**2. Thermochemical conversion**

Thermochemical conversion is defined as the degradation of organic matters due to heat exposition of biomass and chemical reactions. The process is mainly categorized in some processes named combustion, torrefaction, gasification, pyrolysis, and hydrothermal [17, 18]. In the thermochemical conversion of biomass, heat and catalysts are applied to transform biopolymers of biomass into biofuels and other valuable chemical components [19]. Based on the process the outputs mainly are biochar (carbon-rich solid residue,) liquid biofuel including bio-oil, bio-crude oil and tar (condensable vapors), and syngas (non-condensable gases) [20].
