Ethanol is the odorless liquid used as an alternative to petrol and can be used as a blend with gasoline. Biomass is a rich and carbon-neutral renewable energy source and utilized for the production of ethanol and other valuable compounds.
Ethanol is used nowadays instead of gasoline due to the following remarkable properties
- High octane number
- Non-fossil based fuel and environment friendly
- Renewable and sustainable
- Reduced emission of carbon mono oxide
- Higher efficiency and performance
- Low vapor pressure.
Biomass is a very interesting bioresource for ethanol production due to sustainable development. There are various types of biomass that are currently in the production of ethanol and this is categorized in five major groups
Conversion of biomass into ethanol:
The procedure used in ethanol production depends upon the raw material used. Fermentation is the main step that could produce ethanol from any feedstock containing sugar. The main sources used for ethanol production are.
- Sugars (from fruits or sugarcane): Can be directly converted into ethanol by fermentation.
- Starch (from potatoes and corn): Hydrolysis is required prior to fermentation.
- Cellulose (from wood residues): Pretreatment is required that converts complex sugars into simple ones.
Brazil and the USA are major producers of ethanol throughout the world mainly use sugarcane and corn as a feedstock. A general process used for ethanol production is shown in diagram 1. Moreover, sugarcane feedstock is more competitive than other bioresources due to ease in cultivation and eco more ecofriendly nature.
Milling, pretreatment, hydrolysis, and detoxification are not required during the utilization of sugar/molasses as a feedstock. These methods are used during the treatment of starchy and cellulosic materials
Ethanol production from molasses:
Lignocellulosic biomass requires pretreatment that increases the cost of production. So, molasses is the focus presently because it does not include the pretreatment step that lowers its cost of production. Following are the main steps involved in the extraction of ethanol from molasses.
1.Extraction and concentration:
In ethanol production, the first step is the extraction and concentration of juice.
2.Production of molasses:
The second step is the concentration of juice the sugar (sucrose) crystals are separated by centrifugation and drying the remaining syrup is known as molasses used for ethanol production. Molasses is a dark mother liquor that contains almost 50% of the fermentable sugars.
3.Dilution of molasses:
After the formation of molasses, it is diluted in order to maintain the sugar balance.
Fermentation is anaerobic process results in the production of ethanol and carbon dioxide. Fermentation is done in the presence of yeast such as Saccharomyces cerevisiae.
The fermented liquid is distilled by continuous boiling results in the formation of 95% anhydrous ethanol. The aqueous liquid remains after distillation known as stillage. Stillage is used in agriculture as a fertilizer.
Microbes used in fermentation:
There are a variety of microbes that are used during fermentation depending upon the culture conditions and feedstocks such as
- Kluyeromyces marxians Zymomonas mobilis
- Saccharomyces cervisae Pichia stipites
- Saccharomyces uvarum.
- Pichia stipites
- Zymomonas mobilis
Expected outcomes of ethanol:
- Emission of GHG shall be minimized.
- Mitigation carbon dioxide level.
- Ethanol production has social potential and will increase opportunities for the local population.
- Positive impact on the economy.