Ethanol Production

Feedstock1. Biomass2. Starch

DefinitionsBiomass

Lignocellulosic biomass

the relatively large amounts of heterogeneous matterproduced by living organisms. It includes residues

originating from plants, animals, and microorganisms

Biomaterials whose composition is dominated by lignified cell walls from vegetative plants.

Polysaccharide and lignin content of representativelignocellulosic feedstocks a,b

Component Lignocellulosic Material(Straw)

Glucan 31.9Xylan 18.9

Arabinan 2.1Mannan 0.2

Galactan 0.6Lignin 22.8

Sum of above 76.5

a values are percentages on a dry weight basisb data taken from Puls and Schuseil (1992)c measured as Klason lignin

Biomass(cellulose, Hemicellulose, lignin)

Milled Biomass

Ethanol

Prehydrolysate Liquid(xylose, 2-furaldehyde)

Pretreated solid(cellulose, lignin)

Mechanical chipping/grinding

Pretreatment(Dilute acid, 180oC)

FermentationEnzymatic saccharification(fungal cellulases)

Hydrolyzed Solid(lignin)

Hydrolysate Liquid(glucose)

Ethanol

fermentation

Compositions Range Average

Starch 61.0 – 78.0 71.7

Protein 6.0 – 12.0 9.5

Fat 3.1 – 5.7 4.3

Ash 1.1 – 3.9 1.4

Cellulosea 3.3 – 4.3 3.3

Pentosansb 5.8 – 6.6 6.2

Sugarsc 1.0 – 3.0 2.

other 1.0

Chemical Composition of Corn (percent of dry matter)

aplus ligninbas xylosecas glucose

Corn Wet MillingClean Corn

Steeps Steep water (6.5%)

Mill and Screen System

Germ System

Wash

Centrifugal Separator

Losses (1%)

Adapter from C.R. Keim, 1999

Germ (8%)

Fiber (10.2%)

Prime Starch (68%)

Gluten (6.3%)

Enzymatic Starch Conversion

Starch Slurry

Liquefaction Maltodextrin

Purification

Saccharification

Refining

Isomerization

Adapter from H.S. Olsen, 1995

To Fuel Ethanol

Maltose Syrups

Fructose Syrups

-amylase

Glucoamylase/Pullulanase

Glucose SyrupsMixed Syrups

GlucoseIsomerase

Feeder Pathways for Glycolysis

Entry of Fructose into Glycolysis

Fate of Pyruvate• Lactate dehydrogenase

– during exercise– Reversible in liver– Location: cytoplasm

• Pyruvate dehydrogenase– Source of AcetylCoA– Irreversible reaction– Location: Mitochondria

• Ethanol synthesis– In yeast, some bacteria– Location cytoplasm

Reduction of pyruvate to ethanol (microorganism)

• It occurs by the 2 reactions shown below:

• The overall reaction of alcohol fermentation:

• Glc+2ADP +2P---------> 2 Ethanol + 2CO2 + 2ATP + 2 H2O

Pyruvate decarboxylase mechanism

There is no net oxidation-reduction in the conversion of Glc into Ethanol, NAD+ is used first and made it later!

Active site of Alcohol dehydrogenase

Pyruvate decarboxylase is present in brewer’s and baker’s yeast. CO2 produced during alcohol fermentation is responsible for the characteristic

carbonation of champagne.

In baking, CO2 fermentation by pyruvate decarboxylase during fermentation of dough due to CO2 , dough rises.

Alcohol dehydrogenase metabolizes alcohol.

TPP carries “active aldehyde” groups

The pyruvate decarboxylase reaction is the first reaction we see that TPP is involved. TPP------> Vit B1. If B1 is not enough

More about TPP• TPP plays an important role in the cleavage of bonds adjacent to a

carbonyl group such as the decarboxylation of alpha-ketoacids and in chemical rearrangements involving transfer of an activated aldehyde group from one C to another.

• The functional part of TPP is the thiazolium ring. The proton at C-2 of the ring is relatively acidic, loss of this proton, produces an active site in TPP.

• TPP is involved in the following reactions– 1. Pyruvate decarboxylase– 2. Pyruvate dehydrogenase– 3. Alpha-Ketoglutaratedehyrogenase– 4. Transketolase

Microbial fermentation yield other end products of commercial value:

Lactate and ethanol are the common products of microbial fermentation Clostridium acetobutyricum, ferments starch to butanol and acetone.

Here comes industrial fermentation, purpose is to make important products from readily available material (like starch) by using

microorganism.