Syngas (Synthetic Gas) is a mixture of gases primarily composed of hydrogen (H₂), carbon monoxide (CO), and carbon dioxide (CO₂), and it usually also contains methane (CH₄).

The core value of syngas lies in its H₂ and CO components, which are essential chemical feedstocks and energy carriers. The H₂/CO ratio is a key indicator for evaluating syngas quality, as different downstream applications require different ratios. For example, methanol synthesis typically requires an H₂/CO ratio of approximately 2:1, Fischer–Tropsch synthesis requires around 2.1:1, while carbonylation processes demand a lower H₂/CO ratio.

Under pure pyrolysis conditions (a completely oxygen-free environment), biomass thermally decomposes to directly produce volatile gases. These gases include primary pyrolysis products and secondary cracking products.

At lower temperatures, gaseous products mainly originate from the initial decomposition of biomass components, resulting in relatively low hydrogen content and comparatively higher amounts of methane and light hydrocarbons. As the temperature increases, tar undergoes secondary cracking, significantly increasing the concentrations of hydrogen and carbon monoxide.

Gasification is a controlled oxidation process in which biomass is converted into combustible gases in the presence of limited oxygen or steam.

Initially, biomass undergoes thermal decomposition in the pyrolysis zone, producing tar, gases, and biochar. These products then react with gasifying agents (such as air, oxygen, steam, or their combinations) in the oxidation and reduction zones, further converting into syngas primarily composed of hydrogen (H₂) and carbon monoxide (CO).