Studies on the Preliminary Cracking of Heavy Oils: The Effect of Matrix Acidity and a Proposal of a New Reaction Route

Abstract

Viewpoints on the influence of matrix acidity on the catalytic cracking of heavy oil are still inconsistent, hindering the studies of the reaction routes that occur during the matrix-precracking process. In this study, the effects of matrix acidity on heavy oil cracking were systematically studied by preparing alumina and modified alumina with different acidity in a practically meaningful range as the matrix components of fluid catalytic cracking catalysts. Results showed that Brönsted sites presented a much higher activity than Lewis sites on the matrix surface. Increasing the Brönsted acid strength of matrices improved the activity of catalysts, with the aggravated product distribution, while increasing the Lewis acid strength of matrices aggravated the product distribution and decreased the catalyst activity. Interestingly, results also showed that contacting Lewis sites first followed by interacting with Brönsted sites during the matrix-precracking process would facilitate heavy oil cracking more deeply. In addition, a new reaction route was proposed that protolytic cracking route should occur during the matrix-precracking process when cracking heavy oil. Based on this result, one can modify the matrix of the catalyst by introducing Brönsted sites or not to achieve high yield of light olefin or maximize liquid products.