Distillation of Ethanol

Keikhosro Karimi

Department of Chemical Engineering

I f h U i it f T h lIsfahan University of Technology

Content

- Why purification?y p

- What is distillation?

- A short review on distillation?

Eth l Di till ti- Ethanol Distillation

- Ethanol Dehydration- Ethanol Dehydration

Fe mentationFermentation

C6H12O6 2 C2H5OH + 2 CO2C6H12O6 2 C2H5OH + 2 CO2

Fermented broth or “mash” typically t icontains:

- Ethanol (2-12%)

- Microbial biomass

- Fusel oil

- Volatile components

Stillage- Stillage

Fusel oil

Fusel oil is a mixture of primary methylbutanolsd th l l f d f k t id dand methylpropanols formed from ketoacids and

derived from or leading to amino acids. Depending on the resources used, important

components of fusel oil can be isoamylalcohol, n-propylalcohol, sec-butylalcohol, isobutylalcohol, n-butlyalcohol, active amylalcohol, and n-amylalcohol.

Amount and Application of Fusel Oil

The amount of fusel oil in mash highly depends on the pH of the fermentor. Typically,depends on the pH of the fermentor. Typically, 1–5 L of fusel oil are produced per 1000 L of ethanolethanol

F l il i d i l t f i t Fusel oil is used in solvents for paints, polymers, varnishes, and essential oils.

Aldehyde and other volatile components

Acetaldehyde and trace amounts of Acetaldehyde and trace amounts of other aldehydes and volatile esters are usually produced.usually produced.

Typically, 1 L of acetaldehyde are produced per 1000 L of ethanolproduced per 1000 L of ethanol

Odor of ethanol

Stillage- Stillage consists of nonvolatile fraction of materials

remaining after alcohol distillation. - Composition: depends on the type of feedstock used for

fermentation. Stillage generally contains: Solids (Originated from feedstock proteins and spent Solids (Originated from feedstock proteins and spent

cells) Residual sugars, residual ethanol, glycerol Waxes Fats

ib Fibers Mineral salts

Microbial biomass

Mash is usually centrifuged or gsettled in order to separate the pmicrobial biomass from the liquid and qthen the liquid sent to the ethanol recovery system.

Purification of ethanol

Mash

95% - 99%- Ethanol (2-12%)-Water-Fusel oilVolatile components

Ethanol-Volatile components-Stillage

95%, E10, E30, …

Distillation process

- Distillation is the king of separation process, and the most important and most visible pseparation technology.

- Basis: difference in volatilities or separationBasis: difference in volatilities or separation of more volatile materials from those less volatile or non-volatile materialsvolatile or non volatile materials.

- Distillation is typically used for the separation of ethanol fusel oil aldehydes and stillageof ethanol, fusel oil, aldehydes, and stillage.

Ethanol distillation

Various industrial distillation systems f h l ifi ifor ethanol purification are- Simple two-column systems- Three- or four-column Barbet- Three- or four-column Barbet- Three-column Othmer system- Vacuum rectificationacuu ect cat o- Vapor recompression- Multieffect distillation- Six-column reagent alcohol system.

Parameters in selection of the industrial distillation systems:

Energy consumption (e.g., steam and cooling water consumption)-Quality of ethanol (complete separation of fusel oil and light components).- How to deal with the problem associated with clogging of the first distillation column- Simplicity in controlling the system- Simplicity in opening column parts and cleaningthe columns.- Of course, lower capital investment

Simple two-column system

Othmer system

Barbet system

Thermodynamic ofThermodynamic of Ethanol-Water Mixture

- Ethanol-Water mixture (EWM) is a non-ideal mixtures and show a large positive deviation from Raoult's Law.

- EWM has a high vapour pressure it means that it will have a low boiling point. This means that the molecules are escaping easily and it is not necessary to heat the mixture much to overcome theis not necessary to heat the mixture much to overcome the intermolecular attractions completely.

- The boiling point / composition curve have a minimum value lower g p / pthan the boiling points of either water or ethanol.- This minimum occurs with 95.6% by mass of ethanol in the mixture. - The boiling point of this mixture is 78.2°C, compared with the boiling point of pure ethanol at 78.5°C, and water at 100°C.

http://www.chemguide.co.uk/physical/phaseeqia/nonideal.html

References

- MJ Taherzadeh and K Karimi “Bioethanol: MarketMJ. Taherzadeh and K. Karimi, Bioethanol: Market and Production Processes”, In “Biofuels Refining and Performance” by Ahindra Nag, Mc Graw Hill, 2008.

- B. L. Maiorella. Ethanol, In: Comprehensive Biotechnology, Moo-Young, M. (Ed.), First ed., gy, g, ( ), ,Oxford: Pergamon Press Ltd., 1985.

Dehydration ProcessDehydration Process

Ethanol (90-95%) Ethanol (99%)

Pressure swing adsorption (PSA) with molecular sieve is selected for ethanol dehydration. PSA is a modern technology for ethanol dehydration that is commercialized in h 1980the 1980s.

This process uses the adsorption and d ti t f i l l l idesorption nature of special molecular sieve toward the water

Why Molecular Sieve? Low operating cost and energy consumption It can produce fuel ethanol with water content less

than 0.01% (v/v). PSA for ethanol dehydration is just a physical

process with no addition of chemical components toprocess, with no addition of chemical components to the system and no discharge to environment.

High yield of recovery for ethanol. Less capital investment. Advanced and proven technology with sate and

reliable operationreliable operation.

Process Principle

Molecular sieve: Absorb water vapor from ethanol vapor

M l l i Molecular sieve: A type of white clay Manufactured in granule form Manufactured in granule form Synthetic zeolite of type 3Å is used for this application

The pores are 3Å in diameterpWater molecules are 2.8ÅEthanol molecules are 4.4Å

Therefore, water molecules are strongly attracted into the pores but ethanol molecules are excluded.

http://www.alibaba.com/product-gs/208496770/Molecular_Sieve_3A.html

Good luckGood luck