*3.1.2 Pyrolysis of biomass*

Pyrolysis is a process that consists of the thermal decomposition of biomass in the absence of oxygen. Pyrolysis requires temperatures up to 550°C, although it can

#### *Valorization of Biomass as a Raw Material to Obtain Products of Industrial Interest DOI: http://dx.doi.org/10.5772/intechopen.104108*

be carried out at even higher temperatures (700–900°C), depending on the biomass treated. The product is a synthesis gas with considerable calorific value. During the pyrolysis process, solid or carbonized products, liquid products (bio-oils, tars, and water), and a gas mixture consisting mainly of CO2, CO, H2, and CH4 are generated [9, 15].

#### *3.1.3 Biomass gasification*

Gasification consists of the conversion of biomass, normally of woody origin by thermal decomposition through partial oxidation reactions using a gasifying agent, such as steam, oxygen, air, or a mixture of the above and high temperatures (700– 900°C), to obtain a synthesis gas also called as syngas with a considerable calorific value. Depending on the final feedstock conversion requirements, different temperature and pressure ranges can be used, as well as different types of gasifying agents, such as air, oxygen, steam, hydrogen, or carbon dioxide. The gas produced contains CO, H2, CH4, N2, and steam, which is used in internal combustion engines and gas turbines. Fuel gas is mainly used to produce electricity or thermal energy [15].

#### *3.1.4 Biomass combustion*

Combustion is a thermochemical process used for heat production, consisting of a chemical reaction in the presence of oxygen at temperatures between 800 and 1000°C, in which fuel is oxidized, and a large amount of energy is released in the form of heat (exothermic reaction). Depending on the amount of oxygen present in the process, combustion can be complete when the amount of air is sufficient to oxidize all the organic elements that make up the fuel to produce mainly CO2 and H2O, or incomplete when the concentration of air is insufficient to oxidize the fuel and generate CO. This process converts the stored chemical energy of the biomass into heat, mechanical energy or electricity depending on the process equipment used such as furnaces, boilers, steam turbines, turbo generators, etc. [12, 15].

#### **3.2 Chemical processes**

Chemical processes include structural modifications or breaking of chemical bonds to either alter or form new molecules, as well as to hydrolyze macromolecules. Several of the chemical processes presented in this section are used as pretreatments to improve the efficiencies of biological processes, enzymatic reactions, such as fermentation and anaerobic digestion of biomass.
