Wood ChemistryPSE 406

Bioethanol-corn

Agenda

Corn to ethanol» Energy balance» Production

– Dry milling– Wet milling

» Problems

Rise of biofuels (history)

H. Ford 1908 R. Diesel 1987 Sugar cane ethanol 1920 OPEC oil embargo (1973) Methyl tertiary-butyl ether MTBE (started in

1992, phased out in 2000) (2-methoxy-2-methylpropane )» Good blending» Increase octant number» Cheap, produced from natural gas» Toxicity

Oil in Middle East $$$$

Corn plantCorn kernel (without the fibre)-starch alcoholCorn fibre-lignocellulosic alcoholCorn stover-lignocellulosic alcohol

Chemical Composition of Starch

Plants contain two types of starch, linear (helix) amyloses and branched amylopectins.

The amounts of each of these starch types present is plant dependent.» Typical amounts are 25% amylose, 75%

amylopectin

Amylose

14 -D-Glucopyranose Because of the bonding, this molecule forms a helix

» It takes 6 gluopyranose units for each turn» Amylose is not water soluble

O

H

O

H

HO

H

O

OHHH

OH

O

H

H

HO

H

O

OHHH

OH

n

Amylopectin

14 D-Glucopyranose + 16 D Glucopyranose

Amylopectin is a branched polymer» Branching inhibits

helix formation» This starch is

therefore somewhat water (hot) soluble.

O

H

O

H

HO

H

O

OHHH

OH

O

H

H

HO

H

OHHH

OH

O

H

O

H

HO

H

O

OHHH

OH

O

H

H

HO

H

O

OHHH

O

n

US ethanol production

Corn versus crude oil (US)

Corn

One bushel of corn (56 pounds after husks and cobs are removed) provides:» 31.5 pounds of starch or » 33 pounds of sweetener or » 2.8 gallons of ethanol

+ 13.5 pounds of gluten feed 2.6  pounds of gluten meal 1.5 pounds of corn oil

Corn to ethanol

US produces 4,86 billion gallons of ethanol from corn (2006)

Production cost ~$1.09/gallon Fossil fuel energy used to make the fuel

(input) compared with energy in the fuel (output) 1:1.3 or negatives values

Greenhouse gas emission during production and use 22% less compared with gasoline

Dry versus wet milling

Dry versus wet milling » Dry grind process: the entire corn kernel is first ground into flour and

the starch in the flour is converted to ethanol via fermentation– CO2 (used in the carbonated beverage industry) – Animal feed called distillers dried grain

» Wet milling: first the separating the corn kernel into starch, protein, germ and fiber in an aqueous medium prior to fermentation

– The primary products of wet milling include starch and starch-derived products (e.g. high fructose corn syrup and ethanol), corn oil, corn gluten, and corn gluten

Corn (starch) can be converted into ethanol in 3-5 days» Starch + water to form a mash» Mash + heat + enzymes (amlysases)=glucose» Glucose + yeast (fermentation) = CH3CH2OH + CO2 » “Beer”=10 - 15 % CH3CH2OH and 85 % H2O» The "beer" is then boiled in a distillation column to separate H2O and

CH3CH2OH up to 95%» Additional 5% of H2O removed by molecular sieves (size exclusion)

100% ethanol

pH 6+heat 110°C +-amylase30 min liquid, dextrins (5-10 glucose)

Yeast+ mash+glucoamylase (SSF)glucose and maltose fermented to ethanol and CO2, 48-72 hours

5% water removed by sieves

Conventional distillation 95%

52°C, sulfurous acid (0.2%) 30-36 hours

-amylase+heat 90°C+glucoamylase ,SHF, series of reactorssemicontinuous process

Corn wet milling process

Problems (1)

Environmental problems» Greenhouse gas emission

– Ethanol plants burn natural gas or coal to create the steam, adding to fossil fuel emission with CO2 from fermentation

» Energy value» Pesticides, herbicides (nitrogen runoff from fertilizers)» Fertilizers (N, made with natural gas and diesel farm

machinery)» Water demands: 3.6-6gallons of water/1 gallon of

ethanol Social problems

» Competing with food industry– Doubling the price of corn (food riots in Mexico)

Problems (2)land availability

Problems (3)

More environmental problems» “Most economic analyses of corn-to-

ethanol production overlook the costs of environmental damages, should add another 23 cents per gallon”

» Soil erosion– "Corn production in the US erodes soil about 12

times faster than the soil can be reformed, and irrigating corn mines groundwater 25 percent faster than the natural recharge rate of ground water “

David Pimental Cornell University

Corn to ethanol (1)

1 acre of US corn =7,110 pounds of corn = 328 gallons of ethanol

Planting, growing and harvesting that much corn requires about 140 gallons of fossil fuels and costs $347 per acre.

Even before corn is converted to ethanol, the feedstock costs $1.05 per gallon of ethanol.

Corn to ethanol (2)

“If all the automobiles in the United States were fueled with 100 % ethanol, a total of about 97% of U.S. land area would be needed to grow the corn feedstock. Corn would cover nearly the total land area of the United States”

David Pimental Cornell University

Corn to ethanol plants in U.S. (101 plants in 2006)

Based on August 30th, 2006