Download - Ethanol Production
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Ethanol Production
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Ethanol produced as a component of alcoholic fermentation
Used as chemical feed stock and fuel supplement
World wide- 4 million tons of ethanol produced annually [ 80% is by fermentation]
Used as solvent
Used to produce ethylene and other petrochemicalsIntroduction
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Biosynthesis of EthanolProduced by fermentation f sugar rich products with help of yeast- Saccharomyces cerevisiae or some times Kluyveromyces fragilis
Bacteria also used ( widely used one is Zymomonas mobilis)
S.cerevisiae suitable for fermentation of hexosesK.fragilis- suitable source is lactoseCandida sps. suitable source is pentose
Most microbes requires readily available sugar compounds for fermentation ( eg. Sugar cane ,sugar beet juices, Molasses)
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Carbohydrate Hydrolysis Glucose
Glycolysis
Pyruvate Pyruvate decarboxylase, Mg2+
Acetaldehyde + CO2
Alcohol dehydrogenase
Ethanol
Ethanol Biosynthesis Pathway
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Schematic representation of Ethanol productionSterilizationRaw Materials (Starch,Cellulose,Molasse))Pretreatment of substratesFermentationSeparationDistillationEthanol(94.5% w/v)
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Ethanol ProductionEthanol is produced in 3 steps-1. Preparation of substrate2. Fermentation3. DistillationPreparation of substrate 3 types of substrate are used a) Starch containing roots , tubers, or grainsb) Molasses or juice from sugar cane or sugar beetc) Wood or agricultural waste or wood wasteRoot starch is derived from Manihot esculenta (Root contains 20-30% of starch and 1 to 2 % protein)S.cerevisiae donot produce amylase; so roots are first ground, squeezed and dried. Then starch is liquified by boiling under pressure and hydrolyzed enzymaically
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Glucose production glucoamylase and alpha amylase are added after boiling and cooling process
1 tone of starch app. 1 liter of alpha amylase and 3.5 L of glucoamylase are used
Molasses byproduct of sugar ,commonly used
Wood- Is not yet used in commercial production
Sulfite waste liquor- source of sugar formed during production of paper from conifers
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2. Fermentation processBoth Batch and continuous fermentation was employed for ethanol production.
When compared to batch , continuous fermentation is more useful for ethanol production
Industrial production of alcohol is carried out in large fermentaers upto a size 5 lakh liters
Inoculum volume is around 4 % of the fermentor
pH around 4-4.5
Initial temperature is kept between 21-26 C, During fermentation temp. rise to around 30 C
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Cooling devices are necessary to maintain temp. less than 27C
Duration is 2 -3days, but actual time period depends in raw materials used and incubation temp.
After fermentation , spent medium contains ethanol in the range of 6-9% by volume. This represents 90-95 % of substrate isconverted in to ethanol
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3. DistillationEthanol is recovered from fermented medium by distillation
Cell mass is separated initially by centrifugation or sedimentation
1st Distillation 80 % of pure ethanol is obtained
Repeated Distillation- 99.4% or more ethanol is achieved
Final dessication is by chemical dessicants and by absorbtion
Ethanol 92.4% - used as solvent
99.2% - used as fuel
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Methods to increase ProductivityProcess should be carried out in large scale by continuous fermentation
Continuous operation with cell recycle- results in faster conversion of substrates to ethanol
Maximum productivity with glucose as carbon source
82 g/L/h by yeast
120g/L/h by Z. mobilis
Use of immobilized cells ( high cell concentration in fluidized bed bioreactor)
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If Molasses is used as substrate
Batch system yield 2g/L/h of ethanol
Continuous system yield 3.35g/L/h of ethanol
Immobilized cells with continuos system yeild 28.6g/l/h of ethanol
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Solvents - Acetone , Butanol & Glycerol
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Acetone Butanol ProductionAcetone used as solvent for fats ,oils, resins, waxes - used as gelatinizing agent for nitrocellulose - used in dyeing industry
Butanol- used in production of detergent and brake fluids - used as solvents for fats, waxes and resins
Butanol is better fuel additive than ethanol due to its low vapour pressure, low solubility with water, complete solubility with diesel fuel
Acetone, Butanol, Butyric acid & isopropanol are produced by Clostridium sps.- by fermenting starch, molasses, sucrose, pentoses and wood hydrolysate
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Products will vary and it depends o strain and fermentation conditionsAcetone-butanol fermentation C. acetobutylicumButanol-Isopropanol fermentation- C. butylicumButyric acid-Acetic acid fementation-C. butyricum Clostridium acetobutylicum strict anaerobe, hydrolyze gelatinized starch in to glucose & maltose
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Production processCane Molasses ( Raw Material)
C. acetobutylicum
Low inoculum is inoculated into production fermenters (1:3000) Fermentation (pH 5.8-6.0),Temp.34 C, Fermenter Volume is 90 m3 - batch reactor
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After sterilization of fermentor, it is gassed with CO2
Before and after inoculation, the medium contents are also stirred with CO2
This is to ensure that it will support the growth of the organismTo remove any residual O2 present in the fermenterTo maintain anaerobic condition
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Fermentation takes 36 hours to completeFirst Phase (18hrs) pH decreases to 5.2 {formation of acids}
Second phase (18hrs) - pH increases { formation of A/B}
Third phase pH value remain constant 5.8{growth and solvent production stop}
Continuous distillation & fractionation
Product recovered
* Contamination by phages & Lactobacilli is a common problem
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Several ways to improve solvent yieldAddition of Acetic & Butyric acids
High agitation (300rpm) during acid phase followed by low agitation (25 rpm) during solvent phase
Simultaneous removal of inhibitory products (A/B) by extraction and adsorption
Continuous or fed batch operations improve solvent productivities
Use of immobilized cultures
Gene manipulations of C.acetobutylicum
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Glycerol Production
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Glycerol is formed by yeast along with ethanol during alcoholic fermentation
Usually glycerol is formed in low amount . By modifying the fermentation balance high amount of glycerol is produced
Acetaldehyde is the intermediary product in ethanol fermentation
When sodium sulfite is added, it blocks alcohol production and diverts the pathway for large scale production of glycerol.
Sodium sulfite reacts with CO2 in the medium and gets converted to Sodium bisulfite
Then combines with acetaldehyde to form acetaldehyde sulfite complex and blocks alcohol production
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NADH2 formed during glycolysis usually reduces acetaldehyde to ethanol
Due to unavailability of acetaldehyde ,NADH2 reduces Dihydroxyacetone phosphate to form glycerol 3- phosphate then glycerol
Glycerol fermentation carried out in 1000m3 size of fermenters
Fermentation duration within 2 to 3 days
Osmotolerant yeast are used
Commonly used strains S. rouxii & Torulopsis magnoliae
Used in cosmetics & pharmaceutical industries
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Glycerol Production Using AlgaeDunaliella salina is halophilic algae commonly found in salty lakes.
While growing in hypersaline conditions ,this algae synthesizes glycerol within the cells to balance the high osmotic pressure in the surroundings (due to salts)
So Higher the salt concentration in the surroundings results in high intracellular glycerol production.
Extraction of glycerol from algaeCollect the algal cells and place it in low salt environmental condition.
Sudden shift in high salt to low salt condition will excrete the intracellular glycerol into the surrounding medium
This new fermentation process is developed in Israel
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