Following the structure and reactivity of Tuncbilek lignite during pyrolysis and hydrogenation

• Atmospheric pressure hydrogenation removed > 90% of pyritic sulfur present in Tuncbilek lignite.
• XRD revealed stepwise reduction of FeS2 to FeS and Fe.
• FeS and Fe acted as a catalyst for hydrogenation of aliphatics and aromatics present in lignite carbon framework.

Combustion, pyrolysis and hydropyrolysis reactivity of Tuncbilek lignite was monitored by temperature programmed pyrolysis (TPP) under pure nitrogen flow, temperature programmed oxidation (TPO) under air flow and temperature programmed hydrogenation (TPH) under hydrogen flow at atmospheric pressure in a packed bed reactor.The structures of the organic and inorganic components were analyzed by NMR spectroscopy and XRD. Only methane and hydrogen were the main products of TPP while small amounts of CO and CO2 were also observed. Solid-state 1H and 13C CPMAS and 1H liquid Nuclear Magnetic Resonance (NMR) Spectroscopy of the pristine lignite, as well as tar and char products of pyrolysis and hydrogenation (hydropyrolysis), revealed similar tar compositions. TGA of pyrolysis chars indicated that there were more residual volatiles in hydropyrolysis char in comparison to pyrolysis char. Elemental analysis of pyrolysis and hydropyrolysis chars revealed that 25% of sulfur was lost during pyrolysis, whereas > 90% of sulfur was lost during hydropyrolysis indicating efficiency of atmospheric pressure hydropyrolysis for both desulfurization and tar production. Volatile matter and fixed carbon, mostly aromatic, gave rise to distinct oxidation peaks during TPO. The oxidation peak due to volatiles was missing from TPO of pyrolysis char as well as from organic contents determined by NMR spectroscopy.