Co-pyrolysis of lignite and vacuum residue: Product distribution and hydrogen transfer

Abstract

During co-pyrolysis process, hydrogen transfer, which plays an important role on the distributions and properties of products, is closely related to the interaction mechanism between raw materials. In this study, co-pyrolysis of Xilinhot lignite (XL) and vacuum residue (VR) was carried out in an aluminum retort to investigate the product distribution and hydrogen transfer, which is helpful for better understanding the potential interaction mechanism between XL and VR during co-pyrolysis process. Results indicate that, with the increasing ratio of VR, the yield of co-pyrolysis tar significantly increases, while the yields of char, water and gas decrease gradually. The hydrogen contents in co-pyrolysis tar (HP-E, 9.74–10.22 wt%) are higher than the theoretical values (HP-T, 8.64–8.87 wt%), and the contents of n-HEX solubles (nHS) in co-pyrolysis tar are also higher than expected, which are obvious evidences of the improvement of co-pyrolysis tar quality. Besides, nHS in co-pyrolysis tar contains more aliphatics and less aromatics than expected. However, there is no obvious increase on co-pyrolysis tar yield comparing with theoretical value. This may be due to that alkali and alkaline earth metals (AAEMs) in XL intensify the secondary cracking of co-pyrolysis tar, at the same time, the proportion of C2-C4 hydrocarbon in gaseous product is higher than expected. As for hydrogen distribution, more hydrogen transfer into tar and less hydrogen transfer into water than expected. The differences between experimental and theoretical contents of hydrogen transferred to char and gas are not significant.