Biochemical Conversion Processes
The Biomass Program's activities focus on reducing the cost and improving the efficiency of fractionating and converting cellulosic biomass into fermentable sugars, a primary intermediate, which are then fermented to alcohols, ethanol in most cases. The secondary intermediate produced is lignin, which can be burned to produce heat and power, or converted to other fuels and products. The following figure represents a very simplified version of the biochemical conversion process.
Feedstock Logistics
Feedstocks for biochemical processes are selected for ideal composition, quality, and size. Feedstock logistics adapted to serve biochemical processing pretreatment needs are a key component of this technology's growth.
Pretreatment (also known as Prehydrolysis)
Biomass undergoes a thermochemical process, where heat and either water, an acid or a base are used to break down the cellulosic biomass into soluble sugars and make the cellulose more accessible for the hydrolysis step.
Hydrolysis/Saccharification
The pretreated material is saccharified (separating the carbohydrates) and the sugar is released. Enzymes or acid are used in this process to beak down any remaining solid cellulose to simple sugars. This process takes several days after which the mixture of sugars and any solids or un-reacted cellulose is transferred to a fermenter.
Cleanup/Separation
In addition to using sugars as an intermediate to produce fuels, the sugar stream could be separated and cleaned into clean sugar streams and used to produce chemicals and material (products). Separation techniques are developed to reduce the cost of clean up and to concentrate the sugar stream, making them more amenable to high-yield processing to chemicals and materials; and the ultimate goal is to economically recover and purify those products.
Fermentation
In this step, fermenting organisms are added to the mixture to ferment the sugars to alcohol and carbon dioxide.
Product Recovery
This process involves distilling the fermented mixture to separate the ethanol from the water and any residual solids. The remaining solids are primarily composed of lignin (part of the cell wall), which can be burned for heat and power or thermochemically (using heat) converted to synthesis gas or pyrolysis oil intermediates for upgrading to fuels.