermentation.


Fermentation & Distillation


All ethanol production involves two steps: Fermentation – the enzymatic transformation of organic compounds (like sugar) by micro-organisms (yeast). Followed by Distillation – the separation process of components with different boiling points and physical properties.


  • Fermentation is very sensitive to temperature and acidity, and requires close control. Industrial fermentation can be a batch process (the entire process is contained and completed in individual tanks) or continuous (the product overflows from one tank to the next). The cycle lasts 20 to 30 hours at a temperature of 30° to 32°C and the resulting product, known as ‘low wine’ or ‘low beer’, will be 12 % alcohol by volume at most (yeast becomes inactive in higher alcohol concentrations). An alcohol yield of 50 kg per 100 kg of sugar is considered as acceptable. Fermentation residue can be used as animal feed.
  • Distillation concentrates and purifies the alcohol. At industrial levels, ethanol is produced through a continuous distillation process where a distillation column brings ascending vapour into contact with the descending ‘low wine’ or ‘low beer’ liquid using devices such as bubble caps, valves or sieve trays. This leads to a mass transfer; the alcohol vapour is concentrated in the top of the column, while the original liquid, stripped of alcohol, is discarded as slop at the bottom of the column. Removal of impurities is achieved by boiling point differences by which ‘heads’ (esters, aldehydes etc.) are withdrawn at the top of the column and ‘tails’ (such as furfural, higher alcohols or fusel oils) at the bottom. Distillation produces a raw alcohol of 95 or 96% strength by volume.


Synthetic Ethanol Production


Alcohol can also be produced synthetically from ethylene gas or coal. The most common method in the petrochemical industry is the direct hydration of ethylene, often using phosphoric acid as a catalyst. Side reactions producing acetaldehyde and crotonaldehyde affect ethanol quality, but these substances can be removed by further distillation.

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