(293e) Understanding and Avoiding Mass Transport Limitations to Enable Catalyst Design for Low Temperature Polyolefin Cleavage and up-Cycling

Accessing and studying catalytic surface chemistry in polyolefin cleavage catalysis has been significantly hampered and convoluted by mass and energy transport issues and polymer chain dynamics (chain stress) that promote low-temperature uncatalyzed thermal radical side reactions. These fundamental phenomena also limit the observation of catalytic surface chemistry and inhibit catalyst design. Therefore, new reactor designs must be employed to reduce mass and energy transport limitations such that catalytic performance may be more clearly connected to surface chemistry. This study focused upon quantifying the effects of mass and energy transport in the cleavage of polyolefins using reaction environments that either promote or limit transport phenomena, e.g., unmixed static bed vs. flow reactions using static mixing element with entrained catalyst. A combination of deposited solid-acid and intermetallic compound (IMC) catalysts were investigated to understand the role of acid site strength in dehydrogenation and C-C cleavage and metal-like sites in hydrogenation kinetics. Results suggest that mass transport to and from the melt-catalyst interface directly affects the degree of cleavage of the polyolefin and, when limited, promotes over-cleavage and the production of light hydrocarbons. Utilizing the flow reactor with static mixing elements that provide nearly ideal mixing conditions, we were able to more directly investigate the role of acid and metal reaction site chemistry in polyolefin cleavage catalysis. Experimental studies are supplemented by DFT surface reaction modeling to understand reaction energetics and provide direction for ideal catalyst designs.