Ethanol Producers Association of Southern Africa

EPASA

Manufacturing Processes



The traditional route to ethanol is by the fermentation of sugar and this process is widely used globally. The sugar can arise from a number of vegetable sources, e.g. sugar cane, sugar beet and saccharification of carbohydrate derived from maize, sorghum, etc.  The product is then known generically as fermentation ethanol.
 
With the advent and growth of the petroleum industry in the mid 1900's, an alternative route to ethanol was developed. Hydration of ethylene derived from crude oil is a widely used process overseas. However, in South Africa coal is the abundant energy mineral and Sasol South Africa developed a process to beneficiate this to liquid fuels with ethanol being one of the side streams. Crude oil and coal derived ethanol is refered to as synthetic ethanol.
 
The two processes are covered below.

FERMENTATION
                                            
The primary sources of raw material for fermentation in South Africa are sugar cane molasses and maize (grain). Molasses is the syrup remaining after the final sugar extraction process in a sugar mill. Molasses is diluted and a small quantity of yeast is added. Fermentation is allowed to proceed, with cooling when necessary. During the fermentation process, the sugar is converted to alcohol and carbon dioxide is released. The liquid remaining after fermentation is referred to as “beer” in the industry and has a 10% ethanol content.

This liquid is distilled and the first run alcohol of about 95% strength is recovered. This is referred to as “Industrial 95” in the industry. This is then redistilled to produce minimum 96% alcohol known in the industry as “rectified spirit”. Other specialised distillation processes will produce 96% potable grade alcohol and minimum 99,9% known as "anhydrous alcohol"..During the distillations molasses solids (MS) and fusel oil are produced at the heavy end. The former is concentrated to form CMS which is sold to the animal feed industry and also used as a fertiliser.


In the grain production process a suitable source of carbohydrate (e.g. maize, sorghum, etc.) is first milled to a fine slurry and an enzyme added. The starch in the milled material is then enzymatically converted to sugar and thereafter the fermentation process is applied as described above, to produce alcohol. The solids remaining after distillation, are dried and the DDGS then sold as an animal feed.


                                         SYNTHETIC
  
The Sasol Synthol process is unique to South Africa and produces a unique first run synthetic alcohol, i.e., a mixture of ethyl and iso-propyl alcohols in a 95 : 5 ratio. This product is known as  “ethylol 95”.
 
In the Sasol process coal is gasified in the presence of water and air to produce a crude gas stream. Following a gas purification step, the gas (synthesis gas) is passed into the Synthol reactors. Here the gas is converted into hydrocarbons (mostly) and some oxygenates. The latter group, comprising alcohols, aldehydes, ketones and acids, is then separated into the individual components. One of the alcohols is the ethylol 95 mentioned above. This first run alcohol is a mixture because the boiling points of the ethyl and iso-propyl alcohols are extremely close. A portion of this stream is used as feedstock to produce a high purity anhydrous ethyl alcohol. If 96% strength alcohol is ever required, water can be added to the high purity material.