What is biorefining? Flashcards
What is a biorefinery?
Integrates biomass conversion processes and equipment to produce fuels, power, heat and value-added chemicals (ethanol) from biomass.
What are carbohydrates?
Polymers composed of sugars.
Monomer sugars: glucose, fructose, galactose,
Dimer sugars: maltose, sucrose, lactose
What is starch?
Made up of glucose monomers.
Made up of amylose and amylopectin
Enzymes breakdown - amylase
What is amylose?
Smaller polysaccharide which is linear having alpha 1-4 linkage between glucoses.
What is amylopectin?
The larger component of starch which is highly branched. This polymer has amylose as a base but has branching connected by alpha 1-6 linkage.
What are some sources of starch?
Cereal grain seeds like corn, wheat, Tubers and Roots like potato, peas, sago.
What is lignocellulosic resource?
Woody and agricultural resource, that isn’t water soluble and hard to digest. Consists of Cellulose, Hemicellulose, and Lignin.
What is Cellulose?
Structural component of woody plants made of sugar polymers which has a beta-D-linkage.
Have both crystalline and amorphous regions.
What are some recalcitrant properties of cellulose?
Crystallinityy of cellulose makes it harder for enzymes to break it down.
Requires 320C, 25MPa to become amorphous in water.
What base components make-up hemicellulose?
Xylose, mannose, galactose, rhamnose, arabinose and C5 sugars.
How can hemicellulose be extracted & broken down?
Soluble in water so it can be extracted
Dilute acid/base can hydrolyze hemicellulose because of its amorphous structure
What are the steps to extract starch from plants?
a) Plant material is chopped into tiny pieces
b) Rasped to break cell open
c) Starch is rinsed & filtered
What is the difference between flour and starch?
Flour undergoes minimal processing
While starch is heavily processed
If the desired products from starch are gluten feed, gluten meal and corn oil, what type of milling process should be used? Why is this process used and will it cost more or less?
Wet milling should be used
Produces larger variety of products at a higher operating cost
What is the major difference between dry and wet milling
Dry milling is used for larger ethanol productions and operates at lower costs
Wet milling is used when a variety of products are desired, and hence operate at a higher cost
Starch in wet milling doesn’t go through drying process after steeping
What part of the corn should be used if corn oil is desired product?
Corn germ
Why was there a need to replace acid hydrolysis of starch with enzymatic hydrolysis?
Acid hydrolysis required corrosion resistant reactors
Required more energy for heating
Difficult to control
What are the stages in starch conversion? Summarize each step?
1) Gelatinisation
- Dissolution of starch, forming viscous suspension (amorphous gel)
Heated for 5 min @ 100-105C in water
2) Liquifaction
- Enzymes hydrolyze viscous gel, hence decreasing viscosity
time: 1-2hrs @ 90-95C
- Convert starch to dextrins (smaller glucose polymers)
3) Saccharification
- Complete hydrolysis to required Dextrose Equivalent (DE)
- Max temperature of 95C is not exceeded
What are the enzymes involved starch hydrolysis? What function do they serve?
Amylase
- breaks alpha 1-4 bonds
- alpha amylase cleaves 1-4 bonds at random points
- beta amylase cleaves 1-4 bonds at the end of the chain
Pullulanase
- breaks alpha 1-6 bonds
Glucoamylase
- Converts maltose to glucose
What is an oligosaccharide? What function does it serve?
- Polymers containing 3-10 simple sugars
- Used in cell recognition & cell binding
Define Metabolism
Overall sum of enzyme catalyzed chemical reactions in biological systems
Saccharomyces cerevisiae is the most conventional ethanol producer. Under what conditions can this organism be used for fermentation & what limitations?
Must be done in anaerobic conditions (or anoxic)
Can only assimilate C6 sugars
Which type of organisms are used for fermentation? What are the molecules formed as a result of fermentation by these organisms?
Facultative anaerobes, strict anaerobes & aero-tolerant anaerobes are used for fermentation
1 glucose -> 2 ATP + 2 Ethanol
The yeasts Schizosaccharomyces pombe & Kluyveromyces marxianus carry which respective advantage in fermentation?
S. pombe can tolerate high salt content (high osmotic pressure)
K. marxianus can tolerate high temperatures (thermophilic conditions), allowing for increased rate of metabolism & lower refrigeration requirements
What are the disadvantages of fermenting with yeast?
Can only ferment mono or disccaharides
Cannot assimilate cellulose, hemicellulose or lignin directly
Not all yeasts can ferment C5 sugars
What is diauxic growth? Define each step.
Diauxic growth is two-staged cell growth caused by the presence of two sugars, seen in yeasts and/or bacteria that can ferment both C5 & C6 sugars
Stages in Diauxic growth
- Fermentation/metabolism of C6 sugars until depletion
- Lag phase: Synthesis of enzymes for C5 fermentation/metabolism
- Fermentation/metabolism of C5 sugars until depletion
What advantage does using a bacteria such as zymomonas mobilis have over yeasts? What type of bacteria is it?
Higher ethanol yields caused by lower cell yield, increasing amount of ethanol obtained from same substrate
Facultative anaerobe
What are the different pathways that bacteria & yeasts use for fermentation? What are the resulting products?
Bacteria such as Z. Mobilis make use of Entner-Duodoroff pathway
1 Hexose -> 1 ATP + 2 Ethanol
Yeasts such as S. Cerevisiae make use of the Embden Meyerhoff-Parnas pathway
1 Glucose -> 2 ATP + 2 Ethanol
What are the advantages & disadvantages of using a bacteria such as Z. Mobilis?
Advantages
- High ethanol tolerance
- High optimal production temperature
- Easily genetically manipulated
Disadvantages
- Can only ferment glucose, fructose & sucrose
- Sucrose based media leads to levan (increases viscosity) and sorbitol formation
What is the goal of genetically modified organisms?
- Hydrolyze starch & ferment glucose, without addition of amylases
- Ferment pentose
- Eliminate controls that inhibit hyper-production of desired products
- Consolidated bioprocessing (Removal or combination of steps ie Liquefaction & Saccharification into one step or total removal)
- Combine bacterial enzymes into yeast
What is the difference between 1st and 2nd generation biofuels?
1st Gen
- Made from sugar and vegetables
2nd Gen
- Made from biomass sources
- any source of organic carbon that is renewed as a part of the carbon cycle
- lignocellulosic biomass
Why does lignin pose a problem when using lignocellulosic biomass?
- Lignin is a protective barrier of plants
- Prevents cell destruction therefore must be removed to access cellulose and hemicellulose
What are the main goals of pre-treatment?
- Remove lignin
- Reduce crystallinity of cellulose
- Increase porosity of the biomass
What are the requirements for pre-treatment?
- Improve the formation of sugars (or subsequent formation)
- Must not degrade/destroy carbohydrates in biomass
- Avoid formation of inhibitory products = inhibitory to hydrolysis or fermentation process
- Cost effective
What are the different categories of pre-treatment?
Physical: milling, grinding Physio-chemical: Steam explosion Chemical: dilute alkali/acid Biological Electrical
It is required to pre-treat biomass using a chemical method that is lowest hazard to the environment. Which method should be selected? Describe the process.
Ozonolysis should be selected
- Reactions are carried out at RT & normal pressure
- Degrades lignin and hemicellulose
- Ozone decomposed by catalytic bed or by increasing temperature
A company narrows down its choices to 2 pre-treatment methods: AFEX & ARP. The company uses a wide variety of biomass, and requires lignin to be the main component in the biomass to be degraded. Which of the two processes should be chosen? Why?
- Ammonia Recycle Percolation method should be chosen
- ARP uses aqueous ammonia that reacts primarily with lignin, causing depolymerization (cleaves lignin from carbs)
- AFEX only a small amount of solid material is solubilized = almost no lignin or hemicellulose removed
A customer wants to use the steam explosion pre-treatment method for a bioprocessing plant. What are some objections you would bring up before the customer makes the purchase?
- Destruction of xylan fraction (destroys some amount of carbs in biomass)
- Incomplete destruction of the lignin matrix
- Formation of inhibitory compounds
- Pre-trated biomass requires washing
A bioprocessing plant uses a feedstock biomass that conatins residual lignin (6.4wt% - 27.4wt%). The company requires that most products be recovered after pretreating its biomass. Which process should be chosen? Why? Under what conditions does this method operate?
Lignol process should be used
- Used for residual lignin content
- Lignin recovered as precipitate = Achieved by flashing the pulp liquor to atmospheric pressure
- Hemicellulose sugars and furfural are recovered recovered from a water-soluble stream
- 50:50 ethanol water blend at 200C & 400psi extracts most of lignin
