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Pretreatment of different materials: An international perspective . Mohammad J. Taherzadeh School of Engineering University of Borås. A variety of lignocelluloses are attractive in different reagions!. Complex plants cell walls. A challenge by lignin and hemicellulose!. Hemicellulose.

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Pretreatment of different materials: An international perspective

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Pretreatment of different materials: An international perspective

Mohammad J. Taherzadeh

School of Engineering

University of Borås

A variety of lignocelluloses are attractive in different reagions!

Complex plants cell walls

A challenge by lignin and hemicellulose!



Cellulose chains

Challenge of crystallinity!

Alternative patterns of aggregation

Helical form of a 6 by 6 nm nanofibrils is compared with that of nine 2 by 2 helical nanofibrils packed as close as possible, with the same period.

The fibrils were twisted individually and then the assembly also twisted.

The individual fibrils were twisted of 90°over 300 nm and then packed as closely as possible

The fibrils were collectively subjected to twist.

Alternative patterns of aggregation

Cellulose is deposited alone

The most efficient load-bearing structure

Would not be mechanically stable

Changes during Isolation

  • Twostages in isolation willinfluence the final pattern of aggregation:

  • Elevation of temperature

  • Effect of drying

Effects of elevated temperature

  • Cellulose is hydrated in its native state at the level of elementary nanofibril

Temperature elevation changes the state of aggregation of native cellulose.


Drying results in distortion of nanofibrils by:

Removing too much of the water needed to lubricate the motion of the nanofibrils relative to each other.

Changes during Isolation

  • Linear parallel segments, which are artifacts of isolation processes are easily mistaken for naturally accuring crystalline domains.

Pretreatment in order to:

  • Release cellulose from the structure:

    • Remove or hydrolyze hemicelluloses

    • Remove lignin

  • Reduce cellulose crystallinity

  • Provide enough accessible surface area to absorb the enzymes

  • Adsorption/desorption rates of the enzymes

  • Remove inhibitory compounds following the substrate

Pretreatment methods (various efficiency on different factors)

Cellulose solvents effective for crystallinity

Possible non-aqueuous cellulose solvents

Low-temperature Ionic Liquids (80-130 C)

Imidazole salts

Milling: Usually part of the process!

  • Milling:

    • Ball milling

    • Two-roll milling

    • Hammer milling

    • Colloid milling

    • Vibro energy milling

  • Functions:

    • Size reduction

    • Degree of crystallinity

  • High energy costs!


  • irradiation:

    • Gamma-ray irradiation

    • Electron-beam irradiation

    • Microwave irradiation

  • Usuallygoodresults

  • Expensive!

  • Ultrasound mighthave a good a chance for commercialization(already in the market)

Hydrothermal process

  • Cooking in liquid hot water generally at 150-210 °C

  • Water under high pressure can:

    • Penetrate into the biomass,

    • Hydrate cellulose,

    • Remove hemicellulose (a major function),

    • Remove part of lignin (but not so effective),

  • Autohydrolysis occur due to releasing some carboxylic acids such as acetic acid,

  • Advantages:

    • No addition of chemicals,

    • No neutralization afterward,

    • No corrosion-resistant materials for reactor,

    • Could be combined with e.g. a delignification process

  • Industrial application such as by Danish Inbicon

High-pressure steaming (+explosion)

  • Cooking with steam generally at 150-220 °C & 0.5-20 min

  • If followed by explosive releasing of the pressure = Steam explosion

  • Steam explosion is one of the most popular pretreatments

  • Explosion has important function

  • pH reduces due to autohydrolysis

  • Industrtial applications by e.g.

    • Cambi (Norway)

    • Chemtex (Italy)

    • Greenfield (Canada)

Dilute-acid processes!

  • Similar methods in pulp industries

  • Similar temperature/Pressure as steam explosion!

  • Improvement by addition of:

    • Dilute-acid (0.1-1% acids: H2SO4, HCl, etc.)

    • Carboxylic acids (e.g. acetic acid)

    • 1-4% SO2

    • CO2

  • Functions:

    • Open up the polymers

    • Hydrolysis of hemicellulose

  • Potential commercialization by e.g :

    • POET (USA)

    • SEKAB (Sweden)


Alkaline cooking!

  • Treatment with alkaline solutions:

    • NaOH,

    • Ca(OH)2 (lime) or

    • Ammonia (AFEX)

  • Popular in pulp industries (kraft process)

  • To remove lignin effectively (+ sometimes a part of the hemicellulose)

  • To reduce crystallinity of cellulose

  • Generally at about 90-130 C for a few minutes to hours

  • High pH (e.g. 11-12) or alkali concentrations 1-20%

  • High amount of NH3 is needed (e.g. 1:1 kg/kg NH3/biomass)

  • Can also be used with explosion

Oxygen treatments (wet oxidation)!

  • Wet oxidation = treatment with water and air or O2 at 140-200 C for e.g. 30 min.

  • It is exothermic process (because of oxidations)

  • It is a combination of solubilization and degradation reactions

  • Hydrolytic reactions  organic acids

  • The hemicelluloses are extensively cleaved to monomeric sugars;

  • The lignins undergo both cleavage and oxidation;

  • Cellulose is partly degraded.

Organosolves/Ionic liquids!

  • Lignocelluloses are mixed with organic liquid (and water?) and heated to dissolve:

    • Ligning

    • And/or cellulose

  • Temperatures of 80-200 °C can be used:

    • Depends on the solvent used!

  • Simple solvents such as ethanol or acetone can be used!

  • Low Temperature Ionic Liquids are hot research topic today!

Our latest results for high crystalline cellulose!

  • N-Methylmorpholine-N-oxide (NMO or NMMO)

  • No toxicity

  • Solvent of cellulose

  • Industrial solvent

  • 80-130 C


  • Lignocelluloses are diffent:

    • Type,

    • Age,

    • Crystallinity

    • Dryness,

    • Type of the cell wall

    • ….

  • Pretreatments have different effectivities on various lignocelluloses,

  • Great developments in pretreatments, but still long way to go…

Thank you!


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