BIOETHANOL 1. CONTENTS I.What is bioethanol? II.Bioethanol Production III.Fuel Properties IV.Application V.Advantages VI.Disadvantages and Concerns VII.Ethanol.

BIOETHANOL

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CONTENTS

I. What is bioethanol?II. Bioethanol ProductionIII. Fuel PropertiesIV. ApplicationV. AdvantagesVI. Disadvantages and ConcernsVII.Ethanol ControversyVIII.Comparison of Bioethanol and BiodieselIX. Future development

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What is Bioethanol

Bioethanol is an alcohol made by fermentation, mostly from carbohydrates produced in sugar or starch crops such as corn or sugarcane. Cellulosic biomass, derived from non-food sources such as trees and grasses, is also being developed as a feedstock for ethanol production

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• The principle fuel used as a petrol substitute is bioethanol

• Bioethanol fuel is mainly produced by the sugar or cellulose fermentation process

• Ethanol is a high octane fuel and has replaced lead as an octane enhancer in petrol

• Bioethanol is an alternative to gasoline for flexifuel vehicles

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• Wheat/Grains/Corn/Sugar-cane can be used to produce ethanol. (Basically, any plants that composed largely of sugars)

• Bioethanol is mainly produced in three ways.

• Sugar > ethanol• starch > sugar > ethanol • cellulose and hemicellulose > ethanol

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Processes for Bioethanol Production

1. Concentrated Acid Hydrolysis

– ~77% of sulfuric acid is added to the dried biomass to a 10% moisture content.

– Acid to be added in the ratio of 1/25 acid :1 biomass under 50°C. 

– Dilute the acid to ~30% with water and reheat the mixture at100°C for an hour.

– Gel will be produced and pressed to discharge the acid sugar mixture.

– Separate the acid & sugar mixture by using a chromatographic column .

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2. Dilute Acid Hydrolysis

– oldest, simplest yet efficient method

– hydrolyse the bio-mass to sucrose – hemi-cellulose undergo hydrolysis

with the addition of 7% of sulfuric acid under the temperature 190°C.

– to generate the more resistant cellulose portion, 4% of sulfuric acid is added at the temperature of 215°C

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3. Wet milling process

– corn kernel is soaked in warm water – proteins broken down– starch present in the corn is released

(thus, softening the kernel for the milling process)

– microorganisms, fibre and starch products are produced.

– In the distillation process, ethanol is produced.

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4. Dry milling process

– Clean and break down the corn kernel into fine particles

– Sugar solution is produced when the powder mixture (corn germ/starch and fibre) is broken down into sucrose by dilute acid or enzymes.

– Yeast is added to ferment the cooled mixture into ethanol.

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5. Sugar fermentation

– Hydrolysis process breaks down the biomass cellulosic portion into sugar solutions which will then be fermented into ethanol.

– Yeast is added and heated to the solution.– Invertase acts as a catalyst and convert

the sucrose sugars into glucose and fructose. (both C6H12O6).

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6. Fractional Distillation Process

– After the sugar fermentation process, the ethanol still does contain a significant quantity of water which have to be removed.

– In the distillation process, both the water and ethanol mixture are boiled.

– Ethanol has a lower boiling point than water, therefore ethanol will be converted into the vapour state first condensed and separated from water.

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Feedstocks1. Sugar is required to produce ethanol by fermentation.

• Plant materials (grain, stems and leaves) are composed mainly of sugars

• almost any plants can serve as feedstock for ethanol manufactureCrops used in Bioethanol production

Brazil sugar cane

USA corn

India Europe

sugar cane wheat and barley

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2. Choice of raw material depends on several factors

• ease of processing of the various plants available

• prevailing conditions of climate• landscape and soil composition• sugar content

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3. R&D activities on using lignocellulosic (woody materials) as feedstock

• Lignocellulosic biomass is more abundant and less expensive than food crops

• higher net energy balance• accrue up to 90% in greenhouse gas

savings, much higher than the first generation of biofuel

• However, more difficult to convert to sugars due to their relatively inaccessible molecular structure

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Conversion of starch to sugar and then sugar to ethanol

Eg:-1) wheat

Fermentation conditions

Temperature - 32˚C and 35˚C pH - 5.2.Ethanol is produced at 10-15% concentration and the solution is distilled to produce ethanol at higher concentrations

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Eg:- 2) sugar cane

Simplest of all the processes

Fermentation conditions are similar to the previous slide

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Ethanol can be produced from a variety of feedstocks such as sugar cane, bagasse, sugar beet, switchgrass, potatoes, fruit, molasses corn, stover, wheat, straw, other biomass, as well as many types of cellulose waste and harvestings Agricultural feedstocks are considered renewable because they get energy from the sun using photosynthesis

Cornfield in South Africa

Sugar cane harvest Switchgrass

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• This is usually done using molasses.

• Molasses is a thick dark syrup produced by boiling down juice from sugarcane; specially during sugar refining.

• As molasses is a by product, ethanol production from molasses is not done in a large scale around the world.

The main reaction involved is fermentation

C6H12O6

sugar (e.g.:-glucose)

2 C2H5OH

ethanol

2 CO2

carbon dioxide

+yeast

Direct conversion of sugar to ethanol

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The top five ethanol producers in 2010

• Brazil - 16500 billion liters • The United States -16270

billion liters• China - 2000 billion liters• The European Union - 950

billion liters• India - 300 billion liters

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Bioethanol Properties

Colourless and clear liquid Used to substitute petrol fuel for road

transport vehicles One of the widely used alternative

automotive fuel in the world (Brazil & U.S.A are the largest ethanol producers)

Much more environmentally friendly Lower toxicity level

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Fuel PropertiesEnergy content

• Bioethanol has much lower energy content than gasoline

• about two-third of the energy content of gasoline on a volume base

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Fuel Properties Gasoline Bioethanol Molecular weight [kg/kmol] 111 46

Density [kg/l] at 15⁰C 0.75 0.80-0.82

Oxygen content [wt-%] 34.8

Lower Calorific Value [MJ/kg] at 15ºC 41.3 26.4

Lower Calorific Value [MJ/l] at 15ºC 31 21.2

Octane number (RON) 97 109

Octane number (MON) 86 92

Cetane number 8 11Stoichiometric air/fuel ratio [kg air/kg fuel] 14.7 9.0

Boiling temperature [ºC] 30-190 78

Reid Vapour Pressure [kPa] at 15ºC 75 16.5

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Reid vapour pressure (measure for the volatility of a fuel)

• Very low for ethanol, indicates a slow evaporation

• Adv: the concentration of evaporative emissions in the air remains relatively low, reduces the risk of explosions

• Disadv: low vapour pressure of ethanol -> Cold start difficulties

• engines using ethanol cannot be started at temp < 20ºC w/o aids

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Octane number• Octane number of ethanol is

higher than petrol• hence ethanol has better

antiknock characteristics• increases the fuel efficiency of the

engine• oxygen content of ethanol also

leads to a higher efficiency, which results in a cleaner combustion process at relatively low temperatures

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Application

• transport fuel to replace gasoline• fuel for power generation by thermal combustion• fuel for fuel cells by thermochemical reaction• fuel in cogeneration systems• feedstock in the chemicals industry

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• Blending of ethanol with a small proportion of a volatile fuel such as gasoline -> more cost effective

• Various mixture of bioethanol with gasoline or diesel fuels– E5G to E26G (5-26% ethanol, 95-74%

gasoline)– E85G (85% ethanol, 15% gasoline)– E15D (15% ethanol, 85% diesel)– E95D (95% ethanol, 5% water, with ignition

improver)

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Advantages

• Exhaust gases of ethanol are much cleaner • it burns more cleanly as a result of more complete combustion

• Greenhouse gases reduce• ethanol-blended fuels such as E85 (85% ethanol and 15%

gasoline) reduce up to 37.1% of GHGs

• Positive energy balance, depending on the type of raw stock • output of energy during the production is more than the input

• Any plant can be use for production of bioethanol • it only has to contain sugar and starch

• Carbon neutral • the CO2 released in the bioethanol production process is the

same amount as the one the crops previously absorbed during photosynthesis

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• Decrease in ozone formation • The emissions produced by burning ethanol are less reactive

with sunlight than those produced by burning gasoline, which results in a lower potential for forming ozone

• Renewable energy resource• result of conversion of the sun's energy into usable energy• Photosynthesis -> feedstocks grow -> processed into ethanol

• Energy security• esp. Countries that do not have access to crude oil resources• grow crops for energy use and gain some economic freedom

• Reduces the amount of high-octane additives• Fuel spills are more easily biodegraded or diluted to non toxic

concentrations

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Disadvantages and Concerns• Biodiversity

• A large amount of arable land is required to grow crops, natural habitats would be destroyed

• Food vs. Fuel debate• due to the lucrative prices of bioethanol some farmers

may sacrifice food crops for biofuel production which will increase food prices around the world

• Carbon emissions (controversial) • During production of bioethanol, huge amount of carbon

dioxide is released• Emission of GHGs from production of bioethanol is

comparable to the emissions of internal-combustion engines

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• Not as efficient as petroleum• energy content of the petrol is much higher

than bioethanol• its energy content is 70% of that of petrol

• Engines made for working on Bioethanol cannot be used for petrol or diesel• Due to high octane number of bioethanol, they

can be burned in the engines with much higher compression ratio

• Used of phosphorous and nitrogen in the production• negative effect on the environment

• Cold start difficulties• pure ethanol is difficult to vaporise

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• Transportation• ethanol is hygroscopic, it absorbs water

from the air and thus has high corrosion aggressiveness

• Can only be transported by auto transport or railroad

• Many older cars unequipped to handle even 10% ethanol

• Negatively affect electric fuel pumps by increasing internal wear and undesirable spark generation

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Ethanol Controversy

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Is it justifiable?..to use agriculture land to grow energy crops instead of food crops when there are so many starving people in the world. In the developed countries that is not a problem, but in the developing ones where we have a large number of people living below the poverty this may lead to a crisis.

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• Is burning biofuel more environmentally friendly than burning oil?– Fact that producing biofuel is not a "green process“– requires tractors and fertilisers and land– With the increase in biofuel production, more

forests will be chopped down to make room for biofuel, ↑ CO2

• Better alternative suggested by scientists..– steer away from biofuel and focus on reforestation

and maximising the efficiency of fossil fuels instead

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Comparison of Bioethanol and Biodiesel

Bioethanol Biodiesel Process Dry-mill method: yeast, sugars and starch

are fermented. From starch, it is fermented into sugar, afterwards it is fermented again into alcohol.

Transesterification: methyl esters and glycerin which are not good for engines, are left behind.

Environmental Benefit

Both reduce greenhouse gas emissions as biofuels are primarily derived from crops which absorb carbon dioxide.

Compatibility ethanol has to be blended with fossil fuel like gasoline, hence only compatible with selected gasoline powered automobiles.

Able to run in any diesel generated engines

Costs Cheaper More expensive Gallons per acre

420 gallons of ethanol can be generated per acre

60 gallons of biodiesel per acre soybeans cost of soybean oil would significantly increase if biodiesel production is increased as well.

Energy provides 93% more net energy per gallon produces only 25% more net energy.

Greenhouse-gas Emissions (GHG)

12% less greenhouse gas emission than the production and combustion of regular diesel

41% less compared to conventional gasoline.

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Social impacts

– Created jobs for locals (mainly in rural areas)– Brazilian sugarcane industry has a particularly

poor record in respecting worker’s rights– Expansion in sugar cane cultivation may

increase food prices. This would leave the poor with a harder survival.

– Although the ethanol industry has greatly increased the wealth of the sugar and alcohol sector’s industries, the poor have to be the one handling the negative impacts.

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Future development

• For bioethanol to become more sustainable to replace petrol, production process has to be more efficient– Reducing cost of conversion– Increasing yields – Increase the diversity of crop used

• As microbes are use to convert glucose into sugar which is ferment in bioethanol– Microbiology and biotechnology will be

helpful in the genetic engineering