Waste tyre gasification, pyrolysis and liquefaction technology comparison.

Process	Gasification	Pyrolysis	liquefaction
Process definition	Gasification is a sub-stoichiometric thermochemical process that transforms carbon-based feedstock through the controlled supply of a gasifying agent into a fuel gas	The thermal degradation of carbonaceous material in an oxygen-deprived atmosphere to maximize thermal decomposition of solid into gases and condensed liquid and residual char	Liquefaction is the thermochemical conversion of an organic solid into a petroleum-like liquid
Process conditions
Reaction environment	Reducing (oxidant amount lower than that required by stoichiometric combustion)	Total absence of any oxidant	Direct liquefaction may involve the use of solvents such as water and indirect liquefaction employs the use of a gasifying agent
Reactant gas	Air, pure oxygen, oxygen-enriched air, steam	None	Solvents and gasifying agents occasionally employed
Temperature	550–1000 °C	500 and 800 °C	250–350 °C
Pressure	Atmospheric	Slightly above atmospheric pressure	5–20 MPa
Process outputs
Gas product	CO, H2, CO2, H2O, CH4	CO, H2, CH4, paraffins, olefins	CO, H2, CH4, paraffins, olefins
Liquid product	Gasification generates small amounts of oil due to thermal cracking and steam reforming reactions at elevated temperatures, however, a condensable fraction of tar and soot is generated	Pyrolysis produces oil that has properties identical to diesel and can be employed as fuel. It contains a high aromatic content, thus can function as an industrial chemical feedstock	Liquefaction produces a liquid product comprising of viscous molecular compounds with properties comparable, but not alike, to those of petroleum-based fuels
Solid product	Bottom ash is often the residual product that can be directly utilized as backfilling material for road construction. Upon further upgrading, the char has the potential for activated carbon production	The pyrolysis char has a high carbon content and can utilized fuel. Upon further treatment, the char can be utilized for the manufacturing of carbon black, activated carbon and in similar industries
Pollutant	H2S, HCl, COS, NH3, HCN, tar, alkali, particulate matter	H2S, HCl, NH3, HCN, tar, particulate matter	SOx, NOx, CO