Process Development for lignocellulosic ethanol

There are currently a number of process paths that could be used for the production of lignocellulosic ethanol from biomass via the biochemical route.  Generally the production route starts off with preparation of your raw material through milling, communition or chipping of your material to reduce the particle size. The type of preparation depends on the raw material being considered as well as the type of pretreatment that is used to open up the structure.

Following this the prepared raw material undergoes pretreatment in which the aim is to open up structure of the raw material for enzymatic attack. Different pretreatments will results in different products. For example if one performs a pretreatment such as dilute acid hydrolysis, generally the hemicellulosic fraction will be hydrolysed leaving the cellulosic portion intact. This will result in a pretreatment liquor that will containing the hydrolysed hemicellulosic sugars and a solid fraction which contains lignin, cellulose and any remaining hemicellulose that was not hydrolysed during the pretreatment.

Once the pretreatment has finished, the next processing step must be chosen. Currently there are two routes that I know of that could be followed, either seperate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF). Both of these have their own advantages and disadvantages. The result of these two process choices are similar though, resulting in the hydrolysis of the remaining cellulose fraction to monomeric sugars and the fermentation of hydrolysed sugars to ethanol. Finally the product from SSF or SHF can be distilled to produce a pure ethanol which could be used as biofuel.

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