Cellulolysis Process Overview
Summary found at: http://en.wikipedia.org/wiki/Cellulosic_ethanol
Harvest
Expose Cellulose
for Hydrolysis
Break down hemicellulose
Cellulose to Sugars
Chopping
or
Baling
OR
Storage
Convert Sugars Separate alcohol
to alcohol
from water
Chemical
Hydrolysis
Pretreatment
OR
Fermentation
Enzymatic
Hydrolysis
Combined Storage-Pretreatment
(silos, piles, agribags, dry storage)
Combined Hydrolysis & Fermentation
Distillation
Cellulolysis Pretreatment Explanations
1) Acid Hydrolysis
2) Dilute Acid - Steam Explosion
- feedstock is impregnated with acid (H2S04 – sulfuric acid) H2SO4 is used because of its low cost
- feedstock is then processed in a steam explosion reactor
- time in the reactor (residence time) and temperature levels of the reactor seem to determine the ethanol yield
down the line
- A good sample experiment of this using corn stover is at: http://www.nrel.gov/docs/gen/fy03/32119.pdf
2b – How is sulfuric acid made – answer below from http://wiki.answers.com/Q/How_is_sulfuric_acid_made
There are two main ways:
1.
Step 1:- Sulfur is burned to produce sulfur dioxide.
= S(solid) + O2(gas) → SO2(gas)
Step 2:- This is then oxidised to sulfur trioxide using oxygen in the presence of a vanadium(V) oxide catalyst.
= 2 SO2 + O2(g) → 2 SO3(g) (in presence of V2O5)
Step 3.a:-The sulfur trioxide is treated with water (usually as 97-98% H2SO4 containing 2-3% water) to produce 98-99% sulfuric acid.
=SO3(g) + H2O(i.e. water) → H2SO4(liquid) Hey Presto!
Or, way 2.
The SO3, produced at step 2 above, can be processed in an alternative way. i.e.
Step 3.b. The SO3 can be absorbed into H2SO4 (concentrated sulfuric acid!) to produce oleum (H2S2O7)
= H2SO4(l) + SO3 → H2S2O7(l)
Step 4:- Oleum can then be reacted with water to form more concentrated H2SO4.
= H2S2O7(l) + H2O → 2 H2SO4(l)
Cellulolysis Pretreatment Explanations Continued
3) Ammonia Fiber Expansion
– Liquid ammonia is used to pretreat and explode biomass
- Ammonia is recycled
- Process is run at 60-100°C, 20-80% moisture, and biomas ration is .5 to 1.3-1.0
- see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
- Ammonia Fiber Expansion (AFEX) is a promising pretreatment with no inhibitory effect in resulting hydrolysate (meaning it leaves
no impurities that hinder Fermentation)
4) Lime Pretreatment
- see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
- Takes 1 to 2 months – looks to be done in a pile or bunker
5) Flowthrough Pretreatment
- see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
6) Controlled PH Pretreatment
- see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
7) Ozone Pretreatment
8) Alkaline Wet Oxidation
Cellulolysis Chemical (Acid) Hydrolysis Explanations
1) Dilute Acid
- process uses more heat and pressure
- sugar degradation is a problem and can lower sugar yield and toxins can be left over that hamper
fermentation
- uses 1% sulfuric acid solution in a continuous flow reactor at 215°C
- Sugar conversion efficiency is 50%
- Two step process, since hemicellulose (5 carbon sugar) degrades faster than 6 carbon sugars (Cellulose)
a) mild conditions to recover 5 carbon sugars
b) harsher process to recover 6 carbon sugars
- both resulting hydrolyzed solutions are then fermented to alcohol. Lime is used to neutralize acids
prior to fermentation, and leftover lignin is used to as boiler fuel or to make steam to produce
electricity
2) Concentrated Acid
- process uses lower heat and pressure
- uses concentrated sulfuric acid and then dilution with water to dissolve and hydrolyze material into sugar
- process converts cellulose to glucose, and hemicellulose to 5 carbon sugars
- acid is recycled in the process
- Two step process:
a) Hemicellulose hydrolyzation uses a 70% sulfuric acid solution and is hydrolyzed at 100°F for
2-6 hours in a hemicellulose hydrolysis reactor. Material is then soaked with water and drained
many times to recover the sugars
b) Cellulose hydrolyzation – from step a, the solids are taken and soaked in a 30-40% sulfuric acid
solution for 1-4 hours. Material is then drained and dried, and the acid rate is increased to 70%
and placed in another container for 1-4 hours at low temperatures. The sugar and acid are then
recovered. This acid is then used in step A.
- This process has about a 90% sugar conversion efficiency.
Cellulolysis Enzymatic Hydrolysis Explanations
Enzymatic Hydrolysis
In this process, enzymes are used to hydrolyze the cellulose (C6 Sugar) and hemicellulose (C5 sugars)
Trichoderma reesei – produces cellulase enzymes – needed to convert cellulose and hemicellulose to
sugars (glucose molecules)
Enzyme Producers
Iogen - http://www.iogen.ca/
Genecor - http://www.genencor.com/wps/wcm/connect/genencor/genencor
Novozymes - http://www.novozymes.com/en
Dyadic International Inc - http://www.dyadic.com/wt/home
Verenium - http://www.verenium.com/
Direct Microbial Conversion
In this process, ethanol and required enzymes are produced from the same microorganism
Combined Hydrolysis & Fermentation
Some bacteria have been found to convert cellulose directly to ethanol. Examples of these bacteria are:
Clostridium thermocellum (C. thermocellum) – this bacterium will convert cellulose directly to ethanol, but has some other
byproducts that can reduce efficiency during fermentation
Cellulolysis Fermentation Process Explanations
Do C5 and C6 sugars need to be fermented separately?
Zymomonas mobilis (Z. mobilis) – bacterium that converts sugars to pyruvate, which is then fermented to ethanol
and carbon dioxide. NREL has developed a version that leads to more efficient fermentation of both
C5 and C6 sugars. Arkenol will be using the NREL version.
Saccharomyces cerevisiae – bakers yeast used in brewery industry to produce ethanol from C6 sugars
Escherichia coli – (E. coli) uses mixed-acid fermentation in anaerobic conditions, producing lactate, succinate, ethanol,
acetate and carbon dioxide
Cellulolysis Distillation Process Explanations
This process of separating alcohol from water is that same as is used in making
corn ethanol – in simplistic terms, the “beer” is heated to the point where the
Alcohol (which boils at a lower temperature than water” evaporates up leaving water
behind. The alcohol vapor is contained and cooled which turns it back to a liquid, with
this liquid being mainly alcohol (some water will/may remain, so to purify the alcohol
it may be run thru the distillation system repeatedly until the desired % of alcohol is
achieved.
Cellulolysis Process Definitions
Assistance with definitions found at: http://dictionary.reference.com/
Pretreatment – separation of 4 components of biomass – hemicellulose, cellulose, lignin, and extractives so that they can then
be broken down into their sugar components
Saccharification - the process of breaking a complex carbohydrate (as starch or cellulose) into simple sugars
Hydrolyze – to subject to hydrolysis, which is the breaking down of a chemical compound into two or more simpler compounds
by reacting with water. The proteins, fats, and complex carbohydrates in food are broken down in the body by
hydrolysis that is catalyzed by enzymes in the digestive tract
Hemicellulose - (5 carbon sugar) - any of a group of gummy polysaccharides, intermediate in complexity between sugar and
cellulose, that hydrolyze to monosaccharides more readily than cellulose
Cellulose - (6 carbon sugar) - a polysaccharide(C6H10O5) of glucose units that constitutes the chief part of the cell walls of plants,
occurs naturally in such fibrous products as cotton andkapok, and is the raw material of many manufactured goods
(as paper, rayon, and cellophane)
Lignin - A complex polymer, the chief noncarbohydrate constituent of wood, that binds to cellulose fibers and hardens and
strengthens the cell walls of plants
xylose (C5H10O5) – 5 carbon sugar (C5 sugar) derrived from hemicellulose
arabinose – 5 carbon sugar (C5 sugar) derrived from hemicellulose
hexoses – 6 carbon sugars (C6 sugars)
Glucose (C6H12O6) – 6 carbon sugar (C6 sugar) derrived from cellulose
Mannose (C6H12O6) – 6 carbon sugar (C6 sugar)
Galactose (C6H12O6) – 6 carbon sugar (C6 sugar) that is derrived from hemicellulose
Gasification Process Overview
My Fantasy – Local Cellulosic Ethanol then Pellet Production
Transport feedstock
to local plant
Central
Local
Processing
Clean
Energy
Sources
Harvest
Fuel to sell at
local gas station
Ethanol Production
Home heat fuel to
sell at local stores
Drying of
Material
Pellet Pressing
Electric and pellet heat sources for distillation and drying and cooling