Archive for Lignocellulosic structure

Effect of Steam Explosion on Biomass

Before enzymes can efficiently hydrolyse the sugar components of biomass, biomass needs to be pre-treated to expose these sugars to enzymatic attack. Why is this necessary? Well the highly complex lignocellulosic matrix consisting of Cellulose, hemicellulose and lignin forms a barrier against enzymes which prevents degradation of the biomass into its individual components.

Steam explosion is one man-made way in overcoming this barrier, or in other words overcome the recalcitrant propery of biomass that is observed in nature. By subjecting biomass to high pressure steam for a certain period of time and then explosively depressurizing the biomass through release of steam/biomass one can break apart the lignocellulosic structure effectively yielding a highly digestible substrate.

Compare the following pictures of raw un-pretreated triticale straw with that that has been steam exploded at a steam temperature of around 200 degrees and a residence time of 5 – 10 minutes. One can visually see how the biomass has been fragmented and destroyed by this pretreatment technology.

Raw straw for steam explosion

Raw unpretreated triticale straw

Pretreated biomass

Steam Exploded triticale straw

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What is Lignocellulose

What is lignocellulose? Lignocellulose refers to the specific structure of biomass. The main constituents of lignocellulosic biomass comprises lignin, hemicellulose and cellulose. This is a complex structure in which the cellulose is surrounded by a monolayer of hemicellulose and embedded in a matrix of hemicellulose and lignin. Furthermore lignin specifically creates a barrier to enzymatic attack while the highly crystalline structure of cellulose is insoluble in water while the hemicellulose and lignin create a protective sheath around the cellulose. This structure can be seen in the image below.
http://www.engineeringnews.co.za/article/secondgeneration-biofuels-may-offer-a-way-forward-2008-10-31
This structure of lignocellulose therefore plays a huge role in inhibiting degradation of the hemicellulose and cellulose structure to monomeric sugars which is necessary to effectively convert biomass into ethanol. Processing of lignocellulose is therefore essential for the conversion of lignocellulosic biomass to biofuel such as bio-ethanol.

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