r. shanthini bioethanol as an alternative source of energy

R. Shanthiniwww.rshanthini.com

Bioethanol as an alternative source

of energy

What is the problem with petroleum derivatives as the energy source?

Petroleum supply has peaked

24 Jan 2008 R. Shanthini

24 Jan 2008 R. Shanthini Source: http://www.exitmundi.nl/oilcrash.htm

Petroleum supply peaking is however not the only problem with the conventional fossil fuel energy sources!

Fossil fuels releases CO2 that is not part of the carbon cycle


Carbon balance is upset and the excess CO2 accumulates in the environment

Source: http://www.visionlearning.com/library/module_viewer2.php?mid=95&l=&let1=Ear 24 Jan 2008 R. Shanthini

275

300

325

350

375

400

1750 1800 1850 1900 1950 2000Year

CO2 concentration in the atmosphere

Unit: ppmv

Source: http://cdiac.ornl.gov/trends/trends.htm

383.7


To stabilize the atmospheric CO2 concentration below 550 ppmv by 2100 (climate change concern),

global anthropogenic CO2 emissions must be limited to about 7 to 8 GTC (= giga tonne C) per year.

- IPCC, 1996

0

2

4

6

8

10

1750 1800 1850 1900 1950 2000Year

Global CO2 emissions from the burning of fossil fuels & the

manufacture of cement Unit: GTC per year

24 Jan 2008 R. Shanthini Source: http://cdiac.ornl.gov/trends/trends.htm

at 7.9 GTC in 2004

Therefore, we need urgently to switch to energy sources that are

not upsetting the carbon balance


Ethanol as an alternative source of energy

Bioethanol is produced from plantsthat harness the power of the sun

to convert water and CO2 to sugars (photosynthesis),

therefore it is a renewable fuel

Bio


Bioethanol is produced from plantsthat harness the power of the sun

to convert water and CO2 to sugars (photosynthesis),

therefore it is a renewable fuel


Bio



oxygen in the ethanol molecule helps in complete combustion,

which means less emissions


Bio

Ethanol is a high-octane fuel, and is widely used as a blending ingredient in petrol

A growing number of cars and trucks designated as FlexFuel Vehicles (FFV)

can use ethanol blended up to 85 percent with petrol (E85 fuel)

Today there are more than 6 million FFV's on U.S. roads alone


24 Jan 2008 R. ShanthiniSource: http://www.distill.com/World-Fuel-Ethanol-A&O-2004.html

glucose molecule

Bioethanol from simple sugars:

Sugar cane and sugar beets store the energy as simple sugars, glucose (C6H12O6)


2 CH3CH2OH + 2 CO2

yeast

impure cultures of yeast produce glycerine and various organic acids

this simple-looking reaction is a bioreaction and thus very complex


Yeast can be replaced by the bacterium Zymomonas mobilis

- gives up to 98% yields - minimal by-products - simple fermentation requirements - several-fold the production rates of yeast

Z. mobilis industrial strain CP4, originating from Brazil,vigorously fermenting glucose. Photo courtesy Katherine M. Pappas

sugar

cane

sugar cane crushed and soluble sugar

washed out

sugar cane

residue

fermentation of sugars produces 5 - 12%

ethanol

yeast

distilled to concentrate to 80 –

95% ethanol

used as a petrol replacement

dehydrate to 100% ethanol

used as a petrol

additive

CO2

wet solids

Bioethanol from starch:Corn, wheat and cassava store the

energy as more complex sugars, called starch


dextrins

α-amylase

amyloglucosidase

glucose monomer

}starch(glucose polymer)

Liquification Liquification (at 90 – 95 deg C; (at 90 – 95 deg C;

pH = 4 - 4.5; 400 pH = 4 - 4.5; 400 rpm)rpm)Saccharification with Saccharification with

glucosidase enzymeglucosidase enzyme (at 55 - 65 deg C, pH = 4 - 4.5)(at 55 - 65 deg C, pH = 4 - 4.5)

Cooling Cooling (32 deg (32 deg C)C)

Fermentation with Fermentation with yeastyeast (40 – 50 hrs)(40 – 50 hrs)

Distillation Distillation DehydratioDehydration n

80-95% 80-95% ethanol ethanol

100% ethanol 100% ethanol 24 Jan 2008 R. Shanthini

cassava flour + cassava flour + water + water + alpha-alpha-

amylase enzymeamylase enzyme

Dry grind process

is the most common method used to make fuel grade ethanol.

The whole corn kernel is ground and converted into ethanol.

It is relatively cost effective and requires less equipment, but is not ideal for mass producing.


In the wet milling process,

corn is separated into its four basic components: starch, germ, fiber, and protein, which are each made into different products.

Advantage: valuable co-products such as corn oil

Disadvantages: equipment is expensive and the process uses hazardous sulfur dioxide


Bioethanol from Biomass (except sugars and starches):

Rice strawPaddy husksSaw dustGrasses Bagasse


Cellulose (40 to 60% by weight of the biomass) made from the six-carbon sugar, glucose.

Its crystalline structure makes it resistant to hydrolysis (the chemical reaction that releases simple, fermentable sugars).



Hemicellulose (20 to 40% by weight) made mainly from the five-carbon sugar, xylose.

Its relatively easy to hydrolyze hemicellulose into simple sugars but normal yeast can't ferment xylose.

Celunol Corp. has acquired genetically engineered E. coli bacteria which can turn almost all xylose into ethanol.




Lignin (10 to 24% by weight of biomass) is a complex polymer, which provides structural integrity in plants.

It remains as residual material after the sugars in the biomass have been converted to ethanol.

It contains a lot of energy and can be burned to produce steam and electricity for the biomass-to-ethanol process.

Obstacles to commercial production of cellulosic ethanol:

Accelerating the breakdown of cellulose fibers Research on acid / enzymatic hydrolysis

is ongoing. Lignin waste problem

Lignin can fuel Combined Heat and Power plants, however, CHP plants are

expensive.

Use of GM microorganisms Source: DOE's 2006 Annual Energy Outlook


A cellulosic ethanol plant with 50 million gallons per year capacity and a lignin-fired CHP will cost about $300 million to build


A corn ethanol plant with the same capacity could be built for about $65 million

Source: DOE's 2006 Annual Energy Outlook

Currently, ethanol yields 25% more energy output than input to produce it.

Research is on for less costly ways of producing ethanol, and better ways to blend it with petrol.


Is bioethanol a sustainable energy source?

No, it is not

Why do I say that?


Bioethanol will be used in engines that convert heat into work

Engines that convert heat into

work are very inefficient

Take a look at some examples


According to the 2nd Law of Thermodynamics

when heat is converted into work, part of the heat energy must be wasted

Power generation Power generation

typetype

Unit size Unit size (MW)(MW)

Energy Energy wasted (MW)wasted (MW)

Diesel engineDiesel engine 10 - 3010 - 30 7 – 227 – 22

Gas TurbineGas Turbine 50 - 10050 - 100 36 – 7836 – 78

Steam TurbineSteam Turbine 200 - 800200 - 800 120 – 560120 – 560

Combined (ST & GT)Combined (ST & GT) 300 - 600300 - 600 150 – 380150 – 380

Nuclear (BWR & PWR)Nuclear (BWR & PWR) 500 - 1100500 - 1100 330 – 760330 – 760


We throwaway energy that rightfully belong to the future generations

“Development that meets the needs of the present without compromising the ability of future generations to meet their own needs."

Our Common Future (1987)

Recently, Scientists at the Virginia state Polytechnic Institute have developed a breakthrough method of ethanol production method called Advanced Bioethanol Technology (ABT) which lets producers create ethanol from any biological feedstock that contain enough sugars or materials that can be converted into sugar such as starch or cellulose. ABT breaks long chains of sugars down to be fermented.

r. shanthini bioethanol as an alternative source of energy

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