Noncatalytic hydropyrolysis of lignin in a high pressure micro-pyrolyzer

Lignin hydropyrolysis was investigated in a high-pressure micro-reactor with on-line analysis characterization of products. The influences of atmosphere, pressure, and temperature on product formation during lignin pyrolysis were quantitatively discussed. The presence of hydrogen, elevated pressure and temperature favored the production of condensable vapors and permanent gas while inhibited the formation of char. High-pressure hydrogen boosted the conversion of methoxy phenolics to non-methoxy phenolics, and facilitated the generation of hydrocarbon condensable vapors and hydrocarbon gases. Non-methoxy phenolics were major condensable vapor from lignin hydropyrolysis. Yield of non-methoxy phenolics reached 19.68C% at 3 MPa and 500 °C. The monocyclic and polycyclic aromatic hydrocarbons as well as condensable aliphatic hydrocarbons were observed from lignin hydropyrolysis. Methane was the most abundant gas product from lignin hydropyrolysis, yield of which was 10.27C% at 2 MPa and 600 °C. The formation mechanisms of typical products were proposed and verified with experiments using model compounds. The formation of non-methoxy phenolics, monocyclic aromatic hydrocarbons and aliphatic hydrocarbons is related to the substitution of methoxy (and its methyls) and phenolic hydroxyl groups on benzene rings by alkyls, alkenyls and hydrogen radicals, as well as the hydrogenation of π bonds. •A pyrolyzer operating under 3.0 MPa hydrogen with on-line product analysis was used.•Presence of hydrogen enhances demethylation of methoxy groups in phenolic products.•High-pressure H2 promotes hydrocarbon formation while inhibits char formation.•The formation mechanisms of typical products from lignin hydropyrolysis are proposed.