Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 192

Biological conversion (also referred to as biochemical conversion) involves breaking down biomass to make the carbohydrates available for processing into sugars, which can then be converted into biofuels and bioproducts through the use of microorganisms and catalysts. Potential fuel blend stocks and other bioproducts include the following: (i) renewable gasoline, (ii) ethanol and other alcohols, (iii) renewable chemical products, and (iv) renewable diesel. Biochemical conversion uses biocatalysts, such as enzymes, in addition to heat and other chemicals, to convert the suitable portions of biomass (hemicellulose and cellulose) into an intermediate sugar stream. These sugars are intermediate building blocks that can then be fermented or chemically catalyzed into a range of advanced biofuels and value-added chemicals.

Bioconversion processes generally take place in bioreactors, which may be operated in batch, continuous, or semi-continuous mode, among others. Moreover, different bioreactor configurations may be suitable depending on the specific application. The technology may range from solid-phase bioconversion processes to gas-phase ones, besides aqueous phase bioprocesses. In any case, a given amount of moisture is generally needed, as this is required, in most cases, for optimal microbial activity. For any given feedstock, biocatalyst and bioreactor configuration and operating conditions will need to be optimized, in terms of aspects such as residence time in continuous processes, pH, or media composition (such as, for example, the carbon-nitrogen ratio).

Thus, bioconversion processes and biorefineries are environmentally friendly alternatives to common chemical processes and conventional oil refineries. They allow the production of a wide range of products with cheap biocatalysts, usually under mild conditions.

See also: Biohydrogen, Biological Action, Biological Alcohol.