Catalytic pyrolysis of central German lignite in a semi-continuous rotary kiln — Performance of pulverized one-way ZSM-5 catalyst and ZSM-5-coated beads

• Enhanced liberation of propene independent on zeolite catalyst shape
• Dependencies of gaseous hydrocarbons liberation on temperature and catalyst/coal ratio
• Decreasing amounts of long-chain aliphatics during catalytic pyrolysis
• Simple separation of ZSM-5-coated beads from pyrolysis char
• Enhanced propene formation during lignite pyrolysis after repeated regeneration of ZSM-5-coated beads

Central German lignites with high numbers of aliphatic and bituminous molecular structures are potential feedstocks for light hydrocarbons as intermediates for the chemical industry. This study pursues a new approach to the direct conversion of lignites by heterogeneous catalysis under pyrolytic conditions and without additional hydrogenation. Promising results were achieved in lab-scale investigations with ZSM-5 catalyst and these results were confirmed at a semi-technical scale rotary kiln. ZSM-5-coated beads were examined as an interesting alternative for reutilization and simple separation from the solid pyrolysis products.Based on parameter studies, the maximum yields of low molecular hydrocarbons occurred at a reaction temperature of 500 °C at a catalyst-to-coal ratio of 0.1 to 0.2 (maf). Comparison between the pulverized one-way ZSM-5 catalyst and ZSM-5-coated beads shows similar results concerning the amounts of pyrolysis products, especially gaseous alkenes like propene. At a certain catalyst-to-coal ratio, comparable results of propene liberation can be found also. The main reaction pathways were identified based on the distribution of the catalytic pyrolysis products, especially of low molecular hydrocarbons.