Biorefineries convert biomass to fuels, power, and chemicals. The principal products of biorefineries are biofuels which are classified as either bioethanol or biodiesel.

Figure 1: Production of ethanol from biomass.

There is currently a push for two new types of biorefinery. Sugar platform refineries will convert biomass into component sugars for further fermentation and thermochemical biorefineries will produce a gas as the final product.                  

With most plant material being cellulose, hemicellulose, or lignin, an effort is being made to develop a method of breaking down cellulose and hemicellulose into their component sugars. Further processing of these sugars will produce fuel ethanol and other chemical building blocks. The remaining lignin can be used as a fuel source to power the process or it can be converted to fuels and chemicals. These biorefineries will rely on enzymatic hydrolysis of the biomass.

Currently the main way of converting biomass to energy has been the combustion of biomass. This commonly used process is not energy efficient. Converting the solid biomass to fuel by heating it with limited oxygen prior to combustion can greatly increase the overall efficiency. When the biomass is heated with little to no oxygen the material gasifies to a mixture of carbon monoxide and hydrogen called synthesis gas. The synthesis gas can then be burned more efficiently and cleaner than the solid biomass. Pyrolysis is another option when no oxygen is present.
Pyrolysis oil can be used directly as a fuel or can be used as a source for intermediates in the synthesis of other chemicals.