Hydrocracking of asphaltene from coal using ZnCl 2 as catalyst

Abstract

Coal liquefaction catalysis by ZnCl 2 was investigated by analyzing the evolution of structures from a starting material to liquid products under a series of reaction conditions. Asphaltene, derived from reductively methylated coal, has been assumed not to significantly alter macromolecular structures derived from the parent coal because of the large molecular weight of over 3000 and has been adopted as a starting material for hydrocracking. The hydrocracking was carried out using a batch autoclave system at 9.8 MPa initial hydrogen pressure by varying the reaction time (0–5 h), the temperature (350–440°C), and the amount of ZnCl 2 (5–40 wt.%). The hydrocracked products were fractioned by solvents and detailed structural parameters of the materials soluble in n-hexane (HS) and benzene (BS-HI) were estimated. At 400°C with 10 wt.% ZnCl 2, HS was obtained as the main product. The structural parameters of the soluble derivatives indicate that depolymerization proceeds by cleavage of ether bonds, which occurs easily, even at 350°C. Extension of the reaction time led to an increase in the HS yield and gave rise to the saturation of the aromatic rings and moderate subsequent decomposition of the products containing naphthenic rings. On the other hand, highly developed aromatic nuclei were gradually concentrated in BS-HI. When the amount of ZnCl 2 was increased to more than 10 wt.%, decomposition of the aromatic nuclei proceeded extensively at 400°C, in addition to depolymerization by the cleavage of carbon-carbon linkages. Noticeable dealkylation of the asphaltene took place above 400°C in the presence of 10 wt.% ZnCl 2.