Concerning secondary biorefining a distinction is made between thermochemical and biochemical based refinery. Thermochemical based refinery processes are generally consisting of the following interconnected unit operations: pre-treatment (i.e. drying, size reduction), feeding, conversion (e.g. gasification, pyrolysis), product clean up and conditioning, and product end-use. Thermochemical conversion technologies convert biomass and its residues to fuels, chemicals, and power. Gasification, i.e. heating biomass with about one-third of the oxygen necessary for complete combustion, produces a mixture of CO2 and hydrogen, known as syngas. Pyrolysis, i.e. heating biomass in the absence of oxygen, produces a liquid pyrolysis oil. Both syngas and pyrolysis oil can be used as fuels that are cleaner and more efficient than the solid biomass, but can also be chemically converted to other valuable fuels and chemicals.
Biochemical conversion technologies involve three basic steps, i.e., (i) converting biomass to sugar or other fermentation feedstock, (ii) fermenting these biomass intermediates using biocatalysts and (iii) processing the fermentation product to yield fuel-grade ethanol and other fuels, chemicals, heat and/or electricity.
Researchers are working to improve the efficiency and economics of both the thermochemical and biochemical conversion process technologies by focusing their efforts on the most challenging steps in the process, i.e. on syngas production and utilization (thermochemical) and on improving pretreatment technology, for breaking hemicellulose down to component sugars and developing more cost-effective cellulose enzymes, for breaking cellulose down to its component sugar (biochemical).
Researchers are also working to demonstrate the thermochemical and biochemical conversion processes in real-world applications. The integration and production activities require involvement of industrial partners.