The conversion of biomass solids into liquid or gaseous biofuels is a complex process. Today, the most common conversion processes are biochemical- and thermochemical-based. However, researchers are also exploring photobiological conversion processes.
Biochemical Conversion Processes
In biochemical conversion processes, enzymes and microorganisms are used as biocatalysts to convert biomass or biomass-derived compounds into desirable products. Cellulase and hemicellulase enzymes break down the carbohydrate fractions of biomass to five- and six-carbon sugars in a process known as hydrolysis. Yeast and bacteria then ferment the sugars into products such as ethanol. Biotechnology advances are expected to lead to dramatic biochemical conversion improvements.
Learn more about biochemical conversion processes from the EERE Bioenergy Technologies Office.
Thermochemical Conversion Processes
Heat energy and chemical catalysts can be used to break down biomass into intermediate compounds or products. In gasification, biomass is heated in an oxygen-starved environment to produce a gas composed primarily of hydrogen and carbon monoxide.
In pyrolysis, biomass is exposed to high temperatures in the absence of air, causing it to decompose. Solvents, acids, and bases can be used to fractionate biomass into an array of products including sugars, cellulosic fibers, and lignin.
Learn more about thermochemical conversion processes from the EERE Bioenergy Technologies Office.
Photobiological Conversion Processes
Photobiological conversion processes use the natural photosynthetic activity of organisms to produce biofuels directly from sunlight. For example, the photosynthetic activities of bacteria and green algae have been used to produce hydrogen from water and sunlight.
Learn more about current microalgal biofuels research from the National Renewable Energy Laboratory.