Investigation on hydrogen migration and redistribution characteristics during co-pyrolysis of lignite with hydrogen-rich carbonaceous matters

•Hydrogen migration and redistribution characteristics during co-pyrolysis were studied.•The addition of rich husk is favorable for the migration of hydrogen from tar and char to gas and water.•The addition of vacuum residue is conducive to the migration of hydrogen from water to tar.•Co-pyrolysis cannot always enhance tar yield and/or improve tar quality. The hydrogen migration and distribution characteristics in products during co-pyrolysis of Xilinhot lignite (XL) with hydrogen-rich carbonaceous matters, rice husk (RH, abundant in hydroxy hydrogen) and vacuum residue (VR, abundant in aliphatic hydrogen), were investigated, and the interaction mechanisms were also elucidated. The results show that the co-pyrolysis behaviors of XL/RH and XL/VR mixtures are completely different. Co-pyrolysis of XL/RH produces more gas and water and less tar than expected, while XL/VR co-pyrolysis yields more char and less gas. The hydrogen migrated into water and gas are higher than expected during co-pyrolysis of XL/RH, and the hydrogen migrated into tar (12.28–15.30%) and char (35.27–47.70%) are lower than theoretical values (13.33–18.75% and 37.50–49.05%). This indicates that the addition of RH is favorable for the migration of hydrogen from tar and char to gas and water during XL pyrolysis. Differently, the hydrogen migrated into tar (19.73–31.59%) is higher than expected (17.04–30.03%), and hydrogen migrated into water (16.57–21.29%) is less than theoretical values (18.16–23.55%) during XL/VR co-pyrolysis. This implies that the addition of VR is conducive to the migration of hydrogen from water to tar during XL pyrolysis. Consequently, the contents of n-hexane solubles (nHS) in tars from XL/VR co-pyrolysis are higher than expected, indicating the improvement of tar quality. In conclusion, co-pyrolysis of lignite with hydrogen-rich carbonaceous matters cannot always enhance tar yield and/or improve tar quality, which largely depend on the content and occurrence of hydrogen in hydrogen-rich carbonaceous matters.