From biomass to syngas, fuels and chemicals – A review

The gasified form of biomass is called syngas which can be further converted to fuels, liquid products and other chemicals via thermo-chemical and bio-chemical processes. After pretreatment of biomass, gasification occurs at high temperature in the presence of oxidizing agents. The biomass is oxidized to produce syngas through several steps. Syngas contains mainly CO, H2 and small amounts of impurities and these impurities are removed based on downstream usage of the syngas. Through gasification, all the carbon content in the biomass is converted into syngas and the main use of biomass syngas is the generation of heat / power. Common chemicals obtained from the syngas are: methanol from CO and H2; ammonia from N2; H2 and liquid hydrocarbons by Fisher-Tropsch synthesis. Different types of catalysts are used in the thermo-chemical routes like sulphide type mixed alcohol catalyst, Rh/SiO2, Rh/MCM-41, Cu/MCM-41, from which oxygenates and hydrocarbon products can also be produced. In gas fermentation, ethanol is produced using different bio catalyst and CO2/H2 is consumed in this process. Many other chemicals such as butanol, acetic acid, acetone also can be synthesized. When compared to thermo-chemical routes, gas fermentation operates at low pressure and low temperature and produces ethanol with high carbon conversion efficiency.