Catalytic pyrolysis of straight-run light oil to light olefins: Role of molecular structure and catalytic materials

Abstract

The development of straight-run light oil catalytic pyrolysis to light olefins process is an important approach of achieving the transformation and upgrading of the current oil refining industry. However, the industrialization of the catalytic pyrolysis process for straight-run light oil has been slow. Herein, we investigated the decomposition of complex straight-run light oil into different structural units and further examined their effects on light olefins production. The results indicated that the yields of light olefins cracked over MFI zeolite were about 45 % and 30 % for alkane structure and cycloalkane ring structure, respectively. Further analysis showed that the olefin structure could theoretically be cracked to 100 % light olefins, but in fact, 40 % of the light olefins were lost due to the transfer of 10 % hydrogen. Subsequently, the effects of zeolite topology and acid properties on the cracking of different structural units were further analyzed. It was found that zeolites with MTT and MFI topologies contributed to the catalytic pyrolysis of chain and cycloalkane ring structures, respectively, because appropriate pore size helped diffusion of hydrocarbon molecules and inhibited side reactions such as hydrogen transfer. Compared with MFI zeolite, the light olefins yield produced by chain structure cracking over MTT zeolite increased by 5.83 %-10.54 %. In addition, it was discovered that zeolites with total and strong acids in the range of 0.2–0.4 mmol/g and 0.1–0.2 mmol/g, respectively, were beneficial for the cracking of light alkanes in straight-run light oils to light olefins. This work provides useful insights into the fundamental understanding and development of straight-run light oil catalytic pyrolysis to light olefins process.