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Lignocellulose refers to plant dry matter (
biomass Biomass is plant or animal material used as fuel to produce electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position ...

biomass
), so called lignocellulosic biomass. It is the most abundantly available raw material on the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
for the production of
biofuels Biofuel is fuel that is produced through contemporary processes from biomass, rather than by the very slow geological processes involved in the formation of fossil fuels, such as oil. Since biomass technically can be used as a fuel directly (e.g ...

biofuels
, mainly
bio-ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an Organic compound, organic chemical compound. It is a simple alcohol with the chemical formula C2H6O. Its formula can be also written as −− or (a ...
. It is composed of carbohydrate polymers (
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important stru ...

cellulose
,
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov He ...

hemicellulose
), and an aromatic polymer (
lignin Lignin is a class of complex organic polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its s ...

lignin
). These carbohydrate polymers contain different sugar monomers (six and five carbon sugars) and they are tightly bound to lignin. Lignocellulosic biomass can be broadly classified into virgin biomass, waste biomass and
energy crops Energy crops are low-cost and low-maintenance crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. Crops may refer either to the harvested parts or to the harvest in a more refined state. Most crops ...
. Virgin biomass includes all naturally occurring terrestrial plants such as trees, bushes and grass. Waste biomass is produced as a low value byproduct of various industrial sectors such as
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors su ...

agriculture
(
corn stover Corn stover consists of the leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit toge ...
, sugarcane
bagasse Bagasse ( ) is the dry pulpy fibrous material that remains after crushing sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, perennial A perennial plant or simply perennial is a plant Plants are predominan ...
, straw etc.) and
forestry Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forest A forest is an area of land dominated by tree In botany, a tree is a perennial plant with an elongated Plant stem, ste ...
(
saw mill A sawmill (saw mill, saw-mill) or lumber mill is a facility where logs are cut into lumber Lumber, also known as timber, is wood Wood is a porous and fibrous structural tissue found in the Plant stem, stems and roots of trees and ...
and
paper mill A paper mill is a factory A factory, manufacturing plant or a production plant is an industrial Industrial may also refer to: Industry * Industrial archaeology, the study of the history of the industry * Industrial engineering, engineering ...
discards).
Energy crops Energy crops are low-cost and low-maintenance crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. Crops may refer either to the harvested parts or to the harvest in a more refined state. Most crops ...
are crops with high yield of lignocellulosic biomass produced to serve as a raw material for production of second generation biofuel; examples include switchgrass (''
Panicum virgatum ''Panicum virgatum'', commonly known as switchgrass, is a perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a ...

Panicum virgatum
'') and
Elephant grassThe term Elephant grass may refer to the following grass species: * The Asian '' Miscanthus giganteus'', also known as giant miscanthus, commonly used as a biomass crop * The African ''Pennisetum purpureum'', also known as napier grass, Uganda grass ...

Elephant grass
.


Dedicated energy crops

Many crops are of interest for their ability to provide high yields of biomass and can be harvested multiple times each year. These include
poplar
poplar
trees and ''
Miscanthus giganteus
Miscanthus giganteus
''. The premier energy crop is
sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, ...

sugarcane
, which is a source of the readily fermentable
sucrose Sucrose is a type of sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosacchari ...

sucrose
and the lignocellulosic by-product
bagasse Bagasse ( ) is the dry pulpy fibrous material that remains after crushing sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, perennial A perennial plant or simply perennial is a plant Plants are predominan ...
.


Application


Pulp and paper industry

Lignocellulosic biomass is the feedstock for the
pulp and paper industry The pulp and paper industry comprises companies that use wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk ...
. This energy-intensive industry focuses on the separation of the lignin and cellulosic fractions of the biomass.


Biofuels

Lignocellulosic biomass, in the form of
wood fuel Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. ...
, has a long history as a source of energy. Since the middle of the 20th century, the interest of biomass as a precursor to ''liquid'' fuels has increased. To be specific, the
fermentation Fermentation is a metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signalin ...

fermentation
of lignocellulosic biomass to
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
is an attractive route to fuels that supplements the
fossil fuels A fossil fuel is a hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and ...
. Biomass can be a
carbon neutral Carbon neutrality refers to achieving net-zero carbon dioxide emissions. This can be done by balancing emissions of carbon dioxide with its removal (often through carbon offsetting) or by eliminating emissions from society (the transition to the ...
source of energy in the long run. However depending on the source of biomass, it will not be carbon neutral in the short term. For instance if the biomass is derived from trees, the time period to regrow the tree (on the order of decades) will see a net increase in carbon dioxide in the
earth’s atmosphere File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the atmosphere (0.04402961% at April 2019 concentration ). Number ...
upon the combustion of lignocellulosic ethanol. However, if woody material from annual crop residue is used, the fuel could be considered carbon-neutral. Aside from ethanol, many other lignocellulose-derived fuels are of potential interest, including
butanol Butanol (also called butyl alcohol) is a four-carbon alcohol In , alcohol is an that carries at least one (−OH) bound to a atom. The term alcohol originally referred to the primary alcohol (ethyl alcohol), which is and is the main ...
,
dimethylfuran
dimethylfuran
, and
gamma-Valerolactone
gamma-Valerolactone
. One barrier to the production of ethanol from biomass is that the sugars necessary for fermentation are trapped inside the lignocellulose. Lignocellulose has evolved to resist degradation and to confer
hydrolytic Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...

hydrolytic
stability and structural robustness to the cell walls of the plants. This robustness or "recalcitrance" is attributable to the crosslinking between the polysaccharides (cellulose and hemicellulose) and the lignin via
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
and
ether Ethers are a class of organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reaction ...

ether
linkages. Ester linkages arise between oxidized sugars, the
uronic acid 300px, The Fischer projections of glucose and glucuronic acid">glucose.html" ;"title="Fischer projections of glucose">Fischer projections of glucose and glucuronic acid. Glucose's terminal carbon's primary alcohol group has been oxidized to a ...
s, and the phenols and phenylpropanols functionalities of the lignin. To extract the fermentable sugars, one must first disconnect the celluloses from the lignin, and then use acid or enzymatic methods to
hydrolyze Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...
the newly freed celluloses to break them down into simple monosaccharides. Another challenge to biomass fermentation is the high percentage of pentoses in the hemicellulose, such as
xylose Xylose ( grc, ξύλον, , "wood") is a sugar first isolated from wood, and named for it. Xylose is classified as a of the type, which means that it contains five atoms and includes an . It is derived from , one of the main constituents o ...

xylose
, or wood sugar. Unlike hexoses such as glucose, pentoses are difficult to ferment. The problems presented by the lignin and hemicellulose fractions are the foci of much contemporary research. A large sector of research into the exploitation of lignocellulosic biomass as a feedstock for bio-ethanol focuses particularly on the fungus ''
Trichoderma reesei ''Trichoderma reesei'' is a mesophilic and Hypha, filamentous fungus. It is an anamorph of the fungus ''Hypocrea jecorina''. ''T. reesei'' can secrete large amounts of cellulolytic enzymes (cellulases and hemicellulases). Microbial cellulases hav ...
'', known for its cellulolytic abilities. Multiple avenues are being explored including the design of an optimised cocktail of cellulases and hemicellulases isolated from ''T. reesei'', as well as genetic-engineering-based strain improvement to allow the fungus to simply be placed in the presence of lignocellulosic biomass and break down the matter into
D-glucose
<small>D</small>-glucose
monomers In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...

monomers
. Strain improvement methods have led to strains capable of producing significantly more cellulases than the original QM6a isolate; certain industrial strains are known to produce up to 100g of cellulase per litre of fungus, thus allowing for maximal extraction of sugars from lignocellulosic biomass. These sugars can then be fermented, leading to bio-ethanol.


Biocomposites

Lignocellulosic biomasses are gaining attention also in the production of biocomposites materials such as particle panels, wood-plastic composites, and cement/geopolymer wood composites. Even though the production of biocomposites material rely mostly on wood resources, in less forest-covered countries or in countries where wood resources are already being overused, it is possible to utilize alternative sources of biomass such as invasive plants, agricultural and sawmills residues for the creation of new "green" composites.
Biocomposites produced with lignocellulosic biomasses as alternative to conventional materials, are attracting the attention because are renewable and cheaper but also because they fit perfectly into the policy of the "cascade utilization" of the resources.


References

{{Bioenergy Biological matter