Ethanol Production

Ethanol Production

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Introduction

  • Biological process in which sugars (glucose, fructose, sucrose) are converted into cellular energy.
  • Ethanol is produced in the result of this process.
  • It is colorless, volatile or flammable liquid.
  • It is widely used as biofuel as well as an alcoholic beverage is increasingly being consumed globally.
  • This is mainly because of the cheap raw materials available.

Raw material

  • Ethanol can be derived from either sugar, starchy materials or lignocelluloses.
  • The main feedstock for ethanol production includes sugarcane, sugar beet, corn, wheat.

Sugars:

  • Sugarcane (molasses & juice)
  • Cane sugar (clarified concentrated syrup)
  • Sugar beet

Starchy materials:

  • Corn
  • Wheat
  • Sweet sorghum
  • Cassava

Lignocellulosic material:

  • Sugarcane bagasse
  • Corn stover
  • Cereal straws

Feedstock conditioning and Pretreatment

Dilution:

  • Molasses must be diluted to below to 25 °Bx (Brix) as yeast start to ferment quickly at this concentration.

Sedimentation:

  • To prevent any incrustation in the pipelines or distillation towers due to ash content in molasses greater than 10%.
  • The special chelating agent can also be used to remove the incrustation.

Addition of org & inorganic compounds:

  • Done to offset the negative effect of salt which in turn increases the osmotic pressure.
  • Yeast strains resistant to salts are also developed.

Microfiltration:

  • To remove the impurities that stick to the surface of the biocatalyst when immobilize cells are used.

Microorganism involved

Bacteria used:

  • Zymomonas mobilis
  • Clostridium acetobutylicum
  • E.coli

Yeast used:

  • Saccharomyces cerevisiae
  • Saccharomyces uvarum
  • Candida utilis
  • Kluyveromyces fragilis

Features of Microbes:

  • Due to the small size, having a high surface ratio.
  • Due to having a resistant cell wall, producing high concentration substances leads to a faster fermentation rate.
  • The intense metabolism permits the development of a continuous fermentation process.
  • Cells growth rate offsets at which cells are removed from the bioreactor.
  • Have the ability to “predigest” the available food source and release both products and the intermediate metabolites.
  • Using immobilized cells of microbes by treating with Calcium alginate to adsorbed on the surface of materials.
  • Using genetically modified microbes to enhance the fermentation process.

Physical requirements:

  • The ideal pH is around 4.0-4.5.
  • The initial temperature is kept between 21-26 ºC.
  • Ethanol gets evaporated at 27 ºC.
  • Aeration is initially required for the growth of microbes.
  • Later, anaerobic condition are created by withdrawing oxygen coupled with the production of carbon dioxide.

Chemical requirements

Nitrogen source:

  • Urea is the most suitable source.
  • Gaseous ammonium increases the pH of the medium.
  • Ammonium sulfate can lead to incrustation.

Phosphorus source:

  • Diammonium phosphate used as a source.

Hydrolytic enzymes:

  • They can also be added to convert biopolymers and non-fermentable substances in the molasses to monosaccharides or amino acids.

Process flow:

Classical fermentation can be achieved in three steps:

  • During the first phase (22-24 h), yeast cells multiply aerobically by consuming oxygen present in the mash.
  • In the middle phase (24-48 h), alcohol production occurs with post saccharification of sugars and multiplication of yeast falls off.
  • The decrease in alcohol formation along with insignificant yeast growth at the final stage (48-72 h).

Ethanol Production

Image Source: https://doi.org/10.1016/j.biortech.2018.02.125

Production process:

There are following steps in ethanol production:

  • Milling
  • Liquefaction
  • Saccharification
  • Fermentation
  • Distillation
  • Dehydration

1. Milling:

  • The feedstock is passed through a hammer mill which grinds it into a fine powder called a meal.

2. Liquefaction:

  • The meal is mixed with water and alpha-amylase.
  • Then passed through cookers where the starch is liquified and heat is applied here to enable liquefaction.
  • Cookers with the high-temperature stage (120-150˚C) and lower temperature holding period (95˚C) are used.
  • High temperatures reduce bacteria levels in the mash.

3. Saccharification:

  • The mash from the cookers is cooled.
  • And secondary enzyme glucoamylase is added.
  • This converts the liquified starch into the fermentable sugars.

4. Fermentation:

  • Yeast is added to ferment the sugars to ethanol and carbon dioxide.
  • In a continuous process, the fermenting mash can flow through several fermenters until it is fully fermented and leaves the final tank.
  • In a batch process, the mash stays in one fermenter for about 48 hours before distillation starts.

Batch fermentation

´Yeast reuse results in a decrease in new growth with no more sugar available for ethanol production and an increase in the yield from 2 to 7%.

´Traditional yield 1-3g/L.

Continuous fermentation:

  • To ensure system homogeneity and reduce the concentration gradient in the culture broth, CSTRs are employed.
  • Reduce construction costs of bioreactors
  • Lower requirements of maintenance and operation
  • Better control of the process
  • Higher productivities
  • Cultivation of yeast under anaerobic conditions for a long time diminish their ability to produce ethanol.
  • Aeration is important which can enhance cell concentration.

Extraction of the final product:

5. Distillation:

  • Mash is pumped to continuous flow.
  • Multicolumn distillation system where the alcohol is removed from solid and water.
  • The alcohol leaves the top of the final column at about 96% strength.
  • The residue mash is called stillage which is transferred from the base of the column to the co-product processing area.

6. Dehydration:

  • The alcohol from the top of the column is passed through a dehydration system where the remaining water will be removed.
  • Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol.
  • The alcohol product at this stage is called anhydrous alcohol.

Fermentation Byproduct

Dried distiller grains with soluble (DDGS):

  • The form is available to the feed industry.
  • The liquid is separated from mash during the distillation process.
  • It is partially dehydrated into syrup.
  • Then added back on to the dried distiller’s grain to create DDGS.

Carbon dioxide:

  • Used to carbonate the beverages.
  • Manufacture dry ice.
  • Used to flash freeze meat.
  • Used by paper mills and food industries.

References

  1. https://www.sciencedirect.com/topics/engineering/ethanol-production-process
  2. http://www.biologydiscussion.com/industrial-microbiology-2/fermentation-industrial-microbiology-2/production-of-ethanol-microbiology/66072
  3. https://www.chemguide.co.uk/organicprops/alcohols/manufacture.html
  4. https://www.essentialchemicalindustry.org/chemicals/ethanol.html

Ethanol Production

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1 thought on “Ethanol Production”

  1. Dear Sirs
    we are facing bad days due to Corona virus so a big need for Ethanol .
    i need to convert starch or raw potatoes to ethanol , please tell me how?
    we need step by step production system please.

    Reply

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