Catalytic Steam Cracking of n-Hexane

Abstract

The catalytic cracking of n-hexane as a model component was studied at varied reaction conditions for enhancing ethylene and propylene yields on four zeolite catalysts (ZSM-5) with different Si/Al ratio (265, 30) and lanthanum (La-H-ZSM-5) as a promoter. The characterization of all four zeolite catalysts was done by P-XRD, ICP, surface area measurements and TGA for their crystallinity, elements content, BET surface area, pore volume, pore size distribution and thermal stability. Ethylene and propylene yields were improved with an increase in Si/Al ratio of zeolite. Increase in the reaction temperature resulted in the increase in ethylene yield and n-hexane conversion. At 650°Ϲ, higher coke formation was observed which could be due to undesired coke forming side reactions. With increase in WHSV, the ethylene and propylene yield increased up to certain range of WHSV and then decreased over ZSM-5(265) catalyst. Other studied catalysts, ZSM-5(30), H-ZSM-5(30) and La-H-ZSM-5(30) with similar Si/Al ratio were more selective to propane with very higher n- hexane conversion (98%) than the ZSM-(265) catalyst (72%). This could be due to very high activity of the catalyst at lower Si/Al ratio. With introduction of steam in n-hexane cracking at higher temperature (600°C), ZSM-5(265) catalyst showed maximum ethylene and propylene yield and lower coke formation than the ZSM-5(30), H-ZSM-5(30) and La-H-ZSM-5(30) catalysts with low Si/Al ratio.