fundamentals of biofuels

8/12/2019 Fundamentals of Biofuels

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Biofuels Engineering Process

Technology

Miguel Angel Prada De vila


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Fundamentals of biofuels


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Biofuels

Fuente: www.extension.org


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Biofuels

Examples of biofuels include methane gas,

liquid ethanol, methyl esters, oils and solid

charcoal.

Fuente: J. Twider, T Weir, Renewable energy resources, 2nd Ed. Taylor and Francis Group.


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What are biofuels?

The material of plants and animals, including

their wastes and residues, is called biomass.

The initial material may be transformed by

chemical and biological processes to produce

biofuels, i.e. biomass processed into a more

convenient form.



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Why biofuels energy?

The associated energy bound in photosynthesis is2x10(0.7x104) . Of this, about 0.5% byweight is biomass as crops for human food.

Biomass provides about 13% of mankinds energyconsumption.

The domestic use of biofuel as wood, dung and plant

residues for cooking is of prime importance for about50% of the worldspopulation.



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The initial energy of the biomass-oxygen system is capturedfrom solar radiation in photosynthesis when is released in

combustion the biofuel energy is dissipated, but the

elements of the material should be available for recycling in

natural ecological or agricultural processes. Thus the use of

industrial biofuels, when linked carefully to natural ecological

cycles, may be nonpolluting and sustainable.



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Fuente: http://energyfromwasteandwood.weebly.com/


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Why is renewable?

If biomass is to be considered renewable,

growth must at least keep pace with use.


It is disastrous for local ecology and global climate control

that firewood consumption and forest clearing is significantly

outpacing tree growth in ever increasing areas of the world.


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Generations of biofuels

Fuente: http://energyfromwasteandwood.weebly.com/


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First generation

The first generation biofuels refer to the fuels that

have been derived from sources like starch, sugar,

animal fats and vegetable oil.

Fuente: http://biofuel.org.uk/first-generation-biofuels.html


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First generation

The oil is obtained using the conventional techniques

of production. Some of the most popular types of

first generation biofuels are:

Biodiesel

Vegetable oil

Biogas

Bioalcohols Syngas

Fuente: http://biofuel.org.uk/first-generation-biofuels.html


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Second generation

Second generation biofuelsare also known as

advanced biofuels. What separates them from

first generation biofuels the fact that

feedstock used in producing secondgeneration biofuels are generally not food

crops.

http://biofuel.org.uk/first-generation-biofuels.html


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Second generation

The only time the food crops can act as secondgeneration biofuels is if they have already fulfilledtheir food purpose.

For instance, waste vegetable oil is a second generationbiofuels because it has already been used and is nolonger fit for human consumption.

Virgin vegetable oil, however, would be a firstgeneration biofuel.

http://biofuel.org.uk/first-generation-biofuels.html


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Third generation

The term third generation biofuelhas only recently enter the

mainstream it refers to biofuel derived from algae.

Previously, algae were lumped in with second generation

biofuels. However, when it became apparent that algae are

capable of much higher yields with lower resource inputs

than other feedstock, many suggested that they be moved to

their own category.

Fuente: http://biofuel.org.uk/third-generation-biofuels.html


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Third generation

The term third generation biofuelhas only recently enter the

mainstream it refers to biofuel derived from algae.

Previously, algae were lumped in with second generation

biofuels. However, when it became apparent that algae are

capable of much higher yields with lower resource inputs

than other feedstock, many suggested that they be moved to

their own category.

Fuente: http://biofuel.org.uk/third-generation-biofuels.html


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Biofuel Feedstocks


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Lignocellulosic biomass feedstock

Woody biomass (Forest residue, wood waste)

Non-woody biomass

- Agricultural residues: Straws, Bagasse, Stover

Organic Waste (Animal Waste, Sewage Sludge)


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Lignocellulosic biomass

Lignocellulosic biomass is typically nonedibleplant material

composed primarily of the polysaccharides cellulose and

hemicellulose.

The third major component is lignin, a phenolic polymer that

provides structural strength to the plant.

Fuente: J. SLUITER, R. RUIZ, C. SCARLATA, A. SLUITER, D. TEMPLETON,Compositional Analysis of Lignocellulosic Feedstocks. Review and

Description of Methods,J. Agric. Food Chem. 2010, 58, 90439053


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Apart from these primary polymers, plants comprise other

structural polymers (e.g. waxes, proteins). The minor

components in biomass can include protein, ash, organic

acids, and other nonstructural materials.

Although these individual components may make up only a

small fraction of the feedstock, their presence will become

significant in the running of an industrial-scale biorefinery.

Fuente: J. SLUITER, R. RUIZ, C. SCARLATA, A. SLUITER, D. TEMPLETON,

Compositional Analysis of Lignocellulosic Feedstocks. Review and

Description of Methods,J. Agric. Food Chem. 2010, 58, 90439053


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Cellulose

Cellulose is a natural polymer consisting of D-anhydroglucose

(C6H11O5) repeating units joined by 1,4-b-D-glycosidic

linkages at C1 and C4 position. The degree of polymerization

(DP) is around 10,000.

Each repeating unit contains three hydroxyl groups. These

hydroxyl groups and their ability to hydrogen bond play a

major role in directing the crystalline packing and also govern

the physical propertiesof cellulose.


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Lignocellulosic structure

The architecture of lignocellulose structures is directed by a

variety of covalent and non-covalent linkages between the

various constituents.

Cellulose is complexed with hemicellulose, lignin, and other

components, which complicate their hydrolysis.


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Cellulose cristaline regions


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Lignocellulosic structure

Cellulose microfibrils are stabilized by intra- and

intermolecular hydrogen bonds and surrounded by

hemicellulosic polysaccharides (mannans and xylans) linked

to cellulose by covalent and hydrogen bonds (Heredia et al.

1995).

These covalent bonds are extremely resistant to chemical

and biological hydrolysis.


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Cellulose resistance

Cellulose is resistant to strong alkali (17.5 wt%) but is easily

hydrolyzed by acid to water-soluble sugars. Cellulose is relatively

resistant to oxidizing agents ( John and Thomas 2007).


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Hemicellulose

Hemicellulose is not a form of cellulose and the name is a

misnomer. They comprise a group of polysaccharides

composed of a combination of 5- and 6-carbon ring sugars.


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Differences

Hemicellulose differs from cellulose in three aspects.

Firstly, they contain several different sugar units whereascellulose contains only 1,4b-D-glucopyranose units.

Secondly, they exhibit a considerable degree of chainbranching containing pendant side groups giving rise to itsnon crystalline nature, whereas cellulose is a linearpolymer.

Thirdly, the degree of polymerization of native cellulose is10100 times higher than that of hemicellulose.


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Hemicellulose

The degree of polymerization (DP) of hemicellulose is around50300. Hemicelluloses form the supportive matrix forcellulose microfibrils.

Hemicellulose is very hydrophilic, soluble in alkali and easilyhydrolyzed in acids (John and Thomas 2007).


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Lignin

Lignin is a complex hydrocarbon polymer with both aliphatic

and aromatic constituents.

They are totally insoluble in most solvents and cannot be

broken down to monomeric units.

Lignin is totally amorphous and hydrophobic in nature. It is

the compound that gives rigidity to the plants.


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What is?

Lignin has been found to contain five hydroxyl and five

methoxyl groups per building unit. It is believed that the

structural units of lignin molecule are derivatives of 4-

hydroxy-3-methoxy phenylpropane.

The main difficulty in lignin chemistry is that no method has

been established by which it is possible to isolate lignin in its

native state from the fiber.


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Lignin resistance

It is not hydrolyzed by acids, but soluble in hot alkali, readily

oxidized, and easily condensable with phenol (John and

Thomas 2007).

fundamentals of biofuels

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