Lecture 17: How crops can be used for biofuels

Question 1

one of the main challenges set by the industry itself has been to produce:

Answer 1

the liquid biofuels needed to drive cars, rather than providing energy for heating or manufacture

Question 2

types of biofuels:

Answer 2

• first generation biofuels
• second generation
• third generation biofuels

Question 3

First generation biofuels:

Answer 3

• primarily from food products
• -Biotethanol (starch)
• -Biobutanol (starch)
• -Biodiesel

Question 4

second generation biofuels:

Answer 4

• crop and forest residues, non-food energy crops
• -direct combustion of biomass, pyrolysis, gasification
• cellulosic ethanol

Question 5

third generation biofuels:

Answer 5

algae!

Question 6

Ethanol vs Butanol vs Biodiesel: Ethanol:

Answer 6

• miscible with water (3%). Difficult to transport in pipelines as corrosive and volatile
• energy density low compared with petrol

Question 7

Ethanol vs Butanol vs Biodiesel: BUTANOL:

Answer 7

• not miscible with water, not corrosive
• can be blended at any level with petrol
• no engine modification
• generaes ~30% more energy than ethanol from the same amount of corn. Like ethanol can also be made form cellulosic materials

Question 8

Ethanol vs Butanol vs Biodiesel: BIODIESEL:

Answer 8

-can be blended at any level with petroleum diesel and used in diesel engines with no modification

Question 9

conversion of starch/sugar/ cellulose to ethanol:

brazil started ethanol production from sugar cane in the

Answer 9

• 1970’s

- in brazil ethanol derived from sugar cane is in blends of 20-25% ethanol with petrol.

Question 10

Brazil produces about ___ of ethanol annually

Answer 10

about 6.3 billion gallons of ethanol annually ~25% of global total

Question 11

USA produces about ___ of ethanol annually

Answer 11

13.3 billion gallons annually, ~60% global total

Question 12

biobutanol is produced from which feedstocks:

Answer 12

• same as ethanol

- e.g. corn, wheat, sugar beet, sorghum, cassava & sugarcane

Question 13

Biobutanol: ABE fermentation

Answer 13

• used industrially since 1916 for acetone production

- anaerobic conversion of carbohydrates by strains of Clostridium into Acetone, Butanol, and Ethanol.

Question 14

issues with ABE fermentation:

Answer 14

• low yield (now improving)
• slow fermentation
• end-product inhibition

Question 15

oilseed crops for biodiesel:

Answer 15

• Rape (Canola)
• Jatropha
• Soybean

Question 16

what is biodiesel made from:

Answer 16

from vegetable oil (rapeseed [canola], palm or soybean), animal oil/fats, tallow and waste cooking oil

Question 17

Biodiesel: how are the feedstocks of biodiesel converted to biodiesel

Answer 17

TRANSESTERFICATION

Question 18

Biodiesel: the combustion benefits of the transesterfication of the oil are:

Answer 18

• lowered viscosity
• complete removal of the glycerides
• lowered boiling point, flash point and pour point

Question 19

biodiesel: Transesterfication: how does it work

Answer 19

• reaction of triglyceride (fat/oil) with an alcohol to form esters and glycerol with a catalysts, usually KOH or NaOH
• utilises methanol (to produce methyl esters) or ethanol (ethyl esters)

Question 20

Crops for cellulosic ethanol/combustion

Answer 20

• poplar
• miscanthus
• switchgrass (also forage)

Question 21

primary cell wall components are

Answer 21

COMPLEX

Question 22

cellulose microfibrils have a tensile strength equivalent to

Answer 22

steel

Question 23

Goal: Make cellulose available to hydrolytic enzymes.
Problem:

Answer 23

Cell walls are complex structures

Question 24

cell walls:

Middle lamella

Answer 24

‘glue’ that binds adjacent cells, primarily pectic polysaccharides (rich in galacturonic acid)

Question 25

cell walls: Primary wall:

Answer 25

the primary wall comprises pectic polysaccharides , cross-linking glycans, cellulose and protein. All plant sells have a middle lamella and primary wall

Question 26

cell walls: Secondary wall

Answer 26

some cells deposit additional layers inside the primary wall. This occurs after growth stops or when the cells begin to differentiate.
Mainly for support, comprising primarily cellulose and lignin

Question 27

cell wall component: Cellulose:

Answer 27

• up to 25,000 individual glucose molecules

- cellulose readily forms intra- and inter- molecular H-bonds with other cellulose chains to yield a microfibril

Question 28

most abundant organic compound on earth

Answer 28

Cellulose

Question 29

cell wall components: Cross-linking glycans (hemicellulose)

Answer 29

• diverse group of linear or slightly branched structures including glucose, glucuronic acid, mannose, arabinose, xylose
• Forms H bonds with cellulose

Question 30

cell wall components: lignin

Answer 30

-irregular branched polymer of phenolics.
-lignin is a strengthening agent in both primary and secondary walls, like a biological plastic
-difficult to degrade
-

Question 31

whats the most abundant aromatic polymer on earth

Answer 31

lignin

Question 32

microorganisms produce enzymes that degrade cell walls:

Answer 32

Cellulases

Question 33

sources of wood-degrading enzymes:

Answer 33

• fungi. compost heaps & forest floors poorly explored
• termites
• bacteria in ruminants
• marine wood borer

Question 34

termites depend for cellulose digestion on:

Answer 34

celluloses produced by their symbionts (flagellates and bacteria)
-a genomic study of the microbes living within the termite gut has identified ca. 1000 possible enzymes that break down wood

Question 35

current technologies for cellulosic fuels commercialised when?

Answer 35

only recently