(44g) Impact of Secondary Reactions of Fluid Catalytic Cracking on the Yield of Light Olefins

Fundamental understanding of the kinetics and mechanisms of essential reactions in catalytic cracking is still not well-understood and has long been recognized as an imperative task in academia and industry. To keep up with the demand of light olefins production while minimizing both the energy intensity and carbon footprint per high-value chemicals produced, as an example, it is necessary to rationally resolve the puzzle behind controlling the excessive formation of paraffins in cracking processes. The presentation will cover our efforts to explore, quantify, and control the occurrence of side reactions, namely hydrogen transfer reactions, in catalytic cracking. A model component, cyclohexane, is used as a probe molecule in a riser simulator to determine the contribution of hydrogen transfer reactions to coke formation and lost olefins production. The reactions are studied over a range of temperatures and residence times. Thus far, surprisingly, initial findings in analyzing results show a paraffins to olefins ratio of more than 3 at 450 °C. The ratio decreases at elevated temperatures reaching, nearly, 1 at 550 °C. Approximately 65 to 40% of formed olefins are re-consumed in hydrogen transfer reactions over the temperature range in which a naphthene donates hydrogen to an olefin and becomes aromatic whereas the olefin is hydrogenated into a paraffin. The data indicates that the contribution of hydrogen transfer reaction is very significant in the conversion of cyclohexane; it is not similar to paraffins cracking. In addition, the investigation results suggest that steaming the catalyst causes an improvement in the production of olefins and in the reduction of hydrogen transfer reactions. During the presentation, I would like to further illustrate the impact of catalyst modification and reaction conditions on the rate of hydrogen transfer reactions.